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Articles 601 - 630 of 1337

Full-Text Articles in Ceramic Materials

Charge And Spin Structure In Yba2cu3o6.35, Herbert A. Mook, Pengcheng Dai, Fatih Dogan Mar 2002

Charge And Spin Structure In Yba2cu3o6.35, Herbert A. Mook, Pengcheng Dai, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering has been used to measure the charge and spin structure in the highly underdoped superconductor YBa2Cu3O6.35. Incommensurate static charge ordering is found that remains at high temperatures. The magnetic pattern is complex with a resonance and incommensurate structure observed at low temperatures. The results clarify the role of striped phases in YBa2Cu3O6+x superconductors.

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Charge And Spin Structure In Yba2⁢Cu3⁢O6.35, Herbert A. Mook, Pengcheng Dai, Fatih Dogan Feb 2002

Charge And Spin Structure In Yba2⁢Cu3⁢O6.35, Herbert A. Mook, Pengcheng Dai, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering has been used to measure the charge and spin structure in the highly underdoped superconductor YBa2⁢Cu3⁢O6.35. Incommensurate static charge ordering is found that remains at high temperatures. The magnetic pattern is complex with a resonance and incommensurate structure observed at low temperatures. The results clarify the role of striped phases in YBa2⁢Cu3⁢O6+x superconductors.

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Iron Phosphate Glass For The Vitrification Of Ineel Sodium Bearing Waste And Hanford Low Activity Waste, Robert Douglas Leerssen Jan 2002

Iron Phosphate Glass For The Vitrification Of Ineel Sodium Bearing Waste And Hanford Low Activity Waste, Robert Douglas Leerssen

Masters Theses

"The current study investigates the feasibility of using iron phosphate glass for the immobilization of nuclear wastes that have limited solubility in the current borosilicate glass used for vitrification. These wastes contain elements such as sulfur and phosphorus, which have proven problematic (causing phase separation at >1 wt%) for vitrification in borosilicate glasses, as well as having a high soda content (50-75 wt%) which also limits wasteloading"--Abstract, page iv.

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Reactive Hot Pressing Of Alumina-Molybdenum Disilicide Composites, William Fahrenholtz, Ronald E. Loehman, Kevin G. Ewsuk Jan 2002

Reactive Hot Pressing Of Alumina-Molybdenum Disilicide Composites, William Fahrenholtz, Ronald E. Loehman, Kevin G. Ewsuk

Materials Science and Engineering Faculty Research & Creative Works

Al2O3-MoSi2 Composites Were Prepared by Reactive Hot Pressing using Molybdenum, Aluminum, and Mullite Powders as Precursors. the Gibbs Free Energy Was Highly Negative for the Composite-Forming Reaction, Which Indicated that the Products Were Stable Relative to the Reactants. after the Reaction, the Composites Had High Relative Density, ∼96%. based on the Composite-Forming Reaction, the Composites Should Have Contained 18 Vol% MoSi2 in an Al2O3 Matrix. Scanning Electron Microscopy Revealed that the MoSi2 Inclusions Were Elongated, with an Average Thickness of ∼5 Μm and Inclusion Lengths that Ranged from 5 to 50 …

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Charge Fluctuations In Yba2cu3o6+X Superconductors, Herbert A. Mook, Fatih Dogan Nov 2001

Charge Fluctuations In Yba2cu3o6+X Superconductors, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Striped phases in which spin and charge separate into different regions in the material have been proposed to account for the unusual properties of the high-Tc cuprate superconductors. The driving force for a striped phase is the charge distribution, which self-organizes itself into linear regions. In the highest Tc materials such regions are not static but fluctuate in time. Neutrons, having no charge, cannot directly observe these fluctuations but they can be observed indirectly by their effect on the phonons. Neutron scattering measurements have been made using a specialized technique to study the phonon line shapes in four crystals …

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Anisotropy In The Electronic Screening Of Oxygen Lattice Modes In Yba2cu3o6.95, R. J. Mcqueeny, T. Egami, J.-H. Chung, Y. Petrov, M. Yethiraj, M. Arai, Y. Inamura, Y. Endoh, C. Frost, Fatih Dogan May 2001

