Site occupation in the Cr-Ru and Cr-Os phases

The site occupation in the Cr-Ru and Cr-Os phases is computed as a function of temperature. Generally, in phases the larger atoms occupy the sites with larger coordinations numbers, as can be explained on the basis of atomic-size and electronic structure. However, for Cr2Ru and Cr2Os the atomic-size argument predicts that Ru and Os occupy the sites with larger coordination numbers, whereas the reasoning based on the approximate degeneracies of electronic levels predicts that Cr occupies those sites. By comparing these predictions with the theoretically computed and the experimentally measured site occupations, the atomic-size and electronic arguments can be judged on their predictive merits.