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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Effect of Sn microalloying on the nucleation of L1 2 Al 3 Zr precipitates in a dilute aluminum-zirconium alloy

While L1 2 -Al 3 Zr nanoprecipitates provide a balance between strengthening and good electrical conductivity, the precipitation of L1 2 -Al 3 Zr in aluminum requires aggressive heat treatments. An improved age-hardening response was observed during isochronal aging of an Al-0.24Zr (wt%) alloy when microalloyed with Sn. A new mechanism termed Low melting point Element-Assisted Nucleation (LEAN) is proposed to explain the lower temperature nucleation of L1 2 -Al 3 Zr precipitates observed in this alloy based on the addition of a low melting point element, such as Sn. Characterization verified the first-principles density functional theory prediction that Zr and Sn atoms cluster during homogenization owing to the favorable binding energy of Zr-Sn-vacancy triplets. Direct microstructural observations revealed these clusters form Sn nanoprecipitates that assist the nucleation of L1 2 -Al 3 Zr at 200°C, where L1 2 -Al 3 Zr precipitation is not expected due to the low diffusivity of Zr atoms in Al. At higher temperatures (≳350°C), the acceleration of L1 2 -Al 3 Zr precipitation is driven by faster Zr diffusion in Al with Sn microalloying and the nuclei formed via the LEAN mechanism. In conclusion, this combination of mechanisms explains the improvement in age hardening through L1 2 -Al 3 Zr precipitation with Sn microalloying.

36 MATERIALS SCIENCE↗
DOE OSTI2025

The Electron Thermal Conductivity of Pu and Zr Substituted $\mathcal{γ}$-U

Uranium alloys are attractive recycled nuclear fuels because of their high thermal conductivity (𝑘) and fissile density. Limited experimental studies of the 𝑘 of U-Pu-Zr alloys in the range of 15 to 20 wt% Pu and 6 to 15 wt% Zr indicate that increasing the content of either Zr or Pu tends to lower 𝑘. However, which element has the greater effect on 𝑘, and the associated mechanisms, remains unclear. Here, in this study, the electron thermal conductivity (𝑘 𝑒 ) of U-Pu-Zr compositions are calculated using density functional theory. The electronic structure is evaluated to understand the effects of plutonium (Pu) and zirconium (Zr) substitution on the 𝑘 𝑒 of 𝛾-U. Alloys of up to 37.5 at. % Pu and 37.5 at. % Zr are examined. Two methods are applied to calculate 𝑘 𝑒 ; we find that the accuracy of each method depends on the electronic and mass similarities between the solute and solvent atoms. Specifically, when the solute atom is similar in electronic structure and mass, the more accurate method is that which employs the electron relaxation time of 𝛾-U, while if the elements are dissimilar, a mixed method that mixes several parameters associated with JNW_S⁢3033426825100132 from each element in the alloy is best. The introduction of all alloying elements decreases 𝑘 𝑒 ; however, in binary compounds, Pu and Zr have different effects. Pu flattens the electronic bands but compensates for this deleterious effect by increasing electron density near the Fermi level. Zr flattens the electronic bands more severely without adding electron density near the Fermi level. Therefore, Zr decreases 𝑘 𝑒 more than Pu in binary compounds. In ternary compounds, the difference between Pu and Zr is minimal due to the phononic change from the large mass change of Zr substitution, even at 12.5 at. %. Thus, we predict that higher loadings of Pu, and potentially other actinides, can be added to U-Pu-Zr compositions for faster recycling of spent fuel without sacrificing 𝑘. We also note that these 𝑘 𝑒 calculation methods can be applied to non-fuel alloys that require 𝑘 𝑒 predictions, such as cladding, heat exchanger, and structural materials.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on Zr(PO5)2 by Materials Project

