Influence of anisotropy on the electrical conductivity and diffusion coefficient of dry K-feldspar: Implications of the mechanism of conduction

The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K-1223 K and 1.0 GPa-3.0 GPa in a frequency range of 10(-1) Hz-10(6) Hz. The measured electrical conductivity along the perpendicular to [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 +/- 0.06 eV and 2.51 +/- 0.19 cm(3)/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the perpendicular to[001] axis is approximately three times higher than that along the perpendicular to [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst-Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.