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EXAFS studies of lanthanide coordination in crystalline phosphates and amorphous phytates

Description: As part of the DOE Efficient Separations and Processing Integrated Program, techniques are being developed to stabilize radioactive and hazardous contaminants to prevent their migration from buried wastes. This report is part of a study to immobilize actinide ions in the near-surface environment by reacting them with organophosphorus complexants that decompose to phosphates. Nd and Gd ions were used as models for Pu, Am, and Cm ions; phytic acid was used as the complexant. Solid Nd and Gd phytates were prepared and the coordination characterized by EXAFS.
Date: December 31, 1995
Creator: Morss, L.R.; Schmidt, M.A.J. & Nash, K.L.
Partner: UNT Libraries Government Documents Department

Charge Stripes and Antiferromagnetism in Copper-Oxide Superconductors

Description: Superconducting cuprate compounds are obtained by doping holes into antiferromagnetic insulators. Neutron scattering studies have provided evidence that the doped holes tend to segregate into charge stripes, which act like domain walls between antiferromagnetic regions. The interaction between the spatially segregated holes and the magnetic domains may be responsible for the strong pairing interaction found in the cuprates.
Date: December 31, 1997
Creator: Tranquada, J.M.
Partner: UNT Libraries Government Documents Department

Scanning SQUID microscopy on polycrystalline SmFeAsO_{0.85} and NdFeAsO_{0.94}F_{0.06}

Description: The order parameter of the recently-discovered ferric arsenide family of superconductors remains uncertain. Some early experiments on polycrystalline samples suggested line nodes in the order parameter, however later experiments on single crystals have strongly supported fully-gapped superconductivity. An absence of nodes does not rule out unconventional order: {pi} phase shifts between the separate Fermi sheets and time-reversal symmetry-breaking components in the order parameter remain possibilities. One test for unconventional order is scanning magnetic microscopy on well-coupled polycrystalline samples: d- or p-wave order would result in orbital frustration, leading to spontaneous currents and magnetization in the superconducting state. We have performed scanning SQUID microscopy on SmFeAsO{sub 0.85} and NdFeAsO{sub 0.94}F{sub 0.06}, and in neither material do we find spontaneous orbital currents, ruling out p- or d-wave order.
Date: January 8, 2009
Creator: Hicks, Clifford W.; Lippman, Thomas M.; Moler, Kathryn A.; Huber, Martin E.; Ren, Zhi-An & Zhao, Zhong-Xian
Partner: UNT Libraries Government Documents Department

Limits on the Superconducting Order Parameter in NdFeAsO_{1-x}F_y from Scanning SQUID Microscopy

Description: Identifying the symmetry of the superconducting order parameter in the recently-discovered ferrooxypnictide family of superconductors, RFeAsO{sub 1-x}F{sub y}, where R is a rare earth, is a high priority. Many of the proposed order parameters have internal {pi} phase shifts, like the d-wave order found in the cuprates, which would result in direction-dependent phase shifts in tunneling. In dense polycrystalline samples, these phase shifts in turn would result in spontaneous orbital currents and magnetization in the superconducting state. We perform scanning SQUID microscopy on a dense polycrystalline sample of NdFeAsO{sub 0.94}F{sub 0.06} with T{sub c} = 48K and find no such spontaneous currents, ruling out many of the proposed order parameters.
Date: January 8, 2009
Creator: Hicks, Clifford W.; Lippman, Thomas M.; Huber, Martin E.; Ren, Zhi-An; Yang, Jie; Zhao, Zhong-Xian et al.
Partner: UNT Libraries Government Documents Department

Polarization dependence of two-photon transition intensities in rare-earth doped crystals

