First-principles study of the stability of NbC-SiC solid solutions

First-principals calculations were carried out in order to discover stability of the B1-SixNb1−xC solid solutions (alloys). Lattice parameter, total energy, formation energy, phonon spectra, elastic properties were investigated as functions of composition. It was found that phonon spectra for the alloys had imaginary frequencies (the range of the phonon density of states, PHDOS, with the negative wavenumbers). Also, the eigenvalues of the matrix of elastic constants were negative for some compositions. Phonon calculations for pure SiC with lattice parameters that corresponded to different alloy compositions showed that the reason for instability of some solid solutions is the dynamical instability of B1-SiC with the lattice parameters for these alloys.