Abstract
Magnesiowüstite (Mg,Fe)O and silicate perovskite (Mg,Fe)SiO3 are believed to be the dominant mineral phases in the earth’s lower mantle (Jeanloz and Thompson, 1983). However, under sufficiently high pressures, octahedrally coordinated Fe2+ cations are expected to undergo a high-spin (S = 2) to low-spin (S = 0) transition. Such a transition in magnesiowüstite might have implications for the physics and chemistry of the lower mantle. Several investigators have attempted to calculate the pressure at which low-spin FeO becomes stable relative to high-spin FeO (Fyfe, 1960; Strens, 1969; Gaffney and Anderson, 1973; Tossell, 1976; Ohnishi, 1978). The purpose of this chapter is to review the current status of the problem and to improve on previous estimates of the free energy for the HS → LS transition of FeO as a function of pressure and temperature. Using an approximate mantle geotherm, the depth at which low-spin FeO becomes stable relative to high-spin FeO is estimated.
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Sherman, D.M. (1988). High-Spin to Low-Spin Transition of Iron(II) Oxides at High Pressures: Possible Effects on the Physics and Chemistry of the Lower Mantle. In: Ghose, S., Coey, J.M.D., Salje, E. (eds) Structural and Magnetic Phase Transitions in Minerals. Advances in Physical Geochemistry, vol 7. Springer, New York, NY. https://doi.org/10.1007/978-1-4612-3862-1_6
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DOI: https://doi.org/10.1007/978-1-4612-3862-1_6
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