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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Quantum spin ice response to a magnetic field in the dipole-octupole pyrochlore Ce 2 Zr 2 O 7

The pyrochlore magnet Ce 2 Zr 2 O 7 has attracted much attention as a quantum spin ice candidate whose novelty derives in part from the dipolar-octupolar nature of the Ce 3+ pseudospin-1/2 degrees of freedom it possesses. We report heat capacity measurements on single crystal samples of Ce 2 Zr 2 O 7 down to T~0.1K in a magnetic field along the [$1,\bar{1},0$] direction. These measurements show that the broad hump in the zero-field heat capacity moves higher in temperature with increasing field strength and is split into two separate humps by the [$1,\bar{1},0$] magnetic field at ~2T. These separate features are due to the decomposition of the pyrochlore lattice into effectively decoupled chains for fields in this direction: One set of chains (α chains) is polarized by the field while the other (β chains) remains free. This situation is similar to that observed in the classical spin ices Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 , but with the twist that here the strong transverse exchange interactions produce substantial quantum effects. Our theoretical modeling suggests that the β chains are close to a critical state, with nearly-gapless excitations. We also report elastic and inelastic neutron scattering measurements on single crystal Ce 2 Zr 2 O 7 in [$1,\bar{1},0$] and [0,0,1] magnetic fields at temperatures down to T=0.03K. The elastic scattering behaves consistently with the formation of independent chains for a [$1,\bar{1},0$] field, while the [0,0,1] field produces a single field-induced elastic magnetic Bragg peak at (0,2,0) and equivalent wavevectors, indicating a polarized spin ice state for fields above ~3T. For both [$1,\bar{1},0$] and [0,0,1] magnetic fields, our inelastic neutron scattering results show an approximately dispersionless continuum of scattering that increases in both energy and intensity with increasing field strength. By modeling the complete set of experimental data using numerical linked cluster and semiclassical molecular dynamics calculations, we demonstrate the dominantly multipolar nature of the exchange interactions in Ce 2 Zr 2 O 7 and the smallness of the parameter θ, which controls the mixing between dipolar and octupolar degrees of freedom. Finally, these results support previous estimates of the microscopic exchange parameters and place strong constraints on the theoretical description of this prominent spin ice candidate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Effect of thickness and surface composition on the stability of polarization in ferroelectric Hf x Zr 1 - x O 2 thin films

Using density functional theory, we find that tailoring the surface composition provides a route to stabilize the polar phases of the promising ferroelectric material, Hf x Zr 1-x O 2 . First, we show that for pure Hf O 2 , controlling the positively polarized surface to be relatively oxygen rich adequately screens the ferroelectric surface charges and stabilizes the polar orthorhombic phase. We then demonstrate that the ferroelectric polarization, as measured by the structural polar displacements, increases with decreasing thickness, leading to the emergence of a polar rhombohedral-like phase at the ultrathin limit (1.5 unit cells). Our findings extend to the cases of Hf 0.5 Zr 0.5 O 2 and Zr O 2 , both of which have surface energy landscapes similar to that of Hf O 2 . In conclusion, these findings are consistent with and offer insights into the observed absence of a ferroelectric thickness limit in Hf x Zr 1-x O 2 -based thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Assessing Carrier Mobility, Dopability, and Defect Tolerance in the Chalcogenide Perovskite Ba Zr S 3

The chalcogenide perovskite Ba Zr S 3 has attracted much attention as a promising solar absorber for thin-film photovoltaics. Here we use first-principles calculations to evaluate its carrier transport and defect properties. We find that Ba Zr S 3 has a phonon-limited electron mobility of 37 cm 2 / V s, which is comparable to that in halide perovskites, but lower hole mobility of 11 cm 2 / V s. The defect computations indicate that Ba Zr S 3 is intrinsically n -type due to shallow sulfur vacancies, but that strong compensation by sulfur vacancies will prevent attempts to make it p -type. We also establish that Ba Zr S 3 shows some degree of defect tolerance, presenting only few low formation energy, deep intrinsic defects. Among the deep defects, sulfur interstitials are the dominant nonradiative recombination centers but exhibit a moderate capture coefficient. Our work highlights the material’s intrinsic limitations in carrier mobility and p -type doping, and suggests focusing on suppressing the formation of sulfur interstitials to achieve longer carrier lifetime. Published by the American Physical Society 2024

