-
本文用粉末烧结法合成了Tl-Ba-Ca-Cu-O体系TlBa2Can-1CunO2n+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D4h1-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。TlBa2CanCunO2n+2.5,n=3时,零电阻超导转变温度Tc(0)=112K;n=2时,Tc(0)=101K,与Tl2Ba2Can-1CunO2n+4型体心四方晶胞超导相不同,TlBa2Can-1CanO2n+2.5结构中缺氧类钙钛矿型结构单元[Ba2Can-1CunO2n+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[CuO4]和[CuO5]的数目有关,而且与Tl-O的隔层数目有关。We synthesized new superconducting phases in TlBa2Can-1CunO2n+2.5 by solid state reaction. The crystal structures of TlBa2CaCu2O6.5 and TlBa2Ca2Cu3O8.5 were determined by means of X-ray powder diffraction method. The two compounds belong to primary lattice with space group D4h1-P4/mmm. The lattice constants of TlBa2CaCu2O6.5 are α= 3.847 ?, c = 12.73 ?. The lattice constants of TlBa2Ca2Cu3O8.5 are α = 3.847?, c= 15.89?. Each cell contains one chemical formula unit. The cations are distributed alternately at positions of (0,0,z) and (1/2, 1/2, z) along Z axis. TlBa2CaCu2O6.5 shows zero resistance at 101.4K. TlBa2Ca2Cu3O8.5) shows zero resistance at 112K. The oxygen deficient pseudo-perovskite unit Ba2Can-1CunO2n+1 is separated by single Tl-O layer in the crystal structure of TlBa2Can-1CunO2n+2.5, while the oxygen deficient pseudo-perovskite unit Ba2Can-1CunO2n is separated by bilayer of Tl-O in the crystal structure of Tl2Ba2Can-1CunO2n+2. At the same n value, Tc of Tl2Ba2Can-1CunO2n+4 is about 10K higher than Tc of TlBa2Can-1CunO2n+2.5. This indicates that Tc depends on the number of Tl-O layer as well as the number of [CuO5] and [CuO4] in oxygen deficient pseudo-perovskite unit Ba2Can-1CunO2n.
计量
- 文章访问数: 7250
- PDF下载量: 488
- 被引次数: 0
下载:
