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in subjects: "Transition Element Compounds 360204* -- Ceramics, Cermets, & Refractories-- Physical Properties"

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Growth, preparation, and dielectric properties of monodomain single crystal PbTiO sub 3

A method is described for obtaining monodomain PbTiO{sub 3} single crystals with high electrical resistivity (10{sup 10}{Omega} cm) and low dielectric frequency dispersion. The single crystals of PbTiO{sub 3} were grown by flux solution method. Space charge related defects, which result in the large dielectric frequency dispersion, were eliminated by heat treatments. 90{degrees} domains were removed by applying a unidirectional compressive stress along the <100> crystallographic direction. The … more

Date: May 1, 1992

Creator: Li, Z.; Xu, X. Z.; Dai, X. H.; Lam, D. J. & Chan, S. K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Nonlinear optical properties of new KTiOPO sub 4 isostructures

The atomic structures of the nonlinear optical materials potassium titanyl phosphate (KTiOPO{sub 4}, or KTP) and potassium titanyl arsenate (KTiOAsO{sub 4}) feature one-dimensional channels through which the potassium ions are relatively free to migrate. Ion exchange results when these materials are immersed in molten salts containing alkali metal ions. Sodium, lithium and silver all exchange readily for K{sup +} single crystals of both KTP and KTA to yield the exchanged derivatives Na{sub .95}… more

Date: January 1, 1991

Creator: Phillips, M. L. F.; Harrison, W. T. A. & Stucky, G. D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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The use of BaF sub 2 buffer layers for the sputter-deposition of TlCaBaCuO thin-film superconductors

Thin films of the Tl-based superconductors often have relatively poor properties because of film/substrate interdiffusion which occurs during the anneal. We have therefore investigated the use of BaF{sub 2} as a diffusion barrier. TlCaBaCuO thin films were deposited by dc magnetron sputtering onto MgO <100> substrates, both with and without an evaporation-deposited BaF{sub 2} buffer layer, and post-annealed in a Tl over-pressure. Electrical properties of the films were determined by four-point … more

Date: January 1, 1989

Creator: Hubbard, K. M.; Arendt, P. N.; Brown, D. R.; Cooke, D. W.; Elliott, N. E.; Farr, J. D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Spectral weight changes at the superconducting transition of Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8+. delta

An overview of our gap studies in high-{Tc} superconductors is presented for the workshop on Fermiology of high-{Tc}'s. The work is centered on the study of single crystal Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. In a conventional BCS superconductor, a superconducting gap {Delta} is formed when the near Fermi edge electrons condense to form Cooper pairs at low temperatures. As the material goes superconducting the density of states is modified such that the spectral intensity in the regio… more

Date: January 1, 1991

Creator: Dessau, D. S.; Shen, Z. X.; Wells, B. O.; Spicer, W. E. (Stanford Univ., CA (United States). Stanford Electronics Labs.) & Arko, A. J. (Los Alamos National Lab., NM (United States))

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Superconductivity in solid solutions of transition metal carbides. [NbC-TaC]

No Description Available.

Date: June 10, 1964

Creator: Wells, M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Thermal Conductivity of Quasi-One Dimensional Conductors

The thermal conductivity of K{sub 0.3}M{sub 0}O{sub 3}, (TaSe{sub 4}){sub 2}I and TaS{sub 3} have been studied. Together with the specific heat measurement, the anomaly observed in thermal conductivity around the Peierls transition is believed to be due to extra heat carried by the 2k{sub F} soft phonons. The field dependent thermal conductivity of the blue bronze and TaS{sub 3} have also been measured by two distinct methods, and found to be independent of applied electric field. 17 refs., 3 f… more

Date: January 1, 1989

Creator: Kwok, R.S. (California Univ., Los Angeles, CA (USA). Dept. of Physics) & Brown, S.E. (Los Alamos National Lab., NM (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Tricritical behavior in the ferromagnetic superconductor ErRh/sub 4/B/sub 4/

A new tricritical point on the phase boundary between the superconducting vortex phase and the normal paramagnetic phase of ErRh/sub 4/B/sub 4/ is presented. The microscopic origin of the tricritical point and the expected tricritical behavior are briefly discussed.

