Preparation of cubic AuBe5-type YbCu5-xAlx (0≤x≤0.5) under high pressure and their Kondo behavior

Cubic AuBe5-type YbCu5-xAlx (0 less than or equal to x less than or equal to 0.5) has been prepared for the first time under a pressure of 1.5 GPa and at 650 degrees C. Magnetic susceptibility measurements indicate that cubic YbCu5-xAlx exhibits Curie-Weiss behavior down to 4 K, except for YbCu5 that displays a maximum at 10 K due to Fermi liquid formation. The Yb ion in this system is found to be in a stable trivalent state (4f(13), J=7/2) with a localized moment close to 4.54 mu(B) of free Yb3+ ion. Contrary to the consistent magnetic behavior, the temperature dependence of electrical resistivities of YbCu5-xAlx displays a systematic transition from a typical Fermi liquid behaviour rho(T)proportional to T-2 (x less than or equal to 0.1) to a Kondo impurity behavior p(T)proportional to-log T (x greater than or equal to 0.3). The characteristic Kondo temperature T-K is largely lowered during this crossover. (C) 1998 Elsevier Science S.A.