EVOLUTION FROM FIRST-ORDER VALENCE TRANSITION TO HEAVY-FERMION BEHAVIOR IN YBIN1-XAGXCU4

YbInCu4 undergoes a first-order isostructural valence transition near 40 K, whereas YbAgCu4 is a moderately heavy (gamma=250 mJ/mol K-2) mix ed-valence compound. We have succeeded in growing single crystals of t hese compounds, as well as many intermediate alloys, using flux-growth techniques. The evolution from YbInCu4 to YbAgCu4 has been characteri zed using electrical resistivity, magnetic susceptibility, and x-ray p owder diffraction. The data are interpreted in terms of the evolution of the single-impurity Kondo temperature as a function of Ag concentra tion.