CLASSICAL AND QUANTUM SIMULATIONS OF YTTRIUM CUPRATE PROPERTIES

The defect properties of a number of yttrium cuprate materials have been studied with shell-model and quantum mechanical methods. We find that the structures of YBa2Cu3O7, YBa2Cu3O6.5, and YBa2Cu4O8 are reasonably reproduced with a single interatomic potential with deficiencies that are pointed out. Frenkel defects on the oxygen sublattice are the dominant computed defect in those materials. Impurity substitution at particular sites has been studied with a quantum mechanical model. In the case of Ca2+ substitution for Y3+, there is a sharp reduction in the ionization potential for formation of delocalized holes in the CuO2 plane.