Charge compensation in iron-doped rutile

In iron-doped rutile (TiO 2 ) charge compensation is necessary since most of the iron substitutes as Fe 3+ for Ti 4+ . The well known EPR spectrum of iron-doped rutile is due to Fe 3+ substitutional ions in a perfect lattice. However, EPR measurements at 9.2 GHz revealed several additional EPR spectra which are explained as due to substitutional Fe 3+ ions disturbed by nearest-neighbour oxygen vacancies, protons and Ti 4+ interstitials. The number of nearest-neighbour oxygen vacancies and protons was determined from the EPR measurements. In pure rutile the number of oxygen vacancies was determined from measurements of the absorption line at 6.6*10 3 cm -1 which is associated with polarons. Since the number of EPR centres associated with oxygen vacancies is nearly the same as the number of oxygen vacancies it is concluded that the former are mainly located near to iron ions.