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Electrolysis of neodymium oxide. Final report for the period August 19, 1991 through February 28, 1997

Description: The objective of this research was to develop an electrolytic process for the continuous and economic production of neodymium alloys from neodymium oxide. The electrolysis of neodymium oxide continued to show promise for implementation as a low-cost process to produce high- quality neodymium or neodymium-iron alloy.
Date: May 1, 1997
Creator: Keller, R. & Larimer, K.T.
Partner: UNT Libraries Government Documents Department

Dynamic response of physisorbed hydrogen molecules on lanthanide-modified zirconia nanoparticles

Description: We investigated the microstructure and surface properties of ultrafine Ce- and Nd-modified zirconia powders by a joint adsorption-isotherm and neutron-scattering study. While the average pore size distribution and specific surface area can be determined by BET analysis of nitrogen adsorption, neutron inelastic scattering from surface adsorbed hydrogen provides additional information about the modulation of local potential energies over the substrate surfaces and distinguishes subtle differences in the microporous and mesoporous structure of the two samples.
Date: December 31, 1996
Creator: Loong, C.K.; Trouw; Ozawa, Masakuni & Suzuke, Suguru
Partner: UNT Libraries Government Documents Department

Practical superconductor development for electrical power applications: Quarterly report for the period ending December 31, 1999

Description: This is a multiyear experimental research program focused on improving relevant material properties of high-T{sub c} superconductors (HTSS) and on development of fabrication methods that can be transferred to industry for production of commercial conductors. The development of teaming relationships through agreements with industrial partners is a key element of the Argonne (ANL) program. Recent results on substrate deposition for coated conductors, vortex studies, development of hardened Ag-alloy sheaths for powder-in-tube conductors, and sol-gel processing of NdBa{sub 2}Cu{sub 3}O{sub x} (Nd-123) are presented.
Date: February 2, 2000
Partner: UNT Libraries Government Documents Department

Optical properties of lanthanide-containing halide-modified zinc tellurite glasses

Description: As part of an ongoing investigation to characterize the properties and structure of Zn halide-Te oxide glasses, we report preliminary measurements of the optical properties of several Nd- and Er-doped tellurites. Measurements include fluorescence lifetimes and estimates of the theoretical radiative lifetimes (from traditional Judd-Ofelt analysis of optical absorption spectra) as well as phonon sideband studies sensitive to vibrational characteristics near the rare earth ion. Response of these optical features to the substitution of alternative halides is examined.
Date: December 31, 1996
Creator: Sidebottom, D.L.; Hruschka, M.A.; Potter, B.G.; Brow, R.K. & Hudgens, J.J.
Partner: UNT Libraries Government Documents Department

Energy and polarization dependence of resonant inelastic X-ray scattering in Nd{sub 2}CuO{sub 4}

Description: The authors report the energy and polarization dependence of resonant inelastic x-ray scattering from Nd{sub 2}CuO{sub 4}. An energy loss feature at {approximately}6 eV is observed in the vicinity of the Cu K-edge. Numerical calculations based on the Anderson impurity model identify this as a charge transfer excitation to the anti-bonding state. The incident polarization is shown to select the intermediate states participating in the resonance process. Resonances are observed at 8,990 eV and 9,000 eV with the incident polarization perpendicular and parallel to the CuO planes, respectively. In contrast to the single-site model calculations, no resonances are observed associated with the {und 1s}3d{sup 10} {und L} intermediate states, suggesting non-local effects play a role.
Date: December 1998
Creator: Hill, J. P.; Kao, C. C. & Haemaelaeinen, K.
Partner: UNT Libraries Government Documents Department