Yuan, Zhenkun (ORCID:0000000272005973)↗
DOE OSTI2026

Extraction of neutron-capture cross sections on 92 Zr using the charge-exchange Oslo method

The 93 Nb (𝑡, 3 He ) reaction at 115 MeV/nucleon was studied to demonstrate that nuclear level densities and 𝛾-ray strength functions can be extracted from charge-exchange reactions at intermediate energies using the Oslo technique. The matrix of excitation energy in 93 Zr, reconstructed from the (𝑡, 3 He ) reaction, versus the energy of 𝛾 rays emitted by the excited 93 Zr nuclei, was obtained in an experiment with the S800 Spectrograph operated in coincidence with the GRETINA 𝛾 -ray detector. The extracted level density and 𝛾 -ray strength function obtained by applying the Oslo method to this matrix were used to estimate the 92 Zr⁢(𝑛,𝛾) ⁢93 Zr cross section by combining the new results with other experimental data and theoretical calculations for 𝐸⁢1 and 𝑀⁢1 strength functions at higher energies. Good agreement with direct measurements of the 92 Zr⁢(𝑛,𝛾)⁢ 93 Zr cross section was found. The contribution from the upbend in the extracted 𝛾-ray strength function was important to achieve the consistency, as the neutron-capture cross section without this contribution is significantly below the direct measurements otherwise. Since charge-exchange reactions at intermediate energies have long been used for extracting Gamow-Teller strengths, the successful demonstration of the charge-exchange Oslo method enables experiments in which (𝑛,𝛾) cross sections and Gamow-Teller strengths can be measured simultaneously, which is of benefit for astrophysical studies.

90 ≤ A ≤ 149↗
DOE OSTI2025

Ta–Zr carbides: Synthesis advances via carbothermal reduction and defect evolution observed through transmission electron microscopy ion irradiation

The thermodynamic stability of six distinct compositions within the Zr—Ta—C ternary system is investigated in this study, marking the first report of their synthesis through carbothermic reduction in vacuum. A prolonged annealing process at 2200°C enabled high densification and phase equilibrium. Detailed phase identification and microstructural characterization through microscopy and X-ray diffraction techniques revealed clear compositional trends and stable phase formations. Two compositions ((Ta 0.2 Zr 0.8 )C 0.6 and (Ta 0.5 Zr 0.5 )C 1 ) were selected for ion irradiation experiments using 200 keV Kr + at 600°C—representing the first-ever irradiation study on the Zr—Ta—C system. The findings indicated defect accumulation and nanoscale cavity formation without any evidence of amorphization, highlighting the system's structural stability under irradiation. Together, the synthesis and irradiation results provide a basis for further investigation of the system and suggest its relevance for applications under extreme environments.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Removal of Tc-99, Zr-95, and Nb-95, From Solutions Obtained After Dissolution of Irradiated Mo Targets

Decontamination of 99 Tc, Nb, and Zr impurities in dissolved irradiated Mo disks can be accomplished using Fe(II) precipitation. Here, we report bench-scale experiments and large-scale demonstrations on removal of 99 Tc (0.1 mM), 95 Nb, and 95 Zr from dissolved Mo disk simulant solutions. Tc removal is accomplished through the reduction and simultaneous immobilization of Tc(VII) by Fe(II), producing an insoluble, Tcincorporated Fe(II)-Fe(III) solid that is removed by filtration. Large-scale testing showed that Tc (97.6% ± 1.7%) is removed without affecting 99 Mo yields. Other important side reaction product impurities in irradiated Mo targets, namely various isotopes of Nb and Zr, are also removed (>99%) in this process. The effects of metal (Fe, Tc, Mo) concentrations, Fe(II)/Fe(III) ratio, pH, temperature, Fe addition method, and hydrogen peroxide addition were tested. The minimum amount of Fe(II) needed to remove up to 99% Tc is 10 mM and the optimal pH value for simultaneous removal of Tc, Nb, and Zr impurities is pH 13.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Hydrogen Localization and Cluster Formation in α-Zr from First-Principles Investigations

