Engineering topics

Bi, Wenli

Publications and source records attributed to Bi, Wenli.

At least 37 records · Page 2

DOE OSTI2020

Effects of composition and pressure on electronic states of iron in bridgmanite

Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O 3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mössbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mössbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10–50% Fe/total cations, 0–25% Al/total cations, 12–100% Fe 3+ /total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe 3+ provide a Mössbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe 3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at ~70 GPa. Thus center shift can easily distinguish Fe 3+ from Fe 2+ at high pressure, which exhibits two distinct Mössbauer sites with center shift ~1 mm/s and quadrupole splitting 2.4–3.1 and 3.9 mm/s at ~70 GPa. Correct quantification of Fe 3+ /total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. Furthermore, in Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to ~20% of the Fe may be a Fe 2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.

58 GEOSCIENCES↗

DOE OSTI2020

Untersuchung von Schwingungen in Bezug auf Spin‐Phonon‐Kopplung in Einzelmolekülmagneten mittels nuklearer inelastischer Streuung am 161 Dy‐Kern

Abstract Erstmalig wurde Synchrotron‐basierte nukleare inelastische Streuung (NIS) unter Nutzung des Mößbauer‐Isotops 161 Dy für die Untersuchung der vibronischen Eigenschaften eines Dy III ‐basierten Einzelmolekülmagneten, [Dy(Cy 3 PO) 2 (H 2 O) 5 ]Br 3 ⋅2 (Cy 3 PO)⋅2 H 2 O⋅2 EtOH, eingesetzt. Die experimentelle partielle Phononen‐Zustandsdichte, die alle Schwingungen mit einer Auslenkung des Dy III ‐Ions enthält, wurde mit Hilfe von auf Dichtefunktionaltheorie (DFT) basierenden Simulationen reproduziert, was die Zuordnung aller intramolekularen Schwingungsmoden des Moleküls ermöglicht. Diese Studie zeigt, dass 161 Dy‐NIS als eine experimentelle Methode ein hohes Potential besitzt, um zur Klärung der Rolle von Phononen in Einzelmolekülmagneten beizutragen.

Scherthan, Lena↗

DOE OSTI2020

Exploring the Vibrational Side of Spin-Phonon Coupling in Single-Molecule Magnets via 161 Dy Nuclear Resonance Vibrational Spectroscopy

Synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) using the Mossbauer isotope 161 Dy has been employed for the first time to study the vibrational properties of a single-molecule magnet (SMM) incorporating Dy III , namely [Dy(Cy3PO)(2)(H2O)(5)]Br-3•2 (Cy3PO)•2 H2O•2 EtOH. The experimental partial phonon density of states (pDOS), which includes all vibrational modes involving a displacement of the Dy III ion, was reproduced by means of simulations using density functional theory (DFT), enabling the assignment of all intramolecular vibrational modes. This study proves that 161 Dy NRVS is a powerful experimental tool with significant potential to help to clarify the role of phonons in SMMs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Influence of ligand substitution on magnetic hyperfine interaction in Dy 6 -based single-molecule magnets/toroics

161 Dy time-domain Mössbauer spectroscopy (SMS), just recently presented as a novel tool to investigate Dy(III)-based single-molecule magnets (SMMs), has now been applied on two polynuclear Dy 6 -based wheel compounds possessing special features of single-molecule toroics (SMTs). The magnitude of the magnetic hyperfine field revealed for the Dy 6 ring system [Dy 6 (teaH) 6 (NO 3 ) 6 ]·8MeOH is with B 0 =574.3(5) T characteristic for Dy(III) with a 6 H 15/2 ground state. The ligand substituted compound [Dy 6 (Me-teaH) 6 (NO 3 ) 6 ]·6MeCN possesses within the experimental errors the same magnetic hyperfine characteristics (B 0 =574.9(5) T). Furthermore, the organic ligand variation has no influence on the magnetic hyperfine field sensed by the 161 Dy(III) nuclei in these homometallic Dy(III) 6 -wheels.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Elastic and magnetic properties of Fe 3 P up to core pressures: Phosphorus in the Earth's core

