Potassium self-diffusion in a K-rich single-crystal alkali feldspar

The paper reports potassium diffusion measurements performed on gem-quality single-crystal alkali feldspar in the temperature range from 1169 to 1021 K. Natural sanidine from Volkesfeld, Germany was implanted with 43K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}^{43}{\hbox {K}}$$\end{document} at the ISOLDE/CERN radioactive ion-beam facility normal to the 001\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( 001\right)$$\end{document} crystallographic plane. Diffusion coefficients are well described by the Arrhenius equation with an activation energy of 2.4  eV and a pre-exponential factor of 5×10-6m2/s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$5 \times 10^{-6}\,{\hbox {m}}^2/{\hbox {s}}$$\end{document}, which is more than three orders of magnitude lower than the 22Na\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}^{22}{\hbox {Na}}$$\end{document} diffusivity in the same feldspar and the same crystallographic direction. State-of-the-art considerations including ionic conductivity data on the same crystal and Monte Carlo simulations of diffusion in random binary alloy structures point to a correlated motion of K and Na through the interstitialcy mechanism.