Hydrogen segregation and lattice reorientation in palladium hydride nanowires

Abstract

We study palladium hydride nanowires of different sizes and hydrogen concentrations at 300 K using molecular dynamic simulations. Strong surface segregation of hydrogen with a depletion zone behind is observed in the palladium hydride nanowires. We also show that lattice reorientation is controlled by the hydrogen concentration as well as the nanowire size. The interplay of surface stresses and hydrogen induced stresses is responsible for the observations.

Chemical segregation in metallic glass nanowires

“…16 As many applications of nanowires in catalysis, sensors, actuators, coating or corrosion resistance strongly depend on nanowires' chemical and structural makeup, significant chemical concentration variation could lead to modification to the expected functionality of the nanowires. Both beneficial and adversary effects have been found in crystalline nanowires; [17][18][19][20][21] and the same should be expected for metallic glass nanowires.…”

“…17,21,39 The crystalline nanowires are marked by strong crystal orientation or facet effects that lead to the difference in surface stress and the related structural transitions, making it difficult to delineate the causes for chemical segregation. 18,20,40 In contrast, amorphous nanowires are free of these issues and in addition, do not have polymorphic transitions. These properties make metallic glass a perfect candidate for studying chemical segregation and how fabrication methods affect the chemical segregation.…”

Hydrogen-induced plasticity in nanoporous palladium

“…Overshooting behaviour is still plausible in this case, although with a reduced strain amplitude. Lattice reorientations driven by surface stress, suggested by simulations in both pristine [40] and hydrided Pd nanowires [41], could also be indicative for the concept of a surface-stress contribution to the α-phase straining.…”

Surface-induced structural transformation in nanowires

“…This phenomenon increases the stress to up to 20 GPa and promotes lattice reorientation from [1 0 0] to [0 1 1] in the PdH 0.25 nanowires with a width of 3.96 nm. The width is larger than the critical width of about 2.88 nm of the Pd nanowire reflecting the enhancement effects of hydrogen adsorption [208]. Hence, a combination of Pd nanowires and Fiber Bragg grating can be used in a hydrogen sensor.…”

“…Accordingly, variations in the electronic or optical properties of the detecting units can be used to sense the environment. He et al [208] have conducted MD simulation on the stability of palladium hydride nanowires in the [1 0 0]/{1 0 0} configuration using the EAM potential [209]. Sub-surface hydrogen atoms segregate to the surface of the nanowires at 300 K and so the surface hydrogen concentration is roughly tripled.…”