Mn and O defect modulation in birnessite creates multiplicate polyhedra to improve dielectric and magnetic losses

<h2>Summary</h2> Single MnO₆ octahedra possess poor electrical conductivity, limited dipole content, and low electron spin magnetic moment in birnessites, which compromises their dielectric and magnetic loss capabilities. Here, we develop birnessite-Na_0.35Mn_0.92O_1.92<b>·</b>0.63H₂O with multiplicate polyhedra composed of MnO₆ octahedra and MnO₅ square pyramids via an Mn and O vacancy co-modulation approach. Through this modulation, poor electrical conductivity, limited dipole content, and low electron spin magnetic moment are prominently transformed by multiplicate polyhedra, resulting in much promoted dielectric and magnetic loss capabilities. This birnessite-Na_0.35Mn_0.92O_1.92<b>·</b>0.63H₂O with multiplicate polyhedra as an absorber can deliver a minimum reflection loss value of −56.4 dB with an effective absorption bandwidth of 2.7 GHz at a low thickness of 3.0 mm, demonstrating potential application in microwave absorption. This study provides important insights into how polyhedron structure influences electrical conductivity, dipole content, and electron spin magnetic moment to develop high-performance electromagnetic wave-absorbing materials for microwave absorption.