Development of pair distribution function analysis

Description: This is the final report of a 3-year LDRD project at LANL. It has become more and more evident that structural coherence in the CuO{sub 2} planes of high-{Tc} superconducting materials over some intermediate length scale (nm range) is important to superconductivity. In recent years, the pair distribution function (PDF) analysis of powder diffraction data has been developed for extracting structural information on these length scales. This project sought to expand and develop this technique, use it to analyze neutron powder diffraction data, and apply it to problems. In particular, interest is in the area of high-{Tc} superconductors, although we planned to extend the study to the closely related perovskite ferroelectric materials andother materials where the local structure affects the properties where detailed knowledge of the local and intermediate range structure is important. In addition, we planned to carry out single crystal experiments to look for diffuse scattering. This information augments the information from the PDF.
Date: September 1, 1996
Creator: Vondreele, R.; Billinge, S.; Kwei, G. & Lawson, A.
Partner: UNT Libraries Government Documents Department

Twinning microstructure and charge ordering in the colossal magnetoresistive manganite Nd{sub 1/2}Sr{sub 1/2}MnO{sub 3}

Description: Charge ordering (C.O.) in the colossal magnetoresistive (CMR) manganites gives rise to an insulating, high-resistance state. This charge ordered state can be melted into a low-resistance metallic-like state by the application of magnetic field. Thus, the potential to attain high values of magnetoresistance with the application of small magnetic fields may be aided by a better understanding of the charge-ordering phenomenon. This study focused on microstructural characterization in Nd{sub 1/2}Sr{sub 1/2}MnO{sub 3}. In Nd{sub 1/2}Sr{sub 1/2}MnO{sub 3}, the nominal valence of Mn is 3.5+. On cooling, charge can localize and lead to a charge ordering between Mn 3+ and Mn 4+. The ordering of charge results in a superlattice structure and a reduction in symmetry. Thin foil specimens were prepared from bulk samples by conventional thinning and ion milling (at LiqN{sub 2} temperature) methods. The room temperature TEM observation of Nd{sub 1/2}Sr{sub 1/2}MnO{sub 3} reveals that it contains a highly twinned microstructure, together with a small number of stacking faults (SFS). A figure shows the same area of the specimen at different zone axes obtained by tilting around two perpendicular directions as indicated. Three grains A, B and C are labeled for each of the zone axes. The room temperature EDPs from the matrix and twins shows an approximate 90{degree} rotation suggesting a 90{degree} twin orientation. These results are further confirmed by C.O. at low temperatures. The twinning planes can be determined by tilting with large angles.
Date: May 10, 2000
Creator: Luo, Z. P.; Miller, D. J. & Mitchell, J. F.
Partner: UNT Libraries Government Documents Department

Dynamic response of physisorbed hydrogen molecules on lanthanide-modified zirconia nanoparticles

Description: Ultrafine lanthanide (Ln = Ce and Nd)-modified zirconia powders synthesized by a coprecipitation method exhibit high surface areas and adsorption sites that are essential for catalytic applications. We report a study of the surface chemistry of Ce{sub 0.1}Zr{sub 0.9}O{sub 2} and Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} powders. First, the specific surface area and porosity are characterized by nitrogen isotherm-adsorption measurements. Second, the motion of hydrogen molecules physisorbed on Ce- and Nd-doped zirconias is studied by inelastic neutron scattering. Nitrogen adsorption-desorption isotherm measurements yield a BET surface area (26.1 m{sup 2}/g) and mesopore size ({approximately}5 nm radius) in Ce{sub 0.1}Zr{sub 0.9}O{sub 2} as compared to those (72.3 m{sup 2}/g and {approximately}3 nm) in Nd{sub 0.1}Zr{sub 0.9} O{sub 1.95}. The vibrational densities of states of H{sub 2} on Ce{sub 0.1}Zr{sub 0.9}O{sub 2} and Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} were measured at 20 K over the 0-200 meV energy range for three hydrogen coverage. The spectra for both samples consist of two parts: a sharp peak at {approximately}14.5 meV and a broad component extending beyond 200 meV. The sharp peak corresponds to transitions from the J=0 to J=1 rotational states of bulk hydrogen molecules, and its intensity decreases with decreasing H{sub 2} coverage. The broad component corresponds to overdamped motion of surface adsorbed hydrogen molecules. The major difference in the latter component between the Ce- and Nd-doped samples is an excess of intensities in the 5-14 meV region in Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95}. The confined motion of adsorbed H{sub 2} on the different micropore and mesopore surfaces of Ce{sub 0.1}Zr{sub 0.9}O{sub 2} and Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} is discussed.
Date: October 1, 1997
Creator: Loong, C.K.; Trouw, F.; Ozawa, Masakuni & Suzuki, Suguru
Partner: UNT Libraries Government Documents Department

