Stabilization of the ferrielectric phase in NaNbO3-based lead-free ceramics for a wide-temperature large electrocaloric effect

Abstract

The environmentally friendly antiferroelectric NaNbO₃ (NN) has attracted a great deal of attention in recent years due to its special structure and outstanding electrical properties; thus, many efforts have been made to modify its antiferroelectricity in order to achieve a repeatable double polarization–electric field (P–E) loop. In this work, the (1−x)NaNbO₃–xCaZrO₃ (NN–xCZ) system was chosen as a case study in order to reveal the origin of the realization of reversible antiferroelectricity through compositional modification. Through the construction of a phase diagram based on multi-scale structural analysis, the newly discovered high-temperature ferrielectric (FEi) phase with the P2₁ma space group moves to around room temperature after adding a secondary ABO₃ material, leading to the achievement of a repeatable triple P–E loop as well as a large electrocaloric effect in a wide temperature range. Owing to the gradual change in net polarization without a change in the modulation wave vector, the polymorphic phase transition from the antiferroelectric P phase to the new FEi phase on heating exhibits a weak dielectric anomaly with relaxor behavior in NN-based ceramics. The exploration of the mechanism of antiferroelectricity as well as its reversibility in NN-based lead-free ceramics would provide guidance for the design of high-performance materials with novel polarization configurations.