期刊
PHYSICAL REVIEW B
卷 80, 期 9, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.80.094101
关键词
compressibility; decomposition; density functional theory; high-pressure solid-state phase transformations; thorium compounds; X-ray diffraction
资金
- Spanish MALTA-Consolider Ingenio 2010 Program [CSD2007-00045]
- Spanish MICCIN [MAT2007-65990-C03-01]
- DOE-BES [DE-AC0206CH11357]
- DOENNSA
- NSF
- W. M. Keck Foundation
We report here the combined results of angle-dispersive x-ray diffraction experiments performed on ThGeO4 up to 40 GPa and total-energy density-functional theory calculations. Zircon-type ThGeO4 is found to undergo a pressure-driven phase transition at 11 GPa to the tetragonal scheelite structure. A second phase transition to a monoclinic M-fergusonite type is found beyond 26 GPa. The same transition has been observed in samples that crystallize in the scheelite phase at ambient pressure. No additional phase transition or evidence of decomposition of ThGeO4 has been detected up to 40 GPa. The unit-cell parameters of the monoclinic high-pressure phase are a=4.98(2) A degrees, b=11.08(4) A degrees, c=4.87(2) A degrees, and beta=90.1(1), Z=4 at 28.8 GPa. The scheelite-fergusonite transition is reversible and the zircon-scheelite transition nonreversible. From the experiments and the calculations, the room-temperature equation of state for the different phases is also obtained. The anisotropic compressibility of the studied crystal is discussed in terms of the differential compressibility of the Th-O and Ge-O bonds.
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