Grüneisen Parameters of the Alkali Halides

Abstract

The microscopic Gr\"uneisen parameters of 13 alkali halides have been calculated over the entire Brillouin zone by solving the lattice dynamical problem at different pressures. A six-parameter shell model has been used and the variation of the parameters with pressure was deduced from the pressure dependence of the three elastic constants, of the two dielectric constants, and of the infrared absorption frequency. The quasiharmonic-model values of the macroscopic Gr\"uneisen parameter at 295 \ifmmode^\circ\else\textdegree\fi{}K were obtained by appropriate averaging over the microscopic mode gammas. The results are in good agreement, but are systematically larger than Gr\"uneisen parameters deduced from thermal-expansion data.