Tin oxide (SnO2) is a well-known n-type, wide band gap semiconductor with the transparency of the order of 80%. Doping the cation site with aliovalent elements results in increased n-type electronic conductivity (pentavalent doping) or improved p-type conductivity (trivalent doping) while retaining the transparency for potential applications as transparent conducting oxides (TCOs).

In the present work, nanocrystalline pure tin oxide (SnO2), antimony doped tin oxide (Sb:SnO2) and indium doped tin oxide (In:SnO2) powders with systematically varying dopant concentrations were produced using nebular spray pyrolysis (NSP) and flame spray pyrolysis (FSP) by making use of relatively inexpensive precursors. Structural characterisation was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Optical properties were evaluated using absorption spectroscopy and the band gap energies were estimated. The conductivities of the powders were estimated by using a four-probe method on compacted pellets.

Nanocrystalline Sb:SnO2 powders synthesised by FSP were phase-pure cassiterite with rutile structure at 10% Sb doping while the powders produced by NSP showed phase separation at 9% Sb doping. Electrical conductivity studies of the compacted powders produced by both the methods revealed an increase of nearly 3 orders of magnitude in the conductivity with Sb doping. Absorption spectroscopy revealed the powders to be transparent in the visible spectrum.

Nanocrystalline indium doped tin oxide powders containing up to 10% In and having a phase-pure rutile structure were produced in a single-step by FSP and NSP. In all the cases, the nanoparticles were fairly uniform in size (in the range of 10 nm – 25 nm), had a narrow size distribution and were relatively unagglomerated. The as-synthesized powders were transparent in the visible region and showed a sharp absorption below 330 nm. Energy band gaps calculated from absorption spectra show an abrupt decrease in the band gap with increased indium concentration.
The results of the investigations carried out in this thesis show that phase-pure, nanocrystalline Sb or In doped tin oxide powders can be synthesized in a single step using either NSP or FSP and can be used as TCOs.

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