Systematics of the post-spinel tranisition in Fe-bearing compositions
Final Report Abstract
The experimental results from this project are 1) that FeAl2O4 (hercynite) breaks down into its constituent oxides at high pressures and apparently does not have a high-P polymorph (unlike MgAl2O4), 2) the thermodynamic properties of FeAl2O4 are consistent with the earlier values listed by Holland & Powell (1990) with a relatively high S°298 rather than the newer Holland & Powell (1998) formulation, 3) in situ resistivity and diffraction measurements reveal that Fe3O4, magnetite, undergoes a transition to a post-spinel phase with the phase boundary being nearly isobaric at 9.5-10 GPa, 4) the post-spinel phase has a different structure from that previously proposed, 5) a new post-spinel phase is consistent with resistivity measurements, which reveals semiconductor-like behaviour rather than the metallic-like behaviour previously observed for a CaTi2O4-structured polymorph, and 5) the post-spinel phase also occurs in Fe3O4-bearing binary solid solutions with Fe2SiO4 or FeCr2O4, however, the phase relations are more complicated than expected. Determination of the structure of the post-spinel "mystery phase" of Fe3O4 is the subject of continuing study.
Publications
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(2009). Detecting the Spinel-Post-Spinel Transition in Fe3O4 by in situ Electrical Resistivity Measurements. High Pressure Research
Schollenbruch K, Woodland AB, Frost DJ, Langenhorst F
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(2009). Determination of the phase boundary Fe3O4 - h-Fe3O4 at high temperature and pressure using in situ synchrotron radiation. American Geophysical Union (AGU) Fall Meeting, San Francisco Dec. 2009
Schollenbruch K, Woodland AB, Frost DJ, Wang Y, Takeshi S, Boffa-Ballaran T
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(2009). The stability of hercynite at high pressures and temperatures. Physics and Chemistry of Minerals
Schollenbruch, Woodland AB, Frost DJ
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(2010). The post-spinel transition in Fe3O4-Fe2SiO4 and Fe3O4-FeCr2O4 solid solutions. European Geosciences Union (EGU) Meeting, Vienna, 02-07 May 2010
Schollenbruch K, Woodland AB, Frost D, Langenhorst F
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(2010). The post-spinel transition in Si- and Cr-bearing Fe3O4 solid solutions. International Mineralogical Association (IMA) Meeting, Budapest, 21-27 Aug. 2010
Schollenbruch K, Woodland AB, Frost DJ, Langenhorst F, Boffa Ballaran T
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(2011). In situ determination of the spinel - post-spinel transition in Fe3O4 at high temperature and pressure by synchrotron X-ray diffraction. American Mineralogist
Schollenbruch K, Woodland AB, Frost DJ , Wang Y, Sanehira T, Langenhorst
