Infrared evidence for pressure-induced phase transition of α-Si3N4

Abstract

X-ray diffraction (XRD) method and structural refinement were used to characterize the sample of [Formula: see text]-Si3N4. Rietveld analyses of XRD data confirmed that the sample belongs to hexagonal crystal (space group of P31c, No:159). The refined structural parameters are in agreement with the available theoretical and synchrotron radiation experimental results. Then, the infrared (IR) spectra of [Formula: see text]-Si3N4 under 22 GPa were investigated with the diamond anvil cell (DAC). According to the IR absorption spectra at 296.3 K and 2 hPa (Observation range from 400 cm[Formula: see text] to 12,500 cm[Formula: see text]), we observed 23 IR active peaks. Normalized Fourier transform infrared (FTIR) absorption spectra under high pressure and room-temperature (296.3 K) show that [Formula: see text]-Si3N4 undergoes a phase transition at 16.3 GPa and changes from hexagonal to cubic phase, namely, [Formula: see text]-Si3N4, which is very close to the result of our theoretical calculations, i.e., the phase transition pressure is 16.3 GPa.