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.