Synchrotron X-ray diffraction and absorption studies of CeM2X2 (M=Cu, Ni and X=Si, Ge) at high pressure

The equations of state of CeCu2Si2 and CeCu2Ge2 to about 60 GPa, as well as that of CeNi2Ge2 to 22 GPa and the valence state of Ce in CeCu2Ge2 to 20 GPa have been studied at room temperature in a diamond-anvil cell using synchrotron radiation sources. In each compound, the ambient-pressure phase (tetragonal ThCr2Si2-type structure) persisted to the highest pressure studied. The unit cell volumes of CeNi2Ge2 at ∼5 GPa and CeCu2Ge2 at ∼7 GPa, respectively, approached that of CeCu2Si2 taken at ambient pressure. From the equation-of-state data, the bulk modulus was derived to be 112.0±5.1 GPa for CeCu2Si2, 125.6±4.3 GPa for CeCu2Ge2, and 178.4±14.3 GPa for CeNi2Ge2. The valence state of Ce in CeCu2Ge2 remained trivalent throughout the pressure range investigated.