Reflectance and electroreflectance of TiO₂single crystals. II. Assignment to electronic energy levels

Abstract

For pt.I see ibid., vol.10, no.19, p.3893 (1977). The interband optical properties of TiO2 are analysed on the basis of a tight-binding band structure which is calculated by using estimated values for the LCOAO parameters. The major interband transitions giving rise to the pronounced optical structure around 4 eV occur between energy band regions near the Sigma symmetry line of the Brillouin zone. The broad structure of the electroreflectance (ER) is mainly caused by the energy shift of these bands due to the dielectric polarisation. Values for four elements of the polarisation-potential tensor have been deduced from the experimental data which agree with the results of a quantitative model developed for the electro-optic effect. Some features of the ER fine structure are unambiguously identified as Franz-Keldysh oscillations and are designated to specific critical points.

Self-energy and excitonic effects in the electronic and optical properties ofTiO2crystalline phases

“…Transverse and optical phonons determine the lower optical edge observed in experiments. 40,54,55,69 Direct transitions have been observed 45,69 at 3.57 eV for the in-plane directions, in quite good agreement with our estimation for the first bright exciton ͑3.59 eV͒.…”

“…40͒ and, according to the combined results of absorption, photoluminescence, and Raman-scattering techniques 40 a direct exciton is reported at 3.57 eV. 40,45,69 The absorption edge of 3.2 eV ͑Refs. 56 and 57͒ in anatase is also due to indirect transitions.…”

Polarization dependence of soft-x-ray Raman scattering at theLedge ofTiO2

“…There exists, however, few previous works on solids where practical measurements and corresponding analysis are performed on PSXRS. 19 TiO 2 is a representative of a 3d 0 system, and the character of the electronic states near the energy gap has long been discussed in terms of both delocalized [20][21][22][23][24][25][26] and localized [27][28][29][30][31][32] description. Butorin et al measured Ti 2p SXRS of FeTiO 3 and found a broad Raman structure around 3-10 eV and a weak Raman peak at 14 eV below recombination peaks.…”

Molar Volume, Ionic Radii in Stoichiometric and Nonstoichiometric Metal Oxides

“…In oxides with Al 2 O 3 -type hexagonal structure or TiO 2 -type tetragonal structure there are different bond lengths and different distances between oxygen atoms. For example, in TiO 2 (rutile) the shortest distance between oxygen atoms is d = 0.252 nm (Vos, 1977;Meogher & Lager, 1979), whereas in SiO 2 (quartz) d= 0.260 nm, and in its high-pressure form d= 0.216 nm ( Shannon & Prewitt, 1969, 1976. Furthermore, in Ti 2 O 3 d= 0.279 nm (Rice & Robinson, 1977), V 2 O 3 d = 0.279 nm (Robinson, 1975), Fe 2 O 3 d = 0.262 nm (Newnham &Haan, 1962), and in α -Al 2 O 3 d= 0.252 nm (Shannon & Prewitt, 1969).…”