Hydrogen site occupancy and strength of forces in nano-sized metal hydrides

TL;DR

This study combines experimental and theoretical methods to analyze hydrogen site occupancy and force interactions in nano-sized metal hydrides, revealing site preferences and strain effects at different scales and compositions.

Contribution

It provides a detailed quantitative analysis of hydrogen site occupancy and dipole forces in nano-sized metal hydrides using combined experimental and ab-initio approaches.

Findings

Hydrogen in 100 nm V films prefers tetrahedral sites at low concentrations.

Transition to octahedral occupancy occurs at around 0.07 [H/V] at 360 K.

In 3 nm strained FeV/V superlattices, hydrogen occupies octahedral sites even at low concentrations.

Abstract

The dipole force components in nano-sized metal hydrides are quantitatively determined with curvature and x-ray diffraction measurements. Ab-initio density functional theory is used to calculate the dipole components and the symmetry of the strain field. The hydrogen occupancy in a 100 nm thick V film is shown to be tetrahedral with a slight asymmetry at low concentration and a transition to octahedral occupancy is shown to take place at around 0.07 [H/V] at 360 K. When the thickness of the V layer is reduced to 3 nm and biaxially strained, in a Fe_0.5V_0.5/V superlattice, the hydrogen unequivocally occupies octahedral z-like sites, even at and below concentrations of 0.02 [H/V].