Zr(PO4)2O2 crystallizes in the monoclinic P2_1 space group. The structure is two-dimensional and consists of two oxygen molecules and one Zr(PO4)2 sheet oriented in the (0, 0, 1) direction. In the Zr(PO4)2 sheet, Zr is bonded to six O atoms to form ZrO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Zr–O bond distances ranging from 2.06–2.13 Å. There are two inequivalent P sites. In the first P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four equivalent ZrO6 octahedra. The corner-sharing octahedra tilt angles range from 7–34°. All P–O bond lengths are 1.54 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with two equivalent ZrO6 octahedra. The corner-sharing octahedra tilt angles range from 15–33°. There is three shorter (1.54 Å) and one longer (1.55 Å) P–O bond length. There are eight inequivalent O sites. In the first O site, O is bonded in a linear geometry to one Zr and one P atom. In the second O site, O is bonded in a bent 150 degrees geometry to one Zr and one P atom. In the third O site, O is bonded in a bent 150 degrees geometry to one Zr and one P atom. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Zr and one P atom. In the fifth O site, O is bonded in a bent 150 degrees geometry to one Zr and one P atom. In the sixth O site, O is bonded in a linear geometry to one Zr and one P atom. In the seventh O site, O is bonded in a single-bond geometry to one P atom. In the eighth O site, O is bonded in a single-bond geometry to one P atom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Growth and characterization of high-quality Zr doped AlN epilayers

AlN stands out for its remarkable figures of merit for electronic and photonic devices, attributed to its ultrawide bandgap of ∼6.1 eV and an exceptionally high critical field of ∼15 MV/cm. More recently, zirconium (Zr) doped AlN (AlN:Zr) has also been identified as a promising material platform for the exploration of solid-state qubits for quantum information and technology, high performance piezoelectric acoustic wave resonators, and optically triggered ultrafast power switching devices facilitated by optically activating Zr related impurities. Despite the significant potential, the ability for producing AlN:Zr epitaxial structures has yet to be established. In this study, we have achieved AlN:Zr epilayers with a high Zr doping level [NZr] of up to 1020 cm−3 using industrial standard metal-organic chemical vapor deposition growth technique. High crystalline quality of AlN:Zr was confirmed by x-ray diffraction, revealing a narrow full width at half maximum of the (002) rocking curve at 216 arcsec for 1.8 μm thick epilayers deposited on sapphire at [NZr]=1020 cm−3. Zr doping was observed to slightly increase the c-lattice constant to 4.992 Å for AlN:Zr (at [NZr]=1020 cm−3) compared to 4.980 Å for undoped AlN. X-ray photoelectron spectroscopy measurement results verified the substitution of Zr at the Al site (ZrAl). The formation of (ZrAl–VN) complexes, which are predicted to possess all the desired properties required by quantum qubits, was confirmed through optical absorption studies. The realization of high-quality AlN:Zr epilayers significantly broadens the scope of technologically significant device applications for AlN.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Measurement of ( n, γ ) cross section of 90 Zr [Abstract]

The isotopes of Zr with A = [90, 91, 92, 94] make up more than 97% of naturally occurring Zr and are important to many nuclear applications such as nuclear reactors. One of the attractive qualities of naturally occurring Zr isotopes is that they have a low σγ/σt ratio at most neutron energies, such that they improve the neutron economy in reactors by preferentially scattering neutrons rather than absorbing them. This same quality also presents a challenge to measuring the capture cross section, σγ, of Zr isotopes. The ENDF/B-VIII.0 library has a relative uncertainty of approximately 10-20% for incident neutron energies < 0.1 MeV, and uncertainty greater than 20% for energies > 0.1 MeV for the majority of natural Zr isotopes. This motivated the Nuclear Criticality Safety Program (NCSP) to embark on a campaign to accurately measure and evaluate these isotopes of Zr. Here we will show energy-dependent neutron capture cross section measurements for the first enriched sample to be measured: 90 Zr. The measurements of isotopically enriched samples are being carried out at the Geel Electron Linear Accelerator (GELINA) facility of the Joint Research Center - Geel (JRC-Geel) of the European Union. As isotopic enrichment is a costly process we are careful not to activate any of the samples, as this may hinder future radiation-sensitive measurements. The activation analysis is presented in a report by Brown et al.. Once we were satisfied that the Zr samples would not be activated by the measurements, the 90 Zr sample was fabricated at Oak Ridge National Laboratory (ORNL) and shipped to GELINA. The dimensions of the cylindrical sample are approximately 0.12 cm thick and a radius of 2.5 cm. Since 90 Zr is not chemically reactive to air, bare metallic samples were employed. The sample was measured at a flight path (FP) length of 60 m, using four C 6 D 6 detectors on FP14. The final paper will include experimental details and measured cross section data for 90 Zr compared to current evaluated nuclear data libraries.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2020

Methane combustion over Ni/Ce x Zr 1-x O 2 catalysts: impact of ceria/zirconia ratio

