Co-reporter:Weichuan Huang, Yue Lin, Yuewei Yin, Lei Feng, Dalong Zhang, Wenbo Zhao, Qi Li, and Xiaoguang Li
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 16) pp:10422
Publication Date(Web):April 8, 2016
DOI:10.1021/acsami.6b02150
A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents at least four resistance states in a single memory cell and therefore opens an avenue for the development of the next generation of high-density nonvolatile memory devices. Here, using the all-perovskite-oxide La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 as a model MFTJ system, we demonstrate asymmetrical Mn—Ti sublattice intermixing at the La0.7Sr0.3MnO3/BaTiO3 interfaces by direct local measurements of the structure and valence, which reveals the relationship between ferroelectric polarization directions and four-resistance states, and the low temperature anomalous tunneling behavior in the MFTJ. These findings emphasize the crucial role of the interfaces in MFTJs and are quite important for understanding the electric transport of MFTJs as well as designing high-density multistates storage devices.Keywords: interface; intermixing; multiferroic tunnel junctions; tunneling electroresistance; tunneling magnetoresistance
Co-reporter:Lei Feng, Shengwei Yang, Yue Lin, Dalong Zhang, Weichuan Huang, Wenbo Zhao, Yuewei Yin, Sining Dong, and Xiaoguang Li
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 47) pp:26036
Publication Date(Web):November 10, 2015
DOI:10.1021/acsami.5b10210
The electric field effects on the electric and magnetic properties in multiferroic heterostructures are important for not only understanding the mechanisms of certain novel physical phenomena occurring at heterointerfaces but also offering a route for promising spintronic applications. Using the Au/BiFeO3/La0.6Sr0.4MnO3 (Au/BFO/LSMO) multiferroic heterostructure as a model system, we investigated the ferroelectric-resistive switching (RS) behaviors of the heterostructure. Via the manipulation of the BFO ferroelectric polarizations, the nonvolatile tristate of RS is observed, which is closely related to the Au/BFO and BFO/LSMO interface layers and the highly conducting BFO domain walls (DWs). More interestingly, according to the magnetic field dependence of the RS behavior, the negative magnetoresistance effect of the third resistance state, corresponding to the abnormal current peak in current-pulse voltage hysteresis near the electric coercive field, is also observed at room temperature, which mainly arises from the possible oxygen vacancy accumulation and Fe ion valence variation in the DWs.Keywords: domain walls; ferroelectric heterostructures; interface layer; ion interdiffusion; resistive switching;
Co-reporter:Shengwei Yang, Lei Feng, Dalong Zhang, Weichuan Huang, Sining Dong, Jianjun Wang, Liangjian Zou, Xiaoguang Li, Cewen Nan
Journal of Alloys and Compounds 2015 Volume 646() pp:472-476
Publication Date(Web):15 October 2015
DOI:10.1016/j.jallcom.2015.04.239
•A promising side-polarization configuration is constructed to rule out the impact of ferroelectric field effect.•The nonvolatile anisotropic resistive-switching accompanied with magnetization rotation is achieved.•The interplay between AMR results and magnetization rotation processes in different magnetic fields is discussed.The nonvolatile behaviors of magnetically correlated anisotropic resistive switching in Co/0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (Co/PMN-PT) multiferroic heterostructures are systematically investigated. When the polarization state of PMN-PT is reversed, a non-volatile anisotropic resistivity switch occurs, corresponding to the non-volatile 90°-rotation of magnetic-easy-axis in Co film owing to the competition between magnetoelastic and interfacial anisotropies. The anisotropic magnetoresistivities (AMR) between two opposite polarization states in a field below anisotropic field also show a 90° phase-shift. While at fields above anisotropic field, the AMR reveals the asymmetric cos2(θ)-like behaviors. The AMR manipulated by electric and magnetic fields is of benefit for studying the magnetization rotation processes.
Co-reporter:X. X. Wang, X. Y. Cheng, Y. Lin, C. Ma, K. Q. Ruan and X. G. Li
RSC Advances 2015 vol. 5(Issue 123) pp:101544-101551
Publication Date(Web):25 Nov 2015
DOI:10.1039/C5RA18392H
The magnetic and electrical properties of hexagonal Ba3Ti2MnO9 are investigated. The material is a noncentrosymmetric evolution from hexagonal BaTiO3 with a space group P63mc. The existence and distribution of both Mn4+ and Ti4+ are checked using an electron energy-loss spectroscopy line scan by high resolution transmission electron microscopy. Magnetic transitions are attributed to the short range ordering and magnetic frustration. The frequency independent behavior of the dielectric peak shows a ferroelectric transition at 222 K. Both Positive Up and Negative Down (PUND) techniques and the local piezoresponse confirm the ferroelectric behavior of Ba3Ti2MnO9.
