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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Theoretical study of the electronic, thermodynamic, and thermo-conductive properties of y-LiAlO2 with 6Li isotope substitutions for tritium production

Lithium aluminate has attracted researchers’ interests due to its wide applications. The structural, electronic, optical, lattice phonon thermodynamic, and thermo-conductive properties of ?-LiAlO2 with 6Li-isotope substitution are investigated by density functional theory and lattice phonon dynamics. The calculated results show that ?-LiAlO2 possesses a wide band-gap of 4.63 eV. The valence band is mainly formed by p orbitals of Li, O, and Al. The calculated lattice thermal conductivity of ?-LiAlO2 is found to be in good agreement over a wide range of temperatures with the available experimental data. The calculated dielectric matrix shows anisotropic behavior along z and x (or y) axes. Due to the wide band-gap, the optical conductivity of ?-LiAlO2 is mainly contributed from the electron hopping between valence-conduction bands. Substitution of 7Li with 6Li isotope in ?-LiAlO2 leads to observable differences in the lattice phonon frequencies at higher frequencies (>8THz) and to slight changes in corresponding thermal conductivity and the infrared and Raman spectra which are in good agreement with the measured data. The relevance of these properties for tritium production through 6Li absorbing neutron in nuclear reactors is discussed.

ab initio thermodynamics, ?-LiAlO2 and 6Li-isotope↗
DOE OSTI2020

A quantitative study of retention and release of deuterium and tritium during irradiation of y-LiAlO2 pellets

This study reports on the quantification of deuterium in ion-irradiated gamma-LiAlO2 pellets as a function of dose and temperature. The gamma-LiAlO2 pellets were sequentially irradiated with He+ and D2+ ions to the same fluences of 5E16, 1E17 and 2E17 He++D+/cm2 at 188 K. Additional irradiation was performed to 1E17, 2E17 and 4E17 He++D+/cm2 at 573 K. A set of the pellets irradiated at 188 K was shipped and stored at low temperatures from 80 to 132 K and characterized using time-of-flight secondary ion mass spectrometry at ~173 K. The deuterium depth profiles show a Gaussian-like distribution in the low-temperature pellets. The total deuterium retention is found to be directly proportional to the ion fluence. About 27 at.% of the implanted deuterium atoms were released from the pellet irradiated to 2E17 He++D+/cm2 at 188 K during storage at room temperature for ~1 month. Retention of the trapped or bound deuterium during ion irradiation at 573 K increases initially with ion fluence and tends to saturate at a high fluence. The amount of the released deuterium is observed to be quantitatively consistent with that of the released tritium from similar standard pellets during neutron irradiation at 573 K.

Deuterium retention and release, ion irradiation, ↗
DOE OSTI2021

Neutron Irradiation Induced Changes in Isotopic Abundance of 6Li and 3D Nanoscale Distribution of Tritium in LiAlO2 Pellets Analyzed by Atom Probe Tomography

Tritium, a radioactive isotope of hydrogen is produced by neutron irradiation of 6Li enriched LiAlO2 pellets in Tritium producing burnable absorber rods (TPBARs). Three-dimensional nanoscale mapping of Tritium in irradiated pellets is critical to understand its spatial variation and its association with various microstructural features in the pellets. Spatially resolved analysis of 6Li isotopic enrichment in such ceramic pellets before and after irradiation can provide insights to heterogeneities in Li isotopic distribution. However, Li being a light isotope, its spatially resolved compositional or isotopic analysis is a challenging task to most analytical methods. Here we used atom probe tomography, to evaluate the Li isotopic enrichment in both the LiAlO¬2 matrix and the Li deficient secondary phase LiAl5O8 before irradiation. These results were then compared with 6Li isotopic ratio measured by APT analysis of neutron irradiated pellets to clearly demonstrate the unique capability of APT to quantitatively analyze the isotopic enrichment of 6Li as well as for other light elements present in these materials. Evidence for heterogenous nanoscale distribution of 3H and O3H within irradiated pellet microstructure is also provided, which is attributed to 3H trapping in irradiation induced vacancy clusters or voids within the LiAlO2 matrix. The characterization results given here, now prove the feasibility for using APT for analyzing nanoscale spatially resolved isotopic enrichment of Li as well as other light elements such as Tritium in TPBARs. This work also paves way to adopt APT for analyzing light elements such as Li and tritium in materials used for nuclear fusion reactor applications, geochemistry, astrophysics as well as for energy storage applications.

