Neutron scattering study of tantalum monohydride and monodeuteride

Powder samples of TaH0.89 and TaD0.96 are synthesized under a hydrogen (deuterium) pressure of 2.8 GPa and a temperature of 250 C-circle, then quenched to the liquid nitrogen temperature, recovered to ambient pressure and studied by neutron diffraction (ND) and inelastic neutron scattering (INS). The ND study shows that both hydrogen and deuterium atoms occupy tetrahedral interstitial sites in a distorted body centered cubic (bcc) crystal structure of metal atoms, while the ordering scenarios in TaH0.89 and TaD0.96 are different. Hydrogen and deuterium atoms are ordered in a layered fashion, forming long period superstructures with space groups P (4) over bar and P222, respectively, so that the unit cells of the p ffiffi p ffiffi p ffiffi p ffiffi crystal structures of TaH0.89 and TaD0.96 are root 2 x root 2 x 7 and root 2 x root 2 x 8 supercells of the initial cubic unit cell. The INS study demonstrates a pronounced soft (trumpet-like) anharmonicity of the potential well for H and D atoms. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The powder samples of TaH0.89 and TaD0.96 were synthesized under high pressure and temperature conditions, and the neutron diffraction and inelastic neutron scattering studies show that hydrogen and deuterium atoms occupy the crystal structure in different ordering scenarios, forming layered superstructures with long periodicity. The inelastic neutron scattering study also reveals a noticeable soft anharmonicity of the potential well for H and D atoms.