Universität zu Köln

Chidester, Bethany A., Pardo, Olivia S., Fischer, Rebecccca A., Thompson, Elizabeth C., Heinz, Dion L., Prescher, Clemens, Prakapenka, Vitali B. and Campbell, Andrew J. (2018). High-pressure phase behavior and equations of state of ThO2 polymorphs. Am. Miner., 103 (5). S. 749 - 757. CHANTILLY: MINERALOGICAL SOC AMER. ISSN 1945-3027

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Abstract

ThO2 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 ThO2 to similar to 60 GPa and similar to 2500 K. It undergoes a transition from the cubic fluorite-type structure (thorianite) to the orthorhombic alpha-PbCl2 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), alpha K-T = 0.0035(3)] and the high-pressure cotunnite-type phase [V-0 = 24.75(6), K-0 = 190(3), alpha K-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:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Chidester, Bethany A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Pardo, Olivia S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fischer, Rebecccca A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Thompson, Elizabeth C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Heinz, Dion L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Prescher, Clemens UNSPECIFIED UNSPECIFIED UNSPECIFIED Prakapenka, Vitali B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Campbell, Andrew J. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-188249
DOI:	10.2138/am-2018-6212
Journal or Publication Title:	Am. Miner.
Volume:	103
Number:	5
Page Range:	S. 749 - 757
Date:	2018
Publisher:	MINERALOGICAL SOC AMER
Place of Publication:	CHANTILLY
ISSN:	1945-3027
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language URANIUM-DIOXIDE; OF-STATE; TEMPERATURE; 1ST-PRINCIPLES; DIFFRACTION; TRANSITION; DIFFUSION; STABILITY; SYSTEM; CEO2 Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/18824