Phosphorus (P) is considered a possible light element alloying with iron (Fe) in the Earth's core due to its siderophile nature and the ubiquity of P-bearing iron alloys in iron meteorites. The sequestration of P by liquid metals during the core formation possibly results in the relatively low concentration of P in the bulk silicate Earth. Here, we performed single-crystal and powder X-ray diffraction, synchrotron Mossbauer spectroscopy and nuclear resonant inelastic X-ray scattering measurements in diamond anvil cells to investigate the elastic and magnetic properties of Fe 3 P under high pressures. Our X-ray diffraction results suggest that there is no structural phase transition up to 111 GPa. However, a volume collapse was observed at 21.5 GPa in Fe 3 P, ascribed to a magnetic transition as evidenced by synchrotron Mhssbauer spectroscopy results. Fitting the volume-pressure data by the Birch-Murnaghan equation of state gives bulk modulus $K_{T0}$ = 162.4(7) GPa, its first pressure derivative $K'_{T0}$ = 4.0 (fixed) and zeropressure volume $V_0$ = 370.38(6) Å 3 for the magnetic phase and $K_{T0}$ = 220(7) GPa, $K'_{T0}$ = 4.0 (fixed) and $V_0$ = 357(1) Å 3 for the non-magnetic phase. Sound velocities of Fe 3 P were determined up to 152 GPa by nuclear resonant inelastic X-ray scattering, demonstrating that Fe 3 P bears a low shear velocity and high Poisson's ratio at core pressures compared to Fe and Fe 3 S. When forming a solid solution Fe 3 (S,P) with Fe 3 S at core pressures, Fe 3 P may favorably influence the elastic properties of Fe 3 (S,P) to match the seismic observations of the inner core.

58 GEOSCIENCES↗

DOE OSTI2019

Distinct pressure evolution of coupled nematic and magnetic orders in FeSe

We present a microscopic study of nematicity and magnetism in FeSe over a wide temperature and pressure range using high-energy x-ray diffraction and time-domain Mössbauer spectroscopy. The low-temperature magnetic hyperfine field increases monotonically up to ~6 GPa. The orthorhombic distortion initially decreases under increasing pressure but is stabilized at intermediate pressures by cooperative coupling to the pressure-induced magnetic order. Close to the reported maximum of the superconducting critical temperature at p = 6.8GPa, the orthorhombic distortion suddenly disappears and a new tetragonal magnetic phase occurs. As a result, the pressure and temperature evolution of the structural and magnetic order parameters suggests that they have distinct origins.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Bandwidth controlled insulator-metal transition in BaFe 2 S 3 : A Mössbauer study under pressure

BaFe 2 S 3 is a quasi one-dimensional Mott insulator that orders antiferromagnetically below 125 K. The application of pressure induces a transition to a metallic state, and superconductivity emerges.The evolution of the magnetic behavior on increasing pressure has up to now been either studied indirectly by means of transport measurements, or by using local magnetic probes only in the low pressure region. Here, we investigate the magnetic properties of BaFe 2 S 3 up to 9.9GPa by means of synchrotron 57 Fe Mossbauer spectroscopy experiments, providing the First local magnetic phase diagram. The magnetic ordering temperature increases up to 185(5) K at 7.5GPa, and is fully suppressed at 9.9GPa. The low-temperature magnetic hyperne field is continuously reduced from 12.9 to 10.3T between 1.4 and 9.1GPa, followed by a sudden drop to zero at 9.9GPa indicating a First-order phase transition. The pressure dependence of the magnetic order in BaFe2S3 can be qualitatively explained by a combination of a bandwidth-controlled insulator-metal transition as well as a pressure enhanced exchange interaction between Fe-atoms and Fe 3d-S 3p hybridization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Altered chemistry of oxygen and iron under deep Earth conditions

