Relationship between the electronic structure of coherent composition modulated alloys and the supermodulus effect

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Abstract
Describes an approach (essentially a generalisation of Henein's model, 1979) to the electronic structure of coherent composition modulated (CCM) alloys which does not require a full band structure treatment of the modulation to arrive at an understanding of its essential consequences. The approach consists simply of considering the modulation as a perturbation on a suitable reference system whose electronic structure is more easily calculated. The electronic structure of the model is formally equivalent to that of a charge density wave system, with the exception that the gap is not pinned to the Fermi level. The wavelength at which a supermodulus effect has been measured in certain transition metal-noble metal CCM alloys is quantitatively in agreement with this model's explanation as arising from critical contact between the Fermi surface and mini-zone boundary. The model accounts for the supermodulus effect in two systems (Cu-Ni and Ag-Pd) with qualitatively different Fermi surfaces as well as for the lack of supermodulus effect in Cu-Au alloys.