Pressure-induced phase transition in barium hydride studied with neutron scattering

E. Novak; B. Haberl; L. Daemen; J. Molaison; T. Egami; N. Jalarvo

doi:10.1063/5.0011646

Pressure-induced phase transition in barium hydride studied with neutron scattering

E. Novak, B. Haberl, L. Daemen, J. Molaison, T. Egami, N. Jalarvo

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Abstract

Barium hydride can undergo a structural phase transition from an orthorhombic phase to a hexagonal phase induced by high temperature or high pressure. This transition causes an immediate increase in the hydrogen diffusion rates by over an order of magnitude, and therefore, understanding the origin and details of such transition is of great interest not only for fundamental reasons but also for improving materials for future applications. In this work, the pressure evolution of the crystal structure was characterized using neutron powder diffraction up to a maximum pressure of 11.3 GPa. The pressure dependence of the unit cell volumes, lattice parameters, atomic sites, and compressibilities were determined for both phases. A structural phase transition occurred over a wide pressure range of P = 1.3 GPa-4.9 GPa. The transition to the higher density hexagonal phase reduced the volume per formula unit of BaD2 by 13.6%, hence increasing the volumetric storage density. In addition, we investigated the hydrogen diffusion process using high pressure quasi-elastic neutron scattering up to 7.1 GPa. Our results show that the hydrogen mobility increases with pressure in the hexagonal phase. This work sheds light on the structural and dynamical aspects of barium hydride caused by the application of high pressure. The results may aid in the development of advanced metal hydride systems with increased hydrogen dynamics.

Original language	English
Article number	051902
Journal	Applied Physics Letters
Volume	117
Issue number	5
DOIs	https://doi.org/10.1063/5.0011646
State	Published - Aug 3 2020

Funding

We gratefully acknowledge Mark Loguillo for his help with the design and fabrication of the QENS sample environment adapter for the PE press and Robert Sacci for ball milling the barium metal. Research conducted at ORNL’s Spallation Neutron Source and the Center for Nanophase Materials Science was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Financial support was provided by the Ju€lich Center for Neutron Sciences and ORNL. TE was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. QENS fits were performed using QCLIMAX, part of the Integrated Computational Environment-Modeling & Analysis for Neutrons (ICE-MAN) project funded by the Laboratory Directed Research and Development Program at the Oak Ridge National Laboratory, managed by UT-Battelle (No. LDRD 8237).

Funders	Funder number
Ju€lich Center for Neutron Sciences
Materials Science and Engineering Division
Office of Basic Energy Sciences
Scientific User Facilities Division
UT-Battelle
U.S. Department of Energy
Office of Science
Basic Energy Sciences
Oak Ridge National Laboratory

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title = "Pressure-induced phase transition in barium hydride studied with neutron scattering",

abstract = "Barium hydride can undergo a structural phase transition from an orthorhombic phase to a hexagonal phase induced by high temperature or high pressure. This transition causes an immediate increase in the hydrogen diffusion rates by over an order of magnitude, and therefore, understanding the origin and details of such transition is of great interest not only for fundamental reasons but also for improving materials for future applications. In this work, the pressure evolution of the crystal structure was characterized using neutron powder diffraction up to a maximum pressure of 11.3 GPa. The pressure dependence of the unit cell volumes, lattice parameters, atomic sites, and compressibilities were determined for both phases. A structural phase transition occurred over a wide pressure range of P = 1.3 GPa-4.9 GPa. The transition to the higher density hexagonal phase reduced the volume per formula unit of BaD2 by 13.6%, hence increasing the volumetric storage density. In addition, we investigated the hydrogen diffusion process using high pressure quasi-elastic neutron scattering up to 7.1 GPa. Our results show that the hydrogen mobility increases with pressure in the hexagonal phase. This work sheds light on the structural and dynamical aspects of barium hydride caused by the application of high pressure. The results may aid in the development of advanced metal hydride systems with increased hydrogen dynamics.",

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AU - Novak, E.

AU - Haberl, B.

AU - Daemen, L.

AU - Molaison, J.

AU - Egami, T.

AU - Jalarvo, N.

PY - 2020/8/3

Y1 - 2020/8/3

N2 - Barium hydride can undergo a structural phase transition from an orthorhombic phase to a hexagonal phase induced by high temperature or high pressure. This transition causes an immediate increase in the hydrogen diffusion rates by over an order of magnitude, and therefore, understanding the origin and details of such transition is of great interest not only for fundamental reasons but also for improving materials for future applications. In this work, the pressure evolution of the crystal structure was characterized using neutron powder diffraction up to a maximum pressure of 11.3 GPa. The pressure dependence of the unit cell volumes, lattice parameters, atomic sites, and compressibilities were determined for both phases. A structural phase transition occurred over a wide pressure range of P = 1.3 GPa-4.9 GPa. The transition to the higher density hexagonal phase reduced the volume per formula unit of BaD2 by 13.6%, hence increasing the volumetric storage density. In addition, we investigated the hydrogen diffusion process using high pressure quasi-elastic neutron scattering up to 7.1 GPa. Our results show that the hydrogen mobility increases with pressure in the hexagonal phase. This work sheds light on the structural and dynamical aspects of barium hydride caused by the application of high pressure. The results may aid in the development of advanced metal hydride systems with increased hydrogen dynamics.

AB - Barium hydride can undergo a structural phase transition from an orthorhombic phase to a hexagonal phase induced by high temperature or high pressure. This transition causes an immediate increase in the hydrogen diffusion rates by over an order of magnitude, and therefore, understanding the origin and details of such transition is of great interest not only for fundamental reasons but also for improving materials for future applications. In this work, the pressure evolution of the crystal structure was characterized using neutron powder diffraction up to a maximum pressure of 11.3 GPa. The pressure dependence of the unit cell volumes, lattice parameters, atomic sites, and compressibilities were determined for both phases. A structural phase transition occurred over a wide pressure range of P = 1.3 GPa-4.9 GPa. The transition to the higher density hexagonal phase reduced the volume per formula unit of BaD2 by 13.6%, hence increasing the volumetric storage density. In addition, we investigated the hydrogen diffusion process using high pressure quasi-elastic neutron scattering up to 7.1 GPa. Our results show that the hydrogen mobility increases with pressure in the hexagonal phase. This work sheds light on the structural and dynamical aspects of barium hydride caused by the application of high pressure. The results may aid in the development of advanced metal hydride systems with increased hydrogen dynamics.

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Pressure-induced phase transition in barium hydride studied with neutron scattering

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