Co-reporter:Yue-Wei Yin;Wei-Chuan Huang;Yu-Kuai Liu;Sheng-Wei Yang;Si-Ning Dong;Jing Tao;Yi-Mei Zhu;Qi Li;Xiao-Guang Li
Advanced Electronic Materials 2015 Volume 1( Issue 11) pp:
Publication Date(Web):
DOI:10.1002/aelm.201500183
General drawbacks of current electronic/spintronic devices are high power consumption and low density storage. A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents four resistance states in a single device and therefore provides an alternative way to achieve high density memories. Here, an MFTJ device with eight nonvolatile resistance states by further integrating the design of noncollinear magnetization alignments between the ferromagnetic layers is demonstrated. Through the angle-resolved tunneling magnetoresistance investigations on La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 junctions, it is found that, besides collinear parallel/antiparallel magnetic configurations, the MFTJ shows at least two other stable noncollinear (45° and 90°) magnetic configurations. Combining the tunneling electroresistance effect caused by the ferroelectricity reversal of the BaTiO3 barrier, an octonary memory device is obtained, representing potential applications in high density nonvolatile storage in the future.
Co-reporter:Weichuan Huang, Shengwei Yang, Xiaoguang Li
Journal of Materiomics 2015 Volume 1(Issue 4) pp:263-284
Publication Date(Web):December 2015
DOI:10.1016/j.jmat.2015.08.002
Multiferroic heterostructures showing both electric and magnetic orders have attracted much attention because of their promising applications in the next generation of memories, sensors, and microwave devices and so on. The complex electronic and magnetic orders at the interface in multiferroic heterostructures will cause abundant physical phenomena due to the interplay among spin, charge, orbit, and lattice degrees of freedom, and various prototype devices have been achieved. In this review, we summarize some recent progresses mainly in the strain- and charge-mediated effects on the magnetic and electronic transport properties manipulated by electric/magnetic fields in multiferroic heterostructures. The recent advances in multiferroic tunnel junctions with ferroelectric barriers by using the spin polarized nature of magnetic materials are particularly presented, which exhibit magnetoelectric coupling effects at the interface and multi-stable resistance states in a single memory unit cell. Finally, the new inspiration for the design of spintronic devices having more energy efficiency and higher density is discussed.We review the recent advances as well as the potential applications of strain- and charge-mediated magnetoelectric coupling effects on the magnetic and electronic transport properties in multiferroic heterostructures and multiferroic tunnel junctions.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Sheng-Wei Yang;Ren-Ci Peng;Tao Jiang;Yu-Kuai Liu;Lei Feng;Jian-Jun Wang;Long-Qing Chen;Xiao-Guang Li;Ce-Wen Nan
Advanced Materials 2014 Volume 26( Issue 41) pp:7091-7095
Publication Date(Web):
DOI:10.1002/adma.201402774
Co-reporter:Sining Dong, Dalong Zhang, Yukuai Liu, Shengwei Yang, Tao Jiang, Yuewei Yin and Xiaoguang Li
Nanoscale 2014 vol. 6(Issue 24) pp:14766-14771
Publication Date(Web):14 Oct 2014
DOI:10.1039/C4NR03148B
In this paper, we report the structural evolution of Bi4.2K0.8Fe2O9+δ nanobelts to BiFeO3 nanochains and the related variations in multiferroic properties. By using in situ transmission electron microscopy with comprehensive characterization, it was found that the layered perovskite multiferroic Bi4.2K0.8Fe2O9+δ nanobelts were very unstable in a vacuum environment, with Bi being easily removed. Based on this finding, a simple vacuum annealing method was designed which successfully transformed the Bi4.2K0.8Fe2O9+δ nanobelts into one-dimensional BiFeO3 nanochains. Both the Bi4.2K0.8Fe2O9+δ nanobelts and the BiFeO3 nanochains showed multiferroic behavior, with their ferroelectric and ferromagnetic properties clearly established by piezoresponse and magnetic measurements, respectively. Interestingly, the BiFeO3 nanochains had a larger magnetization than the Bi4.2K0.8Fe2O9+δ nanobelts. Moreover, the BiFeO3 nanochains exhibited a surprisingly large exchange bias with small training effects. This one-dimensional BiFeO3 multiferroic nanostructure characterized by a relatively stable exchange bias offers important functionalities that may be attractive for device applications.
