Measurement of temperature dependence in material coefficients of PZT ceramics for acoustic emission sensors

The behaviour of material coefficients of PZT ceramics at temperatures approaching the Curie point is a problem hitherto not examined in detail. However, this field offers several interesting perspectives, such as the possibility of controlled depolarization of the piezoceramic material in the volume of a sample. The measurement of temperature dependences in piezoelectric materials used for sensors is very significant with respect to determining the degree of stability that characterizes the sensitivity and accuracy of a sensor; moreover, such measurement enables us to establish the maximum temperature ranges for regular operation. In the experiment described within the paper, we applied two temperature ranges according to the parameters of the calibration furnaces. While the first range spanned between -20°C and 140 °C, the second one was defined by the boundary temperatures of 30°C and 330°C, where the latter value (330°C) corresponds to the Curie point of the applied NCE 51 piezoelectric ceramics. The samples were cycled at gradually increasing maximum temperatures, and changes of the material constants were observed. We applied the frequency method to measure samples for the radial, thickness, transverse longitudinal, longitudinal, and thickness shear oscillation types. In samples of PZT ceramics, the measurement of temperature dependences up to the Curie temperature is very demanding in view of the characteristics of the applied measuring devices. Thus, the authors have included in this article a detailed discussion of suitable apparatuses and measurement procedures. The major result acquired from the performed research activities consists in both the measured temperature dependences and the sum of recommendations concerning the correct approach to be adopted in the measurement of PZT ceramics at a wide range of temperatures and with minimum error.