We report alpha-zirconium (α-Zr) is a hydrogen atom host material used in nuclear energy and semiconducting applications due to Zr's excellent properties such as corrosion resistance, low thermal neutrons cross-section, and thermodynamically favorable interstitial sequestering of H atoms. Herein we use density functional theory simulations to systematically analyze the initial stages of H insertion in the Zr matrix, and determine optimal hydrogen localization, distribution, and clustering tendencies from a thermodynamics and kinetics perspective. Our results suggest that H occupation of tetrahedral sites is strongly favored, consistent with previous experimental and theoretical studies. Further, a cooperative effect in H localization is shown where H atoms favor clustering. The H pair is found to be the most stable by occupying tetrahedral sites with pairs at second nearest-neighbor positions (TTn2). Among the four H atom clusters, the most favorable configuration has two TTn2 pairs forming "box " or "zig-zag" shaped-cluster with the pairs separated by 3.03 or 3.25 Å, respectively. Nudged elastic band simulations suggest that the formation of TTn2 is facile and is limited by the small diffusion barrier of the monomer of less than 0.1 eV. Further, the formation routes for the 4H atom clusters are also presented. The current study can serve as a foundation to systematically model H atom clustering in metals and alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(IO3)4 by Materials Project

Zr(O3I)4 crystallizes in the tetragonal P4/n space group. The structure is two-dimensional and consists of one Zr(O3I)4 sheet oriented in the (0, 0, 1) direction. Zr4+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.23 Å) and four longer (2.24 Å) Zr–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Zr4+ and one I5+ atom. The O–I bond length is 1.88 Å. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Zr4+ and one I5+ atom. The O–I bond length is 1.85 Å. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.83 Å. I5+ is bonded in a 3-coordinate geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(PO3)4 by Materials Project

Zr(PO3)4 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are two inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Zr–O bond distances ranging from 2.14–2.38 Å. In the second Zr4+ site, Zr4+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Zr–O bond distances ranging from 2.14–2.32 Å. There are eight inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There is two shorter (1.50 Å) and two longer (1.61 Å) P–O bond length. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.61 Å. In the fifth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the sixth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There is two shorter (1.50 Å) and two longer (1.60 Å) P–O bond length. In the seventh P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. In the eighth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There is two shorter (1.50 Å) and two longer (1.61 Å) P–O bond length. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Zr4+ and one P5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one Zr4+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one Zr4+ and one P5+ atom. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to one Zr4+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the twelfth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the fifteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the sixteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the seventeenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the eighteenth O2- site, O2- is bonded in a distorted single-bond geometry to one Zr4+ and one P5+ atom. In the nineteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the twentieth O2- site, O2- is bonded in a distorted single-bond geometry to one Zr4+ and one P5+ atom. In the twenty-first O2- site, O2- is bonded in a 2-coordinate geometry to one Zr4+ and one P5+ atom. In the twenty-second O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the twenty-third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zr4+ and one P5+ atom. In the twenty-fourth O2- site, O2- is bonded in a 1-coordinate geometry to one Zr4+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(InBr3)2 by Materials Project

Zr(InBr3)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Zr2+ sites. In the first Zr2+ site, Zr2+ is bonded in an octahedral geometry to six Br1- atoms. There are four shorter (2.65 Å) and two longer (2.66 Å) Zr–Br bond lengths. In the second Zr2+ site, Zr2+ is bonded in an octahedral geometry to six Br1- atoms. All Zr–Br bond lengths are 2.65 Å. There are two inequivalent In2+ sites. In the first In2+ site, In2+ is bonded in a 4-coordinate geometry to four Br1- atoms. There are three shorter (3.52 Å) and one longer (3.53 Å) In–Br bond lengths. In the second In2+ site, In2+ is bonded in a 4-coordinate geometry to four Br1- atoms. There are a spread of In–Br bond distances ranging from 3.51–3.54 Å. There are twelve inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms. In the second Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms. In the third Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ atom. In the fourth Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms. In the fifth Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ atom. In the sixth Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms. In the seventh Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms. In the eighth Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms. In the ninth Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ atom. In the tenth Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms. In the eleventh Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ atom. In the twelfth Br1- site, Br1- is bonded in a single-bond geometry to one Zr2+ and two equivalent In2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(TiH2)2 by Materials Project

