Electrical conductivity of synthetic iron-bearing olivine

Abstract

The electrical conduction in synthetic, dry polycrystalline, iron-bearing olivine (Fo90) was investigated as a first-order approach to the electrical conductivity in the upper mantle. This fundamental study is of great importance to better understand the charge-transport mechanisms seen in olivine. Conduction processes in synthetic samples are not influenced by a complex geological history in contrast to conductivity in natural olivine. The experiments show that the apparent activation energy for conductivity for Fo90 is 230 kJ mol−1. In currently accepted defect modeling, natural and synthetic olivine requires a mechanism involving small polaron formation (Fe· Mg and magnesium vacancies (V Mg) as the dominant diffusing species to explain a fO 2 1/6 relation to electrical conduction. Here, Fo90 shows no contribution of small polarons to conductivity at temperatures between 1,000 and 1,200°C and almost no dependence on fO2. Instead, under reducing conditions magnesium vacancies (and electrons) appear to be the major charge carriers.