Frequency dependent electrical characteristics of ferroelectric Pb_4.0K_1.0Li_1.0Nb₁₀O₃₀ ceramics

¹ Centre for Piezoelectric Transducer Materials, Department of Physics, Andhra University, Visakhapatnam – 530 003, India
² Department of Physics, Sri Venkateswara University, Tirupati, India

Corresponding author: konapala@sify.com

Received: 10 February 2007
Revised: 5 April 2007
Accepted: 5 June 2007
Published online: 8 August 2007

Abstract

Dielectric, impedance, modulus and conductivity studies were performed over temperature 35 °C–600 °C and frequency 45 Hz–5 MHz range on the Lead Potassium Lithium Niobate (Pb_4.0K_1.0Li_1.0Nb₁₀O₃₀, PKLN) ceramics. These studies established the conduction ion motion and polarization mechanism in the material. The dispersive dielectric loss at high temperature reveals the ionic conductivity. From frequency variation of ε^l response the pre-factor A(T) and critical exponent n(T) are evaluated, and are used in Jonscher's dielectric dispersion relation for ε' to fit with the experimental data. Complex impedance plots showed a non – Debye type relaxation, are used to evaluate the grain and grain boundary conduction and relaxation activation energies. DC and ac conduction activation energies are estimated from Arrhenius plots. Occupancy of Li⁺ for C-sites gave a completely filled structure and enhanced the phase transition temperature to 520 °C compared to PKN. This is supported by the conduction activation energy in ferro region is more than the para region. Also, the dc conductivity characterized from bulk resistance and M^ll peak frequency. Polaron hoping mechanism at room temperature has been confirmed via the linear variation of the plot log (σ_ac – σ_dc) as a function of log ω². Stretched exponential parameter, β (0 < β 1) has been evaluated from impedance plots, interpreted as a result of correlated motions between the Li⁺ ions and distribution of dielectric relaxation. Compared the results from different techniques, and discussed the conduction mechanism in the material.