Co-reporter:Xiaoyan Gan, Ou Wang, Keyong Liu, Xiangjun Du, Liling Guo, Hanxing Liu
Solar Energy Materials and Solar Cells 2017 Volume 162() pp:93-102
Publication Date(Web):April 2017
DOI:10.1016/j.solmat.2016.12.047
•2D (PEA)2(MA)m-1PbmI3 m+1 perovskite films exhibited high moisture stability.•The m=3 (PEA)2(MA)2Pb3I10 perovskite device exhibits best cell performance.•TiO2 nanorods are useful in functionalizing 2D perovskites for PV applications.•The m=3 perovskite cells with 600 nm-long TiO2 NRs exhibit an efficiency of 3.72%.We present the fabrication and characterization of two dimensional (2D) perovskites (PEA)2(MA)m-1PbmI3 m+1 (PEA=phenylethylammonium, MA=methylammonium, m=1,2,3) for application as light absorbers in solar cells. Films of 2D perovskite series show high stability under humid air, with band gaps decreasing with increasing m values, from 2.36 eV for (PEA)2PbI4 (m=1) to 1.94 eV for (PEA)2(MA)2Pb3I10 (m=3). Owning to the smaller bandgap, favorable vertical growth characteristics, and appropriate energy band structure of (PEA)2(MA)2Pb3I10, planer perovskite solar cells based on (PEA)2(MA)2Pb3I10 exhibit best cell performance. Incorporation of TiO2 nanorod arrays into (PEA)2(MA)2Pb3I7 based perovskite solar cells are further found to be useful in improving the cell performance, ascribing to the improved quality and coverage of the perovskite films, as well as the enhanced electronic contact between the perovskites and the electron transporting layer. By optimizing the TiO2 NR lengths, an efficiency of 3.72% is obtained for (PEA)2(MA)2Pb3I10 perovskite cells with 600 nm-long TiO2NRs as scaffolds, which is more than a time higher than that of the planer analogue device. Our study to design 2D perovskite solar cells demonstrates the importance of material structure and device configuration for efficient solar cells, highlighting the validity of TiO2 nanorods in functionalizing 2D perovskites for photovoltaic applications.TiO2 nanorods are demonstrated to be useful in functionalizing two dimensional (PEA)2(MA)m-1PbmI3 m+1 (PEA=phenylethylammonium, MA=methylammonium, m=1,2,3) perovskite hybrids for photovoltaic applications.
Co-reporter:Qi Xu, Juan Xie, Zichen He, Lin Zhang, Minghe Cao, Xindi Huang, Michael T. Lanagan, Hua Hao, Zhonghua Yao, Hanxing Liu
Journal of the European Ceramic Society 2017 Volume 37(Issue 1) pp:99-106
Publication Date(Web):January 2017
DOI:10.1016/j.jeurceramsoc.2016.07.011
0.93Bi0.5Na0.5TiO3-0.07BaTiO3 (BNTBT) and KNbO3 (KN) powders with average particle size of ∼50 nm and ∼300 nm were synthesized by sol-gel method and hydrothermal method, respectively. Then, (1 − x)(BNTBT)-xKN (BNTBT-KN, x = 0, 0.01, 0.03, 0.05, 0.07) ceramic samples were prepared using these two powder precursors. The structure, dielectric and energy-storage properties of BNTBT-KN ceramics were comprehensively investigated. All the ceramic samples were in single perovskite structure, indicating that KN can completely dissolve into BNTBT within the studied composition range. BNTBT-KN ceramics exhibited a high dielectric constant at room temperature, being in the order of 1430–1550. Ferroelectric hysteresis loops at room temperature became more slim with the increase of KN content, which largely improved energy-storage density and efficiency. For the composition of x = 0.05, the maximum recoverable energy-storage density reached 1.72 J/cm3 under 16.8 kV/mm, which is superior to linear dielectrics and even some Pb-based systems. All these results demonstrate that 0.95BNTBT-0.05KN fabricated by wet-chemical method is a promising lead-free dielectric material for energy-storage capacitors.
Ceramics International 2017 Volume 43(Issue 1) pp:484-490
Publication Date(Web):January 2017
DOI:10.1016/j.ceramint.2016.09.183
Abstract
Mg1−xZnxSiO3 (x=0–0.3) ceramics were successfully synthesized by conventional solid-state methods and characterized by scanning electron microscopy, dispersive X-ray spectroscopy, and X-ray diffraction. The microstructures and microwave dielectric properties of Mg1−xZnxSiO3 ceramics were systematically investigated. The lattice parameters of the samples with different Zn2+ contents were analyzed. When the Zn2+ content was increased from 0 to 0.15, the Qufo of the sample increased from 103,453 GHz to a maximum 138,481 GHz. This also resulted in a significant lowering in the sintering temperature (90 °C). Monoclinic structured Mg0.85Zn0.15SiO3 was detected without any secondary phase. In this study, a new combination of microwave dielectric properties (εr∼8.05, Qufo∼138,481 GHz, τf∼−14 ppm/°C) was achieved for Mg0.85Zn0.15SiO3 sample sintered at 1360 °C for 9 h. The prepared material with remarkable useful dielectric properties can be used for millimeter-wave applications.
Journal of Materials Science: Materials in Electronics 2017 Volume 28( Issue 15) pp:11491-11499
Publication Date(Web):18 April 2017
DOI:10.1007/s10854-017-6945-z
We investigated the structure, dielectric properties and energy density performances of cubic perovskite-structured Mg-doped SrTiO3 ceramics that were prepared by the solid-state reaction method. SrTiO3 ceramic exhibited a relatively stable permittivity about 265–290 and enhanced dielectric breakdown strength (DBS) by Mg isovalent doping. Doping effects on the energy-storage properties in SrTiO3 ceramics was performed by complex impedance analysis and polarization–electric field hysteresis loops. The energy storage density was dependent on DBS while energy efficiency was closely related to the remnant polarization. The possible physical mechanisms, including grain, gain boundary and interfacial polarization effects, were discussed to explain the improvement of dielectric breakdown strength. The bulk Mg-doped SrTiO3 materials have shown interesting energy densities (1.86 J/cm3) with good energy storage efficiency (about 89.3%) indicating that they can be a promising candidate for high energy density capacitor applications.
