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DOE OSTI2021

Origin of Insulating Ferromagnetism in Iron Oxychalcogenide Ce 2 O 2 FeSe 2

An insulating ferromagnetic (FM) phase exists in the quasi-one-dimensional iron oxychalcogenide Ce 2 O 2 FeSe 2 , but its origin is unknown. To understand the FM mechanism, here a systematic investigation of this material is provided, analyzing the competition between ferromagnetic and antiferromagnetic tendencies and the interplay of hoppings, Coulomb interactions, Hund’s coupling, and crystal-field splittings. Overall, our intuitive analysis based on second-order perturbation theory shows that large entanglements between doubly occupied and half filled orbitals play a key role in stabilizing the FM order in Ce 2 O 2 FeSe 2 . In addition, via many-body computational techniques applied to a multiorbital Hubbard model, the phase diagram confirms the proposed FM mechanism.

1-dimensional spin chains↗

DOE OSTI2022

Physical properties of the layered $\mathcal{f}$-electron van der Waals magnet Ce 2 Te 5

Here. we report a detailed study of the magnetic, transport, and thermodynamic properties of Ce 2 Te 5 single crystals, a layered $\mathcal{f}$-electron van der Waals magnet. Four consecutive transitions at ~5.2, 2.1, 0.9, and 0.4 K were observed in the ac-plane electrical resistivity $\rho(T)$, which were further confirmed in specific heat $C_\text{p}(T)$ measurements. Analysis of the magnetic susceptibility $\chi(T)$, the magnetic-field variation of $\rho(T)$, and the increase of the first transition temperature ($T_c$ ~ 5.2 K) with applied magnetic field indicates ferromagnetic order, while the decrease of the other transitions with field suggests different states with dominant antiferromagnetic interactions below $T_2$ ~ 2.1 K, $T_3$ ~ 0.9 K, and $T_4$ = 0.4 K. Critical behavior analysis around Tc that gives critical exponents $\beta$ = 0.31(2), $\gamma$ = 0.99(2), $\delta$ = 4.46(1), and $T_c$ = 5.32(1) K indicates that Ce 2 Te 5 shows a three-dimensional magnetic critical behavior. Moreover, the Hall resistivity ρxy indicates that Ce2Te5 is a multiband system with a relatively high electron mobility ~2900 cm 2 V –1 s –1 near $T_c$, providing further opportunities for future device applications.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Beta Radiation Hardness of GYGAG(Ce) Transparent Ceramic Scintillators

GYGAG(Ce) transparent ceramic garnet scintillators were irradiated with electrons from 0.5 to 2 MeV with fluences from 10 16 e – /cm 2 to 10 19 e – /cm 2 , corresponding to doses from 0.3 to 310 Gigarad. Absorption spectra were measured before and after irradiations. Light yields from alpha, beta, and gamma excitations were measured before and after irradiation and compared to preirradiation values to gain a deeper understanding of how electron irradiations can affect light yield, as well as defects generated in both the surface and bulk. Within experimental error, no degradation in light yield was observed for the electron-irradiated samples, as measured via beta or gamma excitation, with minimal degradation observed via alpha excitation. A small increase in optical absorption near the wavelength of emission was observed following the largest dose irradiation. These results suggest that GYGAG(Ce) is radiation hard to electron irradiation up to 10 19 e – /cm 2 and doses up to 310 Gigarad. Furthermore, this robustness to irradiation indicates that transparent ceramic garnets may prove useful for applications such as scintillation-based nuclear batteries by allowing for higher energy beta emitters, increased power densities, and enabling long service lifetimes.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Formation of hydrided Pt-Ce-H sites in efficient, selective oxidation catalysts

Single-atom site catalysts can improve the rates and selectivity of many catalytic reactions. For this work, we have modified Pt 1 /CeO 2 single sites by combining them with molecular groups and with oxygen vacancies of the support. The new sites include hydrided (Pt 2+ -Ce 3+ Hδ) and hydroxylated (Pt 2+ -Ce 3+ OH) sites that exhibit higher reactivity and selectivity to previous single sites for several reactions, including a ninefold increase in the reaction rate for carbon monoxide (CO) oxidation, and a 2.3-fold improvement of propylene selectivity for oxidative dehydrogenation of propane. The atomic structure and reaction steps of these sites were determined with in situ and ex situ spectroscopy techniques and theoretical methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Transport of 12 GeV positron beams at Ce+BAF

