Compressibility and high-pressure structural behavior of Mg₂Fe₂O₅

Abstract

The compressibility and structural behavior of the novel Mg 2 Fe 2 O 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 2 Fe 2 O 5 can be described using a second-order Birch-Murnaghan equation of state (BM2 EoS) with V 0 = 352.4(2) Å 3 and K 0 = 171(4) GPa. Three linear BM2 EoS were used to describe the axial compressibility of Mg 2 Fe 2 O 5 , which was found to be highly anisotropic. The a and b lattice parameters have very similar compressibilies, with a 0 = 2.8917(11) Å and linear modulus M a = 572(16) GPa and b 0 = 9.736(3) Å and linear modulus M b = 583(15) GPa, respectively. The c-axis is the most compressible direction as indicated by the smaller linear modulus [c 0 = 12.520(15) Å and M c = 404(28) GPa]. The Mg 2 Fe 2 O 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 2 Fe 2 O 5 has recently been added to the list of stable end-members of phases with M 4 O 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 2 Fe 2 O 5 (this study) and Fe 4 O 5 .

Ab initio study of lithium intercalation into a graphite nanoparticle

“…To find the interlayer spacing we follow the technique outlined by Bramley et al to expand our unit cell. 63 We iterate upon this technique by only varying a single lattice parameter, or interlayer spacing (c), as demonstrated by Siersch et al , 64 between 2.978 and 4.964 Å. The kinetic energy cutoff was kept constant throughout (732.32 eV) while the number of psinc functions, that form our basis set, along the z -axis were increased.…”

“…1b. 64,66,67 . As only the interlayer spacing is varied this is what is displayed on the x-axis instead of volume.…”

“…1b. 64,66,67 As only the interlayer spacing is varied this is what is displayed on the x-axis instead of volume. We use the least mean square method to fit this equation to our results.…”