Keeping it small—restricting the growth of nanocrystals

A method for preventing the growth of oxide nanoparticles is presented. A second oxide phase (e.g. SiO2) is infiltrated between the principal nanoparticles, acting as a brake on grain growth at elevated temperature. The effect of the second oxide can be significant, for example reducing the growth of SnO2 by nearly an order of magnitude at 1000 deg C. The approach is shown to be generic, being applied to six different oxides. The structures of both the nanoparticles and the even smaller secondary particles are probed by a combination of EXAFS and solid state NMR. From the Sn K-edge EXAFS it is clear that the major component SnO2 nanoparticles are locally highly ordered, with the intensity scaling with particle size, reflecting the proportionate contribution of the lower coordinations on the surface. 29Si MAS-NMR of SiO2 particles between SnO2 demonstrates that they are significantly more disordered than bulk SiO2 after similar heat treatment.