Phase Transitions in Bi/Ca Modified AgNbO Ceramics with Excellent Energy Storage Density and Storage Intensity.

Lead-free antiferroelectric (AFE) ceramics based on AgNbO represent attractive materials for energy storage applications but are limited by their recoverable energy density (W). Here Bi/Ca A-site modification of AgNbO ceramics has yielded a particularly high W of 4.4 J cm and a superhigh recoverable energy storage intensity (ρ) of 21.46 × 10 J kV cm at 205 kV cm, the latter being the highest known value obtained at such a relatively low field for a lead-free ceramic. The modification shifts the dipole freezing temperature, T, to below room temperature, enhancing the room temperature stability of the AFE structure. The high W is attributed to the enhancement of the maximum field-induced dielectric displacement and improved forward (E) and backward (E) fields. The work has also allowed for an examination of the poorly understood ±E current peaks evident in current-electric field loops of AgNbO-based ceramics, which is proposed to be related to a field-induced AFE to ferroelectric (FE) phase transition in the M or M phases and is absent in the M phase due to increased stability of the AFE phase. The exceptional performance of Bi/Ca modified AgNbO ceramics is promising for potential use in ceramic capacitors for high pulsed power applications.