Co-reporter:Yangchun Rong, Kun Lin, Fangmin Guo, Ronghui Kou, Jun ChenYang Ren, Xianran Xing
The Journal of Physical Chemistry C January 26, 2017 Volume 121(Issue 3) pp:
Publication Date(Web):January 9, 2017
DOI:10.1021/acs.jpcc.6b09146
The rare negative thermal expansion (NTE) in ferroelectrics has received significant attention in lead-titanate perovskite oxides. Recently, a notable NTE of −4.7(1) × 10–5 K–1 was reported in a lead-free and nonperovskite ferroelectric Sn2P2S6. The stereochemically active lone-pair of Sn(II) was considered to be responsible for the NTE. Here, the role of the lone-pair is further explored via substitution of Ge(II)/Pb(II) for the cation Sn(II). Both high-energy as well as high-resolution synchrotron X-ray diffraction were employed to reveal the tailored NTE behavior and structure evolution, respectively. Due to the stereochemically inactive Pb(II) 6s2 pair when bonding with anion sulfur, the Pb(II)-substitution depresses the ferroelectricity and reduces the NTE of Sn2P2S6 to –1.9(2) × 10–5/K in (Sn0.85Pb0.15)P2S6. However, for (Sn0.975Ge0.025)P2S6, the ferroelectricity is enhanced by the tiny amount of stereochemically active Ge(II) 4s2 pair but the NTE is weakened to –3.9(1) × 10–5/K. The Raman spectra helps reveal the disparate effects of Ge(II)/Pb(II)-substitution on the local/average spontaneous polarization and the NTE. This work clarifies a further understanding of the role of the lone-pair in the spontaneous volume ferroelectrostriction (SVFS) and the NTE among ferroelectrics.
Co-reporter:Lihong Li, Jinxia Deng, Ranbo Yu, Jun Chen, Xiaowei Wang and Xianran Xing
Inorganic Chemistry February 15, 2010 Volume 49(Issue 4) pp:1397-1403
Publication Date(Web):January 11, 2010
DOI:10.1021/ic902165r
In this paper, we report a catalyst-free topochemical method, combined with molten salt synthesis (MSS), to synthesize, on a large scale, rodlike and platelet single crystals of Nb2O5. Rodlike KNb3O8 and platelet K4Nb6O17, which were fabricated as the precursors by the molten salt method, were treated by proton exchange and heat treatment to synthesize the rodlike H−Nb2O5 and platelet T−Nb2O5 single crystal, respectively. The synthesized niobium pentaoxides retained the rodlike and platelet shapes of their precursors. The structural changes involved in the process were investigated by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A possible topochemical reaction mechanism is proposed. Furthermore, rodlike and platelet KNbO3 powders were derived from stable H−Nb2O5 and T−Nb2O5, respectively.
Co-reporter:Qiang Li, He Zhu, Lirong Zheng, Longlong Fan, Na Wang, Yangchun Rong, Yang Ren, Jun Chen, Jinxia Deng, and Xianran Xing
Nano Letters December 13, 2017 Volume 17(Issue 12) pp:7892-7892
Publication Date(Web):November 21, 2017
DOI:10.1021/acs.nanolett.7b04219
An atomic insight into the local chemical ordering and lattice strain is particular interesting to recent emerging bimetallic nanocatalysts such as PtNi alloys. Here, we reported the atomic distribution, chemical environment, and lattice thermal evolution in full-scale structural description of PtNi alloy nanoparticles (NPs). The different segregation of elements in the well-faceted PtNi nanoparticles is convinced by extended X-ray absorption fine structure (EXAFS). Atomic pair distribution function (PDF) study evidences the coexistence of the face-centered cubic and tetragonal ordering parts in the local environment of PtNi nanoparticles. Further reverse Monte Carlo (RMC) simulation with PDF data obviously exposed the segregation as Ni and Pt in the centers of {111} and {001} facets, respectively. Layer-by-layer statistical analysis up to 6 nm for the local atomic pairs revealed the distribution of local tetragonal ordering on the surface. This local coordination environment facilitates the distribution of heteroatomic Pt–Ni pairs, which plays an important role in the negative thermal expansion of Pt41Ni59 NPs. The present study on PtNi alloy NPs from local short-range coordination to long-range average lattice provides a new perspective on tailoring physical properties in nanomaterials.Keywords: atomic pair distribution function; extended X-ray absorption fine structure; local ordering; negative thermal expansion; PtNi alloy nanoparticles;
Co-reporter:Kun Lin;Na Wang;Li You;Qiang Li;Kenichi Kato;Jun Chen;Jinxia Deng
Dalton Transactions 2017 vol. 46(Issue 3) pp:733-738
Publication Date(Web):2017/01/17
DOI:10.1039/C6DT04364J
Synchrotron radiation-based anomalous dispersion X-ray powder diffraction (ADSPD) was carried out to reveal the Pb/Bi ordering/disordering states in a series of PbTiO3-based negative thermal expansion materials (1 − x)PbTiO3 − xBiFeO3 (x = 0.1, 0.3, 0.5) and (1 − x)PbTiO3 − xBi(Zn1/2Ti1/2)O3 (x = 0.1, 0.2, 0.3). It gives strong evidence of the disordered Pb/Bi distributions in these compositions, which is consistent with electron diffraction studies. Combined with binding energy calculation, we show that the disordered nature of Pb/Bi distributions is likely to be attributed to the similar electron configurations of Pb2+ and Bi3+ as well as their comparable coordinate environments in perovskite structures. The results of this study may be helpful to better understand the structure–property relationship in Pb/Bi-containing perovskites and are useful for further developing underlying physics in relevant materials.
Co-reporter:Zhanning Liu;Chenxi Liu;Qiang Li;Jun Chen
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 36) pp:24436-24439
Publication Date(Web):2017/09/20
DOI:10.1039/C7CP03937A
Two nonporous coordination polymers were found to possess large anisotropic thermal expansion, which was derived from the flexible structures. A “spring-like” thermal motion was proposed to illustrate the mechanism. Compound Cd(eim)2 (eim = 2-ethylimidazole) possesses large linear and reversible thermal expansion properties and the emission intensity shows a linear decrease with temperature, making it a candidate for thermo-responsive materials.
Co-reporter:Zhao Pan, Jun ChenXingxing Jiang, Zheshuai Lin, Linxing Zhang, Longlong Fan, Yangchun Rong, Lei Hu, Hui Liu, Yang Ren, Xiaojun Kuang, Xianran Xing
Inorganic Chemistry 2017 Volume 56(Issue 5) pp:
Publication Date(Web):February 16, 2017
DOI:10.1021/acs.inorgchem.6b02761
Zero thermal expansion (ZTE) behavior is rare but important for both fundamental studies and practical applications of functional materials. Until now, most available ZTE materials are either electrical insulating oxides or conductive metallic compounds. Very few ZTE materials exhibit the semiconductor feature. Here we report a ZTE in a semiconducting ferroelectric of 0.6PbTiO3–0.4Bi(Co0.55Ti0.45)O3−δ. Its unit cell volume exhibits a negligible change over a broad temperature range from room temperature to 500 °C. The ZTE is supposed to be correlated with the spontaneous volume ferroelectronstriction. Intriguingly, the present ZTE material also exhibits the semiconducting characteristic accompanied by negative temperature coefficient of resistance. The mechanism of electric conduction is attributed to the electronic hopping from one ion (Ti3+) to another (Ti4+). The semiconductor nature has also been confirmed by the noticeable visible-light absorption with the relatively lower band gap (Eg) value of 1.5 eV, while the ferroelectric property can be well-maintained with large polarization. The first-principles calculations reveal that the drastically narrowed Eg is related to the Co–Ti substitution. The present multifunctional material containing ZTE, semiconducting, and ferroelectric properties is suggested to enable new applications such as the substrate for solar conversion devices.
Co-reporter:Yilin Wang;Hanqing Zhao;Linxing Zhang;Jun Chen
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 27) pp:17493-17515
Publication Date(Web):2017/07/12
DOI:10.1039/C7CP01347G
Ferroelectric thin films, especially PbTiO3-based perovskite thin films which possess robust spontaneous electrical polarization, are widely investigated and applied in various devices. With the advances in synthesis, characterization and calculation techniques, diverse phenomena and properties are uncovered in ferroelectric thin films. Herein some typical PbTiO3-based perovskite thin films through composition control are introduced, which gives more choices with various ferroelectric or other properties. Strain engineering, as well as some other interfacial effects, is also included to show the possibilities of controlling the lattice structure, the electronic structure as well as the domain structure which are closely connected to ferroelectricity. Multiferroic thin films, which could achieve magnetic-field-controlled polarization reversal, expand the novel applications of ferroelectric thin films. Typical and remarkable progress made in the case of multiferroic PbTiO3-based perovskite thin films is discussed here. Critical problems such as leakage current and fatigue hinder the practical use of ferroelectric and multiferroic thin films, and are also included in this article.
Co-reporter:He Zhu;Qiang Li;Yang Ren;Longlong Fan;Jun Chen;Jinxia Deng
Advanced Materials 2016 Volume 28( Issue 32) pp:6894-6899
Publication Date(Web):
DOI:10.1002/adma.201600973
Co-reporter:Lei Hu; Jun Chen; Andrea Sanson; Hui Wu; Clara Guglieri Rodriguez; Luca Olivi; Yang Ren; Longlong Fan; Jinxia Deng
Journal of the American Chemical Society 2016 Volume 138(Issue 27) pp:8320-8323
Publication Date(Web):June 23, 2016
DOI:10.1021/jacs.6b02370
The understanding of the negative thermal expansion (NTE) mechanism remains challenging but critical for the development of NTE materials. This study sheds light on NTE of ScF3, one of the most outstanding materials with NTE. The local dynamics of ScF3 has been investigated by a combined analysis of synchrotron-based X-ray total scattering, extended X-ray absorption fine structure, and neutron powder diffraction. Very interestingly, we observe that (i) the Sc–F nearest-neighbor distance strongly expands with increasing temperature, while the Sc–Sc next-nearest-neighbor distance contracts, (ii) the thermal ellipsoids of relative vibrations between Sc–F nearest-neighbors are highly elongated in the direction perpendicular to the Sc–F bond, indicating that the Sc–F bond is much softer to bend than to stretch, and (iii) there is mainly dynamically transverse motion of fluorine atoms, rather than static shifts. These results are direct experimental evidence for the NTE mechanism, in which the rigid unit is not necessary for the occurrence of NTE, and the key role is played by the transverse thermal vibrations of fluorine atoms through the “guitar-string” effect.
Co-reporter:Lihong Li, Jinxia Deng, Jun Chen and Xianran Xing
Chemical Science 2016 vol. 7(Issue 2) pp:855-865
Publication Date(Web):16 Oct 2015
DOI:10.1039/C5SC03521J
A topochemical molten salt synthesis (TMSS) method, which is rapid and a modification of the molten salt synthesis method (MSS), to facilitate crystal growth with improved phase-purity and particle homogeneity, is one of the strategic approaches aimed at a controllable morphology synthesis. The TMSS method is an environmentally friendly and mild way to prepare pure and controllable perovskites, which are famous functional materials, used as piezoelectrics, catalysts, ferroelectrics, multiferroics, and negative thermal expansion compounds, at a moderate reaction temperature in a short soaking time. This report reviews various TMSS reactions and their applications in fulfilling the demand for the tunable morphology of perovskite materials, such as one dimensional, two dimensional and three dimensional perovskites in molten salts, which mainly include: piezoelectrics, photocatalysts, negative thermal expansion matters and other functional perovskites. The double and layered perovskites obtained by TMSS methods are also discussed. We believe that a comprehensive understanding of the TMSS method for functional perovskites will definitely promote the development of a clean, efficient and tunable production process for advanced functional materials.
Co-reporter:Kun Lin, Li You, Qiang Li, Jun Chen, Jinxia Deng, and Xianran Xing
Inorganic Chemistry 2016 Volume 55(Issue 16) pp:8130
Publication Date(Web):August 3, 2016
DOI:10.1021/acs.inorgchem.6b01242
Tetragonal tungsten bronze (TTB) makes up a large family of functional materials with fascinating dielectric, piezoelectric, or ferroelectric properties. Understanding the thermal expansion mechanisms associated with their physical properties is important for their practical applications as well as theoretical investigations. Fortunately, the appearance of anomalous thermal expansion in functional materials offers a chance to capture the physics behind them. Herein, we report an investigation of the thermal expansion anomalies in TTBs that are related to ferroelectric transitions and summarize recent progress in this field. The special role of Pb2+ cation is elucidated. The interplay between the thermal expansion anomaly, electric polarization, and framework structure provides new insight into the structure–property relationships in functional materials.