Jefferson Lab (JLab) is developing a concept to upgrade the Continuous Electron Beam Accelerator Facility (CEBAF) to additionally deliver spin-polarized continuous-wave positron beams for its nuclear physics program users (Ce+BAF 12 GeV). The concept involves repurposing the Low Energy Recirculator Facility (LERF) at JLab as a dual injector, first producing 100-300 MeV spin-polarized electron beams which are subsequently used for the generation and formation of 123 MeV continuous-wave positron beams. The positron beams are transported to CEBAF and injected for acceleration up to 12 GeV, tailored to the requirements of its four experimental halls. Given the higher emittance of the secondary positron beams, the CEBAF optics are optimized for low dispersion and low beta functions to enhance transmission within the Ce+BAF acceptance limits and with an R56 to manage the positron beams bunch length and energy spread. Potential bottlenecks are being investigated through both optical modeling and measurements using an electron beam, as well as degraded electron beams, to map the 6d acceptance of CEBAF as it is today. This presentation shares preliminary results from multi-particle tracking simulations of the positron beam up to 12 GeV, including spatial, momentum, and spin characteristics, and explores the feasibility of delivering beams simultaneously to multiple experimental halls via extraction optics.

Accelerator Physics↗

DOE OSTI2025

Polarized positrons at Ce$^+$BAF

A baseline concept for a continuous wave (CW) polarized positron injector was developed for the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab [1]. This concept is based on positron beam generation by a high current polarized electron beam (1 mA, 120 MeV, >85% polarization) irradiating a 4 mm thick rotating water-cooled tungsten target or liquid metal target. The update on the development of the Ce+BAF injector concept including the polarized electron source, the development of high power targets, simulations of positron capture, the design of the transport line from the positron injector to the CEBAF North Linac and the planned experiment to measure the upper limits of transverse and longitudinal emittances accepted by the 12 GeV CEBAF optics are presented. [1] J. Grames et al., "Positron beams at Ce+BAF", in Proc. 14th Int. Particle Accelerator Conf. (IPAC’23), Venice, Italy, MOPL152, pp. 896–899 (2023). doi:10.18429/JACoW-IPAC2023-MOPL152

Ushakov, Andriy↗

DOE OSTI2024

Rare Earth Carbide (Nd-C and Ce-C) Synthesis and Characterization to Inform Phase Equilibrium in Advanced Nuclear Fuels

As advances are being made regarding the performance of nuclear fuels, uranium carbides, and composites, such as (U,Zr)C and UO2 + UCx, have recently gained significant interest for deployment in nuclear space propulsion and high temperature gas-cooled reactors, respectively. However, the phase equilibria of several fission products in carbide systems remain unknown and may impact the overall fuel performance, specifically for particle nuclear fuels that are designed for commercial nuclear energy. Furthermore, comprehensive thermodynamic data on Rare Earth (RE) carbides, such as the Nd-C and Ce-C binary systems, remain limited. Presented in this study are the synthesis methods and characterizations of several Nd-C and Ce-C compositions. The findings from this research provide insights on the stability of RE-C binaries that form in irradiated nuclear fuels and address a critical knowledge gap in the current state of thermodynamics for two key RE-C systems.

Cavazos, Steven J. (ORCID:0009000130329363)↗

NASA NTRS1993

Photometric investigation of a very short period W UMa-type binary - Does CE Leonis have a large superluminous area?

