Large Signal Resonance and Laser Dilatometer Methods

In many piezoelectric devices maximum deformations are desirable. They can only be achieved under high field strengths (1–2 kV mm⁻¹) and cause large mechanical stress amplitudes in the piezoelectric material. This calls for piezoelectric materials with a strong piezoelectric effect that are capable of withstanding both high electric field strengths and large mechanical stresses. Under these large signal conditions, the properties of piezoelectric materials are considerably non-linear and show hysteretic behaviour. As discussed in Chap. 3.3, the non-linear behaviour can be attributed to the motion of non 180° domain walls. Therefore, the non-linearity of the piezoelectric response and the accompanying hysteresis can be described with the aid of Rayleigh’s law (Equations (3.48) and (3.49) in Chap. 3.3). The most important aspect of the Rayleigh-like behaviour is the fact that hysteresis and non-linearity in soft piezoelectric ceramics are essentially linked, as can be seen in Fig. 19.7, that is, both hysteresis and non-linearity are results of the same-domain wall pinning processes. Since the hysteretic response is closely related to the electrical and mechanical losses occurring in piezoelectric ceramics or ferroelectric perovskites, in general, the performance of power ceramics can be tested substantially by measuring either the dielectric losses at large field amplitudes or the mechanical losses at large mechanical stress amplitudes. However, to perform these measurements, it is not sufficient to extend simply the standard small-signal capacitance/loss tangent techniques according to IRE or IEEE standards [1] or the impedance measurement techniques as described in Chap. 18 to higher-signal amplitudes. For then the measurement results would be considerably falsified by an overheating of the test samples. With this in mind, pulsed test signals are mostly used [2].