Abstract
The crystal structure of β-NbPO5 has been solved by threedimensional single crystal X-ray analysis. The refinement in the cell of symmetry P21/c with a = 13.0969(16) Å, b = 5.2799(6) Å, c = 13.2281(16) Å, β = 120.334(8)°, Z = 8, has led to R = 0.035 and Rw = 0.042 for 2888 reflections with σ(I)/I ≤ 0.333. The structure belongs to the structural family P4O8(WO3)2m called monophosphate tungsten bronzes with pentagonal tunnels (MPTBP) and characterized by ReO3-type slabs of various widths connected through single PO4 tetrahedra. β-NbPO5 and the isostructural compound β-TaPO5 can thus be considered as the members m = 2 of the series and their framework described as built up of strands of two MO6 (M = Nb, Ta) octahedra. Adjustment stresses induced by PO4 tetrahedra lead to different octahedral deformations which explain the numerous supercells observed by electron diffraction.
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