Anisotropy In The Electronic Screening Of Oxygen Lattice Modes In Yba2cu3o6.95, R. J. Mcqueeny, T. Egami, J.-H. Chung, Y. Petrov, M. Yethiraj, M. Arai, Y. Inamura, Y. Endoh, C. Frost, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Inelastic neutron scattering data from a twinned single-crystal of YBa2Cu3O6.95 are presented that show a distinct a-b plane anisotropy in the oxygen vibrations. The Cu-O bond-stretching type phonons are simultaneously observed along the a and b directions due to a 4 meV splitting arising from the orthorhombicity. The present results show the bond-stretching branch along b (parallel to the chain) has a continuous dispersion, while the branch along a is discontinuous, suggesting a possibility of short-range cell-doubling along a. Furthermore, the LO mode along a is split in en ergy from its TO partner at …

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Observation Of Magnetic Moments In The Superconducting State Of Yba2⁢Cu3⁢O6.6, Herbert A. Mook, Pengcheng Dai, Fatih Dogan May 2001

Observation Of Magnetic Moments In The Superconducting State Of Yba2⁢Cu3⁢O6.6, Herbert A. Mook, Pengcheng Dai, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering measurements for YBa2⁢Cu3⁢O6.6 have identified small magnetic moments that increase in strength as the temperature is reduced below T* and further increase below Tc. An analysis of the data shows the moments are antiferromagnetic between the Cu-O planes with a correlation length of longer than 195 Å in the a-b plane and about 35 Å along the c axis. The origin of the moments is unknown, and their properties are discussed both in terms of Cu spin magnetism and orbital bond currents.

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Observation Of Magnetic Moments In The Superconducting State Of Yba2⁢Cu3⁢O6.6, Herbert A. Mook, Pengcheng Dai, Fatih Dogan May 2001

Observation Of Magnetic Moments In The Superconducting State Of Yba2⁢Cu3⁢O6.6, Herbert A. Mook, Pengcheng Dai, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering measurements for YBa2⁢Cu3⁢O6.6 have identified small magnetic moments that increase in strength as the temperature is reduced below T* and further increase below Tc. An analysis of the data shows the moments are antiferromagnetic between the Cu-O planes with a correlation length of longer than 195 Å in the a-b plane and about 35 Å along the c axis. The origin of the moments is unknown, and their properties are discussed both in terms of Cu spin magnetism and orbital bond currents.

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Processing Of Erbium Doped High-Tc Superconductor Yba2cu3o7-X Single Crystals For Improved Flux Pinning, William C. Hicks, Fatih Dogan, Michael Strasik, Arthur C. Day, Kevin E. Mccrary Mar 2001

Processing Of Erbium Doped High-Tc Superconductor Yba2cu3o7-X Single Crystals For Improved Flux Pinning, William C. Hicks, Fatih Dogan, Michael Strasik, Arthur C. Day, Kevin E. Mccrary

Materials Science and Engineering Faculty Research & Creative Works

The effect of selected Rare Earth (RE) oxide addi- Tion on growth behavior of large single crystals and the super- conducting properties of YBa2Cu307-x, (Y123) was investigated. The results show that even a small amount (cl mol %) of rare earth addition can have a significant effect on the flux pinning capacity of Y123 single crystals. It was further observed that for Nd and Yb the continuous crystal growth became very unstable for additions greater then 1 mol % while crystal growth remains stable even for additions up to 30 mol % Er2 …

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Processing Of Erbium Doped High-Tc Superconductor Yba2cu3o7-X Single Crystals For Improved Flux Pinning, William C. Hicks, Fatih Dogan, Michael Strasik, Arthur C. Day, Kevin E. Mccrary Mar 2001

Processing Of Erbium Doped High-Tc Superconductor Yba2cu3o7-X Single Crystals For Improved Flux Pinning, William C. Hicks, Fatih Dogan, Michael Strasik, Arthur C. Day, Kevin E. Mccrary

