Asymmetric Hysteresis Loops and the Pyroelectric Effect in Barium Titanate

Abstract

Dynamic pyroelectric techniques have been used to study single crystal BaTiO₃ hysteresis loops which have been reported in several recent investigations to be asymmetric with respect to both the polarization and electric field axes. It is shown that an apparent polarization bias occurs because of electrode‐edge effects and that this bias may be shifted with an appropriate application of a dc field which serves to alter the direction of the polarization in fringe regions which contribute to the observed pyroelectric signal. The pyroelectric hysteresis loops are symmetric with respect to the polarization when electrode‐edge effects are eliminated. These data strongly suggest that asymmetric remanent polarizations reported in several piezoelectric and pyroelectric investigations may have been due to edge effects. The pyroelectric hysteresis loops are found to be biased with respect to the electric field axis in the same manner as that reported in a recent piezoelectric study. Small residual pyroelectric signals observed at temperatures above the Curie point of the bulk material do not result from fringe effects, and the earlier interpretation of the residual signals in terms of a polarized surface layer is consistent with the present results.