Volume diffusion of cobalt in tungsten single crystals.

Abstract

The temperature dependence of volume diffusion coefficients of the $^{57}\mathrm{Co}$ tracer in single crystals of tungsten has been measured in the temperature range 1680--2270 K by a sectioning method of high depth resolution based on anodic oxidation of the specimen. The temperature dependence parameters are ${\mathit{D}}_{0}$=0.${16}_{\mathrm{\ensuremath{-}}0.08}^{+0.17}$ ${\mathrm{cm}}^{2}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and Q=118.7\ifmmode\pm\else\textpm\fi{}2.7 kcal/mole. An analysis of our data shows that the diffusion of cobalt in single crystals of tungsten is ``normal'' and obeys the same regularities as diffusion of tungsten-series impurities in tungsten, for which the diffusion mechanism by monovacancies is well established [N. K. Archipova et al., Phys. Rev. B 30, 1788 (1984)]. Systematic errors in the determination of volume diffusion coefficients have been discussed. They arise when (i) one uses a low-resolution sectioning method and (ii) one does not take into account the complexity of diffusion fluxes occurring near the external surface of real crystals.