HR: 13:55h
AN: MR33B-02    [Abstracts]
TI: High-pressure phases transitions in SnO₂ to 117 GPa: Implications for silica
AU: * Shieh, S R
EM: sshieh@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences, London, ON N6A 5B7 Canada
AU: Kubo, A
EM: akubo@princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AU: Duffy, T S
EM: duffy@princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AU: Prakapenka, V B
EM: prakapenka@cars.uchicago.edu
AF: University of Chicago, GSECARS, Chicago, IL 60637 United States
AU: Shen, G
EM: shen@cars.uchicago.edu
AF: University of Chicago, GSECARS, Chicago, IL 60637 United States
AB: Cassiterite (SnO₂) is regarded to be a good analog material for silica as both SnO₂ and SiO₂ are group IV-B metal dioxides. The high-pressure behavior of SnO₂ has been the subject of many previous investigations extending up to 49 GPa and in addition to the rutile structure, three high-pressure phases, CaCl₂-type, α-PbO₂-type, and pyrite-type were observed. Better knowledge of high-pressure phases of SnO₂ will be useful to understand the behavior of silica at deep mantle conditions. In addition, high-pressure metal dioxide phases may qualify as superhard solids. Our study will also provide insights into interpretation of shock compression data. Pure natural cassiterite (SnO₂) powder was compressed in a diamond anvil cell using an argon medium. Pressure was determined from the equation of state of platinum. In situ monochromatic x-ray diffraction at high pressure was carried out at the GSECARS, Advanced Photon Source. High temperatures were achieved using double-sided laser heating . Three heating cycles were conducted with total heating times up to 30 minutes. Our diffraction results on SnO₂ demonstrate the existence of four phase transitions to 117 GPa. The observed sequence of high-pressure phases for SnO₂ is rutile-type, CaCl₂-type, pyrite-type, ZrO₂ orthorhombic phase I (Pbca), cotunnite-type. Our observations of the first three phases are generally in agreement with earlier studies. The orthorhombic phase I and cotunnite-type structures were observed in SnO₂ for the first time. The Pbca phase is found at 50-74 GPa during room-temperature compression. The cotunnite-type structure was synthesized when SnO₂ was heated at 74 GPa and 1200 K. The cotunnite-type form was observed during compression between 54-117 GPa. Fitting the pressure-volume data for the high-pressure phases to the second-order Birch-Murnaghan equation of state yields a bulk modulus of 259(26) GPa for the Pbca phase and 417(7) GPa for the cotunnite-type phase. Rietveld profile refinements were also carried out successfully for these two phases.
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 4465 Phase transitions
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005