Grain configuration effect on the phase transition, piezoelectric strain and temperature stability of KNN-based ceramics
Lead-free 0.985(0.96KNNT–0.04BNKZ)–0.015CZ ceramics were sintered at 1150–1190 °C. The average grain size increases from ∼0.54 μm to ∼1.26 μm on increasing the sintering temperature (Tsinter) from 1150 °C to 1190 °C. The increase of average grain size induces the R/T phase boundary to change to an O/T phase boundary at room temperature. An abnormal region in the ceramics sintered at 1170–1190 °C was observed where fine grains surround coarse grains that are the result of abnormal growth. The fine grains become smaller and their ratio increases, when Tsinter increases from 1150 °C to 1190 °C. The ceramics sintered at 1180 °C with good temperature stability (Te = 120 °C) and optimal room temperature piezoelectric strain (d33* = 482 pm V−1 at 35 kV cm−1) should be attributed to the suitable grain configuration. At Tsinter = 1150–1190 °C, the piezoelectric strain of the ceramics can be improved evidently without deteriorating the temperature stability visibly due to the formation of an abnormal region.