Transient electrical response of San Quintin Dunite as a function of oxygen fugacity changes: Information about charge carriers

Abstract

The electrical conductivity (σ) of San Quintin dunite (SQD) measured between 950 and 1150°C at controlled oxygen fugacity (fO2) within the olivine stability field shows transients in response to changes in fO2. Such behavior has not been reported previously for measurements made under similar conditions on either olivine single crystals or polycrystalline samples (dunites and lherzolites) in which olivine is the major phase. In general for olivine, an increase in fO2 results in an increase in σ. The transient is manifested as a change in σ from a stable equilibrium value at a specific fO2 to a quickly established subsequent value, the direction of which is opposite that of the final value that will be attained for the fO2 change. This transient may be caused by a changing population of electrons produced by oxygen vacancies, the grain boundaries, or a short‐lived defect. We postulate that the transient is observed in this particular dunite because of its large surface area to volume ratio. The transient is more pronounced at relatively high fO23 and temperatures between 950 and 1100°C. At relatively low fO2s and temperatures higher than 1100°C, the effect is diminished. The Seebeck coefficient (S), at 1200°C, is slightly smaller than that reported for single‐crystal olivine, and at 1100°C is similar to that reported for single crystal olivine.