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

Hergemöller F., Wegner M., Deicher M., Wolf H., Brenner F., Hutter H., Abart R., Stolwijk N.

Abstract

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 at the ISOLDE/CERN radioactive ion-beam facility normal to the (001) 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 x 10-6 m2/s, which is more than three orders of magnitude lower than the 22Na 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.