In this work, a series of Ce x Zr 1–x O 2 (x=1, 0.83, 0.17, 0) supports and 2 wt.% Ni/Ce x Zr 1–x O 2 catalysts were synthesized and evaluated for CH 4 oxidation. The Ce x Zr 1–x O 2 supports showed moderate activity (T 50 =519-638°C) with CO by-product formation. Additionally, nickel incorporation onto Ce x Zr 1–x O 2 lowered the T 50 to 438–477°C and eliminated the formation of CO. The results indicated that moderate Zr doping improved the support oxygen storage capacity (OSC) and reducibility of the catalyst at low temperatures (H 2 -TPR) leading to an enhanced CH 4 combustion turnover frequency: Ni/ZrO 2 <Ni/Ce 0.17 Zr 0.83 O 2 <Ni/CeO 2 <Ni/Ce 0.83 Zr 0.17 O 2 . The apparent activation energies of Ni/Ce x Zr 1–x O 2 catalysts (87-92 kJ/mol) were much lower than the ones of Ce x Zr 1–x O 2 supports and Ni/quartz sand (111-120 kJ/mol) indicating that CH 4 oxidation is facilitated when Ni is deposited on Ce x Zr 1–x O 2 . Moreover, stability tests with H 2 O and CO 2 showed that Zr doping can improve the catalyst stability, while H 2 O had a stronger reversible inhibition effect than CO 2 for CH 4 combustion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Quantifying Kinetically Relevant Species on Zr‐SiO 2 Materials for MPV Reduction

Abstract On supported metal catalysts such as Zr‐SiO 2 , it can be challenging to isolate characteristics that result from intrinsic properties of the active site from those that result from the environment surrounding the active site. In this report, we utilize in situ titration of Lewis acid sites with phosphonic acid to accurately and quantitatively describe kinetically relevant Zr species on Zr‐SiO 2 materials for the MPV reduction of cyclohexanone. We find that rate of MPV reduction on Zr‐SiO 2 materials can be described as a combination of rate over titratable Zr, that is likely well dispersed Zr, and rate over non‐titratable Zr, that is likely supported ZrO x . The fraction of Zr that is well dispersed on the SiO 2 is dependent on the surface density at which Zr is grafted but not the choice of Zr precursor. We demonstrate that phosphonic acid titration can offer a more relevant, quantitative description of Zr dispersion than UV‐vis and can be used to quantitatively describe changes that occur to the material during regeneration.

Chase, Emily↗
DOE OSTI2022

Anion exchange and extraction chromatography tandem column isolation of zirconium-89 ( 89 Zr) from cyclotron bombarded targets using an automated fluidic platform

The long-lived positron emitter 89 Zr is a highly promising nuclide employed in diagnostic Positron Emission Tomography (PET) imaging. Methods of radiochemical processing to obtain 89 Zr for clinical use are traditionally performed with a single hydroxamate resin column. In this work, we present a tandem column purification method for the preparation of high-purity 89 Zr from cyclotron bombarded Y metal foils. The primary column is a macroporous, strongly basic anion exchange resin on styrene divinylbenzene co-polymer. The secondary microcolumn, with an internal volume of 33 µL, is packed with an extraction chromatography resin (ExCR) loaded with HDEHP. A condition of “inverted selectivity” is presented, wherein the 89 Zr elution from the primary column is synonymous with the load condition on the secondary column. The ability to transfer 89 Zr from one column to the next allows two sequential column clean-up methods to be performed prior to the final elution of the 89 Zr product. This approach assures delivery of very high purity 89 Zr . The tandem column purification process has been implemented into a prototype automated fluidic system. Optimization of the method is presented, followed by evaluation of the process using seven cyclotron bombarded Y metal foil targets. Once optimized, we found that 93.7±2.3% of the 89 Zr present in the foils was recovered in the secondary column elution fraction (0.8 M oxalic acid). Radiochromatograms of the product elution peaks enabled determination of full width at half-maximum (FWHM) and 89 Zr collection yields as a function of volume. Because of the small size of the secondary microcolumn, a 89 Zr product volume of ~0.28 mL is reported, which provides a substantially increased nuclide concentration over traditional methods. Finally, we evaluated the transchelation of the resulting 89 Zr oxalate product to deferoxamine mesylate (DFOM) salt. We observed effective specific activities (ESA) and bindable metals concentrations ([M B ]) that exceed those reported by the traditional single hydroxamate column method.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Materials Data on Zr(AsO5)2 by Materials Project

