The crystal chemistry of L-Ta2O5 and related structures |
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Authors: | IE Grey WG Mumme |
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Institution: | a CSIRO Minerals, Bayview Avenue, Clayton, Vic. 3169, Australia b National Institute of Standards and Technology, Gaithersburg, MD, USA |
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Abstract: | Single crystals of a new form of L-Ta2O5 with a 19×b superstructure have been synthesised by flux growth. The phase is most likely stabilised by the incorporation of a small amount of lithium (0.14 wt% Li) from the flux. The phase has C-centred monoclinic symmetry with , (), , γ=90.00(1)°. The structure was refined in space group C112/m to R1=0.044 for 814 unique reflections with F>4σ(F). The structure can be described as comprising chains of edge-shared TaO7 pentagonal bipyramids that are regularly folded at (010) planes to give sinusoidal chains along 010]. These chains are interconnected along 100] and 001] by corner sharing, creating inter-chain regions that are occupied by isolated TaO6 octahedra and pairs of corner-shared octahedra. A comparison with published data for high-quality refinements of related structures has led to the development of a general model that can explain the structural chemistry variations in the known L-Ta2O5-related structures. A shorthand notation is presented for representing the structures, based on the sequence along 010] of the interchain octahedra. |
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Keywords: | L-Ta2O5 structure 19L Ta2O5 superstructure Crystal chemistry of L-Ta2O5-related phases |
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