Materials Science and Engineering Faculty Research & Creative Works

The effect of selected Rare Earth (RE) oxide addition on growth behavior of large single crystals and the super- conducting properties of YBa2Cu3O7-x, (Y123) was investigated. The results show that even a small amount (cl mol %) of rare earth addition can have a significant effect on the flux pinning capacity of Y123 single crystals. It was further observed that for Nd and Yb the continuous crystal growth became very unstable for additions greater then 1 mol % while crystal growth remains stable even for additions up to 30 mol % Er2BaCuO …

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Evolution Of The Resonance And Incommensurate Spin Fluctuations In Superconducting Yba2⁢Cu3⁢O6+X, Pengcheng Dai, Herbert A. Mook, Rodney Dale Hunt, Fatih Dogan Jan 2001

Evolution Of The Resonance And Incommensurate Spin Fluctuations In Superconducting Yba2⁢Cu3⁢O6+X, Pengcheng Dai, Herbert A. Mook, Rodney Dale Hunt, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Polarized and unpolarized neutron triple-axis spectrometry was used to study the dynamical magnetic susceptibility X″⁡(q,w) as a function of energy (ħ⁢w) and wave vector (q) in a wide temperature range for the bilayer superconductor YBa2⁢Cu3⁢O6+x with oxygen concentrations, x, of 0.45, 0.5, 0.6, 0.7, 0.8, 0.93, and 0.95. The most prominent features in the magnetic spectra include a spin gap in the superconducting state, a pseudo gap in the normal state, the much-discussed resonance, and incommensurate spin fluctuations below the resonance. We establish the doping dependence …

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Preparation Of Magnetic Nanoparticles And Their Assemblies Using A New Fe(Ii) Alkoxide Precursor, Suresh Pillai, Grainne Biddlecombe, Yurii Gun’Ko, John Kelly, J. Michael Coey, Alexis Douvalis Jan 2001

Preparation Of Magnetic Nanoparticles And Their Assemblies Using A New Fe(Ii) Alkoxide Precursor, Suresh Pillai, Grainne Biddlecombe, Yurii Gun’Ko, John Kelly, J. Michael Coey, Alexis Douvalis

Articles

No abstract provided.

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Spectrally Selective, Matched Emitters For Thermophotovoltaic Energy Conversion Processed By Tape Casting, L. G. Ferguson, Fatih Dogan Jan 2001

Spectrally Selective, Matched Emitters For Thermophotovoltaic Energy Conversion Processed By Tape Casting, L. G. Ferguson, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

The thermophotovoltaic (TPV) generator converts radiant energy from a high temperature emitter element into electric power using infrared responding photovoltaic cells. Spectral control is a primary issue in TPV applications. Conventional TPV generators have relied on filters to achieve selectivity and spectral control with near-blackbody ceramic emitters. Several practical problems have limited the success of this approach, particularly the present lack of a satisfactory wide-band infrared filter. A new, spectrally selective emitter is described in this work, and will be called the “bandgap matched” emitter because its emissive power spectrum is very efficiently matched with the infrared response of the …

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Effects Of Solvent Mixtures On Dispersion Of Lanthanum-Modified Lead Zirconate Titanate Tape Casting Slurries, Jian-Huei Feng, Fatih Dogan Jul 2000

Effects Of Solvent Mixtures On Dispersion Of Lanthanum-Modified Lead Zirconate Titanate Tape Casting Slurries, Jian-Huei Feng, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

The effects of xylenes/ethanol solvent mixtures on lanthanum-modified lead zirconate titanate (PLZT) nonaqueous suspensions were investigated by measuring sediment height, viscosity, and adsorption of dispersant. Well-dispersed colloidal suspensions were obtained in xylene-rich solvents with a minimum amount of menhaden fish oil as a dispersant. It was also shown that adsorption of dispersant on particle surfaces strongly depends on selection of solvent(s). The ratio of solvent mixture affects PLZT solids content of unfired tapes, in which using insufficient as well as excess dispersant could decrease the packing density of particles. Solubility of other organic additives, such as binder, was also considered …

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Aqueous Processing And Mechanical Properties Of Plzt Green Tapes, Jian-Huei Feng, Fatih Dogan May 2000

