TRANSIENT ELECTRICAL RESPONSE OF SAN QUENTIN-DUNITE AS A FUNCTION OF OXYGEN FUGACITY CHANGES - INFORMATION ABOUT CHARGE-CARRIERS

The electrical conductivity (sigma) of San Quintin dunite (SQD) measur ed between 950 and 1150-degrees-C at controlled oxygen fugacity (f(O2) ) within the olivine stability field shows transients in response to c hanges in f(O2). Such behavior has not been reported previously for me asurements made under similar conditions on either olivine single crys tals or polycrystalline samples (dunites and lherzolites) in which oli vine is the major phase. In general for olivine, and increase in f(O2) results in an increase in sigma. The transient is manifested as a cha nge in sigma from a stable equilibrium value at a specific f(02) to a quickly established subsequent value, the direction of which is opposi te that of the final value that will be attained for the f(O2) change. This transient may be caused by a changing population of electrons pr oduced by oxygen vacancies, the grain boundaries, or a short-lived def ect. We postulate that the transient is observed in this particular du nite because of its large surface area to volume ratio. The transient is more pronounced at relatively high f(O2)S and temperatures between 950 and 1100-degrees-C. At relatively low f(O2)S and temperatures high er than 1100-degrees-C, the effect is diminished. The Seebeck coeffici ent (S), at 1200-degrees-C, is slightly smaller than that reported for single-crystal olivine, and at 1100-degrees-C is similar to that repo rted for single crystal olivine.