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

Abstract

Abstract Lead-free (Na 1−3x Bi x )(Nb 0.75 Ti 0.25 )O 3 (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 Bi 3+ 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 Na 3 NbO 8 -NaNbO 3 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 (P max ) and smallest value of remnant polarization (P r ) were achieved at x = 0.1 due to orthorhombic NaNbO 3 and rhombohedral (Na 0.5 Bi 0.5 )TiO 3 coexistence phases. The substitution of monovalent (Na 1+ ) by trivalent (Bi 3+ ) 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 (W rec = 17.5 J cm −3 ) and energy storage efficiency ( η = 80%) were achieved at x = 0.1, E ∼ 700 kV cm −1 . Partially, (NNTB 0.1 ) 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 NaNbO 3 anti-ferroelectric ceramics.