Measurements were made of self-diffusion coefficients in ceramic samples of solid solutions by using suitable radio-tracers (table 194). It was found that, as the Ti content of the solid solution increased, the self-diffusion coefficients of 90Sr increased. The Ti diffusivity was greater than the Sr diffusivity for all of the compositions within the homogeneity range. This was attributed to the appreciable difference between the ionic radii of Ti (0.0605nm for a coordination number of 6) and Sr (0.118nm for a coordination number of 6 and 0.144nm for a coordination number of 12). This difference was suggested to be responsible for a distortion of the crystal structure of Sr6Nb2O11; thus producing new paths for short-circuit and intercrystalline diffusion of Sr ions. This seemed to be the cause of the increase in the 90Sr effective diffusion coefficient with increasing Ti content. Overall, the present Sr diffusion coefficients in these niobate phases were comparable to those reported for other niobates.

A.L.Podkorytov, M.I.Pantyukhina, V.M.Zhukovskii, N.A.Simaranova, N.V.Sherstneva, G.I.Dontsov: Neorganicheskie Materialy, 1995, 31[8], 1097-9 (Inorganic Materials, 1995, 31[8], 1007-9)

Table 194

Self-Diffusion of 90Sr in Strontium Niobium Titanates