H. Matsuo

Thermal expansion coefficient of GaAs and InP

Abstract The temperature dependence of the thermal expansion for GaAs and InP is investigated theoretically using the experimental pressure derivatives of elastic stiffness constants and phonon frequencies. The linear correlation between the transverse acoustical mode Gruneisen parameter γXTA and the metallic transion pressure Pt obtained by Weinstein is not satisfied for GaAs and InP, but the observed thermal expansion of GaAs is well reproduced. In addition, the linear expansion coefficient of InP is predicted theoretically as a function of temperature. Then, the phonon dispersion curves of GaAs and InP at their covalent-metallic transition pressures are quantitatively shown.

Phase transition under pressure of Si-Ge solid solutions

Abstract The pressure-induced covalent-metallic phase transition to the disordered β-Sn structure of Si1−xGex solid solution is studied theoretically using the electronic theory based on pseudopotentials. Numerical results of transition pressure, volume discontinuity, transition heat and lattice parameters in the high-pressure phase are quantitively obtained. The calculated data for transition pressure and transition heat have a maximum near the atomic fraction x = 0.55: the formation of the disordered solid solution brings about the stabilization of the diamond-type phase under pressure.