Nitrogen Location and Ti–O Bond Distances in Pristine and N-Doped TiO₂ Anatase Thin Films by X-ray Absorption Studies

Abstract

2This paper reports detailed EXAFS analysis of spray pyrolysis synthesized TiO 2 thin films to, 3 locate position of nitrogen in N-doped phase pure(anatase)TiO 2 , evaluate Ti-O bond distances 4 and the co-ordination number of Ti. The thin films were synthesized at three different substrate 5 temperatures viz. 400, 450 and 500 o C leading to concomitant occurrence of varying nitrogen 6 concentration (N/Ti) of 0.282, 0.237, 0.24 respectively. The co-ordination number extracted 7 from the EXAFS fitting revealed that films synthesized at 450 o C are stoichiometric, whereas 8 those synthesized at 400 and 500 o C are sub-stoichiometric. The intensity of near edge peaks 9 in XAS was employed to delineate the contribution from both symmetry of TiO 6 polyhedra 10 and particle size. The axial and equatorial Ti-O bond distances, corresponding to the different nitrogen concentrations, extracted from the EXAFS fitting, showed good agreement with those 12 calculated from DFT calculations quoted in literature. An increase in the axial and equatorial 13 bond distances with respect to pristine TiO 2 is observed and is attributed to the dominant effect 14 of nitrogen occupancy in the interstitial position.15

Consequences of Nitrogen Doping and Oxygen Enrichment on Titanium Local Order and Photocatalytic Performance of TiO2 Anatase

“…EXAFS data analysis was carried out in order to determine the position of the dopants in the titania samples using a similar approach to that reported by Sahoo et al 32 . Crystallographic data for TiO 2 anatase reference phase was used to construct the model for fitting the spectra.…”

“…In a more recent investigation supported by DFT calculations and EXAFS, Ceotto et al postulated that nitrogen preferentially occupies the axial position in the TiO 6 polyhedra replacing the lattice oxygen at low doping levels and forming oxygen-vacancies at high dopant concentrations 31 . Several years later, Sahoo et al found out by means of EXAFS that the nitrogen interstitial doping is responsible for the reduction of Ti-O coordination number and the increase of the axial and equatorial Ti-O bond lengths 32 .…”

Local Structure Investigation of Mn‐ and Co–Doped TiO2 Thin Films by X‐Ray Absorption Spectroscopy

“…The normalised XANES spectra of the Mn doped TiO 2 thin films at Ti K‐edge are shown in Figure . The absorption edge position clearly indicates that Ti is present in +4 oxidation state and the XANES spectral features for undoped TiO 2 sample exactly resemble that of anatase TiO 2 . The white line observed for TiO 2 is transition of 1 s electron to the vacant np orbital of Ti or the anti‐bonding orbital of Ti−O.…”

The role of Ce addition in catalytic activity enhancement of TiO2-supported Ni for CO2 methanation reaction

“…Fig. 10(a 53,54 These three pre-edge peaks intensities were related to the symmetry of the crystal structure. A distortion and oxygen vacancies can cause an increase in the pre-edge intensity.…”