Journal of Materials Science: Materials in Electronics 2017 Volume 28( Issue 5) pp:4204-4210
Publication Date(Web):19 November 2016
DOI:10.1007/s10854-016-6042-8
Nb2O5 doped 0.8BaTiO3–0.2(Na1/4Bi3/4)(Mg1/4Ti3/4)O3 (0.8BT–0.2NBMT) polycrystalline ceramics were prepared by solid state reaction method. 0.8BT–0.2NBMT samples were observed to possess two dielectric peaks, which were attributed to the formation of core–shell structure (Huang et al. in J Eur Ceram Soc 36:533–540, 2015). Longer sintering induced uniform distributions of the additives. The introduction of Nb2O5 into 0.8BT–0.2NBMT could obviously bring about the improvement of the dielectric temperature stability, the degradation of the dielectric loss at room temperature and the decrease of the sintering temperature. The 0.8BT–0.2NBMT ceramics doped with 2.0 at% Nb2O5 could satisfy the temperature range of the X9R (−55 to 200 °C, △C/C25°C = ±15% or less) characteristics, with a moderate dielectric constant of 1130, low dielectric loss of 0.7%, low sintering temperature of 1050 °C and insulation resistivity of 5 × 1012 Ω cm at room temperature, which might be promising for practical use in multilayer ceramic capacitors. The inhomogeneous distribution and the existence of the secondary phases were responsible for this excellent dielectric temperature characteristic. The complex impedance analysis was introduced to elaborate the conduction mechanism.
Journal of the European Ceramic Society 2017 Volume 37, Issue 9(Volume 37, Issue 9) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.jeurceramsoc.2017.03.047
(1-x)Mg0.90Ni0.1SiO3-xTiO2 (x = 0, 0.01, 0.03, 0.05) ceramics were successfully formed by the conventional solid-state methods and characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), and their microstructure and microwave dielectric properties systematically investigated. It was observed that when TiO2 content increased from 0 to 5 wt%, the Qufo of the sample decreased from 118,702 GHz to 101,307 GHz and increases the τf value from −10 ppm/°C to +3.14 ppm/°C accompanied by a notable lowering in the sintering temperature (125 °C). A good combination of microwave dielectric properties (εr ∼ 8.29, Qufo ∼ 101,307 GHz and τf ∼ −2.98 ppm/°C) were achieved for Mg0.90Ni0.1SiO3 containing 3 wt% of TiO2 sintered at 1300 °C for 9 h which make this material of possible interest for millimeter wave applications.
xBa0.7Sr0.3TiO3-SrTiO3 (BST-ST) multilayer ceramics with different BST layers (x=1, 3, 5) were designed and fabricated by lamination of Ba0.7Sr0.3TiO3 (BST) and SrTiO3 (ST) tapes. Dielectric and energy storage properties of the multilayer ceramics were investigated. BST-ST multilayer ceramics exhibited enhanced temperature- and frequency-stability of dielectric properties, accompanying high permittivity (~2000) and low dielectric loss (<0.005) at room temperature. P-E loops revealed that BST-ST multilayer ceramics displayed low remnant polarization and favorable maximum polarization. The optimal energy storage performance was obtained in the composition of x=5 with dielectric breakdown strength of 220 kV/cm and energy storage density of 2.3 J/cm3. These results indicate that BST-ST multilayer ceramics can be a favorable candidate for dielectric capacitor applications.
Solid electrolyte Li7La3Zr2-xTixO12 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) ceramics have been prepared via a conventional solid-state reaction. X-ray diffraction (XRD) analysis confirms that all samples formed a single phase with cubic garnet structure within the limit of instrument measurement, and with increasing Ti content from x = 0 to 0.5, the intensity of diffraction peaks exhibits a tendency of weakening. It is found that Ti doping in Li7La3Zr2O12 (LLZ) can lead to the increase of the densification, which is favorable to improve the ionic conductivity. Finally, optimized conductivity has been obtained for the sample with x = 0.3 for lithium ion battery: the total ionic conductivity reaches a maximum of about 4.16 × 10−4 S cm−1 at 30 °C with an activation energy of about 0.48 eV. XRD analysis and cyclic voltammetry experiments on cells indicate the Li7La3Zr2-xTixO12 pellet is stable with lithium metal.
Co-reporter:Zhonghua Yao;Zhe Song;Hua Hao;Zhiyong Yu;Minghe Cao;Shujun Zhang;Michael T. Lanagan
Advanced Materials 2017 Volume 29(Issue 20) pp:
Publication Date(Web):2017/05/01
DOI:10.1002/adma.201601727
The demand for dielectric capacitors with higher energy-storage capability is increasing for power electronic devices due to the rapid development of electronic industry. Existing dielectrics for high-energy-storage capacitors and potential new capacitor technologies are reviewed toward realizing these goals. Various dielectric materials with desirable permittivity and dielectric breakdown strength potentially meeting the device requirements are discussed. However, some significant limitations for current dielectrics can be ascribed to their low permittivity, low breakdown strength, and high hysteresis loss, which will decrease their energy density and efficiency. Thus, the implementation of dielectric materials for high-energy-density applications requires the comprehensive understanding of both the materials design and processing. The optimization of high-energy-storage dielectrics will have far-reaching impacts on the sustainable energy and will be an important research topic in the near future.
Co-reporter:Chunli Diao, Hanxing Liu, Hua Hao, Minghe Cao, Zhonghua Yao
Ceramics International 2016 Volume 42(Issue 11) pp:12639-12643
Publication Date(Web):15 August 2016
DOI:10.1016/j.ceramint.2016.04.169
Abstract
SiO2-added barium strontium titanate ceramics Ba0.4Sr0.6TiO3-xwt%SiO2 (x=0, 0.5, 1, 3, BSTSx) were prepared via a traditional solid state reaction method. The effect of SiO2 additive on the microstructure, dielectric response and energy storage properties was investigated. The results confirmed that with the increase of SiO2 additive, diffuse phase transition arises and the dielectric constant decreases. An equivalent circuit model and Arrhenius law were used to calculate the activation energy of grain and grain boundary, which indicated that the dielectric relaxation at high temperature was caused by oxygen vacancy. While appropriate SiO2 additive led to improve the breakdown strength, further increase of SiO2 deteriorated the energy storage because of the low densification. Finally, optimized energy storage performance was obtained for BSTS0.5 ceramics: dielectric constant of 1002, dielectric loss of 0.45%, energy density of 0.86 J/cm3 and energy storage efficiency of 79% at 134 kV/cm.
Journal of the European Ceramic Society 2016 Volume 36(Issue 3) pp:533-540
Publication Date(Web):February 2016
DOI:10.1016/j.jeurceramsoc.2015.10.043
Dense (1 − x)BaTiO3−x(Na1/4Bi3/4)(Mg1/4Ti3/4)O3 [(1 − x)BT–xNBMT] polycrystalline ceramics were prepared by solid-state reaction method. The detailed structure analysis was performed by X-ray diffraction (XRD) and Raman spectroscopy, confirming that the Ba and Ti sites were partially replaced by Na+/Bi3+ and Mg2+ ions, respectively. An obvious structural variation from tetragonal to pseudocubic was observed for sample with x = 0.08–0.12. The lattice parameter for sample with x ≥ 0.12 decreased linearly with x value. Three changing modes in frequency, width and intensity were observed with x value in the Raman spectra, indicating intense changes of local structure, accounting for evolved dielectric and ferroelectric macroscopic properties. The subgrain microstructures were observed by conventional transmission electron microscopy (TEM) imaging with an energy-dispersive X-ray spectroscopy (EDS) attachment. A large number of core–shell grains were detected by TEM dark field, for x = 0.20, which were attributed to the dissolution–precipitation mechanism. In this present study, (1 − x)BT–xNBMT ceramics are considered promising for high temperature capacitor applications.
Co-reporter:Qi Xu, Michael T. Lanagan, Wei Luo, Lin Zhang, Juan Xie, Hua Hao, Minghe Cao, Zhonghua Yao, Hanxing Liu
Journal of the European Ceramic Society 2016 Volume 36(Issue 10) pp:2469-2477
Publication Date(Web):August 2016
DOI:10.1016/j.jeurceramsoc.2016.03.011
Electric conduction and dielectric relaxation behavior in (1—x)(Bi0.5Na0.5TiO3-BaTiO3)-xNaNbO3 ((1—x)(BNT–BT)–xNN) ceramics were investigated. All compositions showed negative temperature coefficient of resistance (NTCR) behavior. The bulk conductivity followed the Arrhenius law with Ea = 1.24–1.55 eV, which can be attributed to the electronic conduction. In the modulus (M′′-f) spectra, a peak and a shoulder were observed, corresponding to the bulk and polar nano regions (PNRs) response respectively. With the increase of either temperature or NN content, the shoulder gradually depressed and even disappeared. A correlation between the PNRs evolution and the relaxation behavior was constructed.
Co-reporter:Juan Xie, Hua Hao, Hanxing Liu, Zhonghua Yao, Zhe Song, Lin Zhang, Qi Xu, Jinqiang Dai, Minghe Cao
Ceramics International 2016 Volume 42(Issue 11) pp:12796-12801
Publication Date(Web):15 August 2016
DOI:10.1016/j.ceramint.2016.05.042
Abstract
SrSnxTi(1−x)O3 (x=0, 0.01, 0.03, 0.05, 0.07) dielectric ceramics were fabricated by the solid state reaction method. Significant refinement of grain size and improved resistivity were observed with the addition of Sn, accounting for effectively enhanced dielectric breakdown strength, beneficial for the energy storage applications. Impedance analysis was employed to calculate the conductivities of grain and grain boundary and resistance ratios (Rgb/Rg) of grain boundary to grain. The grain boundary effect was believed to dominate the modified macroscopic performance, which was confirmed by the complex impedance analysis. The optimal properties were achieved for samples with x=0.05, exhibiting a charge energy density of 1.1 J/cm3 and an energy efficiency of 87%.
Co-reporter:Zhonghua Yao, Kang Lu, Chaobing Xu, Hua Hao, Qi Xu, Zhe Song, Zhiyong Yu, Atta Ullah, Hanxing Liu
Journal of Alloys and Compounds 2016 Volume 663() pp:41-45
Publication Date(Web):5 April 2016
DOI:10.1016/j.jallcom.2015.12.103
•Develop a new low-cost Bi-based high temperature piezoceramics with Tc∼580 °C.•La can drive the changes of phase structure and electrical characterization.•La-driven compositions exhibit improved electrical properties.•Thermal stability is closely related to domain type of ferroelectric ceramics.La-doped 0.3(Bi1−xLax)(Zn0.5Ti0.5)O3-0.7PbTiO3 (BLZT-PT) ceramics with 0 ≤ x ≤ 0.30 was studied. La doping reduced the tetragonality/polar distortion, shifted Curie temperature, changed thermal stability and improved ferro-piezoelectric properties of the ceramics. The sample with optimal composition at x = 0.055 exhibited high Curie temperature of about 580 °C with good piezoelectric properties. This makes BLZT-PT a promising candidate for next-generation of piezoelectric ceramics at high-temperatures.Download high-res image (144KB)Download full-size image
Journal of the European Ceramic Society 2016 Volume 36(Issue 13) pp:3157-3163
Publication Date(Web):October 2016
DOI:10.1016/j.jeurceramsoc.2016.05.002
Pore free Ca0.6Sr0.4TiO3 (CST) ceramics with HfO2 additives (0 wt.%, 2.0 wt.%, 4.0 wt.% and 6.0 wt.%) were fabricated via solid state reaction method at 1400 °C. Structure characterization was conducted by XRD and SEM, indicating the existence of HfO2 at grain boundaries as the intergranular phase. The dielectric breakdown strength and energy storage efficiency were found to be greatly enhanced for CST with moderate HfO2 additives, the sample with 4.0 wt.% HfO2 exhibited optimized microstructure and energy storage properties, with maximum average breakdown strength (28.9 kV/mm) and high energy storage efficiency (nearly 95% at 24 kV/mm). In addition, effect of Hf-rich intergranular phase on the charge transportation and interfacial polarization behavior was discussed. With good dispersion, the intergranular HfO2 phase was considered effective to modify the grain boundaries properties and consequently improve the energy storage performance for CST ceramics.
