Moderation of [Bi3+/Na1+] molar ratio for enhancement of dielectric and energy storage properties of NaNbO3 ceramics

Abstract

Lead-free (Na1−3xBix)(Nb0.75Ti0.25)O3 (x = 0.0, 0.05, 0.1, 0.125 and 0.15) (NN-BT) ceramics were synthesized using solid-state reaction technique. The effect of Bi3+ into the crystal structure, dielectric, ferroelectric and energy storage properties of NNT ceramics were investigated. Pure NNT shows present perovskite structure with orthorhombic crystal structure at x ≤ 0.125, while Na3NbO8-NaNbO3 composite phase has been detected at x = 0.15. The tolerance factor (τ) decreased from 0.97 (x = 0.0) to 0.82 (0.15) which signified the composition deviated from perovskite structure at 0.15. Significant enhancement of dielectric constant at room temperature has been achieved by increasing Bi-content and the maximum value (∼1500) obtained at 0.1. The largest value of maximum polarization (Pmax) and smallest value of remnant polarization (Pr) were achieved at x = 0.1 due to orthorhombic NaNbO3 and rhombohedral (Na0.5Bi0.5)TiO3 coexistence phases. The substitution of monovalent (Na1+) by trivalent (Bi3+) lead to create sodium vacancies into the A-sites of NNT lattice subsequently increased the cations disorder and charge misfit. The maximum recoverable energy storage density (Wrec = 17.5 J cm−3) and energy storage efficiency (η = 80%) were achieved at x = 0.1, E ∼ 700 kV cm−1. Partially, (NNTB0.1) exhibit an outstanding stability of energy storage properties in terms of temperature range (25 to 150 °C) and frequency stability (2–20Hz). The present results imply the moderation ratio of Bi/Na plays an important role for enhancement of energy storage properties of NaNbO3 anti-ferroelectric ceramics.