Co-reporter:Kun Lin, Pifu Gong, Jing Sun, Hongqiang Ma, You Wang, Li You, Jinxia Deng, Jun Chen, Zheshuai Lin, Kenichi Kato, Hui Wu, Qingzhen Huang, and Xianran Xing
Inorganic Chemistry 2016 Volume 55(Issue 6) pp:2864-2869
Publication Date(Web):February 29, 2016
DOI:10.1021/acs.inorgchem.5b02702
The incorporation of transition metal element Ag was performed to explore negative thermal expansion (NTE) materials with tetragonal tungsten bronze (TTB) structures. In this study, the structure and thermal expansion behaviors of a polar TTB oxide, Pb2AgNb5O15 (PAN), were systematically investigated by high-resolution synchrotron powder diffraction, high-resolution neutron powder diffraction, transmission electron microscope (TEM), and high-temperature X-ray diffractions. The TEM and Rietveld refinements revealed that the compound PAN displays (√2aTTB, √2bTTB, 2cTTB)-type superstructure. This superstructure within the a–b plane is caused by the ordering of A-site cations, while the doubling of the c axis is mainly induced by a slight tilt distortion of the NbO6 octahedra. The transition metal Ag has larger spontaneous polarization displacements than Pb, but the Pb–O covalence seems to be weakened compared to the potassium counterpart Pb2KNb5O15 (PKN), which may account for the similar Curie temperature and uniaxial NTE behavior for PAN and PKN. Powder second harmonic generation (SHG) measurement indicates that PAN displays a moderate SHG response of ∼0.2 × LiNbO3 (or ∼100 × α-SiO2) under 1064 nm laser radiation. The magnitudes of the local dipole moments in NbO6 and PbOx polyhedra were quantified using bond-valence approach. We show that the SHG response stems from the superposition of dipole moments of both the PbOx and NbO6 polyhedra.
Co-reporter:Hanqing Zhao, Jun Miao, Linxing Zhang, Yangchun Rong, Jun Chen, Jinxia Deng, Ranbo Yu, Jiangli Cao, Huanhua Wang and Xianran Xing
Dalton Transactions 2016 vol. 45(Issue 4) pp:1554-1559
Publication Date(Web):08 Dec 2015
DOI:10.1039/C5DT03611A
Single-phase xNdFeO3–(1 − x)PbTiO3 thin films with different dopant contents were fabricated on the Pt(111)/Ti/SiO2/Si substrate by a sol–gel route. Grain size was influenced by the dopant content effectively. A synchrotron radiation X-ray diffraction study revealed a reduced tetragonality (c/a) of the PbTiO3 lattice in the films. Distortion of the TiO6 octahedron was weakened, as investigated by Raman scattering and X-ray absorption spectra. An electronic structural study indicated that the hybridizations between O 2p and Pb 6s and Ti 3d orbitals were weakened. The decrease of lattice distortion and orbital hybridization gives rise to degradation of the ferroelectric nature in the films.
Co-reporter:Yangchun Rong, Menglei Li, Jun Chen, Mei Zhou, Kun Lin, Lei Hu, Wenxia Yuan, Wenhui Duan, Jinxia Deng and Xianran Xing
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 8) pp:6247-6251
Publication Date(Web):26 Jan 2016
DOI:10.1039/C6CP00011H
Functional materials showing both negative thermal expansion (NTE) and physical performance, such as ferroelectricity and magnetism, have been extensively explored in the past decade. However, among ferroelectrics a remarkable NTE was only found in perovskite-type PbTiO3-based compounds. In this work, a large NTE of −4.7 × 10−5 K−1 is obtained in the non-perovskite lead-free ferroelectric Sn2P2S6 from 243 K to TC (338 K). Structure refinements and first-principle calculations reveal the effects of the Sn(II) 5s–S 3p interaction on spontaneous polarization and its correlation with NTE. Then the mechanism of spontaneous volume ferroelectrostriction (SVFS) is verified and it could well elucidate the nature of NTE in ferroelectric Sn2P2S6. This is the first case to demonstrate the unusual NTE behavior by SVFS in a non-perovskite lead-free ferroelectric material.
Co-reporter:Weigang Cao, He Zhu, Zhanning Liu, Jinxia Deng, Jun Chen, Xianran Xing
Inorganic Chemistry Communications 2016 Volume 73() pp:111-114
Publication Date(Web):November 2016
DOI:10.1016/j.inoche.2016.10.022
The phase formation of Ho2W3O12 is still in debate, and no detailed analysis was carried out until now. In the present study, we synthesized Ho2W3O12 with different treatments to probe the relationship between phase formation and synthesized conditions. It is found that the orthorhombic phase of Ho2W3O12 is stable at high temperature. While the thermodynamic stable phase of low temperature is monoclinic. The temperature of phase transition was determined at 908 °C. Moreover, the phase transition is slow, so it is easy to retain the orthorhombic phase at low temperature. Additionally, the stability and the thermal expansion of orthorhombic Ho2W3O12 were also investigated. The orthorhombic phase can be stabilized by 600 °C, and shows negative thermal expansion (NTE) along three axes with the overall volume thermal contraction of − 2.1 × 10− 5 °C− 1.Orthorhombic Ho2W3O12 shows NTE (− 2.1 × 10− 5 °C− 1) in the temperature range of 200–600 °C.
Co-reporter:Jun Chen, Lei Hu, Jinxia Deng and Xianran Xing
Chemical Society Reviews 2015 vol. 44(Issue 11) pp:3522-3567
Publication Date(Web):13 Apr 2015
DOI:10.1039/C4CS00461B
Negative thermal expansion (NTE) is an intriguing physical property of solids, which is a consequence of a complex interplay among the lattice, phonons, and electrons. Interestingly, a large number of NTE materials have been found in various types of functional materials. In the last two decades good progress has been achieved to discover new phenomena and mechanisms of NTE. In the present review article, NTE is reviewed in functional materials of ferroelectrics, magnetics, multiferroics, superconductors, temperature-induced electron configuration change and so on. Zero thermal expansion (ZTE) of functional materials is emphasized due to the importance for practical applications. The NTE functional materials present a general physical picture to reveal a strong coupling role between physical properties and NTE. There is a general nature of NTE for both ferroelectrics and magnetics, in which NTE is determined by either ferroelectric order or magnetic one. In NTE functional materials, a multi-way to control thermal expansion can be established through the coupling roles of ferroelectricity-NTE, magnetism-NTE, change of electron configuration-NTE, open-framework-NTE, and so on. Chemical modification has been proved to be an effective method to control thermal expansion. Finally, challenges and questions are discussed for the development of NTE materials. There remains a challenge to discover a “perfect” NTE material for each specific application for chemists. The future studies on NTE functional materials will definitely promote the development of NTE materials.
Co-reporter:Lei Hu;Jun Chen;Longlong Fan;Yang Ren;Qingzhen Huang;Andrea Sanson;Zheng Jiang;Mei Zhou;Yangchun Rong;Yong Wang;Jinxia Deng
Advanced Materials 2015 Volume 27( Issue 31) pp:4592-4596
Publication Date(Web):
DOI:10.1002/adma.201500868
Co-reporter:Kun Lin; Zhengyang Zhou; Laijun Liu; Hongqiang Ma; Jun Chen; Jinxia Deng; Junliang Sun; Li You; Hidetaka Kasai; Kenichi Kato; Masaki Takata
Journal of the American Chemical Society 2015 Volume 137(Issue 42) pp:13468-13471
Publication Date(Web):October 16, 2015
DOI:10.1021/jacs.5b08230
Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s2 lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb5O15, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What’s more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb2+–Bi3+ ordering in the large pentagonal caves, which can suppress the local polarization in x–y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.
Co-reporter:Linxing Zhang, Jun Chen, Jiangli Cao, Dongyu He and Xianran Xing
Journal of Materials Chemistry A 2015 vol. 3(Issue 18) pp:4706-4712
Publication Date(Web):31 Mar 2015
DOI:10.1039/C5TC00814J
The destructive readout signal distinguishing the ferroelectric polarization state in a memory device has long been seen as the bottleneck for its commercial application. Both ferroelectric resistive switching and the switchable photovoltaic effect provide multiple choices for non-destructive readout. The polycrystalline ferroelectric BiFeO3-based thin films fabricated by cost-effective chemical solution growth exhibit large resistive switching (with ON/OFF ratios ∼104), which is comparable to switchable diodes and tunnel junctions. Furthermore, switchable photovoltaic response shows stable switching and good retention properties. The standard hysteretic loops of resistive switching current, short circuit current and open circuit voltage versus poling voltage directly indicate hysteretic modulation by ferroelectric polarization, which is the first evidence in polycrystalline BiFeO3 based films. The present films would be potential candidates for non-destructive ferroelectric memory devices with multiple selections.
Co-reporter:You Wang, Yun Wang, Wei Ren, Porun Liu, Huijun Zhao, Jun Chen, Jinxia Deng and Xianran Xing
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 43) pp:29097-29102
Publication Date(Web):28 Sep 2015
DOI:10.1039/C5CP03941J
NdFeO3 is an important candidate material for gas sensors and intermediate-temperature solid oxide fuel cells (IT-SOFC). However, its low conductivity prohibits its applications. In this study, we report that the doping of Ca by partially replacing Nd can effectively increase its conductivity. Through the electronic structure analysis of Nd1−xCaxFeO3 (x = 0.00, 0.25, 0.50, 0.75 or 1.00) based on the first-principles density functional theory calculations, it is found that the hole states introduced by Ca substitution appear just above the Fermi level, which implies a high mobility of electrons/holes along the Fe–O–Fe bonding network. Specifically, it becomes easier to form O vacancies after Ca doping. Since the diffusion of O anions occurs through a vacancy hopping mechanism, the ion conductivity is also improved. These findings help us to gain an in-depth understanding of the colossally increased conductivity of Ca doped NdFeO3 and turn the electronic conduction for its practical application in gas sensors and IT-SOFC.
Co-reporter:You Wang;Yun Wang;Jun Chen;Jinxia Deng;Ranbo Yu
European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 35) pp:5767-5772
Publication Date(Web):
DOI:10.1002/ejic.201500869
Abstract
The use of mesoporous and hollow structures is a promising strategy to enhance gas-sensing properties. The framework of perovskite oxides has the ability to accommodate different cations, which endows it with rich oxygen deficiencies for preferable gas adsorption. Herein, we outline the fabrication of perovskite Nd1–xCaxFeO3 (x = 0, 0.3) hollow core–shell microspheres by using carbonaceous microspheres as templates. The gas-sensing properties of Nd0.7Ca0.3FeO3 core–shell microspheres were systematically investigated. The response to 500 ppm ethanol was 17 at 140 °C, which is much higher than the response of Nd0.7Ca0.3FeO3 nanoparticles. Also, rapid response and recovery characteristics were achieved. Furthermore, after 50 cyclic tests and 10 testing days, the gas response of the Nd0.7Ca0.3FeO3 hollow core–shell microspheres to 500 ppm ethanol at 140 °C was nearly constant. The long-term stability, good sensitivity, and rapid response and recovery times demonstrate the potential application of these hollow core–shell microspheres as a sensing material.
Co-reporter:Hongqiang Ma, Kun Lin, Longlong Fan, Yangchun Rong, Jun Chen, Jinxia Deng, Laijun Liu, Shogo Kawaguchi, Kenichi Kato and Xianran Xing
RSC Advances 2015 vol. 5(Issue 88) pp:71890-71895
Publication Date(Web):10 Aug 2015
DOI:10.1039/C5RA10635D
The crystal structure and electrical properties of a tetragonal tungsten bronze (TTB) compound, BaBiNb5O15, were investigated by high-resolution synchrotron X-ray powder diffraction and AC impedance spectroscopy. The compound is a new type of oxide ion conductor with a total electrical conductivity of 3 × 10−4 S cm−1 at 600 °C and a relatively small activation energy (0.3–0.5 eV). It is suggested that the large amount of cationic vacancies in the A sites, the large free space created by the large Ba2+ cations, and the splits of the Bi atoms are in favor of oxygen ion migration. This stable tungsten bronze compound BaBiNb5O15 with moderate oxide ion conductivity shows potential for applications in SOFC anodes, amperometric gas sensors, and active catalyst supports.
Co-reporter:Hongqiang Ma, Kun Lin, Laijun Liu, Baoling Yang, Yangchun Rong, Jun Chen, Jinxia Deng, Shogo Kawaguchi, Kenichi Kato and Xianran Xing
RSC Advances 2015 vol. 5(Issue 94) pp:76957-76962
Publication Date(Web):04 Sep 2015
DOI:10.1039/C5RA16115K
The crystal structure and electrical microstructure of a tetragonal tungsten bronze (TTB) ceramic, BaCeFeNb4O15 (BCFN), were investigated by high-resolution synchrotron X-ray powder diffraction (SPD), selected area electron diffraction (SAED), and AC impedance spectroscopy. SPD and SAED reveal that the BCFN has a tetragonal structure with space group P4/mbm, and includes an incommensurate modulated behavior. Impedance and AC conductivity tests in the range of 200–360 °C suggest thermally activated electrical behavior which originates from both the bulk and the grain boundary elements of the ceramics. The dielectric relaxation in the grain boundaries is due to the trap-controlled ac conduction around doubly ionized oxygen vacancies while the relaxation of the bulk may be associated with the localized electron hopping between the transition-metal ions. These results could be helpful in understanding the electrical conduction and relaxation processes in Fe-containing TTB-type oxides.
Co-reporter:Lei Hu ; Jun Chen ; Longlong Fan ; Yang Ren ; Yangchun Rong ; Zhao Pan ; Jinxia Deng ; Ranbo Yu
Journal of the American Chemical Society 2014 Volume 136(Issue 39) pp:13566-13569
Publication Date(Web):September 18, 2014
DOI:10.1021/ja5077487
The rare physical property of zero thermal expansion (ZTE) is intriguing because neither expansion nor contraction occurs with temperature fluctuations. Most ZTE, however, occurs below room temperature. It is a great challenge to achieve isotropic ZTE at high temperatures. Here we report the unconventional isotropic ZTE in the cubic (Sc1–xMx)F3 (M = Ga, Fe) over a wide temperature range (linear coefficient of thermal expansion (CTE), αl = 2.34 × 10–7 K–1, 300–900 K). Such a broad temperature range with a considerably negligible CTE has rarely been documented. The present ZTE property has been designed using the introduction of local distortions in the macroscopic cubic lattice by heterogeneous cation substitution for the Sc site. Even though the macroscopic crystallographic structure of (Sc0.85Ga0.05Fe0.1)F3 adheres to the cubic system (Pm3̅m) according to the results of X-ray diffraction, the local structure exhibits a slight rhombohedral distortion. This is confirmed by pair distribution function analysis of synchrotron radiation X-ray total scattering. This local distortion may weaken the contribution from the transverse thermal vibration of fluorine atoms to negative thermal expansion, and thus may presumably be responsible for the ZTE. In addition, the present ZTE compounds of (Sc1–xMx)F3 can be functionalized to exhibit high-Tc ferromagnetism and a narrow-gap semiconductor feature. The present study shows the possibility of obtaining ZTE materials with multifunctionality in future work.
