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A novel approach to quantify the structural distortions of U/Th snub-disphenoids and their role in zircon to reidite type phase transitions of uranothorite
- Publication Year :
- 2019
-
Abstract
- Our density functional study reveals a peculiar relation between the normalized Th content i.e. Th/(U+Th) and the hydrostatic pressure enforcing zircon to reidite type transition in uranothorite solid solution. We found that the transition pressure exhibits a minimum when Th/(U+Th) = 0.50 i.e. when the unit cell contains equal amount of U and Th. Any change in normalized Th content, as we move towards the U and Th end-members of the series, shows a significant jump in zircon-reidite transition pressure. In order to explain this behavior, we proposed a novel method of quantifying the distortions of U/Th-coordination polyhedra which manifest themselves as a triangular dodecahedron or snub-disphenoid. We have theoretically defined two parameters: one related to the two geometrically different U/Th-O bond lengths, having a fixed ratio between them for regular triangular dodecahedra irrespective of the volume and the other with three kinds of O-U-O and O-Th-O bond angles with multiplicities of 2, 4 and 12, respectively. The bond angle distortion for both U and Th-polyhedra were found to show a maximum in zircon phase and a minimum in reidite phase corresponding to Th/(U+Th) = 0.5. Since, the difference in angular distortion is minimum in case of Th/(U+Th) = 0.5, a lesser hydrostatic pressure is capable of triggering the transition, compared to the other members of this series. The bond length distortion is also characterized by a maximum in the reidite phase at the equal concentration of U and Th. Our finding is also complemented by the minimum compressibility observed in the zircon phase when the atomic percentage of U and Th are equal.<br />Comment: Preliminary draft. Any comments are welcome
- Subjects :
- Condensed Matter - Materials Science
Subjects
Details
- Database :
- arXiv
- Publication Type :
- Report
- Accession number :
- edsarx.1907.05115
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1088/1361-648X/ab60e4