APPLICATION OF THE APPROXIMATION OF THE VALENCE FORCE FIELD TO CALCULATE THE STRAIN ENERGY OF CRYSTAL IN THERMODYNAMIC MODEL OF QUASIBINARY SEMICONDUCTOR SOLID SOLUTIONS

The application of the Martin–Keating valence force field approximation (VFF) is described for calculating the strain energy of crystal in the framework of thermodynamic model of quasibinary semiconductor solid solutions. The use of VFF leads to satisfactory results in calculations of strain energy for a sphalerite-type lattice, taking into account the interactions in the first and second coordination spheres. To clarify the Martin–Keating force constants, a lattice dynamics model was used to calculate the phonon spectra of semiconductors with a sphalerite structure. It is shown that the model allows to correctly calculate the force constants for compounds with small atomic masses and atomic radii, but leads to unsatisfactory results for compounds with an increasing metallic character of the bond. A comparison of the values of the force constants calculated from the phonon spectra with their Martin–Keating values determined from fitting to elastic constants shows a fairly good agreement with a discrepancy of no more than 15 %. This allows to conclude that the application of the Martin-Keating force constants in the proposed thermodynamic model of a solid solution is justified.

Authors: I. A. Cheremukhina

Direction: Physics

Keywords: Valence force field approximation, solid solution, strain energy, force constants, bending force of bonds, stretching of bonds, phonon spectrum

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