The crystal structure of some copper compounds of the type RCu6

A number of rare-earth-copper alloys and thorium-copper alloys near 86 at.% Cu have been investigated by X-ray diffraction. It is shown that the compounds ThCu6 and RCu6, with R = Pr, Nd, Sm, Gd are isotypic and have the orthorhombic CeCu6 type of structure. For R = Tb and Dy no stable compound of this structure type exists.