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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Hydrothermal synthesis and structural characterization of an organic–inorganic hybrid sandwich-type tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu(en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O

An organic–inorganic hybrid sandwich-type tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu(en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O (1) has been synthesized by reaction of Sb{sub 2}O{sub 3}, Na{sub 2}WO{sub 4}·2H{sub 2}O, CuCl{sub 2}·2H{sub 2}O with en (en=ethanediamine) under hydrothermal conditions and structurally characterized by elemental analysis, inductively coupled plasma atomic emission spectrometry, IR spectrum and single-crystal X-ray diffraction. 1 displays a centric dimeric structure formed by two equivalent trivacant Keggin [α-SbW{sub 9}O{sub 33}]{sup 9−} subunits sandwiching a hexagonal (Cu{sub 2}Na{sub 4}) cluster. Moreover, those related hexagonal hexa-metal cluster sandwiched tungstoantimonates have been also summarized and compared. The variable-temperature magnetic measurements of 1 exhibit the weak ferromagnetic exchange interactions within the hexagonal (Cu{sub 2}Na{sub 4}) cluster mediated by the oxygen bridges. - Graphical abstract: An organic–inorganic hybrid (Cu{sub 2}Na{sub 4}) sandwiched tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu (en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O was synthesized and magnetic properties was investigated. Display Omitted - Highlights: • Organic–inorganic hybrid sandwich-type tungstoantimonate. • (Cu{sub 2}Na{sub 4} sandwiched) tungstoantimonate [Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]{sup 10−}. • Ferromagnetic tungstoantimonate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

The crystal structure and magnetic properties of Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22}

We have synthesized the Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22} samples (x = 0.1, 0.2, 0.3, 0.4, 0.5) by the solid-state reaction method and investigated their crystalline and magnetic properties by X-ray diffractometer (XRD), Mössbauer spectrometer, vibrating sample magnetometer, and network analyzer. XRD patterns show that all samples are rhombohedral with space group R-3m. The lattice constants a{sub 0} and c{sub 0} decrease with Sr substitution due to smaller ion radius of Sr{sup 2+} (1.27 Å) than that of Ba{sup 2+} (1.43 Å). The Mössbauer spectroscopy measurements show that the relative area ratios of Fe ion were maintained constant regardless of the Sr concentration. However, average magnetic hyperfine field slightly increased with the Sr concentration. This observation agrees with the fact that the saturation magnetization (M{sub s}) linearly increases due to the increasing super-exchange interaction, originated from the difference in the ionic radius between Ba{sup 2+} and Sr{sup 2+}. To investigate its properties at high frequency range, all samples were sintered at 1100 °C, and complex permeability and permittivity were measured by network analyzer between 100 MHz and 4 GHz. For x below 0.3, the initial permeability at 100 MHz increases, at higher values of x, its value decreases. Our study shows that magnetic properties of Sr{sup 2+} substitution for Ba{sup 2+} in Y-type hexaferrite as well as low magnetic loss less than 0.1 in 1 GHz band, indicating the potential application of Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22} samples for RF and antenna devices in ultra high frequency band.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Room temperature dual ferroic behaviour of ball mill synthesized NdFeO{sub 3} orthoferrite

Phase pure NdFeO{sub 3} has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO{sub 3} regulates the multifunctional feature of the material. Rietveld refinement of the room temperature X-ray diffraction pattern shows that the Fe-O-Fe bond angle significantly favors the super exchange interaction, which is predominantly antiferromagnetic in nature. Magnetization measurement illustrates antiferromagnetic behaviour with a weak ferromagnetic component caused by the canted nature of the Fe{sup 3+} spins at room temperature. Absorption bands in the visible ambit, apparent from the UV-Vis diffuse reflectance studies, is found due to the crystal ligand field of octahedral oxygen environment of Fe{sup 3+} ions. The direct band gap is estimated to be 2.39 eV from the diffuse reflectance spectrum. The lossy natured ferroelectric loop having a maximum polarization of 0.23 μC/cm{sup 2} at room temperature is found to be driven by the non-collinear magnetic structure with reverse Dzyaloshinskii–Moriya effect. Magnetic field has influence on the dielectric constant as evident from the impedance spectroscopy, indicating the strong coupling between ferroelectric and the magnetic structure of NdFeO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Coherent spin dynamics of carriers in ferromagnetic semiconductor heterostructures with an Mn δ layer

