Nonaqueous Synthesis of Uniform Indium Tin Oxide Nanocrystals and Their Electrical Conductivity in Dependence of the Tin Oxide Concentration

Indium tin oxide nanoparticles with tin oxide contents varying from 2 to 30 wt % have been synthesized via a nonaqueous sol−gel procedure involving the solvothermal treatment of indium acetylacetonate and tin tert -butoxide in benzyl alcohol. According to powder X-ray diffraction analysis combined with Rietveld refinement all the materials are crystalline with the cubic bixbyite structure of indium oxide without any indication of SnO 2 as an additional phase. Transmission electron microscopy studies proved that the nearly spherical particles are relatively uniform in size and shape with crystallite sizes in the range of 5−10 nm. X-ray photoelectron spectroscopy results showed that the final composition of the nanoparticles coincided well with the initial indium acetylacetonate-to-tin tert -butoxide ratio. Furthermore, a high amount of oxygen vacancies was detected, which contribute to the good electrical conductivity of the nanoparticles. Conductivity measurements on the as-synthesized nanopowders pressed into pellets showed a maximum conductivity of 2.56 S/cm at a dopant concentration of 15 wt % and can be further increased to 52.6 S/cm upon annealing under a nitrogen atmosphere.