Phase relationships and cation disorder in RE{sub 1+x}Ba{sub 2-x}Cu{sub 3}O{sub 7+{delta}}, RE = Pr, Nd, Sm, Gd

Description: Unlike Y123 which forms only a stoichiometric compound, the light arare earth elements (LRE) form a solid solution LRE{sub 1+x}Ba{sub 2-x}Cu{sub 3}O{sub 7+{delta}} (LRE123ss), with increasing substitution of the LRE{sup 3+} for the Ba{sup 2+} as the ionic radii of the LRE increases. The sub-solidus phase relationships around the LRE123ss change for La, Pr and Nd, but are similar for Sm and Gd. However, the solubility limit decreases with decreasing ionic radii. In addition, the solubility limits for Sm and Gd are strongly influenced by PO{sub 2} during high temperature annealing. The range of solubility is, for any given LRE system, strongly dependent on the oxygen partial pressure (PO{sub 2}) providing a new means by which to control the microstructure in the RE123 system.
Date: December 31, 1995
Creator: Kramer, M.J.; Wu, H.; Dennis, K.W.; Polzin, B.I.; Falzgraf, D.K. & McCallum, R.W.
Partner: UNT Libraries Government Documents Department

Charge inhomogeneity and high temperature superconductivity

Description: When the condensation of a gas of fermions into a (self-bound) liquid state is frustrated by the long-range Coulomb interaction, the consequence is a large local fluctuation of the charge density, together with pairing on a high energy scale. The competition between these two effects at long length scales determines the nature of the ordered state at low temperatures. Evidence for the central role of this competition in determining the physical properties of the high temperature superconductors is provided by the delicate interplay of superconductivity, charge and spin ordering, and structural phase transformations in the La{sub 2}CuO{sub 4} family of materials. There the gas-liquid transition corresponds to the phase separation of holes doped into an antiferromagnetic insulator. Because of the low superfluid density and poor conductivity, the critical temperature for the superconducting transition in underdoped and optimally doped materials is governed by the onset of phase coherence and not by the pairing energy scale.
Date: May 1, 1996
Creator: Emery, V.J. & Kivelson, S.A.
Partner: UNT Libraries Government Documents Department

The use of cubic Nd-Ba-Cu-O seeds to create {theta}[100], 90{degree}-{theta}[100], and {theta}[001] tilt Y-Ba-Cu-O grain boundaries.

Description: Using seeding techniques to control the orientation of grains, we have been able to create a wide variety of YBa{sub 2}Cu{sub 3}O{sub 6+x}, grain boundaries. In addition to five domain samples with 90{degree}[100] twist and tilt grain boundaries, we have now developed a method to produce grain boundaries in the same sample that have the misorientations {theta}[001] tilt, {theta}[100] tilt, and 90{degree} {approximately} {theta}[100], where the disorientation angle {theta} is fully controllable. We will demonstrate how these boundaries can be synthesized, give experimental evidence via polarized light microscopy and electron backscatter patterns (EBSP) that the intended grain boundaries were indeed formed, and discuss the importance of these boundaries in future grain boundary studies.
Date: October 20, 1998
Creator: Field, M. B.
Partner: UNT Libraries Government Documents Department

Hadamard transform spectrometry: A new analytical technique; Progress report, Second year, March 15, 1992--November 15, 1992

Description: The document is divided into 4 parts: Hadamard transform photoacoustic spectrometry and depth profiling; Hadamard transform imaging with a 2D Hadamard encoding mask (Raman image using pararosaniline hydrochloride); Hadamard transform Raman spectrometry; and work on the growth of VO{sub 2}(s) crystals for Hadamard masking material. 13 figs, refs.
Date: November 15, 1992
Creator: Fateley, W.G. & Hammaker, R.M.
Partner: UNT Libraries Government Documents Department

