A CUBIC AUBE5-TYPE YBCU5 PHASE WITH TRIVALENT YB ION

The cubic YbCu5 compound with the AuBe5-type structure was prepared fo r the first time under a pressure of 1.5 GPa and annealed at 650 degre es C. The previously reported hexagonal YbCu5 phase with the CaCu5-typ e structure was also confirmed to be stable under relatively lower pre ssure and at higher temperature. In contrast to the divalent non-magne tic state of Yb ion in the hexagonal phase, Yb ion in the cubic phase was found to be in the trivalent magnetic state. The cubic YbCu5 phase probably presents a reasonable conjunction for a family of isostructu ral YbCu(5-x)M(x) (M = In, Ag, etc.) compounds, both in crystallograph ic aspect and in physical properties.