Evidence of Two Simultaneous Mechanisms for Diffusion of Cu in Pb Single Crystals

The radioactive-tracer method and sectioning technique were used to measure the diffusion coefficient of Cu in Pb single crystals under hydrostatic pressures between 1.75 and 9.00 kbar, at temperatures between (206 ± 1) and (326 ± 1)°C. The diffusivity at 1.75 kbar is described by $D_{1.75}=0.95\mathrm{}\times {10}^{-2\mathrm{}}{e}^{-\frac{8800}{\mathrm{RT}}}$ ${\mathrm{cm}}^2$/${\sec }^{-1\mathrm{}}$, which is in good agreement with previously published results; the diffusivity between 3 and 9 kbar is described by $D_{3 \mathrm{to} 9}=6.18\mathrm{}\times {10}^{-2\mathrm{}}{e}^{-\frac{10900}{\mathrm{RT}}}$ ${\mathrm{cm}}^2$/${\sec }^{-1\mathrm{}}$. Average activation volumes between $P=0\mathrm{} \mathrm{and} 1.75$ kbar are in the range of $0.7V$ ($V$ is the atomic volume of Pb); above $P=3.38\mathrm{}$ kbar, they are nearly zero.