Enhanced Electrocaloric Performance in NaNbO3-Based Ferrodistortive Relaxors by Regulating Oxygen Octahedra Configuration and Domain Structure

Abstract

As an alternative to traditional vapor-compression refrigeration, electrocaloric (EC) cooling features high efficiency, convenient miniaturization, and integration. The paradox of simultaneously realizing a high adiabatic temperature change (ΔT) and temperature stability is hardly resolved in conventional relaxors, thus hindering further applications. Emerging NaNbO₃-based ferrodistortive relaxors are poised to achieve the goal of the “best of both worlds”. In this work, (0.82 – x)NaNbO₃–0.18BaTiO₃–xBaSnO₃ (x = 0, 0.01, and 0.02) compositions are designed. Results demonstrate that BaSnO₃ doping effectively regulates the oxygen octahedral tilt (OOT) degree, improves lattice structural stability, and facilitates the transition of long-to-short order polar nanodomains. These are verified by micro/local structure characterizations of Rietveld refinements, transmission electron microscopy, and piezoelectric force microscopy. Such evolution establishes a robust OOT framework and highly correlated slush polar nanodomains. This endows x = 0.01 and 0.02 compositions with a maximal ΔT of 0.70/0.55 K at an electric field of 10 kV/mm and an ultrawide temperature span of 99/104 K, respectively, which is superior to most lead-based and lead-free counterparts. Notably, a comprehensive physical panorama of OOT configuration, domain structure, and EC performances is covered. This work provides a useful compositional extension for designing high-performance EC devices.