Madelung Potentials in YBa2Cu3Ox (x=7 and 8)

Abstract

Calculations of Madelung potentials of ions in YBa₂Cu₃O₈ reveal that the oxygen ions which are found experimentally to have small occupation factors are quite unstable. The most stable ionic configuration of YBa₂Cu₃O₇, which contains a Cu³⁺, two Cu²⁺ ions and an oxygen vacancy per “molecule” in the structure of YBa₂Cu₃O₈, has been obtained by calculating the Madelung energies per YBa₂Cu₃O₇ molecule for several ionic positions. These calculations determine the most stable Cu³⁺ position and also show that the unstable oxygen ions in YBa₂Cu₃O₈ become remarkably stabilized in YBa₂Cu₃O₇.