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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Dipolar Spin Ice Regime Proximate to an All-In-All-Out Néel Ground State in the Dipolar-Octupolar Pyrochlore Ce 2 Sn 2 O 7

The dipolar-octupolar (DO) pyrochlores, R 2 M 2 O 7 ( R = Ce , Sm , Nd ), are key players in the search for realizable novel quantum spin liquid (QSL) states as a large parameter space within the DO pyrochlore phase diagram is theorized to host QSL states of both dipolar and octupolar nature. New single crystals and powders of Ce 2 Sn 2 O 7 , synthesized by hydrothermal techniques, present an opportunity for a new characterization of the exchange parameters in Ce 2 Sn 2 O 7 using the near-neighbor X Y Z model Hamiltonian associated with DO pyrochlores. Utilizing quantum numerical linked cluster expansion fits to heat capacity and magnetic susceptibility measurements, and classical Monte Carlo calculations to the diffuse neutron diffraction of the new hydrothermally grown Ce 2 Sn 2 O 7 samples, we place Ce 2 Sn 2 O 7 ’s ground state within the ordered dipolar all-in-all-out (AIAO) Néel phase, with quantum Monte Carlo calculations showing a transition to long-range order at temperatures below those accessed experimentally. Indeed, our new neutron diffraction measurements on the hydrothermally grown Ce 2 Sn 2 O 7 powders show a broad signal at low scattering wave vectors, reminiscent of a spin ice, in striking contrast from previous powder neutron diffraction on samples grown from solid-state synthesis, which found diffuse scattering at high scattering wave vectors associated with magnetic and suggested an octupolar quantum spin ice state. We conclude that new hydrothermally grown Ce 2 Sn 2 O 7 samples host a finite-temperature proximate dipolar spin ice phase, above the expected transition to AIAO Néel order. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

R-matrix Resolved Resonance Region Evaluation of 140,142 Ce

Oak Ridge National Laboratory completed the resolved resonance region (RRR) evaluation of the two most abundant cerium isotopes, 140 Ce (88.45%) and 142 Ce (11.11%), as requested by the US Nuclear Criticality Safety Program. These evaluations are based on recent high-resolution transmission and capture measurements performed on nat Ce and highly enriched 142 Ce samples at the JRC-Geel Linear Accelerator facility, as well as measured thermal constants available from the EXFOR database. Starting from the resonance parameters of the ENDF/B-VIII.0 library followed by a preliminary R-matrix analysis, an updated set of resonance parameters and corresponding covariance information were derived by fitting these measured data using the Reich–Moore approximation of the R -matrix theory, as implemented in the SAMMY code system. The 140 Ce RRR upper energy limit was kept at 200 keV, whereas the 142 Ce resonance region was extended from 13 to 26 keV. Updated statistical properties were obtained for the new evaluations and compared to those derived from the ENDF/B-VIII.0 nuclear data library. The new evaluation work improved some of the discrepancies found in previous work, such as the capture resonance integral and stellar Maxwellian-averaged cross sections. These integral quantities were mainly derived from the fit of the latest measured data, especially the neutron capture yield data for 142 Ce isotope.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Materials Data on Ce(Al2Fe)4 by Materials Project

CeFe4Al8 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to eight equivalent Fe and twelve Al atoms. All Ce–Fe bond lengths are 3.34 Å. There are four shorter (3.00 Å) and eight longer (3.17 Å) Ce–Al bond lengths. Fe is bonded to two equivalent Ce, two equivalent Fe, and eight Al atoms to form a mixture of distorted edge, face, and corner-sharing FeCe2Al8Fe2 cuboctahedra. Both Fe–Fe bond lengths are 2.51 Å. There are four shorter (2.54 Å) and four longer (2.65 Å) Fe–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Ce, four equivalent Fe, and five Al atoms. There are a spread of Al–Al bond distances ranging from 2.73–2.80 Å. In the second Al site, Al is bonded in a 12-coordinate geometry to two equivalent Ce, four equivalent Fe, and six Al atoms. Both Al–Al bond lengths are 2.75 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(MnAl2)4 by Materials Project