Co-reporter:Sining Dong, Yukuai Liu, Shengwei Yang, Tao Jiang, Yuewei Yin and Xiaoguang Li
CrystEngComm 2013 vol. 15(Issue 44) pp:9057-9063
Publication Date(Web):19 Sep 2013
DOI:10.1039/C3CE41464G
In this paper, Bi4.2K0.8Fe2O9+δ nanostructures with different morphologies, such as dispersible nanobelts, urchin-like and floriated micronanostructures with dendrites in different sizes, were controllably synthesized by a surfactant-free hydrothermal method. The temperatures of the KOH solutions in the co-precipitation step and the hydrothermal reactions had great effects on not only the morphologies but also the magnetic properties of the products. It was found that the low-temperature-fabricated urchin-like samples had a higher magnetization value. The special cores of the urchin-like nanostructures may play a critical role in the enhanced magnetizations and spin-glass dynamic behaviors. These results provide a simple way to manipulate the morphology of low-dimensional Bi4.2K0.8Fe2O9+δ nanostructures as well as their related magnetic properties.
Co-reporter:Yuewei Yin, Hua Liu, Liang Xie, Tongshang Su, Mengli Teng, and Xiaoguang Li
The Journal of Physical Chemistry C 2013 Volume 117(Issue 6) pp:3028-3035
Publication Date(Web):January 22, 2013
DOI:10.1021/jp3089808
Magnetic and superconducting properties of La2-xSrxCuO4 nanoparticles are systematically studied as a function of particle size and Sr doping. Through the magnetization and electron spin resonance measurements, it was found that the suppression of superconductivity and enhancement of ferromagnetism were observed simultaneously with decreasing particle size, which should be related to the uncompensated Cu2+ spins and oxygen defects due to the increasing role of finite size. On the other hand, although Sr doping will introduce more uncompensated spins to the La2-xSrxCuO4 nanoparticles, the low temperature ferromagnetism is reduced. The results suggest that the suppression of superconductivity and the appearance of ferromagnetism for the nanoparticles may be closely related to the destruction of antiferromagnetic correlation in CuO2 planes.
Co-reporter:Tao Jiang, Liang Xie, Yiping Yao, Yukuai Liu, Xiaoguang Li
Materials Letters 2012 Volume 76() pp:25-27
Publication Date(Web):1 June 2012
DOI:10.1016/j.matlet.2012.02.057
The magnetocaloric properties of the CrO2 single crystal films epitaxially grown on TiO2 (100) substrates are studied by dc magnetization measurements. It is reported first time that there is a large magnetocaloric effect (MCE) over a wide temperature range in the vicinity of Curie temperature of CrO2 film. The magnetic entropy change increases monotonically with increasing magnetic fields and reaches a value of 8.46 J/kg·K at 385 K for the field varies from 0 to 5 T, which is the one among the highest for magnetic oxides and comparable to that for Gd. More interestingly the calculated relative cooling power values of CrO2 are found to vary from 143 J/kg at 1.5 T to 410 J/kg at 5 T, much larger than that of CrO2 particles, due to a wide distribution of magnetic entropy changes.Highlights►The large MCE of CrO2 epitaxial film is reported for first time. ►The magnetic entropy change of CrO2 is among the highest in magnetic oxides. ►The RCP of CrO2 film is the largest above room temperature in magnetic oxides.
Co-reporter:Yukuai Liu, Yiping Yao, Sining Dong, Tao Jiang, Shengwei Yang, Xiaoguang Li
Thin Solid Films 2012 Volume 520(Issue 17) pp:5775-5778
Publication Date(Web):30 June 2012
DOI:10.1016/j.tsf.2012.04.074
A colossal magnetocapacitance in magnetic fields was observed near the Curie temperature Tc = 220 K of La5/8Ca3/8MnO3 for the BiFeO3/La5/8Ca3/8MnO3 epitaxial film. It was found that the magnetocapacitance increases with increasing magnetic fields and reaches a maximum up to 1100% enhancement around Tc at 10 T. From the analysis of the dielectric relaxation, one can see that the behavior of relaxation time τ above Tc differs from that below Tc, and the value of τ decreases with increasing magnetic fields. This colossal magnetocapacitance effect near room temperature in BiFeO3/La5/8Ca3/8MnO3 may have potential applications in multifunctional microelectronic device.Highlights►BiFeO3/La5/8Ca3/8MnO3 epitaxial films show well ferroelectric properties. ► A colossal magnetocapacitance effect up to 1100% at 10 T near room temperature. ► The relaxation process above the Curie temperature Tc differs from that below Tc.
