Bi_2（Sr，Ca）_3Cu_2O_y超导体的EXAFS研究

EXAFS Study on Bi_2 (Sr, Ca)_3Cu_2O_y Superconductor

利用扩展Ｘ射线吸收精细结构（ＥＸＡＦＳ），研究了Ｂｉ２（Ｓｒ，Ｃａ）２Ｃｕ２Ｏｙ超导体中Ｃｕ原子与Ｂｉ原子的局域结构．结果表明：Ｃｕ原子第一配位层是五配位的氧原子，第二配位层是四配位的Ｃａ原子和一配位的Ｃｕ原子，但不含Ｓｒ原子的结构信息，这是Ｓｒ－Ｏ层与Ｃｕ－Ｏ层层间距较大所致；同时测定Ｂｉ原子第一配住层含有２．３个氧原子，用非公度调制结构模型解释了Ｂｉ原子的配位状况．

EXAFS has been applied to study the local structure of Cu and Bi atoms in Bi2 (Sr,Ca)3Cu2Oy superconductor with Tc=72. 8K. The results have shown that Cu is five O atoms coordinated at the firSt shell, and four Ca atoms and one Cu atom surrounded at the second Shell, but no information of Sr atom included in this shell ; It is supposed that the phenomina be attributed to the iong distance between Cu-O and Sr-O layers; At the first Shell of Bi atom, the average coordinate number is 2. 3 for O atoms, which is accordance with BVS model and M. B. Wailer's incommensurate modulated structure.