engleski

Structural studies of nanocrystalline Sb-doped SnO_2

SnO2 (cassiterite) is a wide-band gap semiconductor (Eg=3.97 eV) with transmittance cut-off at 333 nm [B. Orel, U. Lavrenčič-Stangar, Z. Crnjak-Orel, P. Bukovac, M. Kosec, J. Non-Cryst. Sol. 167 (1994) 272]. When doped with F, Sb or Mo it becomes a conductor, while its optical transmittance is invariant. In the case of antimony doping, it was evidenced that the resistivity decreased for lightly-doped SnO2, while it increased for heavily-doped SnO2 [A. Rohatgi, T.R. Viverito, L.H. Slack, J. Am. Ceram. Soc. 57 (1974) 278]. Up to now many structural studies have been devoted to antimony doped SnO2 to elucidate the above phenomena, but uncertainty remains as to how antimony is incorporated into the SnO_2 structure. A series of Sb-doped SnO_2 samples with the doping level up to 14.0 at% Sb has been hydrothermally prepared and characterized by X-ray powder diffraction and 119Sn- and 121Sb Mössbauer spectroscopy. Diffraction lines were broadened, the line broadening being anisotropic. Both the line broadening and the line anisotropy were dependent on the Sb doping level. The samples were tetragonal, space group P42/mnm and isostructural with TiO_2 (rutile). Unit-cell parameters increased with Sb content. The structure of samples containing 0, 6.2, 8 and 11.9 at% Sb has been refined by the Rietveld method. Crystal structure indicated that both Sb3+ and Sb5+ are substituted for Sn4+ in the SnO2 structure, Sb3+ being dominant for the investigated doped samples. The XRD results agreed with the Mössbauer spectroscopy results [B. Gržeta, E. Tkalčec, C. Goebbert, M. Takeda, M. Takahashi, K. Nomura, M. Jakšić, J. Phys. Chem. Solids 63 (2002) 765]. The samples containing 4 and 8 at% Sb were also thermally treated at 350, 450, and 550 &ordm ; C for 1 hour, then slowly cooled to RT. Unit-cell parameters of the annealed samples decreased with the increase in thermal treatment temperature. This suggested that the oxidation of the antimony ion took place in the annealing process. Mössbauer spectroscopy confirmed the change in the Sb3+/Sb5+ content ratio. Line broadening and line anisotropy of the annealed samples decreased as well. It was found that the ratio of full-widths at half-maximum (FWHM) for the diffraction lines 110 and 101 is a good indicator of the Sb3+/Sb5+ content in the samples.

SnO_2; Antimony doping; X-ray diffraction; Rietveld method; Mössbauer spectroscopy

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