Co-reporter:Genqiang Zhang;Qingxuan Yu;Wei Wang
Advanced Materials 2010 Volume 22( Issue 17) pp:1959-1962
Publication Date(Web):
DOI:10.1002/adma.200903812
Abstract
Both heterostructures and hollow nanostructures have been predicted as candidates with excellent thermoelectric performance. In this Research News areticle, recent advances with regard to synthetic strategies, growth mechanisms, and thermoelectric properties of one-dimensional heterostructures (segmented and core/shell) and tubular nanostructures are reported. The thermoelectric property studies of Te/Bi core/shell heterostructured nanowires and Bi2Te3 nanotubes indicate that the Seebeck coefficient and thermal conductivity of these materials can be optimized to improve their thermoelectric performance. In addition, the current issues and future research directions for promising thermoelectric nanostructures will be discussed on the basis of these experimental results.
Co-reporter:Genqiang Zhang, Qingxuan Yu and Xiaoguang Li
Dalton Transactions 2010 vol. 39(Issue 4) pp:993-1004
Publication Date(Web):09 Dec 2009
DOI:10.1039/B913462J
Recent advances in both theoretical and experimental studies on optimizing thermoelectric performance have proved to greatly benefit from nanostructure engineering. As a class of materials with the best thermoelectric properties near room temperature, V-VI alloy nanostructures, especially Bi2Te3 and its alloy with Sb, Se and so on, have attracted a broad interest. This perspective gives an overview of the progress in the wet chemical synthesis and property study of V-VI related one- and two-dimensional nanostructures. First, we discuss the preparation of one-dimensional nanowires/tubes, axial and radial modulated heterostructures, and two-dimensional platelet-like structures through various chemical routes. Then, we attempt to give a general outlook on the thermoelectric properties of V-VI single nanowires, and nanostructured films or bulk nanocomposites made of these chemically synthesized nanostructures. On the basis of the research in the synthetic methods and thermoelectric properties, the challenging issues and future research directions are briefly discussed. By no means is this a comprehensive coverage of V-VI related nanostructures, but a selection of those studies that could benefit the advance of thermoelectric properties of this material system in the near future.
Co-reporter:Genqiang Zhang, Wei Wang, Qingxuan Yu and Xiaoguang Li
Chemistry of Materials 2009 Volume 21(Issue 5) pp:969
Publication Date(Web):February 11, 2009
DOI:10.1021/cm803307f
A facile one-pot polyol process for the synthesis of PbSe and NiSe2 hollow spheres, using α-Se solid spheres as starting core materials was successfully developed. The careful characterization of the time-dependent products demonstrates that the Kirkendall effect could be the involved growth mechanism for the evolution process from Se solid spheres to PbSe and NiSe2 hollow spheres, which is schematically illustrated as a two-stage temperature-controlled, Kirkendall-effect-directed formation. The microstructure analysis shows that both the PbSe and NiSe2 hollow spheres are polycrystalline with cubic structure. The band gap of the PbSe hollow spheres exhibits a notable size effect, and the magnetic susceptibility of the NiSe2 hollow spheres is significantly increased compared with that of its bulk counterpart. This work indicates that the nonmetal Se solid spheres can act as an appropriate fast diffusion core material for hollow structure through Kirkendall effect in the solution phase method.
Co-reporter:Genqiang Zhang, Qingxuan Yu, Zhen Yao and Xiaoguang Li
Chemical Communications 2009 (Issue 17) pp:2317-2319
Publication Date(Web):12 Mar 2009
DOI:10.1039/B822595H
We have successfully developed an ethylene glycol mediated solution phase method for synthesizing highly crystalline Bi2Te3nanotubes using Te nanowires as the in situ templates; our work demonstrates the generic feature of a solution phase mediated Kirkendall effect for the synthesis of not only hollow nanoparticles but also highly crystalline tubular structures.
Co-reporter:Genqiang Zhang, Wei Wang, Xiaoli Lu and Xiaoguang Li
Crystal Growth & Design 2009 Volume 9(Issue 1) pp:145
Publication Date(Web):November 26, 2008
DOI:10.1021/cg7012528
General synthesis of both binary and ternary V−VI based thermoelectric alloy hexagonal platelets was carried out for the first time in a unified system using a modified solvothermal method, which adopted convenient oxides as source materials and friendly ethylene glycol as both solvent and reducing agent. The structure and composition analysis reveal that the samples are pure phase with corresponding atomic ratios. Electron microscopy results indicate that the as-prepared products are uniform and highly crystallized. The formation process was studied in detail by observing time-dependent products, and it was found that the oriented attachment mechanism could be responsible for the growth of these hexagonal platelets, which exhibits intrinsic difference compared with the inferred seed-mediated growth mechanism in previous reports. The influence of pH value and polyvinyl pyrrolidone on the morphology of the products was investigated as well. This work may open up a new rationale on designing the solution synthesis of nanostructures for materials possessing similar intrinsic crystal symmetry.
