Effect of Calcination Temperature on the Structural and Electrical Properties of Low-Temperature-Sintered (Na 0.52 K 0.44 Li 0.04 )(Nb 0.88 Sb 0.08 Ta 0.04 )O 3 Ceramics

Low-temperature-sintered lead-free 1.5 mol%-Na2O-excess (Na0.52K0.44Li0.04)(Nb0.88Sb0.08Ta0.04)O3 (NKN-LST) ceramics were calcined at 500 ∼ 950 °C. At 500 °C, a perovskite structure of the calcined powders without crystallinity was obtained. As the calcination temperature increased, an orthogonal structure began to form. And at 750 °C, the NKN-LST powders have a single orthogonal structure. The NKN-LST powders form a tetragonal structure when the calcination temperature ≥ 800 °C. Therefore, in the calcination temperature range of 800 ∼ 900 °C, the NKN-LST powders have two orthogonal and tetragonal structures. However, it can be seen that a two-phase coexistence zone of orthogonal and tetragonal structure exists in all the ceramics sintered in air at 1 020 °C for 3 h. Moreover, with increasing calcination temperature, the tetragonal phase increases. There is also an increase in the abnormal grains with increasing the calcination temperature, which may be attributable to a decrease in the critical driving force. At the same time, it has been found that the composition and structure determine the properties of NKN-LST ceramics. The optimum electrical properties of NKN-LST ceramics with a d33 of 384 pC/N, a kp of 0.53, and an e33 of 2 735, were obtained when the ceramics were calcined at 700 °C. These properties indicated that the ceramics studied have the potential to replace lead-based ceramics in device applications. Therefore, the reduction of the calcination temperature leads to a significant improvement of 1.5 mol%-Na2O-excess NKN-LST piezoelectric ceramics.