Improving energy storage density, piezoelectric, and energy harvesting performances of eco-friendly (Bi_0.49−xBa_xLa_0.01Na_0.40K_0.10)TiO₃ ceramics by composition design strategy

In this research, eco-friendly (Bi_0.49−xBa_xLa_0.01Na_0.40K_0.10)TiO₃ or BiBa_xLNKT ceramics (where x = 0–0.15 mol fraction) were fabricated by solid-state mixed oxide technique, and their phase evolution, physical, microstructure, mechanical, dielectric, piezoelectric, ferroelectric, energy storage density, and energy harvesting properties have been systematically investigated. All ceramics exhibited a single perovskite structure. With increasing Ba content, a phase transition from mixed rhombohedral-tetragonal to be more tetragonal-rich phase was observed. The addition of Ba inhibited grain growth and resulted in densification, mechanical, and dielectric improvement. The maximum values of HV (6.01 GPa), HK (5.78 GPa), E (78 GPa), K_IC (1.38 MPa.m^1/2), ε_r (1604), and tan δ (0.0504) were observed for the x = 0.15 ceramic. The x = 0.15 ceramic also showed excellent piezoelectric performances (d₃₃ = 248 pC/N, g₃₃ = 17.46 × 10⁻³ Vm/N, and k_p = 49%) and good off-resonance figure of merit (FoM) for energy harvesting (4.33 pm²/N). Moreover, after the introduction of Ba content, the ferroelectric long-range order is broken, which contributes to energy storage density improvement. Especially, the x = 0.05 ceramic achieved excellent recoverable energy storage density (W_rec = 1.31 J/cm³) and good energy storage efficiency (η = 96.18%) at 150 °C under driving electric fields (E) of 75 kV/cm. All results indicated that we can efficiently fabricate an environment-friendly (Bi_0.49−xBa_xLa_0.01Na_0.40K_0.10)TiO₃ system with good reliability for energy harvesting and high-temperature energy storage capacity applications.