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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Origin of the magnetic and orbital ordering in α-Sr 2 CrO 4

Motivated by recent experimental progress in transition metal oxides with the K 2 NiF 4 structure, in this study we investigate the magnetic and orbital ordering in α-Sr 2 CrO 4 . Using first principles calculations, first we derive a three-orbital Hubbard model, which reproduces the ab initio band structure near the Fermi level. The unique reverse splitting of t 2g orbitals in α-Sr 2 CrO 4 , with the 3d 2 electronic configuration for the Cr 4+ oxidation state, opens up the possibility of orbital ordering in this material. Using real-space Hartree-Fock for multi-orbital systems, we constructed the ground state phase diagram for the two dimensional compound α-Sr 2 CrO 4 . We found stable ferromagnetic, antiferromagnetic, antiferro-orbital, and staggered orbital stripe ordering in robust regions of the phase diagram. Furthermore, using the density matrix renormalization group method for two-leg ladders with the realistic hopping parameters of α-Sr 2 CrO 4 , we explore magnetic and orbital ordering for experimentally relevant interaction parameters. Again, we find a clear signature of antiferromagnetic spin ordering along with antiferro-orbital ordering at moderate to large Hubbard interaction strength. We also explore the orbital-resolved density of states with Lanczos, predicting insulating behavior for the compound α-Sr 2 CrO 4 , in agreement with experiments. Finally, an intuitive understanding of the results is provided based on a hierarchy between orbitals, with d xy driving the spin order, while electronic repulsion and the effective one dimensionality of the movement within the d xz and d yz orbitals driving the orbital order.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing putative orbital differentiation effects via Eu 2+ spin dynamics in Sr 1-x Eu x Fe 2 As 2

Here, in this work, we report x-ray powder diffraction, elemental analysis, electrical resistivity, magnetic susceptibility, specific heat, and electron spin resonance (ESR) in single crystals of Sr 1-x Eu x Fe 2 As 2 . We observed a breakdown of the previously reported scaling between the Eu 2+ Korringa relaxation rate obtained from ESR and the spin density wave temperature evolution for Sr-rich samples. This result suggests a distinct evolution of the orbital differentiation of the Fe 3d bands along the Sr-based series when compared to the Ba counterpart. We argue that this difference is related to a larger splitting between the structural (tetragonal-to-orthorhombic) and the Fe-driven spin density wave transitions induced by Eu doping in this series. In fact, our results indicate that the two transitions follow an opposite x-Eu dependence for Sr-concentrated samples. Our work shows that Sr 1-x Eu x Fe 2 As 2 series and the comparison with their Ba-based counterparts are exciting platforms to be explored for understanding the interplay among orbital differentiation, magnetism, and structural distortions in the iron pnictides

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Capping Effects on Spin and Charge Excitations in Parent and Superconducting Nd 1-x Sr x⁢ NiO 2

Superconductivity in infinite layer nickelates Nd 1-x⁢ Sr x NiO 2 has so far been achieved only in thin films, raising questions on the role of substrates and interfaces. Given the challenges associated with their synthesis it is imperative to identify their intrinsic properties. We use resonant inelastic x-ray scattering to investigate the influence of the SrTiO 3 capping layer on the excitations of Nd 1-x ⁢Sr x⁢ NiO 2 (x =0 and 0.2). Spin excitations are observed in parent and 20% doped Nd 1-x Sr x ⁢NiO 2 regardless of capping, proving that magnetism is intrinsic to infinite-layer nickelates and appears in a significant fraction of their phase diagram. In parent and superconducting Nd 1-x Sr x ⁢NiO 2 , the spin excitations are slightly hardened in capped samples compared to the noncapped ones. Additionally, a weaker Ni-Nd charge transfer peak at ~0.6 eV suggests that the hybridization between Ni 3⁢d and Nd 5⁢d orbitals is reduced in capped samples. In conclusion, from our data, capping induces only minimal differences in Nd 1-x Sr x NiO 2 and we phenomenologically discuss these differences based on the reconstruction of the SrTiO 3 -NdNiO 2 interface and other mechanisms such as crystalline disorder.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Crystal structure of dicaesium strontium hexacyanidoferrate(II), Cs 2 Sr[Fe(CN) 6 ], from laboratory X-ray powder data

