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High-pressure phase behavior and equations of state of ThO_2 polymorphs

Chidester, Bethany A. and Pardo, Olivia S. and Fischer, Rebecca A. and Thompson, Elizabeth C. and Heinz, Dion L. and Prescher, Clemens and Prakapenka, Vitali B. and Campbell, Andrew J. (2018) High-pressure phase behavior and equations of state of ThO_2 polymorphs. American Mineralogist, 103 (5). pp. 749-756. ISSN 0003-004X. doi:10.2138/am-2018-6212.

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ThO_2 is an important material for understanding the heat budget of Earth's mantle, as well as the stability of nuclear fuels at extreme conditions. We measured the in situ high-pressure, high-temperature phase behavior of ThO_2 to ∼60 GPa and ∼2500 K. It undergoes a transition from the cubic fluorite-type structure (thorianite) to the orthorhombic α-PbCl_2 cotunnite-type structure between 20 and 30 GPa at room temperature. Prior to the transition at room temperature, an increase in unit-cell volume is observed, which we interpret as anion sub-lattice disorder or pre-transformation “melting” (Boulfelfel et al. 2006). The thermal equation of state parameters for both thorianite [V_0 = 26.379(7), K_0 = 204(2), αK_T = 0.0035(3)] and the high-pressure cotunnite-type phase [V_0 = 24.75(6), K_0 = 190(3), αK_T = 0.0037(4)] are reported, holding K_0′ fixed at 4. The similarity of these parameters suggests that the two phases behave similarly within the deep Earth. The lattice parameter ratios for the cotunnite-type phase change significantly with pressure, suggesting a different structure is stable at higher pressure.

Item Type:Article
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Pardo, Olivia S.0000-0003-3964-9272
Prakapenka, Vitali B.0000-0001-9270-2330
Additional Information:© 2018 Mineralogical Society of America. Received: 13 Jun 2017; Accepted: 30 Jan 2018; Published: May 01, 2018. The authors are grateful to Jinyuan Yan for his assistance with the room-temperature measurements. This study was funded by NSF Graduate Research Fellowship Grant DGE-1144082, NSF Grants EAR-1427123, and EAR-0944298, and the Carnegie/DOE Alliance Center (CDAC). Portions of this work were done at GeoSoilEnviroCARS (The University of Chicago, Sector 13) of the Advanced Photon Source, Argonne National Laboratory, and at Sector 12.2.2 of the Advanced Light Source, Lawrence Berkeley National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation—Earth Sciences (EAR-1634415) and Department of Energy, GeoSciences (DE-FG02-94ER14466). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Sector 12.2.2. is funded in part by the Consortium for Materials Properties Research in Earth Sciences (COMPRES) under NSF Cooperative Agreement EAR 10-43050. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144082
Department of Energy (DOE)DE-FG02-94ER14466
Department of Energy (DOE)DE-AC02-06CH11357
NSFEAR 10-43050
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:XRD data, ThO2, Raman spectroscopy, ThO2, phase transition, high-pressure studies, diamond-anvil cell, high-temperature studies, laser-heating
Issue or Number:5
Record Number:CaltechAUTHORS:20180501-140541138
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Official Citation:Bethany A. Chidester, Olivia S. Pardo, Rebecca A. Fischer, Elizabeth C. Thompson, Dion L. Heinz, Clemens Prescher, Vitali B. Prakapenka, Andrew J. Campbell; High-pressure phase behavior and equations of state of ThO2 polymorphs. American Mineralogist ; 103 (5): 749–756. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86159
Deposited By: Tony Diaz
Deposited On:01 May 2018 22:00
Last Modified:15 Nov 2021 20:35

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