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The equation of state of Mg 0.6 Fe 0.4 O to 200 GPa
Author(s) -
Vassiliou M. S.,
Ahrens Thomas J.
Publication year - 1982
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl009i002p00127
Subject(s) - thermodynamics , phase transition , equation of state , isothermal process , materials science , wüstite , isentropic process , porosity , mineralogy , condensed matter physics , physics , geology , hematite , composite material
New Hugoniot data on polycrystalline (avg.porosity 6.9%) samples of the magnesiowustite Mg 0.6 Fe 0.4 O are presented, covering the pressure range up to 200 GPa. When our data are fit by a single 3rd order Eulerian Hugoniot with K O constrained to its ultrasonic value of 161.5 GPa, the required isentropic pressure derivative K O ′ is 4.37 +/− 0.37. This value is significantly lower than the ultrasonic one of 6.18; existing isothermal compression data, however, are in agreement with our value rather than the ultrasonic one. Our data are adequately explained without phase transitions. There is some marginal evidence for a possible phase transition around 120 GPa. If such a transition indeed occurs it is probably of small volume change compared to the transition observed in FeO; we place an extreme upper bound of 3% on the density change such a transformation could involve and still be consistent with the data. Contrary to earlier hypotheses, we believe that a phase transition in magnesiowustite is not a likely explanation of the seismic effects in the D″ region of the lower mantle. The wustite transition may be a more complex phenomenon than initially supposed— perhaps an effect of nonstoichiometry localized to the iron‐rich end of the solid solution series.