Solid solutions of alkali halide compounds. I. Configurational and vibrational contributions

We present a model to do quantitative thermodynamics of pseudobinary ionic solid solutions of the type A1-xBxC (0x1). The model enables us to compute the phase diagram as well as certain physical properties of interest, starting from interionic potentials. The model is demonstrated with three systems: K1-xRbxI, KCI1-xBrx, and Na1-xKxCl. The model incorporates the essential features of pseudobinary ionic solid solutions, namely, (a) the interdependence of volume and energy, (b) the presence of nonrandom distribution of the two species and associated configurational entropy, and (c) the vibrational contributions to the free energy and its derivatives. In this work, we make use of the single-frequency average quasiharmonic approximation to assess the vibrational corrections to the entropy and the phase diagram. © 1991 The American Physical Society.