Transformation between nanosheets and nanowires structure in MnO2 upon providing Co^2+ions and applications for microwave absorption

The phase transition process of the MnO2 phase with increases in Co^2+doping can be described by the Ouroboros symbol.The undoped sample is pureδ-MnO2 with nanosheets structures.Then a small amount of Co^2+ions changes the final products and generatesα-MnO2 nanofibres in theδ-MnO2 matrix.The products become pureα-MnO2 with an appropriate amount of Co added.However,when the Co amount continues to increase,the amount ofα-MnO2 decreases in the products and turns back to form pureδ-MnO2 in the end.Analysing the electromagnetic absorption performance,the relationship between the properties and the proportion ofδ-MnO2/α-MnO2 in the powders adjusted by Co^2+doping has been explored,and the composites ofδ-/α-MnO2 show better absorption ability than the single-phase samples.As a result,the optimal reflection loss(RL)is−54.8 dB,and the effective absorption bandwidth can cover the Ku band at a thickness of 2.2 mm and the X band at a thickness of 3.1 mm with 50 wt.%filler loading ratios.This research might shed new light on the improvement of novel microwave absorption materials.