Structure, room-temperature magnetic and optical properties of Mn-doped TiO₂ nano powders prepared by the sol—gel process

TiO₂ nano powders with Mn concentration of 0 at%-12 at% were synthesized by the sol—gel process, and were annealed at 500 °C and 800 °C in air for 2 hrs. X-ray diffraction (XRD) measurements indicate that the Mn-TiO₂ nano powders with Mn concentration of 1 at% and 2 at% annealed at 500 and 800 °C are of pure anatase and rutile, respectively. The scanning electron microscope (SEM) observations reveal that the crystal grain size increases with the annealing temperature, and the high resolution transmission electron microscopy (HRTEM) investigations further indicate that the samples are well crystallized, confirming that Mn has doped into the TiO₂ crystal lattice effectively. The room temperature ferromagnetism, which could be explained within the scope of the bound magnetic polaron (BMP) theory, is detected in the Mn-TiO₂ samples with Mn concentration of 2 at%, and the magnetization of the powders annealed at 500 °C is stronger than that of the sample treated at 800 °C. The UV—VIS diffuse reflectance spectra results demonstrate that the absorption of the TiO₂ powders could be enlarged by the enhanced trapped electron absorption caused by Mn doping.