Zr(AsO5)2 crystallizes in the monoclinic P2_1 space group. The structure is two-dimensional and consists of one Zr(AsO5)2 sheet oriented in the (0, 0, 1) direction. Zr is bonded to six O atoms to form ZrO6 octahedra that share corners with six AsO4 tetrahedra. There are a spread of Zr–O bond distances ranging from 2.04–2.20 Å. There are two inequivalent As sites. In the first As site, As is bonded to four O atoms to form AsO4 tetrahedra that share corners with four equivalent ZrO6 octahedra. The corner-sharing octahedra tilt angles range from 15–37°. There is one shorter (1.70 Å) and three longer (1.71 Å) As–O bond length. In the second As site, As is bonded to four O atoms to form distorted AsO4 tetrahedra that share corners with two equivalent ZrO6 octahedra. The corner-sharing octahedra tilt angles range from 21–48°. There are a spread of As–O bond distances ranging from 1.70–2.28 Å. There are ten inequivalent O sites. In the first O site, O is bonded in a linear geometry to one Zr and one As atom. In the second O site, O is bonded in a bent 150 degrees geometry to one Zr and one As atom. In the third O site, O is bonded in a bent 150 degrees geometry to one Zr and one As atom. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Zr and one As atom. In the fifth O site, O is bonded in a bent 120 degrees geometry to one Zr and one As atom. In the sixth O site, O is bonded in a bent 150 degrees geometry to one Zr and one As atom. In the seventh O site, O is bonded in a water-like geometry to one As and one O atom. The O–O bond length is 1.25 Å. In the eighth O site, O is bonded in a bent 120 degrees geometry to one As and one O atom. The O–O bond length is 1.27 Å. In the ninth O site, O is bonded in a single-bond geometry to one O atom. In the tenth O site, O is bonded in a single-bond geometry to one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(ClO4)4 by Materials Project

Zr(O4Cl)4 crystallizes in the monoclinic Cc space group. The structure is zero-dimensional and consists of four Zr(O4Cl)4 clusters. Zr is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Zr–O bond distances ranging from 1.90–2.46 Å. There are sixteen inequivalent O sites. In the first O site, O is bonded in an L-shaped geometry to one Zr and one Cl atom. The O–Cl bond length is 1.49 Å. In the second O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.45 Å. In the third O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.43 Å. In the fourth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.21 Å. In the fifth O site, O is bonded in a water-like geometry to one Zr and one Cl atom. The O–Cl bond length is 1.55 Å. In the sixth O site, O is bonded in a bent 150 degrees geometry to one Zr and one Cl atom. The O–Cl bond length is 1.70 Å. In the seventh O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.45 Å. In the eighth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. In the ninth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.45 Å. In the tenth O site, O is bonded in a distorted water-like geometry to two O atoms. The O–O bond length is 1.86 Å. In the eleventh O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.45 Å. In the twelfth O site, O is bonded in a water-like geometry to one Zr and one Cl atom. The O–Cl bond length is 1.57 Å. In the thirteenth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.46 Å. In the fourteenth O site, O is bonded in a water-like geometry to one Zr and one Cl atom. The O–Cl bond length is 1.56 Å. In the fifteenth O site, O is bonded in a single-bond geometry to one Zr and one O atom. The O–O bond length is 1.99 Å. In the sixteenth O site, O is bonded in a 1-coordinate geometry to two O and one Cl atom. The O–Cl bond length is 1.91 Å. There are four inequivalent Cl sites. In the first Cl site, Cl is bonded in a trigonal non-coplanar geometry to three O atoms. In the second Cl site, Cl is bonded in a trigonal non-coplanar geometry to three O atoms. In the third Cl site, Cl is bonded in a tetrahedral geometry to four O atoms. In the fourth Cl site, Cl is bonded in a trigonal non-coplanar geometry to three O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(GaFe)6 by Materials Project

