New low-temperature phase of Yb metal and its relation to alpha-Ce

A new fee phase of Yb metal has been prepared by epitaxial growth below 190 K, which is stable at least up to 400 It. As determined by x-ray diffracti on in situ, the spacing between close-packed layers is reduced by approxima te to 0.6% compared to the well-known fcc phase beta-Yb, corresponding to a lower 4f binding energy observed by photoemission. Growth at room temperat ure, in contrast, results in beta-like Yb films. The existence of two fcc p hases of Yb metal is discussed in analogy to the isostructural gamma-alpha phase transition of Ce metal.