Mechanochemical synthesis and characterization of xIn₂O₃·(1 − x)α-Fe₂O₃ nanostructure system

Indium oxide-doped hematite xIn₂O₃·(1 − x)α-Fe₂O₃ (x = 0.1–0.7) nanostructure system was synthesized using mechanochemical activation by ball milling and characterized by XRD, simultaneous DSC–TGA, and UV/Vis/NIR. The microstructure and thermal behavior of as obtained system were dependent on the starting In₂O₃ molar concentration x and ball milling time. XRD patterns yielded the dependence of lattice parameters and grain size as a function of ball milling time. After 12 h of ball milling, the completion of In³⁺ substitution of Fe³⁺ in hematite lattice occurs for x = 0.1, indicating that the solid solubility of In₂O₃ in hematite lattice is extended. For x = 0.3, 0.5, and 0.7, the substitutions between In³⁺ and Fe³⁺ into hematite and In₂O₃ lattice occur simultaneously. The lattice parameters a and c of hematite and lattice parameter a of indium oxide vary as a function of ball milling time. The changes of these parameters are due to ion substitutions between In³⁺ and Fe³⁺ and the decrease in the grain sizes. Ball milling has a strong effect on the thermal behavior and band gap energy of the as-obtained system. The hematite decomposition is enhanced due to the smaller hematite grain size. The crystallization of hematite and In₂O₃ was suppressed, with drops of enthalpy values due to the stronger solid–solid interactions after ball milling, which caused gradual In³⁺–Fe³⁺ substitution in hematite/In₂O₃ lattices. The band gap for hematite shifts to higher energy value, while that of indium oxide shifts to lower energy value after ball milling.