Pressure-induced electronic phase transition in compound $\mathrm{EuCu_2Ge_2}$

We report the high-pressure XANES study of the electronic phase transition from 4f$^7$ to 4f$^6$ configuration of europium in the rare-earth compound EuCu$_2$Ge$_2$. The hydrostatic pressure dependence of the europium valence was obtained in a wide pressure range (1-30 GPa) at room temperature. It was found that upon the pressure increase above 20 GPa the europium valence does not reach the integer value +3 but stabilizes at 2.87. The experimental results were supported by the band structure calculations in the framework of DFT, which allowed us to discuss the features of 3d-4f hybridization in this system. The study also compares the mechanisms of external and "chemical" pressure by the Si substitution in Ge site in series EuCu$_2$(Si$_x$Ge$_{1-x})_2$