The Influence of Firing Temperatures on the Crystal Structure, Microstructure and Dielectric Properties of 0.79Bi_0.5Na_0.5TiO₃-0.18Bi_0.5K_0.5TiO₃-0.03BiFeO₃Ceramics Prepared via the Combustion Technique

Abstract

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 • C to 800 • C for 2 h. and the sintering temperature ranged from 900 • C to 1075 • C for 2 h. The XRD analysis exhibited that the BNKFT powders belonged to a rhombohedral structure. A second phase of K 4 Ti 3 O 8 was detected in the powders calcined below 750 • 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 (ρ = 5.85 g cm −3 ), maximum dielectric constant (ε r = 8,530), lowest dielectric loss (tanδ = 0.02) maximum remnant polarization measured at 40 kV/cm (P r = 20.1 μC/cm 2 ) and the maximum piezoelectric coefficient (d 33 = 213 pC/N) were obtained from the sample sintered at 1050 • 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.Keywords 0.79Bi 0.5 Na 0.5 TiO 3 −0.18Bi 0.5 K 0.5 TiO 3 −0.03BiFeO 3 ; combustion technique; dielectric constant