  The variation in local atomic structure and chemical bonding of ZrHx (x=0.15,
0.30, 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 towards 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 {\AA} in the hexagonal
closest-packed metal (alpha-phase) to 3.395 {\AA} in the understoichiometric
delta-ZrHx film (CaF2-type structure) with x=1.16 that largely resembles that
of bulk delta-ZrH2. For yet lower hydrogen contents, the structures are mixed
alpha and delta-phases, while sufficient hydrogen loading (x>1) yields a pure
{\delta}-phase that is understoichiometric, but thermodynamically stable. The
change in the hydrogen content and strain is discussed in relation to the
corresponding change of bond lengths, hybridizations, and trends in electrical
resistivity.

Materials Science