PASS‐Derived O/S Donor Field‐Directed Competitive–Cooperative Fe/Co Phase Evolution for Cross‐Band Microwave Absorption

ABSTRACT

Fe/Co bimetallic regulation enables high‐performance microwave absorbers, yet the role of intrinsic coordination disparity in precursor conversion, nonequilibrium phase evolution, and cross‐band loss redistribution remains unclear. We design a poly(arylene sulfide sulfone) (PASS)‐predefined O/S heterogeneous donor‐field strategy to direct competitive–cooperative nonequilibrium phase evolution in Fe/Co systems. Covalently embedded sulfone‐O and thioether‐S sites, with PASS's rigid backbone, create a molecularly preorganized donor field that amplifies non‐equivalent Fe/Co coordination, promoting competitive bonding, differentiated phase pathways, and electronic‐state reconstruction during confined pyrolysis. Fe/Co regulation thus reshapes local phases, O/S chemical environments, and interfacial charge states via Fe─O/Co─S coordination preferences, generating multiphase heterostructures, amorphous/crystalline interfaces, defects, and lattice strain while balancing dielectric polarization, conductive transport, magnetic response, and impedance matching. The resulting CFC absorber achieves cross‐band absorption in low‐frequency 5G and high‐frequency radar bands. CFC‐4 exhibits −73.83 dB at 6.23 GHz (3.20 mm) and −76.59 dB at 16.98 GHz (1.31 mm), with a maximum EAB of 5.03 GHz. CFC‐4∼6 (1–5 mm) show >90% cumulative effective absorption over 2–18 GHz. Finite‐element simulations reveal a maximum RCS reduction of 42.5 dB on PEC. This work establishes O/S donor‐field engineering as a viable route to amplify Fe/Co coordination differentiation for efficient cross‐band microwave absorption.