Internal Stress-Related Vibrational Splitting in Compressed SiO2

The intriguing vibrational splitting of SiO2 (alpha-quartz) is investigated via high-pressure Raman spectroscopy. The degenerate E(LO + TO) modes, including the 128 and 265 cm(-1) vibrations, exhibit a splitting upon compression, and the splitting is found to depend on the initial stress conditions of the sample. The larger the initial stress, the earlier the splitting occurs. When the internal stress is released during compression, the vibrational splitting under pressure is effectively postponed. The study provides a reasonable explanation for the obviously different splitting pressures of E(LO + TO) modes in compressed SiO2 (alpha-quartz) in previous reports.