Fabrication and characterization of melt-processed YBCO

Description: Large domain YBCO are fabricated by using a melt processing technique for magnetic levitation applications. A Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub y} seed is used to initiate grain growth and to control the orientation of YBCO grains. Samples as large as 2 inch have been fabricated by utilizing this method. Microstructural studies reveals two distinct regions in these levitators due to different growth mechanism along a/b and c axis. Some initial results on the mass production of these levitators are also reported.
Date: November 1996
Creator: Sengupta, S.; Corpus, J.; Gaines, J. R., Jr.; Todt, V. R.; Zhang, X. F.; Miller, D. J. et al.
Partner: UNT Libraries Government Documents Department

INVESTIGATIONS IN THE SYSTEM URANIA - NEODYMIA

Description: Urania-neodymia compositions were sintered in air and in hydrogen. The compositions were studied by chemical, x ray, and differential thermal analyses. Solid solutions formed readily in air-sintered compositions in the range from 20 to 60 m/o Nd/sub 2/O/sub 3/. Solid solutions formed slowly and incompletely, up to 1650 deg C, in hydrogen-sintered compositions. There was good correlation between the differential thermal analyses and the chemical and x ray analyses. (auth)
Date: December 1, 1962
Creator: Kolar, D.; Handwerk, J.H. & Beals, R.J.
Partner: UNT Libraries Government Documents Department

Thermodynamic and nonstoichiometric behavior of the GdBa{sub 2}Cu{sub 3}O{sub x} system.

Description: Electromotive force (EMF) measurements of oxygen fugacities as a function of stoichiometry have been made on the GdBa{sub 2}Cu{sub 3}O{sub x} system in the temperature range {approximately}400-600 C by means of an oxygen titration technique with an yttria-stabilized zirconia electrolyte. Equations for the variation of oxygen partial pressure with composition and temperature have been derived from our EMF measurements. The shape of the 400 C isotherms as a function of oxygen stoichiometry for the Gd and Nd cuprate systems suggests the presence of miscibility gaps at values of x that are higher than those in the YBa{sub 2}Cu{sub 3}O{sub x} system. For a given oxygen stoichiometry, oxygen partial pressures above Gd-123 and Nd-123 cuprate systems are higher (above x = 6.5) than that for the Y-123 system. A thermodynamic assessment and intercomparison of our partial pressure measurements with the results of related measurements will be presented.
Date: September 29, 1998
Creator: Tetenbaum, M.
Partner: UNT Libraries Government Documents Department

Neutron and Raman scattering studies of surface adsorbed molecular vibrations and bulk phonons in ZrO{sub 2} nanoparticles

Description: Inelastic neutron scattering was used to study the phonon densities of states of zirconia nanoparticles, the O-H stretch vibrations of physisorbed water molecules, and chemisorbed hydroxyl groups on the surface. Raman scattering was also used to measure the zone-center phonon modes. The observed distinct phonon frequencies and band widths at 10-120 meV reflect the different crystalline symmetries and compositional fluctuations in the small grain and interfacial regions of monoclinic ZrO{sub 2}, tetragonal or mixed cubic and tetragonal rare-earth-modified zirconia. The dynamics of water and hydroxyl groups on varying local structures of these zirconias result in the different frequencies of the O-H stretch vibrations at 400-600 meV.
Date: December 31, 1996
Creator: Ozawa, Masakuni; Suzuki, Suguru; Loong, C.K. & Nipko, J.C.
Partner: UNT Libraries Government Documents Department

Synthesis and characterization of novel group VI metal (Mo, W) nitride and oxide compounds

