Electrical conductivity of San Carlos olivine along [100] under oxygen- and pyroxene-buffered conditions and implications for defect equilibria

The electrical conductivity along [100] of single crystal San Carlos olivine was measured as a function of temperature between 1100° and 1200° and oxygen fugacity between 10^-6 and 10^+0.5Pa (at 1200°C), and either with ("pyroxene-buffered') or without ("self-buffered') an added natural pyroxene buffer from a San Carlos lherzolite. Under these temperature and fO₂ conditions, electrical conduction in the self-buffered sample is attributed to polarons (Fe⁺) and electrons e^o) and in the pyroxene-buffered sample is attributed to polarons (Fe^o) and magnesium vacancies (V^//_Mg). The conductivity of the pyroxene-buffered sample is lower than that of the self-buffered sample, primarily as a result of a decrease in the polaron concentration. The electrical conductivity of both samples was found to decrease irreversibly once the samples experienced an oxygen fugacity more reducing than approximately the wustite-magnetite buffer. This effect results from loss of iron from the olivine samples to the iridium electrodes. -from Authors