Stability of CaCl2-type and α-PbO2-type SiO2 at high pressure and temperature determined by in-situ X-ray measurements

Details Stability of CaCl2-type and α-PbO2-type SiO2 at high pressure and temperature determined by in-situ X-ray measurements Stability of CaCl2-type and α-PbO2-type SiO2 at high pressure and temperature determined by in-situ X-ray measurements

Mar 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003georl..30e..11m&link_type=abstract

Geophysical Research Letters, Volume 30, Issue 5, pp. 11-1, CiteID 1207, DOI 10.1029/2002GL016722

Physics

21

Mineralogy, Petrology, And Mineral Physics: Experimental Mineralogy And Petrology, Mineral Physics: High-Pressure Behavior, Tectonophysics: Earth'S Interior-Composition And State (1212)

Scientific paper

Here we report the phase boundary between CaCl2-type and α-PbO2-type silica at high pressure and temperature up to 151 GPa and 2500-K determined by in-situ X-ray measurements in a laser-heated diamond anvil cell. Amorphous silica was used as starting material, and the sample was heated for more than 1.5 hr to examine the kinetic effects. The results demonstrated that the CaCl2-type silica is a post-stishovite phase and that it undergoes further transition to the α-PbO2-type structure above 121 GPa at 2400-K. Present data together with previous first-principles calculations indicate that the phase boundary between CaCl2-type and α-PbO2-type silica is represented by a linear equation P (GPa) = 98 + (0.0095 +/- 0.0016) * T (K). The α-PbO2-type silica can be present in the deep portion of the lower mantle in the silica-saturated bulk compositions. This phase transition might contribute to the seismic wave velocity anomalies observed in the D'' region.

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