Electrical Cycling of Cu/Pmnzt Multilayer Co-Fired Ceramic Actuators

The electric cycling characteristics of Cu/0.2(PbMg1/3Nb2/3O3)-0.8(PbZr0.475Ti0.525O3) (PMNZT) multilayer ceramic actuators were investigated. Cu/PMNZT co-fired multilayer actuators were fabricated by conventional tape casting, lamination, and sintering at 950 °C in air with subsequent annealing at 225 °C or 400 °C under a hydrogen atmosphere. In such processes, annealing of the multilayer samples under a reducing atmosphere is an important factor in controlling the piezoelectric performance. Unipolar and bipolar electric fields were applied to the actuators to investigate the fatigue behavior of the multilayer ceramic actuators. The sample annealed at 400 °C showed significant degradation in the effective electromechanical coupling coefficient (keff) and dynamic piezoelectric constant (d33*) after 1 × 108 electrical cycles, while the sample annealed at 225 °C showed less degradation. X-ray diffraction and X-ray photoelectron spectroscopy analyses were performed to evaluate the difference in crystalline structures as a function of annealing temperature. The keff, d33*, polarization, and strain were measured and evaluated as a function of the number of cycles. The cyclic dependence of strain was fitted to a linear logarithmic stretched exponential law. The significant degradation of the sample annealed at 400 °C is attributed to the reorientation of oxygen vacancies formed upon annealing, which gives a rise to internal field in the ceramic layer. The degraded performance of cycled sample was refreshed by a heating at 500 °C in air.