Thermodynamics of oxygen in Y 1Ba 2Cu 3O x between 450°C and 650°C

Abstract

We have measured the vapour pressure of oxygen in Y 1Ba 2Cu 3O x as a function of x at constant temperature between 450°C and650°C for pressures between 10 m Torr and 1000 Torr. From these vapour pressure curves we have determined ( ∂x ∂μ ) T (μ is the chemical potential), a thermodynamic response function analogous to the compressibility and specific heat. ( ∂x ∂μ ) T is a quantity which is sensitive to the oxygen configuration and which can be calculated by any candidate theory on the thermodynamics of oxygen. So, the measured ( ∂x ∂μ ) T curves should help in the search to determine the correct model for oxygen thermodynamics in Y 1Ba 2Cu 3O x . In this paper we use a simple quasi-chemical approximation with an empirical x and T dependent on-site energy to accurately fit the vapour pressure curves. This fit provides a fairly simple method to empirically reproduce the vapour pressure as a function of x and T, which should prove useful in materials preparation.