Temperature and concentration dependence of the effective pair interaction parameters in Ni-Pd from high-energy x-ray diffuse scattering

Abstract

The atomic interaction potential between different alloy components is encoded in the diffuse scattering caused by configurational short-range order and lattice distortions in the disordered phase. We performed in situ measurements of the x-ray diffuse scattering on macroscopic ${\mathrm{Ni}}_{55}{\mathrm{Pd}}_{45}$ and ${\mathrm{Ni}}_{25}{\mathrm{Pd}}_{75}$ single crystals in the temperature range from $20\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ up to $920\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. We describe in detail the experiments and the data analysis where we use a formalism based on the spherical model and the Kanzaki-force concept in combination with a simulated annealing algorithm. We demonstrate that one single measurement is sufficient to retrieve the effective pair interaction potentials as well as thermal and elastic properties of the system. With only seven independent and physically motivated parameters we are able to describe short-range-order correlations, lattice distortions, and thermal parameters in a large temperature and concentration range.