Impedance studies of K0.5Na0.5NbO3 ceramics prepared from mechanochemically activated powders

Recently worldwide environmental considerations demand the elimination of lead-based materials from all consumer items. Potassium sodium niobate solid solution seems to be one of the most promising candidate to replace the PZT-based ceramics in piezoelectric devices. In this paper the K1/2Na1/2NbO3 ceramics have been obtained from mechanochemically activated powders containing the stoichiometric ratio of niobium oxide, potassium and sodium carbonates. The activation process occurred in a high energy mill (shaker type), for different periods between 25 h and 100 h. The sintered ceramic samples, prepared from mechanochemically activated powders, have been investigated by XRD, SEM and impedance studies in order to determine the influence of mechantichemical process on the final ceramic properties. The ceramic properties have showed a strong correlation with the milling duration. Based on the performed investigations it is possible to distinguish between the material response related to the grains and the grain boundaries. The resistance of grains and grain boundaries increases with the high energy milling time. The similar trend has been recorded in case of capacitance. Moreover, the anomaly, related to the ferroelectric-paraelectric phase transition, is visible on both temperature dependencies of grains and grain boundaries capacitances.