YBCO超导体中化学键与电子结构

本文用半经验CNDO/2量子化学计算方法,对YBCO的结构单元及晶胞作了计算,结果指出:1.采用簇模型不能较好地反映YBCO晶体性质。2.YBCO中Cu(2)的氧化态为( 2),Cu(1)的氧化态为( 1.5),Cu(1)也可能是在( 2)与( 1)两个氧化态之间共振。3.铜的电子组态分别为Cu(2)(d_(xy)~2d_(x2)~2d_(yz)~2d_(x~2-y~2)~1d_z~(2_2)),Cu(1)(d_(xy)~2d_(xz)~2]d_(yz)~2d_(x~2-y~2)~2d_(z~2)~1)。这种组态是YBCO形成层状氧缺位结构的主要原因。4.超交换作用在YBCO中普遍存在,但铜-氧面间这种作用最大,超导电流在其间进行最为有利。5.Y,Ba在YBCO中的主要作用是促成Cu(d_(xy))与O(P)形成最高占领杂化带。

CHEMICAL BONDS AND ELECTRONIC STRUCTURES IN YBCO SUPERCONDUCTORS

Using semiempiric CNDO/2 method to calculate the structural units andcell of YBCO,the following results arc obtained:1.Cluster models can not show the real propcrtics of YBCO crystal well.2.The oxidation state of Cu(2)is( 2),while that of Cu(1)is( 1.5)and perhaps Cu(1)resonates between( 1)and( 2).3.The electronic configurations of Cu(2)and Cu(1)are d_(xy)~2d_(xz)~2d_(yz)~2 d_(x~2-y~2)~1d_(z~2)~2and d_(xy)~2d_(xz)~2d_(yz)~2d_(x~2-y~2)~2d_z~(12) respectively.4.Generally,there exists superexchange effect in YBCO which is thc mosteffective between Cu-O planes,through which superconducting current flows.5.Y and Ba in YBCO help to bring about d_(xy) orbitals of copper and porbitals of oxygen into the highest occupied hybrid band.