Valence-fluctuation behavior of Yb ions and YbCuGa

The compound YbCuGa has been synthesized and is found to crystallize in the orthorhombic ${\mathrm{CeCu}}_2$-type structure. Its magnetic susceptibility has been measured between 4.2 and 300 K and shows a broad maximum at about 190 K. This maximum is a characteristic feature of the mixed-valent Ce- and Yb-based compounds. The temperature-dependent resistivity exhibits an S-type behavior. The thermoelectric power is negative between 20 and 300 K and also shows a broad minimum at about 190 K. ${\mathit{L}}_3$ x-ray-absorption near-edge-structure (XANES) measurements show the two-peak pattern that corresponds to two different valence states of Yb. Thus, magnetic susceptibility, electrical resistivity, thermoelectric power, and ${\mathit{L}}_{\mathrm{\beta }}$ XANES measurements all point to the mixed-valence nature of Yb ions in YbCuGa.