Effect of tin level on particle size and strain in nanocrystalline tin-doped indium oxide (ITO)

A series of Sn-doped In2O3 samples, with doping levels of 0, 2.1, 4.0, 6.0, 7.8, 9.7, 11.1 and 12.3 at% Sn, has been prepared by a sol–gel technique. The effect of tin doping on microstructure of the samples has been investigated by X-ray diffraction and transmission electron microscopy. Diffraction patterns indicated that all samples were cubic, space group Ia3¯ and isostructural with In2O3. Diffraction lines were broadened, the line broadening increased with tin doping level. Analysis of line broadening was performed by the Rietveld refinement of X-ray diffraction patterns, using silicon powder as an external standard for instrumental diffraction line broadening. The crystallite size decreased with increased tin doping level, from 25.5(1) nm for undoped In2O3 sample to 16.8(1) nm for sample doped with 12.3 at% Sn. Simultaneously, the lattice strain increased from 0.112(6)% for undoped sample to 0.369(9)% for 12.3 at% Sn. Transmission electron microscopy investigations confirmed that the samples were nanocrystalline, having a cubic structure characteristic for In2O3. Interplanar distances, d, of the samples determined by the selected-area electron diffraction were in agreement with those obtained by X-ray diffraction. Particles in the samples had nearly spherical shape at lower tin doping level (<4.0 at% Sn). At higher doping level they were slightly elongated. The particle sizes in the samples as determined by transmission electron microscopy followed the behavior of crystallite sizes obtained by diffraction line broadening analysis.