Anharmonic Properties of Rocksalt Structure Solids of TOECs

Abstract

An effort has been made for obtaining the anharmonic properties of rocksalt structure solid starting from primary physical parameters VIZ. nearest neighbour distance and hardness parameter assuming long- and short-range potentials at an elevated temperature.The elastic energy density for a deformed crystal is expanded as power series of strains for obtaining coefficients of quadratic cubic and quartic terms which are known as the second, third and fourth order elastic constant respectively.When the values of the higher order elastic constants are known for a crystal, many of the anharmonic properties of the crystal can be treated within the limit of the continuum approximation in a quantitative manner.The higher order elastic constant are computed at 300K for rocksalt structure solids which are Alkali cyanides, Sodium and Potassium Halides. The first order pressure derivatives of second and third order elastic constants, the second order pressure derivative of second order elastic constant and partial contractions are evaluated at room temperature for these substances. The results thus obtained are compared with experimental and theoretical data and found in well agreement with present values.