engleski

Thermal Behaviour of Nanocrystalline SnO_2 Doped with Antimony

Tin oxide, SnO_2, is a wide gap semiconductor. It is widely used in electronic devices. When doped with F, Sb or Mo it becomes a coductor. In the case of antimony doping it was evidenced that the conductivity was not linearly dependent on the doping level. So, there is an inevitable interest to understand this phenomenon. Recently a structural study of hydrothermally prepared nanocrystalline SnO_2 samples doped with Sb was performed by X-ray diffraction (XRD) and Moessbauer spectroscopy. Samples contained up to 14.0 at% Sb. Diffraction lines were broadened, the line broadening being anisotropic. Both the line broadening and line anisotropy were dependent on the Sb doping level. The samples were tetragonal, with TiO_2 (rutile)-type structure, in the space group P4_2/mnm. Sb doping of SnO_2 caused an increase of unit-cell parameters. Crystal structure indicated that in the Sb-doped samples both Sb^3+ and Sb^5+ ions were substituted on Sn^4+ sites in the SnO_2 lattice, Sb^3+ being dominant for the examined samples. Moessbauer spectroscopy confirmed the XRD results. The aim of the present work is to examine the influence of thermal treatment on the Sb-doped SnO_2 samples containing 4 and 8 at% Sb. The samples were thermally treated at 350, 450 and 550 &ordm ; C for 1 hour, then slowly cooled to RT and examined by XRD and by 121Sb-Moessbauer specroscopy. Unit-cell parameters of the annealed samples decreased with the increase in thermal treatment temperatures for both Sb contents. This suggested that oxidation of the antimony ion Sb^3+ took place in the annealing process. Moessbauer spectroscopy showed that Sb^3+/Sb^5+ content ratio in the samples decreased upon annealing. The line broadening in XRD pattern increased up to 350 &ordm ; C, then decreased upon further heating. On the other hand, the line anisotropy decreased over the whole temperature range. It was noticed that the ratio of full-widths at half-maximum (FWHM) for the diffraction lines 110 and 101 is directly proportional to the Sb^3+/Sb^5+ content ratio in the samples.

Sb-doped tin oxide; X-ray diffraction; Moessbauer spectroscopy

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