Thesis (M.Sc. (Physics)) -- University of Limpopo, 2015 / Nanocrystalline materials of defect free anatase and rutile SnO2 together with Ti and Y in anatase SnO2 have been modelled successfully using classical molecular dynamics simulations together with Buckingham potential. The structural properties of these SnO2 phases were analysed using radial distribution functions (RDFs). The effect of increasing temperature in pure SnO2 and doped SnO2 were studied. In both pure and doped materials, RDFs suggest phase transition at higher temperature, where anatase SnO2 transforms to rutile SnO2. Rutile SnO2 was found to be more stable than anatase SnO2. The results showed that the dopants have different effects on the SnO2 material. Ti defect is found to lower the transformation temperature of anatase to rutile SnO2. Y defect is found not to have any effect on the anatase to rutile SnO2 transformation. Thermodynamic properties such as volume thermal expansion coefficient and specific heat capacity were also calculated from above Debye temperature. Volume thermal expansion coefficient was obtained from volume versus temperature curves. Volume thermal expansion coefficient for rutile and Ti-anatase SnO2 were found to be not of the same order with the calculated results. Specific heat capacity calculated from energy versus temperature curves was found to be in agreement with the Dulong and Petit law of solids. Nanocrystalline Al/Y co-doped SnO2 powders were successfully synthesized using the sol-gel method. The samples were subjected to different temperatures 100 (as prepared) 200, 400, 600, 800 and 1000 oC. The effects of co-doping and temperature on the structural and optical properties of Al/Y co-doped SnO2 nanoparticles as well as morphology were investigated. The characterization techniques used were X-ray powder diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) and UV-visible spectroscopy (UV-vis). The average particle sizes were found to be in the range between 2.5–8 nm and the strains were calculated to be 2.76–0.53 with increasing temperature for as prepared and the sample sintered at different tempe-ratures. The Raman bands were found to correspond with the literature. At a higher temperature of about 800 oC the materials were found to contain the second phase which is yttrium stannate. However no information about aluminium was found. The optical band gap were found to be between 3.3–3.99 eV in the temperature range 200–1000 oC.