Valency Changes of Ce, Yb and U in Intermetallic Compounds with Ni and Cu

It is well known that in intermetallic compounds Yb as well as Ce can have two different valence states. Recently indications were obtained that this is also the case for U. The valence adopted by these elements depends in general on the composition of the particular intermetallic compound, on the temperature and on the applied pressure. In some cases the valence state seems to be less clearly defined in that the elements mentioned show valences apparently intermediate between two integral values.