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Crystal structures and electronic properties of BaC_2 isomers by theoretical study based on DFT

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Science china Chemistry 2008年第6期51卷 545-550页

作者： FENG Jing1,XIAO Bing2 & CHEN JingChao1 1 key laboratory of Advanced materials of Precious-Nonferrous Metals,education ministry of china,and key Lab of Advanced materials of Yunnan Province,Kunming university of Science and Technology,Kunming 650093,china 2 School of materials Science and Engineering,Xi’an Jiaotong university,Xi’an 710049,china key laboratory of Advanced materials of Precious-Nonferrous Metals Education Ministry of China Kunming China key Lab of Advanced materials of Yunnan Province Kunming University of Science and Technology Kunming China School of materials Science and Engineering Xi’an Jiaotong University Xi’an China

Band structures and electronic properties of two BaC2 isomers were calculated by using density func-tional theory(DFT) *** ionic bond features are all typical between cation(Ba) and anion clusters(C2) in both structures of the ***,a much stronger covalent bond exists in anion clusters which can be seen by inspecting the electron distribution contour that has a dull bell like shape between two carbon *** shortest distance between Ba2+ and C22? and the bond length in anion clusters are different in these isomers of BaC2,which are 0.2945 nm and 0.1185 nm for the structure with the I4/mmm space group and 0.2744 and 0.1136 nm with the C2/c type,*** structures were clarified by combining the DOS to indicate the ionic bonding features more *** analysis provided further evidence on these *** calculation results reveal that the transition temperature of these two polymorphs of BaC2 locates near 132 K,which is consistent with the recent experimental results.

关键词： functional materials metal diaries phase transition electron density first principle calculation orbital bonding state

Structural relaxation of metallic glass forming melts

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Science china(Physics,Mechanics & Astronomy) 2010年第3期53卷 405-408页

作者： BIAN XiuFang, QIN JingYu & QIN XuBo key laboratory for Liquid-Solid Structural Evolution and Processing of materials (ministry of education), Shandong university, Jinan 250061, china key laboratory for Liquid-Solid Structural Evolution and Processing of materials (ministry of education) Shandong University Jinan China

The fragility of superheated melts, M, for 13 kinds of metallic alloys has been evaluated from the data of the dynamic viscosity above their liquidus temperatures. The authors find that the glass forming ability of metallic melts depends on the fragility of superheated melts rather than on the value of viscosity. In the present work the value of fragility is less than 1 for good glass-forming melts but more than 1 for the other melts. The variation rate of atomic coordination number with temperature indicates clearly the relaxation rate of molten structures. The fragility of superheated melts is found in good agreement with the variation rate of the atomic coordination number with temperature.

关键词： structural relaxation metallic glasses melts

Pollen records of Holocene vegetation and climate changes in the Longzhong Basin of the Chinese Loess Plateau

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Progress in Natural Science:materials International 2007年第12期17卷 1445-1456页

作者： Tang Lingyu1 and An Chengbang2(1. Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, china 2. key laboratory of Western china’s Environment Systems, MOE, lanzhou university, lanzhou 730000, china) Nanjing Institute of Geology and Paleontology Chinese Academy of Sciences Nanjing 210008 China key laboratory of Western china's Environment Systems Lanzhou University Lanzhou 730000 China

Pollen records with an average time resolution of 20-200 years from Holocene loess sections at Dingxi, Qin'an, and other localities of Gansu Province reveal a detailed history of vegetation and climate changes in the western Loess Plateau. For most time of the Holocene, the landscape was dominated by grasslands or forest steppes. However, during the middle Holocene (7.5-5.8 ka BP), relatively dense forests developed, and the endemic vegetation flourished, suggesting a much warmer and more humid climate condition than the present. Superimposed upon this general pattern are several dry intervals marked by the episodic expansion of grasslands or forest steppe. Xeric vegetation expanded after 3.8 ka BP, indicating a trend towards dry conditions.

关键词： pollen records glasslands coniferous forests Holocene Loess Plateau.

