Pressure-induced valence and structural changes in YbMn < inf > 2 < /inf > Ge < inf > 2 < /inf > -Inelastic X-ray spectroscopy and theoretical investigations

Abstract

The pressure-induced valence change of Yb in YbMn2Ge2 has been studied by high pressure inelastic X-ray emission and absorption spectroscopy in the partial fluorescence yield mode up to 30 GPa. The crystal structure of YbMn2Ge2 has been investigated by high pressure powder X-ray diffraction experiments up to 40 GPa. The experimental investigations have been complemented by first principles density functional theoretical calculations using the generalized gradient approximation with an evolutionary algorithm for structural determination. The Yb valence and magnetic structures have been calculated using the self-interaction corrected local spin density approximation. The X-ray emission results indicate a sharp increase of Yb valence from v = 2.42(2) to v = 2.75(3) around 1.35 GPa, and Yb reaches a near trivalent state (v = 2.95(3)) around 30 GPa. Further, a new monoclinic P1 type high pressure phase is found above 35 GPa; this structure is characterized by the Mn layer of the ambient (I4/mmm) structure transforming into a double layer. The theoretical calculations yield an effective valence of v = 2.48 at ambient pressure in agreement with experiment, although the pure trivalent state is attained theoretically at significantly higher pressures (above 40 GPa). © 2013 American Chemical Society.