Pressure-induced electronic phase transition in compound EuCu₂Ge₂

We report the high-pressure XANES study of the electronic phase transition from 4f⁷ to 4 f ⁶ configuration of europium in the rare-earth compound EuCu₂Ge₂. 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 3 d -4 f hybridization in this system. The study also compares the mechanisms of external and "chemical" pressure by the Si substitution in Ge site in series EuCu₂(Si_xGe_1-x)₂. (paper)