¹Kanako Yoshihara,²Akira Yoshiasa,³Huimin Shao,⁴Makoto Tokuda,⁵Ginga Kitahara,²Hiroshi Isobe
Meteoritics & Planetary Science (in Press) Open Access Link To Article [https://doi.org/10.1111/maps.70180]
¹Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan
²Department of Earth and Environmental Sciences, Faculty of Advanced Science and Technology, Kumamoto University,Kumamoto, Japan
³Chinese National Space Science Center, Beijing, China
⁴Institute of Industrial Nanomaterials, Kumamoto University, Kumamoto, Japan
⁵Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tokai, Ibaraki, Japan
Published by arrangement with John Wiley & Sons

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.