Abstract
Solid state materials possessing the ability for fast ionic diffusion of hydrogen have immense appeal for a wide range of energy-related applications. Ionic hydrogen transport research is dominated by proton conductors, but recently a few examples of hydride ion conductors have been observed as well. Barium hydride, BaH2, undergoes a structural phase transition around 775 K that leads to an order of magnitude increase in the ionic conductivity. This material provides a prototypical system to understand hydride ion diffusion and how the altered structure produced by the phase transition can have an enormous impact on the diffusion. We employ quasielastic and inelastic neutron scattering to probe the atomic scale diffusion mechanism and vibrational dynamics of hydride ions in both the low- and high-temperature phases. Jump lengths, residence times, diffusion coefficients, and activation energies are extracted and compared to the crystal structure to uncover the diffusion pathways. We find that the hydrogen jump distances, residence times, and energy barriers become reduced following the phase transition, allowing for the efficient conduction of hydride ions through a series of hydrogen jumps of length L = 3.1 Å.
| Original language | English |
|---|---|
| Article number | 6194 |
| Journal | Scientific Reports |
| Volume | 12 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 2022 |
Funding
E.N. and N.J. received financial support from Jülich Center for Neutron Sciences (JCNS). T.E. was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. The Integrated Computational Environment-Modeling & Analysis for Neutrons (ICE-MAN) project used for QENS data analysis was funded by the Laboratory Directed Research and Development Program at Oak Ridge National Laboratory, managed by UT-Battelle (LDRD 8237). Research conducted at ORNL's Spallation Neutron Source and Center for Nanophase Materials Science was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. We would like to thank Rebecca Mills, Robert Marrs, and Matt Rucker for the assistance with the sample environment development at SNS. We would also like to thank the NOMAD instrument team, specifically Joerg Neuefeind and Michelle Everett, for their help with conducting the neutron powder diffraction measurements. Access to the High Flux Backscattering Spectrometer was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under Agreement No. DMR-1508249. We would like to thank Timothy Prisk for the assistance with the measurements at NIST.
| Funders | Funder number |
|---|---|
| Jülich Center for Neutron Sciences | |
| Scientific User Facilities Division | |
| National Science Foundation | DMR-1508249 |
| U.S. Department of Energy | |
| National Institute of Standards and Technology | |
| Office of Science | |
| Basic Energy Sciences | |
| Oak Ridge National Laboratory | |
| Division of Materials Sciences and Engineering | |
| UT-Battelle | LDRD 8237 |