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(Na0.5K0.5)NbO3-0.02(Bi1/2Li1/2)TiO3-0.06BaZrO(3) (6BZ/2BLT/92NKN) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at room temperature and 0.92(Na0.5K0.5)NbO3-0.03(Bi1/2Li1/2)TiO3-0.05BaZrO(3) (5BZ/3BLT/92NKN) features an MPB engineered to be located below room temperature. At 30 degrees C, d(33),d(33)(E=0), S (at 2kV/mm), and k(p) are 252pC/N, 230pm/V, 0.069%, 0.51 for 5BZ/3BLT/92NKN; and 348pC/N, 380pm/V, 0.106%, 0.57 for 6BZ/2BLT/92NKN, respectively. With increasing temperature, the piezoelectric properties decrease. At 200 degrees C, d(33), d(33)(E=0), S (at 2kV/mm), and k(p) are 170pC/N, 160pm/V, 0.059%, 0.36 for 5BZ/3BLT/92NKN; and 181pC/N, 190pm/V, 0.061%, 0.39 for 6BZ/2BLT/92NKN. 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.