Sintering temperature effect on microstructure, electrical properties and temperature stability of MnO-modified KNN-based ceramics

Lead-free 0.955K0.5Na0.5NbO3-0.045Bi0.5Na0.5ZrO3 + 0.6%MnO (KNN-0.045BNZ + Mn0.6) ceramics have been prepared by a conventional solid-state sintering method in air. All the samples sintered at different temperatures possess a coexisting phase boundary (CPB) between rhombohedral (R) phase and tetragonal (T) phase. The increase of sintering temperature (Ts) increases the phase fraction of T phase in CPB region. Mn2+, Mn3+ and Mn4+ ions coexist in all the KNN-0.045BNZ + Mn0.6 ceramics sintered at 1110 °C to 1190 °C. High sintering temperature can induce a transformation from MnNb'' defects to MnNb' defects. The samples with fine grain show stable octahedral structure. The KNN-0.045BNZ + Mn0.6 ceramics with fine grain possess excellent temperature stability of d33* due to the wide phase transition region. The increase of sintering temperature induces the (R-T) phase transition temperature to move to room temperature.