Impedance spectroscopy studies on Ga-ion-modified PLZT ceramics

Abstract

Polycrystalline samples of [Pb 0.92(La 1-zGa z) 0.08][Zr 0.65Ti 0.35] 0.98O 3 (PLGZT) for z = 0.0, 0.3, 0.6, 0.9, and 1.0 were prepared by a solid-state reaction technique. The single-phase formation of the new compounds with tetragonal crystal structures was established by the room-temperature X-ray analysis. The occupancy of Ga ion in the La site has been confirmed by FTIR analysis. Complex impedance spectroscopy (CIS) has provided a convincing evidence for the existence of both grain (bulk) and grain boundary effects in the materials, which is also evident from the microstructures, comprise grains separated by well-defined boundaries. The electrical processes in the sample have been modeled in the form of an electrical equivalent circuit made up of a series combination of two parallel RC circuits attributed to grains and grain boundaries. The real and imaginary parts of dielectric constants have been separated from impedance spectrum results and expressed in terms of loss tangent (tan δ). The ferroelectric transition temperature (T c) of the materials is evaluated from the plot of real permittivity versus temperature and found to be shifted to higher temperature side with increasing Ga-ion concentration. A sharp rise in conductivity is observed in the nature of temperature variation of the bulk electrical conductivity (σ dc) at higher temperature for all the Ga-modified PLZT samples. This type of behavior is typical to dielectric ceramics having conductive grain boundary arising out of a relaxation process of the Maxwell-Wagner type. At higher temperature a substantial increase in conductivity ∼10 -3 S cm -1 is achieved for complete replacement of the La ion by Ga (z = 1.0). © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.