Zr(FeGa)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Zr is bonded to twelve Fe and eight Ga atoms to form distorted ZrGa8Fe12 hexagonal bipyramids that share corners with eight equivalent ZrGa8Fe12 hexagonal bipyramids, faces with twenty-four FeZr2Ga6Fe4 cuboctahedra, and faces with two equivalent ZrGa8Fe12 hexagonal bipyramids. There are four shorter (3.24 Å) and eight longer (3.26 Å) Zr–Fe bond lengths. There are two shorter (2.79 Å) and six longer (2.93 Å) Zr–Ga bond lengths. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Zr, four equivalent Fe, and six Ga atoms to form distorted FeZr2Ga6Fe4 cuboctahedra that share corners with fourteen FeZr2Ga6Fe4 cuboctahedra, edges with seven FeZr2Ga6Fe4 cuboctahedra, faces with nine FeZr2Ga6Fe4 cuboctahedra, and faces with four equivalent ZrGa8Fe12 hexagonal bipyramids. All Fe–Fe bond lengths are 2.49 Å. There are a spread of Fe–Ga bond distances ranging from 2.56–2.61 Å. In the second Fe site, Fe is bonded to two equivalent Zr, four Fe, and six Ga atoms to form distorted FeZr2Ga6Fe4 cuboctahedra that share corners with fourteen FeZr2Ga6Fe4 cuboctahedra, edges with six FeZr2Ga6Fe4 cuboctahedra, faces with ten FeZr2Ga6Fe4 cuboctahedra, and faces with four equivalent ZrGa8Fe12 hexagonal bipyramids. Both Fe–Fe bond lengths are 2.50 Å. There are two shorter (2.54 Å) and four longer (2.58 Å) Fe–Ga bond lengths. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded in a 8-coordinate geometry to one Zr, six Fe, and one Ga atom. The Ga–Ga bond length is 2.88 Å. In the second Ga site, Ga is bonded in a 10-coordinate geometry to one Zr, six Fe, and three Ga atoms. There are one shorter (2.73 Å) and two longer (2.87 Å) Ga–Ga bond lengths. In the third Ga site, Ga is bonded in a 8-coordinate geometry to two equivalent Zr, six Fe, and two equivalent Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria: Soot-ceria contact and interfacial oxygen evolution

Ceria is widely used as a catalyst for soot combustion, but effects of Zr substitution on the reaction mechanism is ambiguous. The present work elucidates effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria. The nanostructured CeO 2 , Ce 0.92 Zr 0.08 O 2 , and Ce0.84Zr0.16O2 composed of 5–6 nm crystallites display Tm-CO 2 (the temperature at maximum CO 2 yield) at 383, 355, and 375°C under 10 vol.% O 2 /N 2 , respectively. Additionally, the size of agglomerate decreases from 165.5 to 51.9–57.3 nm, which is beneficial for the soot-ceria contact. Moreover, Zr increases the amount of surface oxygen vacancies, generating more active oxygen (O2- and O-) for soot oxidation. Thus, the activities of Ce 0.92 Zr 0.08 O 2 and Ce 0.84 Zr 0.16 O 2 in soot combustion are better than that of CeO2. Although oxygen vacancies promote the migration of lattice O 2- , the enriched surface Zr also inhibits the mobility of lattice O 2- . Therefore, the Tm-CO 2 of Ce 0.84 Zr 0.16 O 2 is higher than that of Ce 0.92 Zr 0.08 O 2 . Based on reaction kinetic study, soot in direct contact with ceria preferentially decomposes with low activation energy, while the oxidation of isolated soot occurs through diffusion with high activation energy. The obtained findings provide new understanding on the soot combustion over nanoceria.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Hydrothermally stable Pd/SiO 2 @Zr Core@Shell catalysts for diesel oxidation applications

Hydrothermally stable diesel oxidation catalysts (DOCs) with improved low-temperature activity are desired for the abatement of emissions from diesel vehicles. Herein, novel palladium(Pd)/SiO 2 (core)@Zr(shell) structured DOCs were developed. SiO 2 was completely covered by an 8.4 nm thickness Zr-based shell using a hard template method. The SiO 2 @Zr support was decorated by Pd and evaluated under a simulated diesel exhaust stream. Degreened 1 wt% Pd/SiO 2 @Zr achieved 90% CO and total hydrocarbon conversion at 178 and 372 °C, respectively (feed: 6% CO 2 , 12% O 2 , 6% H 2 O, 400 ppm H 2 , 2000 ppm CO, 100 ppm NO, 1667 ppm C 2 H 4 , 1000 ppm C 3 H 6 , 333 ppm C 3 H 8 ; HCs in C 1 basis and GHSV = 113,000 h –1 ). After hydrothermal aging, only a minor deactivation was observed, while the surface area of 1 wt% Pd/SiO 2 @Zr was as high as 104 m 2 /g. The hydrothermal stability of 1 wt% Pd/SiO 2 @Zr was attributed to the poor crystallinity of SiO 2 @Zr, possibly due to the formation of Si-O-Zr bonds. Lastly, this work highlights the promising potential of utilizing durable Pd/SiO 2 @Zr catalysts for diesel oxidation applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Phase transformations and thermal expansion coefficients of unirradiated U-X wt.% Zr (X = 6, 10, 20, 30) measured via neutron diffraction

