Points Defects and the Mechanisms of Electrical Conduction in Olivine
- Robert N. Schock
Published Online: 18 MAR 2013
Copyright 1985 by the American Geophysical Union.
Point Defects in Minerals
How to Cite
Schock, R.N. and Duba, A.G. (1985) Points Defects and the Mechanisms of Electrical Conduction in Olivine, in Point Defects in Minerals (ed R. N. Schock), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM031p0088
- Published Online: 18 MAR 2013
- Published Print: 1 JAN 1985
Print ISBN: 9780875900568
Online ISBN: 9781118664070
- Mineralogical chemistry—Congresses;
Measurements of electrical conductivity on single crystals of naturally occurring olivine and synthetic forsterite as a function of oxygen fugacity indicate that point defects play a crucial role in this process. Conductivity data (at 1200°C) reveal n-type conduction in forsterite and p-type conduction in natural peridot. Since the activation energies for conduction (2–3 eV) are well below the measured band gap in these olivines, conduction must be either an extrinsic electronic or an ionic process. Expected energy levels of impurities such as iron are such that either ionic or electronic charge carriers are energetically favorable. The electrical conductivity of forsterite decreases with increasing oxygen fugacity, which is consistent with conduction by electrons. Electrons are made available for conduction by the loss of oxygen from the crystal, which produces point defects and free electrons. Favorable defects include oxygen vacancies and magnesium and silicon interstitials. However, in the presence of iron, as in olivine, conductivity increases with increasing oxygen fugacity. Ferrous iron in the olivine can be oxidized to the ferric state as oxygen fugacity increases. In this case it is not necessary to produce electrons to balance the charge, since the creation of magnesium vacancies accomplishes the same result. Trivalent iron now carries the charge as if it were an electron hole. It is likely that the magnesium vacancies created to balance the charge also affect other physical properties, including creep, diffusivity, and possibly acoustic attenuation.