GENERALIZED ANDERSON-GRUNEISEN PARAMETERS FOR NONCUBIC SOLIDS

General thermoelastic equations are developed relating the temperature and the stress derivatives of the effective isothermal elastic moduli of an orthorhombic crystal which is subjected to a purely extensional deformation parallel to the crystallographic axes. When the stress is hydrostatic, these equations are used to obtain finite strain expressions for the generalized isothermal Anderson-Gruneisen parameters of a crystal with orthorhombic or higher elastic symmetry. The expressions are derived in terms of the second-order elastic constants and compliances, the third-order elastic constants and the Gruneisen parameters. Theoretical values of the five independent isothermal Anderson-Gruneisen parameters are then calculated for two hexagonal metals (Mg and Zn). Finally, a relation between the adiabatic and isothermal Anderson-Gruneisen parameters is given which generalizes that previously obtained in the case of cubic crystals.