Defect structure examination of Sn-doped indium oxide (ITO)

Tin-doped indium oxide (ITO) samples with doping level up to 12.3 at% Sn were prepared by a sol-gel technique and characterised by X-ray powder diffraction as well with ^(119)Sn-Mossbauer spectroscopy. Diffraction patterns indicated that all samples were cubic, space group Ia-3, and isostructural with In_2O_3. Diffraction lines were broadened, the line broadening increased with tin content. The unit-cell parameter increased with tin doping level up to 7.8 at% Sn and decreased at higher levels. This behaviour of the unit-cell parameter indicated that the tin substitution for indium on B and D sites of the original In_2O_3 structure is non-uniform and depends on tin content. Rietveld structure refinement showed the presence of interstitial oxygen in the Sn-doped samples. The position of interstitial oxygen indicated the D site preference for tin at low tin doping level, and subsequent increase in the B site occupancy with the increase in tin content. ^(119)Sn-Mossbauer spectroscopy revealed that incorporated tin resided equally sites B and D for 7.8 at% Sn. Below that doping level the preference for tin to occupy D site was noticed, while for doping level higher than 7.8 at% Sn the B site was preferred.