Ceramics International 2016 Volume 42(Issue 15) pp:16782-16788
Publication Date(Web):15 November 2016
DOI:10.1016/j.ceramint.2016.07.165
Abstract
The BaxSr0.97−xSm0.02TiO3 (x=0–0.4) ceramics in different sintering atmosphere were prepared by conventional solid-state reaction methods. The effect of different atmosphere on the dielectric properties of BaxSr0.97−xSm0.02TiO3 ceramics was investigated. The giant permittivity was obtained for BaxSr0.97−xSm0.02TiO3 ceramics sintered in nitrogen especially for x=0.2, which exhibited a weak temperature- and frequency- dependent giant permittivity (>104) as well as a low dielectric loss (mostly <0.05) over a broad temperature range from 20 to 300 °C. Based on the relaxation behaviors, XPS Spectrum and complex- impedance analysis of ceramics in different sintering atmosphere, the giant permittivity and low dielectric loss were due to the existence of the giant defect dipoles [Ti4+·e -- e·Ti4+] generated by the fully ionized oxygen vacancies and Ti3+ ions, while the defect dipoles () and interfacial polarization caused the dielectric relaxation of the ceramics sintered in air or O2.
Mn-doped perovskite oxides, La0.6Sr0.4Co1−xMnxO3 (x = 0.05, 0.1), have been synthesized and Li–O2 batteries based on La0.6Sr0.4Co1−xMnxO3/Super P electrodes and non-aqueous electrolytes were also fabricated and measured in this work. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity of the as-prepared electrode based Li–O2 batteries were measured using cyclic voltammetry (CV) tests. In terms of the ORR and OER peak current, the performance is enhanced in the order of pure Super P, La0.6Sr0.4CoO3, La0.6Sr0.4Co0.95Mn0.05O3 and La0.6Sr0.4Co0.9Mn0.1O3. The Li–O2 batteries based on a La0.6Sr0.4Co0.9Mn0.1O3/Super P electrode exhibited a higher first discharge capacity, lower over-potential and better cycling stability, which was in agreement with the trend shown in the CV curves. The electrochemical impedance spectroscopy measurements revealed that the impedance of the battery increased slowly during cycling due to the accumulation of undecomposed discharge products on the cathode.
Co-reporter:Qi Xu, Michael T. Lanagan, Xuechen Huang, Juan Xie, Lin Zhang, Hua Hao, Hanxing Liu
Ceramics International 2016 Volume 42(Issue 8) pp:9728-9736
Publication Date(Web):June 2016
DOI:10.1016/j.ceramint.2016.03.062
The dielectric behavior, impedance spectroscopy and energy-storage properties of 0.85[(1−x)Bi0.5Na0.5TiO3–xBaTiO3]–0.15Na0.73Bi0.09NbO3 [(BNT–xBT)–NBN] ternary ceramics were investigated. Temperature dependent permittivity curves displayed two depressed anomalies, resulting in significantly improved dielectric temperature stability. (BNT–9BT)–NBN showed a permittivity of 1680 at 150 °C with Δε/ε150 °C varying no more than ±10% up to 340 °C. From the complex impedance analysis, grain and grain boundary shared the same time constant. The high temperature resistivity followed the Arrhenius law with Ea=1.7–2.0 eV, suggesting intrinsic band-type electronic conduction. The maximum energy-storage density of all the samples reached 1.1–1.4 J/cm3, accompanied with good temperature stability in the range of 25–140 °C. These results indicate that (BNT–xBT)–NBN system should be a promising lead-free material for energy-storage capacitor applications.
Ceramics International 2016 Volume 42(Issue 1) pp:379-387
Publication Date(Web):January 2016
DOI:10.1016/j.ceramint.2015.08.120
The typical “core–shell” structure in BT ceramics can easily obtain double dielectric anomalies, which greatly improve the dielectric temperature stability for multilayer ceramic capacitors. In this paper, BaTiO3 particles were coated with 0.3BiAlO3–0.7BaTiO3 shell [xBT@(0.3BA–0.7BT)] by a sol–gel method. Core–shell structure was proved to exist in ceramic grains by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). High-temperature X9R dielectrics were obtained when x=0.3 and 0.2, with a high dielectric constant (~1200) and low dielectric loss (<2.0%). Furthermore, the impedance data was fitted by an effective 4RC equivalent circuit, which could be assigned to the core, the shell, the grain boundary, and the ceramic/internal electrode interface regions. The activation energy of the core was found to decrease with x decreasing, while opposite tendency exists in the shell and the grain boundary.