Ti2ZrH4 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Zr is bonded to four equivalent H atoms to form ZrH4 tetrahedra that share corners with twelve equivalent TiH6 octahedra. The corner-sharing octahedral tilt angles are 62°. All Zr–H bond lengths are 2.04 Å. Ti is bonded to six equivalent H atoms to form TiH6 octahedra that share corners with six equivalent ZrH4 tetrahedra and edges with six equivalent TiH6 octahedra. All Ti–H bond lengths are 1.89 Å. H is bonded to one Zr and three equivalent Ti atoms to form a mixture of edge and corner-sharing HZrTi3 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(PS3)2 by Materials Project

Zr(PS3)2 crystallizes in the tetragonal P4_2/m space group. The structure is one-dimensional and consists of one Zr(PS3)2 ribbon oriented in the (0, 0, 1) direction. Zr2+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are four shorter (2.62 Å) and four longer (2.89 Å) Zr–S bond lengths. P5+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are two shorter (2.02 Å) and one longer (2.05 Å) P–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 1-coordinate geometry to two equivalent Zr2+ and one P5+ atom. In the second S2- site, S2- is bonded in an L-shaped geometry to one Zr2+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(AlC)4 by Materials Project

Zr(AlC)4 crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are two inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded to six C4- atoms to form ZrC6 octahedra that share corners with three equivalent ZrC6 octahedra, corners with three equivalent AlC4 tetrahedra, edges with nine ZrC6 octahedra, and edges with three equivalent AlC4 tetrahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.37 Å) and three longer (2.39 Å) Zr–C bond lengths. In the second Zr4+ site, Zr4+ is bonded to six C4- atoms to form ZrC6 octahedra that share corners with three equivalent ZrC6 octahedra, corners with three equivalent AlC4 tetrahedra, edges with nine ZrC6 octahedra, and edges with three equivalent AlC4 tetrahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.37 Å) and three longer (2.39 Å) Zr–C bond lengths. There are eight inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four C4- atoms to form a mixture of edge and corner-sharing AlC4 tetrahedra. There are one shorter (1.94 Å) and three longer (2.18 Å) Al–C bond lengths. In the second Al3+ site, Al3+ is bonded to four C4- atoms to form a mixture of edge and corner-sharing AlC4 tetrahedra. There are one shorter (1.94 Å) and three longer (2.18 Å) Al–C bond lengths. In the third Al3+ site, Al3+ is bonded to four C4- atoms to form AlC4 tetrahedra that share corners with three equivalent ZrC6 octahedra, corners with six equivalent AlC4 tetrahedra, corners with four AlC4 trigonal pyramids, and edges with three equivalent ZrC6 octahedra. The corner-sharing octahedral tilt angles are 11°. There are one shorter (1.95 Å) and three longer (2.13 Å) Al–C bond lengths. In the fourth Al3+ site, Al3+ is bonded to four C4- atoms to form AlC4 tetrahedra that share corners with three equivalent ZrC6 octahedra, corners with six equivalent AlC4 tetrahedra, corners with four AlC4 trigonal pyramids, and edges with three equivalent ZrC6 octahedra. The corner-sharing octahedral tilt angles are 11°. There are one shorter (1.95 Å) and three longer (2.13 Å) Al–C bond lengths. In the fifth Al3+ site, Al3+ is bonded to four C4- atoms to form a mixture of distorted edge and corner-sharing AlC4 trigonal pyramids. There are three shorter (1.97 Å) and one longer (2.17 Å) Al–C bond lengths. In the sixth Al3+ site, Al3+ is bonded to four C4- atoms to form a mixture of edge and corner-sharing AlC4 trigonal pyramids. There are three shorter (1.97 Å) and one longer (2.16 Å) Al–C bond lengths. In the seventh Al3+ site, Al3+ is bonded to four C4- atoms to form a mixture of edge and corner-sharing AlC4 trigonal pyramids. There are three shorter (1.96 Å) and one longer (2.21 Å) Al–C bond lengths. In the eighth Al3+ site, Al3+ is bonded to four C4- atoms to form a mixture of edge and corner-sharing AlC4 trigonal pyramids. There are three shorter (1.96 Å) and one longer (2.20 Å) Al–C bond lengths. There are eight inequivalent C4- sites. In the first C4- site, C4- is bonded to six Al3+ atoms to form CAl6 octahedra that share corners with six CAl5 trigonal bipyramids and edges with six equivalent CAl6 octahedra. In the second C4- site, C4- is bonded to five Al3+ atoms to form CAl5 trigonal bipyramids that share corners with three equivalent CZr3Al3 octahedra, corners with six equivalent CAl5 trigonal bipyramids, and edges with three equivalent CAl5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 65°. In the third C4- site, C4- is bonded to six Zr4+ atoms to form a mixture of edge and corner-sharing CZr6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the fourth C4- site, C4- is bonded to five Al3+ atoms to form CAl5 trigonal bipyramids that share corners with three equivalent CAl6 octahedra, corners with six equivalent CAl5 trigonal bipyramids, and edges with three equivalent CAl5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 63°. In the fifth C4- site, C4- is bonded to five Al3+ atoms to form CAl5 trigonal bipyramids that share corners with three equivalent CZr3Al3 octahedra, corners with six equivalent CAl5 trigonal bipyramids, and edges with three equivalent CAl5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 65°. In the sixth C4- site, C4- is bonded to three equivalent Zr4+ and three equivalent Al3+ atoms to form CZr3Al3 octahedra that share corners with three equivalent CZr6 octahedra, corners with three equivalent CAl5 trigonal bipyramids, and edges with nine CZr6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the seventh C4- site, C4- is bonded to three equivalent Zr4+ and three equivalent Al3+ atoms to form CZr3Al3 octahedra that share corners with three equivalent CZr6 octahedra, corners with three equivalent CAl5 trigonal bipyramids, and edges with nine CZr3Al3 octahedra. The corner-sharing octahedral tilt angles are 1°. In the eighth C4- site, C4- is bonded to five Al3+ atoms to form distorted CAl5 trigonal bipyramids that share corners with three equivalent CAl6 octahedra, corners with six equivalent CAl5 trigonal bipyramids, and edges with three equivalent CAl5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 62°.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Diffusion, atomic transport, and ordering in Al-Zr alloys: FCC and liquid phases

