Crossover from first-order valence transition to Kondo behavior in C15b-type YbCu5-xInx system

YbCu 5 and YbCu 4 In forms a solid-solution (YbCu 5- x In x ) with cubic AuBe 5 -type (C15b) structure in the In-concentration range 0.1≦ x ≦1; and below x =0.1, it coexists with a hexagonal CaCu 5 -type YbCu 5 phase under ambient pressure. The magnetic susceptibility and high-field magnetization measurements reveal that the first-order valence transition in YbCu 4 In shifts to higher temperature and becomes broadened significantly with decreasing In-content, and simultaneously the delocalized mixed-valent state of Yb ion ( x =1) shows a continuous change toward the localized trivalent state ( x =0). The electrical resistivities of YbCu 5- x In x display various temperature-dependencies: ranging from a pronounced drop at x =1, via a minimum behavior for 0.4≤ x ≤0.7, to a negative logarithmic increasing behavior (-ln T ) for x ≤0.3. Above results suggest that YbCu 5- x In x goes through a crossover from a valence fluctuation system to a dence Kondo one with decreasing x . At x =0, the formation of Kondo la...