A complete photometric analysis of BVRI Johnson-Cousins photometry of the high northern latitude galactic variable, CE Leo is presented. These observations were taken at Kitt Peak National Observatory on May 31, 1989-June 7, 1989. Three new precise epochs of minimum light were determined and a linear and a quadratic ephemeris were computed from these and previous data covering 28 years of observation. The light curves reveal that the system undergoes a brief 20 min totality in the primary eclipse, indicating that CE Leo is a W UMa W-type binary. A systemic velocity of about -40 km/s was determined. Standard magnitudes were found and a simultaneous solution of the B, V, R, I light curves was computed using the new Wilson-Devinney synthetic light curve code which has the capability of automatically adjusting star spots. The solution indicates that the system consists of two early K-type dwarfs in marginal contact with a fill-out factor less than 3 percent. Evidence for the presence of a large (45 deg radius) superluminous area on the cooler component is given.

Samec, Ronald G.↗

NASA NTRS1995

Laser-Induced Photochromic Centers in Ce(3+):La2Be2O5

Intense 355-nm excitation of the lowest 4f to 5d transition of Ce(3+):La2Be2O5 leads to a brownish coloration of the crystal due to the formation of stable photochromic centers. These centers are characterized by a broadband absorption spectrum that spans the 220-840 nm spectral range. Since they can be readily bleached by optical excitation into their absorption band, the centers are photochromic. They are produced by a two-step photoionization of Ce(3+) ions followed by attachment of the detached electrons at trapping sites in the crystal. The dependence of the number of centers on laser intensity and length of exposure have been measured, and the kinetics of growth have been studied.

Cheung, Y. M.↗

NASA NTRS2020

The European Russia Drought Atlas (1400-2016 CE)

We present the European Russia Drought Atlas (ERDA) that covers the East European Plain to the Ural Mountains from 1400–2016 CE. Like the Old World Drought Atlas (OWDA) for the Euro-Mediterranean region, the ERDA is a one-half degree gridded reconstruction of summer Palmer Drought Severity Indices estimated from a network of annual tree-ring chronologies. Ensemble point-by-point regression is used to generate the ERDA with the identical protocols used for developing the OWDA. Split calibration/validation tests of the ERDA indicate that it has significant skill over most of its domain and is much more skillful than the OWDA where they overlap in the western part of ERDA domain. Comparisons to historical droughts over European Russia additionally support the ERDA’s overall validity. The ERDA has been spatially smoothed and infilled using a local regression method to yield a spatially complete drought atlas back to 1400 CE. EOF analysis indicates that there are three principal modes of hydroclimatic variability in the ERDA. After Varimax rotation, these modes correlate significantly with independent climate data sets extending back to the late nineteenth century in a physically interpretable way and relate to atmospheric circulation dynamics of droughts and heatwaves over European Russia based on more recent instrumental data.

Cook, Edward R.↗

NASA NTRS2022

2020 I.F._Wickizer_New CE Tool for MDC_Final Report

Our team surveyed available products and found no readily-available/U.S. commercial or Agency products which supported our envisioned workflow for the Mission Design Center and the concurrent engineering (CE) process we use. Therefore, we sought to create our own CE tool. Changes in agency policy during the performance period allowed us to shift direction and instead adapt our previous legacy tool (Atlas) to include the collaboration features we sorely needed. Atlas relied upon databases for its back-end data management. Poseidon, the work proposed under this effort, was also intended to leverage from that previous back end (in part). However, in May 2021, EUSO announced that “SBU/CUI Information Can Now Be Shared/Stored Within O365 Without Encryption.” Consequently, we made the decision to use O365 in place of our back end. This change provides for version history, collaborative simultaneous editing, and other collaboration tools agency-wide that were previously unavailable with the old database architecture. The new Atlas O365 has more flexibility and capability for users. It’s now easier for users to switch between using the tool for concurrent engineering and individual subsystem engineering. A version was delivered for concurrent engineering of small satellite missions; so far, it has been used successfully on the Aeolus MDC study. Atlas O365 will facilitate the design and assessment of Small Satellite Missions at low Concept Maturity Level at Ames. Feasibility assessments on mission concepts still at a low CML permit strategic planning and decision-making efforts at the center level about which concepts should be pursued and proposed.