Co-reporter:Wei Zou, Jun Chen, Lei Hu, Qiang Li, Xiang Yao, Lin Gu, Jinxia Deng, Ranbo Yu and Xianran Xing
Journal of Materials Chemistry A 2014 vol. 2(Issue 40) pp:8564-8568
Publication Date(Web):21 Aug 2014
DOI:10.1039/C4TC01557F
Synthesis of hollow structures of metal sulphides generally involves various templates and complex chemical processing. In the present study, a general and rapid method of salt-assisted aerosol decomposition (SAD) is presented for the synthesis of hollow spheres of various metal sulfides, including ZnS, ternary sulfides, and solid solutions. The NaCl salt plays a critical role in the formation of hollow spheres of metal sulfides. The hollow spherical microstructure was formed from solid by using a small amount of water soluble NaCl salt. The formation of metal sulphide hollow spheres differs from previous mechanisms and is referred to as molten salt heterogeneous nucleation (MSHN). The present method offers the most promising advantage for controlling the multicomponent composition of hollow spheres. Furthermore, hollow spheres of sulphides have much enhanced properties such as photoluminescence of ZnS:Mn2+ and photocatalytic dye degradation of ZnIn2S4 due to the role of molten salt in the promotion of crystallization, The present method could be explored further by applying the process to other compounds such as sulfides, oxides, and nitrides.
Co-reporter:Huihui Zhu, Jinxia Deng, Jun Chen, Ranbo Yu and Xianran Xing
Journal of Materials Chemistry A 2014 vol. 2(Issue 9) pp:3008-3014
Publication Date(Web):09 Dec 2013
DOI:10.1039/C3TA14832G
A simple synthesis method is proposed for producing aligned and uniform single-crystal one-dimensional hematite (α-Fe2O3) nanostructures on pentlandite. Pentlandite is the most common terrestrial iron-nickel sulfide and the principal ore mineral of nickel. In this study, a pentlandite sample was synthesized from pure components Fe, Ni and S. Oxidation makes the chemical potential of iron reduce more than that of nickel. Iron migrated rapidly to the surface of dense pentlandite and was oxidized preferentially to form an oxide layer. Several micrometers long α-Fe2O3 nanowires grown along the [110] direction were achieved. The ordered oxygen vacancies which lie parallel to the growth direction were observed. Hematite (α-Fe2O3) and magnetite including Ni (NixFe3−xO4) are major components of the oxide layer. Three kinds of morphology are included in this layer: nanowires, dense and porous oxides. The Ni-rich pentlandite coexists with NiS, hexagonal pyrrhotite (Fe1−xS) and/or godlevskite (Ni7S6). This work provides a new strategy to inexpensively and efficiently synthesize nanostructures directly from ore minerals.
Co-reporter:Kun Lin, Yangchun Rong, Hui Wu, Qingzhen Huang, Li You, Yang Ren, Longlong Fan, Jun Chen, and Xianran Xing
Inorganic Chemistry 2014 Volume 53(Issue 17) pp:9174-9180
Publication Date(Web):August 12, 2014
DOI:10.1021/ic501189n
The crystal structure and thermal expansion behaviors of a new tetragonal tungsten bronze (TTB) ferroelectric, Pb2K0.5Li0.5Nb5O15, were systematically investigated by selected-area electron diffraction (SAED), neutron powder diffraction, synchrotron X-ray diffraction (XRD), and high-temperature XRD. SAED and Rietveld refinement reveal that Pb2K0.5Li0.5Nb5O15 displays a commensurate superstructure of simple orthorhombic TTB structure at room temperature. The structure can be described with space group Bb21m. The transition to a paraelectric phase (P4/mbm) occurs at 500 °C. Compared with Pb2KNb5O15 (PKN), the substitution of 0.5K+ with small 0.5Li+ into PKN causes the tilting of NbO6 octahedra away from the c axis with Δθ ≈ 10° and raises the Curie temperature by 40 °C, and the negative thermal expansion coefficient along the polar b axis increases more than 50% in the temperature range 25–500 °C. We present that, by introduction of Li+, the enhanced spontaneous polarization is responsible for the enhanced negative thermal expansion along the b axis, which may be caused by more Pb2+ in the pentagonal caves.
Co-reporter:You Wang, Xuecheng Yan, Jun Chen, Jinxia Deng, Ranbo Yu and Xianran Xing
CrystEngComm 2014 vol. 16(Issue 5) pp:858-862
Publication Date(Web):15 Nov 2013
DOI:10.1039/C3CE41434E
Orthorhombic NdFeO3 (space group: Pnma) crystals with controlled morphologies and sizes were synthesized via a hydrothermal method. The morphologies of the final products strongly depend on the concentration of alkali. When the concentration of the KOH solution was adjusted from 16 M to 19 M, cuboid, cross-shaped and bar-shaped NdFeO3 crystals were obtained respectively. The bar-shaped NdFeO3 crystals are preferentially oriented along the direction of [010]. The formation of NdFeO3 crystals can be explained by a “dissolution–precipitation” mechanism. It is interesting to find that if the precipitates are isolated by centrifugation before hydrothermal treatment, then mixed with KOH solutions, followed by adding an appropriate amount of KNO3, the rod-shaped NdFeO3 crystals with high aspect ratio and small size will be obtained in the hydrothermal route. The magnetic properties of NdFeO3 crystals with different shapes were also explored.
Co-reporter:Fangfang Wang, Ying Xie, Jun Chen, Honggang Fu and Xianran Xing
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 11) pp:5237-5241
Publication Date(Web):17 Dec 2013
DOI:10.1039/C3CP53197J
Recently experiments have found that negative thermal expansion is a common phenomenon in PbTiO3-based materials, and their negative thermal expansion is affected by various substitutions. Interestingly, Cd substitution in PbTiO3 has a unique effect in enhancing negative thermal expansion compared with any other A-site substitutions. Therefore, studying Cd substitution in PbTiO3, the role of which still remains unclear, would bring us deeper understanding on the nature of the negative thermal expansion of PbTiO3-based materials. Structure calculations, density of states, Bader analysis and the minimum electron density of Pb1−xCdxTiO3 supercells have been reported on the chemical bond through first-principles calculations here. We found that the hybridization between (Pb,Cd)–O orbitals exists in tetragonal phase. Furthermore, the hybridization between Cd–O orbitals is stronger than that between Pb–O orbitals, and Cd–O covalency promotes the average A-site hybridization. Simultaneously, the average bulk coefficient of thermal expansion is negative and inversely proportional to the Cd substitution amount. So, (Pb,Cd)–O covalency in the tetragonal Pb1−xCdxTiO3 is responsible for the nature of enhanced negative thermal expansion in accordance with our previous experimental investigations.
Co-reporter:Kun Lin, Hui Wu, Fangfang Wang, Yangchun Rong, Jun Chen, Jinxia Deng, Ranbo Yu, Liang Fang, Qingzhen Huang and Xianran Xing
Dalton Transactions 2014 vol. 43(Issue 19) pp:7037-7043
Publication Date(Web):23 Jan 2014
DOI:10.1039/C3DT53340A
The structure and thermal expansion behavior of the tetragonal tungsten bronze oxide Pb2KNb5O15 were investigated by neutron powder diffraction and high-temperature X-ray diffraction. Below the Curie temperature, TC (orthorhombic phase, TC ≈ 460 °C), the cell parameters a and c increase with temperature, while b decreases. The thermal expansion coefficients are αa = 1.29 × 10−5 °C−1, αb = −1.56 × 10−5 °C−1, and αc = 1.62 × 10−5 °C−1. Temperature-dependent second harmonic generation (SHG), dielectric, and polarization–electrical field (P–E) hysteresis loop measurements were performed to study the symmetry and electric properties. We show that the distortion and cooperative rotation of NbO6 octahedrons are directly responsible for the negative thermal expansion coefficient along the polar b axis. It is suggested that Pb–O covalency, especially in the large and asymmetric pentagonal prisms, may be related to orthorhombic distortion and abnormal spontaneous polarization along the b axis. This study shows that tungsten bronze families are possible candidates for exploring negative thermal expansion materials.
Co-reporter:Xiaoxin An, You Wang, Jinxia Deng, Jun Chen, Ranbo Yu, Xianran Xing
Inorganic Chemistry Communications 2014 Volume 44() pp:79-82
Publication Date(Web):June 2014
DOI:10.1016/j.inoche.2014.03.010
•We obtain well-crystalline YVO4 nanoparticles by one-step MSS at low temperatures.•The temperature range of forming YVO4 is wide, ranging from 350 to 600 °C.•The YVO4 nanoparticles exhibit excellent photocatalytic properties.•The YVO4 nanoparticles are stable under photodegradation environment.Well-crystalline YVO4 nanoparticles were successfully synthesized by a simple and convenient one-step molten salt synthesis (MSS) method in a wide temperature range of 350–600 °C for only 5 h. The UV–Visible absorption spectra measured by a spectrophotometer suggest that visible light absorption exists in the absorption spectra of all the samples prepared under different temperatures and the smaller the particle size, the stronger the absorption, the smaller the onset of UV absorption and the larger the blue shift. The photodegradation of RB indicates that both particle size and crystallinity have effects on the photocatalytic properties of YVO4 nanoparticles. YVO4 nanoparticles were further demonstrated to have excellent photocatalytic stability.(a) The absorption spectra changes of RB solutions as a function of irradiation time for the sample synthesized at 400 °C for 5 h; (b) Photocatalytic activity for degradation of RB with no catalyst and using the YVO4 nanoparticles synthesized under different calcining temperatures by MSS method.
Co-reporter:Yucheng Zhang, Jinxia Deng, Jun Chen, Ranbo Yu, Xianran Xing
Inorganic Chemistry Communications 2014 Volume 43() pp:138-141
Publication Date(Web):May 2014
DOI:10.1016/j.inoche.2014.02.032
Co-reporter:Xiaoxin An, You Wang, Jinxia Deng, Jun Chen, Xianran Xing
Materials Research Bulletin 2014 51() pp: 74-79
Publication Date(Web):
DOI:10.1016/j.materresbull.2013.12.005
Co-reporter:Lihong Li, Jinxia Deng, Ranbo Yu, Jun Chen, Zheng Wang and Xianran Xing
Journal of Materials Chemistry A 2013 vol. 1(Issue 38) pp:11894-11900
Publication Date(Web):30 Jul 2013
DOI:10.1039/C3TA12599H
Herein, we developed a simple template-free synthetic method for producing niobium pentoxide (Nb2O5) hollow nanospheres, and fabricated KNbO3 hollow nanospheres which retained the morphology of the template Nb2O5 hollow nanospheres by the molten salt method. The formation of Nb2O5 hollow nanospheres was via Ostwald ripening, and the structural evolution between niobium oxide and niobates was a kind of self-sacrificing templated process. These Nb2O5 hollow nanospheres with high surface energy (001) planes showed high thermal stability and large surface area. Furthermore, they not only showed strong intensity of blue emission, but they were also able to efficiently split water under visible light irradiation, and show potential for application as sensors, optoelectronic devices and promising photocatalysts for water splitting under visible light. Due to the high thermal stability of Nb2O5 hollow nanospheres and the simplicity of the protocol, we anticipate that this work will enrich the hollow nanostructures of inorganic compounds and provide a new strategy to synthesize hollow nanospheres of niobates and other kinds of materials.
Co-reporter:Linxing Zhang, Jun Chen, Hanqing Zhao, Longlong Fan, Yangchun Rong, Jinxia Deng, Ranbo Yu and Xianran Xing
Dalton Transactions 2013 vol. 42(Issue 2) pp:585-590
Publication Date(Web):06 Nov 2012
DOI:10.1039/C2DT31996A
The applications of ferroelectric thin films such as the sensitivity of nonvolatile ferroelectric random access memories are closely linked with large remnant polarization. The high-TC (1−x)Bi(Zn1/2Zr1/2)O3–xPbTiO3 (x = 0.7–0.9) thin films with high (100) orientation were fabricated on Pt(111)/Ti/SiO2/Si substrates via a sol–gel method. The thin films could be crystallized well in a phase-pure perovskite structure. The electrical properties of the sol–gel-derived BZZ–PT thin films were investigated. A large remanent polarization with 2Pr up to 110 μC cm−2 and a small leakage current of 3.8 × 10−7 A cm−2 under an electric field of 150 kV cm−1 are observed on the 0.2BZZ–0.8PT thin films. Furthermore, a relatively stable polarization fatigue property was achieved, indicating a potential application in high-temperature ferroelectric devices.
