Crystal structure analysis of Scheelite and Zircon type thorium germanates: A neutron diffraction study

• Published in: Journal of alloys and compounds Vol. 438; no. 1; pp. 274 - 278
• Main Authors: Achary, S.N., Patwe, S.J., Krishna, P.S.R., Sindhe, A.B., Tyagi, A.K.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 12-07-2007; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Germanates; Inorganic compounds; Physics; Structure; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Zircon; Structure; Germanates; Zircon; Neutron diffraction; Chemical bonds; Polycrystals; Thorium Germanates; Bond lengths; Coordination polyhedron; Polymorphism; Crystal structure
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2006.08.025

In this communication we report the detailed crystal structure of two polymorphs of ThGeO
4 (scheelite and zircon type) by Rietveld refinement of the neutron diffraction data of polycrystalline samples. Both of crystal structures consist of ThO
8 (bisdisphenoid) and GeO
4 tetrahedra. Scheelite type structure is a meta-stable polymorph and densely packed lattice, with a little larger average bond lengths of Th–O and Ge–O bonds to accommodate better packing. This is responsible for zircon to scheelite transformation under pressure. However, the average anion–anion contact and cation–cation contacts are shorter in scheelite structure compared to the zircon structure, which would causes the meta-stability in the scheelite structure.