Structural, microstructure and electrical properties of La2O3-doped Bi0.5(Na0.68K0.22Li0.1)0.5TiO3 lead-free piezoelectric ceramics synthesized by the combustion technique

The effect of firing temperatures on phase formation, microstructure and physical properties of [Bi0.5(Na0.68K0.22Li0.1)0.5TiO3] doped with La2O3 at 0.1 wt% (BNKLLT) ceramics prepared by the combustion method was studied. Glycine was used as fuel and the ratio of raw material (corresponding oxidant metal nitrate) with fuel was about 1:0.56. The samples were calcined at 600–900 °C for 2 h and sintered at 1075–1150 °C for 2 h. The single rhombohedral peroveskite phase of BNKLLT powders was observed from the sample calcined at 750 °C for 2 h. The BNKLLT ceramics exhibited a pure peroveskite phase in all samples. The microstructures of the BNKLLT powders exhibited an agglomerated form while the grain ceramics exhibited a square shape. The average particle size and average grain size increased with increasing firing temperatures. The density, dielectric constant (εr and εm), Pr and d33 tended to increase with increasing sintering temperatures up to 1100 °C and then decreased. The maximum density (5.73 g/cm2), maximum dielectric constant (εr~2572 and εm~5536), good ferroelectric properties (Pr~35.78 µC/cm2 and Ec~22.42 kV/cm) and highest d33 (210 pC/N) were obtained by the sample sintered at 1100 °C for 2 h.