Novel approach to explore hydrogen trapping sites in aluminum: Integrating Muon spin relaxation with first-principles calculations

This paper provides a novel technique to explore hydrogen trapping in aluminum alloys by combining muon spin relaxation and first-principles calculations. Zero-field muon spin relaxation experiments were conducted on Al-Mn, Al-Cr, Al-Fe, and Al-Ni alloys, resulting in temperature-dependent variations of the dipole field widths (Delta) that elucidated four distinct peaks for the prepared alloys. Our first-principles calculations have clarified that atomic configurations of the muon trapping, which correspond to the Delta peaks below 200 K, are consistent with hydrogen trapping sites in proximity to a solute and solute-vacancy pair. However, significant deviations from this linear relationship were observed for the fourth Delta peaks above 200 K in Al-Mn, Al-Cr, Al-Fe, and Al-Ni alloys. This discrepancy can be interpreted by considering the disparate distribution functions of muon and hydrogen within the tetrahedral site, wherein two of the four Al atoms are substituted by the solute element and vacancy (solute-vacancy pair).