Title: A density functional theory and neutron diffraction study of the ambient condition properties of sub-stoichiometric yttrium hydride

Abstract

Several mechanical and thermophysical properties are required as a function of non-stoichiometry for the successful implementation of YH_2-x for nuclear reactor moderator applications. Density functional theory calculations, in combination with neutron diffraction experiments, were used to study the structural and mechanical properties of YH_2-x. Point defect analysis indicated H occupation primarily at the tetrahedral site within an fcc Y sub-lattice, confirming a fluorite YH₂ structure. The small positive formation energy for H vacancies under Y-rich conditions predicted that hypo-stoichiometry is accommodated by Y+YH₂ at ambient conditions and by H vacancies in the YH_2-x single phase that is relevant to high temperatures. Neutron diffraction studies were used to confirm both the occupation of H on tetrahedral sites and the near-stoichiometric composition of the hydride phase in the two-phase Y+YH₂ region of the phase diagram that dominates at room temperature. Energy minimized special-quasirandom-structures of H vacancies were used to calculate lattice parameters, elastic constants, and several other properties as a function of composition for the single phase YH_2-x. The lattice parameter of YH_2-x decreased by only 0.004 Å with increasing H/Y for the range $1.31\le H/Y\le 2.0$ indicating a negligible effect on lattice parameters due to vacancy formation. In the two-phase region, however, calculations predicted the density of $zY+\left(1-z\right)Y{H}_{2-x}$ to increase with decreasing H/Y at lower temperatures due to the increased fraction of high-density Y metal. Additionally, for the high temperature single phase, decreasing H/Y reduced the density as a consequence of the lattice expansion associated with vacancy formation. All elastic constants and moduli increased with increasing hydrogen content in single-phase YH_2-x.

Authors:

Mehta, Vedant Kiritkumar  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-6705-739X"

Vogel, Sven C.  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-2049-0361"

Shivprasad, Aditya Prahlad  ^[2];

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• Search DOE PAGES for ORCID "0000-0001-8515-2756"

Luther, Erik Paul  ^[2];

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Andersson, Anders David Ragnar  ^[2];

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• Search DOE PAGES for ORCID "0000-0001-5863-1372"

Rao, Dasari V. ^[3]; Kotlyar, Dan ^[4]; Cooper, Michael William Donald  ^[2];

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• Search DOE PAGES for ORCID "0000-0001-8270-7947"

Clausen, Bjorn  ^[2]

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• Search DOE PAGES for ORCID "0000-0003-3906-846X"

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+ Show Author Affiliations

1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Georgia Institute of Technology, Atlanta, GA (United States)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Civilian Nuclear Energy Programs
4. Georgia Institute of Technology, Atlanta, GA (United States)

Publication Date:

Sat Jan 23 00:00:00 EST 2021

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE Office of Nuclear Energy (NE). Nuclear Reactor Technologies; USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1764213

Alternate Identifier(s):

OSTI ID: 1810975

Report Number(s):

LA-UR-20-24029
Journal ID: ISSN 0022-3115; TRN: US2206430

Grant/Contract Number:  

89233218CNA000001; 20190649DI

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Nuclear Materials

Additional Journal Information:

Journal Volume: 547; Journal ID: ISSN 0022-3115

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; DFT; high temperature moderators; neutron diffraction; mechanical properties; yttrium hydride; crystal structure