Low-temperature sintering of KNN with excess alkaline elements and the study of its ferroelectric domain structure

•KNNLN ceramics were fabricated and investigated.•An approach was proposed to determine the phase volume in as-sintered samples.•The reason for the best performance of sample was studied.

In the present work, lead-free K0.48Na0.52NbO3 (KNN) ceramics were synthesized by conventional ceramics processes. The excess 3.3 mol% Na2CO3 and 1.1 mol% K2CO3 were added to decrease the sintering temperature to 990 °C and effectively promote the densification of KNN ceramics. X-ray diffraction results indicated that the excess Na2CO3 and K2CO3 would induce the formation of the A-site riched secondary phase with the sintering temperature. Compositional segregation phenomenon enhanced by different sintering temperature, spurs the formation of secondary phase in KNN-AEe ceramics. In addition, the difference between ferroelectric domain structure of the poled and as-sintered KNN-AEe samples for 990 °C was investigated. Via XRD analysis and SEM observation, it was found that the domain orientation was urged during the poling process.