Dielectric spectroscopy characteristics of ferroelectric Pb0.77K0.26Li0.2Ti0.25Nb1.8O6 ceramics

Abstract

Temperature and frequency dependence of dielectric constant and conductivity properties of Pb0.77K0.26Li0.2Ti0.25Nb1.8O6 (PKLTN) ceramics are modelled through the universal dielectric response (UDR). Partial substitution of Ti4+ for Nb5+ was compensated by charge and the creation of oxygen vacancies according to the Kroger-Vink notation. The electrons released by this reaction are captured by Nb5+ and Ti4+ to generate Nb3+ and/or Ti3+. The hopping of electrons between Nb5+–Nb3+ and Ti4+–Ti3+ are believed to participate in conductivity. Characterization of the dielectric constant has been performed from room temperature to 590°C in the frequency range from 45 Hz to 5 MHz. The measured dielectric constant obeyed Jonscher's dielectric dispersion relations: ε l = ε ∞ + sin(n(T)π/2)(a(T)/ε 0)(ωn ( T )−1) and ε ll = σ/iε 0 ω + cos(n(T)π/2)(a(T)/ε 0)(ωn ( T )−1). Cole-Cole plots inclined at an angle (1 − n(T))π/2 and followed the trend of universal material behavior ε ∞ + A(T)(ωn ( T )−1). The exponent n(T) and coefficient A(T) = (a(T)S/L) exhibited a minimum and maximum at T c = 425°C, respectively. The conductivity studies show the contribution of the hopping of bound charge carriers to conduction in PKLTN.