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

Obtaining both large piezoelectric responses and broad service temperature range of ferroelectric ceramics is a key challenge for practical applications due to the so-called piezoelectric coefficient (d33)-Curie temperature (TC) trade-off. Here we report the strategy of employing Li substitution and Al2O3 doping in order to enhance the depolarization temperature (Td) and thermal stability of (K,Na)NbO3 (KNN)-based lead-free piezoelectric ce-ramics. All KNN-based ceramics are fabricated using conventional solid-state reaction techniques. Optimal comprehensive properties of d33 = 205 pC/N, kp = 46.5%, epsilon T33/epsilon 0 = 998, tan delta = 0.047, Td = 470 degrees C are obtained with Li substitution of 6.5 mol%. Furthermore, doping 0.2 mol% Al2O3 improves the thermal stability in the whole working temperature range of 25 - 470 degrees C with a d33 decrement less than 10%, keeping the relatively high d33 of 200 pC/N even at high temperature (400 - 470 degrees C). The Al2O3 doping shows a further effect of inhibiting grain growth, which significantly reduces the grain size of ceramics. The results obtained in this work pave the way for the practical application of KNN-based ceramics at high temperature, such as aerospace sensors, oilfield logging, engine monitoring and injection nozzles in automobiles.

Automated summary

By employing Li substitution and Al2O3 doping, the thermal stability and depolarization temperature of (K,Na)NbO3 (KNN) piezoelectric ceramics are enhanced, resulting in large piezoelectric responses for potential applications in high temperature environments.