Grain boundaries and their effect on thermonigration in pure lead at low diffusion temperatures

Thermomigration in pure lead has been observed by a material flow technique over the temperature range 595-475 K. In all circumstances the flow of material was from hot to cold. At high diffusion temperatures this flow could be described, in both single crystals and polycrystals, by a reduced heat of transport $\text{Q}{}^1\text{? h}{}_{\mathrm{<mtext>f</mtext>}}\text{= 0.106±0.004}\text{eV}$. In the temperature range 515-475 K thermomigration rates in polycrystals were found to exceed those in single crystals maintained under the same conditions. The observed increases in the polycrystal flow rates varied inversely with grain diameter and were consistent with a model of grain boundary thermomigration with an effective grain boundary heat of transport ΔE′ = 0.25 eV.While the atomic flow in grain boundaries is more sensitive to temperature gradients than is that in the volume, it is suggested that the bias in atomic movement due to the asymmetry of scattering interactions is relatively smaller in grain boundaries.