Annealing temperature effect on structural and optical investigations of Fe₂O₃ nanostructure

Ferric oxide (Fe₂O₃) was synthesized at different temperatures (T_S) between 300 and 500 °C by spray pyrolysis technique. Surface of annealed Fe₂O₃ nanostructure was characterized by field emission scanning electron microscopic (FESEM). Annealed Fe₂O₃ nanostructure has showed rhombohedral hexagonal structure with the preferred orientation along (104) plane in X-ray diffraction patterns (XRD). Crystallite size was increased from 43 to 63 nm with increasing of T_S between 300 and 500 °C. The maximum transmittance was found to be 72% for Fe₂O₃ nanostructure at T_S = 300 °C. The energy gap for direct band transitions was measured to be 2.05-2.09 eV. Refractive index of Fe₂O₃ nanostructure in the visible region was found in the range of 2.37-2.62. Fe₂O₃ nanostructure has showed n-type electrical conductivity and electrical resistivity was found in the range of 1.02 × 10³-6.23 × 10³ ω m. Formation of transparent Fe₂O₃ nanostructure with band gap and high refractive index suggests the suitability of Fe₂O₃ nanostructure in gas sensors.