Phase Transitions in Bi/Ca Modified AgNbO ₃ Ceramics with Excellent Energy Storage Density and Storage Intensity

Lead-free antiferroelectric (AFE) ceramics based on AgNbO₃ represent attractive materials for energy storage applications but are limited by their recoverable energy density (W_rec). Here Bi³⁺/Ca²⁺ A-site modification of AgNbO₃ ceramics has yielded a particularly high W_rec of 4.4 J cm^-3 and a superhigh recoverable energy storage intensity (ρ) of 21.46 × 10^-3 J kV^-1 cm^-2 at 205 kV cm^-1, 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_f, to below room temperature, enhancing the room temperature stability of the AFE structure. The high W_rec is attributed to the enhancement of the maximum field-induced dielectric displacement and improved forward (E_F) and backward (E_B) fields. The work has also allowed for an examination of the poorly understood ±E_U current peaks evident in current-electric field loops of AgNbO₃-based ceramics, which is proposed to be related to a field-induced AFE to ferroelectric (FE) phase transition in the M₁ or M_2a phases and is absent in the M_2b phase due to increased stability of the AFE phase. The exceptional performance of Bi³⁺/Ca²⁺ modified AgNbO₃ ceramics is promising for potential use in ceramic capacitors for high pulsed power applications.