Enhancement of Dielectric Properties via Crystal Structure and Microstructure Control in the (K0.5Na0.5)NbO3-SrTiO3 System

Solid solutions and composites of a mixture of (K0.5Na0.5)NbO3 (KNN) and SrTiO3 (ST) were respectively synthesized by different process routes using a conventional solid state reaction. All starting materials were mixed simultaneously and calcined at 800 degrees C for 4 h to obtain the solid solutions of KNN-ST. Meanwhile, the composites of KNN-ST were obtained by mixing the synthesized KNN and synthesized ST, respectively. KNN-ST calcined powders were sintered at 1150, 1250 and 1300 degrees C for 2 h. The calcined powders, in which all starting materials were mixed at once, showed a single-phase pseudo-cubic structure after sintering. On the other hand, the powders with the mixture of KNN and ST had two phases of cubic ST and orthorhombic KNN as composites. The dielectric loss values of all samples decreased as the sintering temperature increased because of increased densification. The dielectric constants of the solid solutions were increased as the sintering temperature increased, however, the dielectric constants of the composites decreased with increasing sintering temperature. It was concluded that, for enhanced dielectric properties, the dielectric materials should be synthesized as solid solutions.