Temperature dependence of dielectric and ferroelectric properties for (1-x)Bi0.5(Na0.8K0.2)0.5TiO3-xBaZn0.5W0.5O3 lead-free piezoelectric ceramics

The ferroelectric and piezoelectric properties of (1-x)Bi-0.5(Na-0.8-K-0.2)(0.5)TiO3-xBaZn(0.5)W(0.5)O(3) ((1-x)BNKT-xBZW) ceramics have been studied to clarify the temperature dependence of the polarization-electric field (P-E) hysteresis and dielectric properties. Based on the temperature dependence of the dielectric constant, it was found that the depolarization temperature (T-d) shifted to lower temperatures, depending on the composition x. The crystal structure refinement of (1-x)BNKT-xBZW ceramics with rhombohedral and tetragonal phases revealed that the fraction of tetragonal phase to rhombohedral phase increased in the composition range of 0-0.05, which implies a formation of a morphotropic phase boundary (MPB). The piezoelectric constant (d(33)) of the (1-x)BNKT-xBZW ceramics increased with the composition x up to x = 0.05 and the maximum value was 168 pC/N. Such an increase in d(33) is attributed to the increase in the dielectric constant at room temperature which is due to the shift of T-d; a pinched P-E hysteresis loop was obtained at x = 0.05. The temperature dependence of the P-E hysteresis loops indicated that the shape of the hysteresis loop is closely related to the coexistence of ferroelectric and antiferroelectric phases.