Studies on Ba2Nb5-xTixO9 (0<=x<=1.75)

The structure of Ba2Nb5O9 can be described as an intergrowth between perovskite- (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 less than or equal to 1.75) has been investigated. The decrease in unit cell parameters as a function of overall composition determined by microanalysis 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. This 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 electrical 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 metallic conductors and temperature-independent paramagnetic.