Co-reporter:Hanqing Zhao, Jiaou Wang, Linxing Zhang, Yangchun Rong, Jun Chen, Kurash Ibrahim and Xianran Xing
Dalton Transactions 2013 vol. 42(Issue 28) pp:10358-10364
Publication Date(Web):10 May 2013
DOI:10.1039/C3DT50257K
The single phase Pb0.8Co0.2TiO3 thin films were synthesized on a Pt/Ti/SiO2/Si substrate by the sol–gel route. The present films exhibited homogeneous microstructure with low porosity. O 1s X-ray photoelectron spectroscopy (XPS) was used to detect the amount of oxygen vacancies. The ferroelectric measurements showed that the ferroelectricity deteriorates with the increase in the number of oxygen vacancies. X-ray absorption spectroscopy (XAS) and XPS were used to study the electronic structure. The results indicated that the decreased ferroelectricity might be ascribed to the weakened hybridization between O 2p and Pb 6s and Ti 3d orbitals. The ferromagnetic behaviors were also observed in the thin films and saturated magnetization raised monotonously with the oxygen vacancy rising due to the enhanced F-center exchange interaction. Magnetoelectric coupling of the films weakened with oxygen vacancy increase.
Co-reporter:Huajun Kang, Jun Chen, Laijun Liu, Changzheng Hu, Liang Fang, Xianran Xing
Inorganic Chemistry Communications 2013 Volume 31() pp:66-68
Publication Date(Web):May 2013
DOI:10.1016/j.inoche.2013.03.006
•The piezoelectric property can reach 510 pC/N.•By doping PbZrO3, leakage current of ceramics can obviously diminish.•By doping PbZrO3, the coercive field gets smaller.The piezoelectric ceramics (1 − x − y)PbTiO3 − xPbZrO3 − yBi(Ni1/2Ti1/2)O3 exhibit greatly enhanced piezoelectric properties at morphotropic phase boundaries (MPB). X-Ray diffraction (XRD) analysis was used to investigate the MPB structure of (1 − x − y)PbTiO3 − xPbZrO3 − yBi(Ni1/2Ti1/2)O3 ceramics. The dielectric, ferroelectric, and piezoelectric properties were systematically investigated. The morphotropic phase boundaries are at x = 0.10, 0.20, 25; y = 0.46, 0.39, 0.34, respectively. An optimum high temperature piezoelectric ceramic is obtained at the composition of x = 0.20 and y = 0.39 (d33 = 510 pC/N, d⁎33(bi) = 462 pm/V, Tc = 318 °C, Ec = 20.0 kV/cm and Pr = 25.5 μC/cm2).P–E hysteresis loops of PZ10–BNT46–PT, PZ20–BNT39–PT and PZ25–BNT34–PT; S–E bipolar loops of PZ10–BNT46–PT, PZ20–BNT39–PT and PZ25–BNT34–PT.
Co-reporter:Xin Peng, Huajun Kang, Laijun Liu, Changzheng Hu, Liang Fang, Jun Chen, Xianran Xing
Solid State Sciences 2013 Volume 15() pp:91-94
Publication Date(Web):January 2013
DOI:10.1016/j.solidstatesciences.2012.09.007
Multiferroic solid solution of (1 − x)PbTiO3 − xNdFeO3 (PT − NF) compounds are synthesized by a conventional solid state reaction. XRD investigations indicate the phase PT − NF transition from tetragonal to pseudo-cubic and then orthorhombic phase by increasing the dopant NdFeO3. The multiferroic and magnetoelectric (ME) behaviors in (1 − x)PbTiO3 − xNdFeO3 solid solutions are observed in the tetragonal phase (0 ≦ x ≦ 0.3). Further addition of the dopant NdFeO3 results into severe leakage currents and phase transitions. The solid solution compounds achieve strong ferromagnetism with high remnant magnetization (Mr = 0.786 emu/g) at x = 0.8. This work demonstrates a way to tailor the ferroelectric, magnetic properties and ME coupling in multiferroic PT-based compounds.
Co-reporter:X.R. Xing, Xin Peng, Huajun Kang, Laijun Liu, Changzheng Hu, Liang Fang, Jun Chen
Solid State Sciences 2013 Volume 17() pp:156
Publication Date(Web):March 2013
DOI:10.1016/j.solidstatesciences.2012.12.011
Co-reporter:Huajun Kang, Jun Chen, Laijun Liu, Changzheng Hu, Liang Fang, Xianran Xing
Inorganic Chemistry Communications 2013 Volume 27() pp:9-12
Publication Date(Web):January 2013
DOI:10.1016/j.inoche.2012.10.013
The piezoelectric ceramics 0.45PbTiO3-0.55Bi(Ni1/2Ti1/2)O3 doped with PbO, Bi2O3, NiO and TiO2 were synthesized by conventional solid state reaction method. Thereafter, the structural, ferroelectric and piezoelectric properties of modified ceramics were investigated systematically. By adding Bi2O3, NiO and TiO2, the leakage current of ceramics was found to diminish pronouncedly. Moreover, the coercive field was observed to decrease by modification with TiO2 in these ceramics. It was also proven that NiO can only be added in the B-site in PT-55BNT from the results of X-ray photoelectron spectroscopy analysis. Therefore, the modification with oxides can inhibit the volatilization of Pb during the sintering process that eventually improves the performance of materials.By adding Bi2O3, NiO, and TiO2 the leakage current of ceramics can pronouncedly diminish. The modification of TiO2 can also reduce the coercive field. The X-ray photoelectron spectroscopy analysis measurements prove that NiO can only be added in B-site in PT-55BNT.Highlights► We do not introduce any other impurities. ► By adding Bi2O3, NiO, and TiO2 the leakage current of ceramics can obviously diminish. ► The XPS analysis tests prove that NiO can only be added in B-site in PT-55BNT.
Co-reporter:Xiaoxin An, Jinxia Deng, Jun Chen, Xianran Xing
Materials Research Bulletin 2013 48(12) pp: 4984-4988
Publication Date(Web):
DOI:10.1016/j.materresbull.2013.05.060
Co-reporter:Hanqing Zhao, Jiaou Wang, Ce Sun, Jun Chen, Abduleziz Ablat, Emin Muhemmed, Kurash Ibrahim, Shizhang Qiao, Lijie Qiao, Xianran Xing
Thin Solid Films 2013 Volume 542() pp:155-159
Publication Date(Web):2 September 2013
DOI:10.1016/j.tsf.2013.07.007
•Hybridizations between O 2p and Pb 6s and Ti 3d orbitals.•Hybridizations weakened leading to reduced ferroelectricity.•Enhanced ferromagnetism ascribed to raised superexchange interaction among Ni ions.•Magnetoelectric effect enhanced with increasing dopant concentration.The single phase (1 − x)PbTiO3 – xBi(Ni1/2Ti1/2)O3 thin films were synthesized on Pt/Ti/SiO2/Si substrate at 600 °C by a chemical solution deposition route. The present films exhibit homogeneous and crackfree microstructure with low porosity. The surface roughness decreases from 5.56 nm to 1.62 nm with solubility. The remanent polarization monotonously decreases with the dopant Bi(Ni1/2Ti1/2)O3 increase. The leakage current desity increases when the solubility increases. O K-edge X-ray absorption spectroscopy and valence-band edge X-ray photoelectron spectroscopy were used to study the electronic structure. The results indicated that the change of ferroelectricity might be ascribed to the hybridizations between O 2p and Pb 6s and Ti 3d orbitals. The ferromagnetic behaviors were also observed in the thin films and saturated magnetization raises monotonously with the Ni solubility due to enhanced superexchange interaction. Magnetoelectic effects increases with dopant Bi(Ni1/2Ti1/2)O3 increase.
Co-reporter:Huajun Kang, Jun Chen, Laijun Liu, Liang Fang, Xianran Xing
Materials Research Bulletin 2013 48(5) pp: 2006-2009
Publication Date(Web):
DOI:10.1016/j.materresbull.2013.02.002
Co-reporter:Penghao Hu, Jun Chen, Ziyou Yu, Lili Zhou, Jinxia Deng and Xianran Xing
Journal of Materials Chemistry A 2012 vol. 22(Issue 13) pp:6311-6315
Publication Date(Web):21 Feb 2012
DOI:10.1039/C2JM15952J
A series of solid solutions (1−x−y)PbTiO3-xBi(Ni1/2Ti1/2)O3-yBiScO3 were prepared to search for a high performance multifunctional ceramic material. Through contents tailoring, a compound at the morphotropic phase boundary 0.50PT-0.30BNT-0.20BS was found, which displays excellent ferroelectric and piezoelectric properties. The mechanical performances, hardness and fracture toughness of the highly compact ceramic are superior among the similar piezoceramics, and its thermal stability is great. The durability of the material is expected to be much increased in various applications. Ferromagnetism was observed in the solid solution due to the introduction of magnetic atoms, Ni, accounted for the superexchange interaction. This multiferroic material has promising applications due to its high piezoelectricity, superior mechanical performances and excellent thermal stability.
Co-reporter:Jinxia Deng, Lihong Li, Jun Chen, Ranbo Yu, Xianran Xing
Inorganic Chemistry Communications 2012 Volume 21() pp:92-95
Publication Date(Web):July 2012
DOI:10.1016/j.inoche.2012.04.021
Co-reporter:Huihui Zhu;Jun Chen;Jinxia Deng;Ranbo Yu
Metallurgical and Materials Transactions B 2012 Volume 43( Issue 3) pp:494-502
Publication Date(Web):2012 June
DOI:10.1007/s11663-011-9630-2
The oxidation behavior of synthetic pentlandite at 973 K (700 °C) under isothermal conditions was investigated. The pentlandite sample (Ni,Fe)9S8 was synthesized from pure components and oxidized at 973 K (700 °C) in air in a muffle furnace. The phase identification and components analysis of the oxidation products were performed by using the Rietveld quantitative analysis method based on the powder X-ray diffraction (XRD) profiles and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The magnetic hysteresis loops were determined by a vibrating sample magnetometer. Fe2O3, NixFe3-xO4, and NiO were dominant oxidation products, and their weight fractions changed in different ways along with the oxidation time. The nickel-rich phase and sulfur-rich phase were observed as intermediate phases in unreacted cores during oxidation, which led to the formation of gaps and holes. The oxidation reaction rate was rapid in the first 2 hours, and then it slowed down sharply.
Co-reporter:Jun Chen ; Krishna Nittala ; Jennifer S. Forrester ; Jacob L. Jones ; Jinxia Deng ; Ranbo Yu
Journal of the American Chemical Society 2011 Volume 133(Issue 29) pp:11114-11117
Publication Date(Web):June 22, 2011
DOI:10.1021/ja2046292
PbTiO3-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO3–0.3BiFeO3 and 0.7PbTiO3–0.3Bi(Zn1/2Ti1/2)O3, whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (δzPb/Bi) is weakened in 0.7PbTiO3–0.3BiFeO3 but well-maintained in 0.7PbTiO3–0.3Bi(Zn1/2Ti1/2)O3. There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi–O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides.
Co-reporter:Penghao Hu, Huajun Kang, Jun Chen, Jinxia Deng and Xianran Xing
Journal of Materials Chemistry A 2011 vol. 21(Issue 40) pp:16205-16209
Publication Date(Web):13 Sep 2011
DOI:10.1039/C1JM12410B
A low thermal expansion and ferromagnetism enhanced compound (1−x−y)PbTiO3-xBi(Ni1/2Ti1/2)O3-yBiFeO3 was developed by chemical composition controlling. The appropriate ratio of dopants Bi(Ni1/2Ti1/2)O3 and BiFeO3 not only tailored the thermal expansion but also realized high thermal stability in a wide temperature range. The ferromagnetism was improved by BiFeO3 and the ferroelectric and piezoelectric properties were well retained with Bi(Ni1/2Ti1/2)O3. The ceramics show good mechanical performances such as high hardness and satisfied fracture toughness due to the Bi(Ni1/2Ti1/2)O3 stabilizing the structure and reducing the internal stress. These good properties make the material multifunctional and promising in the application. The present work provides a way to design and explore multifunctional materials with required properties.
Co-reporter:Xiaowei Wang ; Qingzhen Huang ; Jinxia Deng ; Ranbo Yu ; Jun Chen
Inorganic Chemistry 2011 Volume 50(Issue 6) pp:2685-2690
Publication Date(Web):February 21, 2011
DOI:10.1021/ic200003n
Two phase transformations of TaVO5 were observed by DSC and/or dilatometry measurements in the studied temperature range. X-ray diffraction and neutron powder diffraction structure refinements indicated a phase transformation at −14 °C from a monoclinic symmetry with space group P21/c to an orthorhombic symmetry with space group Pnma above this temperature. The rigid TaO6 octahedron in orthorhombic phase becomes nonregular at −14 °C, which results in the transition from Pnma to P21/c. TaVO5 was found to be a negative thermal expansion material above room temperature. The calculated volumetric thermal expansion coefficients (TECs) are −8.92 × 10−6 °C−1 in the range of 20−600 °C, and −2.19 × 10−5 °C−1 above 600 °C, respectively. The negative thermal expansion behavior is accounted for by the tilt of the TaO6 and VO4 polyhedra, where the shrinkage of the VO4 tetrahedra result in the increase of Ta−O−V angles on heating, while the angle of Ta−O1−Ta maintains at 180° in the framework.
