The microwave electromagnetic characteristics of manganese dioxide with different crystallographic structures

MnO₂ with different morphologies and crystal structures were prepared via a low-temperature hydrothermal method in a stainless-steel autoclave at 120 °C at different dwell times. The products were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electromagnetic and microwave-absorption properties of the as-obtained MnO₂ were reported. The results show that the different dwell times play a crucial role in the phase purity, the crystal structure, the morphology, and the electromagnetic properties of the products. The real and imaginary parts of the complex permittivity of the as-prepared MnO₂ increased systematically with increasing dwell times, while the complex magnetic permeability values showed the contrary. The absorbing peak value of the reflection loss of the MnO₂/paraffin wax visibly shifted to the lower frequency band with the increase in the reaction times of the MnO₂ products. The microwave absorption properties of the MnO₂ products were mainly attributed to both the dielectric and magnetic losses. In the total loss, however, the dielectric loss played the more important role, especially in the dielectric polarization loss versus frequency test.