Devaraj, Arun↗
DOE OSTI2020

Materials Data on LiAlO2 by Materials Project

LiAlO2 is beta beryllia-derived structured and crystallizes in the tetragonal P4_12_12 space group. The structure is three-dimensional. Li1+ is bonded to four equivalent O2- atoms to form LiO4 tetrahedra that share corners with four equivalent LiO4 tetrahedra, corners with six equivalent AlO4 tetrahedra, and an edgeedge with one AlO4 tetrahedra. There are two shorter (1.98 Å) and two longer (2.08 Å) Li–O bond lengths. Al3+ is bonded to four equivalent O2- atoms to form AlO4 tetrahedra that share corners with four equivalent AlO4 tetrahedra, corners with six equivalent LiO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There is two shorter (1.77 Å) and two longer (1.78 Å) Al–O bond length. O2- is bonded to two equivalent Li1+ and two equivalent Al3+ atoms to form a mixture of corner and edge-sharing OLi2Al2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlO2 by Materials Project

LiAlO2 crystallizes in the tetragonal P-4m2 space group. The structure is three-dimensional. there are seven inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with two AlO6 octahedra, corners with four equivalent LiO6 octahedra, edges with four LiO6 octahedra, and edges with eight AlO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (1.95 Å) and two longer (2.30 Å) Li–O bond lengths. In the second Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with two AlO6 octahedra, corners with four equivalent LiO6 octahedra, edges with four LiO6 octahedra, and edges with eight AlO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There are a spread of Li–O bond distances ranging from 1.96–2.33 Å. In the third Li1+ site, Li1+ is bonded to six O2- atoms to form distorted LiO6 octahedra that share a cornercorner with one AlO6 octahedra, corners with five LiO6 octahedra, edges with four LiO6 octahedra, and edges with eight AlO6 octahedra. The corner-sharing octahedra tilt angles range from 0–19°. There are a spread of Li–O bond distances ranging from 1.95–2.46 Å. In the fourth Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with two equivalent AlO6 octahedra, corners with four equivalent LiO6 octahedra, edges with four equivalent LiO6 octahedra, and edges with eight AlO6 octahedra. The corner-sharing octahedra tilt angles range from 0–12°. There are four shorter (1.96 Å) and two longer (2.32 Å) Li–O bond lengths. In the fifth Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with two AlO6 octahedra, corners with four equivalent LiO6 octahedra, edges with four LiO6 octahedra, and edges with eight AlO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There are a spread of Li–O bond distances ranging from 1.96–2.34 Å. In the sixth Li1+ site, Li1+ is bonded to six O2- atoms to form distorted LiO6 octahedra that share a cornercorner with one AlO6 octahedra, corners with five LiO6 octahedra, edges with four LiO6 octahedra, and edges with eight AlO6 octahedra. The corner-sharing octahedra tilt angles range from 0–19°. There are a spread of Li–O bond distances ranging from 1.95–2.46 Å. In the seventh Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with two equivalent AlO6 octahedra, corners with four equivalent LiO6 octahedra, edges with four equivalent LiO6 octahedra, and edges with eight AlO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There are four shorter (1.96 Å) and two longer (2.31 Å) Li–O bond lengths. There are seven inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share a cornercorner with one LiO6 octahedra, corners with five AlO6 octahedra, edges with four AlO6 octahedra, and edges with eight LiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There are a spread of Al–O bond distances ranging from 1.87–2.12 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two LiO6 octahedra, corners with four equivalent AlO6 octahedra, edges with four AlO6 