Anharmonic lattice mode of Ca₂SiO₄: Ultraviolet laser Raman spectroscopy at high temperatures

Raman spectra of Ca₂SiO₄ 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 γ-Ca₂SiO₄ was recorded. In the region of 1073-1123 K, two strong bands of the γ phase around 800 and 900 cm^-1 disappeared, which indicates the γ→α′_L transformation. Raman frequencies decreased in the α′_L and α′_H 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 cm^-1), the band related to the lattice vibration mode (around 250 cm^-1) shows stronger anharmonic behavior.