METASTABLE PHASES IN EPITAXIAL Nb-La AND Nb-Ce SYSTEM

Epitaxial metal film sandwiches of Nb-La-Nb and Nb-Ce-Nb have been prepared in an ultra high vacuum environment. In the sandwiches the La layers and Ce layers are found to be fcc La and bcc Ce, respectively, different from that of bulks. The transmission electron microscope (TEM) observations indicate that La or Ce was grown with partial pseudomorphism epitaxy on bcc Nb layers. The origin of the unusual epitaxies has been discussed.