Influence of annealing environments on the conduction behaviour of KNN-based ceramics

The electrical conduction behaviour of the lead-free (1-x)K0·5Na0·5Nb0·95Sb0·05O3-xBi0.5Na0·41K0·09ZrO3 (x = 0.05) ceramics annealed in air, oxygen, and argon environments at various temperatures was investigated. Post-sintering annealing in different atmospheres affected the temperature of dielectric phase transition and electrical conductivity values significantly. The ceramic sample annealed in an oxygen environment showed the lowest conductivity for grain (σg ∼ 1.22 × 10−5 S/m) and grain boundary (σgb ∼ 1.56 × 10−6 S/m) regions at 250 °C which is due to the reduction in oxygen vacancy defects. The activation energy Ea for DC conduction in this sample obeyed the Arrhenius relation and was found to be ∼ 0.99 ± 0.03 eV. An additional anomaly observed at T ∼ 250 °C dielectrics vs. temperature plots for the as-sintered and argon-annealed samples is ascribed to defect relaxation, which was inconspicuous in the samples annealed in air and oxygen. In addition, the in-situ impedance measurement was performed to analyze the impact of argon atmosphere on the electrical conductivity of the O2-annealed samples with high-temperature electrode curing.