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Compressibility and high-pressure structural behavior of Mg (sub 2) Fe (sub 2) O (sub 5)

Nicki Caroline Siersch, Tiziana Boffa Ballaran, Laura Uenver-Thiele and Alan B. Woodland
Compressibility and high-pressure structural behavior of Mg (sub 2) Fe (sub 2) O (sub 5)
American Mineralogist (April 2017) 102 (4): 845-850


The compressibility and structural behavior of the novel Mg (sub 2) Fe (sub 2) O (sub 5) oxide has been investigated by in situ single-crystal X-ray diffraction in a diamond-anvil cell up to a pressure of 17 GPa. The bulk compressibility of Mg (sub 2) Fe (sub 2) O (sub 5) can be described using a second-order Birch-Murnaghan equation of state (BM2 EoS) with V (sub 0) =352.4(2) A (super 3) and K (sub 0) =171(4) GPa. Three linear BM2 EoS were used to describe the axial compressibility of Mg (sub 2) Fe (sub 2) O (sub 5) , which was found to be highly anisotropic. The a and b lattice parameters have very similar compressibilies, with a (sub 0) =2.8917(11) A and linear modulus M (sub a) =572(16) GPa and b (sub 0) =9.736(3) A and linear modulus M (sub b) =583(15) GPa, respectively. The c-axis is the most compressible direction as indicated by the smaller linear modulus [c (sub 0) =12.520(15) A and M (sub c) =404(28) GPa]. The Mg (sub 2) Fe (sub 2) O (sub 5) structure consists of edge-sharing octahedra alternating with layers of trigonal prisms. The compression behavior of the M-O bonds of the M1 and M2 octahedra and of the M3 prisms depend on their location in either an edge-sharing environment, which makes them stiffer, or a corner-sharing environment where they have more freedom to distort and compress. The main compression mechanism consists of a polyhedral tilting around the M2-O1-M2 angle, which decreases with increasing pressure. Mg (sub 2) Fe (sub 2) O (sub 5) has recently been added to the list of stable end-members of phases with M (sub 4) O (sub 5) stoichiometry, making it a potentially relevant phase in the Earth's upper mantle and transition zone. To develop thermodynamic activity-composition models for high-pressure phases, it is crucial to know the accurate elastic parameters of each individual end-member. Currently these have only been measured for Mg (sub 2) Fe (sub 2) O (sub 5) (this study) and Fe (sub 4) O (sub 5)

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 102
Serial Issue: 4
Title: Compressibility and high-pressure structural behavior of Mg (sub 2) Fe (sub 2) O (sub 5)
Affiliation: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, Germany
Pages: 845-850
Published: 201704
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 23
Accession Number: 2017-041516
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Goethe-Universitaet Frankfurt, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201723
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