Co-reporter:X.G. Li, T. Zhang
Ceramics International 2009 Volume 35(Issue 1) pp:151-155
Publication Date(Web):January 2009
DOI:10.1016/j.ceramint.2007.10.026
Abstract
The size effects on the charge ordering (CO) and magnetic properties in La0.25Ca0.75MnO3 with mean particle size ranging from 40 to 2000 nm were studied. With decreasing particle size the CO transition temperature shifts to lower temperature and the transition width becomes increasingly wide, indicating the weakening of the CO state. Meanwhile the ferromagnetic (FM) cluster glass state appears and the magnetization at low temperature increases significantly. The behaviour is due to the increasing uncompensated surface spins which weaken the antiferromagnetic interaction and disfavour the formation of the CO state. The suppression of the CO state and appearance of the FM cluster glass state are also found in La0.25Ca0.75MnO3 nanowires fabricated by a sol–gel template method. These results indicate that the CO state can be modulated effectively by varying particle size, which has an important implication for nano-device applications of manganites.
Co-reporter:Genqiang Zhang;Wei Wang
Advanced Materials 2008 Volume 20( Issue 19) pp:3654-3656
Publication Date(Web):
DOI:10.1002/adma.200800162
Co-reporter:Haiwu Zheng, Jianfeng Su, Zhuxi Fu, Guang Li, Xiaoguang Li
Ceramics International 2008 Volume 34(Issue 3) pp:657-660
Publication Date(Web):April 2008
DOI:10.1016/j.ceramint.2007.02.011
Abstract
Cubic SiC (3C-SiC) film has been deposited on Si (1 1 0) substrate by the low pressure chemical vapor deposition (LPCVD) with gas sources of SiH4, C3H8 and carrier gas of H2. The 3C-SiC crystalline film can be confirmed through the observations using reflection high-energy electron diffraction (RHEED) images. The X-ray diffraction (XRD) pattern and the rocking curve indicate that the (1 1 1) plane of SiC film is parallel to the surface of the Si (1 1 0) substrate and the film is of high crystallinity. The results of the field emission scanning electron microscope (FESEM) images show that the film has smooth surface morphology. Transmitted electron diffraction (TED) pattern and high resolution transmission electron microscope (HRTEM) image further confirm the high quality of the film.
Co-reporter:T. Qian;T. F. Zhou;X. G. Li
Journal of Electroceramics 2008 Volume 21( Issue 1-4) pp:85-90
Publication Date(Web):2008 December
DOI:10.1007/s10832-007-9077-7
We report the study on the stability of charge-ordered (CO) state and rectifying properties of heteroepitaxial structure for manganites R1-xCaxMnO3 (R = La, Pr, and Sm) by measuring magnetoresistance, magnetization, specific heat, I−V characteristics, and X-ray diffraction. For the La1-xCaxMnO3 system, near the Ca2+concentration of x = 0.75 the CO state is mostly stabilized and insensitive to external magnetic fields, which is supported by the charge transport, magnetic, and specific heat properties. By analyzing powder X-ray diffraction patterns, we found that the Jahn–Teller (JT) distortion in the CO state is the largest at x = 0.75, which confirms the close relationship between the JT lattice distortion and the stability of the CO state for La1-xCaxMnO3. The stability of the CO state is also related to the A-site average ionic radius, 〈rA〉. With decreasing the radius of the doped rare-earth elements (La, Pr, and Sm), the most stable CO state for the each doped system shifts gradually toward lower Ca2+concentration. In addition, we have fabricated simple p–n junctions using a heteroepitaxial structure of La1-xCaxMnO3/Nb-doped SrTiO3. These junctions show good rectifying properties for temperature from 85 to 305 K. The photovoltage as a function of light wavelength at room temperature has also been studied and the maximum photovoltage can reach 180 mV. The good rectifying behaviors and strong photovoltaic effect make these simple p–n junctions promising for applications.
Co-reporter:Wei Wang ; Genqiang Zhang
The Journal of Physical Chemistry C 2008 Volume 112(Issue 39) pp:15190-15194
Publication Date(Web):September 9, 2008
DOI:10.1021/jp803207r
High-density thermoelectric Bi2Te3/Sb multilayered nanowire arrays with a minimum period of 10 nm are successfully fabricated by a template-assisted pulsed electrodeposition process based on the deep investigation of Bi−Sb−Te electrolyte solution. Large-scale, solid, and continuous nanowire arrays with multisegment characters and uniform diameters can be observed by FE-SEM and TEM, and the randomly selected neighboring segments were characterized to be Bi2Te3 and Sb, respectively, by SAED and EDS. It is demonstrated that the segment length and length ratios can be effectively tuned by manipulating the deposition time, which presents good candidates for further thermoelectric applications.
