Effects of LiNbO₃-doping on properties of (Na_0.535K_0.48)NbO₃ piezoelectric ceramics with high electromechanical coupling coefficient for application in surface acoustic wave devices

In this study, lead-free LiNbO₃-doped (Na_0.535K_0.48)NbO₃ (NKN) ceramics (NKL_xN, x = 0–0.09) were prepared using a conventional mixed oxide method to investigate the effects of LiNbO₃ additives on the microstructure and electrical properties. The addition of LiNbO₃ reduced the optimal sintering temperature from 1100 to 950 ℃ and increased the bulk relative density to 99.61% (g/cm³) at x = 0.05 through the formation of a homogeneous microstructure. The electrical properties remained highly stable, even when the ambient temperature was increased from room temperature to 140 ℃. NKL_xN ceramics sintered at 950 ℃ with x = 0.05 exhibited the following excellent piezoelectric properties: k_p：50% (34%); k_t：53% (40%); Q_m：168 (112); d₃₃：150 pC/N (80 pC/N); and tan δ：4% (8%). These values far exceed those of pure NKN ceramics sintered at 1100 ℃. Surface acoustic wave (SAW) devices fabricated using the proposed NKL_xN (x = 0.05) ceramics presented high phase velocity of 3210 m/s, k² of 6.7%, and TCF of approximately −282 ppm/℃. Our results clearly demonstrate the effectiveness of adding LiNbO₃ to prevent deliquescence and thereby enhance resistance to the effects of humidity. The resulting devices are highly sensitive to changes in temperature, making them ideally suited to electromechanical transducers as well as SAW temperature sensors.