PREPARATION OF CUBIC AUBE5-TYPE YBCU5-XALX LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5) UNDER HIGH-PRESSURE AND THEIR KONDO BEHAVIOR

Cubic AuBe5-type YbCu5-xAlx (0 less than or equal to x less than or eq ual 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 indi cate 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 f ormation. The Yb ion in this system is found to be in a stable trivale nt state (4f(13), J=7/2) with a localized moment close to 4.54 mu(B) o f free Yb3+ ion. Contrary to the consistent magnetic behavior, the tem perature dependence of electrical resistivities of YbCu5-xAlx displays a systematic transition from a typical Fermi liquid behaviour rho(T)p roportional to T-2 (x less than or equal to 0.1) to a Kondo impurity b ehavior p(T)proportional to-log T (x greater than or equal to 0.3). Th e characteristic Kondo temperature T-K is largely lowered during this crossover. (C) 1998 Elsevier Science S.A.