Ferrocyanides with general formula A I x B II y [Fe(CN) 6 ], where A and B are cations, are thought to accept many substitutions on the A and B positions. In this communication, the synthesis and crystal structure of Cs 2 Sr[Fe(CN) 6 ] are reported. The latter was obtained from K 2 Ba[Fe(CN) 6 ] particles, put in contact with caesium and strontium ions. Hence, a simultaneous ion-exchange mechanism (Cs for K, Sr for Ba) occurs to yield Cs 2 Sr[Fe(CN) 6 ]. The synthesis protocol shows that K 2 BaFe(CN) 6 particles can be used for the simultaneous trapping of radioactive caesium and strontium nuclides in water streams. Cs 2 Sr[Fe(CN) 6 ] adopts the cryolite structure type and is isotypic with the known compound Cs 2 Na[Mn(CN) 6 ] [dicaesium sodium hexacyanidomanganate(III)]. The octahedrally coordinated Sr and Fe sites both are located on inversion centres, and the eightfold-coordinated Cs site on a general position.

Massoni, Nicolas↗
DOE OSTI2023

Finchite, Sr(UO 2 ) 2 (V 2 O 8 )·5H 2 O, a new uranyl sorovanadate with the francevillite anion topology

Finchite (IMA2017-052), Sr(UO 2 ) 2 (V 2 O 8 )·5H 2 O, is the first uranium mineral known to contain essential Sr. The new mineral occurs as yellow-green blades up to ~10 µm in length in surface outcrops of the calcrete-type uranium deposit at Sulfur Springs Draw, Martin County, Texas, U.S.A. Crystals of finchite were subsequently discovered underground in the Pandora mine, La Sal, San Juan County, Utah, U.S.A., as diamond-shaped golden-yellow crystals reaching up to 1 mm. In this work, the crystal structure of finchite from both localities was determined using single-crystal X-ray diffraction and is orthorhombic, Pcan, with a = 10.363(6) Å, b = 8.498(5) Å, c = 16.250(9) Å, V = 1431.0(13) Å 3 , Z = 4 (R 1 = 0.0555) from Sulfur Springs Draw; and a = 10.3898(16), b = 8.5326(14), c = 16.3765(3) Å, V = 1451.8(4) Å 3 , Z = 4 (R 1 = 0.0600) from the Pandora mine. Electron-probe microanalysis provided the empirical formula (Sr 0.88 K 0.17 Ca 0.10 Mg 0.07 Al 0.03 Fe 0.02 ) Σ1.20 (UO 2 ) 2 (V 2.08 O 8 )·5H 2 O for crystals from Sulfur Springs Draw, and (Sr 0.50 Ca 0.28 Ba 0.22 K 0.05 ) Σ0.94 (U 0.99 O 2 ) 2 (V 2.01 O 8 )·5H 2 O for crystals from the Pandora mine, based on 17 O atoms per formula unit. The structure of finchite contains uranyl vanadate sheets based upon the francevillite topology. Finchite is a possible immobilization species for both uranium and the dangerous radionuclide 90 Sr because of the relative insolubility of uranyl vanadate minerals in water.

