The smallest anions, induced porosity and graphene interfaces in C12A7:e− electrides: a paradigm shift in electromagnetic absorbers and shielding materials

Abstract

Advanced conducting ceramics with desirable high-frequency electromagnetic responses are essential to function as fifth-generation (5G) microwave absorbing and shielding materials. Mayenite electride (C12A7:e⁻) is a room-temperature stable ionic solid having unique structural features and consist of anionic electrons trapped inside positively charged sub-nanometer cages. This is the first report focusing on developing a 5G microwave absorber and shielding material based on the highly conducting and chemically stable C12A7:e⁻ with induced porosity and modified graphene (MG) interfaces. This material exhibits an EMI shielding effectiveness of 34.8 dB at 26.5 GHz for a thickness of 2.5 mm and an average specific shielding effectiveness of 107 dB cm² g⁻¹, a comparatively better result among ceramic composites. Unlike the conventional microwave absorbing materials, C12A7:e⁻ exhibits impedance matching at high frequencies and is verified theoretically by delta-parameter evaluation. The microwave absorption from 5 to 40 GHz exhibits a minimum reflection loss of −22.9 dB at 30.9 GHz for a thickness of 2.54 mm with an ultra-high bandwidth of 10.1 GHz. The unique structure-derived electromagnetic response and various dissipation mechanisms like high electrical conductivity, polarizations from the cavity-trapped electron anions, interfacial polarizations at macropores and MG/C12A7:e⁻ interfaces, and dipolar polarization at defect sites in MG makeC12A7:e⁻ a potential candidate for microwave attenuation in 5G bands.