Solid structure of Li2BeF4 (FLiBe) from room temperature to melting studied by neutron and X-ray diffraction

Gardner, D. Nathanael; Williams, Haley; Vogel, Sven C.; Fayfar, Sean; Khaykovich, Boris; Srivastava, Shivani; Hwang, Andrea; Asta, Mark; Sprouster, David; Olds, Dan; Vershbow, Gregory; Neuefeind, Jörg C.; Scarlat, Raluca O.

doi:10.1107/s1600576725000548

Title: Solid structure of Li₂BeF₄ (FLiBe) from room temperature to melting studied by neutron and X-ray diffraction

Journal Article · Thu Mar 13 00:00:00 UTC 2025 · Journal of Applied Crystallography

DOI: https://doi.org/10.1107/s1600576725000548 · OSTI ID:2530687

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University of California, Berkeley, CA (United States)
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Stony Brook Univ., NY (United States)
Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)
Univ. of Pennsylvania, Philadelphia, PA (United States)
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Molten fluoride salts such as Li₂BeF₄ (FLiBe) are used in molten salt reactors, fluoride-salt-cooled high-temperature reactors and fusion reactors as a fuel solvent, coolant and/or tritium breeding medium. In engineered systems that use molten salt, solid-state material will be present during melting and freezing scenarios, and therefore the temperature-dependent properties of the solid and solid/liquid phase transition merit investigation. To observe the behavior of the solid state of Li₂BeF₄ from room temperature to melting, this work used neutron and X-ray diffraction to measure the changes in the lattice parameters and volume of the crystalline unit cell and compared the results with prior low-temperature data for solid Li₂BeF₄. From neutron diffraction data it is also possible to identify anisotropy: centimetre-scaled crystals align preferentially with the a axes parallel to the direction of freezing front propagation, and the c axes expand 54% more than the a axes. This work provides the lattice constants as a function of temperature, quantifies the thermal expansion, and determines the equation describing the change in density for solid Li₂BeF₄ from room temperature to 459°C to be ρ_solid (kg m⁻³) = 2182 (3) − 0.115 (2) T (°C) and the volume expansion upon melting to be less than 5%. Furthermore, this density changes depending on molecular weight and enrichment.

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Research Organization:: Brookhaven National Laboratory (BNL), Upton, NY (United States)

Sponsoring Organization:: USDOE; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Nuclear Energy (NE); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)

Grant/Contract Number:: SC0012704

OSTI ID:: 2530687

Report Number(s):: BNL--228854-2025-JAAM

Journal Information:: Journal of Applied Crystallography, Journal Name: Journal of Applied Crystallography Journal Issue: 2 Vol. 58; ISSN 1600-5767

Publisher:: International Union of Crystallography (IUCr)Copyright Statement

Country of Publication:: United States

Language:: English

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36 MATERIALS SCIENCE
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crystal structure
lattice parameters
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neutron diffraction
nuclear materials
volume change upon melting

Title: Solid structure of Li2BeF4 (FLiBe) from room temperature to melting studied by neutron and X-ray diffraction

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References (47)

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Title: Solid structure of Li₂BeF₄ (FLiBe) from room temperature to melting studied by neutron and X-ray diffraction