The coherent spin dynamics of carriers in the heterostructures that contain an InGaAs/GaAs quantum well (QW) and an Mn δ layer, which are separated by a narrow GaAs spacer 2–10 nm thick, is comprehensively studied by the magnetooptical Kerr effect method at a picosecond time resolution. The exchange interaction of photoexcited electrons in QW with the ferromagnetic Mn δ layer manifests itself in magnetic-field and temperature dependences of the Larmor precession frequency of electron spins and is found to be very weak (several microelectron volts). Two nonoscillating components related to holes exist apart from an electron contribution to the Kerr signal of polarization plane rotation. At the initial stage, a fast relaxation process, which corresponds to the spin relaxation of free photoexcited holes, is detected in the structures with a wide spacer. The second component is caused by the further spin dephasing of energyrelaxed holes, which are localized at strong QW potential fluctuations in the structures under study. The decay of all contributions to the Kerr signal in time increases substantially when the spacer thickness decreases, which correlates with the enhancement of nonradiative recombination in QW.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structural, optical, and ferromagnetic characterization of Sm-doped LaOCl nanocrystalline synthesized by solvothermal route: Significant effect of hydrogen post treatment

Pure and Sm-doped lanthanum oxychloride (LaOCl) nanomaterials were synthesized by solvothermal route followed by a subsequent heat treatment process. The objective of the present work is to study and develop conditions required to create stable room-temperature ferromagnetic (RT-FM) properties in LaOCl. To achieve that aim, magnetic samarium Sm{sup 3+} ions were used as dopant sources for stable FM properties. Systematic structural, optical, and magnetic properties of undoped and Sm-doped LaOCl samples were investigated as function of post-annealing conditions (temperature and atmosphere). The optical absorption properties were studied by diffuse reflection spectroscopy (DRS). The magnetic measurements reveal that Sm-doped LaOCl nanopowders have partial RT-FM properties due to the doped ions. The variations of magnetic properties with pre-annealing temperature were investigated. Furthermore, the electronic medium of host LaOCl crystalline lattice, which carries the spin-spin (S.S) exchange interaction between localised dopant Sm{sup 3+}(4f{sup 5}) spins, was developed by annealing in hydrogen gas (hydrogenation). It was established that annealing in hydrogen atmosphere boosts the RT-FM properties so that the saturation magnetisation could be increased by more than 100%. Physical explanations and discussions were given in this paper. Thus, it was proved that the magnetic properties could be tailored to diamagnetic LaOCl compound by Sm-doping and post treatment under H{sub 2} atmosphere. Therefore, LaOCl nanocrystals could be used as a potential candidate for optical phosphor applications with magnetic properties. - Graphical abstract: M-H dependence of Sm-doped LaOCl powders. Study the effect of hydrogenation. - Highlights: • Synthesis of Sm-doped LaOCl nanoparticles. • DM LaOCl transforms to FM with dilute concentration of Sm doping. • Annealing under H{sub 2} atmosphere induces drastic boost in the FM properties. • Saturation magnetization attained 29 memu/g with little doping and hydrogenation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Enhancement of electrical conductivity in CoO-SiO{sub 2} nanoglasses and large magnetodielectric effect in ZnO-nanoglass composites

Nanoglasses of compositions xCoO·(100-x)SiO{sub 2} (mol. %) with x having values 10, 15, and 20, respectively, were grown within the nanopores of a pellet comprising of ZnO nanoparticles by soaking the latter in a suitable sol followed by necessary heat treatment. Both Co{sup 2+} and Co{sup 3+} ions were present and confirmed by X-ray photoelectron spectroscopy, the fraction of Co{sup 2+} species being ∼ 0.70. Small polaron hopping conduction was found to be present in the nanoglasses. The activation energy in the latter was observed to be smaller (range of 0.32–0.44 eV) than that in the corresponding bulk glass (0.70–0.77 eV). This was caused by the higher free volume in the nanoglass as compared to that of the bulk glass. This was confirmed by the extracted values of intersite separation between cobalt ions, which were higher in the nanoglass. Weak ferromagnetism was exhibited by the nanocomposites. This was ascribed to super exchange interaction between spin moments associated with Co{sup 2+} and Co{sup 3+} ions, respectively, leading to an antiferromagnetic spin alignment. The nanocomposites showed magnetodielectric effect with the magnetodielectric parameter having values in the range of 5.5% to 10%. The experimental data were fitted to equations derived from Catalan's model by invoking a negative and a positive magnetoresistance for nanoglasses of compositions having x = 20 and x = 10, respectively. A weak spin-orbit coupling and wave function shrinkage in a magnetic field for strongly localized states, respectively, are believed to cause such behaviour in the nanoglass systems concerned. Direct magnetoresistance measurements were carried out on the nanocomposites containing nanoglasses having 10CoO and 20CoO, respectively. The trend of results obtained indeed confirmed the presence of positive and negative magnetoresistance in the two nanoglasses, respectively. The materials would be suitable for magnetic sensor applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Anomalous magnetic configuration of Mn{sub 2}NiAl ribbon and the role of hybridization in the martensitic transformation of Mn{sub 50}Ni{sub 50−x}Al{sub x} ribbons

