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in subjects: "Lanthanum"

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Synthesis, characterization, phase diagrams and superconducting and normal state magnetic properties of La{sub 2{minus}x}Sr{sub x}CuO{sub 4} (0 {le} x {le} 0.08) and electrochemically oxidized La{sub 2{minus}x}Sr{sub x}CuO{sub 4+{delta}} (0 {le} x {le} 0.33, 0 {le} {delta} {le} 0.12)

La{sub 2{minus}x}Sr{sub x}CuO{sub 4} (0 {le} x {le} 0.15) can all be intercalated with oxygen by a novel electrochemical oxidation method. Bulk superconductivity is found with an onset {Tc} {approx} 40 K for the whole range 0.01 {le} x {le} 0.15; for x = 0.25 and 0.33, the electrochemical oxidation did not improve the superconducting properties. The magnetic susceptibility {chi}(T = 50--320 K) data for La{sub 2}CuO{sub 4.11} and La{sub 1.92}Sr{sub 0.08}CuO{sub 4.07} are nearly identical with th… more

Date: August 1, 1993

Creator: Chou, F.

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

open access

The role of rare-earth dopants in nanophase zirconia catalysts for automotive emission control.

Rare earth (RE) modification of automotive catalysts (e.g., ZrO{sub 2}) for exhaust gas treatment results in outstanding improvement of the structural stability, catalytic functions and resistance to sintering at high temperatures. Owing to the low redox potential of nonstoichiometric CeO{sub 2}, oxygen release and intake associated with the conversion between the 3+ and 4+ oxidation states of the Ce ions in Ce-doped ZrO{sub 2} provide the oxygen storage capacity that is essentially to effectiv… more

Date: July 16, 1999

Creator: Loong, C.-K. & Ozawa, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A summary of the fission product metabolism studies up to March 1944

The metabolic properties of the carrier free long lived fission products in the adult rat have been investigated at different intervals ranging from one to sixty-eight days following administration of the radioactive material. The radio elements studied include the most important long lived fission products, namely, Sr, Y, Zr, Cb, Ra, I, Xe, Cs, Ba, La, Ce, Pr, Np, and the unseparated uranium free fission mixture. The routes of administration included intraperitoneal, intramuscular, oral and in… more

Date: March 30, 1944

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Short range spin correlations in the CMR material La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7}.

The (La{sub 1{minus}} x Sr{sub x}){sub 3}Mn{sub 2}O{sub 7} compounds are layered materials that exhibit higher magneto-resistance than the corresponding 3D manganite perovskites. Quasi-elastic neutron scattering on a polycrystalline sample of La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} shows that the spin fluctuation spectrum of the these layered CMR materials is qualitatively similar to those found in the perovskite manganites (La,Ca)MnO{sub 3}; their concentration, lifetime, and coherence length … more

Date: March 23, 1998

Creator: Kelley, T. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Solid oxide materials research accelerated electrochemical testing

The objectives of this work were to develop methods for accelerated testing of cathode material for solid oxide fuel cells under selected operating conditions. The methods would be used to evaluate the performance of LSM cathode material.

Date: December 31, 1995

Creator: Armstrong, T.R.; Windisch, C. & Arey, B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Imprinted spiral structures as neutron polarizers.

Neutron diffraction from magnetic spiral structures is governed by strong selection rules for the polarization of the outgoing beam. When the sample is entirely of one chirality--for instance a right handed spiral--the neutrons diffracted by some Bragg reflections are fully polarized. While the scattering theory has been formulated long ago, attempts to controllably modify the population of left handed and right handed spiral domains in natural magnetic structures (which for instance occur in s… more

Date: October 7, 1998

Creator: Lohstroh, W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Advanced materials for solid oxide fuel cells

The purpose of this research is to improve the properties of the current state-of-the-art materials used for solid oxide fuel cells (SOFCs). The objectives are to: (1) develop materials based on modifications of the state-of-the-art materials; (2) minimize or eliminate stability problems in the cathode, anode, and interconnect; (3) Electrochemically evaluate (in reproducible and controlled laboratory tests) the current state-of-the-art air electrode materials and cathode/electrolyte interfacial… more

Date: December 31, 1995

Creator: Armstrong, T. & Stevenson, J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Magnetization studies of oxides related to the high temperature cuprate superconductors

The magnetic properties related to the following high temperature superconductors were measured utilizing a Faraday magnetometer: BaCuO{sub 2+x}, La{sub 2} CuO{sub 4}, Sr{sub 2} RhO{sub 4}, Sr{sub 2} VO{sub 4}, and Sr{sub 2} CuO{sub 3}. Neutron diffraction, magnetic susceptibility, and heat capacity measurements are discussed.

Date: June 19, 1995

Creator: Wang, Z.

