Dielectric spectroscopy characteristics of ferroelectric Pb_0.77K_0.26Li_0.2Ti_0.25Nb_1.8O₆ ceramics

Abstract

Temperature and frequency dependence of dielectric constant and conductivity properties of Pb_0.77K_0.26Li_0.2Ti_0.25Nb_1.8O₆ (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)(ω^{n ( T )−1}) and ε ^ll = σ/iε ₀ ω + cos(n(T)π/2)(a(T)/ε ₀)(ω^{n ( 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)(ω^{n ( 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.

Keywords:

• niobate ceramics
• dielectric constant
• electrical conductivity
• relaxation

Acknowledgements

KSR and PMK thank the Defence Research and Development Organization (DRDO) Government of India for sanctioning the research project and providing fellowships.