Influence of oxygen pressure on defect concentrations in olivine with a fixed cationic ratio

Details Influence of oxygen pressure on defect concentrations in olivine with a fixed cationic ratio Influence of oxygen pressure on defect concentrations in olivine with a fixed cationic ratio

Sep 1978

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978pepi...17..118s&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 17, Issue 2, p. 118-129.

Physics

15

Scientific paper

The variation of the point-defect concentrations with oxygen partial pressure, PO2, and temperature are derived for forsterite, Mg2SiO4, and Mg-rich olivine (Mg,Fe)2SiO4 assuming the cation/cation ratios are fixed. These dependencies differ from the open-system situation in which matter is easily transferable between forsterite or olivine and other solid phases. The details depend on whether the cation/cation ratio is exactly stoichiometric, or, if non-stoichiometric, the nature of the majority defects at precise oxygen stoichiometry. One generality which emerges is that regardless of the cation/cation stoichiometry the dominant defects in forsterite at low PO2 are free electrons, Mg and Si interstitials; at high PO2 the majority defects are holes, Mg and Si vacancies. In Mg-rich olivine the same defect species exist at the extremes of oxygen partial pressure with the exception of trivalent Fe on Mg sites replacing holes. At low PO2, therefore, both behave as n-type conductors. The models also suggest that in the PO2 range around precise oxygen stoichiometry the electrical conductivity in both materials can be a complex function of PO2.

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