The magnetic configuration of Mn{sub 2}NiAl ribbon has been investigated. In contrast to Ni{sub 2}MnAl, the compound Mn{sub 2}NiAl with considerable disorder does exhibit ferromagnetism and, due to exchange interaction competition, both ferromagnetic and antiferromagnetic moment orientations can coexist between nearest neighbor Mn atoms. This is unexpected in Heusler alloys. Regarding the mechanism of the martensitic transformation in Mn{sub 50}Ni{sub 50−x}Al{sub x}, it is found that increasing the Al content results in an unusual change in the lattice constant, a decrease of the transformation entropy change, and enhancement of the calculated electron localization. These results indicate that the p-d covalent hybridization between Mn (or Ni) and Al atoms gradually increases at the expense of the d-d hybridization between Ni and Mn atoms. This leads to an increased stability of the austenite phase and a decrease of the martensitic transformation temperature. For 11 ≤ x ≤ 14, Mn{sub 50}Ni{sub 50−x}Al{sub x} ferromagnetic shape memory alloys are obtained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Spatial confinement of the IBEX Ribbon: A dominant turbulence mechanism

The narrow ribbon of enhanced energetic neutral atom flux observed by the Interstellar Boundary Explorer spacecraft has prompted numerous ideas to explain its structure and properties. One of these ideas is the 'neutral solar wind' scenario, which identifies the source particles as pickup protons in the local interstellar medium originating in solar wind charge-exchange interactions. This scenario has been thought to require unrealistically weak pitch-angle scattering of the pickup protons to explain the narrow structure. Recently, Schwadron and McComas suggested that this structure could result from a spatial retention of the pickup protons, rather than from a restricted pitch-angle distribution. Here, we present a physically motivated, quantitative mechanism to produce such a spatial configuration. This mechanism is based on the 'dominant turbulence' assumption, which can be applied where the production of new pickup protons is slow, and has been used to successfully explain the level of turbulent heating observed in the outer solar wind. This formalism predicts a pickup isotropization process which adds or subtracts energy from the ambient turbulent fluctuations, depending on the initial pitch angle of the pickup protons. We show that a simple model of this process can yield a ribbon structure in qualitative agreement with the observations. The results of this simple model are not yet quantitatively satisfactory, but we suggest several improvements which may reduce the quantitative discrepancy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

New rare-earth metal germanides with bismuth substitution. Synthesis, structural variations, and magnetism of the RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=Y, Pr, Nd, Sm, Gd-Tm, Lu) compounds

Single-crystals of the novel rare-earth metal-bismuth digermanides with idealized formula RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=Y, Pr, Nd, Sm, Gd-Tm, Lu; x<0.16(1)) have been obtained using the Bi-flux technique. Their structures have been established by single-crystal X-ray diffraction; they can be divided into three classes, closely related to the ZrSi{sub 2} structure with the space group Cmcm (no. 63). The structural relationship and the variations with the type of the rare-earth metal have been explored and discussed. Temperature-dependent magnetization measurements on the single-crystals reveal magnetic behavior, which have been rationalized based on the mean-field theory. At cryogenic temperatures, the localized 4f electrons in most of the compounds exhibit antiferromagnetic ordering, mediated by the conduction electrons via Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interactions. - Graphical abstract: This paper details the synthesis and the structural characterization of an extended series of rare-earth metal-bismuth-germanides RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=Y, Pr-Sm, Gd-Tm, Lu). They crystallize with the same extended symmetry (space group Cmcm), but with three distinct structures, which are closely related. Magnetization measurements show low-temperature antiferromagnetic ordering. RE[Bi{sub x}Ge{sub 1-x}]{sub 2} are the first compounds between these elements. Highlights: Black-Right-Pointing-Pointer RE[Bi{sub x}Ge{sub 1-x}]{sub 2} (RE=rare-earth metal) are the first compounds of the respective elements. Black-Right-Pointing-Pointer Their structures are closely related. Black-Right-Pointing-Pointer Three structures can be distinguished based on the packing of the REGe{sub 6} triangular prisms. Black-Right-Pointing-Pointer All compounds show low-temperature antiferromagnetic ordering.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Site-mixing effect on the XMCD spectrum in double perovskite Bi 2 FeMnO 6

