Thermodynamics of high-temperature superconducting materials
In this paper, the problem of thermodynamic stability of new high-temperature superconductors is discussed. This problem can only be solved with the help of thermodynamic investigations, including experimental studies of thermodynamic properties and calculations of equilibria, which require a considerable amount of thermodynamic data. Now such a set of data is only available for the phases in the Y-Ba-Cu-0 system. In this system, phase equi- libria have been calculated and the stability regions of the super- conducting compounds and solutions established. It has been found that the 123, 247 and 124 superconductors are thermodynamically unstable under application conditions. The methods of theoretical and experimental investigations and available thermodynamic properties of phases are briefly reviewed.