State equations and properties of various polymorphous modifications of silicon and germanium

The state equations and the pressure dependences of the lattice properties have been obtained for various polymorphous modifications of silicon and germanium using the Mie–Lennard-Jones pair interatomic potential and the Einstein crystal model. It is shown that the elastic-type interatomic potential gives the best results for the semiconductor phase and the plastic-type interatomic potential for the metalized phases whose potential well depth is significantly smaller. The pressure dependences of the lattice properties are calculated along isotherm 300 K and the jumps of the properties during the phase transition from the diamond structure to the $\beta$-Sn phase are evaluated for both silicon and germanium. The calculated results agree well with the experimental data.