High-pressure phase transformation of cobalt monoxide due to electronic transition

High-pressure behavior of rocksalt-type CoO was investigated by shock and s tatic experiments up to 106 and 131 GPa, respectively. A phase transition w as detected at 81 +/- 1 GPa from the measurements of shock compression curv e. X-ray diffraction study under static high-pressure revealed two phase tr ansitions at about 80 GPa and 120 GPa. The crystal structure of both high-p ressure phases was closely related to the rocksalt structure. The volume de crease accompanied by the phase transition was estimated to be about 5%. Th e high-pressure phase was reversibly transformed to the ambient phase on un loading. From comparison of recent first principle calculations, electronic transition with magnetic collapse in Co2+ was inferred.