Structural, thermally stable dielectric, and energy storage properties of lead-free (1 − x)(Na0.50Bi0.50)TiO3 − xKSbO3 ceramics

Abstract

Effect of substitution and external applied static electric field on the structural and dielectric properties for lead-free (1 − x)(Na0.50Bi0.50)TiO3 − xKSbO3 (0 ≤ x ≤ 0.06) polycrystalline ferroelectric ceramics, fabricated via a modified sol–gel method, were investigated. Structural analysis of synchrotron radiation X-ray diffraction data confirmed the rhombohedral R3c phase for all unpoled samples. After poling, the tetragonal P4bm phase appeared with the rhombohedral phase in all the substituted samples. In poled samples, the phase fraction of the rhombohedral phase suppressed from ~ 93 (for x = 0.03) to ~ 87% (for x = 0.06), while tetragonal phase fraction increased from ~ 7 to ~ 13% as a function of substitution. The high-temperature dielectric analysis confirmed the reduction in depolarization temperature with increasing substitution. Also lattice disorder creates a plateau type dielectric anomaly, which leads to thermally stable dielectric constant ~ 2970 ± 10% (200–390 °C) and ~ 2830 ± 10% (125–400 °C) for x = 0.03 and 0.06 samples, respectively. Ferroelectric measurements showed that ambient temperature ferroelectric properties are improved for x = 0.03 composition with an observed remnant polarization (2Pr ~ 53.4 µC/cm2) and coercive field (2Ec ~ 94.7 kV/cm) as compared to parent NBT compound (2Pr ~ 44.7 µC/cm2, 2Ec ~ 124.5 kV/cm). In addition, at high-temperature, antiferroelectric like ordering enhances the recoverable energy density ~ 0.73 J/cm3 (efficiency ~ 72.3%) for x = 0.06 samples as compared to parent NBT (recoverable energy density ~ 0.05 J/cm3, efficiency ~ 2.4%). These improvements in electrical properties were correlated with structural changes as a function of composition and temperature. Obtained properties suggest that substituted samples might be a suitable candidate for high-temperature stable capacitors (operating temperature > 200 °C), ferroelectric, and energy storage applications.