s8.m28.p4 Thermal Behaviour of Nanocrystalline SnO2 Doped with Antimony

Tin oxide, SnO2, is a wide-band gap semiconductor. It is widely used in electronic devices. When doped with F, Sb, or Mo it becomes a conductor. In the case of antimony doping it was evidenced that the conductivity was not linearly dependent on the doping level [1]. So, there is an inevitable interest to understand this phenomenon. Recently a structural study of hydrothermally prepared nanocrystalline SnO2 samples doped with Sb was performed by X-ray diffraction (XRD) and Mössbauer spectroscopy [2]. 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 TiO2 (rutile)-type structure [3], in the space group P42/mnm. Sb doping of SnO2 caused an increase of unit-cell parameters. Crystal structure indicated that in the Sb-doped samples both Sb and Sb ions were substituted on Sn sites in the SnO2 lattice, Sb 3+ being dominant for the examined samples. Mössbauer spectroscopy confirmed the XRD results. The aim of the present work is to examine the influence of thermal treatment on the Sb-doped SnO2 samples containing 4 and 8 at% Sb. The samples were thermally treated at 350, 450 and 550 oC for 1 hour, then slowly cooled to RT and examined by XRD and by Sb-Mössbauer spectroscopy. 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 took place in the annealing process.Mössbauer spectroscopy showed that Sb/Sb content ratio in the samples decreased upon annealing. The line broadening in XRD pattern increased up to 350 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/Sb content ratio in the samples.