Tunable dielectric response and electronic conductivity of potassium-ion-doped tunnel-structured manganese oxides

Potassium-ion-doped MnO2 has been successfully synthesized using the hydrothermal method, and the influence of the doped potassium ions on the electrical conductivity and permittivity is studied. X-ray powder diffraction, scanning electron microscopy, electron-probe micro-analysis, and a vector network analyzer are used to perform characterization. The densities of states of doped and undoped MnO2 tunnel structures are also discussed based on first-principles calculations. Results show that the conductivity and dielectric resonance of MnO2 can be elevated by means of K+ doping. The conductivity of K+-doped MnO2 prepared at different reaction times shows a decreasing trend and is generally 1 order of magnitude higher than that of pure MnO2. The electrical conductivity of K+-doped MnO2 (R-3) shows the highest value of 3.33 x 10(-2) S/cm at the reaction time of 24 h, while that of pure MnO2 is 8.50 x 10(-4) S/cm. When treated with acid, the conductivity of samples remains basically stable along with the increase of treatment time. In addition, acid treatment plays a very significant role in controlling the amount of K+ ions in crystals. The K+ contents of acid-treated samples are 5 times lower than that of the untreated R-1. The dielectric losses of the samples with different reaction times are enhanced markedly with frequency increment. The complex permittivity of pure MnO2 only exhibits a resonance at similar to 12 GHz, while K+-doped MnO2 exhibits another resonance behavior at similar to 9 GHz. The capacity of the dielectric property in the net structure is enhanced by the interfacial polarization, dielectric relaxation, multiple internal reflections, and multiple scattering benefiting. Published by AIP Publishing.