Pressure-induced formation of intermediate-valence quasicrystalline system in a Cd-Mg-Yb alloy

A quasiperiodic intermediate-valence system was prepared by applying pressure to an icosahedral Cd-Mg-Yb quasicrystal. X-ray absorption spectroscopy near the Yb L₃ edge demonstrates that the Yb valence increases continuously upon compression from the divalent state (4f14) at ambient pressure and reaches a value of 2.71 at 57.6 GPa, which is close to the trivalent state (4f13). By following the trend of Yb-based intermediate-valence crystalline compounds, this large valence increase suggests the change of 4f character in the Cd-Mg-Yb quasicrystal from an itinerant state with weak electron correlations to an intermediate region between an itinerant and a localized state with strong correlations. The valence increases sensitively with pressure below ∼30 GPa; however, the increase is significantly suppressed above ∼30 GPa. The rate of valence increase with respect to pressure in the lower-pressure region is twice larger than that of a Cd-Yb quasicrystal in our previous study. This is mainly explained by the smaller bulk modulus of the Cd-Mg-Yb quasicrystal compared to the Cd-Yb system. The suppression of valence increase with respect to pressure in the higher-pressure region is most likely due to an increase of conduction-4f electron hybridization that counteracts 4f localization and reduces the Yb valence increase.