PREVIEW / CITATION / ENGLISH - "Using density functional theory plus Hubbard U calculations, we show that the ground state of (Mg; Fe)(Si; Fe)O₃ perovskite, the major mineral phase in Earth’s lower mantle, has high-spin ferric iron (S = 5=2) at both dodecahedral (A) and octahedral (B) sites. With increasing pressure, the B-site iron undergoes a spin-state crossover to the low-spin state (S = 1=2) between 40 and 70 GPa, while the A-site iron remains in the high-spin state. This B-site spin-state crossover is accompanied by a noticeable volume reduction and an increase in quadrupole splitting, consistent with recent x-ray diffraction and Mössbauer spectroscopy measurements. The anomalous volume reduction leads to a significant softening in bulk modulus during the crossover, suggesting a possible source of seismic-velocity anomalies in the lower mantle."

DOI:10.1103/PhysRevLett.106.118501
PACS:91.60.Pn, 76.80.+y, 91.60.Fe, 91.60.Gf

"FIG. 1 (color online). Atomic structure of (Mg_0,875Fe_0,125)(Si_0,875Fe_0,125)O₃ Pv, configured with the shortest iron-iron distance, viewing along the [001] direction. Large (orange) and small (green) spheres represent Fe and Mg sites, respectively. Si-O and Fe-O octahedra are shown in opaque [dark(blue)] and translucent [light (orange)] colors."

Project Part:

P07 Electronic Structure of Solids, Surfaces and Nanostructures

External Link:

PRL - Physical Review Letters

Remark:

Cover Highlight of Volume 106, Issue 11 (Print)

Remark:

Mentioned in "Physics Today" from May 2011 - Volume 64, Issue 5, Search and Discovery