Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy

TL;DR

This study uses X-ray spectroscopy to analyze how hydrogen content affects the atomic structure and bonding in ZrHx thin films, revealing phase changes and bond length variations.

Contribution

It provides detailed insights into the local atomic structure and chemical bonding variations in ZrHx thin films with different hydrogen contents using advanced X-ray spectroscopic techniques.

Findings

Hydrogen content increases Zr-Zr bond length.

Higher hydrogen levels lead to a phase transition to delta-ZrHx.

Bonding shifts towards ionic or polar covalent with more hydrogen.

Abstract

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.