Additive manufacturing of materials with controlled microstructure demands knowledge of atomic scale properties near the solid-liquid transition state. Many of these properties are not affordable by experimental techniques and computer modeling is the possible solution to the problem. In this paper, we present the results of an extended atomistic study of intrinsic atomic transport due to vacancy diffusion in FCC and L12 solid phases and diffusion in the liquid phase of Al-Zr alloys. A deceleration of the overall self-diffusion was observed when Zr was added to Al. The effect was stronger in the solid and weaker in the liquid. Additionally, the effect was strongly temperature dependent in the solid phases, but not in the liquid. Atomic transport was chemically biased: transport of Zr atoms was significantly slower than that of Al atoms, and this bias effect was stronger in the solid phases. The overall diffusion and chemical ordering processes in the liquid state were five to six orders in magnitude faster than in the solid. Chemical short-range order parameters in the liquid saturated at values close to those in the ordered L12 structure of Al3Zr. Chemical and structural ordering in the solid phases was negligible over the modeled microsecond time scale. Here, the results are discussed in view of optimizing additive manufacturing parameters for the controlled formation of metastable L1 2 precipitates.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mesoscale modeling of microstructure-dependent thermal conductivity in U-Zr fuels

In uranium-zirconium (U-Zr) based metallic fuels, different phases can form at different compositions and temperatures. Typically, lamellar δ-UZr 2 and α-U phases are the dominant microstructures in U-rich U-Zr alloys at temperatures below 880 K. In this work, a finite element method based mesoscale modeling technique is used to calculate the effective thermal conductivities of such heterogeneous microstructures, using the thermal conductivities of two individual phases and their interphase thermal resistance (Kapitza resistance) as input parameters. The Kapitza resistance between δ-UZr 2 and α-U is determined at different temperatures, which shows an approximately T 3 dependence in the temperature range between 300 and 800 K. In addition, the Kapitza resistance exhibits a strong dependence on the aspect ratio of the δ-UZr 2 phase. Further, an analytical model is therefore developed to quantify the effects of both temperature and δ-UZr 2 aspect ratio on the Kapitza resistance. Using this newly developed Kapitza resistance model, the effective thermal conductivities of a number of δ-UZr 2 + α-U heterogeneous microstructures in U-Zr alloys, including non-lamellar microstructures, can be estimated accurately.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Elucidating the effect of minor-actinide addition on fuel-cladding chemical interaction in an HT-9 clad U-Pu-Zr metallic fuel irradiated to 6.15 at.% burnup in EBR-II