Co-reporter:Jinrui Wang, Jinxia Deng, Ranbo Yu, Jun Chen and Xianran Xing
Dalton Transactions 2011 vol. 40(Issue 13) pp:3394-3397
Publication Date(Web):18 Feb 2011
DOI:10.1039/C0DT01562H
We develop a coprecipitation synthesis route to prepare NbVO5 with simple oxide Nb2O5 and NH4VO3 as starting materials. No metal alkoxide or organometallic substance was used in the process. Nano-crystal NbVO5 was obtained by calcination of the coprecipitates at 550 °C for 2 h. DSC/TG and XRD investigations indicate that the target compound NbVO5 is completely formed up to 504.5 °C and is thermally stable below 658 °C. Rietveld XRD refinements give an orthorhombic structure with space group Pnma and lattice parameters, a = 11.8453(2), b = 5.5126(3) and c = 6.9212(2) Å, respectively. In particular, HTXRD determinations show a negative thermal expansion in NbVO5 with a TEC of −6.63 × 10−6 °C−1 in the temperature range of RT–600 °C. This fact is ascribed to the tilting of NbO6 octahedra and VO4 tetrahedra in the flexible framework structure. The present synthesis route is facile and easy to be extended to prepare analogues such as TaVO5, etc.
Co-reporter:Penghao Hu ; Jun Chen ; Jinxia Deng
Journal of the American Chemical Society 2010 Volume 132(Issue 6) pp:1925-1928
Publication Date(Web):January 22, 2010
DOI:10.1021/ja908014u
A zero thermal expansion and multiferroic compound 0.8PbTiO3−0.2Bi(Ni1/2Ti1/2)O3 was developed by a chemical modification route. The structure studies showed that the tetragonality of (1 − x)PbTiO3−xBi(Ni1/2Ti1/2)O3 was gradually weakened to cubic by introducing the dopant Bi(Ni1/2Ti)1/2O3, and the thermal expansion coefficient changed from −8.81 × 10−6/°C to 8.46 × 10−6/°C in 0.1 ≤ x ≤ 0.3 around a wide temperature range (from RT to about 500 °C). Weak ferromagnetic behavior was observed in the solid solutions, and the superexchange interaction was incorporated to explain its nonmonotonous evolution. Meanwhile, the good piezoelectricity and ferroelectricity were well retained. Further investigations demonstrated that the (1 − x)PbTiO3−xBi(Ni1/2Ti1/2)O3 ceramics possessed good mechanical properties, such as high density and excellent fracture toughness. The improved behaviors make the (1 − x)PbTiO3−xBi(Ni1/2Ti1/2)O3 promising piezoceramics with high thermal stability and mechanical performance. The present work provides a way to design and explore high-performance multiferroic compounds in the synthesis route.
Co-reporter:Ce Sun, Jinguo Wang, Penghao Hu, Moon J. Kim and Xianran Xing
Dalton Transactions 2010 vol. 39(Issue 21) pp:5183-5186
Publication Date(Web):04 May 2010
DOI:10.1039/C000608D
Al-doped PbTiO3 solid solutions were synthesized by a solid state method. Since Al does not have bonding d-orbit or d-electrons, and the substitutions of Al3+ for Ti4+ in PbTiO3 is aliovalent, the effect of Al on the structure and spontaneous polarization is quite different from that of Hf, Zr, etc. substitutions in PbTiO3. Usually, the spontaneous polarization is weakened with decreased tetragonality in PbZrxTi1−xO3 and PbHfxTi1−xO3 systems; PbTi1−xAlxO3 (0 ≤x≤ 0.10) solid solutions exhibit improved spontaneous polarization with decreased tetragonality (c/a). Lattice dynamics and the crystal structure of PbTi1−xAlxO3 with enhanced spontaneous polarization were investigated by FT-IR, Raman scattering technique, and X-Ray Rietveld method. The Al-doping reinforced the covalence of Pb–O(II), which indicated that the Pb–O hybridization was strengthened. The three transverse optical (TO) modes of A1-symmetry in Raman and the “stretching” and “bending” vibration modes in FTIR further verified the increase of spontaneous polarization (PS) in the A- and B-sites.
Co-reporter:Ce Sun, Jinguo Wang, Huajun Kang, Jun Chen, Moon J. Kim and Xianran Xing
Dalton Transactions 2010 vol. 39(Issue 41) pp:9952-9955
Publication Date(Web):27 Sep 2010
DOI:10.1039/C0DT00681E
Single phase Pb(Ti0.8Fe0.2)O3−δ thin films with a thickness of 210 nm and 120 nm were fabricated on Pt/Ti/SiO2/Si substrate by a chemical solution deposition technique. The thin film with a thickness of 210 nm showed a homogeneous microstructure, low porosity, low oxygen vacancies, and preferred orientation. It had negligible leakage current and well saturated ferroelectric hysteresis loop compared with the Pb(Ti0.8Fe0.2)O3−δ bulk sample. Polarization fatigue characteristic indicated that this film has a potential application as a switcher in some electrical devices. The saturation magnetization in the Fe-doped PbTiO3 film is weaker than that for bulk sample, and its ferromagnetism is correlated to the F-center exchange (FCE) mechanism. The present results revealed the multiferroic nature of the Pb(Ti0.8Fe0.2)O3−δ thin film.
Co-reporter:Lihong Li, Jinxia Deng, Jun Chen, Xueyi Sun, Ranbo Yu, Guirong Liu and Xianran Xing
Chemistry of Materials 2009 Volume 21(Issue 7) pp:1207
Publication Date(Web):March 16, 2009
DOI:10.1021/cm802776g
Perovskite alkaline niobates, especially of one-dimensional morphology, have many important industrial applications. Wirelike Nb2O5 and ANbO3 (A = K, Na, (Na,K)) were fabricated by a topochemical method based on the molten salt synthesis. First, the precursor KNb3O8 with wire structure was prepared under the condition of molten salt KCl environment at 800 °C for 3 h. Then, rodlike H3ONb3O8 and Nb2O5 were obtained from the wirelike KNb3O8 precursor. Finally, the rodlike ANbO3 (A = K, Na, (Na,K)) were achieved with the intermediate oxide Nb2O5. The wirelike structure of the final product can be achieved when using wirelike Nb2O5 precursor only. The structural evolution was investigated among protonic niobate, niobium oxide, and niobates. The mechanism of these shape transitions was elucidated in the view of structure recombining and atomic diffusing. The (Na,K)NbO3 ceramic sintered from the as-prepared rodlike particles under pressureless condition in the air performed with high piezoelectricity (d33 = 140 pC/N), which is much better than that of ceramics obtained from cubic or spheric particles.
Co-reporter:Penghao Hu, Jun Chen, Xueyi Sun, Jinxia Deng, Xi Chen, Ranbo Yu, Lijie Qiao and Xianran Xing
Journal of Materials Chemistry A 2009 vol. 19(Issue 11) pp:1648-1652
Publication Date(Web):04 Feb 2009
DOI:10.1039/B816822A
The compounds (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 (x = 0–0.7) were prepared in order to hunt for low thermal expansion piezoceramics, in particular for zero thermal expansion over a wide temperature range. The negative thermal expansion of PbTiO3 was much weakened by forming a solid solution with Bi(Mg,Ti)1/2O3. Solutions of (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 with x = 0.2 and x = 0.4 exhibited zero thermal expansion covering a wide temperature range (from RT to about 500 °C). The (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 ceramics had high density and their mechanical performances were satisfactory with high fracture toughness. The promising applications of the zero thermal expansion materials (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 are due to its high piezoelectric d33, controllable thermal expansion, and high thermal stability.
Co-reporter:Lihong Li, Jinxia Deng, Jun Chen, Ranbo Yu, Lijie Qiao, Xianran Xing
Journal of Alloys and Compounds 2009 Volume 471(1–2) pp:428-431
Publication Date(Web):5 March 2009
DOI:10.1016/j.jallcom.2008.03.102
0.96(Na,K)(Nb0.9Ta0.1)O3–0.04LiSbO3 powders in the orthorhombic phase were synthesized in the molten salt KCl at a low temperature 800 °C. It was revealed that K+ in the molten salt tended to substitute Na+ in the A-sites and the final product 0.96(Na0.29K0.71)(Nb0.9Ta0.1)O3–0.04LiSbO3 was synthesized from the nominal composition 0.96(Na0.5K0.5)(Nb0.9Ta0.1)O3–0.04LiSbO3. The dense ceramics under pressureless were obtained by sintering in the air. The ceramics exhibited high piezoelectric constant d33 of 239 pC/N and good remnant polarization Pr of 30.79 μC/cm2 with coercive electric field Ec of 2.01 kV/mm. And leakage current was reduced by muffling the ceramics with the as-prepared powders during the sintering process.
Co-reporter:Jinxia Deng, Jun Chen, Ranbo Yu, Guirong Liu, Xianran Xing
Journal of Alloys and Compounds 2009 Volume 472(1–2) pp:502-506
Publication Date(Web):20 March 2009
DOI:10.1016/j.jallcom.2008.05.006
The crystal structure of the microwave dielectric ceramics Ba(Ca1/3Nb2/3)O3 synthesized by the molten salt method has been refined, from X-ray diffraction, in a trigonal order–disorder lattice with the P3¯m1(D3d3) space group. The lattice distortion and cation ordering are attributed to the large Ca2+ ions at B′-site, which induces a large deviation of bond valence sums of the B-site ions. The ordering degree determined by the variations of the occupancies of Ca and Nb ions is 0.44. High-resolution transmission electron microscopy (HRTEM) and Raman spectrum show the evidence in support of the 1:2 B-site order–disorder model. The complete Raman mode assignment for Ba(Ca1/3Nb2/3)O3 with order–disorder structure is also presented.
Co-reporter:Jinrong Bao;Ranbo Yu;Jiayun Zhang;Xiaodan Yang;Dan Wang;Jinxia Deng;Jun Chen
European Journal of Inorganic Chemistry 2009 Volume 2009( Issue 16) pp:2388-2392
Publication Date(Web):
DOI:10.1002/ejic.200900060
Abstract
Nanostructured terbium orthophosphate (TbPO4·H2O) nanostructures with enhanced photoluminescence were prepared through a controlled, simple, and template-free hydrothermal route. The structures and micromorphologies of the as-synthesized TbPO4·H2O were investigated by X-ray powder diffraction (XRD), thermogravimetric analysis, differential scanning calorimetry (TG-DSC), field-emission scanning electronic microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS). The results showed that the TbPO4·H2O spindle-like hierarchical nanostructures are composed of ordered nanorods of 80–90 nm in diameter and lengths of up to 200–300 nm. It was found that the reactant molar ratios and pH values played key roles in the morphology control of the product. A possible formation mechanism for the spindle-like morphology is also proposed. A photoluminescence study of the products indicated that the self-assembled spindle-like nanostructures display better photoluminescence than TbPO4·H2O that was synthesized on both the nano- and microscale.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Co-reporter:Jinxia Deng, Jun Chen, Ranbo Yu, Guirong Liu, Xianran Xing, Songbai Han, Yuntao Liu, Dongfeng Chen, Linfeng He
Solid State Sciences 2009 Volume 11(Issue 1) pp:170-175
Publication Date(Web):January 2009
DOI:10.1016/j.solidstatesciences.2008.05.014
Microwave dielectric powder Ba(Ca1/3Nb2/3)O3 with high B-site cation ordering was synthesized by the molten salt method. Neutron powder diffraction (NPD) and Raman scattering spectra were introduced to investigate the variable ordering degree during the sintering process. It was revealed that the as-synthesized Ba(Ca1/3Nb2/3)O3 powder had a nearly completely ordered structure, and the sintered Ba(Ca1/3Nb2/3)O3 presented a bit higher ordering degree based on the detailed quantitative NPD Rietveld full profile fitting. The complete Raman mode assignment for the Ba(Ca1/3Nb2/3)O3 was presented. The phonon bands could also confirm the order–disorder structural model and increasing ordering degree with the increasing sintering temperature. Final microwave dielectric measurements on sintered samples showed the present compound to tailor other dielectric materials for microwave applications with the dielectric properties of ɛr = 47.11, and Qf = 1389 GHz, and τf was about 113 ppm/°C.
Co-reporter:Lai Yan, Ranbo Yu, Jun Chen and Xianran Xing
Crystal Growth & Design 2008 Volume 8(Issue 5) pp:1474
Publication Date(Web):March 25, 2008
DOI:10.1021/cg800117v
Uniform single-crystalline CeO2 nano-octahedrons and nanorods were synthesized by a facile hydrothermal synthesis process only using Ce(NO3)3·6H2O as cerium resource and Na3PO4·6H2O as mineralizer, into which no surfactant or template was introduced. By tuning the hydrothermal treatment time, the morphology evolution between the nano-octahedron and nanorod was observed. Furthermore, the synthesizing mechanism and the morphological evolution of different shapes were investigated. Unlike traditional hydrothermal synthesis of CeO2 nanostructures using strong base as precipitant, Na3PO4 does not leave any impurity in the hydrothermal reaction system and makes the process very simple to obtain and separate the octahedral and rodlike morphology.
Co-reporter:Zongying Cai, Xianran Xing, Lu Li, Yeming Xu
Journal of Alloys and Compounds 2008 Volume 454(1–2) pp:466-470
Publication Date(Web):24 April 2008
DOI:10.1016/j.jallcom.2006.12.128
Lead lanthanum zirconate titanate (Pb0.95La0.03)(Zr0.52Ti0.48)O3 (PLZT) was synthesized by one step molten salt method with the starting materials of PbC2O4, La2O3, ZrO(NO3)2·2H2O and TiO2 in the NaCl–KCl eutectic mixtures in the temperature range of 700–1000 °C. The single phase of (Pb0.95La0.03)(Zr0.52Ti0.48)O3 powders was prepared at a temperature as low as 850 °C for 5 h. The effects of process parameters, such as soaking temperature and time, salt species, and the amount of flux with respect to the starting materials were investigated. The growth process of the PLZT particles in the molten salt undergoes a transition from a diffusion controlled mechanism to an interfacial reaction controlled mechanism at 900 °C.
