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Structural Relations Between Weberite and Zirconolite Polytypes-Refinements of Doped 3T and 4M Ca2Ta2O7 and 3T CaZrTi2O7



I E. Grey, W G. Mumme, T J. Ness, Robert S. Roth, K L. Smith


New weberite-type Ca2Ta2O7 and zirconolite-type CaZrTi2O7 polytypes have been prepared by doping with Nd/Zr and Th/Alrespectively and their structures have been refined using single crystal X-ray diffraction intensity data. The 3T zirconolitepolytype, CaO.8Til.35Zrl.3ThO.15AI0.407, has a = 7.228 (1), c = 16.805 (1) A. The 3T weberite-type polytype,Cal.95Tal.89NdO.08ZrO.0806.96 , has a = 7.356 (1), c = 18.116 (1) A. Both 3T polytypes have space group P3121, Z = 6.The 4M Ca2Ta2O7 polytype has approximately the same composition, from microprobe analyses, as the 3T polytype, with threfined formula of Cal.92Tal.92NdO.08ZrO.0807 he cell parameters are a = 12.761 (1), b = 7.358 (1), c = 24.565 (1) A, b100. 1 7 (1)', space group = C2, Z = 16. The structural relationships between the different zirconolite and weberite polytypesare discussed. A consideration of the structures from the viewpoint of anion-centred tetrahedral arrays shows that zirconolitecan be considered as an anion-deficient fluorite derivative phase. However, although the Ca2Ta2O7 weberite-type polytypesmaintain a fluorite-like fcc packing of metal atoms, the fluorite-type topology of edge-shared OM4 tetrahedra is not maintainedOne of the oxygen atoms moves from a tetrahedral Ta3Ca interstice to an adjacent Ta2Ca4 octahedral interstice.
Journal of Solid State Chemistry
No. 2


calcium tantalate, calcium zirconium titanate, crystal structure refinement, weberite zirconolite


Grey, I. , Mumme, W. , Ness, T. , Roth, R. and Smith, K. (2003), Structural Relations Between Weberite and Zirconolite Polytypes-Refinements of Doped 3T and 4M Ca<sub>2</sub>Ta<sub>2</sub>O<sub>7</sub> and 3T CaZrTi<sub>2</sub>O<sub>7</sub>, Journal of Solid State Chemistry (Accessed March 4, 2024)
Created August 31, 2003, Updated October 12, 2021