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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Mapping the structural, magnetic and electronic behavior of (Eu 1-x Ca x ) 2 Ir 2 O 7 across a metal-insulator transition

In this study, we employ bulk electronic properties characterization and x-ray scattering/spectroscopy techniques to map the structural, magnetic and electronic properties of (Eu 1-x Ca x ) 2 Ir 2 O 7 as a function of Ca-doping. As expected, the metal-insulator transition temperature, T-MIT, decreases with Ca-doping until a metallic state is realized down to 2 K. In contrast, T-AFM becomes decoupled from the MIT and (likely short-range) AFM order persists into the metallic regime. This decoupling is understood as a result of the onset of an electronically phase separated state, the occurrence of which seemingly depends on both synthesis method and rare earth site magnetism. PDF analysis suggests that electronic phase separation occurs without accompanying chemical phase segregation or changes in the short-range crystallographic symmetry while synchrotron x-ray diffraction confirms that there is no change in the long-range crystallographic symmetry. X-ray absorption measurements confirm the $J_{eff}$ = 1/2 character of (Eu 1-x Ca x ) 2 Ir 2 O 7 . Surprisingly these measurements also indicate a net electron doping, rather than the expected hole doping, indicating a compensatory mechanism. Lastly, XMCD measurements show a weak Ir magnetic polarization that is largely unaffected by Ca-doping. Keywords: term, term, term.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Phonon excitations in Eu 2 Ir 2 O 7 probed by inelastic x-ray scattering

The study of phonon dynamics and its interplay with magnetic ordering is crucial for understanding the unique quantum phases in the pyrochlore iridates. Here, through inelastic x-ray scattering on a single crystal sample of the pyrochlore iridate Eu 2 Ir 2 O 7 , we map out the phonon excitation spectra in Eu 2 Ir 2 O 7 and compare them with the theoretical phonon spectra calculated using the density functional theory. Further, possible phonon renormalization across the magnetic long-range order transition is observed in our experiments, which is consistent with the results of the previous Raman scattering experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Free-energy analysis of the nonhysteretic first-order phase transition of Eu 2 In

Binary intermetallic Eu 2 In was recently reported to exhibit a giant anhysteretic magnetocaloric effect due to a first-order magnetic phase transition between paramagnetic and ferromagnetic states. Experimentally, the transition occurs with a small phase volume change, ΔV/V, of approximately 0.1% around T C of ca. 55 K. We representmagnetic and computemagnetocaloric properties of a Eu 2 In compound using a microscopic description based on a model Hamiltonian that takes into account magnetic exchange and magnetoelastic interactions. In the model the thermodynamic nature of the transition is conveniently represented by a single magnetoelastic interaction parameter. We report a good agreement between the theoretical results and earlier published experimental data confirms the effectiveness of our approach.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Mapping out the emergence of topological features in the highly alloyed topological Kondo insulators Sm 1-$x$ M $x$ B 6 ( M =Eu, Ce)

SmB 6 is a strongly correlated material that has been attributed as a topological insulator and a Kondo insulator. Recent studies have found the topological surface states and low temperature insulating character to be profoundly robust against magnetic and nonmagnetic impurities. Here, we use angle resolved photoemission spectroscopy to chart the evolution of topologically linked electronic structure features versus magnetic doping and temperature in Sm 1-$x$ M $x$ B 6 ( M =Eu, Ce). Topological coherence phenomena are observed out to ~30% Eu and 50% Ce concentrations that represent extreme nominal hole and electron doping, respectively. Finally, theoretical analysis reveals that a recent redesignation of the topologically inverted band symmetries provides a natural route to reconciling the persistence of topological surface state emergence even as the insulating gap is lost through decoherence.

36 MATERIALS SCIENCE↗
DOE OSTI2021

$A$-type antiferromagnetic order and magnetic phase diagram of the trigonal Eu spin-$\frac{7}{2}$ triangular-lattice compound $\mathrm{EuSn_2As_2}$

