Relationship between superconducting transition temperature and combinative energy in YBa₂Cu₃O_7-δ

Separating the unit cell of YBa₂Cu₃O_7-δ into perovskite and rock salt blocks and considering the interaction between the two blocks, a computer program has been developed to calculate the interaction called combinative energy, between the blocks. The combinative energy in YBa₂ Cu₃ O_7-δ with different δ value from 0.07 to 0.62 has been calculated. A close relationship between the superconducting transition temperature and the combinative energy in YBa₂ Cu₃ O_7-δ has been established, and the change of the combinative energy found to be closely related to the transformation from orthorhombic I to II. It is believed that the interaction between the two blocks in the unit cell is of great importance to the superconductivity in YBa₂ Cu₃ O_7-δ.