Structural, Mechanical, and Thermal Properties of β-Si3N4 under High Pressure

Intensive calculations have been carried out to study the structural, mechanical, and thermal properties of beta-Si3N4 with hexagonal P63/m structure. The calculated lattice constants a and c are in agreement with the available experimental data and similar theoretical calculations. Through a series of researches, the mechanical parameters (the elastic constants, bulk modulus, shear modulus, and Young's modulus) and Debye temperature, the wave velocities are systematically investigated. Additionally, the mechanical anisotropy has been characterized by calculating Young's modulus and described by the three-dimensional (3D) surface constructions and its projections. By using the born stability criteria and phonon frequency, it is concluded that the beta-Si3N4 is stable mechanically and dynamically up to 35 GPa. Finally, the thermal properties have been calculated by employing the quasi-harmonic Debye model at different temperatures (0-800 K) and pressures (0-35 GPa).