Stability of CaCl2‐type and α‐PbO2‐type SiO2 at high pressure and temperature determined by in‐situ X‐ray measurements
- 5 March 2003
- journal article
- Published by American Geophysical Union (AGU) in Geophysical Research Letters
- Vol. 30 (5)
Abstract
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.Keywords
This publication has 16 references indexed in Scilit:
- Equation of state of hexagonal aluminous phase in basaltic composition to 63 GPa at 300 KPhysics and Chemistry of Minerals, 2002
- Post-stishovite phase boundary in SiO2 determined by in situ X-ray observationsEarth and Planetary Science Letters, 2002
- Pressure-induced transformations of cristobaliteChemical Physics Letters, 2001
- A Post-Stishovite SiO 2 Polymorph in the Meteorite Shergotty: Implications for Impact EventsScience, 1999
- Pressure-Induced Landau-Type Transition in StishoviteScience, 1998
- Ab initio elasticity of three high‐pressure polymorphs of silicaGeophysical Research Letters, 1997
- Experimental and theoretical identification of a new high-pressure phase of silicaNature, 1997
- Transformation of stishovite to a denser phase at lower-mantle pressuresNature, 1995
- Earth's Core-Mantle Boundary: Results of Experiments at High Pressures and TemperaturesScience, 1991
- The equation of state of platinum to 660 GPa (6.6 Mbar)Journal of Applied Physics, 1989