Description: A polarization dependence technique has been developed as a tool to investigate phonon scattering (PS), electronic Raman scattering (ERS), and two-photon absorption (TPA) transition intensities in vanadate and phosphate crystals. A general theory for the polarization dependence (PD) of two-photon transition intensities has been given. Expressions for the polarization dependent behavior of two-photon transition intensities have been tabulated for the 32 crystallographic point groups. When the wavefunctions for the initial and final states of a rare-earth doped in crystals are known, explicit PD expressions with no unknown parameters can be obtained. A spectroscopic method for measuring and interpreting phonon and ERS intensities has been developed to study PrVO{sub 4}, NdVO{sub 4}, ErVO{sub 4}, and TmVO{sub 4} crystals. Relative phonon intensities with the polarization of the incident and scattered light arbitrarily varied were accurately predicted and subsequently used for alignment and calibration in ERS measurements in these systems for the first time. Since ERS and PS intensities generally follow different polarization curves as a function of polar angles, the two can be uniquely identified by comparing their respective polarization behavior. The most crucial application of the technique in ERS spectroscopy is the establishment of a stringent test for the Axe theory. For the first time, the F{sub 1}/F{sub 2} ratio extracted from the experimental fits of the ERS intensities were compared with those predicted by theories which include both the second- and third-order contributions. Relatively good agreement between the fitted values of F{sub 1}/F{sub 2} and the predicted values using the second-order theory has been found.
Date: May 1, 1996
Creator: Le Nguyen, An-Dien
Partner: UNT Libraries Government Documents Department

Modulated spin and charge densities in cuprate superconductors

Description: Neutron scattering experiments have played a crucial role in characterizing the spin and charge correlations in copper-oxide superconductors. While the data are often interpreted with respect to specific theories of the cuprates, an attempt is made here to distinguish those facts that can be extracted empirically, and the connections that can be made with minimal assumptions.
Date: August 1, 1997
Creator: Tranquada, J.M.
Partner: UNT Libraries Government Documents Department

X-ray resonant exchange scattering of rare-earth nickel borocarbides

Description: The purpose of this thesis is to investigate the systematics of the microscopic magnetic order within a series of isostructural compounds and, at the same, to develop the relatively young experimental method of x-ray resonant exchange scattering (XRES). In this thesis, the author presents XRES studies of several rare-earth nickel borocarbides, RNi{sub 2}B{sub 2}C. He shows that XRES, similar to the neutron techniques, allows the determination of the orientation of the magnetic moment by measuring the Q-dependence of the scattered intensity of magnetic Bragg reflections. As samples in this study, he chose the recently discovered family of rare-earth nickel borocarbides, RNi{sub 2}B{sub 2}C, which display a wide variety of magnetic structures. Furthermore, in several of these materials, long range magnetic order coexists with superconductivity over some temperature range.
Date: October 8, 1997
Creator: Detlefs, C.
Partner: UNT Libraries Government Documents Department

Rare earth chalcogenides for use as high temperature thermoelectric materials

Description: In the first part of the thesis, the electric resistivity, Seebeck coefficient, and Hall effect were measured in X{sub y}(Y{sub 2}S{sub 3}){sub 1-y} (X = Cu, B, or Al), for y = 0.05 (Cu, B) or 0.025-0.075 for Al, in order to determine their potential as high- temperature (HT)(300-1000 C) thermoelectrics. Results indicate that Cu, B, Al- doped Y{sub 2}S{sub 3} are not useful as HT thermoelectrics. In the second part, phase stability of {gamma}-cubic LaSe{sub 1.47-1.48} and NdSe{sub 1.47} was measured periodically during annealing at 800 or 1000 C for the same purpose. In the Nd selenide, {beta} phase increased with time, while the Nd selenide showed no sign of this second phase. It is concluded that the La selenide is not promising for use as HT thermoelectric due to the {gamma}-to-{beta} transformation, whereas the Nd selenide is promising.
Date: January 2, 1996
Creator: Michiels, J.
Partner: UNT Libraries Government Documents Department

