Application of the Yb-172 PAC probe to the study of Yb atom charge states in solids

We present PAC measurements performed using the 172Yb probe in two Yb intermetallic compounds, Yb4As3 and Yb5Si3. The hyperfine quadrupole interaction was measured in a wide temperature range from 78 to 850 K. The temperature dependence of the electric field gradient differentiates divalent and trivalent Yb ions. In Yb4As3 we observe a phase transition at 295 K and a heterogenous mixed valence state in the low temperature phase. By contrast, the Yb ions in the two crystallographic sites in Yb5Si3 can be classified as trivalent Yb ions with a large crystal field interaction