THE ORIGIN OF SHORT-RANGE ORDER IN AG-MG ALLOYS

We have calculated the Fermi surfaces of a number of alpha-phase Ag Mg solid solution alloys. We find that there are well-defined, parallel regions of surface in the [110] directions at which nesting could occu r giving rise to the formation of concentration waves and satellite pe aks in the electron diffuse scattering. The positions of the intensity maxima are related directly to the vector spanning such parallel regi ons and we show that the calculated variation of the peak separation w ith Mg concentration is in excellent agreement with the experimentally measured values. Thus, we provide strong evidence that the short-rang e-order in alpha-phase Ag-Mg alloys is Fermi surface driven.