title: Structural characterization of titania by X-ray diffraction, photoacoustic, Raman spectroscopy and electron paramagnetic resonance spectroscopy.
abstract: A titania mineral (obtained from East coast, Orissa, India) was investigated by X-ray diffraction (XRD), photoacoustic spectroscopy (PAS), Raman and Electron Paramagnetic Resonance (EPR) studies. XRD studies indicated the presence of rutile (91%) and anatase (9%) phases in the mineral. Raman investigation supported this information. Both rutile and anatase phases have tetragonal structure (rutile: space group P4(2)/mnm, a=4.5946(1) Å, c=2.9597(1) Å, V=62.48(1) (Å)(3), Z=2; anatase: space group I4(1)/amd, 3.7848(2) Å, 9.5098(11) Å, V=136.22(2) (Å)(3), Z=4). The deconvoluted PAS spectrum showed nine peaks around 335, 370, 415,485, 555, 605, 659, 690,730 and 785 nm and according to the ligand field theory, these peaks were attributed to the presence of V(4+), Cr(3+), Mn(4+) and Fe(3+) species. EPR studies revealed the presence of transition metal ions V(4+)(d(1)), Cr(3+)(d(3)), Mn(4+)(d(3)) and Fe(3+)(d(5)) at Ti(4+) sites. The EPR spectra are characterized by very large crystal filed splitting (D term) and orthorhombic distortion term (E term) for multiple electron system (s>1) suggesting that the transition metal ions substitute the Ti(4+) in the lattice which is situated in distorted octahedral coordination of oxygen. The possible reasons for observation of unusually large D and E term in the EPR spectra of transition metal ions (S=3/2 and 5/2) are discussed.
authors.affiliation: Radiochemistry Division, Bhabha Atomic Research Centre, Trombay 400 085, India. Electronic address: rmkadam2003@yahoo.co.in.
authors.forename: R M
authors.initials: RM
authors.lastname: Kadam
authors.affiliation: Radiochemistry Division, Bhabha Atomic Research Centre, Trombay 400 085, India.
authors.forename: B
authors.initials: B
authors.lastname: Rajeswari
authors.affiliation: Radiochemistry Division, Bhabha Atomic Research Centre, Trombay 400 085, India.
authors.forename: Arijit
authors.initials: A
authors.lastname: Sengupta
authors.affiliation: Chemistry Division, Bhabha Atomic Research Centre, Trombay 400 085, India.
authors.forename: S N
authors.initials: SN
authors.lastname: Achary
authors.affiliation: High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay 400 085, India.
authors.forename: R J
authors.initials: RJ
authors.lastname: Kshirsagar
authors.affiliation: Radiochemistry Division, Bhabha Atomic Research Centre, Trombay 400 085, India.
authors.forename: V
authors.initials: V
authors.lastname: Natarajan
mesh_terms: D002857:Chromium / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D007194:India; D007501:Iron / Q000737:chemistry; D008345:Manganese / Q000737:chemistry; D008903:Minerals / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods*; D013059:Spectrum Analysis, Raman; D014025:Titanium / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D008903:Minerals; D014639:Vanadium; D002857:Chromium; C009495:titanium dioxide; D008345:Manganese; D014025:Titanium; D007501:Iron
keywords: Anatase; EPR; PAS; Raman spectroscopy; Rutile; XRD