Investigation of the atomic vibration amplitudes in two alloys: silver-copper and gold-copper

The paper gives an account of the determination of the atomic vibration amplitudes in two alloys: silver-copper (409 at.% Cu) and gold-copper (AuCu3). It is found that the introduction of copper to the extent of 409 at.% into pure silver does not alter the inter-atomic binding forces of the silver atoms appreciably whereas the binding energy of the copper atom in the alloy is reduced to about 75% of its value in pure copper. Curves are given showing how the atomic root-mean-square displacement varies with temperature for copper in pure copper and in the alloy and for silver in pure silver and in the alloy. The second part of the paper is devoted to the determination of the characteristic temperature of the atom of `mean mass' in the gold-copper alloy AuCu3, and the study of the parallelism which exists in the changes with temperature that occur in the reflected X-ray intensity, the atomic r.m.s. displacement and the specific heat. The values of both the specific heat and the reflected X-ray intensity are governed by the extent of the atomic vibration. Increase of specific heat corresponds to a drop in the value of the characteristic temperature and a corresponding increase in the atomic r.m.s. displacement. Curves in the paper give information concerning the disappearance of long-range and short-range order amongst the atoms as the temperature is raised.