SOME OBSERVATIONS REGARDING RARE-EARTH LACTATES

Description: Lactates of all the rare earths except lanthanum, cerium, and praseodymium were prepared and studied. In the case of lanthanum, cerium, and praseodymium the laciates are apparently so soluble that they cannot be crystallized directly from aqueous solution. Products obtained by addition of anhydrous ethanol to sirupy solutions of the iight-rare-earth lactates were not well characterized and were deliquescent. Neodymium lactate trinydrate was prepared only by the addition of alcohol to a sirupy solution. Since it was not as deliquescent as the lactates of lanthanum, cerium, and praseodymium, some of its properties could be studied. The lactates of all the other rare earths, samarium through lutetium, as well as the lactate of yttrium, separated readily from aqueous media as trinydrates---the solubility of the hydrated lactate decreasing as the atomic number of the rare earth increased. Thermal decomposition of the crystalline lactates, except those of neodymium and samarium, proceeded through dihydrated and anhydrous states to a composition corresponding roughly to LnlacCOa at a temperature of about 290 to 300 deg C. Ln/ sub 2/(CO/sub 3/)/sub 3/ or Ln/sub 2/O(CO/sub 3/)/sub 2/ was obse rved. In order to make a comparison, thermal decomposition of the rareearth glycolates was studied also. Solubilities in water at both 20 and 60 deg C are tabulated. (auth)
Date: March 28, 1962
Creator: Powell, J.E. & Farrell, J.L.
Partner: UNT Libraries Government Documents Department

Solubility and speciation results from over- and undersaturation experiments on neptunium, plutonium, and americium in water from Yucca Mountain region well UE-25p {number_sign}1

Description: Solubility and speciation are important in understanding aqueous radionuclide transport through the geosphere. Results are compared from solubility and speciation experiments from oversaturation and undersaturation of {sup 237}NpO{sub 2{sup +}}, {sup 239}Pu{sup 4+}, and {sup 241}Am{sup 3+}/Nd{sup 3+} in a modified UE-25p-1 groundwater (from the Yucca Mountain region, Nevada, which is being investigated as a potential high-level nuclear waste disposal site) at 60 C and three pH values (6.0, 7.0, 8.5). In the oversaturation experiments, the solubility-controlling steady-state solids were identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The characterized solids were then reintroduced into fresh solutions of the modified UE-25p-1 groundwater to approach the steady state from undersaturation. For the undersaturation experiments, the solubility-controlling steady-state solids were also identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The Np solubility decreased with increasing pH in both the over- and undersaturation experiments. The steady-state concentrations from the two experiments agreed to within an order of magnitude. Pu concentrations from over- and undersaturation agree very well in the pH 6 and 7 experiments. The pH 8.5 oversaturation experiment resulted in a steady-state concentration one order of magnitude above its undersaturation counterpart. For the Am/Nd solutions, the pH 6 and pH 7 experiments resulted in equivalent steady-state concentrations from both over and undersaturation. The pH 8.5 oversaturation experiment was 100 times more soluble than its undersaturation counterpart. 48 refs.
Date: November 1, 1995
Creator: Nitsche, H.; Roberts, K.; Becraft, K.; Prussin, T.; Keeney, D.; Carpenter, S.A. et al.
Partner: UNT Libraries Government Documents Department

Optical properties of tetravalent uranium in the solid state

Description: The optical spectra are fit to the parameters of a phenomenological Hamiltonian from which a calculated spectrum is obtained. The goodness of fit is determined by the value of sigma (cm/sup -1/), the rms deviation. The sigma and crystal field are tabulated for U/sup 4 +/ in various host crystals, Pr/sup 3 +/ or Nd/sup 3 +/ in various crystals, and the free ion U/sup 4 +/. The rms deviation sigma for the U/sup 4 +/ compounds is much worse on the average than for the Pr/Nd examples. There appears to be a correlation between a poor fit and a large sigma, and a large crystal field. 28 refs., 1 tab. (DLC)
Date: April 1, 1987
Creator: Edelstein, N.
Partner: UNT Libraries Government Documents Department

Production of a handbook: Nd-doped glass spectroscopic and physical properties

Description: The production of Lawrence Livermore Laboratory publication M-095, a handbook containing a collection of properties of Nd/sup 3 +/-doped glasses, is described. The pros and cons of the method are presented. The bulk of the report is contained in detailed appendices which cover major aspects of production.
Date: April 9, 1979
Creator: Saroyan, R.A.
Partner: UNT Libraries Government Documents Department

