Browsing by Author "Zhang, FX"
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- ItemIncorporation of uranium in pyrochlore oxides and pressure-induced phase transitions(Elsevier - ScienceDirect, 2014-11-01) Zhang, FX; Lang, M; Tracy, C; Ewing, RC; Gregg, DJ; Lumpkin, GRUranium-doped gadolinium zirconates with pyrochlore structure were studied at ambient and high-pressure conditions up to 40 GPa. The bonding environment of uranium in the structure was determined by x-ray photoelectron and Raman spectroscopies and x-ray diffraction. The uranium valence for samples prepared in air is mainly U6+, but U4+ is present in pyrochlores fabricated in an argon atmosphere. Rietveld refinement of the XRD pattern suggests that uranium ions in pyrochlores are on the 16d site in 6-fold coordination with oxygen. At pressures greater than 22 GPa, the pyrochlore structure transformed to a cotunnite-type phase. The cotunnite high-pressure phase transformed to a defect fluorite structure on the release of pressure. © 2014 Elsevier Inc.