Effects of the phase content and grain size on the electrical and energy storage properties of lead-free BNBT ceramics with substituted La3+.

Lead-free [(Bi_0.5Na_0.5)_0.94Ba_0.06]_1-xLa_xTiO₃ (BNBT-xLa) ceramics with x = 0, 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06 mol.% were synthesized by the solid-state combustion technique with calcination and sintering temperatures of 750 °C and 1150 °C, respectively, for 2 h. The phase formation, microstructure, dielectric, ferroelectric and energy storage properties of the BNBT-xLa ceramics were investigated. The XRD patterns of the powders showed a pure perovskite phase for all samples. The average particle size increased from 298 to 379 nm with increasing x. All ceramics showed coexisting rhombohedral and tetragonal phases. When x rose, the content of the tetragonal phase increased, as validated by the Rietveld refinement method. The average grain size decreased from 1.43 to 0.81 µm when x increased from 0 to 0.05 and then started to increase. The Curie temperature (T_d) of the samples shifted to lower temperatures with rising x, owing to an increased tetragonal phase. The maximum dielectric constant (ε_m), remanent polarization (P_r) and coercive field (E_c) decreased with increasing x. The BNBT-0.05La ceramic exhibited the smallest grain size, and lowest P_r = 0.8 µC/cm² and E_c = 2.9 kV/cm, with the highest energy storage efficiency (η ∼ 78.31%) and a large effective energy storage density (W ∼ 0.83 J/cm³) measured in an electric field of 80 kV/cm. [ABSTRACT FROM AUTHOR]