The trigonal compound EuSn 2 As 2 was recently discovered to host Dirac surface states within the bulk band gap and orders antiferromagnetically below the N´eel temperature T N = 23.5(2) K from neutron-diffraction measurements. Here the magnetic ground state of single-crystal EuSn 2 As 2 and the evolution of its properties versus temperature T and applied magnetic field H are reported. Included are the zero-field single-crystal neutron diffraction measurements versus T, magnetization M(H, T), magnetic susceptibility χ(H, T) = M(H,T)/H, heat capacity C p (H, T), and electrical resistivity ρ(H, T) measurements. The neutron-diffraction and χ(T) measurements both indicate a collinear A-type antiferromagnetic (AFM) structure below T N , where the Eu 2+ spins S = 7/2 in a triangular ab-plane layer (hexagonal unit cell) are aligned ferromagnetically in the ab plane whereas the spins in adjacent Eu planes along the c axis are aligned antiferromagnetically. The χ(H ab , T) and χ(Hc, T) data together indicate a smooth crossover between the collinear AFM alignment and an unknown magnetic structure at H ≈ 0.12 T. Dynamic spin fluctuations up to 60 K are evident in the χ(T), Cp(T) and ρ(H, T) measurements, a temperature that is more than twice T N . The ρ(H, T) is consistent with a low-carrier-density metal with strong magnetic scattering and does not reflect a contribution of the topological state of the material as reported earlier by ARPES measurements. This observation is consistent with previous ones for other topological insulators where the chemical potential is above the Dirac point so that ARPES readily detects the surface states, whereas resistivity measurements do not. Finally, the magnetic phase diagrams for both H ∥ c and H ∥ ab in the H-T plane are constructed from the T N (H), χ(H, T), Cp(H, T), and ρ(H, T) data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Surface and electronic structure at atomic length scales of the nonsymmorphic antiferromagnet Eu 5 In 2 Sb 6

We performed scanning tunneling microscopy and spectroscopy (STM/STS) measurements to investigate the Zintl phase Eu 5 ⁢In 2 ⁢Sb 6 , a nonsymmorphic antiferromagnet. The theoretical prediction of a nontrivial Fermi surface topology stabilized by the nonsymmorphic symmetry motivated our research. On the cleaved (010) plane, we obtained striped patterns that can be correlated to the stacking of the [In 2 ⁢Sb 6 ] 10- double chains along the crystallographic c axis. The attempted cleavage along the a axis revealed a more complex pattern. We combined the STS measurement on nonreconstructed (010) and (081) surfaces with DFT calculations to further elucidate the electronic structure of Eu 5 ⁢In 2 ⁢Sb 6 . From our investigations so far, direct experimental evidence of the predicted topological surface states remains elusive.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Colossal piezoresistance in narrow-gap Eu 5 In 2 Sb 6

Piezoresistance, the change of the electrical resistance (R) of a material in response to an applied mechanical stress (σ), is the driving principle of electromechanical devices such as strain gauges, accelerometers, and cantilever force sensors. Enhanced piezoresistance has been traditionally observed in two classes of uncorrelated materials: nonmagnetic semiconductors and composite structures. In this study, we report the discovery of a remarkably large piezoresistance in Eu 5 In 2 Sb 6 single crystals, wherein anisotropic metallic clusters naturally form within a semiconducting matrix due to electronic interactions. Eu 5 In 2 Sb 6 shows a highly anisotropic piezoresistance, and uniaxial pressure along [001] of only 0.4 GPa leads to a resistivity drop of >99.95%, which results in a colossal piezoresistance factor of 5000×10 –11 Pa –1 . Our result not only reveals the role of interactions and phase separation in the realization of colossal piezoresistance, but it also highlights a route to multifunctional devices with large responses to both pressure and magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Complex magnetic properties in the mixed 4 f - 5 d double perovskite iridates X 2 ZnIrO 6 ( X = Nd , Sm , Eu , Gd )

Here in this paper, we report on the synthesis and magnetic properties of a series of double perovskites Ln 2 ZnIrO 6 with Ln = Nd, Sm, Eu, Gd. These compounds present examples of the rare case of double perovskites (general formula A 2 BB'O6) with a magnetic 4ƒ-ion on the A site in combination with the strongly spin-orbit coupled 5d transition-metal ion Ir 4+ on the B sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. Gd 2 ZnIrO 6 and Eu 2 ZnIrO 6 show ferrimagnetic or canted antiferromagnetic order below T N = 23 and 12 K, respectively. Sm 2 ZnIrO 6 orders antiferromagnetically at T N = 13 K. Nd 2 ZnIrO 6 exhibits more complex magnetic properties with a strong field dependence ranging from a two-step spin reorientation at μ 0 H = 0.01 T to an antiferromagnetic ground state at intermediate external fields to a spin-flop phase for 0H ≥ 4 T. This unique behavior suggests an interesting interplay between Nd 3+ and Ir 4+ . To further shed light on the relevant magnetic interaction, the zero-field magnetic ground state of Nd 2 ZnIrO 6 is examined via neutron powder diffraction. In general, the magnetic properties of Ln 2 ZnIrO 6 hint towards a substantial contribution of the rare-earth ions and a significant correlation between 5d and 4ƒ magnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Precise absolute 𝛾–ray intensities following the 𝛽 decay of 156 Eu

