The effects of Fe-doping on MnO2: phase transitions, defect structures and its influence on electrical properties.

The composition of Mn1-x Fe x O2 (x = 0-0.15) was synthesized by a hydrothermal method at 140 °C for 5 hours of reaction time. Investigations were carried out including XRD, FTIR, Raman spectroscopy, FESEM, and TEM for crystallographic phase analysis. Furthermore, XPS and XAS were used to analyze the oxidation states of Mn and dopant Fe in the octahedron sites. For electrical characterizations, an impedance analyzer was used to explore the conductivity and dielectric properties. It was discovered that the undoped MnO2 possessed an α-MnO2 structure performing (2 × 2) tunnel permitting K+ insertion and had a nanorod morphology. The Fe ion that was doped into MnO2 caused a phase transformation from α-MnO2 to Ramsdellite R-MnO2 after x = 0.15 was reached and the tunnel dimension changed to (2 × 1). Furthermore, this caused increased micro-strain and oxygen vacancies. An oxidation state analysis of Mn and substituted Fe in the octahedron sites found mixed 3+ and 4+ states. Electrical characterization revealed that the conductivity of Fe-doped MnO2 is potentially electron influenced by the oxidation state of the cations in the octahedron sites, the micro-strain, the dislocation density, and the movement of K+ ions in the tunnel.