氧化物超导材料的键价计算

Y-Ba-Cu—O和Tl(Bi)-Ba-Cu-O氧化物体系的晶体结构与其超导转化温度T_c存在密切关系。以统计法则为基础的键价计算结果表明,具有超导性的 Y系、Tl系氧化物晶体中各离子接近其正常价态,CuO-维链与CuO_2二维面中的铜离子的价态无显著差异。这和对Y-Ba-Cu-O 系进行的紧束缚带电子结构计算的结果不同,所以CuO-维链的存在与否对氧化物超导性的出现不一定必需,Tl(Bi)系不存在CuO-一链,而它的T_c甚至比Y系更高就是个很好的实例。

Bond-Valence Calculation for Oxide Superconductor

There is an intimate relationship between crystallographic structure and the superconducting transition temperature To of Y-Ba-Cu-O and TI(Bi)-Ba-Ca-Cu-O systems. Based on the statistical principle, the bond-valence method was used and a conclusion was drawn :the vaiences of alt ions in oxide superconductors were equal approximately to their normal values and there was not remarkable differece between the valence of copper ions in the CuO chain and the CuO22- D plane. This result was different from the tight-binding band electronic structure calculation for Y-Ba-Cu-O system and that meant. CuO chain was not essential for the occurrence of high Tc superconductivity. There was not CuO chain in TI(Bi) oxide superconductors and they had higher To than the Y-Ba-Cu-O system. It may be a good evidence.