Inert gas pressure effects on phase stability of oxides

Phase stability of Y-Ba-Cu-O superconducting phases was evaluated as a func tion of temperature, oxygen partial pressure and total gas pressure by the hot isostatic pressing method using argon and oxygen mixtures as a surround ing atmosphere. The phase transformation temperature from Y2Ba4Cu7Oy to YBa 2Cu4O8 increased with increasing the total gas pressure, even if the oxygen partial pressure was kept constant. It indicates that the equilibrium part ial pressure of a gas involving the chemical reaction changes if a solid-ga s reaction is progressed under high total gas pressure. Dependence of chemi cal potential of the reactant gas on the inert gas pressure was thermodynam ically discussed on the basis of Lewis-Randall's empirical scaling law and Ishizaki's approximation. These two approximations resembled each other at pressures less than the usual HIPing pressure.