concurrent engineering↗

DOE OSTI2020

Materials Data on Ce(P3Ru)4 by Materials Project

CeRu4P12 crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Ce3+ is bonded to twelve equivalent P1- atoms to form CeP12 cuboctahedra that share faces with eight equivalent RuP6 octahedra. All Ce–P bond lengths are 3.11 Å. Ru+2.25+ is bonded to six equivalent P1- atoms to form RuP6 octahedra that share corners with six equivalent RuP6 octahedra and faces with two equivalent CeP12 cuboctahedra. The corner-sharing octahedral tilt angles are 62°. All Ru–P bond lengths are 2.36 Å. P1- is bonded in a 5-coordinate geometry to one Ce3+, two equivalent Ru+2.25+, and two equivalent P1- atoms. There are one shorter (2.32 Å) and one longer (2.33 Å) P–P bond lengths.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ce(FeP3)4 by Materials Project

CeFe4P12 crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Ce3+ is bonded to twelve equivalent P1- atoms to form CeP12 cuboctahedra that share faces with eight equivalent FeP6 octahedra. All Ce–P bond lengths are 2.98 Å. Fe+2.25+ is bonded to six equivalent P1- atoms to form FeP6 octahedra that share corners with six equivalent FeP6 octahedra and faces with two equivalent CeP12 cuboctahedra. The corner-sharing octahedral tilt angles are 59°. All Fe–P bond lengths are 2.24 Å. P1- is bonded in a 2-coordinate geometry to one Ce3+, two equivalent Fe+2.25+, and two equivalent P1- atoms. There are one shorter (2.32 Å) and one longer (2.36 Å) P–P bond lengths.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ce(MgSi)2 by Materials Project

CeMg2Si2 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Mg2+ is bonded in a square co-planar geometry to four equivalent Si4- atoms. All Mg–Si bond lengths are 2.75 Å. Ce4+ is bonded to eight equivalent Si4- atoms to form a mixture of edge and face-sharing CeSi8 hexagonal bipyramids. All Ce–Si bond lengths are 3.19 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Mg2+, four equivalent Ce4+, and one Si4- atom. The Si–Si bond length is 2.29 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ce(BO2)3 by Materials Project

CeB3O6 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ce3+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Ce–O bond distances ranging from 2.40–2.86 Å. There are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.46 Å) and two longer (1.50 Å) B–O bond length. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.34–1.42 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Ce3+ and two B3+ atoms. In the second O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Ce3+ and one B3+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Ce3+ and two B3+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ce(NiAs)2 by Materials Project

CeNi2As2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce3+ is bonded in a distorted body-centered cubic geometry to eight equivalent As3- atoms. All Ce–As bond lengths are 3.19 Å. Ni+1.50+ is bonded to four equivalent As3- atoms to form a mixture of corner and edge-sharing NiAs4 tetrahedra. All Ni–As bond lengths are 2.37 Å. As3- is bonded in a 9-coordinate geometry to four equivalent Ce3+, four equivalent Ni+1.50+, and one As3- atom. The As–As bond length is 2.64 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ce(SiPt)2 by Materials Project

CePt2Si2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Ce4+ is bonded in a 8-coordinate geometry to eight Pt2- atoms. There are four shorter (3.26 Å) and four longer (3.28 Å) Ce–Pt bond lengths. There are two inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded in a 4-coordinate geometry to four equivalent Ce4+ and four equivalent Si atoms. All Pt–Si bond lengths are 2.50 Å. In the second Pt2- site, Pt2- is bonded in a 5-coordinate geometry to four equivalent Ce4+ and five Si atoms. There are one shorter (2.42 Å) and four longer (2.44 Å) Pt–Si bond lengths. There are two inequivalent Si sites. In the first Si site, Si is bonded to four equivalent Pt2- atoms to form a mixture of edge and corner-sharing SiPt4 tetrahedra. In the second Si site, Si is bonded in a 5-coordinate geometry to five Pt2- atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ce(MnSi)2 by Materials Project

CeMn2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce4+ is bonded in a body-centered cubic geometry to eight equivalent Si4- atoms. All Ce–Si bond lengths are 3.06 Å. Mn2+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing MnSi4 tetrahedra. All Mn–Si bond lengths are 2.38 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Ce4+, four equivalent Mn2+, and one Si4- atom. The Si–Si bond length is 2.53 Å.

36 MATERIALS SCIENCE↗