Bulk and surface valence inYbPdxcompounds

The bulk and surface valence v¯ of Yb is investigated for ${\mathrm{YbPd}}_{\mathrm{x}}$ intermetallic compounds (with x=1,1.33,3) by photoemission using synchrotron radiation. YbPd is found to be of intermediate valence (v¯≃2.75), while ${\mathrm{Yb}}_3$ ${\mathrm{Pd}}_4$ and ${\mathrm{YbPd}}_3$ are identified as bulk trivalent systems. The outermost atomic surface layer of both YbPd and ${\mathrm{Yb}}_3$ ${\mathrm{Pd}}_4$ is found to be divalent, while only a fraction of Yb surface atoms turns divalent in ${\mathrm{YbPd}}_3$. The results are compared with bremsstrahlung isochromat spectroscopy measurements and predictions based on Miedema’s scheme.