Dielectric and Piezoelectric Properties of Barium Titanate

Abstract

The dielectric constant and loss of barium titanate and barium-strontium titanate have been measured at biasing field strengths from 0 to 5 megavolts per meter, at temperatures from -50\ifmmode^\circ\else\textdegree\fi{}C to +135\ifmmode^\circ\else\textdegree\fi{}C and at frequencies from 0.1 to 25 megacycles. The measurements versus temperature indicate the expected agreement with the Curie-Weiss law at temperatures above the Curie point. Measurements versus field strength indicate that the electric field intensity can be expressed as a simple function of the electric displacement, consisting of a linear and a cubic term. At temperatures below the Curie point the results are more complicated, presumably because there are spontaneously polarized domains which give rise to hysteresis and remanence. At field strengths low enough to avoid hysteresis and remanent polarization, no anomalies in the dielectric characteristics versus frequency have been observed. When polarized, however, by a momentary application of a strong d.c. field, a resonance spectrum appears in these ceramics. These resonances are attributed to a piezoelectric effect which exists only in the polarized samples. The piezoelectric voltage developed upon squeezing a specimen of polarized barium titanate has been measured directly with a vacuum tube electrometer. Both the longitudinal effect (electric field parallel to mechanical stress) and the transverse effect (field perpendicular to stress) have been observed.