Fundamental magnetic studies of iron-rare-earth-metalloid alloys

Description: This research is focused on the synthesis of new iron-rare-earth magnetic phases which may have significant technological properties. An important aim is to investigate new methods for producing these materials such as melt spinning and sputtering plus specific heat treatments. Studies are made of the relationship between microstructure and properties such as coercivity, spontaneous magnetization, and anisotropy (magnitude and direction) in bulk and thin film samples. Our goal is to understand these relatively complex materials on the basis of fundamental electronic structure, theory is of itinerant magnetism and localized 4f electronic states, and the microstructural effects which control the extrinsic properties. To achieve this a broad range of experiments and calculations are performed. In the following we describe briefly some of our recent accomplishments, with emphasis on work performed in the last six months.
Date: January 1, 1989
Creator: Sellmyer, D.J.
Partner: UNT Libraries Government Documents Department

Low-temperature ceramic radioactive waste form characteriztion of supercalcine-based monazite-cement composites

Description: Simulated radioactive waste solidification by a lower temperature ceramic (cement) process is being investigated. The monazite component (simulated by NdPO/sub 4/) of supercalcine-ceramic has been solidified in cement and found to generate a solid form with low leachability. Several types of commercial cements and modifications thereof were used. No detectable release of Nd or P was found through characterizing the products of accelerated hydrothermal leaching at 473/sup 0/K (200/sup 0/C) and 30.4 MPa (300 bars) pressure.
Date: April 18, 1980
Creator: Roy, D.M.; Wakeley, L.D. & Atkinson, S.D.
Partner: UNT Libraries Government Documents Department

Vapor phase spectroscopy of complex lanthanide halide--aluminum halide molecular species

Description: The absorption spectrum of ErCl/sub 3/ (AlCl/sub 3/)/sub x/ vapor complex was measured and analyzed using the Judd-Ofelt theory. Structural correlations in other AlCl/sub 3/ vapor complexes and radiation emission are discussed. Fluorescence of TbCl/sub 3/ (AlCl/sub 3/)/sub x/ vapor complex and in the NdCl/sub 3/ (AlCl/sub 3/)/sub x/ system were studied. (DLC)
Date: January 1, 1977
Creator: Carnall, W T; Hessler, J P; Williams, C W & Hoekstra, H R
Partner: UNT Libraries Government Documents Department

Thermoelectric Materials Evaluation Program. Annual technical report for fiscal years 1980/1981

Description: During this contract period, all major contract milestones were accomplished. This included the fabrication and test of two N-legs, three single-couple assemblies, and three six-couple modules. The BOL performance objective was met and the degradation rate of 0.3%/1000 hours was nearly met for elements, couples, and modules. Considerable effort was spent in understanding the ratcheting phenomenon on the P-leg (cycle resistance changes at the hot end). A designed series of experiments was performed to identify the effect of contact pressure and hot junction temperature on P-leg degradation (time to onset of ratcheting, etc.). At the end of the fiscal year the results of this experimentation indicated that the theoretical estimate of an acceleration factor of twenty-one for module tests (915/150/sup 0/C, 14.0 amperes) is valid.
Date: April 1, 1981
Creator: Hinderman, J.D.
Partner: UNT Libraries Government Documents Department

Use of oxide targets in 2-keV average neutron capture measurements

Description: Large samples (approx. = 10 to 100 grams) are usually required for 2-keV filtered-beam measurements and such samples invariably come in the oxide form. Monte Carlo calculations show that the resulting neutron spectrum is degraded by approx. = 0.2 keV in a /sup 145/Nd/sub 2/O/sub 3/ sample. Otherwise, oxide samples are acceptable for such measurements.
Date: January 1, 1981
Creator: Tang, J.S. & Raman, S.
Partner: UNT Libraries Government Documents Department

Magnetic correlations in high T/sub c/ oxides: Neutron scattering studies

Description: A review is given of current neutron scattering experiments on La/sub 2/minus/x/Sr/sub x/CuO/sub 4/ and Nd/sub 2/minus/x/Ce/sub x/CuO/sub 4/. Incommensurate magnetic excitations are observed in a high quality single crystal of La/sub 1.85/Sr/sub 0.15/CuO/sub 4/, which exhibits a sharp superconducting transition at 33 K. The study of magnetic correlations in the electron-superconductor Nd/sub 2/minus/x/Ce/sub x/CuO/sub 4/ is now being carried out. 18 refs., 7 figs.
Date: January 1, 1989
Creator: Shirane, G.
Partner: UNT Libraries Government Documents Department

