High-pressure Structural Research Using DAC： XRD and XES Measurements of Transition Metal Difluorides under High Pressure

Abstract

Regarding to pressure response to the high-pressure phase, generally the fluoride is more sensitive than oxides. Therefore, fluorides are frequently used as analog materials for investigating novel high-pressure phases in oxides. The high-pressure phase sequence in metal MnF₂, and CoF₂ was investigated with x-ray diffraction (XRD) and x-ray emission spectrum (XES) measurements under high pressure by using a laser-heated diamond anvil cell at synchrotron radiation facilities. The transition from rutile to orthorhombic I phase, and further transformation to cotunnite phase were confirmed in MnF₂ at 3.9 GPa and 9.9 GPa, respectively. An anomaly exhibiting a negative linear compressibility in the b axis was detected by XRD measurements of the cotunnite phase above 80 GPa. The anomaly may be related to the intensity change of MnKβ’ in XES suggesting high-spin low-spin in Mn²⁺. The PdF₂-to-CaF₂ phase transition occurred at 12 GPa in CoF₂. The XES reflects the coordination change from PdF₂ to CoF₂ structure.