Effect of Na2+ and Bi3+ substitution in lead-free BZT-Pr multifunctional ceramics for energy storage and thermal energy conversion

For this study, Ba_1−y−xPr_2y/3□_y/3(Na_0.5Bi_0.5)_xTi_0.9Zr_0.1O₃ (y = 0.5%; x = 0.05, 0.1 and 0.15) (abbreviated as BZT-Pr–xNBT) ceramics were prepared by a solid state reaction method. The samples were structurally characterized by X-ray diffraction (XRD) and the software Fullprof, which showed the atomic positions, bond distances, and bond angles of these materials in the tetragonal structure. The crystallite size, determined by both the Williamson–Hall and Debye–Scherrer methods, increases with increasing Na_0.5Bi_0.5TiO₃ (abbreviated as NBT) content in Ba_1−yPr_2y/3□_y/3Ti_0.9Zr_0.1O₃ (y = 0.5%) (abbreviated as BZT-Pr) ceramic. The ultraviolet-visible (UV-Vis) diffuse reflectance spectrum indicated that the BZT-Pr–xNBT ceramics exhibited direct band gap values in the range of 2.90–2.78 eV. Moreover, this study investigates the ferroelectric, energy storage, and pyroelectric energy harvesting properties of BZT-Pr–xNBT ceramics with varying NBT contents (x = 0.05, 0.10 and 0.15). The results reveal that NBT substitution significantly influences the ferroelectric characteristics and enhances recoverable energy storage density (W_rec) and energy storage efficiency (η). Temperature-dependent scaling relations for the coercive field (E_C) and remnant polarization (P_r) were derived for all samples. For BZT-Pr–0.15NBT ceramic, the scaling relation for E_C and P_r (E_C ∝ T^−0.089, P_r ∝ T^−0.233) highlights improved thermal stability in this composition. Pyroelectric energy harvesting under the Olsen cycle identified BZT-Pr–0.05NBT as the most efficient composition. These findings emphasize the crucial impact of NBT substitution in optimizing the ferroelectric and pyroelectric properties of BZT-Pr–xNBT ceramics.