octahedra, and edges with eight LiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There are a spread of Al–O bond distances ranging from 1.89–1.96 Å. In the third Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two LiO6 octahedra, corners with four equivalent AlO6 octahedra, edges with four AlO6 octahedra, and edges with eight LiO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There is two shorter (1.90 Å) and four longer (1.95 Å) Al–O bond length. In the fourth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two LiO6 octahedra, corners with four equivalent AlO6 octahedra, edges with four AlO6 octahedra, and edges with eight LiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There are a spread of Al–O bond distances ranging from 1.90–1.96 Å. In the fifth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent LiO6 octahedra, corners with four equivalent AlO6 octahedra, edges with four equivalent AlO6 octahedra, and edges with eight LiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–12°. There is two shorter (1.89 Å) and four longer (1.96 Å) Al–O bond length. In the sixth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share a cornercorner with one LiO6 octahedra, corners with five AlO6 octahedra, edges with four AlO6 octahedra, and edges with eight LiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There are a spread of Al–O bond distances ranging from 1.87–2.12 Å. In the seventh Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent LiO6 octahedra, corners with four equivalent AlO6 octahedra, edges with four equivalent AlO6 octahedra, and edges with eight LiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. There is two shorter (1.91 Å) and four longer (1.96 Å) Al–O bond length. There are thirteen inequivalent O2- sites. In the first O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–19°. In the second O2- site, O2- is bonded to two equivalent Li1+ and four Al3+ atoms to form OLi2Al4 octahedra that share corners with six OLi2Al4 octahedra and edges with twelve OLi3Al3 octahedra. The corner-sharing octahedral tilt angles are 0°. In the third O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of distorted edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–12°. In the fourth O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of distorted edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. In the fifth O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. In the sixth O2- site, O2- is bonded to four Li1+ and two equivalent Al3+ atoms to form a mixture of edge and corner-sharing OLi4Al2 octahedra. The corner-sharing octahedral tilt angles are 0°. In the seventh O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of distorted edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. In the eighth O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–12°. In the ninth O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form distorted OLi3Al3 octahedra that share corners with six OLi2Al4 octahedra and edges with twelve OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. In the tenth O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–19°. In the eleventh O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form a mixture of edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. In the twelfth O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form distorted OLi3Al3 octahedra that share corners with six OLi2Al4 octahedra and edges with twelve OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. The O–Li bond length is 2.46 Å. In the thirteenth O2- site, O2- is bonded to three Li1+ and three Al3+ atoms to form distorted OLi3Al3 octahedra that share corners with six OLi2Al4 octahedra and edges with twelve OLi3Al3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. The O–Al bond length is 1.87 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlO2 by Materials Project

