Preparation and crystal structure of a new reduced calcium niobium oxide: CaNb2O4

Single crystals of a new reduced calcium niobium oxide, CaNb2O4, were prepa red in an evacuated quartz tube at 1100 degrees C. The calcium niobium oxid e crystallizes in the orthorhombic space group Pbcm with a = 5.054(1), b = 11.904(1), and c = 5.839(1) Angstrom, Z = 4, and the final R factors are R = 0.027 and R-w = 0.029 for 799 unique reflections. The crystal structure h as the layer built up by edge-sharing of NbO6 trigonal prisms to form infin ite metal-metal bondings as seen in ANbO(2) (A = Li,Na). The Ca2+ ion is lo cated at the trigonal prism site in the interlayer. No evidence for superco nductivity was found down to 2.0 K. (C) 1999 Academic Press.