Simultaneous modeling of thermopower and electrical conduction in olivine |
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| Authors: | Steven Constable Jeffery J Roberts |
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| Institution: | (1) Institute of Geophysics and Planetary Physics, University of California San Diego, La Jolla, CA 92093–0225, USA, US;(2) Lawrence Livermore National Laboratory, L201, Livermore, CA 94551, USA, US |
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| Abstract: | Measurements of conductivity and thermopower as a function of oxygen fugacity (ƒO
2) are used to derive a model for conduction in olivine. Thermopower at 1000–1200 °C is between 50 and 400 μV/K and has a positive
ƒO
2 dependence, and electrical conductivity exhibits approximately a 1/11 power dependence on ƒO
2. However, small polarons, considered to be the conducting defect in olivine at these temperatures, would produce a larger
thermopower than observed, with a negative ƒO
2 dependence, as well as 1/6 power dependence of conductivity on ƒO
2. At least one other conducting defect species must be invoked to explain the observed magnitude and ƒO
2 dependence of thermopower. An electron/polaron model cannot be made to fit the conductivity and thermopower data well, but
a polaron/magnesium vacancy model fits the data if a constant polaron or magnesium vacancy term is included. Concentrations
from our fits are consistent with predictions from theoretical models, and our analysis predicts a transition from polaron
dominance in conduction to magnesium vacancy dominance at around 1300 °C, as has been previously inferred from other data.
Received April 2, 1996 / Revised, accepted September 6, 1996 |
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