Co-reporter:Mingzhen Zheng, Xianran Xing, Jinxia Deng, Lu Li, Jie Zhao, Lijie Qiao, Chunying Fang
Journal of Alloys and Compounds 2008 Volume 456(1–2) pp:353-357
Publication Date(Web):29 May 2008
DOI:10.1016/j.jallcom.2007.02.039
Hexagonal ilmenite-type (Zn1−xMnx)TiO3 (0 ≤ x ≤ 0.9) ceramic powders were synthesized by a sol–gel route including the Pechini process with heat treatments at 600 °C for 3 h and 800 °C for 6 h. The thermal stability of ZnTiO3 dielectric ceramics was improved (>1200 °C) by doping manganese. The dielectric constant of (Zn1−xMnx)TiO3 ceramic was higher than those of (Zn, M)TiO3 (M = Co, Ni, etc.), increased with the amount of manganese in the range of 0 ≤ x < 0.7 then decreased after the maximum point at x = 0.7 in the same frequency. Both the dielectric loss tangent and the dielectric constant decreased with increasing the measured frequencies. The value of dielectric loss tangent was relatively high because of magnetoresistive effect of manganese.
Co-reporter:Lai Yan, Ranbo Yu, Guirong Liu, Xianran Xing
Scripta Materialia 2008 Volume 58(Issue 8) pp:707-710
Publication Date(Web):April 2008
DOI:10.1016/j.scriptamat.2007.12.007
Large-scale uniform Pr(OH)3 nanorods were prepared by a facile template-free precipitation method. Upon calcining, the Pr(OH)3 converted to Pr6O11 and largely retained the nanorod morphology. X-Ray diffraction and selected-area electron diffraction results indicated that the Pr(OH)3 and Pr6O11 nanorods had good hexagonal and cubic single crystalline structures, respectively. Thermal and surface properties were also characterized in detail by means of thermogravimetry/differential scanning calorimetry, X-ray photoelectron spectroscopy and nitrogen physisorption.
Co-reporter:Lihong Li;Jun Chen;Jinxia Deng;Ranbo Yu;Lijie Qiao;Guirong Liu
European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 13) pp:2186-2190
Publication Date(Web):
DOI:10.1002/ejic.200701263
Abstract
Micron-scale platelet (Na, K)NbO3 particles were synthesized from the platelet precursor K4Nb6O17 in a KCl medium using a topochemical method . The salt took part in the reaction and affected the composition of the products. Stoichiometric (Na0.5K0.5)NbO3 could be accurately synthesized by controlling the amount of the reactant Na2CO3. X-ray diffraction analysis revealed that the crystallographic {010} plane of K4Nb6O17 was converted into the pseudo-cubic {001} plane of (Na0.5K0.5)NbO3. The polycrystalline Na0.5K0.5NbO3 particles exhibited a plate-like shape with a high aspect ratio, and were suitable for preparing textured ceramics by the template grain growth process. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Co-reporter:Jun Chen;Ranbo Yu;Lihong Li;Ce Sun;Teng Zhang;Houwen Chen
European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 23) pp:3655-3660
Publication Date(Web):
DOI:10.1002/ejic.200800263
Abstract
A facile and environmentally friendly synthesis method has been employed to prepare micron or submicron single-crystal Bi1–xLaxFeO3 with different particle shapes. Various forms of the crystallite are obtained, such as cubic, tetragonal, and semi-sphere crystallites, by means of molten salt synthesis. The thermal stability of BiFeO3 perovskite is greatly enhanced by substitution with LaFeO3. The pure phase ofBi1–xLaxFeO3 can be obtained without the use of the rapid thermal technique by introducing with small amounts of LaFeO3 into BiFeO3. The structure of Bi1–xLaxFeO3 changes from rhombohedral BiFeO3 (R3c) to orthorhombic LaFeO3 (Pnma) with an intermediate orthorhombic phase (C222), which is demonstrated by the X-ray diffraction, Raman spectoscopy, and electron diffraction. The formation of Bi1–xLaxFeO3 can be completed in a short time (i.e. 30 min), as the reaction temperature reaches the melting point of NaCl. For the synthesis of Bi0.4La0.6FeO3, the nuclei occur with an irregular tetragonal shape in the initial nucleation stage and then grow with a regular tetragonal profile in the following growth stage. The Bi1–xLaxFeO3 crystal growth was revealed to follow the Ostwald ripening mechanism.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Co-reporter:Jun Chen, Caiyan Zhang, Xianran Xing
Materials Letters 2008 Volume 62(Issue 15) pp:2332-2334
Publication Date(Web):31 May 2008
DOI:10.1016/j.matlet.2007.11.099
The single-crystalline Bi3.25La0.75Ti3O12 micro-platelets were directly synthesized in the NaCl–KCl medium at the relative low temperature by means of molten salt synthesis method (MSS). The as-prepared Bi3.25La0.75Ti3O12 solid solution exhibits the monoclinic symmetry (P1a1) which was revealed by the X-ray and electron diffractions. In the NaCl–KCl medium, the square platelet of single-crystal Bi3.25La0.75Ti3O12 grew along its crystal habit plane (001), and its thickness increased layer by layer. The growth mechanism could be that it was an edge nucleation, grew in amorphous as early stage, and then preferentially crystallized along (001) plane.
Co-reporter:Penghao Hu, Zhanmin Cao, Jun Chen, Jinxia Deng, Ce Sun, Ranbo Yu, Xianran Xing
Materials Letters 2008 Volume 62(Issue 30) pp:4585-4587
Publication Date(Web):15 December 2008
DOI:10.1016/j.matlet.2008.08.028
Pb1-xBixTiO3 (x = 0.0–0.1) compounds were prepared to study the unique dopant effect of bismuth in PbTiO3. Their thermal expansions and structures were investigated by high-temperature X-ray diffraction and X-ray Rietveld method. The results indicated that Bismuth substitution evidently weakened the tetragonality of PbTiO3 solid solution, but increased the spontaneous polarization. Both the enhanced spontaneous polarization and the decreased tetragonality led to small volume shrinkage with temperature rising, where the average volumetric thermal expansion coefficient changed from − 1.99 × 10− 5/°C for pure PbTiO3 to − 0.56 × 10− 5/°C for Pb0.90Bi0.10TiO3. The Curie point of Pb1 − xBixTiO3 was slightly raised compared to PbTiO3 and permitted one to use it in a wide temperature range.
Co-reporter:Ranbo Yu, Lai Yan, Peng Zheng, Jun Chen and Xianran Xing
The Journal of Physical Chemistry C 2008 Volume 112(Issue 50) pp:19896-19900
Publication Date(Web):2017-2-22
DOI:10.1021/jp806092q
Large-scale CeO2 hierarchical architectures composed of well-aligned nanorods were controllably prepared through a simple Na3PO4 assisted hydrothermal reaction without any templates. The products were characterized with X-ray diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. It was found that the CeO2 architectures are in flower-like and vertically aligned nanorod morphologies and composed of numerous fluorite cubic single-crystalline nanorods of 20−40 nm in diameter and lengths of up to several micrometers. The possible mechanism for the nanostructures formation was discussed.
Co-reporter:Jinxia Deng, Xianran Xing, Jun Chen, Ranbo Yu, Guirong Liu
Scripta Materialia 2007 Volume 56(Issue 1) pp:65-68
Publication Date(Web):January 2007
DOI:10.1016/j.scriptamat.2006.08.055
The crystal structures of the perovskite ceramic Ba(Cd1/3Nb2/3)O3 prepared by the molten salt method have been studied. The X-ray Rietveld method and selected-area electron diffraction apparently show an ordered trigonal structure. Furthermore Ba(Cd1/3Nb2/3)O3 exhibits a large perturbation away from the totally ordered structure and the ordering degree determined by the variations of the occupancies of Cd2+ and Nb5+ cations in B′/B″ sites is 0.443.
Co-reporter:Lai Yan, Xianran Xing, Ranbo Yu, Lijie Qiao, Jun Chen, Jinxia Deng, Guirong Liu
Scripta Materialia 2007 Volume 56(Issue 4) pp:301-304
Publication Date(Web):February 2007
DOI:10.1016/j.scriptamat.2006.09.013
Well monodispersed and large-scaled Pr-doped ceria nanorods were prepared via a high-temperature precipitation and low-temperature aging route without further sintering. X-ray diffraction, transmission electron microscopy and selected-area electron diffraction indicated that the as-prepared ceria nanorods had a cubic fluorite structure and the morphologies of the products were uniform, being ∼30 nm in diameter and ∼400 nm in length. The physisorption experiments showed a high specific surface area of Pr-doped ceria nanorods.
Co-reporter:Ce Sun;Jun Chen;Jinxia Deng;Lu Li;Ranbo Yu;Lijie Qiao;Guirong Liu
European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 13) pp:
Publication Date(Web):20 MAR 2007
DOI:10.1002/ejic.200601131
(K1–xNax)NbO3 (x = 0.01, 0.24, 0.89, 0.91, 0.99) single crystalline powders with perovskite structure were synthesized by a hydrothermal method with Nb2O5 in a mixed solution of KOH and NaOH at 220 °C for 24 h. XRD investigations showed that the structure of the synthesized (K1–xNax)NbO3 ceramics changed from a KNbO3-type orthorhombic phase (space group Bmm2) to a NaNbO3-type monoclinic phase (space group Pm) with the increase of Na content. The present results confirmed that (K1–xNax)NbO3 exhibited a morphotropic phase boundary (MPB) at around 50 %K separating the orthorhombic phase and monoclinic phase. FE-SEM images showed that the morphological structures of niobates were cubes and nanofingers. The TEM image and the selected area electron diffraction pattern of (K0.01Na0.99)NbO3 showed the as-synthesized powder was single crystalline and indexed to be monoclinic. The phase evolution of the products in the hydrothermal route revealed that the hydrothermal synthesis of (K1–xNax)NbO3 underwent two steps, where an intermediate product (K8–8xNa8x)Nb6O19·n H2O was found in the early stage and then pure (K1–xNax)NbO3 was obtained after another 30 min of hydrothermal treatment.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Co-reporter:Zhanheng CHEN, Xianran XING, Wenxia YUAN, Xiaowei HUANG, Hongwei LI
Rare Metals 2006 Volume 25(Issue 5) pp:562-566
Publication Date(Web):October 2006
DOI:10.1016/S1001-0521(06)60099-5
The nano powders of LaCrO3 were prepared by a sol-gel route. The heat capacity of LaCrO3 nano powders from 350 to 550 K was measured by DSC method and expressed as: Cp(LaCrO3) (±0.112) = 166.844 − 8.500 × 10−3T − 1.022 × 106T−2 (J/(mol·K)) (350–550 K). An EMF measurement assembly was developed with CaF2 as an electrolyte for the galvanic cell. From measured EMF data of the reversible cell, (−) Pt, La2O3, LaF3, O2 (1 atm)|CaF2|O2(1 atm), LaF3, LaCrO3, Cr2O3, Pt(+), and the relevant value of Gibbs free energy, the Gibbs free energy of formation of LaCrO3 was calculated from 700 to 885 K: ΔGf,LaCrO3 = −1555.364 + 0.354T (kJ/mol) (700–885 K). And the Gibbs free energy change of reaction from simple oxides La2O3 and Cr2O3 was calculated to be: ΔGf,ox(LaCrO3) = −94.758 + 8.530 × 10−2T(kJ/mol) (700–885 K).
Co-reporter:Jun Luo, Xianran Xing, Ranbo Yu, Qifeng Xing, Daofan Zhang, Xiaolong Chen
Journal of Alloys and Compounds 2005 Volume 402(1–2) pp:263-268
Publication Date(Web):27 October 2005
DOI:10.1016/j.jallcom.2005.04.153
Purely hexagonal ilmenite-type zinc metatitanate (ZnTiO3) and (Zn1−xCox)TiO3 (x = 0.5–1) ceramic powders were successfully synthesized at low temperature by a sol–gel route including the Pechini process. The process was modified by using a two-step heat treatment so as to obtain pure products, as was proved by the XRD, FT-IR and TG-DTA measurements. The thermodynamic stability of (Zn1−xCox)TiO3 products improved with increasing solubility x. The average crystalline grain sizes of the final products varied from ∼220 to 100 nm with increasing solubility x as confirmed by FE-SEM observation. The dielectric properties of (Zn1−xCox)TiO3 were measured at different frequencies and the results showed that there existed maximum values both for the dielectric constants and the loss tangents at x = 0.5.
Co-reporter:Xianran Xing, Shuyu Dai, Zhenqi Zhu, Toshihiro Tanaka
Thermochimica Acta 2002 Volume 383(1–2) pp:31-35
Publication Date(Web):7 February 2002
DOI:10.1016/S0040-6031(01)00675-X
The intermediate compounds, K3DyCl6, K2DyCl5 and KDy2Cl7, in the DyCl3–KCl system, are confirmed by X-ray powder diffraction method. With CALPHAD technology the phase diagram of the DyCl3–KCl system is re-optimized and calculated using ChemSage software. A set of thermodynamic functions has been optimized based on an interactive computer-assisted analysis. The calculated phase diagram and optimized thermodynamic parameters are thermodynamically self-consistent.
