Improvement of piezoelectric and dielectric properties and expansion of stably working temperature range of KNN-based crystals through Li-doping

Improving the electrical properties is one of the key technologies that need to be solved to promote the application of lead-free piezoelectric materials. This paper reports Li, Bi and Al co-doped (K_0.5Na_0.5)NbO₃ lead-free piezoelectric single crystals grown via a Seed-Free Solid-State Crystal Growth (SFSSCG) method, and especially the effects of Li doping on the morphology, structure, and electrical properties of the single crystals. The results indicate that Li doping increases the crystal size and electrical performance of the crystals. When x = 0.004, the crystal obtains the best comprehensive electrical performance: d₃₃ ~ 468 pC/N, P_r ~ 35.3 μC/cm², Q_m ~ 58, k_t ~ 0.41, tanδ ~ 0.029, T_O-T ~ 142 ℃, T_C ~ 420 ℃. This provides an available route for the development and application of the potassium sodium niobate (KNN) system and has theoretical and practical significance for further regulating the functional properties of lead-free piezoelectric single crystals.