This work characterizes the crystallographic evolution of unirradiated U-X wt.% Zr (X = 6, 10, 20, 30) while cooling from equilibration, single phase γ-U-Zr, at 900 °C to ambient temperature using time-of-flight neutron diffraction. The β-U phase was unobserved during cooling at 1 °C/min in all alloys. All alloys followed the phase transformation pathway of γ-U-Zr→γ-U-Zr+α-U→α-U +δ-UZr2 with an observed miscibility gap in γ-U-Zr. The α-U and δ-UZr2 transformation took place simultaneously in the U-30 wt.% Zr sample. These findings strengthen the need to re-approach the U-Zr phase diagram in entirety. Bulk volumetric CTEs agree well with published data, strengthening the quantification of lattice-specific CTEs reported in this study. A compositionally dependent discontinuity in thermal expansion, increasing in magnitude with decreasing U content, occurs during the γ-U-Zr→α-U+δ-UZr2 transformation. The γ-U-Zr lattice parameter was measured to have a compositional dependency.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effective Landau-type model of a Hf x Zr 1 - x O 2 -graphene nanostructure

Here, to describe the charge-polarization coupling in the nanostructure formed by a thin Hf x Zr 1-x O 2 film with a single-layer graphene as a top electrode, we develop the “effective” Landau-Ginzburg-Devonshire model. This approach is based on the parametrization of the Landau expansion coefficients for the polar (FE) and antipolar (AFE) orderings in thin Hf 1-x Zr x O 2 films from a limited number of polarization-field curves and hysteresis loops. The Landau expansion coefficients are nonlinearly dependent on the film thickness h and Zr/[Hf+Zr] ratio x, in contrast to h-independent and linearly x-dependent expansion coefficients of a classical Landau energy. We explain the dependence of the Landau expansion coefficients by the strong nonmonotonic dependence of the Hf 1-x Zr x O 2 film polar properties on the film thickness, grain size and surface energy. The proposed Landau free energy with five “effective” expansion coefficients, which are interpolation functions of x and h, describes the continuous transformation of polarization dependences on applied electric field and hysteresis loop shapes induced by the changes of x and h in the range 0 < x < 1 and 5 nm < h < 35 nm. Using the effective free energy, we demonstrated that the polarization of Hf 1-x Zr x O 2 film influences strongly on the graphene conductivity, and the full correlation between the distribution of polarization and charge carriers in graphene is revealed. In accordance with our modeling, the polarization of the (5 – 25) nm thick Hf 1-x Zr x O 2 films, which are in the ferroelectric-like or antiferroelectric-like states for the chemical compositions 0.35 ≤ x ≤ 0.95, determine the concentration of carriers in graphene and can control its field dependence. The result can be promising for creation of next generation Si-compatible nonvolatile memories and graphene-ferroelectric FETs, because the working voltages applied to the Hf 1-x Zr x O 2 film (which acts as a gate) can be relatively low (less than 2 V). These low voltages are sufficient to induce the pronounced hysteresis of ferroelectric polarization in the Hf 1-x Zr x O 2 gate, which, due to the strong electric coupling, induces the hysteresis of the graphene charge.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Pathway to tune sputter coated Nb$_3$Sn with Zr

