Robust Electrocaloric Performance Enabled by Highly-Polar Frustrated Nanodomains in NaNbO3-Based Ferrodistortive Relaxor

Abstract

Solid-state refrigeration technologies, represented by electrocaloric effect (ECE), are renowned for zero global-warming-potential and high cooling efficiency. Synergistically achieving high electrocaloric effect ({\Delta}T) and wide temperature span ({\Delta}Tspan) for EC materials takes a leapfrog toward practical cooling applications, typical for integrated circuits. Guided by phase-field simulation, Ba(Ti, Hf)O3 dubbed as a polar wrench, establishes polar frustration by setting up local stress field and manipulating octahedral oxygen tilt (OOT) in NaNbO3-based relaxor. The resultant P4bm framework entails short-range and highly-polar ferrodistortive nanodomains, i.e., the abundant highly-polar nanodomains facilitate to increase entropy change and robust OOT enables to impede thermal perturbations. Consequently, a large {\Delta}T of 0.85 K and 0.70 K with an ultrawide {\Delta}Tspan of 118 K and 130 K is obtained, contributing to an ultrahigh figure of merit of > 90 K2 in NaNbO3-Ba(Ti, Hf)O3, significantly outperforms its counterparts. The local structure responsible for robust EC performances are decrypted through 2D information from atomic-resolution scanning transmission electron microscope, 3D big-box model constructed from neutron total scattering and DFT calculations. These findings highlight that polar frustration strategy in ferrodistortive relaxor enables to pioneer emergent EC performances, and also unearth potential entropy-change-based ferroelectric and ferromagnetic materials beyond.