Effect of Samarium Doping on the Energy Storage Properties of Bismuth Sodium Titanate-Based Lead-Free Ceramics

Lead-free electroceramics have attracted significant research interest as alternatives to lead-containing systems due to concerns related to lead's toxicity to human health and the environment. Solid solutions based on bismuth sodium titanate (BNT) and barium titanate (BT), particularly those with compositions near the morphotropic phase boundary (MPB), such as 0.94 Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (BNT-6BT), exhibit promising piezoelectric and ferroelectric properties. In this study, samarium (Sm) was introduced to partially replace both Bi and Na ions within the structure of BNT-6BT, at concentrations of 0.5 and 5 mol %, in samples labeled as BNTS0.5 and BNTS5, respectively. The addition of Sm modifies the A-site disorder on a nanometer scale, resulting in a decrease of the temperature T_s corresponding to a frequency-dependent shoulder in the dielectric permittivity and a significant increase of the temperature T_m corresponding to the maximum permittivity. Additionally, it was found that BNTS0.5 ceramic exhibits a relatively high piezoelectric coefficient (d₃₃ = 164.7 pC N^-1), while BNTS5 shows high recoverable energy density and energy storage efficiency (W_rec = 3.88 J cm^-3 and η = 71.06%) at room temperature. With an exceptional recoverable energy storage intensity of 12.93 J V^-1 cm^-2 at room temperature, BNTS5 outperforms other similar materials, representing an excellent candidate for energy storage applications associated with the contribution of polar nanoregions. The two ceramics show significant potential for applications in piezoelectric energy conversion and energy storage devices.