LiAlO2 is Caswellsilverite structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Li1+ is bonded to six equivalent O2- atoms to form LiO6 octahedra that share corners with six equivalent AlO6 octahedra, edges with six equivalent LiO6 octahedra, and edges with six equivalent AlO6 octahedra. The corner-sharing octahedral tilt angles are 8°. All Li–O bond lengths are 2.13 Å. Al3+ is bonded to six equivalent O2- atoms to form AlO6 octahedra that share corners with six equivalent LiO6 octahedra, edges with six equivalent LiO6 octahedra, and edges with six equivalent AlO6 octahedra. The corner-sharing octahedral tilt angles are 8°. All Al–O bond lengths are 1.93 Å. O2- is bonded to three equivalent Li1+ and three equivalent Al3+ atoms to form a mixture of edge and corner-sharing OLi3Al3 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tritium diffusion and formation in the bulk and defective surface of γ-LiAlO2 pellets: First-principles investigation

In tritium-producing burnable absorber rods (TPBAR), γ-LiAlO2 is used in the form of an annular ceramic pellet enriched with the 6Li isotope. When irradiated in a pressurized water reactor (PWR), the <sup>6</sup>Li pellets absorb neutrons and produce tritium (<sup>3</sup>H) through <sup>6</sup>Li + n <sup>3</sup>H + α. The 3H chemically reacts with the metal getter where it is captured and leads to formation of a metal hydride. For TPBARs to enable effective tritium production in PWRs, we investigated the <sup>3</sup>H diffusion pathways in the bulk and surface of γ-LiAlO<sub>2</sub> with different concentrations of lithium defects. The calculated results for bulk and low-index surfaces, thermal conductivity, 3H activation energy barriers, and the 3H diffusion coefficients in γ-LiAlO<sub>2</sub> are in good agreement with the available experimental values. In the bulk, our results show that the smallest activation energy barrier is 0.63 eV for substitutional <sup>3</sup>H diffusion with a diffusion coefficient of 3.25x10<sup>-12</sup> m<sup>2</sup>/s. After <sup>3</sup>H diffused from bulk to the surface, it could form different species (such as <sup>3</sup>H<sub>2</sub>, <sup>3</sup>H<sub>2</sub>O, C<sup>3</sup>H<sub>4</sub>) depending on the surface structure, vacancy types and the impurity carbon. Our results indicate that the <sup>3</sup>H<sub>2</sub> is the main product from γ-LiAlO<sub>2</sub> pellets. As the number of V<sub>Li</sub> vacancies and <sup>3</sup>H atoms increases under irradiation (<sup>3</sup>H-rich condition), <sup>3</sup>H<sub>2</sub>O release could increase from the surface of γ-LiAlO<sub>2</sub> pellets.

Jia, Ting↗
DOE OSTI2024

Molecular dynamics simulations of displacement cascades in LiAlO2 and LiAl5O8 ceramics

Abstract Molecular dynamics was employed to investigate the radiation damage due to collision cascades in LiAlO 2 and LiAl 5 O 8 , the latter being a secondary phase formed in the former during irradiation. Atomic displacement cascades were simulated by initiating primary knock-on atoms (PKA) with energy values = 5, 10 and 15 keV and the damage was quantified by the number of Frenkel pairs formed for each species: Li, Al and O. The primary challenges of modeling an ionic system with and without a core–shell model for oxygen atoms were addressed and new findings on the radiation resistance of these ceramics are presented. The working of a variable timestep function and the kinetics in the background of the simulations have been elaborated to highlight the novelty of the simulation approach. More importantly, the key results indicated that LiAlO 2 experiences much more radiation damage than LiAl 5 O 8 , where the number of Li Frenkel pairs in LiAlO 2 was 3–5 times higher than in LiAl 5 O 8 while the number of Frenkel pairs for Al and O in LiAlO 2 are ~ 2 times higher than in LiAl 5 O 8 . The primary reason is high displacement threshold energies (E d ) in LiAl 5 O 8 for Li cations. The greater E d for Li imparts higher resistance to damage during the collision cascade and thus inhibits amorphization in LiAl 5 O 8 . The presented results suggest that LiAl 5 O 8 is likely to maintain structural integrity better than LiAlO 2 in the irradiation conditions studied in this work.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Enhanced Tritium Retention in LiAlO2 Pellets via Engineered Glazes: Tritium Science Project

This project investigated the impact of adding a thin (10 – 50 µm) layer of amorphous glaze to the surface of a TPBAR pellet on its retention of helium, hydrogen (as a surrogate for tritium), and water (as a surrogate for tritiated water). The hypothesis was that the glaze would significantly reduce permeation of hydrogen species with a lesser impact on hindering helium permeation. A non-crystallizing soda-lime-silicate glass, known as SCN-1, was selected for this proof-of-concept study. It was found that continuous glaze layers of the desired thickness could be applied to the pellets with two or more dip coats, depending on the targeted thickness. At 330°C, the glaze was found to have a permeability that was lower than that of the pellet by a factor of ~10 6 , implying that a thin 10 – 50 µm layer can significantly increase pellet retention of hydrogen. Meanwhile, the permeation rate of helium through the glaze was found to be ~20 times higher than that of hydrogen or water. An unanticipated outcome of the study was that unglazed pellets were measured to have hydrogen diffusivities that are a factor of ~105 greater than the diffusivity value used in the TPBAR COMSOL model to achieve observed tritium retention rates. When the higher measured diffusivity was substituted into the model and the model was run with all tritium species in the pellet in the form of T 2 O at a partial pressure of 20 Pa in equilibrium with LiOT, the resulting retention was 50% after 500 days.

36 MATERIALS SCIENCE↗