Vibrational and dielectric properties and ideal strength of Si2N2O ceramic from first principles

Silicon oxynitride (Si2N2O) is a functional ceramic having many possible applications. In this work, we studied the vibrational and dielectric properties and ideal strength as well as the related deformation mechanism of Si2N2O using first principles calculations. Factor group analysis was performed and vibrational frequencies were calculated to assign the observed vibrational modes. Infrared dielectric and absorption spectra were simulated and their origins were revealed. Tensile, compressive and shear strengths along the representative directions were investigated, which gave Si2N2O an ideal strength agreeing well with its experimental hardness. The calculated minimum compressive stress also coincides well with the starting amorphization pressure observed in shock experiments, providing a theoretical method to study mechanical effects of shock wave. Analyses on the deformation mechanisms at the critical strains imply that Si-O bond is stronger than other bonds, which is opposite to the previous speculation.