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 SnO2 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.