Theoretical Study of Oxygen Disorder Effects in YBa2(Cu1−xMx)3O7+y (M = Al, Co, Fe, Ga)

We study structural changes in YBa2Cu3O7−δ resulting from alloying with Al, Co, Fe and Ga. For the various interatomic interactions we use a bond model. Then we find at T = 0 that the tetragonal phase seemingly observed by x-ray diffraction consists of differently oriented orthorhombic domains. The observed uptake of excess oxygen as a consequence of doping with Al, Co and Fe is explained by domain formation. In addition, we propose a model to treat the system at T > 0.