A drastically altered chemistry was recently discovered in the Fe-O-H system under deep Earth conditions, involving the formation of iron superoxide (FeO 2 Hx with x =0 to 1), but the puzzling crystal chemistry of this system at high pressures is largely unknown. Here we present evidence that despite the high O/Fe ratio in FeO 2 Hx, iron remains in the ferrous, spin-paired and non-magnetic state at 60–133 GPa, while the presence of hydrogen has minimal effects on the valence of iron. The reduced iron is accompanied by oxidized oxygen due to oxygen-oxygen interactions. The valence of oxygen is not –2 as in all other major mantle minerals, instead it varies around –1. This result indicates that like iron, oxygen may have multiple valence states in our planet’s interior. Laslty, our study suggests a possible change in the chemical paradigm of how oxygen, iron, and hydrogen behave under deep Earth conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

161 Dy Time‐Domain Synchrotron Mössbauer Spectroscopy for Investigating Single‐Molecule Magnets Incorporating Dy Ions

Abstract Time‐domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of 161 Dy has been used to investigate the magnetic properties of a Dy III ‐based single‐molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy 3 PO) 2 (H 2 O) 5 ]Br 3 ⋅2 (Cy 3 PO)⋅2 H 2 O⋅2 EtOH is with B 0 =582.3(5) T significantly larger than that of the free‐ion Dy III with a 6 H 15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the Dy III ion. This study demonstrates that 161 Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy‐containing compounds.

Scherthan, Lena↗

DOE OSTI2018

161 Dy Time-Domain Synchrotron Mössbauer Spectroscopy for Investigating Single-Molecule Magnets Incorporating Dy Ions [ 161 Dy time-domain synchrotron Mössbauer spectroscopy as a new way forward for investigating single molecule magnets incorporating Dy ions]

Time–domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of 161 Dy has been used to investigate the magnetic properties of a Dy III –based single–molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy 3 PO) 2 (H 2 O) 5 ]Br 3 •2 (Cy 3 PO)•2 H 2 O•2 EtOH is with B 0 =582.3(5) T significantly larger than that of the free–ion Dy III with a 6 H 15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the Dy III ion. Furthermore this study demonstrates that 161 Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy–containing compounds.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2018

Microscopic phase diagram of LaFeAsO single crystals under pressure

We investigated a LaFeAsO single crystal by means of synchrotron Mössbauer spectroscopy under pressure up to 7.5 GPa and down to 13 K and provide a microscopic phase diagram. We found a continuous suppression of the magnetic hyperfine field with increasing pressure and it completely vanishes at ~7.5 GPa which is in contrast to the behavior in polycrystalline samples where the magnetic order vanishes at ~ 20 GPa. The different behavior of the polycrystalline samples might be due to As-vacancies. Our results are in qualitative agreement with density functional theory calculations where a reduction of the magnetic moment with increasing pressure was found. Here, we found that among different samples the magnetic phase transition temperature as well as the low-temperature magnetic hyperfine field decrease with increasing unit cell volume.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Iron isotopic fractionation in mineral phases from Earth's lower mantle: Did terrestrial magma ocean crystallization fractionate iron isotopes?

Iron is the most abundant transition metal in the Earth's interior, yet considerable uncertainties remain as to why mantle-derived rocks have diverse iron isotopic compositions. In particular, the isotopic fractionation behavior of iron in the lower-mantle minerals bridgmanite and ferropericlase are largely unexplored. The reason is that it is challenging to study isotopic fractionation at the high pressures relevant to the deep mantle. Here we report in situ measurements of the mean force constants of iron bonds in these minerals pressurized in diamond anvil cells using the technique of nuclear resonant inelastic X-ray scattering (NRIXS). We find that the transition from high- to low-spin iron in ferropericlase ((Mg 0.75 Fe 0.25 )O) at approximately 60 GPa drastically stiffens its iron bonds in the low-spin state. The mean force constant of iron bonds in both Fe-bearing and (Fe,Al)-bearing bridgmanite exhibits softening by 21% at approximately 40-60 GPa, which seems to be associated with changes in the iron local environment during the transition from low to high quadrupole splitting states. These results indicate that in the lower mantle, low-spin ferropericlase is enriched in heavy iron isotopes relative to bridgmanite and metallic iron by +0.15 parts per thousand and +0.12 parts per thousand, respectively. Based on these results, we investigate whether terrestrial magma ocean crystallization could have fractionated iron isotopes. We conclude that this process cannot be responsible for the heavy iron isotope enrichment measured in terrestrial basalts.

