SURFACE RECONSTRUCTION OF Y(1120)

We report the first observation of surface reconstruction in a HCP metal. Above about 610 K low-energy electron diffraction (LEED) patterns from the (11 OVER BAR 20) face of yttrium metal have two-fold symmetry and are characteristic of the ideal surface. Below this temperature the patterns comprise two principal and congruent sets of diffraction spots, each with sixfold symmetry, rotated by 30 degree with respect to each other. We suggest that the transition, which is accompanied by substantial changes in UV photoemission spectra, corresponds to the formation of terraces of close-packed atoms on the surface, involving an approximately 60% increase in atom density.