Electromechanical Response and Dielectric Loss of Prepolarized Barium Titanate Ceramics under Maintained Electric Bias

Abstract

The effect of a maintained aiding direct current bias field on the performance of prepolarized barium titanate ceramics has been investigated with respect to both loss factor and electromechanical response over the temperature range from 25° to 120°C as a function of bias field strength. In addition the effect on the temperature variation of the reversible dielectric constant was studied. The dielectric losses under high ac fields are considerably reduced by the application of bias, and the magnitude of this effect shows a pronounced temperature dependence. Aiding bias also proves beneficial by substantially increasing the electromechanical coupling, and it raises the Curie point by up to about 4°C. Dielectric loss factors were determined semiquantitatively by bridge measurements at moderate ac fields and by means of hysteresis loop areas at higher fields. Both the electrostrictive coefficient u31 relating transversal strain to the square of the total charge density and the linear piezoelectric coefficient g31 relating the increment of strain to the increment of charge density in prepolarized ceramics have been measured directly. From these results, approximate values of retained polarization referring to various physical conditions have been determined; they range to about 11 microcoulombs per square centimeter.