Atom probe imaging locates hydrogen between metal atoms in alloys for the first time

Researchers at the University of Sydney report direct observations of hydrogen sitting in the gaps between metal atoms in several alloys. The work, led by Professor Julie Cairney and published in Nature, shows that the arrangement and chemical makeup of the metal atoms influence where the hydrogen prefers to settle.

Why hydrogen in metals is hard to study

Hydrogen is central to many plans for cleaner energy, but storing and moving it safely is difficult. The gas can enter pipelines and storage equipment and make strong metals crack unexpectedly, a problem known as hydrogen embrittlement. Reducing that risk requires knowing how much hydrogen enters a metal, where it ends up and how it interacts with the surrounding atoms.

Hydrogen can be present in three main forms: as hydrides, trapped at defects in the material, or dissolved in the interstitial spaces of the crystal lattice. The first two have been seen experimentally before. The third has been well described in theory but has been extremely hard to observe, because hydrogen atoms are tiny and highly mobile. Earlier observations therefore tended to show hydrogen gathered at imperfections rather than dispersed within the lattice itself.

Swapping in deuterium

The team used cryogenic atom probe tomography (cryo-APT), a technique that maps the three-dimensional position of individual atoms in a sample. To make hydrogen easier to follow, they replaced it with deuterium, its heavier isotope, in a number of metallic alloys. This allowed them to track the hydrogen introduced during the experiments and limited its loss while the samples were being prepared.

The deuterium was not spread evenly. It accumulated preferentially in certain regions, which indicated that the local atomic arrangement and chemical composition of the alloy shape where hydrogen resides. The researchers then added electron microscopy and theoretical calculations to check their interpretation. Together, these methods supported the conclusion that hydrogen was present in an interstitial state, and not only at defects.

What the findings could mean

The results give materials scientists a way to test, at the atomic scale, ideas about hydrogen behaviour that had mostly rested on modelling. Knowing why hydrogen favours particular atomic environments could help explain how it moves through a metal, where it collects and how it might contribute to damage. In turn, that could guide the design of alloys better suited to hydrogen-rich conditions.

Cairney said the findings are an important step towards understanding the fundamental physics of hydrogen in metals. The source describes the observation as a world first, though the paper's title refers to working towards observing interstitial hydrogen, which suggests the authors regard it as progress in a developing area. The source gives no details of the specific alloys studied or the hydrogen concentrations involved, and the use of deuterium as a stand-in means the results describe a close isotopic proxy rather than ordinary hydrogen.

Next steps

First author Dr Chao Huang, a postdoctoral researcher who recently completed his PhD in the Faculty of Engineering, said the next aim is to understand how hydrogen inside metals affects the way they deform and perform under stress. The group is already pursuing this through work on ultra-high-strength steels, with the longer-term goal of developing stronger, more hydrogen-resistant steels for engineering use.

The research was carried out in the School of Aerospace, Mechanical and Mechatronic Engineering and the Australian Centre for Microscopy and Microanalysis. The paper is Huang et al., "Towards observing interstitial hydrogen in solution in metal lattices", Nature (2026), DOI: 10.1038/s41586-026-11238-4.

Source: First direct observations reveal hydrogen dissolved in tiny gaps between metal atoms (Phys.org, 5 November 2026).

Image: AI-generated illustration.