The valence state of yb in ybxcu₄ (x=al, ag and ga) compounds

New ternary compounds of the type YbXCu₄, where X=Al, Ag and Ga, have been prepared. The compounds with X=Al and X=Ga are found to have the hexagonal CaCu₅-type structure while the compound with X=Ag has the cubic MgSnCu₄-type structure. Magnetic susceptibility measurements reveal that Yb is in a nearly trivalent state in YbAlCu₄, but in a divalent state in YbGaCu₄. The susceptibility of YbAgCu₄ shows a broad maximum at around 33 K, but follows a Curie-Weiss behaviour at high temperatures with an effective moment close to that of Yb³⁺. Thus both the structure type and the valence state of Yb appear to be strongly influenced by the nature of the X atom in YbXCu₄ compounds.