LAUSR

The variation in local atomic structure and chemical bonding of ZrHx (x = 0.15, 0.30, and 1.16) magnetron sputtered thin films are investigated by Zr K-edge (1s) X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies. A chemical shift of the Zr K-edge toward higher energy with increasing hydrogen content is observed due to charge-transfer and an ionic or polar covalent bonding component between the Zr 4d and the H 1s states with increasing valency for Zr. We find an increase in the Zr–Zr bond distance with increasing hydrogen content from 3.160 A in the hexagonal closest-packed metal (α-phase) to 3.395 A in the understoichiometric δ-ZrHx film (CaF2-type structure) with x = 1.16 that largely resembles that of bulk δ-ZrH2. For even lower hydrogen contents, the structures are mixed α- and δ-phases, while sufficient hydrogen loading (x > 1) yields a pure δ-phase that is understoichiometric, but thermodynamically stable. The change in the hydrogen content and strain is...