Exploring Solute-Defect Interactions in Nanosized Palladium Hydrides across Multiple Time Scales

TL;DR

This study combines diffusive molecular dynamics and traditional molecular dynamics to investigate solute-defect interactions in nanosized palladium hydrides, revealing phase boundary dynamics, defect behavior, and atomic site preferences across multiple time scales.

Contribution

It introduces a multi-scale simulation approach linking DMD and MD to analyze hydride phase transformation and defect evolution in Pd-H systems.

Findings

DMD captures phase boundary propagation and defect dynamics effectively.

H concentration reduces vibrational energy, while stacking faults increase it locally.

MD results agree with DMD on energy, phase boundary, and defect distribution.

Abstract

We employ two different atomistic methods to investigate solute-defect interactions in nanosized palladium-hydrogen (Pd-H) systems across multiple time scales. The first method, referred to as Diffusive Molecular Dynamics (DMD), focuses on capturing hydride phase transformation and the evolution of solute-induced lattice defects over a diffusive time scale. The second method, Molecular Dynamics (MD), provides more detailed insights into atomic movements and lattice relaxation over the time scale of thermal vibrations. These two methods are connected with MD simulations initialized using statistical measures of microscopic variables obtained from DMD at different H/Pd ratios. Our study demonstrates that DMD effectively captures the propagation of an atomistically sharp hydride phase boundary as well as the dynamics of solute-induced misfit dislocations and stacking faults. While the H-concentrated phase leads to a reduction in the vibrational energy, the presence of stacking faults locally increases the vibrational energy of both Pd and H atoms. Furthermore, the MD simulation results align with DMD in terms of equilibrium potential energy, the preservation of hydride phase boundary, and the spatial distribution of stacking faults. We thoroughly characterize the lattice crystalline structures in four key regions of the particle. We observe a preference for H atoms to occupy tetrahedral interstitial sites near stacking faults due to the lower stacking fault energies provided by these sites within the H-concentrated phase.