Tunable negative permittivity behavior and electromagnetic shielding performance of silver/silicon nitride metacomposites

•A plasma-like negative permittivity was observed in the metacomposites, which resulted from the low frequency plasmonic state provided by formed silver networks.•The frequency band and absolute magnitude of negative permittivity could be adjusted by controlling Ag content, which was well described by Drude model. It was found that the construction of inductive conductive networks was vital for effectively tailoring the negative permittivity.•The average total SE of our obtained metacomposite with high Ag content could reach ~30 dB. The reflection was the primary electromagnetic shielding mechanism, which was attributed to the intense impedance mismatching originated from the negative permittivity.•The larger magnitude of negative permittivity resulted in stronger impedance mismatching, which made the SE value get larger in the metacomposites. The recent rise of metacomposites offered a new research strategy for electromagnetic shielding materials owing to their negative electromagnetic parameters, such as negative permittivity. Herein, we prepared silver/silicon nitride (Ag/Si3N4) metacomposites with tunable negative permittivity by a facile impregnation-calcination process, and explored their electrical conductivity, permittivity and electromagnetic shielding properties. As the Ag content increased, formative metal networks in the composites rendered their conductivity characteristic changing from a hopping conductivity to a metal-like conductivity. Tunable negative permittivity behavior combined with enhanced shielding effectiveness (SE) was observed at 2–18 GHz in the metacomposites with high Ag contents. The plasma-like negative permittivity was accounted for by a low frequency plasmonic state of free electrons in the inductive Ag networks, and the frequency band and absolute magnitude of negative permittivity could be adjusted by controlling Ag content, which was well described by Drude model. The average total SE of our obtained metacomposite could reach ~30 dB, and the reflection was the primary shielding mechanism, which was attributed to the intense impedance mismatching stemmed from the negative permittivity. Our work opens up the possibility of designing metacomposites for promising electromagnetic shielding materials, promoting their application in microwave field.