We investigate magnetization in double perovskite multiferroic Bi 2 FeMnO 6 (BFMO) thin film using density functional theory (DFT) simulations, and X-ray magnetic circular dichroism (XMCD) measurements. The exchange interaction between Fe and Mn sites gives rise to a ferrimagnetic ordering in BFMO. When grown without structural defects, distinct XMCD signal is expected from this system. The site resolved magnetization, thus, can be extracted using XMCD sum rules. Although our theoretical calculations are consistent with this expectation for the ideal BFMO system, experimental measurements find evidence of anomalous peak for the L 2 and L 3 edges of XMCD signals, and thus, the XMCD sum rules are no longer valid. We theoretically explain this phenomenon by considering both tetragonal (near interface), and monoclinic (bulk) phases of BFMO system, with Fe and Mn ions interchanged between their respective sites. Such site-mixing between magnetic cations are commonly found during the synthesis process. Our DFT calculations of XMCD for site interchanged Fe and Mn ions in the bulk phase (monoclinic) of BFMO are in good agreement with experimental XMCD signal and reproduce the anomalous peak features at L 2 /L 3 edges.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

A two photon absorption laser induced fluorescence diagnostic for fusion plasmas

The quality of plasma produced in a magnetic confinement fusion device is influenced to a large extent by the neutral gas surrounding the plasma. The plasma is fueled by the ionization of neutrals, and charge exchange interactions between edge neutrals and plasma ions are a sink of energy and momentum. Here we describe a diagnostic capable of measuring the spatial distribution of neutral gas in a magnetically confined fusion plasma. A high intensity (5 MW/cm{sup 2}), narrow bandwidth (0.1 cm{sup -1}) laser is injected into a hydrogen plasma to excite the Lyman {beta} transition via the simultaneous absorption of two 205 nm photons. The absorption rate, determined by measurement of subsequent Balmer {alpha} emission, is proportional to the number of particles with a given velocity. Calibration is performed in situ by filling the chamber to a known pressure of neutral krypton and exciting a transition close in wavelength to that used in hydrogen. We present details of the calibration procedure, including a technique for identifying saturation broadening, measurements of the neutral density profile in a hydrogen helicon plasma, and discuss the application of the diagnostic to plasmas in the DIII-D tokamak.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Sol–gel synthesis, structure and luminescence properties of Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors

Graphical abstract: The phosphor powders of Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} were prepared by sol–gel method. The dependence of luminescence intensity on the Eu{sup 3+} concentration was investigated. - Highlights: • We synthesize Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors by the sol–gel method. • The effect of temperature on the crystallinity and morphology is investigated. • The phosphor presents an intense CT band in near UV range (370–410 nm). • The concentration quenching mechanism is the exchange interaction. - Abstract: Double-perovskite Ba{sub 2}Zn{sub 1−x}MoO{sub 6}:xEu{sup 3+} (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) orange–red emitting phosphors were synthesized by using the sol–gel method. The crystalline structure and photoluminescence properties of the phosphors were investigated. The X-ray diffraction (XRD) patterns indicate that the structure of matrix Ba{sub 2}ZnMoO{sub 6} is cubic double-perovskite with space group Fm-3m. The Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors present an intense broad charge transfer (CT) band absorption in near UV range (370–410 nm), which attributes to the charge transfer state of MoO{sub 6}, and performs orange–red emission of Eu{sup 3+} ({sup 5}D{sub 0} → {sup 7}F{sub 1} transition) at around 596 nm. A low concentration quenching occurs in Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} and the optimal doping concentration is about 6 mol%. The Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors are considered to be a promising orange–red emitting phosphor for near ultraviolet GaN-based white light emitting diode.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation of the Structural, Magnetic, Magnetocaloric, Electrical Properties, and Spin-Polarized Tunneling Effect of the La{sub 0.5}Ca{sub 0.3}Te{sub 0.2}MnO{sub 3} System

