The effect of hydrothermal temperature on the crystallographic phase of MnO₂ and their microwave absorption properties

Rod-like α-MnO₂ and β-MnO₂ were obtained successfully by hydrothermal method under different temperatures. The as-prepared samples have been characterized by XRD, SEM, TG, TEM and HRTEM. The β-MnO₂ was obtained under the condition of 150 °C and 220 °C, and the crystallinity of 220 °C would be better, the α-MnO₂ was synthesize at 180 °C. The thermal stabilities of manganese oxide were affected by their crystal phases. The microwave absorption properties of rod-like α-MnO₂ and β-MnO₂ were studied at 2.0–18.0 GHz, and β-MnO₂ show much better absorption properties than α-MnO₂. The β-MnO₂ prepared under the condition of 220 °C presents the optimal microwave absorption properties with the RL values of − 25.5 dB at 14.7 GHz, a thickness of 1.5 mm and an effective bandwidth of 5.0 GHz (13–18.0 GHz). These results indicate that MnO₂ were dielectric loss materials, their absorption properties were influenced by the crystal phase, morphological size and crystallinity significantly. Special rod-like morphology and good crystallinity lead to superior impedance matching and moderate attenuation constant, α, and eventually enhanced microwave absorption.