A cubic AuBe5-type YbCu5 phase with trivalent Yb ion

The cubic YbCu5 compound with the AuBe5-type structure was prepared for the first time under a pressure of 1.5 GPa and annealed at 650 C. The previously reported hexagonal YbCu5 phase with the CaCu5-type structure was also confirmed to be stable under relatively lower pressure and at higher temperature. In contrast to the divalent non-magnetic 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 isostructural YbCu5-xMx (M=In, Ag, etc.) compounds, both in crystallographic aspect and in physical properties. (orig.)