新系列超导相TlBaCa_(n-1)Cu_nO_(2n+2.5)(n=2,3)的晶体结构和超导电性

本文用粉末烧结法合成了Tl-Ba-Ca-Cu-O体系TlBa_2Ca_(n-1)Cu_nO_(2n+2.5)新系列超导相,用粉末衍射法测定了n=2和3的晶体结构,属简单四方单胞,空间群为D_(4h)~1-P4/mmm,点阵常数a相同,而c值不同,随n值而增大。a=3.847,c分别为12.73和15.89,每单胞含一个化合式单位,阳离子沿四方晶系的(0,0,z)和(1/2,1/2,z)位置交替排列,排列的顺序相同,n=3比n=2依次多增加Ca和Cu及相应的氧离子。 TlBa_iCa_()Cu_O_(2n+2.5),n=3时,零电阻超导转变温度T_c(0)= 112K;n=2时,T_c(0)=101K,与Tl_2Ba_2Ca_()Cu_O_(2n+4)型体心四方晶胞超导相不同,TlBa_2Ca_(n-1)Ca_O_(2n+2.3)结构中缺氧类钙钛矿型结构单元[Ba_2Ca_(n-1)Cu_nO_(2n+1)]仅被TI-O单层所隔开,当n相同时,Tl-O双隔层的体心四方单胞比Tl-O单层的简单四方单胞的超导转变温度高10K左右,这说明Tl-Ba-Ca-Cu-O体系中超导相的转变温度不仅与类钙钛矿结构单元的[CuO_4]和[CuO_5]的数目有关,而且与Tl-O的隔层数目有关。

PHASE RELATION AND SUPERCONDUCTIVITY IN La-Ba(Sr)-Cu-O SYSTEM

The important progress of the superconductivity in R-Ba(Sr)-Cu-O system (R=La, Y)made by Zhao Zhongxian, Bednorz and Cava et al. has interested the science and technology circles greatly. In order to understand the mechanism of superconductivity in the system, it is important to determine the phases and structures existing in the system, and to pick up superconductive phases. The structures of some compounds in the system were re-