The diffusion of Ga into quartz and bulk-fused silica was studied by means of neutron

activation analysis. Slow and fast diffusion of Ga was observed in the bulk-fused silica (table 167) whereas, in the quartz, only slow diffusion was observed. The difference in the diffusion mechanisms was explained on the basis of the difference in porosity of the two materials. In the bulk-fused silica, which had a lower density (2.20g/cm3), there were 2 regions, with high and low densities. The higher-density region was composed of cristobalite, which had a maximum distance between atomic strings of less than 6Å. The lower-density region was composed of a random network of Si and O atoms and, in the network, there existed many micro-channels whose average diameter and real density were estimated to be 17Å and 7.5 x 1011/cm2, respectively. These micro-channels acted as high-speed diffusion paths, while the cristobalite region was the slow diffusion path. In quartz, which had a density of 2.65g/cm3, the widest interatomic spacing, perpendicular to the c-axis was about 5Å and only slow (bulk) diffusion could occur.

Diffusion of Gallium in Quartz and Bulk-Fused Silica. S.Mizutani, I.Ohdomari, T.Miyazawa, T.Iwamori, I.Kimura, K.Yoneda: Journal of Applied Physics, 1982, 53[3], 1470-3

Table 167

Diffusivity of Ga in Fused Silica