Scanning and transmission electron microscopy (S/TEM) were used to characterize the local fuel-cladding chemical interaction (FCCI) in one cross-section taken from a HT-9 clad U-20.3Pu-10Zr-1.2Am-1.3Np (in wt.%) fuel irradiated to 6.15 at.% burnup with inner cladding temperatures ranging between 460–490 °C. Results showed that the total interaction thickness between fuel and cladding was <10 µm. Fe infiltrated the fuel to form U-Zr-Fe phases while fuel elements or lanthanides did not infiltrate into the cladding. Np was not involved in the formation of any phases in the examined locations; however, Am played a role by forming a ∼2 µm thick homogeneous Fe-Pu-Am planar front at the inner cladding wall. An oxidized Na layer existed in the fuel-cladding gap with Fe and lanthanide particles dispersed within, suggesting Na could facilitate the transport of fuel and cladding constituents. Secondary phases, including an FCC Zr-rich phase, lanthanide phases, and α’-Cr(Fe) were identified in the outer fuel and FCCI regions. Furthermore, this study suggests that, for the irradiation conditions specific to this cross-section, minor actinides have little impact on FCCI behavior beyond what would be observed in typical HT-9 clad U-Pu-Zr fuel pins systems.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Microstructural evolution and strengthening mechanisms in a heat-treated additively manufactured Al–Cu–Mn–Zr alloy

In this report the microstructural and strength evolution of an additively manufactured Al-8.6Cu-0.5Mn-0.9Zr alloy upon aging at 300, 350, and 400 °C is investigated. The strengthening phases of the alloy evolve significantly upon aging, with breakdown and spheroidization of the interconnected θ-Al 2 Cu network, dissolution of metastable θ'-Al 2 Cu precipitates, and precipitation of nanometric L1 2 -Al 3 Zr from a matrix supersaturated in Zr. In the peak-aged states, the alloy displays a favorable combination of strength and ductility, with a room-temperature yield strength of 314–341 MPa and ductility of 11–13%. The measured yield strengths for microstructures with different aging treatments are compared to predictions of yield strengths from grain boundary, solid solution, and particle strengthening contributions. The observed strain hardening behavior is related to fundamental precipitate and dislocation interactions. Comparison between predicted and measured strength values indicates a continued need for strengthening models specifically developed for the heterogeneous microstructures of additively manufactured alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Analysis of orientation-dependent deformation mechanisms in additively manufactured Zr using in-situ micromechanical testing: Twinning and orientation gradient

Here, orientation-dependent plasticity in zirconium (Zr)-alloy, which is produced through ultrasonic additive manufacturing (UAM) with subsequent hot-isostatic pressing (HIP), was analyzed by recording electron backscattered diffraction (EBSD) data during in-situ micromechanical testing. Three (0001) plane orientations of a hexagonal close-packed (HCP) structure were analyzed parallel to (1) the rolling direction [X||tensile direction (TD)], (2) the build direction [Z], and (3) the transverse direction [Y]. The analysis revealed that the grains with ~<0001>||TD show twin-dominant plasticity with three variants from {10 $\overline{1}$ 2}<$\overline{1}$ 011>; minor slipping with ($10\overline{1}$ 1)[$\overline{2}$ 113], and ($11\overline{2}$ 2)[$\overline{1} \overline{1}$ 23] pyramidal slip has also been observed. However, grains with orientation ~<0001>⊥TD are mainly sensitive to dislocations assisted plasticity-leading to orientation gradients formation. Furthermore, the neck formation was identified as originating from higher populated micro-crack locations and their association with localized plasticity at defect points in the UAM material. These results demonstrate that minimization of impurities to enable grain growth across prior foil interfaces makes HIP an effective methodology for producing Zr plate, with deformation characteristics expected for conventionally manufactured Zr.

36 MATERIALS SCIENCE↗