A theory is developed for the hcp-fcc structural phase transition in close-packed metals as a function of the average electron concentration per atom. It is found that the transition can be continuous at low temperatures. Ordered polytypic stacking sequences are found near the transition point. Short-period structures are stabilized by Fermi-surface effects but long-period structures result from elastic distortion of the lattice. Unusual ‘‘staircase’’ crystallographic data for Mg-based Friauf-Laves alloys are accounted for successfully and the structure of rare-earth intermetallic alloys is discussed.

• Received 1 March 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.214