Effect of Cu doping on structure, morphology, and microwave absorption performance of MnO₂

Doping is an effective method to modify the physical and chemical properties of materials by altering their local lattice structure and electronic structure. Herein, manganese dioxide (MnO₂) was modified with Cu, which has a large atomic radius, in order to obtain excellent electromagnetic absorption materials. Both experimental and theoretical methods were employed to investigate the effect mechanism of doping on the structure and properties of MnO₂. After Cu doping, the (100) surface energy of MnO₂ decreases and becomes more stable. Numerous thick secondary MnO₂ nanowires are generated from primary thinner nanowires to eliminate the higher-energy (110) surfaces, which act as the force to drive the oriented attachment. At the atomic level, heteroatom Cu promotes electron rearrangement, leading to an increase in both energy and length of Mn–O bonds. Consequently, diploe polarization increases and dielectric response is enhanced after Cu doping. However, due to the large diameter of nanowires, surface polarization is reduced, and excessive Cu doping weakens the electromagnetic response. As a result, when doping ratio Cu/Mn = 1/8, Cu-doped MnO₂ exhibits an ultra-wide effective absorption bandwidth of 6.64 GHz with a thickness of 2 mm and a filler ratio of just 20 wt%. These findings provide both theoretical and experimental support for improving properties of absorption materials by doping strategy.