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

open access

Synthesis and characterization of metal hydride electrodes. Interim report

The objective of this project is to elucidate the compositional and structural parameters that affect the thermodynamics, kinetics and stability of alloy hydride electrodes and to use this information in the development of new high capacity long life hydride electrodes for rechargeable batteries. The work focuses on the development of AB{sub 5} alloys and the application of in situ methods, at NSLS, such as x-ray absorption (XAS), to elucidate the role of the alloying elements in hydrogen stora… more

Date: October 1, 1995

Creator: McBreen, J. & Reilly, J. J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Imprinting artificial magnetic structures.

Recently we created La/Fe multilayers with a helical magnetic structure imprinted from the conditions of growth rather than by the magnetic interactions between layers. Each sublayer was 30{angstrom} thick, and during deposition the sample was rotated in an external field of 3 Oe. a field strong enough to magnetize the Fe layer being deposited but not sufficient to perturb the magnetization of the Fe layers already grown. As a result adjacent Fe layers formed a helical structure with a chiralit… more

Date: September 25, 1998

Creator: Lohstroh, W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Technology development for cobalt F-T catalysts. Quarterly technical progress report number 10, January 1--March 31, 1995

The goal of this project is the development of a commercially-viable, cobalt-based Fischer-Tropsch (F-T) catalyst for use in a slurry bubble column reactor. The major objectives of this work are (1) to develop a cobalt-based F-T catalyst with low (< 5%) methane selectivity, (2) to develop a cobalt-based F-T catalyst with water-gas shift activity, and (3) to combine both these improvements into one catalyst. The project consists of five major tasks: catalyst development; catalyst testing; cataly… more

Date: June 28, 1995

Creator: Singleton, Alan H.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Magnetic spiral structures in La/Fe multilayers.

The magnetic properties of La/Fe multilayers were tested by magneto-optical Kerr effect and polarized neutron reflectometry. The experiments indicated that above a layer thickness t{sub la} = 25{angstrom} the magnetic state of the virgin sample is represented by a spiral-like arrangement of magnetizations of subsequent Fe layers, whereas each Fe layer itself is ferromagnetic. Polarized neutron reflectometry shows that the helix has predominantly one chirality over the entire surface area of sev… more

Date: September 25, 1998

Creator: Lohstroh, W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Superconducting thermoelectric generator

This invention is comprised of an apparatus and method for producing electricity from heat. The present invention is a thermoelectric generator that uses materials with substantially no electrical resistance, often called superconductors, to efficiently convert heat into electrical energy without resistive losses. Preferably, an array of superconducting elements is encased within a second material with a higher thermal conductivity than that of the superconducting material. The second material … more

Date: December 31, 1992

Creator: Metzger, J.D. & El-Genk, M.

Item Type: Patent

Partner: UNT Libraries Government Documents Department

open access

Electrochemical properties of mixed conducting La{sub 1{minus}x}M{sub x}Co{sub 1{minus}y}Fe{sub y}O{sub 3{minus}{delta}} (M = Sr,Ca,Ba) perovskites

At elevated temperatures, some ABO{sub 3} perovskite type oxides having Co and Fe as B site cations exhibit substantial mixed (anionic and electronic) conductivity. Because of this behavior, they are candidate materials for applications such as solid oxide fuel cell cathodes and oxygen separation membranes. The purpose of the present study is to increase the understanding of the effects of composition, temperature, and environment on the electrochemical properties of selected materials within t… more

Date: October 1, 1995

Creator: Stevenson, J. W.; Armstrong, T. R.; Pederson, L. R. & Weber, W. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The effect of temperature, growth kinetics, and substrate on the microstructure of RF off-axis sputter deposited YBa{sub 2}Cu{sub 3}O{sub 7} thin films

YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) thin films were grown on single crystal substrates by RF off-axis sputter deposition under different growth condition, systematically varied to change the kinetic and thermodynamic processes that determine both the film microstructure and its crystallographic orientation. The effect of substrate temperature, position, and material, total chamber pressure, and RF power on the final film structure was examined. The growth matrix was bounded by temperatures from … more

Date: July 1, 1995

Creator: Hawley, M.; Houlton, R. J.; Garzon, F. H. & Raistrick, I. D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Structure and properties of metal hydrides prepared by mechanical alloying

Our research examines the structure and reversible hydrogen storage capacity of alloys based on the LaNi{sub 5} intermetallic. The alloys are prepared by mechanical alloying (MA), a technique particularly useful when alloying LaNi{sub 5} with low melting point elements such as tin and calcium. In LaNi{sub 5-y}Sn{sub y}, x-ray diffraction and Rietveld analysis show that tin preferentially occupies the Ni(3g) sites in the LaNi{sub 5} structure, and the unit cell volume increases linearly with tin… more

Date: September 1, 1995

Creator: Wasz, M.L. & Schwarz, R.B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Overview of recent magnetic studies of high T{sub c} cuprate parent compounds and related materials

