Structural study of the NaCdVO4–Cd3V2O8 and CdO–V2O5 sections of the ternary system Na2O–CdO–V2O5

The NaCdVO4–Cd3V2O8 and CdO–V2O5 sections of the ternary system Na2O–CdO–V2O5 have been studied and the crystal structures of Cd3V2O8 and Cd18V8O38 compounds were determined from single-crystal X-ray diffraction data. Cd3V2O8 crystallizes with the maricite-type structure in space group Pnma, a=9.8133(10) Å, b=6.9882(10) Å, c=5.3251(10) Å and Z=4, whereas Cd18V8O38 crystallizes in space group P1 with a new-type structure, a=8.5761(14), b=8.607(3), c=12.896(2) Å, α=95.64(1), β=102.45(1), γ=108.42(1)° and Z=1. The Cd3V2O8 structure is made up of Cd1O4 infinite chains of edge-sharing Cd1O6 octahedra which are parallel to the b direction. The Cd1O4 chains are linked together by VO4 tetrahedra and strongly distorted Cd2O4 tetrahedra. The structure of Cd18V8O38 is based on an ordered three-dimensional framework of cadmium and vanadium polyhedra that share corners. The distorted CdO6 octahedra, CdO5 trigonal bipyramids and CdO5 square pyramids share corners, edges or faces.