High electric field measurement of dielectric constant and losses of ferroelectric ceramics

Nonlinear behaviour of power piezoceramic materials has to be studied under strong electric fields. A bridge designed for measuring it at low frequency is described. It consists basically of a capacitance comparison bridge that can be used in two different modes: balanced and unbalanced. The nonlinear electric displacement is split into dissipative and nondissipative terms. Dielectric constant is computed from the last term and related to the instantaneous field. The behaviour of soft and hard PZT ceramic materials has been tested according to this model. In both materials, the dielectric constant not only depends on the instantaneous value of the field but also on its amplitude. While the dependence of the real and imaginary parts of the dielectric constant in soft ceramics is large and practically linear to the field amplitude, in hard PZT it is low and nearly quadratic. The rate between both parts depends on the type of ceramic. Dielectric constant can be divided into two terms. One term is allied to the irreversible motion of domain walls. while the other is related to reversible motion. Balanced and unbalanced modes have been tested for both materials. and results are coherent. Accuracy and limitations of the method are discussed.