Antimony-doped tin oxide nanoparticles for conductive polymer nanocomposites
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R. van de Belt Kriya Materials B.V., Geleen, The Netherlands
Z. Chenb) and G. de With Laboratory of Materials and Interface Chemistry, Eindhoven University of Technology, 5600 MB, Eindhoven, The Netherlands (Received 14 November 2007; accepted 2 January 2008)
Nanoparticles of antimony-doped tin oxide (ATO) were characterized for 0–33.3% Sb doping, both in aqueous dispersion and as dried powder. Antimony is incorporated in the cassiterite SnO2 structure of the ATO nanoparticles (d ≈ 7 nm) up to the highest doping levels, mainly as SbV, but with increasing Sb doping the SbIII content increases. We found adsorption of NH3 at the particle surface and evidence for the incorporation of nitrogen in the crystal lattice of the particles. The total nitrogen content increases with increasing Sb doping of the particles. Compact powder conductivity measurements show an increase in conductivity of ATO powder up to 13% Sb and a small decrease for higher Sb contents. Furthermore, we show that these particles can be used to prepare highly transparent conductive cross-linked ATO/acrylate nanocomposites with a continuous fractal particle network through the polymer matrix and a very low percolation threshold (c ≈ 0.3 vol%).
I. INTRODUCTION
Antimony-doped tin oxide (ATO) is well known as a semiconductive and optically transparent material that may be used, e.g., in antistatic coatings for displays, electrochromic (“smart”) windows, or solar cells.1,2 Thin films of ATO can be made from dispersions of ATO nanoparticles, e.g., by sol-gel dip coating3 or spin coating with subsequent curing of films at high temperatures.4 Alternatively, dispersions of ATO nanoparticles can be used to make semiconductive polymer nanocomposites where the particles form a network structure through a polymer matrix.5,6 In this way, conductive films can be made with quite different mechanical properties compared with the thin layers mentioned previously. Aqueous dispersions of ATO nanoparticles can be prepared from coprecipitation of metal chlorides from solution, e.g., SnCl4 with SbVCl54 or SbIIICl3,7,8 or reaction of granulated tin with Sb2O3,9 followed by hydrothermal
a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: General Electric China Technology Center, 1800 Cailun Road, Zhangjiang Hi-Tech Park, Pudong, Shanghai, 201203 People’s Republic of China DOI: 10.1557/JMR.2008.0109 J. Mater. Res., Vol. 23, No. 3, Mar 2008
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processing steps. Dialysis and subsequent evaporation of water then result in powders of ATO nanoparticles. Powders of ATO nanoparticles can also be obtained by heating the dried coprecipitate at, e.g., 60010 or 900 °C11 (“calcination”). Using a hydrothermal process for particle synthesis, more hydroxy groups are likely to be present on the surface of the ATO nanoparticles than after calcination of the dried coprecipitate.12 ATO is generally described as an n-type semiconductor having a cassiterite (SnO2) crystal structure. Replacement of Sn
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