Size effects in the NMR of SnO2 powders

Using tin dioxide powders obtained from different thermal treatments, we investigated the effects of powder granule size on parameters such as chemical shift, linewidth, and spin-lattice relaxation, via magic-angle spinning (MAS) room temperature nuclear magnetic resonance (NMR) on the 119Sn nucleus. Mean size, as determined by the Scherrer formula applied to the X-ray diffraction data, varied from 4 to 32 nm. We compared the properties of the 119Sn power samples with normal 10 μm cassiterite SnO2 bulk properties. Linewidth showed a general broadening as size decreased, but there was evidence in the anisotropy of the chemical shift, and in the spin-lattice relaxation, of a size-dependence effect. The largest modification in bulk properties occurred at about 8 nm. We discuss the correlation between anisotropy and spin-lattice relaxation in relation to the change of vibrational modes, as observed by Raman spectroscopy, as particle size decreases.