Effect of lanthanum doping on phase transition, piezoelectric and energy storage properties of lead-free 0.93(Bi\(_{0.5}\)Na\(_{0.5}\))TiO\(_{3}\)‒0.07BaTiO\(_{3}\) ceramics

In this study, lead-free (Bi0.465Na0.465Ba0.07)(1–x)LaxTiO3 (x=0.0‒0.04) ceramics were synthesized using a conventional solid-state reaction method. All samples showed a single-phase perovskite structure with pseudocubic symmetry. The dense microstructure revealed a decrease in average grain size as x increased. La3+ addition stabilized polar nanoregions (PNRs), shifting the ferroelectric to relaxor phase transition temperature (TF₋R=104℃ for x=0.0) to below room temperatures as La3+ content increased. This resulted in a transition from a rectangular to a relaxor-like thin P–E loop (x≥0.01), indicating a shift from ferro-electric (FE) to relaxor ferroelectric (RFE), which led to enhanced recoverable energy storage density (Wrec=0.55 J∙cm‒3 for x=0.01 and 0.02) and efficiency (η=75%) at x=0.03 under a 60 kV∙cm‒1 field. Additionally, the composition at x=0.01 achieved a maximum strain (Smax) of 0.21% with a high normalized strain of 350 pm∙V‒1 under 60 kV∙cm‒1 at ambient temperature. These changes in the physical and electrical properties of the A-site doped BNT-based system are attributed to alterations in domain structure and defect chemistry.