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 and Cu3Pd (of relatively large M) and Ag3Mg (of relatively small M). The nature of two-dimensional incommensurate LPS in the Au3Cu and Cu3Pd has been revealed. Analysis of the relationship between the nesting properties of the Fermi surface (FS) and the structure of LPS in the alloys under study is performed. 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 sensitivity of the nesting vector 2k→F to variations in the long-range order parameter.