Li_2K(IO_3)_3与Li_2NH_4(IO_3)_3的晶体结构

本文用X射线粉末法测定了Li_2K(IO_3)_3与Li_2NH_4(IO_3)_3的晶体结构和原子参数。发现Li_3K(IO_3)_3,Li_2NH_4(IO_3)_3与Li_2Rb(IO_3)_3同晶型,属单斜晶系,空间群为P2_1/α,每个单胞含有四个化合式量。室温的点阵常数分别为α=11.198A,b=11.046A,c=8.254A,β=111.53°,及α=11.327A,b=11.078A,c=8.341A,β=111.87°。讨论了二元化合物的形成与离子半径的关系。     

WEAK QUANTUM FLUX CREEP AND STRONG PINNING IN THE NEW SUPERCONDUCTOR MgB2

The newly discovered superconductor MgB₂ has a transition temperature T_c of about 40 K, which is touching the upper line of that predicted by the phonon-mediated Bardeen--Cooper--Schrieffer (BCS) theory. It is interesting to investigate the flux creep in MgB₂ and compare it with other superconductors. We have measured the magnetization relaxation of MgB₂ sintered at high temperature and high pressure. It is found that the quantum tunnelling and the thermally activated flux creep are very weak, implying a strong pinning in this material.     

用广角纪尼叶单色聚焦相机精确测量钆镓石榴石的点阵常数

文献[1]对德拜一谢乐照相中精确测定点阵常数的方法进行了研究.用衍射仪精确测量多晶点阵常数的方法,在文献[2]中作了归纳总结.本文简要介绍用广角纪尼叶(Guinier)相机精确测定钆镓石榴石(GGG)和掺杂钆镓石榴石点阵常数的方法和结果. 一、广角纪尼叶单色聚焦相机的特点 广角纪尼叶相机与纪尼叶四重聚焦粉末相机的基本原理相同[3].广角纪尼叶相机的主要特点是,可收集到角度很广(1—89°)的衍射线和可得到严格的单色入射辐射.我们使用的Huber广角纪尼叶相机,通过适当的调节可获得严格的Ka1;辐射. 众所周知,点阵常数测量的精度,取决于衍射线…     

Li3VO4-Li4SiO4-Li4GeO4赝三元系相图的研究

本文用差热分析法和高温、室温X射线衍射法对Li₃VO₄,Li₄SiO₄的相变过程,Li₃VO₄-Li₄SiO₄,Li₃O₄-Li-4GeO₄赝二元系相图以及Li₃VO₄-Li₄SiO₄-Li₄GeO₄赝三元系相图室温截面进行了研究。发现在Li₃VO₄-Li₄SiO₄,Li₃VO₄-Li₄GeO₄赝二元系中,由于Li₄SiO₄或Li₄GeO₄的加入而使Li₃VO₄的高温γ_II相稳定存在于室温,从而得到一种新的具有高电导率的锂离子导体。作者认为探寻使高温态稳定存在于室温的方法是探索新的离子导体研究中有效途径之一。 关键词：     

碘酸盐的晶体结构与热力学性质——(Ⅰ)碘酸盐的晶体结构特点

本文根据作者等人的实验结果并结合文献报导的数据,综述了碘酸盐及其复盐的晶体结构特点和分类。对α-LiIO_3,Li_2H(IO_3)3,Mg(IO_3)_2,Mg(IO_3)_2-LiIO_3固溶体,Zn(IO_3)_2等晶体结构变迁的情况进行了分析。阐述了由于空位数量和分布的不同,以及阳离子性质(电价、离子极化能力和离子半径等)的不同,晶格场发生变化,引起了IO_3~-在不同方向和不同程度的移动或转动,因而有可能在不同方向上形成不同程度的各种畸变型结构和超结构。     

Li4SiO4-Li3VO4赝二元系和Li4GeO4-Li4SiO4-Li3VO4赝三元系中新的锂离子导体

本文在室温到300℃的温度范围内研究了Li₄SiO₄-Li₃VO₄和Li₄GeO₄-Li₄SiO₄-Li₃VO₄体系中的离子导电性,发现γ_II相固溶体Li_3+xV_1-xSi_xO₄是好的锂离子导体。所研究的成分中Li_3.3V_0.7Si_0.3O₄的离子电导率最高,室温下为1×10^-5Ω^-1·cm^-1,在42—192℃的电导激活能为0.36eV,电子电导率可以忽略,因而这是迄今所发现的最好的锂离子导体之一。粗略确定了Li₄GeO₄-Li₄SiO₄-Li₃VO₄三元系中电导率高的范围,发现在Li_3.5V_0.5Ge_0.5O₄中Si部分取代Ge可以使电导率进一步提高,Li_3.5V_0.5Ge_0.4Si_0.1O₄的室温电导率可达1.3×10^-5Ω^-1·cm^-1,电导激活能为0.40eV。 关键词：     

一种好的锂离子导体

近年来,探索锂的快离子导体的工作,虽然一直在努力进行,但并未取得突破性进展.自从发现LISICON以来。人们对固溶体锂离子导体发生了浓厚兴趣.我们的研究表明,LISICON是由于Zn械GeO4溶入Li4GeO4后而形成的固溶体,它把Li4GeO4的高温相稳定到了室温[1].最近据文献[2]报道,适量的 L     

Li_4SiO_4-Li_3VO_4赝二元系和Li_4GeO_4-Li_4SiO_4-Li_3VO_4赝三元系中新的锂离子导体

本文在室温到300℃的温度范围内研究了Li_4SiO_4-Li_3VO_4和Li_4GeO_4-Li_4SiO_4-Li_3VO_4体系中的离子导电性,发现γ_(II)相固溶体Li_(3 x)V_(1-x)Si_xO_4是好的锂离子导体。所研究的成分中Li_(3.3)V_(0.7)Si_(0.3)O_4的离子电导率最高,室温下为1×10~(-5)Q~(-1)·cm~(-1),在42—192℃的电导激活能为0.36eV,电子电导率可以忽略,因而这是迄今所发现的最好的锂离子导体之一。粗略确定了Li_4GeO_4-Li_4SiO_4-Li_3VO_4三元系中电导率高的范围,发现在Li_(3.5)V_(0.5)Ge_(0.5)O_4中Si部分取代Ge可以使电导率进一步提高,Li_(3.5)V_(0.5)Ge_(0.4)Si_(0.1)O_4的室温电导率可达1.3×10~(-5)Q~(-1)·cm~(-1),电导激活能为0.40eV。     

Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2

We have performed low temperature resistivity p（T） and specific heat C（T） measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is -4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat γn=4.51 mJmol^-1K^2 and the Debye temperature θD=419 K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/γnTc = 2.84 exp（-1.21Tc/T）. This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.     

PREPARATION, SUPERCONDUCTIVITY AND STRUCTURE OF THE LaBaCaCu3O7-x SUPERCONDUCTORS WITH Tc HIGHER THAN 80 K

In this paper, the preparation process of the tetragonal LaBaCaCu₃O_7-x (LBCCO) superconductor with T_c=84 K is repored. The superconductivity and structure of the LBCCO superconducting phase are investigated by means of X-ray diffraction (XRD), transmission electron microscope(TEM) and superconductivity measurements, The results indicate that the superconducting phase with T_c=82K in the LBCCO system has a tetragonal structure with a=0.3966nm, c=l.1838nm and space group P4/mmm. About 50% of the Ca and La atoms are located in 1d sites (i.e. Y site in the YBCO structure). It is confirmed that there is in fact no orthorhombic to tetragonal transition in this material. The relationship between the oxygen content and T_c is also presented.