Tin-, titanium-, and magnesium-doped α-Cr2O3: characterisation and rationalisation of the structures

Tin- and titanium-doped α-Cr2O3 have been prepared by the calcination of precipitates. Rietveld structure refinement of the X-ray powder diffraction patterns shows that the dopant metals occupy interstitial sites and partially substitute on octahedral chromium sites in the corundum-related α-Cr2O3 structure. Interatomic potential calculations show that such defects are energetically more favourable than the exclusive substitution of chromium or the occupation by the dopant of interstitial sites in α-Cr2O3 with charge balance being achieved by an appropriate number of cation vacancies. However, the attempted incorporation of magnesium within α-Cr2O3 results in the formation of spinel-related MgCr2O4. The observation is rationalised in terms of the greater thermodynamic stability of the spinel-related structure.