58 GEOSCIENCES↗

DOE OSTI2018

High-pressure investigations on the semi-Heusler compound CuMnSb

The antiferromagnetic semi-Heusler compound CuMnSb has been investigated under high pressure by electrical resistivity and angle dispersive synchrotron x-ray diffraction measurements to 53 and 36 GPa, respectively. The Néel temperature at ~50 K is found to initially increase rapidly with pressure, reaching 83 K at 7 GPa. However, near 8 GPa at ambient temperature a sluggish first-order structural transition begins from a semimetallic cubic phase to a likely semimetallic tetragonal phase; thermal cycling to 355°C at 9.6 GPa serves to complete the transition. In the tetragonal phase no sign of magnetic ordering is visible in the resistivity R ( T ) over the measured temperature range 4–295 K. This suggests that magnetic ordering may have shifted to temperatures well above ambient. Indeed, density functional calculations find the magnetic ground state in the tetragonal phase to be antiferromagnetic. In conclusion, following decompression to 1 bar at ambient temperature, the high-pressure tetragonal phase is retained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

SciPhon : a data analysis software for nuclear resonant inelastic X-ray scattering with applications to Fe, Kr, Sn, Eu and Dy

We present the synchrotron radiation technique of nuclear resonant inelastic X-ray scattering (NRIXS), also known as nuclear resonance vibrational spectroscopy or nuclear inelastic scattering, provides a wealth of information on the vibrational properties of solids. It has found applications in studies of lattice dynamics and elasticity, superconductivity, heme biochemistry, seismology, isotope geochemistry and many other fields. It involves probing the vibrational modes of solids by using the nuclear resonance of Mössbauer isotopes such as 57 Fe, 83 Kr, 119 Sn, 151 Eu and 161 Dy. After data reduction, it provides the partial phonon density of states of the Mössbauer isotope that is investigated, as well as many other derived quantities such as the mean force constant of the chemical bonds and the Debye velocity. The data reduction is, however, not straightforward and involves removal of the elastic peak, normalization and Fourier–Log transformation. Furthermore, some of the quantities derived are highly sensitive to details in the baseline correction. A software package and several novel procedures to streamline and hopefully improve the reduction of the NRIXS data generated at sector 3ID of the Advanced Photon Source have been developed. The graphical user interface software is named SciPhon and runs as a Mathematica package. It is easily portable to other platforms and can be easily adapted for reducing data generated at other beamlines. Several tests and comparisons are presented that demonstrate the usefulness of this software, whose results have already been used in several publications. Here, the SciPhon software is used to reduce Kr, Sn, Eu and Dy NRIXS data, and potential implications for interpreting natural isotopic variations in those systems are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Impact of Pressure on Magnetic Order in Jarosite

