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 [(Bi0.5Na0.5)0.94Ba0.06]1-xLaxTiO3 (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 (Td) of the samples shifted to lower temperatures with rising x, owing to an increased tetragonal phase. The maximum dielectric constant (εm), remanent polarization (Pr) and coercive field (Ec) decreased with increasing x. The BNBT-0.05La ceramic exhibited the smallest grain size, and lowest Pr = 0.8 µC/cm2 and Ec = 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.