Insight into electromagnetic absorbing performance of MnO2 from two dimensions: Crystal structure and morphology design

Crystal structure design and the relevant morphology design are two main methods to get a quality microwave absorber. To figure out the effective mechanism of these two factors on microwave absorption, MnO2 was chosen due to the characteristic of multiphase and multimorphology. In this paper, four independence samples have been successfully obtained, combining with the dipole calculation, the efforts of phases (alpha and delta) and morphologies (nanowires and microspheres) of MnO2 on microwave absorption performance have been full-scale discussed. Due to the larger dipole moment and higher conductivity, the alpha-MnO2 perform better dielectric loss than delta-MnO2; nanowires with more interfaces and trapping centers is the optimal structure for the absorbers compared with microspheres. As a result, nanowires-alpha-MnO2 (NA) shows the best absorption performance, reflection loss value of NA-wax composite can reach - 39.6 dB at 2.64 GHz with 6 mm thickness, and effective absorbing can be achieved in the band of 2.4-18 GHz by selecting the proper thickness of absorber. This work not only provides the design concept of MnO2 as microwave absorbing materials, but also exhibits the insight that to get an excellent absorber is to synthesize the proper kind of materials and optimize the microstructure.