CeMn4Al8 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to eight equivalent Mn and twelve Al atoms. All Ce–Mn bond lengths are 3.38 Å. There are four shorter (3.01 Å) and eight longer (3.27 Å) Ce–Al bond lengths. Mn is bonded to two equivalent Ce, two equivalent Mn, and eight Al atoms to form distorted MnCe2Mn2Al8 cuboctahedra that share corners with eight equivalent AlCe2Mn4Al6 cuboctahedra, corners with ten equivalent MnCe2Mn2Al8 cuboctahedra, edges with four equivalent MnCe2Mn2Al8 cuboctahedra, edges with four equivalent AlCe2Mn4Al6 cuboctahedra, faces with six equivalent MnCe2Mn2Al8 cuboctahedra, and faces with eight equivalent AlCe2Mn4Al6 cuboctahedra. Both Mn–Mn bond lengths are 2.58 Å. There are four shorter (2.57 Å) and four longer (2.68 Å) Mn–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Ce, four equivalent Mn, and five Al atoms. There are a spread of Al–Al bond distances ranging from 2.78–2.83 Å. In the second Al site, Al is bonded to two equivalent Ce, four equivalent Mn, and six Al atoms to form distorted AlCe2Mn4Al6 cuboctahedra that share corners with eight equivalent MnCe2Mn2Al8 cuboctahedra, corners with ten equivalent AlCe2Mn4Al6 cuboctahedra, edges with three equivalent AlCe2Mn4Al6 cuboctahedra, edges with four equivalent MnCe2Mn2Al8 cuboctahedra, faces with seven equivalent AlCe2Mn4Al6 cuboctahedra, and faces with eight equivalent MnCe2Mn2Al8 cuboctahedra. Both Al–Al bond lengths are 2.82 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(Al2Cu)4 by Materials Project

Al8Cu4Ce crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to eight equivalent Cu and twelve Al atoms. All Ce–Cu bond lengths are 3.39 Å. There are four shorter (3.09 Å) and eight longer (3.22 Å) Ce–Al bond lengths. Cu is bonded to two equivalent Ce, two equivalent Cu, and eight Al atoms to form a mixture of distorted face, edge, and corner-sharing CuCe2Al8Cu2 cuboctahedra. Both Cu–Cu bond lengths are 2.56 Å. There are four shorter (2.58 Å) and four longer (2.71 Å) Cu–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Ce, four equivalent Cu, and five Al atoms. There are a spread of Al–Al bond distances ranging from 2.70–2.83 Å. In the second Al site, Al is bonded in a 12-coordinate geometry to two equivalent Ce, four equivalent Cu, and six Al atoms. Both Al–Al bond lengths are 2.76 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(GePt)2 by Materials Project

Ce(PtGe)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Pt and eight equivalent Ge atoms. All Ce–Pt bond lengths are 3.33 Å. All Ce–Ge bond lengths are 3.35 Å. Pt is bonded in a 4-coordinate geometry to four equivalent Ce and four equivalent Ge atoms. All Pt–Ge bond lengths are 2.53 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Ce, four equivalent Pt, and one Ge atom. The Ge–Ge bond length is 2.49 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(Sn3Ru2)2 by Materials Project

CeRu4Sn6 crystallizes in the tetragonal I-42m space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to four equivalent Ru and twelve Sn atoms. All Ce–Ru bond lengths are 3.27 Å. There are a spread of Ce–Sn bond distances ranging from 3.38–3.78 Å. Ru is bonded in a 7-coordinate geometry to one Ce and six Sn atoms. There are a spread of Ru–Sn bond distances ranging from 2.61–2.78 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded in a 6-coordinate geometry to two equivalent Ce and four equivalent Ru atoms. In the second Sn site, Sn is bonded in a 5-coordinate geometry to two equivalent Ce and four equivalent Ru atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(Ni2Sn)2 by Materials Project

Ce(Ni2Sn)2 crystallizes in the tetragonal I-4c2 space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Ni and eight equivalent Sn atoms. There are four shorter (2.75 Å) and four longer (2.88 Å) Ce–Ni bond lengths. All Ce–Sn bond lengths are 3.28 Å. Ni is bonded in a 10-coordinate geometry to two equivalent Ce, four equivalent Ni, and four equivalent Sn atoms. There are two shorter (2.38 Å) and two longer (2.52 Å) Ni–Ni bond lengths. There are a spread of Ni–Sn bond distances ranging from 2.39–2.53 Å. Sn is bonded in a 12-coordinate geometry to four equivalent Ce and eight equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(Ni2Sn)2 by Materials Project

