Dielectric Characteristics of the Lead-free Piezoelectric Ceramics K0.50Na0.50Nb0.95Ta0.05O3

In order to improve the sintering density and dielectric properties of the lead-free K0.5Na0.5NbO3-based ceramics, by the use of solid-state reaction, part of the Nb atoms are substituted by the Ta atoms to form K0.50Na0.50Nb0.95Ta0.05O3 ceramics and the dielectric characteristics are detail investigated in this letter. It is found that the phases of K0.50Na0.50Nb0.95Ta0.05O3 ceramics are pure perovskite with typical orthorhombic symmetry, in addition, no other secondary phases could be certified. For pure K0.50Na0.50Nb0.95Ta0.05O3 ceramics, the shapes of the grains are quadrate and which would due to the increase of the porosity and can not be eliminated easily. Because of the phase stability of pure K0.50Na0.50Nb0.95Ta0.05O3 ceramics is limited to 1140 degrees C in this study, higher sintering temperature (over than 1140 degrees C) is not suitable for the fabrication of K0.50Na0.50Nb0.95Ta0.05O3 ceramics. Moreover, the Ta atoms in the K0.5Na0.5NbO3-based ceramics could be used to improve the dielectric properties effectively, and it also reveals lower Curie temperature and lower phase transition temperature than the pure K0.5Na0.5NbO3 ceramics. In this letter, for 1120 degrees C-sintered K0.50Na0.50Nb0.95Ta0.05O3 ceramics, the optimum bulk density is 95.6 % of the theorical density, the Curie temperature is 380 degrees C, and the optimum relative dielectric constant is 6107 at 10 kHz.