Lead-Free Relaxor Ferroelectrics Based on Bi0.5Na0.5TiO3 Achieve Excellent Energy Storage Performance through Equivalent High-Entropy Doping

Title

J. Eur. Ceram. Soc.: Lead-Free Relaxor Ferroelectrics Based on Bi_0.5Na_0.5TiO₃ Achieve Excellent Energy Storage Performance through Equivalent High-Entropy Doping

Research Background

Dielectric ceramic capacitors are widely used in pulse power systems and hybrid electric vehicles due to their ultra-high power density, ultra-fast charge-discharge rates, wide operating temperature range, and low cost. However, their low energy storage density and efficiency limit miniaturization, lightweight design, and integration. The high-entropy strategy is recognized to improve the energy storage performance of dielectric materials, but the underlying mechanisms need further exploration. Bi_0.5Na_0.5TiO₃ (BNT) based ceramics, as environmentally friendly lead-free candidates, exhibit high P_max but low breakdown strength (E_b) and high remnant polarization (P_r), resulting in low recoverable energy density (W_rec) and efficiency (η). Previous studies have shown the potential of high entropy, but the performance is still far from meeting practical application requirements.

Research Content

① A series of (Bi_0.25La_0.25Na_0.25K_0.25)Ti_1-xZr_xO₃ (BLNKTZ) ceramics were prepared by equivalent doping of La/K and Zr, varying configuration entropy (ΔS_config).

② Structural characterization showed that the increase in entropy led to grain refinement, phase transition to pseudo-cubic phase, formation of multi-phase polar nanoregions (PNRs), and improved lattice integrity.

③ Electrical performance tests indicated that the P-E loops became thinner, and E_b significantly increased (from 100 kV/cm to 675 kV/cm), enhancing energy storage performance.

④ The optimal sample (x=0.05, ΔS_config=1.58R) achieved W_rec=6.6 J/cm³ and η=84%, and tested for temperature/frequency stability.

⑤ Charge-discharge performance showed high power density (129 MW/cm³) and fast discharge speed (51 ns), demonstrating excellent fatigue resistance.

Innovations

① The equivalent high-entropy doping strategy avoids the valence state fluctuations caused by aliovalent doping, reduces structural defects, and improves lattice integrity and stability.

② By combining common advantages of high entropy such as multi-phase PNRs and ultra-fine grains, high E_b and linearized P-E loops are achieved, enhancing energy storage performance.

③ Doping with La³⁺ and Zr⁴⁺ reduces the concentration of oxygen vacancies, enhances metal-oxygen bonds, and improves structural stability and energy storage efficiency.

Paper Summary

This study introduces La³⁺/K⁺ (equivalent to Bi³⁺/Na⁺) and Zr⁴⁺ (equivalent to Ti⁴⁺) into BNT-based ceramics through the equivalent high-entropy doping strategy, resulting in BLNKTZ ceramics. As entropy increases, grain size decreases (from 0.79μm to 0.31μm), polar phases decrease, multi-phase PNRs increase, lattice integrity improves, and oxygen vacancy concentration decreases. The optimal sample (ΔS_config=1.58R) exhibits excellent energy storage performance: W_rec=6.6 J/cm³, η=84%, with outstanding temperature stability (30-100°C variation <12%), frequency stability (50-3000 Hz variation <6%), fatigue resistance (change <1.6% after 10⁷ cycles), high power density (129 MW/cm³) and fast discharge speed (51 ns). This work highlights equivalent high-entropy doping as a viable strategy, providing key insights for a wide range of material design.

Original Article

doi:10.1016/j.jeurceramsoc.2025.117837