Investigations Concerning Polarization in Barium Titanate Ceramics

Abstract

Considerable information can be obtained concerning polarization in barium titanate ceramics by a careful analysis of hysteresis loops. Mathematically it was shown that both symmetrical and unsymmetrical loops, the latter being characteristic of polarized specimens, can be represented best by a Fourier series. It was found that direct voltage and even harmonic components are present in the unsymmetrical loops. The percent second harmonic and the electromechanical coupling coefficient both rise with increasing dc polarizing voltage and reach a maximum value at approximately 15000 volts per centimeter. The measurement of the second harmonic is possible even when the activity is so small that measurement of the coupling coefficient becomes very inaccurate or impossible. The addition of calcium titanate in small percentages markedly raises the coercive force but lowers the spontaneous and remanent polarization in the range from 0 to 80°C but does not have marked effect between the latter temperature and the Curie point. It was found from studies of the discharge currents on depolarizing specimens by sudden immersion in hot oil that depolarization apparently occurs in two steps: rapid removal of the induced polarization and more gradual disorientation of the domain structure.