Appearance of a new coherent Kondo state by In substitution for Cu in CeCu6

The CeCu6-xInx compounds crystallize in the orthorhombic CeCu6-type structure with a large homogeneity range 0 <= x <= 1.75. At low temperatures increasing electrical resistivity with decreasing temperature, reminiscent of an incoherent Kondo state, is observed for x = 0.5, 1.25 and 1.38. However, for x = 1.0, the electrical resistivity exhibits a maximum at about 35 K and decreases rapidly at lower temperatures following the T-2 law, suggesting that the coherent Kondo state is realized in CeCu5In. From the measurements of the specific heat and the magnetic susceptibility of a single crystal, it is found that T-K of CeCu5In is 28 K, about six times as large as that of CeCu6. Among the four 4c sites for Cu in CeCu6, one of them may be preferentially occupied by the In atoms.