Photoemission studies of mixed valence in Yb3Si3, YbSi and Yb5Si3: Equivalent versus inequivalent Yb sites

Abstract We present angle integrated 4ƒ photoemission from Yb 3 Si 5 , YbSi and Yb 5 Si 3 taken with synchrotron radiation ( hv = 80 eV, hv = 450 eV, and hv at the 4d-4ƒ threshold). The Yb valence is determined and Si2 p shifts are also given. Yb 3 Si 5 and YbSi are homogeneous mixed valent in the bulk; in Yb 5 Si 3 , which has inequivalent Yb sites, one Yb specie is divalent and the other is mixed valent. This shows the connection between mixed valence and local steric effects due to crystal structure. In all compounds the Yb is divalent in the surface region.