58 GEOSCIENCES↗
DOE OSTI2022

Hall Effect Study of the Metamagnetic Transition in the Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 Nanosheet

Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 shows a ferromagnetic (FM) transition at T C ~ 105 K with the magnetic easy axis in the ab plane, followed by a metamagnetic transition (MMT) at low temperatures when the magnetic field H is applied along the c axis, which is in sharp contrast to that of the pure Sr 4 Ru 3 O 10 , where the easy axis is along the c axis and the MMT is in the ab plane. Here, we studied the MMT in the Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 nanosheet by the Hall effect. It was found that the ordinary Hall coefficient of Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 is almost the same as that of the pure Sr 4 Ru 3 O 10 , while a sudden increase in the Hall resistance R xy is observed below ~50 K, above which the R xy presents the conventional anomalous Hall effect up to T C . Analysis of the results indicates that the MMT has no direct correlation to the electronic structure but closely relates to the magnetic moment locking, where the magnetic-field-induced breakdown of the locked moments is responsible for the MMT.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(AlPb)2 by Materials Project

Sr(AlPb)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a body-centered cubic geometry to eight equivalent Pb atoms. All Sr–Pb bond lengths are 3.65 Å. Al is bonded to four equivalent Pb atoms to form a mixture of edge and corner-sharing AlPb4 tetrahedra. All Al–Pb bond lengths are 2.91 Å. Pb is bonded in a 9-coordinate geometry to four equivalent Sr and four equivalent Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(MnGe)2 by Materials Project

Sr(MnGe)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a distorted body-centered cubic geometry to eight equivalent Ge atoms. All Sr–Ge bond lengths are 3.27 Å. Mn is bonded to four equivalent Ge atoms to form a mixture of edge and corner-sharing MnGe4 tetrahedra. All Mn–Ge bond lengths are 2.44 Å. Ge is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent Mn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(GaAs)2 by Materials Project

Sr(GaAs)2 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. there are three inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to six As3- atoms to form edge-sharing SrAs6 octahedra. There are two shorter (3.09 Å) and four longer (3.15 Å) Sr–As bond lengths. In the second Sr2+ site, Sr2+ is bonded to six As3- atoms to form edge-sharing SrAs6 octahedra. There are four shorter (3.11 Å) and two longer (3.15 Å) Sr–As bond lengths. In the third Sr2+ site, Sr2+ is bonded to six As3- atoms to form edge-sharing SrAs6 octahedra. There are a spread of Sr–As bond distances ranging from 3.17–3.26 Å. There are four inequivalent Ga2+ sites. In the first Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. There are one shorter (2.54 Å) and two longer (2.58 Å) Ga–As bond lengths. In the second Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. There are one shorter (2.54 Å) and two longer (2.56 Å) Ga–As bond lengths. In the third Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. There are two shorter (2.56 Å) and one longer (2.58 Å) Ga–As bond lengths. In the fourth Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. All Ga–As bond lengths are 2.58 Å. There are four inequivalent As3- sites. In the first As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–78°. In the second As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. In the third As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–18°. In the fourth As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–78°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(Cd2Pt)2 by Materials Project

Sr(PtCd2)2 crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Sr is bonded to six equivalent Pt atoms to form a mixture of distorted edge and corner-sharing SrPt6 octahedra. The corner-sharing octahedral tilt angles are 41°. There are two shorter (3.34 Å) and four longer (3.45 Å) Sr–Pt bond lengths. Pt is bonded in a 9-coordinate geometry to three equivalent Sr and six equivalent Cd atoms. There are two shorter (2.81 Å) and four longer (2.82 Å) Pt–Cd bond lengths. Cd is bonded in a distorted trigonal non-coplanar geometry to three equivalent Pt atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(InHg)2 by Materials Project

Sr(HgIn)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent Hg atoms. All Sr–Hg bond lengths are 3.57 Å. Hg is bonded in a 9-coordinate geometry to four equivalent Sr, one Hg, and four equivalent In atoms. The Hg–Hg bond length is 2.85 Å. All Hg–In bond lengths are 3.00 Å. In is bonded to four equivalent Hg atoms to form a mixture of distorted edge and corner-sharing InHg4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(MgIn)2 by Materials Project

