Design and wide range microwave absorption of porous Co-Co3O4 hybrid hollow sphere with magnetic multi-resonance mechanisms

Porous Co-Co3O4 hybrid hollow spheres were synthesized by a facile reduction method via hydrogen reduction of as-prepared C@Co3O4 solid spheres obtained by means of hydrothermal reaction between Co(NO3)(2) and D-glucose. Owing to the consumption of amorphous carbon of C@Co3O4 solid spheres and the generation of metallic Co phase and oxygen vacancies in Co3O4 crystals during high-temperature reduction process, the electrical conductivity of the composites was increased and a higher concentration of charge carriers was produced in Co3O4 crystal. The imaginary permittivity dispersion behaviors have been explained based on the Cole-Cole model and the conductivity contribution model. A new simple empirical model was also supposed to find the fitted curves of the multi-resonance imaginary permeability spectrum of the composites. The electromagnetic wave can hardly be reflected on the absorber surface because of a better match between dielectric loss and magnetic loss, which originates from the combination of dielectric polarization and magnetic multi-resonance mechanisms of the special Co-Co3O4 hybrid nanostructures. (C) 2015 Elsevier Inc. All rights reserved.