RAMAN-SPECTRA OF STOICHIOMETRIC AND DEFECT RUTILE

An explanation for the puzzling high dielectric constant of rutile is sought in a dynamic disordering of the Ti4+ ion. To test the model, Raman spectra were measured on single crystals of stoichiometric and reduced TiO2, at temperatures from 4.2 to 400 K. The narrowing of the Raman lines with temperature in stoichiometric rutile is interpreted as due to an ordering of a disordered dipole arising from an off-center titanium atom. Additional broadening is present in the spectra of the non-stoichiometric crystals and is interpreted as due to the randomizing effect of oxygen vacancies in the defect crystal.