CALCULATIONS AND MODELING OF GRAIN-BOUNDARY ACCEPTOR STATES FOR (BA,PB)TIO3 POSITIVE TEMPERATURE-COEFFICIENT CERAMICS

Abstract

The electrical properties of high-Curie-point positive temperature coefficient of resistance ceramics of composition Ba0.497Pb0.5La0.003Ca0.005Ti0.995O3 prepared from commercial BaTiO3 powder were studied. The acceptor-state energy and acceptor-state density were determined from the calculated rho(max) vs T(max) plot, where rho(max) and T(max) are the resistivity and temperature corresponding to the maximum in resistivity. These two parameters, combined with the effect of nonvanishing spontaneous polarization below the Curie point, were treated quantitatively to demonstrate the dependence of measured resistivity rho(dc) on the measured permittivity epsilon(m). The obtained values of potential barrier height and acceptor-state density based on the procedure above were found to be in excellent agreement with those extracted from the slope in the Arrhenius plots of resistivity versus 1/(Tepsilon(m)), where T is the absolute temperature. Also, the deviation of the measured dielectric constant epsilon(m) from the Curie-Weiss law's prediction was explained by the narrowing of the grain-boundary barrier layers.