Structural, magnetic, magnetocaloric, electrical properties, and spin-polarized tunneling effect in La{sub 0.5}Ca{sub 0.3}Te{sub 0.2}MnO{sub 3} polycrystalline were studied in details. The temperature dependence of the inverse of the magnetic susceptibility indicates the presence of ferromagnetic exchange interaction between the nearest neighbors at the Weiss temperature θp = 265.32 ± 0.109. Based on the magnetic field dependence of magnetization, M(H), and employing the thermodynamic Maxwell equation, the magnetic entropy change |ΔS{sub M}| of the studied sample was determined. The maximum entropy change value of the system was around 4.99 J kg{sup −1} K{sup −1} under a magnetic field of 5 T. Electrically, the upturned region of resistivity was observed at low temperature. The recovery of the resistivity was found to be strongly affected by the external magnetic field. The electrical data were analyzed considering various models. Interestingly, the exception of the spin-polarized tunneling (SPT) model is in good agreement with the experimental data among other models. In the current work, the SPT is the dominant mechanism leading to the rise of resistivity, while decreasing the temperature values. Magnetotransport analysis was successfully carried out using percolation model in the temperature range between around 50 K to nearly 300 K under different magnetic fields up to 8 T. The isothermal field dependence of magnetoresistance was recorded fairly well via a phenomenological model based on the spin-polarized tunneling model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Correlation between oxygen vacancies and sites of Mn ions in YMnO{sub 3}

In multiferroic hexagonal manganites (RMnO{sub 3}, R = Y, Sc, Ho-Lu), positions of Mn ions can affect both their in-plane and inter-plane exchange interactions, thus they are of utmost importance for the magneto-elastic coupling of rare-earth compounds. However, the reported in-plane positions of Mn ions by different groups are controversial and there is a lack of convenient method to identify the shift of Mn ions from the center of MnO{sub 5} bipyramids. Here, we demonstrate that the transmission electron microscopy is an efficient technique to characterize the positions of Mn ions and the shift of Mn ions can be directly recognized from the selected area electron diffraction (SAED) patterns. Through systematic studies on the SAED patterns acquired from regions with stoichiometric and non-stoichiometric ratio, we conclude that the intensities of (11{sup ¯}0) and (22{sup ¯}0) diffraction spots are very sensitive to the in-plane positions of Mn ions. We ascribe the off-centered shift of Mn ions to the in-plane oxygen vacancies and this is verified by combined electron microscopy and electron diffraction pattern calculations. Our results indicate that SAED can be used to judge both local positions of Mn ions and local oxygen deficiency in RMnO{sub 3} systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Electrical, optical, and magnetic properties of amorphous yttrium iron oxide thin films and consequences for non-local resistance measurements

We present magnetic characterization, charge resistivity, and optical photoluminescence measurements on amorphous yttrium iron oxide thin films ( ⁠a-Y–Fe–O), with supporting comparisons to amorphous germanium (⁠ a-Ge) films. We measured magnetic properties with both SQUID magnetometry and polarized neutron reflectometry. These results not only confirm that a-Y–Fe–O is a disordered magnetic material with strong predominantly antiferromagnetic exchange interactions and a high degree of frustration, but also that it is best understood electrically as a disordered semiconductor. As with amorphous germanium, a-Y–Fe–O obeys expectations for variable-range hopping through localized electron states over a wide range of temperature. We also clarify the consequences of charge transport through such a semiconducting medium for non-local voltage measurements intended to probe spin transport in nominally insulating magnetic materials. We further compare non-local resistance measurements made with “quasi-dc” automated current reversal to ac measurements made with a lock-in amplifier. These show that the “quasi-dc” measurement has an effective ac current excitation with frequency up to approximately 22 Hz, and that this effective ac excitation can cause artifacts in these measurements including incorrect sign of the non-local resistance. Here, this comprehensive investigation of non-local resistance measurements in a-Y–Fe–O shows no evidence of spin transport on micrometer length scales, which is contrary to our original work, and in line with more recent investigations by other groups.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Development of Eu{sup 3+} activated monoclinic, perovskite, and garnet compounds in the Gd{sub 2}O{sub 3}–Al{sub 2}O{sub 3} phase diagram as efficient red-emitting phosphors

