Abstract: The plane-wave pseudo-potential method within the framework of first-principles technique is used to investigate the fundamental structural properties of Si₃N₄. The calculated ground-state parameters agree quite well with the experimental data. Our calculation reveals that α-Si₃N₄ can retain its stability to at least 45 GPa when compressed below 300 K. No phase transition can be seen in the pressure range of 0--45 GPa and the temperature range of 0--300 K. Actually, the α→β transition occurs at 1600 K and 7.98 GPa. Many thermodynamic properties, such as bulk modulus, heat capacity, thermal expansion, Gruneisen parameter and Debye temperature of α-Si₃N₄ were determined at various temperatures and pressures. Significant differences in these properties were observed at high temperature and high pressure. The calculated results are in good agreement with the available experimental data and previous theoretical values. Therefore, our results may provide useful information for theoretical and experimental investigations of the N-based hard materials like α-Si₃N₄.

Key words: First-principle, Bulk modulus, Density of state, Debye temperature