Growth process and microwave absorption properties of nanostructured γ-MnO2 urchins

A low-temperature hydrothermal method was developed to synthesize urchinlike γ-MnO2 nanostructures. Time-dependent evolutions of morphology and crystallinity were investigated to explore the growth mechanism of the γ-MnO2 urchins. The results show that the growth process of the γ-MnO2 urchins occurs in two main stages, which are the generation of γ-MnO2 microspheres and the following epitaxial growth of γ-MnO2 nanoneedles on the surface of the initial microspheres. Microwave absorption properties of the urchinlike γ-MnO2 nanostructures were studied in terms of complex permittivity and permeability. An effective absorption bandwidth (reflection loss lower than −10 dB) of 8.8 GHz was achieved from the γ-MnO2/paraffin wax composite.