Investigation of H atoms occupation within ZrCo alloys during hydrogen absorption and desorption

The disproportionation reaction of ZrCo will occur at high temperature resulting in a substantial reduction of hydrogen absorption, and the driving force of which was widely accepted as the non-equivalent occupation of hydrogen atom within ZrCo hydride. However, the H atoms occupation within ZrCo alloys is still ambiguous to date. Herein, hydrogen atom occupation behaviors in ZrCo hydride were studied by thermal analysis and X-ray diffraction combined with first-principle calculation during absorption and desorption. The results shown that hydrogen atoms in ZrCo alloys were preferentially occupied 8f1 site instead of 4c2 site in the situation of x <= 1.4, while for the case of 1.4 <= x <= 2.0 hydrogen atoms began to occupy 4c2 site, and the order of occupation at this stage is roughly 4c2, 8f1 and 4c2. As for the case of 2.0 <= x <= 2.5, the crystal structure expanded with the increase of x value and hydrogen atoms occupied 8f1, 4c2 and 8e site at the same time. In the process of hydrogen desorption, hydrogen atom at 8e site was firstly released, then the 4c2 site and finally 8f1 site. We believe the work can provide some experimental basis for further research on the relationship between hydrogen occupation and hydrogen-induced disproportionation of ZrCo.