Calculation of combinative energy between perovskite and rocksalt blocks in YBa2Cu3O7-δ

Based on a block model, separating the unit cell of YBa2Cu3O7-delta into perovskite and rock salt blocks, the combinative energy between the two blocks in the YBa2Cu3O7-delta with the different delta value, from 0.07 to 0.62, was calculated. A close relationship between the superconducting transition temperature and the combinative energy in YBa2CU3O7-delta is established, and the change of the combinative energy is closely related to the transformation from orthorhombic I to II. The results also give a clue to reconsider the role of the orthorhombic I and II in YBa2Cu3O7-delta The calculation of the holes in different planes supplies abundant information about the charge distribution in YBa2Cu3O7-delta which may possibly connect the electronic phase diagram and the fluctuations of the stripe phase. The results show that the interaction between the two blocks is of great importance for high T-c superconductivity.