Hydrogen solution in tetrahedral or octahedral interstitial sites in Al

It is reported that H atoms prefer to stay at interstitial (defect) sites with larger space in most metals. However, H atom prefers to occupy tetrahedral interstitial sites (T-site) that provide smaller space than octahedral sites (O-site) in Al. This paper studied the H–Al interactions from first principles calculations. Through analysis of the H-induced electronic states and the local atomic relaxations, we show that H–Al bonding interaction is stronger for T-site H, which is in favor of the solution energy. On the other hand, larger local atomic distortion is observed around the T-site H, which increases the total energy.

► The physical nature of the site preference for H solution in BCC Al is revealed.
► The site preference is result of competition between Al–H bonding interaction and local lattice distortion.
► The Al–H bonding interaction lowers the solution energy while the local lattice distortion increases the solution energy.