摘要
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。
Using semiempiric CNDO/2 method to calculate the structural units and
cell 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)~2
and 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 most
effective 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 p
orbitals of oxygen into the highest occupied hybrid band.
关键词
超导体
YBCO
化学键
电子结构
superconductor
chemical bonds
electronic stuctures/YBCO
