Infrared spectra of silica polymorphs

The existence of silica within several debris disks has been suggested.We investigate the annealing conditions of α-cristobalite, and further prepare various types of silica, including α-cristobalite, α-quartz, coesite, stishovite, and fused quartz, which are natural, synthetic or commercial samples.We compare the results to previous studies and find that α-cristobalite synthesized at higher temperature than annealed silica.The interesting result of features similar to those of forsterite should be highlighted, where αcristobalite and coesite showed similar peaks at 16, 33, and 69 μm as forsterite.The 69 μm band for αcristobalite is especially very broad and strong, and shifts largely to a shorter wavelengths under cooling to low temperatures.The band for coesite, however, is very sharp, and shifts only a small amount to longer wavelengths under cooling to low temperatures.The peak positions of 16 and 69-μm band due to α-cristobalite can become index for temperature of silica dust.We discuss the possibility of silica detection around debris disks.