Co-reporter:X. L. Lu;W. Wang;G. Q. Zhang;X. G. Li
Advanced Functional Materials 2007 Volume 17(Issue 13) pp:
Publication Date(Web):20 JUL 2007
DOI:10.1002/adfm.200700011
A binary surfactant mixture of cetyltrimethylammonium bromide and polyvinyl pyrrolidone is used as the tailoring agent in the fabrication of lead micro/nanostructures. Electron microscopy studies indicate that the morphologies of the products can be efficiently controlled in this simple one-step synthetic procedure. Intriguingly, well-defined asymmetric functional colloids, Pb hemispheres, are obtained for the first time, and a dual-activity-controlled growth process is proposed to explain their formation. The magnetization measurements show that the as-prepared samples are superconducting with the same transition temperature as bulk Pb. These findings prove the unique morphology tailoring efficacy of mixed surfactants, which could be used to obtain more variform structures or architectures in the fabrication of advanced materials.
Co-reporter:Xiaoli Lu Dr.;Genqiang Zhang;Wei Wang
Angewandte Chemie International Edition 2007 Volume 46(Issue 30) pp:
Publication Date(Web):25 JUN 2007
DOI:10.1002/anie.200701591
Superthin cables: Superconducting coaxial lead–polymer nanocables (see TEM/EDX element maps (top) and line scan (bottom)) are fabricated by a one-step method. Self-assembled polymer tubes act as both templates and microreactors for the growth of lead cores. The polymer shells also improve the oxidation resistance of the inner nanowires. EDX=energy dispersion X-ray spectroscopy.
Co-reporter:Xiaoli Lu Dr.;Genqiang Zhang;Wei Wang
Angewandte Chemie 2007 Volume 119(Issue 30) pp:
Publication Date(Web):25 JUN 2007
DOI:10.1002/ange.200701591
Extradünne Kabel: Supraleitende Blei-Polymer-Koaxialnanokabel (siehe TEM/EDX-Elementkarten (oben) und Linien-Scan (unten)) werden mit einer einstufigen Methode hergestellt. Selbstorganisierte Polymerröhren fungieren zugleich als Template und als Mikroreaktoren für das Wachsen der Bleikerne. Die Polymerhüllen verbessern außerdem die Oxidationsbeständigkeit der inneren Nanodrähte.
Co-reporter:X. L. Lu;T. Zhang;J. F. Qu;C. G. Jin;X. G. Li
Advanced Functional Materials 2006 Volume 16(Issue 13) pp:
Publication Date(Web):18 JUL 2006
DOI:10.1002/adfm.200500595
Superconducting La1.85Sr0.15CuO4 nanowire arrays are successfully synthesized through a sol–gel method combined with porous alumina as a morphology-directing hard template for the first time. The morphology, structure, and composition of the as-prepared nanowire arrays are characterized by field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. These experimental results indicate that the nanowires are well crystallized with an approximately uniform diameter of about 30 nm. The superconducting transition temperature Tc (ca. 30 K) of the annealed nanowires is lower than that in bulk La1.85Sr0.15CuO4. It is suggested that this superconductivity suppression is derived from the weakening of in-plane hybridization in the nanowire system.
Co-reporter:J.F. Qu, Y.Q. Zhang, X.Q. Xiang, X.L. Lu, X.G. Li
Materials Science and Engineering: A 2006 Volume 442(1–2) pp:216-219
Publication Date(Web):20 December 2006
DOI:10.1016/j.msea.2006.03.127
We have studied the effect of a magnetic field on the charge-stripe phase in La1.48Nd0.4Sr0.12CuO4 and La2−xSrxCuO4 (x = 0.04, 0.12) by ultrasonic attenuation measurements. For La1.48Nd0.4Sr0.12CuO4, a magnetic field of 14 T has been found to have no essential influence on the attenuation peak around 70 K, which is associated with the formation of static charge stripes, and on the anomalous increase in the sound velocity below this temperature either, indicating that the static stripe order is very stable. For La1.88Sr0.12CuO4, the attenuation peak and the accompanying increase in sound velocity, which are located below the superconducting transition temperature, are shifted toward high temperature with increasing magnetic field, and simultaneously the increase in sound velocity is enhanced. The results indicate that an applied magnetic field can stabilize the charge stripes in La1.88Sr0.12CuO4. These measurements provide further evidence for the competition between superconductivity and charge-stripe order. In La1.48Nd0.4Sr0.12CuO4, the static stripe order is very stable while in La1.88Sr0.12CuO4 the stripe order is suppressed by superconductivity. With increasing magnetic field, the superconductivity is suppressed gradually and thus the charge-stripe order emerges. Measurements on La1.96Sr0.04CuO4 suggest that the magnetic field does not affect the charge stripes in the non-superconducting state.