Date: August 1, 1985

Creator: Crabtree, G.W.; Kalia, R.K.; Hinks, D.G.; Behroozi, F. & Tachiki, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Study of the defect structure of ''pure'' and doped nonstoichiometric CeO/sub 2/. Final report, January 1, 1965--May 31, 1977

The defect structure and transport properties of defects in nonstoichiometric oxides was studied based on their electrical and thermodynamic behavior. Similar studies were also made on doped-nonstoichiometric oxides to determine the effect of the ionic radii, valence and concentration of the dopant cation on the nonstoichiometric defect structure and the transport properties of these defects. The thermodynamic and electrical property study on ''pure'' and doped-nonstoichiometric CeO/sub 2//sub … more

Date: November 1, 1977

Creator: Blumenthal, R.N.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Low-temperature resistivity of amorphous iron--phosphorus alloys

No Description Available.

Date: September 1, 1975

Creator: Logan, J. & Yung, M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Photoemission in YbCu Sub 2 si Sub 2 : Problems With the Kondo Impurity Model

We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J=7/2) final state peak, centered 60meV below the Fermi level {epsilon}{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with the recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. 7 refs., 3 figs.

Date: January 1, 1991

Creator: Lawrence, J. M.; Arko, A. J.; Joyce, J. J.; Canfield, P. C.; Fisk, Z. & Thompson, J. D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Structure and properties of nanophase TiO/sub 2/

Ultrafine-grained, nanophase samples of TiO/sub 2/ (rutile) were synthesized by the gas-condensation method and subsequent in-situ compaction, and then studied by transmission electron microscopy, Vickers hardness measurements, and positron annihilation spectroscopy as a function of sintering temperature. The nanophase compacts densified rapidly above 500/sup 0/C, with only a small increase in grain size. The hardness values obtained by this method are comparable to or greater than coarser-grai… more

Date: July 1, 1987

Creator: Siegel, R.W.; Hahn, H.; Ramasamy, S.; Zongquan, Li; Ting, Lu & Gronsky, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Neutron scattering studies of spin correlations in metallic YBa sub 2 Cu sub 3 O sub 6+x

Electron-electron correlations appear to play an important role in determining many properties of the copper oxide superconductors. One significant consequence of the electronic coulomb interactions are spin correlations. In the insulating phases of the layered cuprates, where the antibonding band due to Cu 3d{sub x}{sup 2} {minus} {sub y}{sup 2}-O 2p{sub {sigma}} hybridization in the CuO{sub 2} planes is half filled, long-range antiferromagnetic order is observed. As the layers are doped with … more

Date: January 1, 1991

Creator: Tranquada, J.M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Tunneling spectroscopy measurements on low-leakage junctions of Nd sub 1. 85 Ce sub 0. 15 CuO sub 4 minus y and Ba sub 1 minus x K sub x BiO sub 3

Tunneling measurements are reported for Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}y} (NCCO) and Ba{sub 1{minus}x}K{sub x}BiO{sub 3} (BKBO) using the point-contact technique with a Au or Nb tip. The junctions display very low zero-bias conductance values of <1% for BKBO and {approximately}10% for NCCO, and show sharp conductance peaks at eV = {plus minus} {Delta}. In the case of BKBO, the normalized conductance can be fit with a BCS density of states with thermal smearing only. The energy gaps are… more

Date: January 1, 1990

Creator: Zasadzinski, J. F.; Tralshawala, N.; Huang, Qiang; Gray, K. E. & Hinks, D. G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Microprobe field measurements in ErRh/sub 4/B/sub 4/

A small hyperfine field at Fe impurity sites in ErRh/sub 4/B/sub 4/ at 0.38 K was observed. The magnitude of the field at the nonmagnetic impurity sites was 0.5 T. This hyperfine field reflects spin order at the Er sites but the sensitivity of the probe technique employed turned out to be marginal for investigating quantitatively the shape of the ordering curve with temperature near and below T/sub c2/.

