Materials science scientists working specially with magnetic materials
Iron oxides are compounds of constant composition and do not have oxygen vacancies when they are produced in closed equilibrium systems. In FexO can be x = 0.96. Vacancies of Fe. This purity of the compound is comparable with the error of the analysis by the energy dispersion method. Dioxide of titanium is an oxide of variable composition with oxygen vacancies. The green radiation (500-580 nm) of photoluminescence of nanoparticles of titanium dioxide is associated with defects in oxygen vacancies. I did not see luminescence of iron oxides.
All iron oxides do show homogeneity ranges, not constant compositions even at equilibrium. Since iron takes oxidation states II or III, vacancies are likely to occur for the cations. For instance, iron monoxide always contains Fe(III) as well as Fe(II), i.e. it is never strictly stoichiometric! An equilibrium diagram Fe-O illustrates the situation for FeO, Fe3O4 and Fe2O3. The latter has the narrowest homogeneity range.
It is easy to connect the vacancy concentration with the distribution Fe(III)/Fe(II) by considering the charges -- assuming that there are no oxygen vacancies to speak of.
Dear Attique,
I concur with Mr. Berger that all iron oxides show homogeneity ranges. There is abundant literature on how to create oxygen deficient oxides. In general the partial oxygen pressure at the sinter temperature determines the stoichiometry of FeO, Fe2O3 or Fe3O4. But also the partial O2 pressure during cool down is important to keep the right stoichiometry and prevent different phases to be formed.
See MERCK
http://www.sigmaaldrich.com/catalog/product/aldrich/400866?lang=en®ion=RU
FeO
assay 99.8% trace metals basis
Fe3O4
assay 99.99% trace metals basis
Fe2O3 assay
≥99.995% trace metals basis
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