The most recent 𝛽-decay data for 156 Eu is over 40 years old, and the 𝛾-ray intensities are only known with a fractional precision of about 10% or worse. Here, in this work, we present new results for the absolute intensities of more than 60 𝛾 rays emitted following the 𝛽 decay of 156 Eu with many measured to ≲1% accuracy, representing an order-of-magnitude improvement in precision. This was achieved by leveraging the fission-product beams produced at the CARIBU facility to create radio-pure samples and detecting the radiation with a 4⁢𝜋 𝛽-particle counter coupled with a precisely efficiency-calibrated HPGe detector at Texas A and M University.

Physics - Nuclear physics and radiation physics↗
DOE OSTI2024

Migration of 60 Co, 133 Ba, 137 Cs, and 152 Eu from cementitious wasteforms in field lysimeter experiments

Safe and effective storage of radioactive waste is essential to protect environmental health. Due to the potential for accidental releases and the severity of the associated risks, it is imperative to further understand radionuclide transport should an accident occur. This work analyzed the vadose zone migration of radionuclides from cementitious wasteforms at the Savannah River Site after ten years. The observed radionuclides are prominent constituents of radioactive waste or analogs for other groups or series of radionuclides. Lysimeters were first analyzed in 2016 using a collimated high-purity germanium gamma-ray spectrometer to non-destructively measure the concentration of each radionuclide in the sediment column as a function of depth. Following these measurements, the lysimeters were redeployed in the field for another 4 years. All radionuclides in all lysimeters were observed to transport further during the redeployment period; however, the extent of migration varied with the material used for introduction. Except for 137 Cs, migration through the sediment control system increased with decreasing ionic potential (ionic charge/radius); migration order: 152 Eu< 137 Cs< 60 Co< 133 Ba. Overall, the cementitious wasteforms were observed to decrease radionuclide migration extent relative to the filter paper. In both cementitious wasteforms, the migration extent increased in the order 152 Eu< 133 Ba< 60 Co< 137 Cs. However, less migration was measured when the radionuclides were incorporated into a reducing grout wasteform. The novelty of this paper is the demonstration of a technique capable of creating non-destructive measurements over decade time scales. Ultimately, this work provides insight into the long-term migration of alkali, alkali earth, divalent transition metal, and trivalent actinide element isotopes.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Improved decay data for the long-lived fission products 147 Nd, 111 Ag, and 156 Eu

We have completed the successful campaign on improving the branching ratios following the decay of 147 Nd with the publication of our manuscript titled “Precise measurements of the γ-ray intensities following the β decay of 144 Ce and 147 Nd” in Phys Rev C. Continuing the work this collaboration, we have results on the decay of 156 Eu that report updated intensities with reduced uncertainties of most intense emissions by an order of magnitude or more. We expect to submit our manuscript to Phys Rev C with these results on 156 Eu in the upcoming weeks.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Materials Data on Eu(CdSb)2 by Materials Project

EuCd2Sb2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent Sb3- atoms to form EuSb6 octahedra that share corners with twelve equivalent CdSb4 tetrahedra, edges with six equivalent EuSb6 octahedra, and edges with six equivalent CdSb4 tetrahedra. All Eu–Sb bond lengths are 3.33 Å. Cd2+ is bonded to four equivalent Sb3- atoms to form CdSb4 tetrahedra that share corners with six equivalent EuSb6 octahedra, corners with six equivalent CdSb4 tetrahedra, edges with three equivalent EuSb6 octahedra, and edges with three equivalent CdSb4 tetrahedra. The corner-sharing octahedra tilt angles range from 15–56°. There are three shorter (2.91 Å) and one longer (3.00 Å) Cd–Sb bond lengths. Sb3- is bonded to three equivalent Eu2+ and four equivalent Cd2+ atoms to form a mixture of distorted edge and corner-sharing SbEu3Cd4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(CoP)2 by Materials Project

