Pressure induced phonon stiffening and softening in III-V phosphides

A lattice dynamical study of InP, GaP and BP under pressure is reported by using two lattice dynamical model theories namely, the rigid ion and deformation bond approximation models. It is observed that the energies of the optical phonons and longitudinal acoustic phonons stiffen with pressure, while the transverse acoustic phonon frequency softens. The phonon density of states shows pronounced shift in the frequency spectra with pressure. The mode Gruneisen parameter indicates that the TA phonon modes have negative values and responsible for the lattice softening. The lattice specific heat at constant volume, C(V) increases with pressure. The obtained results are, in general, good agreement with available data.