Atomic ordering in Au-(42 to 50) at.%Pd: A diffuse scattering and first-principles investigation

Abstract

Atomic ordering in Au-Pd alloys was studied by diffuse x-ray scattering and first-principles methods. Diffuse scattering was done of a single crystal of Au-48 at.% Pd that was aged at 703 K for 24 days. The weakly modulated short-range-order scattering exhibits diffuse maxima with an incommensurate wave vector, which can be related to a Fermi-surface nesting mechanism. From effective pair interaction parameters determined by the inverse Monte Carlo method, a one-dimensional long-period superstructure of the CH structure, LPS1, was found for AuPd. Concurrent electronic-structure calculations of the effective cluster interaction (ECI) parameters indicated the presence of another closely related superstructure, LPS2, at 0 K. At the same time, direct first-principles calculations of the total energies of the CH structure and further one-dimensional long-period superstructures predicted the stabilization of LPS4. Although the energy differences between these structures are small and a complex behavior of the effective interactions is expected due to the Fermi-surface nesting, experimental data and theoretical results both support the stabilization of a long-period superstructure of the CH structure for AuPd at 0 K. The ECI parameters determined by the screened generalized perturbation method also predicted a groundstate structure different from Au 7 Pd 5 , previously obtained from cluster expansion calculations. Its energetic preference was confirmed by direct total-energy calculations.

Probing Atomic Distributions in Mono- and Bimetallic Nanoparticles by Supervised Machine Learning

“…Also, the access to the distant coordination shells is necessary to discriminate between different alloying motifs. For example, a weak ordering of Pd and Au atoms was observed in thin films of PdAu − and experimental and theoretical studies reported the formation of various superstructures in bulk PdAu. , Moreover, theoretical studies of configurations of Pd atoms on bimetallic surfaces indicate that configurations consisting of first-neighbor Pd pairs are unstable, but that the formation of second-neighbor Pd ensembles is energetically favorable. , The presence of such structural motifs can clearly have an impact on the catalytic properties of bimetallic NPs, and tools are needed to detect them in experiment.…”

Interatomic interactions and thermodynamic parameters in dilute solid solutions of the Ag-Au system

“…As in other substitutional solid solutions [7][8][9], the chemical interactions on the first CS are most essen tial; on the following CSs, they are less by approxi mately an order of magnitude and exhibit an alternat ing character.…”

“…In contrast to the chemical interactions, the defor mational interactions on the first CS are small; they are less by approximately two orders of magnitude than the deformational interactions for the first CS in the Au-Pd system [9]. On the other CSs, they are also substantially less, since the atoms of Au and Ag are close in size.…”

“…The theoretical values of the thermody namic parameter of interaction and of the first order enthalpy parameter calculated according to the for mulas (6), (7), (9), and (10) are given in Table 2.…”

“…It has been shown that the calculated parameters of the short range order in the alloy well reproduce the results of neutron scattering experiments. Similar calculations have also been performed in the analyses of ordered structures in Ni-Pt [8] and Au-Pd [9] alloys, the experimental data for which have been obtained by the method of the diffuse scattering of X rays.…”