Ce(Ni2Sn)2 crystallizes in the tetragonal I-4c2 space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Ni and eight equivalent Sn atoms. There are four shorter (3.00 Å) and four longer (3.04 Å) Ce–Ni bond lengths. All Ce–Sn bond lengths are 3.50 Å. Ni is bonded in a 10-coordinate geometry to two equivalent Ce, four equivalent Ni, and four equivalent Sn atoms. There are a spread of Ni–Ni bond distances ranging from 2.53–2.73 Å. There are a spread of Ni–Sn bond distances ranging from 2.54–2.68 Å. Sn is bonded in a 12-coordinate geometry to four equivalent Ce and eight equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(AsPd)2 by Materials Project

Ce(PdAs)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Pd and eight equivalent As atoms. All Ce–Pd bond lengths are 3.43 Å. All Ce–As bond lengths are 3.24 Å. Pd is bonded to four equivalent Ce, four equivalent Pd, and four equivalent As atoms to form a mixture of distorted corner, edge, and face-sharing PdCe4As4Pd4 cuboctahedra. All Pd–Pd bond lengths are 2.99 Å. All Pd–As bond lengths are 2.56 Å. As is bonded in a 9-coordinate geometry to four equivalent Ce, four equivalent Pd, and one As atom. The As–As bond length is 2.53 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(PRu)2 by Materials Project

Ce(RuP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Ru and eight equivalent P atoms. All Ce–Ru bond lengths are 3.18 Å. All Ce–P bond lengths are 3.14 Å. Ru is bonded in a 12-coordinate geometry to four equivalent Ce and four equivalent P atoms. All Ru–P bond lengths are 2.37 Å. P is bonded in a 9-coordinate geometry to four equivalent Ce, four equivalent Ru, and one P atom. The P–P bond length is 2.48 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(ClO4)3 by Materials Project

Ce(ClO4)3 crystallizes in the trigonal R3c space group. The structure is three-dimensional. Ce is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of Ce–O bond distances ranging from 2.48–2.58 Å. There are four inequivalent O sites. In the first O site, O is bonded in a water-like geometry to one Ce and one Cl atom. The O–Cl bond length is 1.48 Å. In the second O site, O is bonded in a bent 150 degrees geometry to one Ce and one Cl atom. The O–Cl bond length is 1.47 Å. In the third O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. In the fourth O site, O is bonded in a water-like geometry to one Ce and one Cl atom. The O–Cl bond length is 1.48 Å. Cl is bonded in a tetrahedral geometry to four O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(Sn2Pd)2 by Materials Project

CePd2Sn4 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to four equivalent Pd and ten Sn atoms. All Ce–Pd bond lengths are 3.53 Å. There are a spread of Ce–Sn bond distances ranging from 3.40–3.55 Å. Pd is bonded in a 6-coordinate geometry to two equivalent Ce and six Sn atoms. There are a spread of Pd–Sn bond distances ranging from 2.74–2.82 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded in a 8-coordinate geometry to four equivalent Ce, two equivalent Pd, and two Sn atoms. There are one shorter (2.87 Å) and one longer (3.03 Å) Sn–Sn bond lengths. In the second Sn site, Sn is bonded in a 6-coordinate geometry to one Ce, four equivalent Pd, and one Sn atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(BRh)4 by Materials Project

Ce(RhB)4 crystallizes in the tetragonal P4_2/nmc space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to twelve equivalent Rh and twelve equivalent B atoms. There are four shorter (2.99 Å) and eight longer (3.18 Å) Ce–Rh bond lengths. There are eight shorter (3.04 Å) and four longer (3.17 Å) Ce–B bond lengths. Rh is bonded in a 5-coordinate geometry to three equivalent Ce and five equivalent B atoms. There are a spread of Rh–B bond distances ranging from 2.22–2.27 Å. B is bonded in a 6-coordinate geometry to three equivalent Ce, five equivalent Rh, and one B atom. The B–B bond length is 1.79 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(Sn2Rh)2 by Materials Project

