Thermoelectric properties of niobium doped hexagonal barium titanate

The ceramic samples of Nb doped hexagonal barium titanate (h-Ba1NbxTi1-xO3) were prepared by the usual solid state reaction using stoichiometric amoun ts of BaCO3, TiO2, and Nb2O5 powders for different concentrations of Nb. Th ese samples were characterized by X-ray diffraction (XRD), electric and mag netic measurements. The XRD patterns of all these samples showed an average hexagonal structure refined in space group P6(3)/mmc. The electrical resis tivity showed a semiconducting like behavior from 400 K down to the lowest possible measured temperature. The magnetic susceptibility measured up to 4 00 K in an applied field of 1 T changes from diamagnetic to paramagnetic on e, reaches a certain maximum at x = 0.02 and then decreases with increased dopant concentration. The density of states (DOS) deduced from the paramagn etic susceptibility showed a peak at x = 0.02 nominal concentration of Nb. We attribute this phenomenon as an increase in the effective mass of carrie rs with dopant concentration. The thermoelectric power measured from 77-300 K for all these samples is negative showing that conduction carriers are e lectrons in this system and its magnitude is directly proportional to the t emperature. We suggest that conduction in this system occurs through variab le range hopping between localized states within an impurity band at low te mperature. (C) 2001 Elsevier Science B.V. All rights reserved.