THERMODYNAMIC PROPERTIES OF THE GENERALIZED MURNAGHAN EQUATION OF STATE OF SOLIDS

In the Murnaghan approximation, an isothermal relation between pressur e (P) and volume (V) for solids is derived from the assumption that th e isothermal bulk modulus (B) is a linear function of P. This paper pr esents a thermodynamic analysis of a generalized form of the equation, based on treating all its various parameters [viz., V, B, and (partia l derivative B/partial derivative P)(T) at P = O] as functions of temp erature. Extending a previous study, the effect of T upon (partial der ivative B/partial derivative P)(T) is accounted for by using a dimensi onless parameter introduced by us, which is used in formulating genera l expressions for the volume dependence of various thermophysical quan tities, viz., the thermal expansion coefficient (alpha), the product a lpha B, and the Gruneisen and Anderson-Gruneisen parameters. Some comb inations of these parameters are identified, which show a simple depen dence upon P. The new expressions are used in analyzing current approx imations and the behavior of the solid in the low-compression range. I n particular, an expression for alpha at high P is reported which gene ralizes the Anderson equation and previous results by us.