Dielectric and electromechanical properties of lead zirconate titanate ceramics containing neodymium ions

Abstract

Lead zirconate titanate (PZT) ceramics have been the subject of extensive investigations by several workers [1-6]. These studies were confined to two types of additives. One of these is characterized by an increase in the coercive field, electrical and mechanical quality factors of the ceramics caused by elements such as Fe 3+ , Sc 3+ , etc. The other category of additives involves the addition of rare earths such as La 3+, Nb 5+ and Ta 5+, etc., which cause an increase in the dielectric constant and piezoelectric coupling coefficient and a reduction in the coercive field. Both types of additives are effective so far as metal atoms are incorporated in the lattice of the perovskite. The resulting effect may be explained on the basis of valency compensation in the lattice. However, there has not beenany systematic study incorporating the effect of Nd 3+ ions, which are found to have a significant influence on the resultant dielectric and electromechanical behaviour of these ceramics. This letter describes the effect of Nd 3+ ions on the dielectric and electromechanical properties of PZT ceramics. The raw materials used for the present study were powders of PbO, ZrO2, TiO2 and Nd203, all having a purity of about 99.5%. These materials were weighed to make a composition corresponding to Pb(Zr0.53Ti0.47)O3 + (0.00-7.00) mol % Nd 3+ ions. The mixed powders were calcined at 900 °C for 2 h in air after milling using a polyethylene container and zirconia balls for 10 h. The powders were pressed in the form of pellets having 20 mm diameter and 3 mm thickness. These pressed pellets were sintered for 1220 °C for 4 h. The sintered specimens were then lapped and silver electrodes were provided on them and these were subsequently poled under high d.c. fields. The dielectric parameters were measured using an HP-4192A LF impedance analyser at 1 kHz and electromechanical parameters were evaluated per Institution of Radio Engineers specifications [7]. The resistivity was measured by a Million Megohmmeter Model RM 160 Mk IIA-BPL (India) at room temperature. The microstructural studies were performed on a JeolCF-35 scanning electron microscope. The variation of the Curie temperature with Nd203 content is shown in Fig. 1. It is evident that the change in the Curie temperature is negligible for ceramics containing Nd203 up to about 2 mol % and subsequently is decreases sharply. These samples possessed high resistivity of the order of 1012 ~ cm (Fig. 2) which increases further with the addition of Nd203 and attains a maximum value around 4 mol %, after which it drops slowly. The associated dielectric constant and loss (measured at 1 kHz) are shown in Figs 3 and 4, respectively. The dielectric constant of unpoled samples was higher than the poled ones and rose almost linearly with increasing Nd203 content up to 3 mol %, subsequently rising at a slower rate. The dielectric loss for all of the well-poled samples lay in the range approximately 0.01-0.03 (Fig. 4) and was higher than for unpoled samples. It may be mentioned here that some of these samples having dielectric constant around 1500 and dielectric loss of about 0.005 could find great applications as a high-power material capable of handling large powers.