Enhancing depolarization temperature and thermal stability of KNN-based piezoelectric ceramics through Li substitution and Al2O3 doping

•(Na0.5K0.5-xLix)NbO3 system is designed to raise the depolarization temperature and Curie temperature by replacing K at A site with a small amount of Li. When x = 0.065, the desired depolarization temperature and piezoelectric activity are obtained: Td = 470 °C, d33 = 205 pC/N. After optimizing the process conditions, the piezoelectric coefficient finally reaches at 265 pC/N.•The purpose of Al2O3 doping is to enhance the thermal stability of KNN-based piezoelectric ceramics. the d33 of 0.2 mol% Al2O3 doping remains the relatively high value of 200 pC/N even at high temperatures (400–470 °C) with a decrement less than 10% (25–470°C).•This work opens a new perspective for enhancing the thermal stability of lead-free piezoelectric ceramics, and paves the way for the practical application of KNN-based ceramics at high temperatures.