Dielectric response and ac-conductivity studies of Gd2O3- contained K0.5Na0.5NbO3 piezoelectric ceramics

We report the role of Gd₂O₃ substitution on the dielectric properties of alkali niobate K_0.5Na_0.5NbO₃ (KNN) ceramics. This system exhibits relaxor behaviour for 0.5 wt% of Gd₂O₃ in KNN matrix and shows enhanced dielectric permittivity (ε_r = 4147 at T = 628 K) and low loss (Tanδ ~ 0.008) at frequency f = 1 MHz. The position of crystallographic phase transitions of Orthorhombic to Tetragonal (T1) and Tetragonal to Cubic (T₂) shifts significantly from 480 K to 413 K and 668 K to 582 K, respectively. The temperature and the frequency dependence of the position of maximum dielectric permittivity Tm obeys the Vogel-Fulcher law, with the attempt frequency f₀ = 5.32×10¹¹ Hz, freezing temperature T_f = 598 K and activation energy E_A= 0.038 eV for KNN + 0.5 wt% Gd₂O₃. The temperature dependence of AC-conductivity σ_ac (T) analysis in the range 300 K <; T <; 600 K reveals the existence of variable range hopping of charge carriers with average hopping length R_H in the range 7.93-29.24 nm and 5.55-26.41 nm for x = 0 and x = 0.5, respectively. The diffuseness exponent `γ´ (~1.74) estimated from the high temperature slopes of the diffused dielectric permittivity data reveals the weakly coupled relaxor behavior.