Due to the recent availability of accurate measurements, the use of partial molar quantities (free energy, enthalpy, and entropy) has emerged as a tool aimed at evaluating effective pair interactions in nonstoichiometric compounds. In the present paper, this approach has been used to ascertain the validity of inverse methods in a simple academic case and to discuss available thermodynamic data in the most extensively studied system, i.e., ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+2\mathit{x}}$, in the framework of asymmetric two-dimensional lattice-gas models proposed for this system.

• Received 9 March 1993

DOI:https://doi.org/10.1103/PhysRevB.48.10090