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 D1.75=0.95×10^-2e^-8800/RT cm²/sec^-1, which is in good agreement with previously published results; the diffusivity between 3 and 9 kbar is described by D3 to 9=6.18×10^-2e^-10900/RT cm²/sec^-1. Average activation volumes between P=0 and 1.75 kbar are in the range of $0.7V$ (V is the atomic volume of Pb); above $P=3.38$ kbar, they are nearly zero.