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

JOURNAL OF NUCLEAR MATERIALS

卷:547

Article

Mehta, Vedant K.^1,2  Vogel, Sven C.³  Shivprasad, Aditya P.³  Luther, Erik P.⁴  Andersson, David A.³  Rao, Dasari, V⁵  Kotlyar, Dan²  Clausen, Bjorn³  Cooper, Michael W. D.³ 

[1] Los Alamos Natl Lab, Nucl Engn & Nonproliferat Div, POB 1663, Los Alamos, NM 87545 USA

[2] Georgia Inst Technol, Dept Nucl Engn, Atlanta, GA 30332 USA

[3] Los Alamos Natl Lab, Mat Sci & Technol Div, POB 1663, Los Alamos, NM 87545 USA

[4] Los Alamos Natl Lab, Sigma Div, POB 1663, Los Alamos, NM 87545 USA

[5] Los Alamos Natl Lab, Civilian Nucl Energy Programs, POB 1663, Los Alamos, NM 87545 USA

关键词: DFT;    High temperature moderators;    Neutron diffraction;    Mechanical properties;    Yttrium hydride;    Crystal structure;   

DOI  :  10.1016/j.jnucmat.2021.152837

来源: Elsevier

【 摘 要 】

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 YH2-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 YH2-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 YH2-x. The lattice parameter of YH2-x decreased by only 0.004 angstrom with increasing H/Y for the range 1.31 <= H/Y <= 2.0 indicating a negligible effect on lattice pa- rameters due to vacancy formation. In the two-phase region, however, calculations predicted the density of zY + (1 - z)YH2-x to increase with decreasing H/Y at lower temperatures due to the increased fraction of high-density Y metal. 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 YH2-x. (C) 2021 Elsevier B.V. All rights reserved.

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