Thermally robust energy-storage performance of BaMg1/3Nb2/3O3-modified 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 relaxor ceramics

In this work, a series of (1 − x)[0.94Bi 0.5 Na 0.5 TiO 3 –0.06BaTiO 3 ]–xBaMg 1/3 Nb 2/3 O 3 (BNBM, x = 0.03, 0.05, 0.07, 0.09, named as BNBM3, BNBM5, BNBM7, BNBM9) ceramic compositions were synthesized via a conventional solid-state route to systematically investigate the effects of BaMg 1/3 Nb 2/3 O 3 substitution on structural evolution, dielectric relaxation, dielectric thermal stability and energy-storage behaviour. Structural analysis reveals a transition from the tetragonal P4bm structure of the parent BNT–BT to an average pseudo-cubic Pm 3 ¯ m structure upon BMN incorporation. Raman spectroscopy further evidences local rhombohedral/tetragonal-like distortions and enhanced local structural disorder associated with BMN-induced B-site modification. UV–Vis analysis shows a gradual increase in the optical band gap from 3.10 eV for pure BNT–BT to ∼3.19 eV for the BMN-modified ceramics, indicating modification of the local electronic environment. All compositions exhibited pronounced relaxor ferroelectric behaviour, while the BNBM5, BNBM7, and BNBM9 compositions demonstrated excellent thermal stability of dielectric permittivity (Δε r /ε r ≤ ±15%) over a broad temperature range extending up to ∼384 °C. Polarization–electric field (P–E) measurements exhibited slim hysteresis loops, indicating low remnant polarization and reduced hysteresis loss, which are favorable for energy-storage applications. Among the investigated compositions, BNBM3 delivered the best overall performance, exhibiting a recoverable energy density (W rec ) of ∼0.708 J cm −3 , a total energy density (W tot ) of ∼0.97 J cm −3 , and an energy efficiency of ∼73% at 80 kV/cm at room temperature. At room temperature, BNBM5 achieved the highest energy efficiency (∼74%), while BNBM7 and BNBM9 exhibited slightly lower energy densities but maintained stable efficiencies along with excellent thermal stability. The normalized total energy density of BNBM3 reached ∼12.2 mJ kV −1 cm −2 at room temperature and remained as high as ∼8.65 mJ kV −1 cm −2 at 170 °C, with the energy efficiency increasing to ∼93% due to temperature-induced slimming of the P–E loops. Furthermore, the negligible variation in energy-storage parameters with frequency and temperature confirms excellent operational stability. Overall, the optimized BNBM ceramics exhibit a desirable balance of high energy density, superior efficiency, and excellent thermal robustness, making them promising candidates for high-temperature dielectric energy-storage capacitors.