Lattice dynamical theory of thermal expansion and mode Grüneisen parameters in cubic BP

Abstract

Lattice dynamical theory of thermal expansion and mode Gr\uneisen parameters in cubic boron monophosphide is reported in the quasiharmonic approximation within the framework of a second-neighbor rigid-ion model. In this scheme, we optimized the involved force constants by using nonlinear least-squares procedures with constrained parameters and weighting of the available data on critical-point phonons and elastic and lattice constants. Theoretical results of the phonon dispersion curves along high-symmetry directions (both at ambient and 89 kbar pressures), mode Gr\uneisen parameters, and thermal expansion coefficient {\ensuremath{\alpha}(T)} are compared and discussed with the existing experimental and ab initio calculations. Consistent with x-ray data, our calcualtion for the variation of \ensuremath{\alpha}(T) with temperature in BP is found to be remarkably similar to that of \ensuremath{\mathrm{B}}-SiC, and unlike most other III-V-compounds, it does not attain negative values at lower temperatures.