•Cubic Li7La3Zr2O12 electrolyte was synthesized by Chemical co-precipitation method.•Tetragonal LLZO transformed into cubic LLZO when the temperature was above 1150 °C.•The particle size of LLZO precursor powder was in the range of 0.5 ~ 1 μm.•The total ionic conductivity of sample sintered at 1180 °C was 2.0 × 10− 4 S cm− 1 at 30 °C.•The activation energy was 0.25 eV.Solid electrolyte Li7La3Zr2O12 (LLZO) powder was successfully synthesized by co-precipitation method. The LLZO powder calcined at 850 °C with a tetragonal phase was confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) showed that the particles sizes of LLZO precursor powder were in the range of 0.5 ~ 1 μm. LLZO pellets were sintered at different temperatures from 1150 to 1200 °C in air atmosphere. When the temperature was above 1150 °C, tetragonal LLZO would completely transform into cubic phase. The total ionic conductivity of LLZO pellet sintered at 1180 °C was 2.0 × 10− 4 S cm− 1 at 30 °C, and the activation energy was 0.25 eV. This result indicates that high quality LLZO solid electrolytes can be obtained by chemical co-precipitation method.
Ni doped perovskite oxides La0.6Sr0.4Co1-xNixO3 (x = 0, 0.05, 0.1) have been synthesized by a dry gel combustion method using citric acid and EDTA (ethylene diamine tetraacetic acid) as complex agent. The Li-O2 batteries on the basis of the La0.6Sr0.4Co1-xNixO3 perovskite nanoparticles and non-aqueous electrolytes were also fabricated and measured. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity of as-prepared electrodes were measured by cyclic voltammetry (CV) curves. The peak current increased in the order of pure Super P, La0.6Sr0.4CoO3, La0.6Sr0.4Co0.95Ni0.05O3, and La0.6Sr0.4Co0.9Ni0.1O3. The electrochemical impedance spectroscopy (EIS) measurements revealed that La0.6Sr0.4Co1-xNixO3 catalyst could restrain the increase of impedance during discharge process and promote the decomposition of discharge products during charge process. La0.6Sr0.4Co0.95Ni0.05O3 and La0.6Sr0.4Co0.9Ni0.1O3 catalysts displayed enhanced performances compared with La0.6Sr0.4CoO3 catalyst. The initial capacity of batteries using La0.6Sr0.4Co0.95Ni0.05O3 and La0.6Sr0.4Co0.9Ni0.1O3 as the cathode catalyst displayed enhanced performances compared with La0.6Sr0.4CoO3 catalyst, which was in agreement with the trend of CV curves.
Journal of the European Ceramic Society 2015 Volume 35(Issue 2) pp:545-553
Publication Date(Web):February 2015
DOI:10.1016/j.jeurceramsoc.2014.09.003
(1 − x)BNTBT-x NN ceramics were prepared by conventional solid state reaction method. X-ray fluorescence analysis shows that the volatilization of Na element occurs during sintering process, the resulted concentration variation of V′Na−VO−V′Na defect dipoles facilitate the grain growth. XRD analysis and dielectric properties analysis indicate that rhombohedral polar phase and tetragonal weakly polar phase coexist in BNTBT ceramics at room temperature. By increasing the NN amount, the rhombohedral polar phase content sharply decreases, leading to a smaller remnant polarization. The dielectric anomaly corresponding to the depolarization temperature disappears from the temperature range investigated. According to the XRD results, the amount of tetragonal weakly polar phase decreases with increasing NN content and the structure evolves toward a pseudocubic symmetry. The phase structure change results in more slim P–E loops. The optimum energy storage properties was obtained for the composition of x = 0.10, with energy storage density of 0.71 J/cm3 at 7 kV/mm and a good temperature stability around 25–150 °C.
Co-reporter:Yue Sun, Hanxing Liu, Hua Hao, Lin Zhang, Shujun Zhang
Ceramics International 2015 Volume 41(Issue 1) pp:931-939
Publication Date(Web):January 2015
DOI:10.1016/j.ceramint.2014.08.140
Ceramics in BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–Co3O4 (BT–NBT–Nb–Co) system were fabricated to satisfy the EIA-X9R specification (−55~200 °C, ΔC/C≤±15%) of multilayer ceramic capacitors. The role of Co in this system was investigated. The core–shell structure was found to exist in the system, as confirmed by transmission electron microscopy (TEM), accounting for the high dielectric temperature stability. The Co can regulate the reaction between Nb and BT–NBT to adjust the core–shell structure, where the optimum dielectric properties were achieved at Nb/Co=3, with dielectric constant being 930 at room temperature and capacitance variation being less than 15% in the temperature range from −55 °C to 200 °C. The impedance spectroscopy was fitted by 3RC equivalent circuit, corresponding to the grain, grain boundary and ceramic/electrode interface region for the Co modified BT–NBT system. The conduction activation energy of grain was found to decrease with increasing Co concentration, where the conduction mechanism of grain and grain boundary are both sensitive to the Co concentration.
Co-reporter:Xuechen Huang, Hanxing Liu, Hua Hao, Shujun Zhang, Yue Sun, Wenqin Zhang, Lin Zhang, Minghe Cao
Ceramics International 2015 Volume 41(Issue 6) pp:7489-7495
Publication Date(Web):July 2015
DOI:10.1016/j.ceramint.2015.02.070
MgO-doped 0.97BaTiO3–0.03BiYO3 (0.97BT–0.03BY) polycrystalline ceramics were prepared by the solid-state sintering method. Then the structural, dielectric and resistant properties were investigated as functions of MgO addition. Microstructure was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The results show that Bi3+, Y3+ and Mg2+ ions exhibit nonuniform distribution behavior in BT–BY ceramics, demonstrating the existence of a “core–shell” structure, which plays important roles in the capacitance-temperature characteristics, where 0.97BT–0.03BY with the addition 2.2–2.8 at% MgO meets the Electronic Industries Association (EIA) X8R (−55 to 150 °C, ΔC/C25 °C=±15% or less) specification. Moreover, the fine-grained samples with core–shell structure show much higher bulk resistance than the coarse-grained samples over the studied temperature range, which is attributed to the higher proportion of grain boundaries and the lower concentration of the effective acceptor.
