Rational A-Site Entropy Engineering in Perovskites: Dual-Exchange Enhanced Magnetoelectric Coupling for Ultra-Efficient Microwave Absorption.

High-entropy engineering at the A-site, combined with the variable valence states of Mn ions and diverse bonding configurations of perovskite elements and structures, presents new opportunities for the development and application of high-temperature electromagnetic wave-absorbing materials. In this study, the magnetic and dielectric properties of AMnO₃ are controlled by designing A-site elements with various ionic radii and entropies. The microwave-absorption performance of (La_0.2Ba_0.2Sr_0.2Ca_0.2Na_0.2)MnO₃ high-entropy perovskites is significantly higher than those of AMnO₃ with different ionic radii and (Ba_1/3Sr_1/3Ca_1/3)MnO₃ medium-entropy perovskites. Specifically, the high-entropy samples exhibit a minimum reflection loss (RL_min) of -60.86 dB at a thickness of 1.0 mm and an effective absorption bandwidth of 3.26 GHz, whereas the medium-entropy ceramics show RL_min values of -17.93 and -44.59 dB at 8.5 mm ((Ba_1/3Sr_1/3Ca_1/3)MnO₃) and 8.8 mm ((La_0.25Ba_0.25Sr_0.25Ca_0.25)MnO₃), respectively. In high-entropy perovskites, aliovalent ions and oxygen vacancies at the A-site promote exchange interactions between Mn─O─Mn bonds, enhancing magnetism. Additionally, oxygen vacancies and lattice distortions in high-entropy systems enhance the dielectric loss, achieving magnetoelectric cooperative coupling in high-entropy perovskites. This work provides a new research direction for designing single-phase perovskites with excellent electromagnetic wave-absorbing properties via magnetoelectric cooperative-loss coupling.