The Effect of PbO-Nonstoichiometry on Dielectric and Semiconducting Properties of PbFe0.5Nb0.5O3-Based Ceramics

Dielectric, X-ray and electric resistivity studies of nonstoichiometric PbFe0.5Nb0.5O3-based ceramics obtained by solid-state reaction route with PbO/(Fe0.5Nb0.5O2) molar ratio differing from 0.6 to 1.2 have been carried out. Deviation from stoichiometric PbFe0.5Nb0.5O3 composition leads to formation of diphase mixtures containing ferroelectric perovskite PbFe0.5Nb0.5O3 phase and nonferroelectric PbO or pyrochlore Pb3Nb4O13 phases and to decreasing of the dielectric permittivity values. The electric resistivity of PbFe0.5Nb0.5O3 ceramics decreases dramatically when the sintering temperature increases. The formation of the pyrochlore phase decreases the room temperature resistivity values while the anomaly of the positive temperature coefficient of resistivity above the ferroelectric Curie temperature gradually diminishes with the increase of the pyrochlore content.