Valence fluctuations in the 3D+3 modulated Yb3Co4Ge13 Remeika Phase

Yb3Co4Ge13 is the first example of a Remeika phase with a 3D + 3 [space group P43n(a,0,0)000(0,a,0)000(0,0,a)000; a = 8:72328(1) Å, Q1 = Q2 = Q3 = 0:4974(2)] modulated crystal structure. A slight shift of the composition towards higher Ybcontent (i:e: Yb3:2Co4Ge12:8) leads to the disappearance of the satellite reflections and stabilization of the disordered primitive cubic [space group Pm3n, a = 8:74072(2) Å] Remeika prototype structure. The stoichiometric structurally modulated germanide is a metal with hole-like charge carriers, where Yb-ions are in a temperature dependent intermediate valence state of +2:60+2:66 for the temperature range 85-293 K. The valence fluctuations have been investigated by means of temperature dependent X-ray absorption spectroscopy, magnetic susceptibility and thermopower measurements