Linear-like lead-free relaxor antiferroelectric (Bi0.5Na0.5)TiO3–NaNbO3 with giant energy-storage density/efficiency and super stability against temperature and frequency
A novel lead-free polar dielectric ceramic with linear-like polarization responses was found in (1 − x)(Bi0.5Na0.5)TiO3–xNaNbO3 ((1 − x)BNT–xNN) solid solutions, exhibiting giant energy storage density/efficiency and super stability against temperature and frequency. High-resolution transmission electron microscopy, Raman scattering and Rietveld refinements of X-ray diffraction data suggest that these property characteristics can be derived from temperature and electric field insensitive large permittivity as a result of relaxor antiferroelectricity (AFE) with polar nanoregions. Additionally, this feature intrinsically requires a high driving field for AFE to ferroelectric (FE) phase transitions due to large random fields. Measurements of temperature-dependent permittivity and polarization versus electric field hysteresis loops indicate that the high-temperature AFE P4bm phase in BNT was gradually stabilized close to room temperature, accompanying a phase transition from relaxor rhombohedral FEs to relaxor tetragonal AFEs approximately at x = 0.15–0.2. A record high of recoverable energy-storage density W ∼ 7.02 J cm−3 as well as a high efficiency η ∼ 85% was simultaneously achieved in the x = 0.22 bulk ceramic, which challenges the existing fact that W and η must be seriously compromised. Furthermore, desirable W (>3.5 J cm−3) and η (>88%) with a variation of less than 10% can be accordingly obtained in the temperature range of 25–250 °C and frequency range of 0.1–100 Hz. These excellent energy-storage properties would make BNT-based lead-free AFE ceramic systems a potential candidate for application in pulsed power systems.