V A Pai
Articles written in Bulletin of Materials Science
Volume 14 Issue 4 August 1991 pp 951-957 International Conference On Superconductivity—III
Charge self-consistent LCAO band structure (CSCBS) calculations are reported for orthorhombic YBa2Cu3O7 and tetragonal YBa2Cu3O6 assuming ordered vacancy models. The effective atomic charges are used to study the charge transfer. In YBa2Cu(1)1Cu(2)2O7, the two types of copper atoms have their energy bands almost overlapping with effective valency of each copper as 7/3 (or effective valency of each oxygen as approximately — 13/7), so that electron hopping can take place without any loss or gain of energy while in YBa2Cu(1)1Cu(2)2O6, Cu(1)1 is monovalent and Cu(2)2 are divalent with significant difference in their bands. Therefore, YBa2Cu3O7 should conduct much better compared to YBa2Cu3O6. This corroborates the experimental observations that YBa2Cu3O7 is a (super)conductor while YBa2Cu3O6 is not. The calculated effective charges and DOS support the above view.
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