Anomalous magnetotransport in LaMn_(1-x)Te_xO_3

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Science china(Physics,Mechanics & Astronomy) 2009年第7期52卷 987-992页

作者： TAN GuoTai1,2, CHEN ZhengHao3 & ZHANG XiaoZhong4,5 1 key laboratory of Beam Technology & materials Modification of the ministry of education, Institute of Low Energy Nuclear Physics, Beijing Normal university, Beijing 100875, china 2 Beijing Radiation Center, Beijing 100875, china 3 laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, china 4 key laboratory of Advanced materials of the ministry of education, Department of materials Science and Engineering, Tsinghua university, Beijing 100084, china 5 Beijing National Center for Electron Microscopy, Tsinghua university, Beijing 100084, china key laboratory of Beam Technology & materials Modification of the ministry of education Institute of Low Energy Nuclear Physics Beijing Normal University Beijing China Beijing Radiation Center Beijing China laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing China key laboratory of Advanced materials of the ministry of education Department of Materials Science and Engineering Tsinghua University Beijing China Beijing National Center for Electron Microscopy Tsinghua University Beijing China

The LaMn1-xTexO3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3+ and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3+ is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3+ is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.

关键词： colossal magnetoresistance La-Te-Mn-O magnetotransport

Microstructure and Orientation Evolution of Unidirectional Solidification Pure Copper during ECAP

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稀有金属材料与工程 2011年第S3期40卷 171-175页

作者： Guo Tingbiao, Ding Yutian, Yuan Xunfeng, Hu Yong State key Lab. of Gansu Advanced Non-ferrous Metal materials, lanzhou university of Technology, lanzhou 730050,china lanzhou Univ Technol State Key Lab Gansu Adv Nonferrous Met Mat Lanzhou 730050 Peoples R China

Experiment were conducted to unidirectional solidification pure copper during ECAP by route C, the samples were investigated by XRD and EBSD. The results shown that the effect of original microstructure on the subgrains orientation decrease with the increasing of strain. At low strain, in the column grain interiors first formed a band structure that the orientation quite different with the matrix. With the strain increasing, the boundaries of the band structure expanding towards to two sides, gradually partition the original column grains into subgrains, the distribution of the subgrains possesses a directional distribution characteristics and the twins occurring in subgrains. Keep on increasing strain, the original grain boundaries began to broken, low angles grain boundaries and high angles grain boundaries both occur simultaneously shows a diffusion distribution characteristics.

关键词： equal channel angular extrusion (ECAE) electron back-scattering diffraction (EBSD) grain boundaries (GBs) texture

Ln_2MO_4 cathode materials for solid oxide fuel cells

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Science china Chemistry 2011年第6期54卷 898-910页

作者： ZHAO Hui, LI Qiang & SUN LiPing key laboratory of Functional Inorganic Material Chemistry, ministry of education School of Chemistry and materials Science, Heilongjiang university, Harbin 150080, china key laboratory of Functional Inorganic Material Chemistry Ministry of Education School of Chemistry and materials Science Heilongjiang University Harbin China

One of the major challenges to develop "intermediate temperature" solid oxide fuel cells is finding a novel cathode material, which can meet the following requirements: (1) high electronic conductivity; (2) chemical compatibility with the electrolyte; (3) a matched thermal expansion coefficient (TEC); (4) stability in a wide range of oxygen partial pressure; and (5) high catalytic activity for the oxygen reduction reaction (ORR). In this short review, a survey of these requirements for K2NiF4-type material with the formula Ln2MO4, Ln = La, Pr, Nd, Sm; M = Ni, Cu, Fe, Co, Mn, is presented. The composition-dependent TEC, electrical conductivity and oxygen transport property are considered. The Ln2MO4 materials exhibit improved chemical stability and compatibility with most of the traditional electrolytes. The complete fuel cells integrated with Ln2MO4 materials as cathodes show promising results. Furthermore, these materials are considered as cathodes of protonic ceramic fuel cell (PCFC), and/or anodes of high temperature steam electrolysis (HTSE). First results show excellent performances. The versatility of these Ln2MO4 materials is explained on the basis of structural features and the ability to accommodate oxygen non-stoichiometry.

