Modulated band structure and phase transitions in calcium hafnate titanate modified silver niobate ceramics for energy storage

Lead-free silver niobate (AgNbO3, AN)-based dielectric ceramics have attracted intense attention for high-power energy storage applications since 2016 due to their electric-field-assisted antiferroelectric-fermelectric phase transition. In this work, chemical compositions of 0.2 wt.% Mn-doped (1-x)AgNbO3-xCa(Hf0.2Ti0.8)O-3 (AN-CHTx, x = 0.00-0.08) were designed and their ceramic samples were prepared in flowing oxygen via solid-state route. Our results show that the CHT modification not only enhance the antiferroelectricity stability but also the breakdown field (E-b). Further investigation reveals that the wider band gap (E-g) and suppression of oxygen vacancy play more important role in increasing E-b of AN-CHTx ceramics. Consequently, an ultrahigh recoverable energy density (W-rec) of 5.4 J/cm(3) together with a relatively high energy conversion efficiency (eta) of 66% is achieved under an electric field of 300 kV/cm in AN-CHT0.06 ceramics. Meanwhile, this ceramic also exhibits a good thermal stability with W-rec (4.5 J/cm(3)) and eta (69%) over a wide temperature range (25-120 degrees C) under external electric field of 280 kV/cm. The finding in present work indicates that modulating the band structure and oxygen vacancy of AN-based ceramics may lead to the discovery of new antiferroelectric materials with pronounced energy storage properties.