Temperature Stability of Lead‐Free Niobate Piezoceramics with Engineered Morphotropic Phase Boundary

The temperature dependence of piezoelectric properties (direct piezoelectric coefficient d 33 , converse piezoelectric coefficient d 33 ( E = 0), strain S and electromechanical coupling coefficient k p ) for two niobate‐based lead‐free piezoceramics have been contrasted. 0.92(Na 0.5 K 0.5 )NbO 3 –0.02(Bi 1/2 Li 1/2 )TiO 3 –0.06BaZrO 3 (6 BZ /2 BLT /92 NKN ) has a morphotropic phase boundary ( MPB ) between rhombohedral and tetragonal at room temperature and 0.92(Na 0.5 K 0.5 )NbO 3 –0.03(Bi 1/2 Li 1/2 )TiO 3 –0.05BaZrO 3 (5 BZ /3 BLT /92 NKN ) features an MPB engineered to be located below room temperature. At 30°C, d 33 , d 33 ( E = 0), S (at 2 kV/mm), and k p are 252 pC/N, 230 pm/V, 0.069%, 0.51 for 5 BZ /3 BLT /92 NKN ; and 348 pC/N, 380 pm/V, 0.106%, 0.57 for 6 BZ /2 BLT /92 NKN , respectively. With increasing temperature, the piezoelectric properties decrease. At 200°C, d 33 , d 33 ( E = 0), S (at 2 kV/mm), and k p are 170 pC/N, 160 pm/V, 0.059%, 0.36 for 5 BZ /3 BLT /92 NKN ; and 181 pC/N, 190 pm/V, 0.061%, 0.39 for 6 BZ /2 BLT /92 NKN . It is found that the electromechanical coupling coefficient has a better temperature stability than the piezoelectric coefficient in the studied system due to a large temperature‐dependent compliance change. The results demonstrate that engineering an MPB is highly effective in tailoring temperature stability of piezoceramics.