Microscopic Behavior of Hydrogen and Hydride Molecules in Atom Probe Tomography of Zirconium

We study the microscopic field evaporation behavior of hydrogen and related molecules in Atom Probe Tomography (APT) of pure Zr and a Zr hydride phase obtained by electrochemical charging. Our results show the presence of hydrogen ions H+, H2+, and H3+ for both systems, while hydride molecular ions ZrH2+ are found in the hydride phase. The distribution of the hydrogen ions H+, H2+ density map on the detector space of the charged sample reveals a crystallographic structure with symmetry close to a face-centered cubic (FCC) phase. The distribution of relative abundances of hydrogen ions and Zr2+ and hydride molecules also correlates with the crystallography, while a weaker correlation is found with the surface field distribution. In particular, the distribution of the detected species shows preferential formation for hydride molecules along selected crystallographic zone lines. These results are interpreted with the support of density functional theory (DFT) calculations and through the analysis of multiple detection events.