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Method for quick estimation of the Sb^(3+)/Sb^(5+) content ratio in ATO

Antimony doped SnO_2 is well known by the name ATO (antimony tin oxide). It is widely used in various optoelectronic applications. Thin ATO films possess an excellent combination of superior optical and electrical properties: high transparency in the visible range and high electrical conductivity. However, it was evidenced that the conductivity was not linearly dependent on the doping level. Many structural studies of ATO have been performed so far with the purpose of elucidating the above phenomena, but still there are some uncertainties on antimony incorporation in the SnO_2 structure. ATO samples containing up to 14 at% Sb were hydrothermally prepared and characterized by X-ray powder diffraction as well as with ^(121)Sb Mössbauer spectroscopy. The prepared samples were nanocrystalline. XRD patterns showed that all the prepared samples were tetragonal, space group P42/mnm, and isostructural with TiO_2 (rutile). Diffraction lines were broadened, the line broadening being anisotropic. Both the line broadening and the line anisotropy were dependent on the Sb-doping level. Unit-cell parameters increased with the Sb content up to 11.9 at% Sb, and then decreased for 14 at% Sb. Crystal structure indicated that both Sb^(3+) and Sb^(5+) are substituted for Sn^(4+) in the samples, with variable Sb^(3+)/Sb^(5+) content ratio. The ^(121)Mössbauer spectroscopy confirmed the XRD results. The sample containing 6.2 at% Sb was additionally annealed at 350, 450 and 550 oC for 1 h. Broadening of diffraction lines increased due to annealing at 350 oC then decreased upon further heating. The lines anisotropy decreased over the whole temperature range. Unit-cell parameters of the annealed ATO sample decreased with the increase in thermal treatment temperature. The ^(121)Mössbauer spectroscopy showed that Sb^(3+)/Sb^(5+) content ratio decreased upon annealing. The changes in full-widths at half-maximum (FWHM) for various diffraction lines on the Sb^(3+)/Sb^(5+) content ratio were examined. The 110 and 101 lines were chosen to calculate the FWHM ratio since their full-widths at half-maximum strongly changed with sample compositions. A linear correlation between the Sb^(3+)/Sb^(5+) content ratio in ATO samples and the FWHM_(110)/FWHM_(101) ratio was found, which can be used as the basis for a quick and easy estimation of the Sb^(3+)/Sb^(5+) content ratio in ATO samples.

antimony tin oxide (ATO); X-ray powder diffraction; Moessbauer spectroscopy

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