Harnessing Pseudo‐Jahn−Teller Disordering of Monoclinic Birnessite for Excited Interfacial Polarization and Local Magnetic Domains

Abstract The symmetry in a polymorph is one of the most important elements for determining the inherent lattice nature. The MnO 2 host tends to high‐symmetry MnO 6 octahedra as a result of the electronic structure t 2g 3 e g 0 of Mn 4+ ions, displaying an ordered structure accompanying with poor polarization loss and limiting its application toward high‐performance microwave absorbers. Here, a pseudo‐Jahn−Teller (PJT) distortion and PJT disordering design with abundant self‐forming interfaces and local magnetic domains in the monoclinic birnessite–MnO 2 host is first reported. The PJT distortion can give rise to asymmetric MnO 6 octahedra, inducing the formation of interfaces and increased electron spin magnetic moment in the lattice. The resultant birnessite with PJT distortions and PJT disordering delivers an outstanding reflection loss value of −42.5 dB at an ultralow thickness of 1.7 mm, mainly derived from the excited interfacial polarization and magnetic loss. This work demonstrates an effective approach in regulating the lattice structure of birnessite for boosting microwave absorption performance.