Eu{sup 3+} doped Gd{sub 4}Al{sub 2}O{sub 9} (GdAM), GdAlO{sub 3} (GdAP), and Gd{sub 3}Al{sub 5}O{sub 12} (GdAG, containing 10 at% of Lu{sup 3+} for lattice stabilization) have been developed in this work as efficient red-emitting phosphors. With coprecipitated carbonate precursors, phase evolution studies found minimum processing temperatures of ∼1000, 1100, and 1300 °C for the three phosphors to crystallize as pure phases, respectively. Compared with their yttrium aluminate counterparts, the gadolinium-based phosphors exhibit red-shifted O{sup 2−}–Eu{sup 3+} charge transfer excitation band (CTB) centers due to the lower electronegativity of Gd{sup 3+} and appreciably higher quantum yields of photoluminescence owing to the occurrence of efficient Gd{sup 3+}→Eu{sup 3+}energy transfer. The optimal Eu{sup 3+} contents were determined to be ∼7.5 at% for GdAM and 5.0 at% for both GdAP and GdAG, and concentration quenching of luminescence was suggested to be due to exchange interactions. Fluorescence decay analysis found a shorter lifetime for the phosphor powder processed at a higher temperature or with a higher Eu{sup 3+} content, and the underlying mechanism was discussed. Fluorescence lifetimes were also compared between the yttrium and gadolinium phosphor systems for the dominant emissions. - Graphical abstract: Eu{sup 3+} doped Gd{sub 4}Al{sub 2}O{sub 9} (GdAM), GdAlO{sub 3} (GdAP), and Gd{sub 3}Al{sub 5}O{sub 12} (GdAG, containing 10 at% of Lu{sup 3+} for lattice stabilization) have been developed as efficient red-emitting phosphors. Owing to the Gd{sup 3+} to Eu{sup 3+} energy transfer, improved luminescence is observed for the compounds than their yttrium-based counterparts. Display Omitted - Highlights: • Eu{sup 3+} doped Gd{sub 4}Al{sub 2}O{sub 9}, GdAlO{sub 3} and (Gd{sub 0.9}Lu{sub 0.1}){sub 3}Al{sub 5}O{sub 12} developed as red phosphors. • Improved red-emissions than their yttrium-based counterparts confirmed. • Efficient Gd{sup 3+}→Eu{sup 3+}energy transfer observed. • Applications in various lighting, display, and scintillation areas expected.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Influence of thermal processing on magnetotransport characteristics of NdSr{sub 2}Mn{sub 2}O{sub 7+δ}

Highlights: • The NdSr{sub 2}Mn{sub 2}O{sub 7+δ} compounds with different oxygen non-stoichiometry were prepared. • According to XRD analysis, all the oxides were completely single-phase. • The strong competition between different types of magnetic exchange interactions was revealed. • The samples demonstrate semiconducting behavior over the explored temperature range. • A large negative magnetoresistance effect for all the compounds below 200 K was observed. - Abstract: Background: Influence of oxygen non-stoichiometry on magnetic and electric properties of the compounds has not almost been studied yet. Aim: Synthesis of a number of the NdSr{sub 2}Mn{sub 2}O{sub 7+δ} samples subjected to various thermal processing in air atmosphere and investigation of their structure, oxygen non-stoichiometry, electrical and magnetic properties. Method: The compounds obtained have been characterized by using X-ray diffraction (XRD) analysis, a modified gravimetric method, vibrating sample magnetometry (VSM) and standard DC four-probe method. Results: It was established that additional firing of the samples at different temperatures leads to essential changes in the oxygen non-stoichiometry. The noticeable magnetoresistance (MR) effect is observed for all the compounds below 200 K and increases monotonically as the temperature decreases. The MR values for the compounds as a function of oxygen content vary nonlinearly. The largest MR value of 380% at the 5 K and magnetic field of 7 T was achieved for the sample with the oxygen non-stoichiometry of δ = 0.03. Conclusions: The results observed are discussed in the assumption of ferromagnetic cluster formation in the compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Control of Wannier orbitals for generating tunable Ising interactions of ultracold atoms in an optical lattice

In this study, we propose a method for generating cluster states of atoms in an optical lattice. By utilizing the quantum properties of Wannier orbitals, we create an tunable Ising interaction between atoms without inducing the spin-exchange interactions. We investigate the cause of errors that occur during entanglement generations, and then we propose an error-management scheme, which allows us to create high-fidelity cluster states in a short time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