Platinum particles in the Nd:doped disks of phosphate glass in the Nova laser

Description: The disks of Nd:doped phosphate glass in the amplifiers of the Nova laser contain platinum particles with sizes ranging from <5 ..mu..m (detection limit) to about 100 ..mu..m. The particle density varies from about 0.01 to 1.0 cm/sup -3/. These particles cause fractures when irradiated at fluences >2.5 J/cm/sup 2/ delivered in 1-ns, 1054-nm pulses. Under repeated irradiation at 5 to 7 J/cm/sup 2/, damage from small (<5 ..mu..m) particles asymptotically approaches a limiting size, but damage surrounding the larger particles grows steadily. The damage threshold fluence, 2.5 J/cm/sup 2/, corresponds to operation of Nova at one-half the desired output for pulse durations longer than 1 nsec. Operation at higher fluences causes accumulation of damage in the output amplifiers and requires replacement of the disks in those amplifiers on an accelerated schedule. 9 refs., 5 figs.
Date: February 20, 1986
Creator: Milam, D.; Hatcher, C.W. & Campbell, J.H.
Partner: UNT Libraries Government Documents Department

New approaches to the study of lanthanide/actinide chloride: aluminum chloride vapor phase complexes

Description: The spectrophotometric technique for vapor density measurements of complexed metal ions has been reformulated to account for temperature dependent effects and multi-species systems. Analysis of vapor pressure information indicates that the NdCl/sub 3/--AlCl/sub 3/ and HoCl/sub 3/--AlCl/sub 3/ systems are adequately explained by the existence of three vapor species. The two higher molecular weight complexes LnAl/sub 4/Cl/sub 15/ and LnAl/sub 3/Cl/sub 12/ were first proposed by Oeye and Gruen. The newly identified higher temperature species, HoAl/sub 2/Cl/sub 9/, contributes significantly to the vapor density above 750/sup 0/K and below 3 atm of dimer pressure. In view of the consistency of the Nd/sup +3/ and Ho/sup +3/ chemistry the data for the Sm/sup +3/ system should be viewed with reservation. A new method for vapor density measurements involving use of radioactive tracers has been discussed in terms of its applicability to the study of (Ln,An)Cl/sub 3/(AlCl/sub 3/)/sub x/ systems.
Date: January 1, 1979
Creator: Peterson, E.J.; Caird, J.A.; Carnall, W.T.; Hessler, J.P.; Hoekstra, H.R. & Williams, C.W.
Partner: UNT Libraries Government Documents Department

Investigation of highly reduced halides of cerium, praseodymium, and neodymium

Description: Results of studies of the light lanthanide chlorides, Ce, Pr, and Ne are presented and discussed. It was found that to form a monohalide in these systems the following conditions are required: (1) no stable +2 state; (2) at least 2 outer electrons (or a very low promotion energy to a state with 2 electrons); (3) a low value of rare earth sublimation energy. The stability of CsReCl/sub 3/ is dependent on the following: strong metal-metal interactions; or a highly stable +2 state (large value of negative rare earth sublimation energy and positive rare earth ionization energy). (JRD)
Date: August 1, 1978
Creator: Lawson, L.D.
Partner: UNT Libraries Government Documents Department

Characterization of high power flashlamps and application to Nd:glass laser pumping

Description: Detailed spectral and temporal measurements of the output radiation from Xe flashlamps are reported together with their use in predicting the pumping efficiency of Nd-doped laser glass. We have made absolute spectral-intensity measurements for 0.5, 1.5, and 4.2-cm-bore flashlamps for input powers ranging from 5 to 90 kW/cm/sup 2/ and pulselengths of 600 ..mu..s. Under quasi-stationary conditions these flashlamps emit essentially identical spectra when excited at equal input power per unit-area of the bore. This behavior is characteristic of an optically-thick radiator although it is not completely clear why flashlamps should behave this way. A simple model is also described which accounts for the transient response of flashlamps by characterizing the output spectra and radiation efficiencies in terms of the radiant output power rather than the electrical input power. 23 refs., 16 figs.
Date: January 17, 1986
Creator: Powell, H.T.; Erlandson, A.C. & Jancaitis, K.S.
Partner: UNT Libraries Government Documents Department