Resolving hydrogen atoms at metal-metal hydride interfaces

TL;DR

This paper demonstrates a novel imaging technique using integrated differential phase contrast in a scanning transmission electron microscope to visualize hydrogen atoms at metal-metal hydride interfaces, revealing atomic details and stability mechanisms.

Contribution

It introduces a new method for visualizing hydrogen atoms at interfaces, resolving a long-standing challenge and validating a model of hydrogen positioning after three decades.

Findings

Hydrogen atoms can be imaged at interfaces using the new technique.

The stability of the hydride phase is linked to stress and interfacial coherence.

The study identifies the correct model for hydrogen atom positioning at interfaces.

Abstract

Hydrogen as a fuel can be stored safely with high volumetric density in metals. It can, however, also be detrimental to metals causing embrittlement. Understanding fundamental behavior of hydrogen at atomic scale is key to improve the properties of metal-metal hydride systems. However, currently, there is no robust technique capable of visualizing hydrogen atoms. Here, we demonstrate that hydrogen atoms can be imaged unprecedentedly with integrated differential phase contrast, a recently developed technique performed in a scanning transmission electron microscope. Images of the titanium-titanium monohydride interface reveal remarkable stability of the hydride phase, originating from the interplay between compressive stress and interfacial coherence. We also uncovered, thirty years after three models were proposed, which one describes the position of the hydrogen atoms with respect to the interface. Our work enables novel research on hydrides and is extendable to all materials containing light and heavy elements, including oxides, nitrides, carbides and borides.