The Influence of Firing Temperatures on the Crystal Structure, Microstructure and Dielectric Properties of 0.79Bi0.5Na0.5TiO3-0.18Bi0.5K0.5TiO3-0.03BiFeO3 Ceramics Prepared via the Combustion Technique

Polycrystalline samples of 0.79Bi(0.5)Na(0.5)TiO(3)-0.18Bi(0.5)K(0.5)TiO(3)-0.03BiFeO(3) (abbreviated as BNKFT) lead-free piezoelectric ceramics were synthesized by the combustion technique. BNKFT was calcined from 600 degrees C to 800 degrees C for 2h. and the sintering temperature ranged from 900 degrees C to 1075 degrees C for 2h. The XRD analysis exhibited that the BNKFT powders belonged to a rhombohedral structure. A second phase of K4Ti3O8 was detected in the powders calcined below 750 degrees C. The sintered pellets showed a pure perovskite phase in all samples. The microstructure of BNKFT powders exhibited an almost-spherical morphology and had a porous agglomerated form. The average particle size and the average grain size of BNKFT powders and ceramics increased with the increase of firing temperatures. The highest densities ( = 5.85g cm(-3)), maximum dielectric constant (E-r = 8,530), lowest dielectric loss (tan = 0.02) maximum remnant polarization measured at 40kV/cm (P-r = 20.1C/cm(2)) and the maximum piezoelectric coefficient (d(33) = 213 pC/N) were obtained from the sample sintered at 1050 degrees C. With a lower firing temperature, the properties of the BNKFT ceramics prepared by the combustion technique were better than those prepared by the solid-state reaction method.