A novel approach to the structural distortions of U/Th snub-disphenoids and their control on zircon  →  reidite type phase transitions of U1−xThxSiO4. (7th January 2020)

• Record Type: Journal Article
• Authors: Mondal, Sudip Kumar; Das, Pratik Kr; Mandal, Nibir; Arya, Ashok
• Is Part Of: Journal of physics. Volume 32:Number 14(2020)
• Publication Date: 2020-01-07
• Subjects: phase transition -- polyhedral distortion -- density functional theory -- uranothorite solid solution -- mechanical properties -- snub-disphenoid; Condensed matter -- Periodicals; Matière condensée -- Périodiques; Vaste stoffen; Vloeistoffen; Natuurkunde; Electronic journals; Computer network resources; 530.4105
• DOI: 10.1088/1361-648X/ab60e4
• Languages: English
• ISSNs: 0953-8984

Abstract

Abstract: Coffinite (USiO4 ) and thorite (ThSiO4 ) are conspicuous radiogenic silicates in the geonomy. They form U1− x Th x SiO4 (uranothorite) solid solutions in zircon-type phase. Investigating the phase-evolution of these minerals is of utmost significance in realizing their applicability in the front-as well as at the back-end of nuclear industries. We carried out a systematic study of zircon- to reidite-type (tetragonal I41 /amd to I41 /a) structural transitions of U1− x Th x SiO4 solid solution, and investigated their mechanical behaviour. We found a unique behaviour of transition pressure with the change in U-Th concentration in the solid solution. The phase transition pressure ( p t ) is found to be minimum for x = 0.5. We develop the necessary formalism and present an efficient method to estimate the longitudinal and angular distortions of U/ThO8 -triangular dodecahedra (snub-disphenoids). We have parameterized two new factors: δ (longitudinal distortions) and σ 2 (angular distortions) to quantify the polyhedral distortions. A detailed analysis of U/ThO8 snub-disphenoidal distortions is presented to address such variation of p t with U and Th concentration. We argue that our approach is independent of polyhedral volume and can be used for any AB8 (A: cation, B: anion) type snub-disphenoidal system.