Synergy of Oxygen Octahedra Distortion and Polar Nanodomains Induced Emergent Electrocaloric Effect in NaNbO₃-Based Ceramics

High-performance electrocaloric materials are essential for the development of solid-state cooling technologies; however, the contradiction of the electrocaloric effect (ECE) and temperature span in ferroelectrics frustrates practical applications. In this work, through modulating oxygen octahedra distortion and short-range polar nanodomains with moderate coupling strength, an EC value of Δ T ∼ 0.30 K with an ultrawide temperature span of 85 K is obtained in the x = 0.04 composition [(0.88 – x )NaNbO 3 –0.12BaTiO 3 - x LiSbO 3 ( x = 0–0.06)]. The LiSbO 3 dopant induces a P4bm -to- R3cH phase transition and intensifies the oxygen octahedra distortion degree, accompanied by the ferroelectric domain smashing into polar nanodomains. Also, LiSbO 3 addition enhances the relaxation degree with a downshift of T fd (ferroelectric-to-diffuse phase transition temperature) and T J (temperature of the maximal current density value), and T fd is shifted to near room temperature with an absence of T J in x = 0.04. Local energy barriers induced by oxygen octahedra distortion inhibit the phase transition in conjunction with activation of short-range polar order switching under thermal stimuli, which is the underlying mechanism for an excellent EC performance for x = 0.04. This work not only clarifies that ferroelectrics with oxygen octahedra distortion and short-range polar order are expected to achieve remarkable EC performances but also provides a design strategy to seek emergent EC behaviors in complex oxygen-octahedra-distortion materials.