We present that jarosite, a mineral with a kagome lattice, displays magnetic frustration yet orders magnetically below 65 K. As magnetic frustration can engender exotic physical properties, understanding the complex magnetism of jarosite comprises a multidecade interdisciplinary challenge. Unraveling the nature of the disparate magnetic coupling interactions that lead to magnetic order in jarosite remains an open question. Specifically, there is no observed trend in the interlayer spacing with magnetic order. Similarly, the relationship between metal-ligand bond distance and magnetic order remains uninvestigated. Here, we use applied pressure to smoothly vary jarosite's structure without manipulating the chemical composition, enabling a chemically invariant structure-function study. Using single-crystal and powder X-ray diffraction, we show that high applied pressures alter both the interlayer spacing and the metal-ligand bond distances. By harnessing a suite of magnetic techniques under pressure, including SQUID-based magnetometry, time-resolved synchrotron Mossbauer spectroscopy, and X-ray magnetic circular dichroism, we construct the magnetic phase diagram for jarosite up to 40 GPa. Notably, we demonstrate that the magnetic ordering temperature increases dramatically to 240 K at the highest pressures. Additionally, we conduct X-ray emission spectroscopy, Mossbauer spectroscopy, and UV-visible absorption spectroscopy experiments to comprehensively map the magnetic and electronic structures of jarosite at high pressure. Finally, we use these maps to construct chemically pure magnetostructural correlations which fully explain the nature and role of the disparate magnetic coupling interactions in jarosite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Superconducting and magnetic phase diagram of RbEuFe 4 As 4 and CsEuFe 4 As 4 at high pressure

The recently discovered (Rb,Cs)EuFe 4 As 4 compounds exhibit an unusual combination of superconductivity ( T c ~35K) and ferromagnetism ( T m ~15K). We have performed a series of x-ray diffraction, ac magnetic susceptibility, dc magnetization, and electrical resistivity measurements on both RbEuFe 4 As 4 and CsEuFe 4 As 4 to pressures as high as ~30GPa. We find that the superconductivity onset is suppressed monotonically by pressure while the magnetic transition is enhanced at initial rates of dT m /dP~1.7K/GPa and 1.5K/GPa for RbEuFe 4 As 4 and CsEuFe 4 As 4 , respectively. Near 7 GPa, T c onset and T m become comparable. At higher pressures, signatures of bulk superconductivity gradually disappear. Room-temperature x-ray diffraction measurements suggest the onset of a transition from tetragonal (T) to a half-collapsed-tetragonal (hcT) phase at ~10GPa (RbEuFe 4 As 4 ) and ~12GPa (CsEuFe 4 As 4 ). In conclusion, the ability to tune T c and T m into coincidence with relatively modest pressures highlights (Rb,Cs)EuFe 4 As 4 compounds as ideal systems to study the interplay of superconductivity and ferromagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Suppression of the magnetic order in CeFeAsO: Nonequivalence of hydrostatic and in-plane chemical pressure

We present a detailed investigation of the electronic properties of CeFeAsO under chemical (As by P substitution) and hydrostatic pressure by means of in-house and synchrotron Mossbauer spectroscopy. The Fe magnetism is suppressed due to both pressures and no magnetic order was observed above a P-substitution level of 40 % or 5.2 GPa hydrostatic pressure. We compared both pressures and found that the isovalent As by P substitution change the crystallographic and electronic properties differently than hydrostatic pressure.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Experimental constraints on the sound velocities of cementite Fe 3 C to core pressures

Sound velocities of cementite Fe 3 C have been measured up to 1.5 Mbar and at 300 K in a diamond anvil cell using the nuclear resonant inelastic X-ray scattering (NRIXS) technique. From the partial phonon density of states (pDOS) and equation of state (EOS) of Fe 3 C, we derived its elastic parameters including shear modulus, compressional (V-p) and shear-wave (V-s) velocities to core pressures. A pressure-induced spin-pairing transition in the powdered Fe3C sample was found to occur gradually between 10 and 50 GPa by the X-ray Emission Spectroscopy (XES) measurements. Following the completion of the spin-pairing transition, the V p and V s of low-spin Fe 3 C increased with pressure at a markedly lower rate than its high-spin counterpart. Our results suggest that the incorporation of carbon in solid iron to form iron carbide phases, Fe 3 C and Fe 7 C 3 , could effectively lower the V s but respectively raise the Poisson's ratio by 0.05 and 0.07 to approach the seismically observed values for the Earth's inner core. In conclusion, the comparison with the preliminary reference Earth model (PREM) implies that an inner core composition containing iron and its carbon-rich alloys can satisfactorily explain the observed seismic properties of the inner core.

58 GEOSCIENCES↗