Journal of Materials Science 2015 Volume 50( Issue 24) pp:7866-7874
Publication Date(Web):2015 December
DOI:10.1007/s10853-015-9267-7
In this study, we report on the electrodeposition of p-type semiconductor copper thiocyanate (CuSCN) nanorods on ITO substrate from an aqueous solution. The influence of the bath temperature and deposition potential on the properties of CuSCN layers was studied. Nanorods deposited at low temperature (25 °C) exhibited better crystalline quality and orientation along the c-axis than the nanorods grown at elevated temperatures. The deposition potential turned out to influence strongly the crystallographic orientation, the morphology, as well as the optical properties of the product. Mott–Schottky measurement demonstrates that the CuSCN nanorods are p-type semiconductor, with a hole concentration (NA) eight times larger than that of the 2D thin films when the cylindrical geometry of the nanorods was taken into consideration. The CuSCN nanorods obtained in this study can be used as inexpensive inorganic hole-transporting material in solar energy application and it offers new possibilities to fabricate nanostructured solar cells in reversed process, which starts from the formation of nanostructured p-type electrode.
Journal of Materials Science: Materials in Electronics 2015 Volume 26( Issue 5) pp:2726-2732
Publication Date(Web):2015 May
DOI:10.1007/s10854-015-2749-1
The energy storage properties of Ca-doped (Sr, Ca)TiO3 (SCT) paraelectric ceramics have been intensively investigated by traditional solid state sintering method. Phase structures and morphology were detected by the X-ray diffraction and SEM, respectively. The electric field strength dependence of polarization was measured and employed to calculate the energy storage density. The doped SCT ceramics exhibit high permittivity, low loss, and higher breakdown strength. At 333 kV/cm electric field strength, the energy storage density of the 2 mol % Ca-doped SrTiO3 ceramics with fine grain can achieve 1.95 J/cm3, which is 2.8 times of pure SrTiO3 in the literature, and its energy storage efficiency reaches 72.3 %. Therefore, the SCT ceramics might be a kind of promising energy storage dielectric material.
Journal of the European Ceramic Society 2014 Volume 34(Issue 5) pp:1209-1217
Publication Date(Web):May 2014
DOI:10.1016/j.jeurceramsoc.2013.11.039
(Ba0.4Sr0.6)TiO3 (BST) ceramics with various grain sizes (0.5–5.6 μm) were prepared by conventional solid state reaction methods. The effect of grain size on the energy storage properties of BST ceramics (Tc ≈ −65 °C) was investigated. With decreasing grain sizes, a clear tendency toward the diffuse phase transition was observed and the dielectric nonlinearity was reduced gradually, which can be explained by the Devonshire's phenomenological theory (from the viewpoint of intrinsic polarization). Based on the multi-polarization mechanism model, the relationship between the polarization behavior of polar nano-regions (the extrinsic nonlinear polarization mechanisms) and grain size was studied. The variation of the grain boundary density was thought to play an important role on the improvement of dielectric breakdown strength, account for the enhanced energy density, which was confirmed by the complex impedance spectroscopy analysis based on a double-layered dielectric model.
Journal of Materials Science: Materials in Electronics 2014 Volume 25( Issue 11) pp:4730-4734
Publication Date(Web):2014 November
DOI:10.1007/s10854-014-2224-4
The effects of TiO2 addition on the densification, microstructure and microwave dielectric properties of pseudo-wollastonite ceramics (α-CaSiO3) have been investigated. The X-ray diffraction (XRD) patterns results indicate that samples exhibit a two-phase system, which has a wollastonite-structured α-CaSiO3 primary phase associated with a CaTiSiO5 minor phase. However, the TiO2 addition undermines the microwave dielectric properties because of the poor quality factor of the secondary phase of CaTiSiO5, which can inhibit the growth of α-CaSiO3 grains by surrounding their boundaries. The α-CaSiO3 ceramics containing 2 wt% of TiO2 sintered at 1,300 °C showed excellent microwave dielectric properties: an εr value of 7.86, a quality factor Q × f value of 16,491 GHz, and a τf value of 0.76 ppm/ °C.
Solid State Ionics 2014 Volume 268(Part A) pp:125-130
Publication Date(Web):15 December 2014
DOI:10.1016/j.ssi.2014.10.015
•The Li-O2 battery based on the La0.6Sr0.4CoO3/Super-p electrode was fabricated and measured.•The electrochemical performance was analyzed by the electrochemical impedance spectroscopy (EIS) change of battery.•The cycle life of battery could be improved by controlling the depth of discharge.The La0.6Sr0.4CoO3 (LSCO) perovskite oxide has been synthesized by a dry gel combustion method and characterized by TGA, XRD, SEM and BET. The initial discharge capacities of LSCO/super-p electrode were 3672.1 mA h · g− 1(carbon), 1418.4 mA h·g− 1(carbon) and 1237.5 mA h · g− 1(carbon) at the current densities of 30 mA · g− 1 50 mA · g− 1 and 80 mA · g− 1 respectively. The discharge capacity was maintained 16 times when the cut-off capacity was set as 500 mA h · g− 1(carbon). The electrochemical impedance spectroscopy (EIS) data revealed that the impedance of battery would increase more quickly if the current density became larger after the same cycles.
Ceramics International 2012 Volume 38(Supplement 1) pp:S45-S48
Publication Date(Web):January 2012
DOI:10.1016/j.ceramint.2011.04.046
Nb2O5 and Nb–Co doped 0.85BaTiO3–0.15Bi(Mg1/2Ti1/2)O3 (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb2O5/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb2O5 was found to possess a moderate dielectric constant (ɛ ∼ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from −55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.
Ceramics International 2012 Volume 38(Supplement 1) pp:S41-S44
Publication Date(Web):January 2012
DOI:10.1016/j.ceramint.2011.04.045
In this work, Na0.5Bi0.5TiO3 (NBT) was used to improve the high temperature dielectric properties of Nb, Co-doped BaTiO3 (BT). Different x was selected (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4) to optimize the ratio of BT to NBT in (1 − x) BT–xNBT solid solution. The dielectric constant of the original X7R material is about 4900 at room temperature, decreasing to 2500 with NBT addition (x = 0.2). Of important is that the temperature stability was improved with dielectric constant variation being less than ±15% up to 160 °C.
