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Abstract
Complex impedance spectroscopy (CIS) analysis on polycrystalline lanthanum modified lead zirconate titanate (PLZT) has been carried out to investigate its electrical, dielectric and electromechanical properties. CIS has been shown to be an important and very convenient experimental tool to correlate the electrical and dielectric behaviour of ferroelectric ceamics with their microstructure/structure in terms of the relaxations of defect species. The physical structure of the sample pellet has been visualized as comprising of grains separated by grain boundary in accordance with the impedance spectrum observations. The electrical processes in the sample has 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 evaluated from impedance spectrum results and expressed in terms of complex permittivity spectrum (Cole-Cole plot). The dielectric phenomenon in PLZT has been observed to be of polydispersive nature with marked deviation from Debye type relaxation process. This result has also been confirmed by complex modulus analysis. Conductivity dispersion has been observed throughout the frequency range in the present investigation up to 400°C beyond which low frequency dispersion and high frequency plateau was found. It has been attributed to Warburg type diffusion phenomenon arising due to ion migration/charge transport at higher temperature.