Fe3+ spin transition in CaFe2O4 at high pressure

作者：Merlini Marco^*; Hanfland Michael; Gemmi Mauro; Huotari Simo; Simonelli Laura; Strobel Pierre

来源：American Mineralogist, 2010, 95(1): 200-203.

DOI：10.2138/am.2010.3347

• CaFe2O4
• high pressure
• spin transition
• single crystal

Single-crystal diffraction data collected for CaFe2O4 at high pressure reveal above 50 GPa an isosymmetric phase transition (i.e., no change in symmetry) marked by a volume decrease of 8.4%. X-ray emission spectroscopic data at ambient and high pressure confirm that the nature of the phase transition is related to the Fe3+ high-spin/low-spin transition. The bulk modulus K-0 calculated with a Birch Murnaghan EoS (K' = 4) is remarkably different [K-0 = 159(2) GPa for CaFe2O4 "high spin" and K-0 = 235(10) GPa for CaFe2O4 "low spin"]. Crystal structure refinements reveal a decrease of 12% of the Fe3+ crystallographic site volume. The geometrical features of the low-spin Fe3+ crystallographic site at high pressure (bond lengths, volume) indicate a relevant decrease of Fe3+-O bond lengths, and the results are in agreement with tabulated values for crystal radii of Fe3+ in high- and low-spin state. The reduced crystal size of Fe3+ in the low-spin state suggest that in lower mantle assemblages, Fe3+ partitioning in crystallographic sites should be strongly affected by the iron spin state.

• 出版日期2010-1