Microstructures and Piezoelectric Properties in the Li ₂ O‐Excess 0.95(Na 0.5 K 0.5 )NbO ₃ –0.05LiTaO ₃ Ceramics

As a candidate for lead‐free piezoelectric materials, Li 2 O‐excess 0.95(Na 0.5 K 0.5 )NbO 3 –0.05LiTaO 3 (NKN–5LT) ceramics were developed by a conventional sintering process. The sintering temperature was lowered by adding Li 2 O as a sintering aid. Abnormal grain growth in NKN–5LT ceramics was observed with varying Li 2 O content. This grain‐growth behavior was explained in terms of interface reaction‐controlled nucleation and growth. In the 1 mol% Li 2 O excess NKN–5LT samples sintered at 1000°C for 4 h in air, the electromechanical coupling factor and the piezoelectric constant of NKN–5LT ceramics were found to reach the highest values of 0.37 and 250 pC/N, respectively.