关键词： intermediate temperature solid oxide fuel cells (ITSOFCs) cathode K2NiF4-type structure oxygen non-stoichiometry

Thermodynamic Functions and Phase Transformation of Metal Nanocrystals

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Journal of materials Science & Technology 2005年第5期21卷 705-709页

作者： Jinping GAO, Xiaoyan SONG , Jiuxing ZHANG, keyong YANG and Xuemei LIUCollege of materials Science and Engineering, the key laboratory of Advanced Functional materials of the education ministry,Beijing university of Technology, Beijing 100022, china key laboratory of Advanced Functional materials College of Materials Science and Engineering Beijing University of Technology Beijing 100022 China

A model to calculate the thermodynamic functions of the pure metal nanocrystals has been developed, with the consideration of the effects of both the interfaces and the crystal in the nano-grain interior. As an example, the enthalpy, entropy and Gibbs free energy, as functions of the excess free volume at interfaces, temperature and grain size, are calculated for the Co nanocrystals. Furthermore, the characteristics of β-Co→α-Co phase transformation are studied, and the transformation temperatures at different levels of grain size, as well as the critical grain sizes at different temperatures, are predicted. The calculation results show that, the nano-grained β-Co （fcc） is thermodynamically stable at temperatures much lower than that for the conventional coarse-grained materials, and may also stably exist at room temperature when the grain size is reduced to be small enough. The present model is verified by comparisons between the experimental findings and the theoretical predictions.

关键词： Thermodynamic function Nanocrystal Phase transformation

Advances in Thermionic Cathode of Tungsten and Molybdenum

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Rare Metals 2001年第3期20卷 137-141页

作者： Jinshu Wang,Meiling Zhou, Tieyong Zuo, Juan Liu, Jiuxing Zhang, Zuoren Nie The key laboratory of Advanced Functional materials, ministry of education, School of materials Scence and Engineering, Beijing Polytechnic university, Beijing 100022, china 北京工业大学教育部新型功能材料重点实验室北京 100022.

Several kinds of tungsten thermonic cathodes have been introduced. As a promising alternative for thoriated tungsten, rare earth doped molybdenum cathode has been studied. Compared with the traditional thoriated tungsten, La-Mo cathode has higher emission current density at lower temperature, but it has poor emission stability. In order to improve the emission stability, systematical study on the emission mechanism of La-Mo cathode has been carried out. The life of La-Mo cathode has been improved and has achieved 1400 It, which exceeds the minimum life for practical uses (1000 h). As another alternative for thoriated tungsten cathode, Y-Mo cathode has shown better performance. The thermionic emission capability of Y-Mo cathode is between that of La-Mo cathode and Th-W cathode.

关键词： tungsten molybdenum thermonic cathode emission

A highly efficient electric additive for enhancing photovoltaic performance of dye-sensitized solar cells

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Science china Chemistry 2010年第6期53卷 1352-1357页

作者： LAN Zhang,WU JiHuai,LIN JianMing & HUANG MiaoLiang Engineering Research Center of Environment-Friendly Functional materials,ministry of education key laboratory of Functional materials for Fujian Higher education Institute of materials Physical Chemistry,Huaqiao university,Quanzhou 362021,china Engineering Research Center of Environment-Friendly Functional materials Ministry of Education key laboratory of Functional materials for Fujian Higher education Institute of Materials Physical Chemistry Huaqiao University Quanzhou China

N-cetylpyridinium iodide (N-CPI) as a new electric additive for enhancing photovoltaic performance of the dye-sensitized solar cell (DSSC) was *** showed high efficiency for enhancing both the open-circuit voltage and the short-circuit current density of DSSC when the suitable amount of N-CPI as 0.02 M was added in liquid *** energy conversion effi- ciency of DSSC increased from 4.429% to 6.535%,with 47.55% ***,it is a highly efficient electric addi- tive for *** intrinsic reason is owing to the special molecular structure of N-CPI,which contains two different polarity *** a surfactant,N-CPI could form ordered arrangement in liquid electrolyte,which affects the diffusing ability and the redox reaction of I-/I3-,and further affects the photovoltaic performance of DSSC.

关键词： dye-sensitized solar cell electric additive photovoltaic performance N-cetylpyridinium iodide Dapp