Recent studies of the magnetic properties of several high superconducting transition temperature (T{sub c}) cuprate parent compounds and related materials will be reviewed. The observations of a Heisenberg to XY-like crossover upon cooling below {approximately}300K towards the Neel temperature T{sub N} = 257 K and a subsequent magnetic field-induced XY-like to Ising-like crossover near TN in single crystals of the K{sub 2}NiF{sub 4} type spin 1/2 model compound Sr{sub 2}CuO{sub 2}Cl{sub 2} will… more

Date: December 1995

Creator: Johnston, D. C.; Ami, T. & Borsa, F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Effect of Ce composition on the structural and electronic characteristics of some metal hydride electrodes: A XANES and EXAFS investigation

Substitution of the B component in the prototype AB{sub 5} type (LaNi{sub 5}) metal hydride alloys have resulted in their increased acceptance as anodes for rechargeable alkaline batteries. Recently substitution of the A component (La) for imparting properties such as increased corrosion resistance has received attention. This investigation deals with the role of Ce as a substituent for the La and its effect in terms of corrosion resistance. The alloys chosen have the general composition of La{… more

Date: December 31, 1994

Creator: Mukerjee, S.; McBreen, J.; Reilly, J. J.; Johnson, J. R.; Adzic, G.; Kumar, M. P. S. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Direct imaging of the first order spin flop transition in the layered manganite La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7}.

The spin-flop transition in the antiferromagnetic layered manganite La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} was studied using magnetization measurements and a high-resolution magneto-optical imaging technique. We report the direct observation of the formation of ferromagnetic domains appearing at the first order spin-flop transition. The magnetization process proceeds through nucleation of polarized domains at crystal defect sites and not through the expansion of polarized domains due to domain… more

Date: August 31, 1999

Creator: Berger, A.; Gray, K. E.; Miller, D. J.; Mitchell, J. F.; Vlasko-Vlasov, V. K. & Welp, U.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The phase diagrams and doped-hole segregation in La{sub 2}CuO{sub 4+{delta}} and La{sub 2-x}Sr{sub x}CuO{sub 4+{delta}} (x {le} 0.15, {delta} {le} 0.12)

The magnetic and structural phase diagrams of the La{sub 2}CuO{sub 4+{delta}} system and the La{sub 2-x}Sr{sub x}CuO{sub 4+{delta}} are reviewed, with emphasis on recent results obtained from magnetic and structural neutron diffraction, thermogravimetric analysis, iodometric titration, magnetic susceptibility {chi}(T), and {sup 129}La nuclear quadrupole resonance (NQR) measurements.

Date: October 31, 1993

Creator: Johnston, D.C.; Borsa, F. & Canfield, P.C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Magnetic correlations in doped transition metal oxides

The authors review recent reactor- and spallation-source-based neutron scattering experiments on the magnetic fluctuations and order in a variety of doped transition metal oxides. In particular, data are shown for the NiO chain compound, Y{sub 2{minus}x}Ca{sub x}BaNiO{sub 5}, the two-dimensional cuprate superconductors La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3} O{sub 6+x}, and the classical three-dimensional ``Mott-Hubbard`` system V{sub 2{minus}y}O{sub 3}.

Date: February 15, 1995

Creator: Aeppli, G.; Bao, W. & Broholm, C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Development of metal hydride composites

Most of current hydride technology at Savannah River Site is based on beds of metal hydride powders; the expansion upon hydridation and the cycling results in continued breakdown into finer particles. Goal is to develop a composite which will contain the fines in a dimensionally stable matrix, for use in processes which require a stable gas flow through a hydride bed. Metal hydride composites would benefit the advanced Thermal Cycling Absorption process (hydrogen isotope separation), and the Re… more

Date: December 1, 1992

Creator: Congdon, J. W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Role of intergrowths in the properties of the naturally layered manganites.

The structural and magnetic properties of the two-layered Ruddlesden-Popper phase SrO(La{sub 1{minus}x}Sr{sub x}MnO{sub 3}){sub 2} with x = 0.3 and x = 0.4 are investigated. These naturally layered manganites exhibit a colossal magnetoresistance, a magnetic anisotropy which is strongly composition-dependent, almost no remanence, and a non-vanishing magnetization in an extended temperature range above the Curie temperature (T{sub c}). The magnetization in this temperature range is not intrinsic … more

Date: October 27, 1998

Creator: Bader, S. D.; Berger, A.; Jiang, J. S.; Miller, D. J.; Mitchell, J. F. & Osgood, R. M., III

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Measurement of lanthanum and technetium in uranium fuels by inductively coupled plasma atomic emission spectroscopy.

An important parameter in characterizing an irradiated nuclear fuel is determining the amount of uranium fissioned. By determining the amount of uranium fissioned in the fuel a burnup performance parameter can be calculated, and the amount of fission products left in the fuel can be predicted. The quantity of uranium fissioned can be calculated from the amount of lanthanum and technetium present in the fuel. Lanthanum and technetium were measured in irradiated fuel samples using an Inductively … more

Date: June 10, 1999

Creator: Carney, K.; Crane, P.; Cummings, D.; Krsul, J. & McKnight, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department