Date: January 1, 1979

Creator: Taylor, R. D. & Willis, J. O.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Wear and friction of thin film high temperature oxide superconductors

We have examined the sliding properties of a Nd-Fe-B magnet against a thin film YBa/sub 2/Cu/sub 3/O/sub 7/ superconductor. Pin-on-disk experiments were performed at room temperature and in normal air using a 10 mm magnetic Nd-Fe-B ball loaded to 31.22 g and a sliding speed of approximately 0.57 cm/sec. Such condition produced a steady state friction coefficient of 1.1 +- 0.3. Wear rate measurements indicated that Nd-Fe-B will wear YBa/sub 2/Cu/sub 3/O/sub 7/ at a rate 1.3 /times/ 10/sup /minus… more

Date: January 1, 1989

Creator: Nastasi, M.; Hirvonen, J.-P. & Toivanen, R.O.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Rietveld refinement with time-of-flight powder diffraction data from pulsed neutron sources

The recent development of accelerator-based pulsed neutron sources has led to the widespread use of the time-of-flight technique for neutron powder diffraction. The properties of the pulsed source make possible unusually high resolution over a wide range of d spacings, high count rates, and the ability to collect complete data at fixed scattering angles. The peak shape and other instrument characteristics can be accurately modelled, which make Rietveld refinement possible for complex structures… more

Date: October 1, 1990

Creator: David, W.I.F. (Rutherford Appleton Lab., Chilton (UK)) & Jorgensen, J.D. (Argonne National Lab., IL (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Nuclear relaxation rates at copper and oxygen sites in YBa/sub 2/Cu/sub 3/O/sub 7/

We report NMR measurements of the nuclear relaxation rate at all copper and oxygen sites in magnetically aligned powder samples of YBa/sub 2/Cu/sub 3/O/sub 7/. There is no peak in the oxygen relaxation rate below T/sub c/ at any oxygen site supporting the possibility that d-wave pairs are formed in the superconducting state. Comparison of the oxygen and copper rates in the planes reveals a characteristic temperature greater than T/sub c/. 6 refs., 2 figs.

Date: January 1, 1989

Creator: Hammel, P. C.; Takigawa, M.; Heffner, R. H.; Fisk, Z. & Ott, K. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Microstructure of epitaxial YBa sub 2 Cu sub 3 O sub 7 thin films

Thin epitaxial films of YBa{sub 2}Cu{sub 3}O{sub 7} on single crystal substrates have been prepared in situ by laser ablation and by post situ annealing of evaporated films of Cu, Y and BaF{sub 2}. Substrates include (001) SrTiO{sub 3}, LaGaO{sub 3}, and LaAlO{sub 3}. For both in situ and post situ annealed films, epitaxial (001) grains of YBa{sub 2}Cu{sub 3}O{sub 7} form near the substrate but (100) and (010) grains tend to nucleate for thicknesses greater than {approximately}0.5{mu}m. 90{degr… more

Date: January 1, 1990

Creator: Mitchell, T.E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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The derivation of effective spin Hamiltonians and the origin of the magnetic field induced transition in orthormbic La sub 2 CuO sub 4

La{sub 2}CuO{sub 4} undergoes a magnetic field induced transition in a field of {approx}5.7 Tesla at low temperatures. The origin of this transition is the Dzyaloshinskii-Moriya interaction which is present in effective spin Hamiltonians for systems of sufficiently low symmetry, and, which leads to weak ferromagnetism in the CuO planes in La{sub 2}CuO{sub 4}. It is shown here how this interaction depends on symmetry and how its form changes with structural phase transitions which occur in compo… more

