Anharmonic lattice mode of (formula presented): Ultraviolet laser Raman spectroscopy at high temperatures

Raman spectra of (formula presented) have been obtained at temperatures up to 1723 K by using a continuous-wave ultraviolet Raman spectroscopic system. At room temperature, the typical Raman spectrum of (formula presented) was recorded. In the region of 1073-1123 K, two strong bands of the γ phase around 800 and 900 (formula presented) disappeared, which indicates the (formula presented) transformation. Raman frequencies decreased in the (formula presented) and (formula presented) phases with increasing temperature. The measured shifts are used in conjunction with available high-pressure Raman data to calculate the Gruneisen parameter related to pressure variation at constant temperature, the corresponding parameter related to temperature variation at constant pressure, and the anharmonic parameter. Although the anharmonicity is weaker for the bands related to the internal vibrations of Si-O bonds (more than around 400 (formula presented)), the band related to the lattice vibration mode (around 250 (formula presented)) shows stronger anharmonic behavior.