Rayleigh behaviour and the threshold field in ferroelectric ceramics

The threshold field, Et, values for various barium titanate and PZT-based ceramics have been determined by examination of the εr |-E 0 and εr ∥-E 0 relationships. The results obtained for both ‘soft’ and ’hard’ PZT ceramics gave a good fit to the Rayleigh Law over a wide range of field amplitude for E 0 E t. The linear increases in εr | and εr ∥ as a function of field amplitude were attributed to a lossy ferroelectric domain wall translation mechanism, by analogy with similar behaviour in ferromagnetic materials. At high field levels approaching the coercive field, E c, the measured εr |-E 0 and εr ∥-E 0 curves deviated from a linear relationship due to the onset of partial ferroelectric domain switching. Pure and Mn-doped barium titanate ceramics exhibited nonlinear εr |-E 0 and εr ∥-E 0 plots with a gradually increasing gradient. However, all of the materials studied yielded a linear εr | and εr ∥ relationship, from which a critical field for the initiation of ferroelectric domain switching, E sw, could be determined