Novel complex-perovskite NaNbO₃ − Bi(Li_1/3Hf_2/3)O₃ lead-free ceramics with improved energy-storage performance and reduced leakage current

Dielectric capacitors are gaining attention due to their significant applications in high-power electronics. However, achieving both high efficiency and excellent energy storage density in lead-free ceramics remains challenging. This study investigates the impact of incorporating the Bi complex perovskite compound Bi(Li_1/3Hf_2/3)O₃ (BLH) into NaNbO₃, creating novel (1 − x)NaNbO₃ − xBi(Li_1/3Hf_2/3)O₃, x = 0 − 0.10, ceramics. The XRD results revealed a pure perovskite structure for 0 ≤ x ≤ 0.10 compositions, with a structural change from orthorhombic to pseudo-cubic at x = 0.04. The average grain size significantly decreased from 8.04 μm (x = 0.0) to 0.78 μm (x = 0.08) before experiencing a slight increase. As BLH content increased, changes in dielectric properties demonstrated a successive replacement of the antiferroelectric (AFE) P phase with the relaxor AFE R phase, which is consistent with the Raman spectroscopic data. Moreover, increasing BLH resulted in reduced leakage current density and significant increase in resistivity (ρ). Enhanced relaxor characteristics, smaller grain size, lower dielectric loss, lower leakage current density, and higher resistivity synergistically contributed to an improvement in the electrical breakdown strength (E_b). This led to optimal energy storage performance for the composition with x = 0.08, yielding energy-storage density (W_rec) of 0.85 J/cm³ and energy storage efficiency (η) of 78% under applied electric field of 165 kV/cm. The optimum composition also exhibited temperature stability in the range of 25–150 °C. This research provides a guideline for developing lead-free ceramics with improved energy storage density and energy storage efficiency, suitable for applications in electronic devices or energy-storage technology.