Raman Spectra of α and β Cristobalite

Abstract

Raman spectra of polycrystalline crystobalite were measured over the frequency interval of the fundamental optical modes from 77°K to 538°C. Spectra recorded above and below the α–β transition temperature were strikingly different. The strong bands measured at 416 and 230 cm⁻¹ with α cristobalite at 25°C were not observed from spectra of the β phase. The Raman spectrum of β cristobalite exhibited only three bands and, in contrast to crystalline quartz, a strongly temperature dependent band was not observed from measurements at temperatures near the transition point. Infrared reflection spectra of α cristobalite also were recorded, and the longitudinal optical mode frequencies were determined. Raman spectra of β cristobalite showed that the structure of this material should not be employed as a lattice model for noncrystalline SiO₂.