Ultrafast Preparation of High‐Entropy Rare‐Earth Borides via Joule Heating Toward Enhanced Microwave Absorption

ABSTRACT Modern electromagnetic wave (EMW) absorbers face challenges in simultaneously achieving high absorption efficiency, robust thermal/chemical stability, and strong environmental adaptability. This study addresses these limitations through the ultrafast synthesis of high‐entropy rare‐earth borides (HERBs) containing five to eight cations (Y, Dy, Gd, Nd, La, Sm, Yb, and Er) via Joule heating. This technique overcomes key drawbacks of conventional methods, such as carbon contamination, strict stoichiometric sensitivity, and severe grain coarsening, by enabling rapid (∼30 s), low‐temperature (1300°C) processing. The octonary HERB (8ReB 4 /8ReB 6 ), namely ((Y 1/8 Dy 1/8 Gd 1/8 Nd 1/8 La 1/8 Sm 1/8 Yb 1/8 Er 1/8 )B 4 /(Y 1/8 Dy 1/8 Gd 1/8 Nd 1/8 La 1/8 Sm 1/8 Yb 1/8 Er 1/8 )B 6 ), achieves a record‐high configurational entropy (2.08 R ), thereby inducing severe lattice distortion, numerous point defects, and significant microstrain. These structural features act as polarization centers, while the abundant heterogeneous interfaces promote interfacial polarization. Defect‐enhanced conduction loss combined with intrinsic magnetic properties optimizes the electromagnetic parameters, yielding exceptional impedance matching and attenuation capability. 8HERB exhibits outstanding microwave absorption performance, with a minimum reflection loss (RL min ) of −46.14 dB at 2.1‐mm thickness and an effective absorption bandwidth (EAB) of 3.52 GHz at 2.2‐mm thickness. Radar cross‐section simulations confirm superior wide‐angle stealth performance, with a maximum reduction of 32.55 dB·m 2 . This work establishes ultrahigh configurational entropy as a pivotal design strategy for enhancing dielectric/magnetic loss mechanisms and demonstrates Joule heating as an efficient, scalable route for developing advanced EMW absorbers with multifunctional stability.