Superconducting radio frequency (SRF) cavities are essential elements of many modern-day particle accelerators such as, European XFEL (DESY), LCLS II-HE (SLAC) and PIP II (Fermilab). Nb$_3$Sn superconducting material promises significant potential to exceed the performance of conventional niobium based SRF cavities. We aim to advance the ongoing R$&$D efforts to achieve Nb$_3$Sn coated cavities with high material quality. In this work, we have developed to achieve a route for effectively reducing the intrinsic defects in magnetron sputter coated Nb$_3$Sn SRF cavities and eventually improve the overall RF performance. We have observed that Zr is mainly being incorporated as ZrO$_2$ precipitates of average dimensions ranging from 20-100nm. By increasing the concentration of Zr, we have three major effects in the physical properties. Firstly, we noted that the density of the surface and bulk voids as well as their average dimensions are dramatically reduced on increasing the Zr content in Nb$_3$Sn. These surface voids are believed to be detrimental to cavity applications due to increase the local dissipation of electric and magnetic fields. These results indicate that inclusion of Zr in Nb$_3$Sn sputtered coating will improve the material quality and might help to reduce the overall RF power dissipation. Secondly, we observed that increasing Zr concentration from 0 to 2.4% substantially improves both superconducting transition temperature (Tc) and upper critical magnetic field (Hc2). However, on further increasing the Zr concentration to 24%, we noticed a small decrement in the Hc2 value. These results infer that the increase in Zr concentration up to an optimal concentration will be beneficial to enhance the superconducting properties. Increase in Tc promises lesser RF losses and improvement in accelerating gradient, whereas the increase in Hc2 suggests more efficient flux pinning which could give rise to high quality factors in presence of multi-Tesla magnetic field. Additionally, we also observed that increasing Zr concentration possibly prevents the oxygen diffusion and leads to thinner formation of primary surface oxide (Nb$_2$O$_5$ and SnO). This study gives a route to tune Zr fraction in Nb3Sn to modify the physical properties that control the high field performance of Nb3Sn RF cavities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

The Electron Thermal Conductivity of Pu and Zr Substituted Gamma-Uranium

Uranium alloys are attractive recycled nuclear fuels because of their high thermal conductivity (k) and fissile density; however, the effects of alloying elements on k remain unclear. Here, the electron thermal conductivity (k_e) of U-Pu-Zr compositions are calculated using density functional theory. The electronic structure is evaluated to understand the effects of plutonium (Pu) and zirconium (Zr) substitution on the k_e of ?-U. Alloys of up to 37.5 at. % Pu and 37.5 at. % Zr are examined. Two methods are applied to calculate k_e; we find that the accuracy of each method depends on the electronic and mass similarities between the solute and solvent atoms. Specifically, when the solute atom is similar in electronic structure and mass, the method that applies the electron relaxation time of ?-U is best, while if the elements are dissimilar, a mixed method that mixes several parameters associated with k_e from each element in the alloy is best. The introduction of all alloying elements decreases k_e; however, in binary compounds, Pu and Zr have different effects. Pu generally flattens the electronic bands but compensates for this deleterious effect by increasing electron density near the Fermi level. Zr flattens the electronic bands more severely without adding electron density near the Fermi level. Therefore, Zr decreases the k_e more than Pu in binary compounds. In ternary compounds, the difference between Pu and Zr is minimal due to the phononic change from the large mass change of Zr substitution, even at 12.5 at. %. Thus, we predict that higher loadings of Pu, and potentially other actinides, can be added to U-Pu-Zr compositions for faster recycling of spent fuel with without sacrificing k. We also note that these k_e calculation methods can be applied to non-fuel alloys that require k_e predictions, such as cladding, heat exchanger, and structural materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(TiGa2)2 by Materials Project

Zr(TiGa2)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Zr is bonded in a distorted square co-planar geometry to twelve Ga atoms. There are four shorter (2.82 Å) and eight longer (3.29 Å) Zr–Ga bond lengths. Ti is bonded in a 10-coordinate geometry to two equivalent Ti and eight Ga atoms. Both Ti–Ti bond lengths are 2.73 Å. All Ti–Ga bond lengths are 2.74 Å. There are five inequivalent Ga sites. In the first Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Zr, four equivalent Ti, and four Ga atoms. There are two shorter (2.58 Å) and two longer (2.91 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Zr, four equivalent Ti, and four Ga atoms. Both Ga–Ga bond lengths are 2.58 Å. In the third Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Zr, four equivalent Ti, and four Ga atoms. There are two shorter (2.58 Å) and two longer (2.91 Å) Ga–Ga bond lengths. In the fourth Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Zr, four equivalent Ti, and four Ga atoms. The Ga–Ga bond length is 2.58 Å. In the fifth Ga site, Ga is bonded in a 11-coordinate geometry to three equivalent Zr, four equivalent Ti, and four Ga atoms. There are one shorter (2.58 Å) and two longer (2.91 Å) Ga–Ga bond lengths.

36 MATERIALS SCIENCE↗