EuCo2P2 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Eu2+ is bonded in a body-centered cubic geometry to eight equivalent P3- atoms. All Eu–P bond lengths are 3.11 Å. Co2+ is bonded to four equivalent P3- atoms to form a mixture of corner and edge-sharing CoP4 tetrahedra. All Co–P bond lengths are 2.21 Å. P3- is bonded in a 8-coordinate geometry to four equivalent Eu2+ and four equivalent Co2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(FeP)2 by Materials Project

EuFe2P2 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Eu2+ is bonded in a body-centered cubic geometry to eight equivalent P3- atoms. All Eu–P bond lengths are 3.13 Å. Fe2+ is bonded to four equivalent P3- atoms to form a mixture of edge and corner-sharing FeP4 tetrahedra. All Fe–P bond lengths are 2.20 Å. P3- is bonded in a 4-coordinate geometry to four equivalent Eu2+ and four equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(SiPd)2 by Materials Project

EuPd2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Eu2+ is bonded to eight equivalent Si4- atoms to form EuSi8 hexagonal bipyramids that share corners with sixteen equivalent PdSi4 tetrahedra, edges with four equivalent EuSi8 hexagonal bipyramids, edges with eight equivalent PdSi4 tetrahedra, and faces with four equivalent EuSi8 hexagonal bipyramids. All Eu–Si bond lengths are 3.25 Å. Pd3+ is bonded to four equivalent Si4- atoms to form PdSi4 tetrahedra that share corners with eight equivalent EuSi8 hexagonal bipyramids, corners with four equivalent PdSi4 tetrahedra, edges with four equivalent EuSi8 hexagonal bipyramids, and edges with four equivalent PdSi4 tetrahedra. All Pd–Si bond lengths are 2.48 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Eu2+, four equivalent Pd3+, and one Si4- atom. The Si–Si bond length is 2.42 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(MnAs)2 by Materials Project

EuMn2As2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent As3- atoms to form EuAs6 octahedra that share corners with twelve equivalent MnAs4 tetrahedra, edges with six equivalent EuAs6 octahedra, and edges with six equivalent MnAs4 tetrahedra. All Eu–As bond lengths are 3.04 Å. Mn2+ is bonded to four equivalent As3- atoms to form MnAs4 tetrahedra that share corners with six equivalent EuAs6 octahedra, corners with six equivalent MnAs4 tetrahedra, edges with three equivalent EuAs6 octahedra, and edges with three equivalent MnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–50°. There are one shorter (2.42 Å) and three longer (2.45 Å) Mn–As bond lengths. As3- is bonded in a 7-coordinate geometry to three equivalent Eu2+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(AlSi)2 by Materials Project

EuAl2Si2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent Si4- atoms to form EuSi6 octahedra that share corners with twelve equivalent AlSi4 tetrahedra, edges with six equivalent EuSi6 octahedra, and edges with six equivalent AlSi4 tetrahedra. All Eu–Si bond lengths are 3.07 Å. Al3+ is bonded to four equivalent Si4- atoms to form AlSi4 tetrahedra that share corners with six equivalent EuSi6 octahedra, corners with six equivalent AlSi4 tetrahedra, edges with three equivalent EuSi6 octahedra, and edges with three equivalent AlSi4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–52°. There are three shorter (2.53 Å) and one longer (2.59 Å) Al–Si bond lengths. Si4- is bonded to three equivalent Eu2+ and four equivalent Al3+ atoms to form a mixture of distorted edge and corner-sharing SiEu3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(Sb3Ru)4 by Materials Project

EuRu4Sb12 crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Eu2+ is bonded to twelve equivalent Sb1- atoms to form EuSb12 cuboctahedra that share faces with eight equivalent RuSb6 octahedra. All Eu–Sb bond lengths are 3.54 Å. Ru+2.50+ is bonded to six equivalent Sb1- atoms to form RuSb6 octahedra that share corners with six equivalent RuSb6 octahedra and faces with two equivalent EuSb12 cuboctahedra. The corner-sharing octahedral tilt angles are 55°. All Ru–Sb bond lengths are 2.65 Å. Sb1- is bonded in a 2-coordinate geometry to one Eu2+, two equivalent Ru+2.50+, and two equivalent Sb1- atoms. Both Sb–Sb bond lengths are 2.99 Å.

36 MATERIALS SCIENCE↗