Effect of tin level on microstructure of tin-doped indium oxide

Abstract

Tin-doped In2O3 (ITO) is a transparent conductive oxide [1] . Its electrical and optical properties are associated with microstructure as well as with the preparation methods [2]. Both In2O3 and ITO crystallize in a cubic bixbyite-type structure [3]. Recently, a detailed structural study of ITO has been reported [4]. Powder ITO samples with Sn doping level up to 12.3 at% were prepared by a sol-gel technique from InCl3 and SnCl4. The samples were examined by XRD and TEM. Diffraction lines were broadened. The line broadening increased with Sn content. Analysis of line broadening was performed in the Rietveld structure refinement by the PANalytical X'Pert HighScore Plus program. Silicon powder was used as a size-strain standard. Crystallite sizes decreased from 25.5 to 16.8 nm, while strain increased from 0.112 to 0.369 %, as Sn level increased from 0 to 12.3 at%. The interplanar distances, d, in the samples determined by the selected area electron diffraction (SAED) agreed with XRD data. SAED showed that the observed regions appear to be nanocrystalline with a bixbyite– type structure, giving a strong evidence on incorporation of Sn in the starting structure of In2O3. TEM studies proved that ITO samples contained nanosized particles/grains. The grains had nearly spherical shape at lower tin level, while at higher level (>8 at%) they were elongated. The crystallite sizes determined by TEM well agreed with those obtained from XRD. HRTEM gave an additional insight into ITO microstructure.