Co-reporter:Lihong Li ; Jinxia Deng ; Ranbo Yu ; Jun Chen ; Xiaowei Wang
Inorganic Chemistry () pp:
Publication Date(Web):January 11, 2010
DOI:10.1021/ic902165r
In this paper, we report a catalyst-free topochemical method, combined with molten salt synthesis (MSS), to synthesize, on a large scale, rodlike and platelet single crystals of Nb2O5. Rodlike KNb3O8 and platelet K4Nb6O17, which were fabricated as the precursors by the molten salt method, were treated by proton exchange and heat treatment to synthesize the rodlike H−Nb2O5 and platelet T−Nb2O5 single crystal, respectively. The synthesized niobium pentaoxides retained the rodlike and platelet shapes of their precursors. The structural changes involved in the process were investigated by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A possible topochemical reaction mechanism is proposed. Furthermore, rodlike and platelet KNbO3 powders were derived from stable H−Nb2O5 and T−Nb2O5, respectively.
Co-reporter:Linxing Zhang, Jun Chen, Jiangli Cao, Dongyu He and Xianran Xing
Journal of Materials Chemistry A 2015 - vol. 3(Issue 18) pp:NaN4712-4712
Publication Date(Web):2015/03/31
DOI:10.1039/C5TC00814J
The destructive readout signal distinguishing the ferroelectric polarization state in a memory device has long been seen as the bottleneck for its commercial application. Both ferroelectric resistive switching and the switchable photovoltaic effect provide multiple choices for non-destructive readout. The polycrystalline ferroelectric BiFeO3-based thin films fabricated by cost-effective chemical solution growth exhibit large resistive switching (with ON/OFF ratios ∼104), which is comparable to switchable diodes and tunnel junctions. Furthermore, switchable photovoltaic response shows stable switching and good retention properties. The standard hysteretic loops of resistive switching current, short circuit current and open circuit voltage versus poling voltage directly indicate hysteretic modulation by ferroelectric polarization, which is the first evidence in polycrystalline BiFeO3 based films. The present films would be potential candidates for non-destructive ferroelectric memory devices with multiple selections.
Co-reporter:Linxing Zhang, Jun Chen, Hanqing Zhao, Longlong Fan, Yangchun Rong, Jinxia Deng, Ranbo Yu and Xianran Xing
Dalton Transactions 2013 - vol. 42(Issue 2) pp:NaN590-590
Publication Date(Web):2012/11/06
DOI:10.1039/C2DT31996A
The applications of ferroelectric thin films such as the sensitivity of nonvolatile ferroelectric random access memories are closely linked with large remnant polarization. The high-TC (1−x)Bi(Zn1/2Zr1/2)O3–xPbTiO3 (x = 0.7–0.9) thin films with high (100) orientation were fabricated on Pt(111)/Ti/SiO2/Si substrates via a sol–gel method. The thin films could be crystallized well in a phase-pure perovskite structure. The electrical properties of the sol–gel-derived BZZ–PT thin films were investigated. A large remanent polarization with 2Pr up to 110 μC cm−2 and a small leakage current of 3.8 × 10−7 A cm−2 under an electric field of 150 kV cm−1 are observed on the 0.2BZZ–0.8PT thin films. Furthermore, a relatively stable polarization fatigue property was achieved, indicating a potential application in high-temperature ferroelectric devices.
Co-reporter:Huihui Zhu, Jinxia Deng, Jun Chen, Ranbo Yu and Xianran Xing
Journal of Materials Chemistry A 2014 - vol. 2(Issue 9) pp:NaN3014-3014
Publication Date(Web):2013/12/09
DOI:10.1039/C3TA14832G
A simple synthesis method is proposed for producing aligned and uniform single-crystal one-dimensional hematite (α-Fe2O3) nanostructures on pentlandite. Pentlandite is the most common terrestrial iron-nickel sulfide and the principal ore mineral of nickel. In this study, a pentlandite sample was synthesized from pure components Fe, Ni and S. Oxidation makes the chemical potential of iron reduce more than that of nickel. Iron migrated rapidly to the surface of dense pentlandite and was oxidized preferentially to form an oxide layer. Several micrometers long α-Fe2O3 nanowires grown along the [110] direction were achieved. The ordered oxygen vacancies which lie parallel to the growth direction were observed. Hematite (α-Fe2O3) and magnetite including Ni (NixFe3−xO4) are major components of the oxide layer. Three kinds of morphology are included in this layer: nanowires, dense and porous oxides. The Ni-rich pentlandite coexists with NiS, hexagonal pyrrhotite (Fe1−xS) and/or godlevskite (Ni7S6). This work provides a new strategy to inexpensively and efficiently synthesize nanostructures directly from ore minerals.
Co-reporter:Wei Zou, Jun Chen, Lei Hu, Qiang Li, Xiang Yao, Lin Gu, Jinxia Deng, Ranbo Yu and Xianran Xing
Journal of Materials Chemistry A 2014 - vol. 2(Issue 40) pp:NaN8568-8568
Publication Date(Web):2014/08/21
DOI:10.1039/C4TC01557F
Synthesis of hollow structures of metal sulphides generally involves various templates and complex chemical processing. In the present study, a general and rapid method of salt-assisted aerosol decomposition (SAD) is presented for the synthesis of hollow spheres of various metal sulfides, including ZnS, ternary sulfides, and solid solutions. The NaCl salt plays a critical role in the formation of hollow spheres of metal sulfides. The hollow spherical microstructure was formed from solid by using a small amount of water soluble NaCl salt. The formation of metal sulphide hollow spheres differs from previous mechanisms and is referred to as molten salt heterogeneous nucleation (MSHN). The present method offers the most promising advantage for controlling the multicomponent composition of hollow spheres. Furthermore, hollow spheres of sulphides have much enhanced properties such as photoluminescence of ZnS:Mn2+ and photocatalytic dye degradation of ZnIn2S4 due to the role of molten salt in the promotion of crystallization, The present method could be explored further by applying the process to other compounds such as sulfides, oxides, and nitrides.
Co-reporter:Lihong Li, Jinxia Deng, Jun Chen and Xianran Xing
Chemical Science (2010-Present) 2016 - vol. 7(Issue 2) pp:
Publication Date(Web):
DOI:10.1039/C5SC03521J
Co-reporter:Jun Chen, Lei Hu, Jinxia Deng and Xianran Xing
Chemical Society Reviews 2015 - vol. 44(Issue 11) pp:NaN3567-3567
Publication Date(Web):2015/04/13
DOI:10.1039/C4CS00461B
Negative thermal expansion (NTE) is an intriguing physical property of solids, which is a consequence of a complex interplay among the lattice, phonons, and electrons. Interestingly, a large number of NTE materials have been found in various types of functional materials. In the last two decades good progress has been achieved to discover new phenomena and mechanisms of NTE. In the present review article, NTE is reviewed in functional materials of ferroelectrics, magnetics, multiferroics, superconductors, temperature-induced electron configuration change and so on. Zero thermal expansion (ZTE) of functional materials is emphasized due to the importance for practical applications. The NTE functional materials present a general physical picture to reveal a strong coupling role between physical properties and NTE. There is a general nature of NTE for both ferroelectrics and magnetics, in which NTE is determined by either ferroelectric order or magnetic one. In NTE functional materials, a multi-way to control thermal expansion can be established through the coupling roles of ferroelectricity-NTE, magnetism-NTE, change of electron configuration-NTE, open-framework-NTE, and so on. Chemical modification has been proved to be an effective method to control thermal expansion. Finally, challenges and questions are discussed for the development of NTE materials. There remains a challenge to discover a “perfect” NTE material for each specific application for chemists. The future studies on NTE functional materials will definitely promote the development of NTE materials.
Co-reporter:Penghao Hu, Jun Chen, Xueyi Sun, Jinxia Deng, Xi Chen, Ranbo Yu, Lijie Qiao and Xianran Xing
Journal of Materials Chemistry A 2009 - vol. 19(Issue 11) pp:NaN1652-1652
Publication Date(Web):2009/02/04
DOI:10.1039/B816822A
The compounds (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 (x = 0–0.7) were prepared in order to hunt for low thermal expansion piezoceramics, in particular for zero thermal expansion over a wide temperature range. The negative thermal expansion of PbTiO3 was much weakened by forming a solid solution with Bi(Mg,Ti)1/2O3. Solutions of (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 with x = 0.2 and x = 0.4 exhibited zero thermal expansion covering a wide temperature range (from RT to about 500 °C). The (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 ceramics had high density and their mechanical performances were satisfactory with high fracture toughness. The promising applications of the zero thermal expansion materials (1−x)PbTiO3–xBi(Mg,Ti)1/2O3 are due to its high piezoelectric d33, controllable thermal expansion, and high thermal stability.
Co-reporter:Ce Sun, Jinguo Wang, Huajun Kang, Jun Chen, Moon J. Kim and Xianran Xing
Dalton Transactions 2010 - vol. 39(Issue 41) pp:NaN9955-9955
Publication Date(Web):2010/09/27
DOI:10.1039/C0DT00681E
Single phase Pb(Ti0.8Fe0.2)O3−δ thin films with a thickness of 210 nm and 120 nm were fabricated on Pt/Ti/SiO2/Si substrate by a chemical solution deposition technique. The thin film with a thickness of 210 nm showed a homogeneous microstructure, low porosity, low oxygen vacancies, and preferred orientation. It had negligible leakage current and well saturated ferroelectric hysteresis loop compared with the Pb(Ti0.8Fe0.2)O3−δ bulk sample. Polarization fatigue characteristic indicated that this film has a potential application as a switcher in some electrical devices. The saturation magnetization in the Fe-doped PbTiO3 film is weaker than that for bulk sample, and its ferromagnetism is correlated to the F-center exchange (FCE) mechanism. The present results revealed the multiferroic nature of the Pb(Ti0.8Fe0.2)O3−δ thin film.
Co-reporter:Weigang Cao, Qingzhen Huang, Yangchun Rong, You Wang, Jinxia Deng, Jun Chen and Xianran Xing
Inorganic Chemistry Frontiers 2016 - vol. 3(Issue 6) pp:NaN860-860
Publication Date(Web):2016/03/22
DOI:10.1039/C5QI00292C
In the present work, we have developed an effective way to control the thermal expansion of ZrW2O8 by the insertion of NH3 into the void of the framework structure. Neutron powder diffraction (NPD) and XPS studies reveal that N is bonding to W in the ammoniated ZrW2O8 and retains the original structure with the space group P213. This kind of ammoniation improves the thermal stability, raised the phase transition temperature about 50 K, and weakens the negative thermal expansion (NTE) from −7.8 × 10−6 K−1 to −2.1 × 10−6 K−1. These behaviors account for bonding of NH3 to the neighboring atoms of ZrW2O8, and hinder the rocking motion of the corner shared polyhedral structure.
Co-reporter:Kun Lin, Na Wang, Li You, Qiang Li, Kenichi Kato, Jun Chen, Jinxia Deng and Xianran Xing
Dalton Transactions 2017 - vol. 46(Issue 3) pp:NaN738-738
Publication Date(Web):2016/12/12
DOI:10.1039/C6DT04364J
Synchrotron radiation-based anomalous dispersion X-ray powder diffraction (ADSPD) was carried out to reveal the Pb/Bi ordering/disordering states in a series of PbTiO3-based negative thermal expansion materials (1 − x)PbTiO3 − xBiFeO3 (x = 0.1, 0.3, 0.5) and (1 − x)PbTiO3 − xBi(Zn1/2Ti1/2)O3 (x = 0.1, 0.2, 0.3). It gives strong evidence of the disordered Pb/Bi distributions in these compositions, which is consistent with electron diffraction studies. Combined with binding energy calculation, we show that the disordered nature of Pb/Bi distributions is likely to be attributed to the similar electron configurations of Pb2+ and Bi3+ as well as their comparable coordinate environments in perovskite structures. The results of this study may be helpful to better understand the structure–property relationship in Pb/Bi-containing perovskites and are useful for further developing underlying physics in relevant materials.
Co-reporter:Yilin Wang, Hanqing Zhao, Linxing Zhang, Zhanning Liu, Jun Chen, Jinxia Deng, Jiaou Wang, Kurash Ibrahim, Nina I. Ilinykh and Xianran Xing
Inorganic Chemistry Frontiers 2016 - vol. 3(Issue 11) pp:NaN1479-1479
Publication Date(Web):2016/09/26
DOI:10.1039/C6QI00321D
A chemical solution deposition technique was applied to fabricate single-phase 0.9PbTiO3–0.1SmFeO3 thin films on Pt/Ti/SiO2/Si substrates. The film was determined as a tetragonal perovskite structure by synchrotron radiation grazing incident X-ray diffraction (GI-XRD). A well saturated ferroelectric hysteresis loop, free from obvious change from room temperature to 120 °C, was achieved with a large remanent polarization (2Pr ≈ 130 μC cm−2). A weak magnetic nature was also observed, with a saturated magnetization (Ms) ≈ 3 emu cc−1. X-ray absorption spectra (XAS) and X-ray photoelectron spectroscopy (XPS) techniques were employed to detect the oxygen vacancies and study the bonding states of the film.
Introduction to the international collaboration
On the occasion of attending the 14th International IUPAC Conference on High Temperature Materials Chemistry in 2012, Dr Nina Ilinykle (Ural Technical Institute of Telecommunications and Informatics, Russia) visited Beijing and started to cooperate with Dr Xing's group. Our common interests involve phase thermal stability, phase structure and thermodynamic modeling of functional inorganic materials.
