Electronic structure and character of long-period superstructures in precious-metal alloys

Based on ab initio calculations of the electronic structure, an attempt is made to identify reasons for the qualitatively different character of long- period superstructures (LPS) with large and small superperiods 2M in alloys of noble metals. Two different groups of alloys were investigated: Au3Cu a nd Cu3Pd (of relatively large M) and Ag3Mg (of relatively small M). The nat ure of two-dimensional incommensurate LPS in the Au3Cu and Cu3Pd has been r evealed. Analysis of the relationship between the nesting properties of the Fermi surface (FS) and the structure of LPS in the alloys under study is p erformed. it is shown that the dependence of LPS character on the value of 2M is controlled by the quality of nesting on the Fermi surface and sensiti vity of the nesting vector 2 (k) over bar (F) to variations in the long-ran ge order parameter. (C) 2000 Elsevier Science B.V. All rights reserved.