The chemical bonds and electronic configurations in YBCO superconductor

Abstract

With semiempiric CNDO/2 calculations on the structural units and unit cell of YBCO, the following results are obtained: 1) Cluster models can not describe the real properties 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 Cu + and Cu 2+. 3) The electronic configurations of Cu(2) and Cu(1) are d 2 xy d 2 xz d 2 yz d x 2− y 2 d 2 z 2 and d 2 xy d 2 xz d 2 yz d 2 x 2− y 2 d 1 z 2 respectively. 4) Superexchange effect exists in YBCO generally that is the 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.