Description: Investigations into the preparation of tungsten nitrides have involved the synthesis of molecular precursors, and their conversion to tungsten nitrides at relatively low temperatures. Two interesting molecular precursors, [WNCl{sub 3}{center_dot}NCCH{sub 3}]{sub 4} and WN(N{sub 3}){sub 3}{center_dot}xNCCH{sub 3}, have been prepared and characterized. The molecular structure of the first consists of a W{sub 4}N{sub 4} tetrameric core with multiple and single W-N bonds arranged in an alternating fashion. Three new solid state phases, amorphous W{sub 3}N{sub 5}, cubic WN, and W{sub 2}N{sub 2}(C{sub 2}N{sub 2}), have been discovered by solid state and chemical vapor transport reactions. The structures have been investigated. A systematic study in the Ln{sub 2}O{sub 3}-MoO{sub 3}-Mo (Ln = La, Ce, Pr, Nd, Sm) system has been explored to better understand LnMo{sub 8}O{sub 14}. The study has shown that the sizes of the rare-earth cations affect the formation of these phases. Larger cations (La, Ce, and Pr) aid in the formation of trans-Mo{sub 8} bicapped octahedra, and the smaller cations (Nd, Sm) only stabilize the cis-Mo{sub 8} bicapped octahedra. Magnetic susceptibility measurements have indicated that no effective moment contribution arises from the Mo{sub 8} metal clusters, even though the cis-Mo{sub 8} cluster in LnMo{sub 8}O{sub 14}, containing all cis-Mo{sub 8} octahedra, apparently contains an odd number of electrons (23). Electrical resistivity measurements and electronic structure calculations have shown that the LnMo{sub 8}O{sub 14} compounds containing cis-Mo{sub 8} clusters are metallic, and the LnMo{sub 8}O{sub 14} compounds containing a 1:1 ratio of cis- to trans-Mo{sub 8} clusters are semiconducting.
Date: February 23, 1998
Creator: Zhang, Z.
Partner: UNT Libraries Government Documents Department

Layered CMR manganites: Structure, properties, and unconventional magnetism

Description: Neutron powder diffraction studies of the layered compounds R{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}, (R = La, Pr, Nd), RSr{sub 2}Mn{sub 2}O{sub 7} (R = Pr, Nd), and La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} show that the degree of distortion of the MnO{sub 6} octahedra do not correlate with the appearance of a metal-insulator (MI) transition in these compounds. Instead, the in-plane Mn-O bond length appears to be a better indicator of the electronic behavior. Detailed bulk magnetization studies on single crystal La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} show that there are three magnetic regimes as a function of temperature: paramagnetic insulator, short-range ordered (SRO) ferromagnet, and long-range ordered (LRO) ferromagnet. Scaling analysis indicates that a 2D finite-size XY model is an appropriate description of the magnetic state in the SRO regime.
Date: 1997
Creator: Mitchell, J. F.; Argyriou, D. N.; Potter, C. D.; Jorgensen, J. D.; Hinks, D. G. & Bader, S. D.
Partner: UNT Libraries Government Documents Department

Superconductivity and structure in La{sub 2{minus}x}M{sub x}CuO{sub 4}, M=Ba, Sr, and (Nd,Sr)

Description: The identification of charge stripes in La{sub 2{minus}x{minus}y}Nd{sub y}Sr{sub x}CuO{sub 4} (Nd-214) has reenergized research on the original high transition temperature {Tc} superconductor, La{sub 2{minus}x}Ba{sub x}CuO{sub 4} (Ba-214), and related compounds. Early in the study of Ba-214, a low temperature phase transition was associated with changes in electrical properties. An apparent suppression of {Tc} near Ba x=0.125, was initially associated with a first order low temperature phase transformation. However, it was later shown that only very near Ba x=0.125 was {Tc} reduced markedly, and that the relationship between crystal structure and {Tc} is more complicated. This review well describe the low temperature crystal structures and microstructures, as well as the superconducting properties as determined from low field (1-100G) dc magnetometer measurements for Ba-214, Nd-214, and La{sub 2{minus}x}Sr{sub x}CuO{sub 4} (Sr-214). The authors will also describe some work in the related La{sub 2{minus}x}Ca{sub x}CuO{sub 4} (Ca-214). A basic knowledge of the interactions among superconductivity and low temperature phases will allow one to better understand the significance of the underlying charge stripe phases.
Date: January 21, 2000
Creator: Moodenbaugh, A. R.
Partner: UNT Libraries Government Documents Department