Effect of firing temperatures on properties of BNT-BCTZ-0.007mol%BFCO lead free piezoelectric ceramics synthesized by the solid state combustion method

Abstract In this study, the effects of calcination temperature (550–750 °C for 2 h) and sintering temperature (1100–1200 °C for 2 h) on the phase formation, microstructure, electric and magnetic properties of the 0.94Bi 0.5 Na 0.5 TiO 3 -0.06(Ba 0.85 Ca 0.15 )(Ti 0.90 Zr 0.10 ) lead-free piezoelectric ceramic doped with 0.007 mol%Bi 2 FeCrO 6 (BNT-BCTZ-BFCO) were investigated. These ceramics were prepared by the solid state combustion technique using glycine as fuel. The pure perovskite phase was observed in the BNT-BCTZ-BFCO powders attained at the calcined temperature of 650 °C for 2 h. The morphology of the BNT-BCTZ-BFCO powders exhibited an almost-spherical shape and the average particle size increased when the calcination temperature increased from 550 to 750 °C. TEM results of pure BNT-BCTZ-BFCO powder calcined at 650 °C for 2 h showed rounded shapes and the average particle size was ∼ 200 nm. The XRD results of all ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phases. The average grain size increased with increasing sintered temperature. The density, dielectric constant (e at T r and T m ) and piezoelectric constant (d 33 ) increased when the sintered temperature increased up to 1150 °C and then reduced in values. At a sintered temperature of 1150 °C, BNT-BCTZ-BFCO ceramic showed the highest relative density (97.2%), maximum dielectric properties (e at T r = 1783 and e at T m = 5117), d 33 value (178 pC/N), d * 33 (549 pm/V) and the remnant polarization (P r = 34.66 µC/cm 2 ). At higher sintering temperatures, the properties of BNT-BCTZ-BFCO ceramics decreased due to the evaporation of Bi and Na. All ceramics exhibited the paramagnetic behavior and the magnetization increased with increasing sintering temperature.