Effect of temperature on the charge-field hysteresis phenomena in lanthanum-doped lead zirconate titanate-poly(vinylidine fluoride) composite

Abstract

In recent years a lot of work has been done on the development of various types of polymer-ceramic composites for different applications [1-3]. This is due mainly to the fact that composites allow the flexibility to have a resultant product combining the required properties of the two materials to suit the specific application [3]. However, attention is focused more on the preparation of the composite samples, their poling for obtaining net polarization [4-6] and understanding the mechanisms involved. The lead zirconate titanate (PZT)-poly(vinylidene fluoride) (PVDF) system has been found to be a good composite system [7] from the application point of view, but very little attention has been paid to studying the hysteresis phenomenon in these composite systems. In this letter we report the effect of temperature on the charge-field hysteresis phenomenon of a lanthanum-doped PZT (PLZT)-PVDF composite prepared with a weight ratio of 90:10, respectively. The PLZT and PVDF used in the experiment were obtained from Central Electronics Limited (India) and Aldrich (Switzerland), respectively. The composites were made by taking the required weight ratio of PLZT and PVDF (i.e. 90:10 in the present work) and were mixed and ground thoroughly using acetone as a thinner, so that all of the grains of PLZT were covered with PVDF and the powder became dry. This dry powder was pressed in a 1 cm diameter die under a load of 10 t at 160 °C. The die was cooled to room temperature under the applied pressure. The load was released and the pellet was taken out at room temperature. Quick-drying silver paint was used for electrodes. The Sawyer and Tower circuit was used for hysteresis studies and the loops were traced using Philips PM 3055 oscilloscope. The temperature was controlled within an accuracy of _+ 2 °C by using an electronic relay. An a.c. field (50 Hz) was applied through an isolated step-up transformer. Dielectric measurements were done on a Hewlett-Packard impedance analyser (no. 4192A). A representative charge-field hysteresis loop is shown in Fig. 1. The results of the effect of temperature on the coercive field (Ec), total polarization (Pt), which is the sum of saturation polarization (Ps) and induced polarization (Pi), and the remanent polarization (Pr) are given in Table I. It can be seen from the table that Pt and Pr decrease with increasing temperature up to 100 °C and then