Figure 4
From: High-Pressure Orthorhombic Ferromagnesite as a Potential Deep-Mantle Carbon Carrier
Comparison of the pressure-volume relations in the (Mg,Fe)CO3 phases.
(A) Unit cell volume of siderite I and II phases as a function of pressure at ambient temperature. The vertical axis is plotted as the unit cell volume per formula unit (V/Z). The number of molecules per unit cell (Z) is 6 for siderite I and 12 for siderite II. HS: high-spin state; LS: low-spin state. Solid curves: modeled BM EoS fits of the experimental results. The volume collapse of 9.2 (±0.5)% and 3.9 (±0.4)% for siderite I and II can be associated with their respective spin transition at high pressures. Solid diamond: V/Z of magnesite II re-calculated from Isshiki et al.10 (Table S5); Solid triangle: V/Z of the high-pressure phase of magnesiosiderite [(Mg0.25Fe0.75)CO3] re-calculated from Boulard et al.16 (Table S6). (B) Lattice parameters of the siderite II as a function of pressure at 300 K. The lattice collapse in siderite II is 1.9%, 1.0% and 1.0% for a/a0, b/b0 and c/c0, respectively, at approximately 60 GPa. Filled symbols: compression; open symbols: decompression.
