Modulation of electrical properties of KNNS-BNKZ lead-free ceramics by calcination temperatures

In this work, the 0.96(K0.5Na0.5)(Nb0.96Sb0.04)O-3-0.04Bi(0.5)(Na0.5K0.5)(0.5)ZrO3 (KNNS-BNKZ) ceramics were prepared by the conventional solid-state method, and effects of calcination temperatures (T-cal) on their microstructure, phase structure, and electrical properties were investigated in detail. It was found that the calcination temperatures strongly affect the phase structure of the ceramics, that is, rhombohedral-orthorhombic-tetragonal phase coexistence for T-cal = 500-600 degrees C and rhombohedral-tetragonal phase coexistence for T-cal = 650-950 degrees C. In addition, their electrical properties are also very sensitive to the calcination temperatures. A high piezoelectricity of 450-475 pC/N can be attained in a wide calcination temperature of 750-900 degrees C, and especially the ceramics calcined at 850 degrees C exhibit optimum electrical properties: d(33) = 475 pC/N, k(p) = 0.51, epsilon(r) = 2561, tan delta = 0.033, P-r = 15.2 mu C/cm(2), E-C = 7.1 kV/cm, and T-C = 222 degrees C. In addition, all the ceramics exhibit a good thermal stability of piezoelectric activity. As a result, we believe that the electrical properties of KNN-based ceramics can be well controlled by optimizing calcination condition.