Electrical conductivity, thermopower and 57Fe M�ssbauer spectroscopy of an Fe-rich amphibole, arfvedsonite

Abstract

The electrical charge transport was examined in an Fe-rich amphibole, arfvedsonite, using frequency dependent AC resistivity (impedance spectroscopy) and thermopower Θ measurements in the temperature range 30–800°C. Two different semiconducting charge transfer mechanisms were observed which are due to volume conduction for measurements parallel and perpendicular to the [001] direction; they arise probably from a conduction mechanism related to lattice defects, both with activation energies EA ≈ 0.4 eV. The extrapolated DC conductivity, for a fixed temperature, along [001] is about 5–6 times higher than that perpendicular to [001]. From the temperature independent positive Θ values it follows that hole conduction occurs, and a hopping-type charge transport is acting, probably effected by electron hopping Fe2+ → Fe3+. Possible charge transfer paths are discussed. 57Fe Mossbauer spectra enabled to determine the relative concentrations of Fe2+ and Fe3+. From a comparison of these data and from Θ results it is concluded that the main fraction of Fe2+ and Fe3+ take part in long range charge transport.