Synthesis, structure, and physical properties of Nb18P2.5O50

The crystal structure of a new niobium phosphate bronze, Nb 18 P 2.5 O 50 , was determined by single-crystal X-Ray diffraction, and its physical properties were studied. Nb 18 P 2.5 O 50 crystallizes in the tetragonal system with space group I4/m (No. 87) and Z=1. The unit cell parameters are a=15.593(1) A, c=3.8282(3) A, and V=930.8(1) A 3 . The structural refinement by a full-matrix least-squares technique led to R=0.055 (R w =0.052). The structure of Nb 18 P 2.5 O 50 is built up from 3×3 slabs of ReO 3 -type NbO 6 octahedra