Embedded-atom-method study of coherency and elastic moduli of Pd-Cu multilayers

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Abstract
The embedded-atom method was utilized to study coherent and incoherent interfaces and elastic moduli in Pd-Cu multilayers with wavelengths of 2, 4, and 6 monolayers (ML) of (111) planes. The multilayer with a wavelength of 2 ML was coherent, and the multilayer with a wavelength of 6 ML was incoherent with a misfit dislocation structure similar to a Pd-Cu bicrystal. The lattice of the multilayer with wavelength of 2 ML was highly strained with a lattice parameter of 3.83 Å within the (111) plane and a lattice parameter of 3.66 Å normal to the (111) planes. In the incoherent multilayer the lattice parameter normal to the (111) planes was larger than the coherent multilayer, but the total volume of the incoherent multilayer was less than the coherent multilayer, indicating that atoms had relaxed into lower-energy positions with the formation of misfit dislocations. Elastic moduli that related stresses to strains where the registry of the (111) planes was not distorted were observed to increase as the volume (or coherency) decreased. Elastic moduli that related stresses to strains that distorted the registry of the (111) planes were observed to increase as coherency (or volume) increased. Changes in moduli calculated were typically 10–20 %.