Co-reporter:T. Zhang, C. G. Jin, T. Qian, X. L. Lu, J. M. Bai and X. G. Li
Journal of Materials Chemistry A 2004 vol. 14(Issue 18) pp:2787-2789
Publication Date(Web):03 Aug 2004
DOI:10.1039/B405288A
Single-crystalline La0.5Ca0.5MnO3 nanowires have been successfully prepared by a hydrothermal method at low temperature. X-Ray diffraction (XRD) results show that the La0.5Ca0.5MnO3 nanowires have an orthorhombic perovskite structure without any other impurity phase. Transmission electron microscopy (TEM) images demonstrate that the as-synthesized samples are made up of a large quantity of nanowires with lengths ranging from several to several tens of micrometers and uniform diameter (∼80 nm). High-resolution transmission electron microscopy (HRTEM) images reveal that the nanowires with very clean surfaces grow along [100]. The result of magnetic measurements indicates that the nanowires have an enhanced Tc due to the shrinkage of the unit cell volume.
Co-reporter:G Li, T Qian, S.-J Feng, F Liu, H.-D Zhou, X.-G Li
Solid State Communications 2004 Volume 131(Issue 6) pp:417-418
Publication Date(Web):August 2004
DOI:10.1016/j.ssc.2004.05.041
The author of the comment objects to the characterization and the interpretation of magnetoresistance (MR) effects observed by us in La1−xCaxMnO3 (0≤x<0.4) samples. In this reply, arguments are used to show that the samples' characterization and explanation of the MR by considering the role of the short-charge ordering (CO) regions and magnetic domains are reasonable and acceptable.
Co-reporter:C. G. Jin, G. W. Jiang, W. F. Liu, W. L. Cai, L. Z. Yao, Z. Yao and X. G. Li
Journal of Materials Chemistry A 2003 vol. 13(Issue 7) pp:1743-1746
Publication Date(Web):16 May 2003
DOI:10.1039/B302303F
Bi nanowire arrays have been successfully synthesized using potentiostatic electrochemical deposition into the channels of an anodic alumina membrane (AAM). The morphology and structure of Bi nanowires have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The results demonstrate that Bi nanowire arrays are compact, high filling rate and have a large area. The individual single crystal Bi nanowires are dense and continuous with uniform diameters (∼60 nm) throughout the entire length. The optimum synthesis conditions of Bi single crystal nanowire arrays were also discussed.
Co-reporter:L. Shi, G. Li, Y. Pu, X.D. Zhang, S.J. Feng, X.-G. Li
Materials Letters 2003 Volume 57(24–25) pp:3919-3923
Publication Date(Web):August 2003
DOI:10.1016/S0167-577X(03)00241-6
The resistivity, electron paramagnetic resonance (EPR) and microstructure of polycrystallines Ru1−xPbxSr2Gd1.4Ce0.6Cu2O10−δ (x=0, 0.03, 0.2, 0.4, 0.5) have been studied systematically. Pb doping reduces the conductivity and suppresses the superconductivity, which may reflect the increase in hole localization due to disorder effects resulting from Pb doping. The temperature dependencies of magnetic resonance for samples Ru1−xPbxSr2Gd1.4Ce0.6Cu2O10−δ show that there are two absorption peaks. The first one around the magnetic field 3300 Oe corresponds to the electron paramagnetic resonance (EPR) of the Gd ions, and the second that appears below the ferromagnetic transition temperature is a ferromagnetic resonance (FMR) due to the ordered Ru ions.
Co-reporter:G. Li, T. Qian, S.-J. Feng, F. Liu, H.-D. Zhou, X.-G. Li
Solid State Communications 2003 Volume 128(Issue 5) pp:171-176
Publication Date(Web):October 2003
DOI:10.1016/j.ssc.2003.08.004
The magnetic and transport properties of La1−xCaxMnO3 (0≤x<0.4) have been systematically studied. The magnetoresistance (MR) maximum appears at x=0.2–0.25 and the temperature dependence of MR for x>0.25 shows a much broader profile than that of samples for x=0.2–0.25. Based on a scenario in which there is a short-range charge ordering (CO) state coexisting in the ferromagnetic state matrix for x>0.25, and the least or even no short-range CO state exists in samples for x=0.2–0.25, the above observations can be understood.