Sr(MgIn)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent In atoms. All Sr–In bond lengths are 3.62 Å. Mg is bonded to four equivalent In atoms to form a mixture of corner and edge-sharing MgIn4 tetrahedra. All Mg–In bond lengths are 2.97 Å. In is bonded in a 9-coordinate geometry to four equivalent Sr, four equivalent Mg, and one In atom. The In–In bond length is 2.87 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(AlGe)2 by Materials Project

Sr(AlGe)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sr is bonded to six equivalent Ge atoms to form SrGe6 octahedra that share corners with twelve equivalent AlGe4 tetrahedra, edges with six equivalent SrGe6 octahedra, and edges with six equivalent AlGe4 tetrahedra. All Sr–Ge bond lengths are 3.19 Å. Al is bonded to four equivalent Ge atoms to form AlGe4 tetrahedra that share corners with six equivalent SrGe6 octahedra, corners with six equivalent AlGe4 tetrahedra, edges with three equivalent SrGe6 octahedra, and edges with three equivalent AlGe4 tetrahedra. The corner-sharing octahedra tilt angles range from 22–50°. There are three shorter (2.58 Å) and one longer (2.65 Å) Al–Ge bond lengths. Ge is bonded to three equivalent Sr and four equivalent Al atoms to form a mixture of distorted corner and edge-sharing GeSr3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Sr-Nd-Pb isotope systematics of Australasian tektites: Implications for the nature and composition of target materials and possible volatile loss of Pb

The Australasian tektite (AAT) strewn field is the largest strewn field on the Earth with about ~10–30% coverage, both land and ocean, but a clearly identified source impact crater is absent despite the young age of AAT of ca. 790 ka. A genetic link between the Australasian tektites and their unequivocal parental materials is therefore largely impossible to establish. Nevertheless, the nature of the parental materials and the extent of volatilization can be constrained using the splash form tektites, carrying the chemical signatures of high-temperature processes, and the layered (so-called Muong Nong-type) tektites, which are less chemically homogenized and exceptionally abundant in the AAT field. New high-precision Sr, Nd and Pb isotopic measurements were obtained for a chemically and petrographically well-characterized suite of AAT, which included the Muong Nong-type (MN-AAT) with precisely known field locations in Laos and splash forms (SF-AAT) from different parts of the strewn field. Additionally, optically dark and light zones of the MN-AAT were also separately analyzed. Homogeneous ε Nd values from -11.8 to -11.2, combined with a narrow range of two-stage Nd model ages from 1.67 to 1.72 Ga for the entire AAT suite, point to a well-mixed source, in terms of REE, of the crustal segment from which the sedimentary material for tektites was ultimately derived. The Sr isotopic data largely overlap for SF-AAT and MN-AAT ( 87 Sr/ 86 Sr = 0.71636–0.72021) and indicate Paleozoic to Mesozoic sedimentary parentage. However, late Neogene to early Quaternary re-deposition and formation of a thick silt-sized sedimentary section with vertical stratification is required to comply with 10Be data. Lead isotope systematics documents at least three different components which can perhaps be represented by different mineral phases, such as feldspar, zircon, organic matter adsorbed on young sediments etc., sorted during fluvial transport and final deposition. In addition, the SF-AAT have systematically lower Pb contents than the MN-AAT, and generally show isotopically heavier Pb isotopic ratios. This is theoretically consistent with a preferential volatilization of lighter Pb isotopes during evaporation and considerably larger Pb loss from SF-AAT when compared to MN-AAT. Nevertheless, further experimental work would be necessary to unambiguously distinguish kinetic fractionation from source mixing.