Journal of Alloys and Compounds 2011 Volume 509(Issue 18) pp:5637-5640
Publication Date(Web):5 May 2011
DOI:10.1016/j.jallcom.2011.02.106
Ceramic samples of xBi(Al0.5Fe0.5)O3–(1 − x)PbTiO3 (BAF-PT, x = 0.05–0.5) solid solutions were fabricated using the conventional solid state reaction method. X-ray diffraction analysis revealed that all compositions can form single perovskite phase with tetragonal symmetry. The relationship between the tetragonal lattice parameters, tetragonality c/a, cell volume, and ferro-piezoelectric characterization as a function of x was systematically investigated. The BAF modification can effectively improve the poling condition at a proper BAF content. A combination of piezoelectric constant of d33 (50–60 pC/N), electromechanical planar coupling coefficients of kp (20.3–22.5%), and high Curie temperature Tc (>478 °C) suggested that BAF–PT could be a good candidate for high-temperature piezoelectric applications.Highlights► Low-cost Bi-based high temperature piezoceramics. ► A new high temperature system with Curie point >478 °C, compared to BiScO3–PbTiO3 (450 °C). ► Effectively improve the poling conditions.
Solid State Communications 2011 Volume 151(Issue 3) pp:250-255
Publication Date(Web):February 2011
DOI:10.1016/j.ssc.2010.11.014
Dielectric properties and impedance spectra of (1−x)Ba(Ti0.8Sn0.2)O3–x(Na0.5Bi0.5)TiO3 ceramics with x=0.01x=0.01–0.05 are investigated. The addition of (Na0.5Bi0.5)TiO3 can bring about significant changes in the dielectric properties of Ba(Ti0.8Sn0.2)O3. Impedance/modulus analyses indicate that several dielectric processes in the system play important roles in the significant dielectric relaxational behaviors, which can be observed from the relaxation time ττ. A transition region between relaxor behavior and dielectric relaxation behavior is observed for x=0.01x=0.01–0.02. Further analysis on the activation energy (Ea)(Ea) of grains proves the existence of a phase transition, which lowers the activation energy of the grains by ∼0.5 eV. However, this transition does not influence EaEa for grain boundaries very considerably.Research highlights► The dielectric state of (1−x)Ba(Ti0.8Sn0.2)O3–x(Na0.5Bi0.5)TiO3 (x=0.01x=0.01–0.05) was studied. ► Addition of (Na0.5Bi0.5)TiO3 can bring about significant changes in dielectric properties. ► A transition between relaxor and dielectric relaxation behavior is observed. ► The impedance/modulus, relaxation time, and activation energy support the conclusion. ► Several dielectric processes play important roles in the significant relaxation behaviors.
Lead-free (1−x)Ba(Zr0.15Ti0.85)O3–x(K0.5Na0.5)NbO3; x=0–0.05) (BZT–KNN) perovskite ceramics, a materials with potential applications for energy storage, are investigated. The samples are prepared by a solid-state reaction method. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to study the microstructure of the samples. Their dielectric properties and impedance spectra are reported as functions of temperature and frequency. The addition of 1 mol % (K0.5Na0.5)NbO3 to Ba(Zr0.15Ti0.85)O3 improves the dielectric constant and enhances its diffuseness in a wide temperature range. The small amount of (K0.5Na0.5)NbO3 is found to markedly affect the microstructure of the Ba(Zr0.15Ti0.85)O3 ceramic (grain size and other characteristics) without changing the phase or crystal symmetry. In addition, we report that fine substructures in the grains, so-called sheet structures, are responsible for the dielectric properties (both diffuseness and dielectric constant) of (1−x)Ba(Zr0.15Ti0.85)O3–x(K0.5Na0.5)NbO3 (x=0–0.03; especially x=0.01) ceramics.
Co-reporter:Xuan Zhao, Yunjiang Cui, Liang Xiao, Haixia Liang, Hanxing Liu
Solid State Ionics 2011 Volume 192(Issue 1) pp:321-325
Publication Date(Web):16 June 2011
DOI:10.1016/j.ssi.2010.04.002
Li1 + x(Ni0.5Mn0.5)1 − xO2 cathode material for Li-ion batteries has been prepared by a molten salt method using Li2CO3 salt. The influences of synthetic temperature and time have been intensively investigated. It is easy to obtain materials with a hexagonal α-NaFeO2 structure except broad peaks between 20° and 25°. Nickel in Li1 + x(Ni0.5Mn0.5)1 − xO2 is oxidized to a trivalent state while manganese maintained a tetravalent state. It is found that the discharge capacities of all samples increase with cycling. The sample prepared at 850 °C for 5 h has a discharge capacity of 130 mAh g− 1 between 2.5 and 4.5 V versus VLi+/Li at a specific current of 0.13 mA cm− 2 after 50 cycles at 25 °C.
Co-reporter:Liang Xiao, Xiaojun Liu, Xuan Zhao, Haixia Liang, Hanxing Liu
Solid State Ionics 2011 Volume 192(Issue 1) pp:335-338
Publication Date(Web):16 June 2011
DOI:10.1016/j.ssi.2010.06.039
Layered LiNi0.5Mn0.5O2 has been successfully synthesized via urea hydrolysis coprecipitation method. Well-crystallized LiNi0.5Mn0.5O2 was obtained after calcinations of coprecipitation precursors and lithium salts at 450 °C for 3 h and following 900 °C for 10 h in air. Both the precursors and LiNi0.5Mn0.5O2 powders show an agglomerated secondary structure with crystalline particles inside. The quasi-spherical morphology of the precursors was maintained during the calcinations. The first charge and discharge capacities of as-prepared LiNi0.5Mn0.5O2 were 200 and 165mAh/g respectively. The discharge capacity of about 160mAh/g was retained after 10cycles for as-prepared samples.
