ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
In close-packed ordered alloys of composition ABn the lattice constant a and all interatomic distances are determined to a good approximation by the quantity (RA + nRB). This observation, the Pauling-Simon law [Pauling (1957). Acta Cryst. 10, 374-375; Simon (1983). Angew. Chem. 22, 95-113], is analogous to Vegard's law [Pearson (1972). The Chemistry and Physics of Metals and Alloys. New York: Wiley] for random alloys. No exact proof is possible but here a theoretical discussion is given using the spirit of Froyen & Herring's 'proof' of Vegard's law [Froyen & Herring (1981). J. Appl. Phys. 52, 7165-7167]. The effect of a change in radius ratio can be discussed precisely with the virial Σi FiDi either in terms of the exact crystal structure surrounding each type of atom or by approximating it as a close-packed medium treated as a uniform isotropic continuum. The essential point is that the A and B sites have to be elastically equivalent in the sense that a radius change δR on either site has to produce the same overall volume change. From this it is found that the interatomic force constant is proportional to D-m, where D is the spacing between atoms and m lies between 3 and 4, more or less consistent with Badger's law [Badger (1934). J. Chem. Phys. 2, 128-131].
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S010876738400057X