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

Surface Gibbs free energy analyses of Sr segregation in lanthanum strontium iron oxide

Sr surface segregation in mixed-cation oxides often causes degradation of chemical or electrochemical performance. In this work, the thermodynamic driving force for Sr segregation is investigated to explain the Sr segregation behavior in La0.5Sr0.5FeO3 (LSF). Specifically, Density Functional Theory is used to calculate the surface Gibbs free energy of various surface terminations of cubic (100) LSF as a function of chemical potential and temperature. Here, SrO-terminated surfaces are predicted to be dominant, promoting Sr segregation at high temperatures and low oxygen partial pressure.

08 HYDROGEN↗
DOE OSTI2021

Nickelate Superconductivity without Rare‐Earth Magnetism: (La,Sr)NiO 2

Abstract The occurrence of unconventional superconductivity in cuprates has long motivated the search for manifestations in other layered transition metal oxides. Recently, superconductivity is found in infinite‐layer nickelate (Nd,Sr)NiO 2 and (Pr,Sr)NiO 2 thin films, formed by topotactic reduction from the perovskite precursor phase. A topic of much current interest is whether rare‐earth moments are essential for superconductivity in this system. In this study, it is found that with significant materials optimization, substantial portions of the La 1− x Sr x NiO 2 phase diagram can enter the regime of coherent low‐temperature transport ( x = 0.14 ‐ 0.20), with subsequent superconducting transitions and a maximum onset of ≈9 K at x = 0.20. Additionally, the unexpected indication of a superconducting ground state in undoped LaNiO 2 is observed, which likely reflects the self‐doped nature of the electronic structure. Combining the results of (La/Pr/Nd) 1− x Sr x NiO 2 reveals a generalized superconducting dome, characterized by systematic shifts in the unit cell volume and in the relative electron‐hole populations across the lanthanides.

Osada, Motoki↗
DOE OSTI2021

High-precision measurements of half-lives for 69 Ge, 73 Se, 83 Sr, 85 mSr, and 63 Zn radionuclides relevant to the astrophysical p-process via photoactivation at the Madison Accelerator Laboratory

The ground state half-lives of 69 Ge, 73 Se, 83 Sr, 63 Zn, and the half-life of the 1/2 - isomer in 85 Sr have been measured with high precision using the photoactivation technique at an unconventional bremsstrahlung facility that features a repurposed medical electron linear accelerator. The γ -ray activity was counted over about 6 half-lives with a high-purity germanium detector, enclosed into an ultra low-background lead shield. The measured half-lives are: T 1/2 ( 69 Ge) = 38.82 ± 0.07 (stat) ± 0.06 (sys) h; T 1/2 ( 73 Se) = 7.18 ± 0.02 (stat) ± 0.004 (sys) h; T 1/2 ( 83 Sr) = 31.87 ± 1.16 (stat) ± 0.42 (sys) h; T 1/2 ( 85m Sr) = 68.24 ± 0.84 (stat) ± 0.11 (sys) min; T 1/2 ( 63 Zn) = 38.71 ± 0.25 (stat) ± 0.10 (sys) min. These high-precision half-life measurements will contribute to a more accurate determination of corresponding ground-state photoneutron reaction rates, which are part of a broader effort of constraining statistical nuclear models needed to calculate stellar nuclear reaction rates relevant for the astrophysical p -process nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Inorganic resins enable the increased purification efficiency of 82 Sr from rubidium targets for use in PET imaging isotope production

The 82 Sr/ 82 Rb generator system has found use in positron emission tomography (PET) imaging of myocardial perfusion. 82 Sr is produced by proton irradiation of Rb metal/RbCl salt followed by chemical separation. Inorganic ion-exchangers were synthesized by hydrothermal methods and evaluated for the purification of accelerator-produced 82Sr from a RbCl target and co-produced impurities like 75 Se, Fe, Cr, and Ni. A process consisting of removal of bulk RbCl using sodium nonatitanate (SNT), then removal of remaining tracers of Rb and Se using poorly crystalline silicotitanate (pCST) is suitable for 82 Sr separation and achieves higher purity of 82 Sr vs. commonly used organic resins.

43 PARTICLE ACCELERATORS↗