Interdiffusivities in silver-palladium composition-modulated foils

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Abstract
Interdiffusion coefficients were measured from the decay rate of x-ray diffraction satellite intensities at 375 °C in 13 Ag-Pd foils containing composition modulations with wavelengths between 0.94 and 5.08 nm. A sharp decrease in the interdiffusivity was observed at a wavelength of 2.3 nm and a gradual decrease between 4.0 and 5.0 nm. A screening singularity or an increase in the shear modulus (or both) are believed to be responsible for the decrease at 2.3 nm. The drop at 4.0 nm is consistent with a loss of coherency in the foils. A nonlinear regression fit to the wavelength dependence of the diffusion coefficient yielded values of the first four gradient energy coefficients for the system.