High electric field measurement of dielectric constant andlosses of ferroelectric ceramics

Abstract

Nonlinear behaviour of power piezoceramic materials has to be studiedunder strong electric fields. A bridge designed for measuring it at lowfrequency is described. It consists basically of a capacitancecomparison bridge that can be used in two different modes: balanced andunbalanced. The nonlinear electric displacement is split intodissipative and nondissipative terms. Dielectric constant is computedfrom the last term and related to the instantaneous field. The behaviourof soft and hard PZT ceramic materials has been tested according to thismodel. In both materials, the dielectric constant not only depends onthe instantaneous value of the field but also on its amplitude. Whilethe dependence of the real and imaginary parts of the dielectricconstant in soft ceramics is large and practically linear to the fieldamplitude, in hard PZT it is low and nearly quadratic. The rate betweenboth parts depends on the type of ceramic. Dielectric constant can bedivided into two terms. One term is allied to the irreversible motion ofdomain walls, while the other is related to reversible motion. Balancedand unbalanced modes have been tested for both materials, and resultsare coherent. Accuracy and limitations of the method are discussed.