Ce(RhSn2)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ce is bonded in a 6-coordinate geometry to seven Sn atoms. There are a spread of Ce–Sn bond distances ranging from 3.18–3.37 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 7-coordinate geometry to seven Sn atoms. There are a spread of Rh–Sn bond distances ranging from 2.71–2.89 Å. In the second Rh site, Rh is bonded in a 7-coordinate geometry to seven Sn atoms. There are a spread of Rh–Sn bond distances ranging from 2.70–2.83 Å. There are four inequivalent Sn sites. In the first Sn site, Sn is bonded in a 6-coordinate geometry to two equivalent Ce and four Rh atoms. In the second Sn site, Sn is bonded in a 5-coordinate geometry to two equivalent Ce and three equivalent Rh atoms. In the third Sn site, Sn is bonded in a 3-coordinate geometry to three equivalent Ce and three equivalent Rh atoms. In the fourth Sn site, Sn is bonded to four Rh atoms to form a mixture of distorted edge and corner-sharing SnRh4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(Ge2Rh3)2 by Materials Project

Ce(Rh3Ge2)2 crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Ce is bonded to six equivalent Rh and six equivalent Ge atoms to form face-sharing CeGe6Rh6 cuboctahedra. All Ce–Rh bond lengths are 3.16 Å. All Ce–Ge bond lengths are 3.15 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 5-coordinate geometry to five Ge atoms. There are one shorter (2.50 Å) and four longer (2.57 Å) Rh–Ge bond lengths. In the second Rh site, Rh is bonded in a 6-coordinate geometry to two equivalent Ce and four Ge atoms. There are two shorter (2.49 Å) and two longer (2.57 Å) Rh–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 9-coordinate geometry to nine Rh atoms. In the second Ge site, Ge is bonded in a 8-coordinate geometry to two equivalent Ce and six Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(SiIr)2 by Materials Project

CeIr2Si2 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight Ir and eight equivalent Si atoms. There are four shorter (3.24 Å) and four longer (3.26 Å) Ce–Ir bond lengths. There are four shorter (3.27 Å) and four longer (3.31 Å) Ce–Si bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a 9-coordinate geometry to four equivalent Ce, one Ir, and four equivalent Si atoms. The Ir–Ir bond length is 2.65 Å. All Ir–Si bond lengths are 2.42 Å. In the second Ir site, Ir is bonded in a 9-coordinate geometry to four equivalent Ce, one Ir, and four equivalent Si atoms. All Ir–Si bond lengths are 2.42 Å. Si is bonded in a 4-coordinate geometry to four equivalent Ce and four Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Characterization of EJ-270 and Ce-doped LiCAF scintillators for the development of high-rate neutron reflectometer detectors

The Second Target Station of the Spallation Neutron Source at Oak Ridge National Laboratory is anticipated to provide a neutron source with ∼20 times increase in peak brightness than the First Target Station. The neutron reflectometers currently in operation at the First Target Station need to be upgraded due to the increased neutron flux. A prototype neutron detector module based upon a pixelated scintillator array readout by silicon photomultipliers is being developed to address the high-rate challenge faced with future neutron reflectometer instruments at the Second Target Station. Two types of scintillator materials were considered for this detector development, i.e., 6 Li-loaded EJ-270 plastic scintillator and Ce-doped LiCAF single crystal. This paper reports the scintillator characterization results, including light yield, pulse shape discrimination performance, capability to detect thermal neutrons in a high γ-ray field, and γ-ray sensitivity. The number of photons produced per neutron capture by EJ-270 and LiCAF:Ce was measured to be 2176 ± 91 and 2651 ± 108, respectively. EJ-270 demonstrated a good capability to discriminate between neutrons and γ-rays by employing the commonly used charge comparison method (figure-of-merit: 1.13 ± 0.01 for an energy cut of 292–426 keVee) and a reasonable performance when using the time-over-threshold techniques; however, no discrimination was observed from LiCAF:Ce regardless of the pulse shape discrimination approaches utilized, making pulse height discrimination necessary for LiCAF:Ce to differentiate between neutrons and γ-rays. Both EJ-270 and LiCAF:Ce exhibited an acceptable capacity to detect thermal neutrons at high exposure rates up to approximately 584 mR/h. Furthermore, the γ-ray sensitivities measured with a 60 Co source at an exposure rate of around 1145 mR/h were determined to be (6.11 ± 0.87) × 10 −6 and (7.64 ± 1.08) × 10 −7 for EJ-270 and LiCAF:Ce, respectively.

EJ-270↗