Co-reporter:R.K Zheng, R.X Huang, A.N Tang, G Li, X.G Li, J.Q Xie
Journal of Alloys and Compounds 2002 Volume 345(1–2) pp:68-71
Publication Date(Web):28 October 2002
DOI:10.1016/S0925-8388(02)00479-6
The resistivity, ac susceptibility and ultrasonic sound velocities have been measured for the single-phase Nd0.5Sr0.5MnO3 bulk sample. With decreasing temperature both the transverse and longitudinal ultrasonic sound velocities show two large stiffening stages just below the ferromagnetic transition temperature TC and the charge ordering transition temperature TCO, respectively. The sound velocity stiffening below TC was interpreted in terms of a significant decrease of the static Jahn–Teller distortion of the MnO6 octahedra due to the spin-lattice coupling, whereas the dramatic sound velocity stiffening below TCO was attributed to the formation of coherent static Jahn–Teller distortion of the MnO6 octahedra associated with the charge ordering. In an applied magnetic field of 0.5 T, the stiffening of the sound velocity near TCO shifts noticeably to a lower temperature.
Co-reporter:R.K. Zheng, C.F. Zhu, J.Q. Xie, R.X. Huang, X.G. Li
Materials Chemistry and Physics 2002 Volume 75(1–3) pp:121-124
Publication Date(Web):28 April 2002
DOI:10.1016/S0254-0584(02)00064-0
The resistivity, ac susceptibility, ultrasonic sound velocity and attenuation have been measured in the single-phase La0.57Ca0.43MnO3 bulk sample. Sharp attenuation peaks and dramatic stiffening in sound velocities for both longitudinal and transverse waves were observed near the paramagnetic to ferromagnetic phase transition temperature, TC, implying a strong Jahn–Teller effect. The ultrasonic anomalies near TC are interpreted in terms of a significant reduction of the Jahn–Teller distortion of the Mn3+O6 octahedra, resulting from the coupling of the ferromagnetic spin ordering to the crystal lattice (i.e. spin–lattice coupling) below TC. The resistivity undergoes a broad insulator–metal transition far below TC. This phenomenon is related to a sufficiently strong electron–lattice coupling in the ferromagnetic state.
Co-reporter:H.-D Zhou, G Li, F Liu, S.-J Feng, Y Liu, X.-G Li, J Fang
Solid State Communications 2002 Volume 124(Issue 3) pp:83-87
Publication Date(Web):October 2002
DOI:10.1016/S0038-1098(02)00491-X
Co-reporter:Genqiang Zhang, Qingxuan Yu, Zhen Yao and Xiaoguang Li
Chemical Communications 2009(Issue 17) pp:NaN2319-2319
Publication Date(Web):2009/03/12
DOI:10.1039/B822595H
We have successfully developed an ethylene glycol mediated solution phase method for synthesizing highly crystalline Bi2Te3nanotubes using Te nanowires as the in situ templates; our work demonstrates the generic feature of a solution phase mediated Kirkendall effect for the synthesis of not only hollow nanoparticles but also highly crystalline tubular structures.
Co-reporter:Genqiang Zhang, Qingxuan Yu and Xiaoguang Li
Dalton Transactions 2010 - vol. 39(Issue 4) pp:NaN1004-1004
Publication Date(Web):2009/12/09
DOI:10.1039/B913462J
Recent advances in both theoretical and experimental studies on optimizing thermoelectric performance have proved to greatly benefit from nanostructure engineering. As a class of materials with the best thermoelectric properties near room temperature, V-VI alloy nanostructures, especially Bi2Te3 and its alloy with Sb, Se and so on, have attracted a broad interest. This perspective gives an overview of the progress in the wet chemical synthesis and property study of V-VI related one- and two-dimensional nanostructures. First, we discuss the preparation of one-dimensional nanowires/tubes, axial and radial modulated heterostructures, and two-dimensional platelet-like structures through various chemical routes. Then, we attempt to give a general outlook on the thermoelectric properties of V-VI single nanowires, and nanostructured films or bulk nanocomposites made of these chemically synthesized nanostructures. On the basis of the research in the synthetic methods and thermoelectric properties, the challenging issues and future research directions are briefly discussed. By no means is this a comprehensive coverage of V-VI related nanostructures, but a selection of those studies that could benefit the advance of thermoelectric properties of this material system in the near future.
