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

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