Electron Paramagnetic Resonance and Optical Absorption of Yellow Anatase TiO₂ Single Crystal

Abstract

Electron paramagnetic resonance (EPR) measurements revealed the inclusion of nitrogen in yellow anatase single crystals grown by chemical vapor transport using NH 4 Cl as the transport agent. The angular-dependence of EPR triplets suggests that nitrogen occupies a substitutional site of oxygen in the bulk. The paramagnetic nitrogen observed at room temperature becomes diamagnetic at lower temperatures by trapping another electron. Below 50 K, only one symmetric differential EPR signal from titanium with an unpaired electron can be observed. These changes in the electric states of nitrogen and titanium can be explained by the presence of oxygen vacancies and by the contribution of trapped electrons to oxygen vacancies. The optical absorption observed at 3.0 eV in an E k a configuration, which is characteristic of yellow anatase is almost independent of temperature.

High-Pressure Study of Anatase TiO2

“…Although S decreases with temperature like in metals, its high value at room-temperature (~300 μV/K) and its non-linear temperature dependence indicate a complex charge transport mechanism. The overall shape and the magnitude of the curve resemble those of boron carbides measured by Aselage and co-workers [ 9 ]. In that system thermo-electric power is believed to be enhanced by polaronic effects, which are present despite the high concentration of carriers [ 10 ].…”

Nitrogen-doped semiconducting oxides. Implications on photochemical, photocatalytic and electronic properties derived from EPR spectroscopy

“…As a point of reference, only one example is available in the literature reporting EPR spectra of N-TiO 2 in a single crystal. In their paper T. Sekiya et al 44 report careful measurements on a crystal obtained by CVT in the presence of NH 4 Cl (Fig. 4).…”

UV irradiation effect on Al‐doped anatase titanium dioxide

“…The addition of Al 2 O 3 to TiO 2 results in the introduction of oxygen vacancies. Note that the broadening of signal C with increasing temperature up to 40 K is due to the change in the spin relaxation time of Ti 3+ , which was also observed in yellow anatase [5]. This suggests that it is impossible to observe Ti 3+ above 40 K if Ti 3+ is formed.…”