Suppression of the ferroelectric phase for (K0.5Na0.5)NbO3 ceramic by A/ B-sites disorder for enhancement the energy storage properties and dielectric breakdown strength

In the present study, we propose a new strategy called suppression ferroelectricity of (K0.5Na0.5)NbO3 (KNN) lead-free ceramics for significant enhancement of energy storage properties (ESPs) and dielectric breakdown strength (DBSs). Both of pure KNN and (Na0.6Ag0.1Bi0.1)(Nb0.8Ti0.25)O3 (abbreviate NN-ABT) were synthesized using solid reaction technique. The crystal structure, dielectric and ferroelectric properties of both prepared ceramics were investigated. NN-based ceramics shown ferroelectric to relaxor phase crossover with pseudo-cubic crystal structure at ambient temperature. Present relaxor phase is attributed to substitution of monovalent (K1+) by trivalent (Bi3+) which can cause A-site cation vacancies and charge misfit of KNN lattice. The inhabitation of grain size to sub-micrometer observed by scanning electron microscope and this could be attributed to the lower ionic radius of (Ag1+ = 1.15 & ANGS;) and (Bi1+ = 1.38 & ANGS;) compared to (K1+ = 1.64 & ANGS;) which can suppressed the tolerance factor (& tau;) from 1.01 for KNN (ideal ferroelectric phase) to & tau; = 0.85 for NN-ABT . Suppression of the (& tau;) value can enhanced the degree of the relaxor phase, while inhibition of grain size can improved the DBSs or Eb. Superior enhancement of energy storage properties were achieved in NN-based ceramic due to hybridization between Bi3+ 6 P and O2- 2 P orbitals instead of K1+ 1 S and O2- 2 P orbitals which resulting in increasing the maximum polarization. The results shown that (NN-ABT) is acquired the preeminent of recoverable energy storage density Wrec - 11 J/cm3, energy storage efficiency (n = 89%) at E = 550 kV/cm. Furthermore, the sample shown an excellent thermal and frequency stabilities variation in a wide range of temperature (25-175 degrees C) and frequency (2-50 Hz). The significant enhancement in energy storage performance of NN-ABT ceramic is attributed to disturb the ferroelectric phase of KNN and forming PNRs of relaxor phase at ambient temperature. Therefore, the present study provides a good guideline for optimizing the ESPs and DBSs of NNbased ceramics to be more applicable for pulsed power and energy storage applications.

Automated summary

In this study, a new strategy called suppression ferroelectricity of KNN lead-free ceramics was proposed for enhancing energy storage properties and dielectric breakdown strength. The synthesis of KNN and NN-ABT ceramics using the solid reaction technique was conducted, and their crystal structure, dielectric, and ferroelectric properties were studied. The results showed that by inhibiting grain size and modifying the crystal structure, significant improvement in energy storage performance and dielectric breakdown strength could be achieved.