Structural and optical properties of α-Fe2O3 nanoparticles realized by simple thermal decomposition route

Herein, we present the synthesis and thermal treatment effect of Hematite (alpha-Fe2O3). Hematite nanoparticles were prepared by repeated calcination of a precursor obtained from Fe(NO3)(3).9H(2)O and Hexamethylenetetramine (HMTA). Thermal treatment of the precursor at 400 degrees C for 4 h, resulted in the formation of Fe3O4 nanoparticles, which on repeated calcination at 400 degrees C, 500 degrees C and 600 degrees C, resulted in alpha-Fe2O3 nanoparticles. Synthesized samples were characterized by using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy and UV-vis spectroscopy techniques. XRD result reveals the formation of cubic Fe3O4 phase at 400 degrees C, which is transformed into rhombohedral alpha-Fe2O3 polymorphs on repeated calcination. Crystallinity of the alpha-Fe2O3 is enhanced on repeated calcination up to 500 degrees C after that it gets slightly amorphized at 600 degrees C. Raman and FTIR results further corroborate the XRD result. Optical band gap of most crystalline alpha-Fe2O3, as estimated from UV-vis results, is 1.87 eV. Urbach energy of the samples has been calculated from absorption data, which shows the minimum value for most crystalline material. These findings demonstrate the close relation between structure and optical properties of alpha-Fe2O3.