STUDIES ON BA2NB5-XTIXO9 ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.75)

The structure of Ba2Nb5O9 can be described as an intergrowth between p erovskite- (BaNbO3) and NbO-type slabs. The substitution of Ti for Nb according to the formula Ba2Nb5-xTixO9 (0.00 less than or equal to x l ess than or equal to 1.75) has been investigated. The decrease in unit cell parameters as a function of overall composition determined by mi croanalysis shows the maximum value of n to be around 0.9. At higher x values increasing amounts of BaNb1-yTiyO3 and Nb were found. Rietveld refinements of the structure using X-ray powder diffraction data show Ti to prefer Nb positions in the perovskite slab (NbO6 octahedra) and the Nb positions in the NbO slab closest to the perovskite slabs. Thi s latter Nb is five-fold coordinated by oxygen atoms, forming a square pyramid. The third Nb position, in the middle of the NbO slab with a square planar coordination of oxygen atoms, remains undoped. The elect rical resistivity and magnetic susceptibility of the x = 0.0, 0.25, 0. 50 and 0.75 samples were measured. All samples were found to be metall ic conductors and temperature-independent paramagnetic.