Low frequency dielectric dispersion studies in ferroelectric ceramics of Pb₀․₇₇K₀․₂₆Li₀․₂Ti₀․₂₅Nb₁․₈O₆

Abstract

Temperature and frequency dependence of dielectric constant and conductivity properties of Pb₀․₇₇K₀․₂₆Li₀․₂Ti₀․₂₅Nb₁․₈O₆ (PKLTNO) ceramics are modeled through universal dielectric response (UDR). Partial substitution of Ti⁴⁺ in Nb⁵⁺ increased the B- sites ordering, supported by charge compensation and creation of oxygen vacancies that obeys Kroger-Vink notation. The release of electrons by this reaction are captured by the Nb⁵⁺ and Ti⁴⁺ to generate Nb³⁺ and or Ti³⁺. Thus the possibility of the hopping of electrons among Nb⁵⁺ and Nb³⁺ and Ti⁴⁺ and Ti³⁺ entering in the crystal structure participate in the conductivity. The dielectric characterization is performed from room temperature to 590°C, in the frequency range of 45 Hz-5 MHz. The measured dielectric constant has been found to fit to Jonscher’s dielectric dispersion relations: Ɛ' = Ɛ∞ + sin(n(T)л/2) (a(T)/ Ɛ0) (ω ⁿ(T)⁻¹) and Ɛ" = σ/i Ɛ0 ω + cos(n(T)л/2) (a(T)/ Ɛ0) (ωⁿ(T)⁻¹). Cole-Cole plots are found inclined at an angle (1-n(T))X л/2 which obeys the universal material behaviour Ɛ∞ + A(T) (ωⁿ (T) ⁻¹). The exponent n(T) and coefficient A(T) = [a(T)S/L] has been observed to be minimum and maximum respectively at TC~425°C. The conductivity studies reveal the conduction in the material arisising due to hopping of bound charges.