The crystal chemistry of L-Ta2O5 and related structures

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 a=6.1939(4)Å, b=69.549(5)Å (=19×3.66Å), c=3.8895(3)Å, γ=90.00(1)°γ=90.00(1)°. The structure was refined in space group C112/mC112/m to R1=0.044R1=0.044 for 814 unique reflections with F>4σ(F)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.

Graphical AbstractSchematic of Structural basis for L-Ta2O5-related phases.Figure optionsDownload as PowerPoint slide