Co-reporter:Yilin Wang, Hanqing Zhao, Linxing Zhang, Jun Chen and Xianran Xing
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 27) pp:NaN17515-17515
Publication Date(Web):2017/06/19
DOI:10.1039/C7CP01347G
Ferroelectric thin films, especially PbTiO3-based perovskite thin films which possess robust spontaneous electrical polarization, are widely investigated and applied in various devices. With the advances in synthesis, characterization and calculation techniques, diverse phenomena and properties are uncovered in ferroelectric thin films. Herein some typical PbTiO3-based perovskite thin films through composition control are introduced, which gives more choices with various ferroelectric or other properties. Strain engineering, as well as some other interfacial effects, is also included to show the possibilities of controlling the lattice structure, the electronic structure as well as the domain structure which are closely connected to ferroelectricity. Multiferroic thin films, which could achieve magnetic-field-controlled polarization reversal, expand the novel applications of ferroelectric thin films. Typical and remarkable progress made in the case of multiferroic PbTiO3-based perovskite thin films is discussed here. Critical problems such as leakage current and fatigue hinder the practical use of ferroelectric and multiferroic thin films, and are also included in this article.
Co-reporter:Lihong Li, Jinxia Deng, Ranbo Yu, Jun Chen, Zheng Wang and Xianran Xing
Journal of Materials Chemistry A 2013 - vol. 1(Issue 38) pp:NaN11900-11900
Publication Date(Web):2013/07/30
DOI:10.1039/C3TA12599H
Herein, we developed a simple template-free synthetic method for producing niobium pentoxide (Nb2O5) hollow nanospheres, and fabricated KNbO3 hollow nanospheres which retained the morphology of the template Nb2O5 hollow nanospheres by the molten salt method. The formation of Nb2O5 hollow nanospheres was via Ostwald ripening, and the structural evolution between niobium oxide and niobates was a kind of self-sacrificing templated process. These Nb2O5 hollow nanospheres with high surface energy (001) planes showed high thermal stability and large surface area. Furthermore, they not only showed strong intensity of blue emission, but they were also able to efficiently split water under visible light irradiation, and show potential for application as sensors, optoelectronic devices and promising photocatalysts for water splitting under visible light. Due to the high thermal stability of Nb2O5 hollow nanospheres and the simplicity of the protocol, we anticipate that this work will enrich the hollow nanostructures of inorganic compounds and provide a new strategy to synthesize hollow nanospheres of niobates and other kinds of materials.
Co-reporter:Ce Sun, Jinguo Wang, Penghao Hu, Moon J. Kim and Xianran Xing
Dalton Transactions 2010 - vol. 39(Issue 21) pp:NaN5186-5186
Publication Date(Web):2010/05/04
DOI:10.1039/C000608D
Al-doped PbTiO3 solid solutions were synthesized by a solid state method. Since Al does not have bonding d-orbit or d-electrons, and the substitutions of Al3+ for Ti4+ in PbTiO3 is aliovalent, the effect of Al on the structure and spontaneous polarization is quite different from that of Hf, Zr, etc. substitutions in PbTiO3. Usually, the spontaneous polarization is weakened with decreased tetragonality in PbZrxTi1−xO3 and PbHfxTi1−xO3 systems; PbTi1−xAlxO3 (0 ≤x≤ 0.10) solid solutions exhibit improved spontaneous polarization with decreased tetragonality (c/a). Lattice dynamics and the crystal structure of PbTi1−xAlxO3 with enhanced spontaneous polarization were investigated by FT-IR, Raman scattering technique, and X-Ray Rietveld method. The Al-doping reinforced the covalence of Pb–O(II), which indicated that the Pb–O hybridization was strengthened. The three transverse optical (TO) modes of A1-symmetry in Raman and the “stretching” and “bending” vibration modes in FTIR further verified the increase of spontaneous polarization (PS) in the A- and B-sites.
Co-reporter:Penghao Hu, Jun Chen, Ziyou Yu, Lili Zhou, Jinxia Deng and Xianran Xing
Journal of Materials Chemistry A 2012 - vol. 22(Issue 13) pp:
Publication Date(Web):
DOI:10.1039/C2JM15952J
Co-reporter:Jinrui Wang, Jinxia Deng, Ranbo Yu, Jun Chen and Xianran Xing
Dalton Transactions 2011 - vol. 40(Issue 13) pp:NaN3397-3397
Publication Date(Web):2011/02/18
DOI:10.1039/C0DT01562H
We develop a coprecipitation synthesis route to prepare NbVO5 with simple oxide Nb2O5 and NH4VO3 as starting materials. No metal alkoxide or organometallic substance was used in the process. Nano-crystal NbVO5 was obtained by calcination of the coprecipitates at 550 °C for 2 h. DSC/TG and XRD investigations indicate that the target compound NbVO5 is completely formed up to 504.5 °C and is thermally stable below 658 °C. Rietveld XRD refinements give an orthorhombic structure with space group Pnma and lattice parameters, a = 11.8453(2), b = 5.5126(3) and c = 6.9212(2) Å, respectively. In particular, HTXRD determinations show a negative thermal expansion in NbVO5 with a TEC of −6.63 × 10−6 °C−1 in the temperature range of RT–600 °C. This fact is ascribed to the tilting of NbO6 octahedra and VO4 tetrahedra in the flexible framework structure. The present synthesis route is facile and easy to be extended to prepare analogues such as TaVO5, etc.
Co-reporter:Hanqing Zhao, Jun Miao, Linxing Zhang, Yangchun Rong, Jun Chen, Jinxia Deng, Ranbo Yu, Jiangli Cao, Huanhua Wang and Xianran Xing
Dalton Transactions 2016 - vol. 45(Issue 4) pp:NaN1559-1559
Publication Date(Web):2015/12/08
DOI:10.1039/C5DT03611A
Single-phase xNdFeO3–(1 − x)PbTiO3 thin films with different dopant contents were fabricated on the Pt(111)/Ti/SiO2/Si substrate by a sol–gel route. Grain size was influenced by the dopant content effectively. A synchrotron radiation X-ray diffraction study revealed a reduced tetragonality (c/a) of the PbTiO3 lattice in the films. Distortion of the TiO6 octahedron was weakened, as investigated by Raman scattering and X-ray absorption spectra. An electronic structural study indicated that the hybridizations between O 2p and Pb 6s and Ti 3d orbitals were weakened. The decrease of lattice distortion and orbital hybridization gives rise to degradation of the ferroelectric nature in the films.
Co-reporter:Fangfang Wang, Ying Xie, Jun Chen, Honggang Fu and Xianran Xing
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 11) pp:NaN5241-5241
Publication Date(Web):2013/12/17
DOI:10.1039/C3CP53197J
Recently experiments have found that negative thermal expansion is a common phenomenon in PbTiO3-based materials, and their negative thermal expansion is affected by various substitutions. Interestingly, Cd substitution in PbTiO3 has a unique effect in enhancing negative thermal expansion compared with any other A-site substitutions. Therefore, studying Cd substitution in PbTiO3, the role of which still remains unclear, would bring us deeper understanding on the nature of the negative thermal expansion of PbTiO3-based materials. Structure calculations, density of states, Bader analysis and the minimum electron density of Pb1−xCdxTiO3 supercells have been reported on the chemical bond through first-principles calculations here. We found that the hybridization between (Pb,Cd)–O orbitals exists in tetragonal phase. Furthermore, the hybridization between Cd–O orbitals is stronger than that between Pb–O orbitals, and Cd–O covalency promotes the average A-site hybridization. Simultaneously, the average bulk coefficient of thermal expansion is negative and inversely proportional to the Cd substitution amount. So, (Pb,Cd)–O covalency in the tetragonal Pb1−xCdxTiO3 is responsible for the nature of enhanced negative thermal expansion in accordance with our previous experimental investigations.
Co-reporter:Hanqing Zhao, Jiaou Wang, Linxing Zhang, Yangchun Rong, Jun Chen, Kurash Ibrahim and Xianran Xing
Dalton Transactions 2013 - vol. 42(Issue 28) pp:NaN10364-10364
Publication Date(Web):2013/05/10
DOI:10.1039/C3DT50257K
The single phase Pb0.8Co0.2TiO3 thin films were synthesized on a Pt/Ti/SiO2/Si substrate by the sol–gel route. The present films exhibited homogeneous microstructure with low porosity. O 1s X-ray photoelectron spectroscopy (XPS) was used to detect the amount of oxygen vacancies. The ferroelectric measurements showed that the ferroelectricity deteriorates with the increase in the number of oxygen vacancies. X-ray absorption spectroscopy (XAS) and XPS were used to study the electronic structure. The results indicated that the decreased ferroelectricity might be ascribed to the weakened hybridization between O 2p and Pb 6s and Ti 3d orbitals. The ferromagnetic behaviors were also observed in the thin films and saturated magnetization raised monotonously with the oxygen vacancy rising due to the enhanced F-center exchange interaction. Magnetoelectric coupling of the films weakened with oxygen vacancy increase.
Co-reporter:You Wang, Yun Wang, Wei Ren, Porun Liu, Huijun Zhao, Jun Chen, Jinxia Deng and Xianran Xing
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 43) pp:NaN29102-29102
Publication Date(Web):2015/09/28
DOI:10.1039/C5CP03941J
NdFeO3 is an important candidate material for gas sensors and intermediate-temperature solid oxide fuel cells (IT-SOFC). However, its low conductivity prohibits its applications. In this study, we report that the doping of Ca by partially replacing Nd can effectively increase its conductivity. Through the electronic structure analysis of Nd1−xCaxFeO3 (x = 0.00, 0.25, 0.50, 0.75 or 1.00) based on the first-principles density functional theory calculations, it is found that the hole states introduced by Ca substitution appear just above the Fermi level, which implies a high mobility of electrons/holes along the Fe–O–Fe bonding network. Specifically, it becomes easier to form O vacancies after Ca doping. Since the diffusion of O anions occurs through a vacancy hopping mechanism, the ion conductivity is also improved. These findings help us to gain an in-depth understanding of the colossally increased conductivity of Ca doped NdFeO3 and turn the electronic conduction for its practical application in gas sensors and IT-SOFC.
Co-reporter:Yangchun Rong, Menglei Li, Jun Chen, Mei Zhou, Kun Lin, Lei Hu, Wenxia Yuan, Wenhui Duan, Jinxia Deng and Xianran Xing
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 8) pp:NaN6251-6251
Publication Date(Web):2016/01/26
DOI:10.1039/C6CP00011H
Functional materials showing both negative thermal expansion (NTE) and physical performance, such as ferroelectricity and magnetism, have been extensively explored in the past decade. However, among ferroelectrics a remarkable NTE was only found in perovskite-type PbTiO3-based compounds. In this work, a large NTE of −4.7 × 10−5 K−1 is obtained in the non-perovskite lead-free ferroelectric Sn2P2S6 from 243 K to TC (338 K). Structure refinements and first-principle calculations reveal the effects of the Sn(II) 5s–S 3p interaction on spontaneous polarization and its correlation with NTE. Then the mechanism of spontaneous volume ferroelectrostriction (SVFS) is verified and it could well elucidate the nature of NTE in ferroelectric Sn2P2S6. This is the first case to demonstrate the unusual NTE behavior by SVFS in a non-perovskite lead-free ferroelectric material.
Co-reporter:Kun Lin, Hui Wu, Fangfang Wang, Yangchun Rong, Jun Chen, Jinxia Deng, Ranbo Yu, Liang Fang, Qingzhen Huang and Xianran Xing
Dalton Transactions 2014 - vol. 43(Issue 19) pp:NaN7043-7043
Publication Date(Web):2014/01/23
DOI:10.1039/C3DT53340A
The structure and thermal expansion behavior of the tetragonal tungsten bronze oxide Pb2KNb5O15 were investigated by neutron powder diffraction and high-temperature X-ray diffraction. Below the Curie temperature, TC (orthorhombic phase, TC ≈ 460 °C), the cell parameters a and c increase with temperature, while b decreases. The thermal expansion coefficients are αa = 1.29 × 10−5 °C−1, αb = −1.56 × 10−5 °C−1, and αc = 1.62 × 10−5 °C−1. Temperature-dependent second harmonic generation (SHG), dielectric, and polarization–electrical field (P–E) hysteresis loop measurements were performed to study the symmetry and electric properties. We show that the distortion and cooperative rotation of NbO6 octahedrons are directly responsible for the negative thermal expansion coefficient along the polar b axis. It is suggested that Pb–O covalency, especially in the large and asymmetric pentagonal prisms, may be related to orthorhombic distortion and abnormal spontaneous polarization along the b axis. This study shows that tungsten bronze families are possible candidates for exploring negative thermal expansion materials.
Co-reporter:Penghao Hu, Huajun Kang, Jun Chen, Jinxia Deng and Xianran Xing
Journal of Materials Chemistry A 2011 - vol. 21(Issue 40) pp:NaN16209-16209
Publication Date(Web):2011/09/13
DOI:10.1039/C1JM12410B
A low thermal expansion and ferromagnetism enhanced compound (1−x−y)PbTiO3-xBi(Ni1/2Ti1/2)O3-yBiFeO3 was developed by chemical composition controlling. The appropriate ratio of dopants Bi(Ni1/2Ti1/2)O3 and BiFeO3 not only tailored the thermal expansion but also realized high thermal stability in a wide temperature range. The ferromagnetism was improved by BiFeO3 and the ferroelectric and piezoelectric properties were well retained with Bi(Ni1/2Ti1/2)O3. The ceramics show good mechanical performances such as high hardness and satisfied fracture toughness due to the Bi(Ni1/2Ti1/2)O3 stabilizing the structure and reducing the internal stress. These good properties make the material multifunctional and promising in the application. The present work provides a way to design and explore multifunctional materials with required properties.
