DIFFERENCES BETWEEN HIGH-TC OXIDES CONTAINING 6-FOLD, 5-FOLD, 4-FOLD AND 2-FOLD COORDINATED COPPER

Atomistic simulation techniques are used to investigate the defect properties and redox energies of a series of ternary cuprates with different copper coordinations to oxygen. In particular, results are reported for La2CuO4, LaNdCuOr, Nd2CuO4, Y2CuO4 and YBa2Cu3O6, amongst others. The implications for the high-temperature superconducting behaviour of these oxides when made non-stoichiometric are discussed in detail. We compare ''hole'' and ''electron'' superconductors. In addition we suggest that the variation of T(C) with oxygen content, X, for YBa2Cu3O6+X and Y1-ZCaZBa2Cu3O6+X is linked to the two very different environments of Cu in this system.