The Fermi surface of the HCP Cu-Ge alloys containing 12-15 at.% Ge studied by positron annihilation

Abstract

The Fermi surface of the Cu-Ge alloy in the HCP zeta phase field is studied by measurements of momentum distributions of annihilation photons from two single crystals at e/a=1.38 and 1.45. The Fermi surface of the alloy at e/a=1.38 lies inside the Jones zone, and has a high degree of contact with the zone faces. A normal to (10.0) and a small degree of contact with the zone faces B normal to (00.1). The overlap of the Fermi surface across the A faces is observed for the alloy at e/a=1.45. Remarkable bulges of the Fermi surface are detected along the directions towards the faces C normal to (10.1) in both the compositions. The present results reveal the correlation between the overlapping of the Fermi surface across the zone faces and the change of lattice constant. The relative stability of the HCP zeta phase is discussed in the light of the experimental results.