PVP-assisted hydrothermal synthesis of rod-like NiCo2O4 powders as high-performance microwave absorbers

Rod-like NiCo2O4 powders were synthesized by hydrothermal method in the presence of polyvinylpyrrolidone (PVP) surfactant for absorption the microwaves (1–18 GHz). The structural, microstructural, magnetic, and electromagnetic properties were analyzed by various characterization techniques. By adding the PVP surfactant, the wood-like texture morphology was transformed to the rod-like morphology composed of spherical nanoparticles (∼15 nm). The single-phase NiCo2O4 obtained by PVP agent had the higher crystallinity and oxygen vacancies in compared with the wood-like texture NiCo2O4 morphology. The specific surface area and pore volume decreased from 83 to 65 m2/g and from 0.13 to 0.05 cm3/g by using PVP agent, respectively. The rod-like NiCo2O4 powders exhibited the wider effective absorption band of ∼4.9 GHz in the Ku (12–18 GHz) band at a matching thickness of 1.4 mm in comparison with 3.9 GHz for the wood-like NiCo2O4 powders at the matching thickness of 1.2 mm. The better microwave absorption performance of the rod-like NiCo2O4 powders was attributed to their good impedance matching caused by their lower permittivity and higher permeability.