Oxygen vacancy ordering in YBa 2 Cu 3 O 7-y

Abstract

Abstract First principles total energy calculations have been performed for YBa 2 Cu 3 O x with x varying from 6.0 to 7.5. The results of these calculations have been used to determine the effective pair interactions for the oxygen ordering in the basal plane. The phase diagram calculated with these “first principles” pair interactions is in very good agreement with experiment. Comparison of the total energies for the O 6 , O 6.5 and O 7 structures shows that the double-cell phase is thermodynamically stable.