CRYSTAL-STRUCTURE OF THE LOW-TEMPERATURE FORM OF BISMUTH NIOBIUM OXIDE [ALPHA-BINBO4]

Single crystals of low temperature form of BiNb4 (alpha-form) are grow n from BiOF flux below 900-degrees-C. The crystals are colorless, trap ezodial in shape and electrically insulating. The compound has orthorh ombic [a = 5.673 (2), b = 11.714(4) and c = 4.978(2) angstrom] symmetr y with a centric space group Pnna (No. 52) and z = 4. The crystal stru cture was solved by means of single crystal x-ray diffraction and refi ned to R = 0.031. Both Bi and Nb have distorted octahedral oxygen coor dination. The NbO6 octahedra are linked over four comers and thus the structure can be viewed as consisting of sheets of [NbO4]3- units sepa rated by Bi3+ cations. The structure of alpha-BiNbO4 is essentially sa me as that of the low temperature form of alpha-Sn2+W6+O4.