Atomistic simulation of ionic and electronic defects in YBa2Cu3O7.

An empirical two-body potential model has been developed in order to describe the electronic and ionic defect properties of orthorhombic YBa/sub 2/Cu/sub 3/O/sub 7/. The potential model was derived starting from known potentials and calculated potentials and fits the crystal structure to better than 0.03 A for the major bonds. Oxygen vacancy formation and hole trapping as a localized polaron are most favorable at the chain oxygen ion site 1. Hole trapping on Cu/sup +/ ions is most favorable for ions in the copper-oxygen plane. Divalent impurity ions such as Ni/sup 2+/, Zn/sup 2+/, and Cd/sup 2+/ can dissolve in the crystal preferentially at the Cu/sup 2+/ plane site 2. On the other hand, trivalent impurities such as Al/sup 3+/, Fe/sup 3+/, and Ga/sup 3+/ dissolve in the crystal at the chain Cu/sup 2+/ site 1 along with the incorporation of oxygen ions. Anions such as S/sup 2-/, Cl/sup -/ or F/sup -/ would preferentially substitute for O/sup 2-/ at sites near the Cu/sup 2+/ chain position.