Enhanced energy storage performance in reaction-sintered AgNbO₃ antiferroelectric ceramics

In this research, AgNbO₃ ceramics were produced by two sintering methods: reaction sintering (RS) and conventional solid-state sintering (CSSS). The process was similar for both methods, except that in RS, Ag₂O and Nb₂O₅ precursors were mixed, then formed into pellets, skipping the calcination step, and sintered at 1100 °C for 6 hours. Both prepared ceramics had the same perovskite crystal structure with an orthorhombic crystal system and Pbcm and Pmc2₁ space groups with similar lattice dynamic vibration modes at room temperature. The average grain size of the polycrystalline samples prepared by RS and CSSS was found to be ∼2.03 ± 0.77 and ∼1.85 ± 0.96 μm, respectively. The relative bulk densities of the ceramics produced by RS and CSSS were found to be ∼94.0 ± 1.8 and ∼96.5 ± 1.3%, respectively. Ceramics prepared by both methods showed antiferroelectric behavior, and reaction-sintered AgNbO₃ ceramics exhibited lower energy loss density than CSSS samples. In addition, a recoverable energy storage density (W_rec) of 3.1 J cm^-3 and higher energy storage efficiency (η) for RS samples were measured at 175 kV cm^-1. Moreover, the η values of 74.2% and 57.7% were measured for samples sintered by RS and CSSS, respectively. This energy storage efficiency is the highest ever reported for pure AgNbO₃ ceramics. Furthermore, reaction-sintered samples showed good temperature stability for W_rec and η in the 30-80 °C temperature range.