Co-reporter:Haixia Liang, Xuan Zhao, Zhiyong Yu, Minghe Cao, Hanxing Liu
Solid State Ionics 2011 Volume 192(Issue 1) pp:339-342
Publication Date(Web):16 June 2011
DOI:10.1016/j.ssi.2010.06.046
Two kinds of spinel LiMn2O4 thin film for lithium ion micro-batteries were successfully prepared on polycrystal Pt substrates by spin coating methods, which were carried out under ultrasonic irradiation (USG) and magnetic stirring (MSG), respectively. The microstructures and electrochemical performance of LiMn2O4 thin films were characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge–discharge measurements. It was found that the crystalline structure of USG samples grew better than that of the MSG samples. At the same time, higher discharge capacity and better cycle stability were obtained for the LiMn2O4 thin films of USG at the current density of 50 μAh/cm2 between 3.0 and 4.3 V. The 1st discharge capacity was 57.8 μAh/cm2-μm for USG thin films and 51.7 μAh/cm2-μm for MSG thin films. After 50 cycles, 91.4% and 69% of discharge capacity could be retained respectively, indicating that ultrasonic irradiation condition during spin coating was more suitable for preparing spinel LiMn2O4 thin films with better electrode performance for lithium ion micro-batteries.
Lead-free piezoelectric ceramics, (Bi1/2Na1/2)1 − x(Bi1/2K1/2)xTiO3–0.03(Na0.5K0.5)NbO3 (x = 0.10–0.40) were synthesized by conventional solid-state sintering. A morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases was confirmed. Two dielectric anomalies can be observed, showing diffused phase transition behavior. There is no shift of the dielectric maximum temperature with frequency due to the contribution of space charge at high temperatures, similar to pure (Bi1/2Na1/2)TiO3. The materials near MPB show a strong compositional dependence with the optimal properties of a d33 of 167 pC/N, a kp of 35.5%, a Pr of 27.6 μC/cm2 and a Ec of 27.9 kV/cm, suitable for future application.
Journal of Materials Processing Technology 2008 Volume 197(1–3) pp:151-155
Publication Date(Web):1 February 2008
DOI:10.1016/j.jmatprotec.2007.06.006
This paper investigates Bi-doped Sr(Ti0.95Zr0.05)O3 ceramics prepared by solid state method. Both the effect of grinding time on particle size distribution of ceramic powders and the effect of sintering temperature on microstructure and dielectric properties of ceramics are studied. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Apparent density measurements and their dielectric properties are established at room temperature. XRD analysis shows that the ceramics kept cubic perovskite structure with the grain size about 1–2 μm observed by SEM image. The relative density of the obtained materials reaches higher than 94% and they exhibit properties as follows: dielectric constant ɛr > 500 and dielectric loss tanδ < 6.0 × 10−3 under 1 MHz and the breakdown strength Eb > 10 kV/mm.
Journal of Wuhan University of Technology-Mater. Sci. Ed. 2008 Volume 23( Issue 4) pp:490-494
Publication Date(Web):2008 August
DOI:10.1007/s11595-007-4490-y
The structural change in phase transition of hybrid (Cl2H25NH3)2MnCl4 was investigated. The temperature and the structures of the phase transition is investigated by thermal gravimetry (TG) and differential scanning calorimetry (DSC), infrared spectrum (IR) and X-ray diffraction (XRD). The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain. The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase. This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs. Combining the experimental data with theoretical calculation, we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond alternating with trans bond (noted as GTG′TGTG′TGTG′T).
Solid State Ionics 2008 Volume 179(27–32) pp:1679-1682
Publication Date(Web):30 September 2008
DOI:10.1016/j.ssi.2007.11.025
Monoclinic lithium vanadium phosphate, Li3V2(PO4)3, was synthesized by carbon-thermal reduction (RTC) under Ar atmosphere. The influence of sintering temperatures on the synthesis of Li3V2(PO4)3 has been investigated using X-ray diffraction (XRD), SEM and electrochemical methods. XRD patterns show that the Li3V2(PO4)3 compound with monoclinic crystal structure begins to appear at the temperature of less than 900 °C. As the temperature was ≥ 900 °C, pure monoclinic Li3V2(PO4)3 phase can be obtained. SEM results indicate that the particle size of as-prepared samples increased with the sintering temperature increase, as well as the presence of minor carbon particles on the surface of the sample particles, which are very useful to enhance the electronic conductivity of Li3V2(PO4)3. Charge/discharge tests show the 900 °C-sample exhibits the highest initial discharge capacity of 119.3 mAh/g at 10 mA/g in the voltage range of 3.0–4.2 V with good capacity retention. CV experiment exhibits that there are three anodic peaks at 3.61, 3.69 and 4.09 V on lithium extraction as well as three cathodic peaks at 3.58, 3.66 and 4.03 V on lithium reinsertion at 0.05 mV/s between 3.0 and 4.3 V. It is suggested that the optimal sintering temperature is 900 °C in order to obtain pure monoclinic Li3V2(PO4)3 with good electrochemical performance by CRT method, and the monoclinic Li3V2(PO4)3 can be used as candidate cathode materials for lithium-ion batteries.
Co-reporter:MingHe Cao;Wei Tian;MingFa Li;WenHua Sun
Science China Technological Sciences 2007 Volume 50( Issue 5) pp:658-663
Publication Date(Web):2007 October
DOI:10.1007/s11431-007-0066-5
The NaNbO3 powders were synthesized and their crystal structure changes were analyzed by ultrahigh pressure up to 6 GPa. The results indicate that the pure NaNbO3 powders can be synthesized at 300°C under a pressure of 4 GPa, to significantly restrain the Na element volatilization compared with the traditional synthesis method. It is found that the crystal structure of synthesized NaNbO3 changes from low symmetry to high symmetry with the increase of the pressure.
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