Owing to the electrically charged nature of crystal defects in oxides, the possibility existed of reducing diffusivity with a two-phase microstructure of sufficiently small dimensions. A diminution of the order of 10 times in the chemical diffusivity at 1153C was repeatedly observed in polycrystalline rutile with an initial second-phase particle size of about 50Å. The dependence of the diffusivity and electrical conductivity upon particle size and volume fraction was explained in terms of the alteration of concentrations of transport-related point defects by the transfer of charged species to internal surfaces.

Chemical Diffusivity and Electrical Conductivity in TiO2 Containing a Submicron Dispersion of SiO2. Crosbie, G.M.: Journal of Solid State Chemistry, 1978, 25[4], 367-78