Infrared Spectra of Silica Polymorphs and the Conditions of Their Formation

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C. Koike1, R. Noguchi2, H. Chihara3,5, H. Suto4, O. Ohtaka2, Y. Imai2, T. Matsumoto2 and A. Tsuchiyama3

1Department of Physics, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
2Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
3Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8052, Japan
4National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
5Currently at College of General Education, Osaka Sangyo University, Daito, Osaka 574-8530, Japan.

The existence of silica within several debris disks has been suggested. Data on both the spectroscopy and annealing conditions of the various polymorphs of silica need to be investigated, as these data are lacking and incomplete in the literature. We investigate the annealing conditions of silica and prepare various types of silica, including α-cristobalite, α-quartz, coesite, stishovite, and fused quartz, which are natural, synthetic, or commercial samples. This paper presents a new study of both the spectroscopy of relevant silica polymorphs and the conditions under which they form. We compare the results to previous studies and find that there are discrepancies. The interesting result of features similar to those of forsterite should be highlighted, where α-cristobalite and coesite showed similar peaks at 16, 33, and 69 μm as forsterite. The 69 μm band for α-cristobalite 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. We discuss the possibility of silica detection around debris disks.

Reference
Koike C, Noguchi R, Chihara H, Suto H, Ohtaka O, Imai Y, Matsumoto T and Tsuchiyama A (2013) Infrared Spectra of Silica Polymorphs and the Conditions of Their Formation. The Astrophysical Journal 778:60.
[doi:10.1088/0004-637X/778/1/60]

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