Influence of Calcination on the TiO2 Polymorphs and its Electronic Structure Analysis through Optical Absorption Studies

Pure nanocrystalline titanium Oxide (TiO2) powder has been synthesized by the sol-gel technique using titanium tetra-isopropoxide as the starting precursor. As-prepared samples were calcined at different temperatures, 400, 600, 800 and 900°C. X-ray diffraction (XRD) analysis was used to find the crystalline structure and changes in the polymorphs with calcination. The as-synthesized TiO2 powder dried at 100oC in air was amorphous. The powder samples calcined at 400 oC (a=3.788 Å, c=9.499 Å) and 600oC (a=3.787 Å, c=9.518 Å) revealed only the anatase phase with the tetragonal structure belongs to the space group of I41/amdD4h 19 , whereas the sample calcined at 800oC (a=4.597 Å, c=2.962 Å) exhibited mixed anatase and rutile phases with tetragonal structure. Calcined TiO2 powders at 900 oC rendered rutile phase with the tetragonal structure and space group of P42/mnm-D4h 14 (a=4.599 Å, c=2.963 Å). The Fourier transform infrared spectrometer (FTIR) was used to confirm the metal-oxide phase formation and to test the presence of any organic residues. The electronic structure of TiO2 has been investigated using the optical absorption spectra based on combined density functional theory and many-body perturbation theory. Absorption edge observed nearer to 410 nm showed the bandgap values between 2.97 and 3⋅24 eV. Electrical conductivity study was performed to understand the conduction mechanism of the samples and it effect variation with calcination. --------------------------------------------------------------------------------------------------------------------------------------*Corresponding author e-mail: [email protected] (A. Moses Ezhil Raj) Phone: +91 4652 232888 | Fax: +91 4652 229800