Hydrogen isotope role in the crystal orientation change of erbium oxide coatings

Erbium oxide (Er ₂O ₃ ) is a candidate material for tritium permeation barriers (TPB) applied to fusion blanket systems. To permeate through a TPB coating on a metal substrate, a hydrogen isotope must first adsorb on the surface, and then penetrate from the surface into the interior. In this work, Er ₂O ₃ coatings were fabricated by arc source assisted deposition and annealing at 973 K in vacuum (<10 ⁻⁵ Pa). The effect of hydrogen on the crystal orientation change of Er ₂O ₃ coatings was examined by X-ray diffraction and density-functional theory studies. It was found that the surface energy of a partially H-covered initially {111} Er ₂O ₃ slab increases upon annealing at 973 K, and that the associated crystal orientation change from {111} to {100} never occurs without hydrogen even at high temperature.