Thermodynamics and stability of superconductive phases in yttrium-barium-copper-oxygen system

A review of thermodynamic properties of phases in Y-Ba-Cu-O system is given. Thermodynamic functions of YBa4Cu3O8.5 compound, wich were not earlier investigated, were evaluated. Equilibria of 123, 124 and 247 superconducting phases with other phases of Y-Ba-Cu-O system were calculated, and the regions of thermodynamic stability of these superconductors were obtained. It is shown that orthorhombic structure of 123 phase is characterized by thermodynamic instability at all contents and temperatures. The calculated diagrams with stability fields of phases can be used directly for choosing conditions of 123, 124 and 247 superconductor synthesis