Extension of an LVDT sensor system for thermal analysis for field-induced strain measurements of nonlinear ferroelectrics

Increased demand for piezoelectric ceramics for actuators require application-orientated characterisation methods. For reasons of speed and cost it is of great advantage if existing measurement systems can be extended to include this option. Based on a LVDT (Linear Variable Differential Transformer) sensor system for thermal investigations, a sample holder for strain measurements with an applied electric field was developed. The sample holder can be used from -150°C to +400°C to determine the strain as a function of the applied electric field as well as the temperature. Using SF₆ as an insulating gas, electric fields of several kV/mm can be applied. Specimens may be up to 12 mm in diameter and 50 mm in height. A confirmation of the flexibility of the measurement method is discussed in two examples. On the one hand, the influence of temperature on electrically induced strain of soft-doped PZT ceramics is shown. On the other hand, investigations of the electric fatigue behaviour of soft-doped PZT ceramics display constant or rising reversible strain with increasing numbers of cycles up to 10⁵ cycles