Evidence of a local BCC-type coordination of cobalt in FCC taenite of iron meteoritesOPEN ACCESS
Kanako Yoshihara, Akira Yoshiasa, Huimin Shao, Makoto Tokuda, Ginga Kitahara, Hiroshi Isobe
MAPS, First published: 09 June 2026
“Ni, Co, and Fe K-edge X-ray absorption fine structure (XAFS) measurements were performed, revealing an unexpected local structure around Co in well-known iron and stony-iron meteorites. Cobalt is enriched in kamacite but remains in taenite at concentrations of at least 0.3 atom%. The Co K-edge X-ray absorption near-edge structure (XANES) spectra of taenite with a face-centered cubic (FCC) structure in all examined iron meteorites exhibited an unexpected body-centered cubic (BCC)-type local coordination, with Co showing a coordination number of 8 + 6. The local FCC and BCC structures can be clearly distinguished based on their XANES patterns. In taenite, up to 20% of the local structure is inferred to be BCC in regions where three-dimensional periodicity is maintained. Moreover, local BCC structures are likely to predominate in subregions that do not contribute to three-dimensional periodicity. Co transforms into a locally ordered BCC structure within the high-temperature parent FCC phase of iron meteorites. In this phase, Co appears to have a stronger affinity for Fe than for Ni, leading to the formation of Co-Fe clusters with a regular BCC arrangement.”