Date: January 1, 1991

Creator: Coffey, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Anomalous temperature dependence of Cu NMR line width and magnetization in YBa/sub 2/Cu/sub 3/O/sub 7/minus/delta/

We report an anomalous temperature dependence of the magnetization and the NMR line width at the planar Cu(2) and oxygen sites in the mixed state of aligned YBa/sub 2/Cu/sub 3/O/sub 7-delta/ powder at relatively high field (greater than or equal to30 kOe), where hysteresis of the magnetization due to flux pinning is not important. Both the magnetization and the NMR line width at all sites show a steep increase at low temperature. We found a much larger line width at Cu(2) sites than at oxygen s… more

Date: January 1, 1989

Creator: Takigawa, Masashi; Hammel, C. P.; Heffner, R. H.; Fisk, Z.; Thompson, J. D. & Maley, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Characterization of hydrogen species on metal-oxide surfaces by electron-stimulated desorption: TiO/sub 2/ and SrTiO/sub 3/*

The hydrogen species on TiO/sub 2/ and SrTiO/sub 3/ have been characterized using the site specificity of electron-excited Auger Stimulated Desorption (ASD). Hydrogen is found to be bonded to surface Ti's in hydride-type bonds, to subsurface or bridgebonded O's in a hydroxyl-like bond, or be part of a surface hydroxyl. On SrTiO/sub 3/ the Ti-H and surface OH species are also found plus a high density of Sr-H and very little Sr-OH bonding. The general features of ASD, both electron- and photon-e… more

Date: January 1, 1979

Creator: Knotek, M.L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Neutron diffraction study of the magnetic ordering of the Cu sup ++ spins in Nd sub 1. 5 Ba sub 1. 5 Cu sub 3 O sub 6+x

Elastic neutron scattering experiments performed on single crystals of Nd{sub 1.5}Ba{sub 1.5}Cu{sub 3}O{sub 6+y} reveal successive antiferromagnetic (AF) ordering of the Cu{sup ++} spins. The as grown single crystals show an AF structure characterized by a Neel temperature T{sub N1} {approximately} 390K and a magnetic wave vector (1/2 1/2 0) referring to the tetragonal structure of NdBa{sub 2}Cu{sub 3}O{sub 6}. As the temperature is lowered below T{sub N2} {approximately} 150K, a spin reorienta… more

Date: January 1, 1991

Creator: Moudden, A. H.; Hennion, B.; Schweiss, P.; Gehring, P. M. & Shirane, G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Elastic after-effect due to oxygen relaxation in YBa sub 2 Cu sub 3 O sub 7-. delta. above Tc

Isothermal elastic after-effect measurements to obtain relaxation times for the stress-induced motion of oxygen in YBa{sub 2}Cu{sub 3}O{sub 7 {minus}{delta}} have been made from 50{degree}C to 110{degree}C. These results extend our previous internal friction measurements of the same oxygen relaxation to lower temperatures. The combined results, which cover nine orders of magnitude in relaxation time, show a classical Arrhenius temperature dependence, activation, energy Q=1.3 {plus minus} 0.01 e… more

Date: January 1, 1990

Creator: Cost, J.R.; Armstrong, P.E. (Los Alamos National Lab., NM (USA)); Poeppel, R.B. (Argonne National Lab., IL (USA)) & Stanley, J.T. (Arizona State Univ., Tempe, AZ (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Re-analysis of photoemission data for CuO: Revision of the configuration-energy scheme for cuprate materials

The author has recently carried out a very careful analysis of photoemission and inverse photoemission (BIS) data for CuO, probably the most refined and thorough such analysis for any transition-metal compound to date. This has led to a configuration-energy scheme for cuprate materials which is quite different from a generally-accepted one, due largely to Sawatzky and co-workers. For example, it is commonly believed that the doping holes in La{sub 2-x}Sr{sub x}CuO{sub 4} are hosted almost entir… more

Date: January 1, 1991

Creator: Brandow, B.H.

Item Type: Article

Partner: UNT Libraries Government Documents Department