Aqueous Processing And Mechanical Properties Of Plzt Green Tapes, Jian-Huei Feng, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Aqueous tape casting of lanthanum-modified lead zirconate titanate (PLZT) was performed using commercial poly (vinyl alcohol) (PVA) binders and various plasticizers. Colloidal properties of PLZT suspensions containing only polyelectrolyte dispersant were characterized by zeta potential, conductivity, and viscosity measurements. The effects of molecular weight as well as chemical structures of plasticizers and binders on green tapes were investigated by tensile testing. The tapes made from low molecular weight plasticizers showed higher plasticity, and glycerol was found to be the most effective plasticizer for PVA. Strong hydrogen bonding in high hydrolysis PVAs led to green tapes with high strength and high …

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One-Dimensional Nature Of The Magnetic Fluctuations In Yba2cu3o6.6, Herbert A. Mook, Pengcheng Dai, Fatih Dogan, Rodney Dale Hunt Apr 2000

One-Dimensional Nature Of The Magnetic Fluctuations In Yba2cu3o6.6, Herbert A. Mook, Pengcheng Dai, Fatih Dogan, Rodney Dale Hunt

Materials Science and Engineering Faculty Research & Creative Works

There is increasing evidence that inhomogeneous distributions of charge and spin—so-called ‘striped phases’—play an important role in determining the properties of the high-temperature superconductors. For example, recent neutron-scattering measurements on the YBa2Cu3O7-x family of materials show both spin and charge fluctuations that are consistent with the striped-phase picture. But the fluctuations associated with a striped phase are expected to be one-dimensional, whereas the magnetic fluctuations observed to date appear to display two-dimensional symmetry. We show here that this apparent two-dimensionality results from measurements on twinned crystals, and that similar measurements on substantially detwinned crystals of …

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Making Large, Single Crystal, 123 Ybco Superconductors, Kay Y. Blohowiak, Darryl F. Garrigus, Thomas S. Luhman, Kevin E. Mccrary, Michael Strasik, Ilhan Aksay, Fatih Dogan, William C. Hicks, Corrie B. Martin Apr 2000

Making Large, Single Crystal, 123 Ybco Superconductors, Kay Y. Blohowiak, Darryl F. Garrigus, Thomas S. Luhman, Kevin E. Mccrary, Michael Strasik, Ilhan Aksay, Fatih Dogan, William C. Hicks, Corrie B. Martin

Materials Science and Engineering Faculty Research & Creative Works

We make large (in excess of 2 cm in diameter), Single crystal YBa-Cu-Oz-123 YBCO crystals, where X ≤ O.6, in a seventeen Step process or Some variant thereof from finely ground and well mixed 123 YBCO and 211 YBCO powders with a Small amount of Pt by controlling the rate of cooling from within a compact of the powders using a temperature gradient in the radial and axial planes (independently) of about 1-1 C./inch diameter of compact to nucleate the crystal growth. We promote crystal growth as well using a Samarium oxide seed crystal, preferably SmBa-Cu-Ozo where y ≤ 1.6. …

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Xafs Study Of The Low-Temperature Tetragonal Phase Of La2−X⁢Bax⁢Cuo4: Disorder, Stripes, And Tc Suppression At X =0.125, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh Mar 2000

Xafs Study Of The Low-Temperature Tetragonal Phase Of La2−X⁢Bax⁢Cuo4: Disorder, Stripes, And Tc Suppression At X =0.125, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh

Materials Science and Engineering Faculty Research & Creative Works

Angular dependent x-ray absorption fine structure (XAFS) measurements of all La, Ba, and Cu sites determined the origin and nature of the intrinsic disorder present in the low temperature tetragonal (LTT) structural ground state of La2−x⁢Bax⁢CuO4 with x =0.125,0.15 at T =10 K. Ba doping induces major local distortions that extend as far as 5 Å from its lattice site. Despite the low Ba content the large distortions significantly affect the XAFS of the majority La and Cu sites. The distribution of the local LTT tilt angle of CuO6 octahedra was directly determined from single …

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Al2o3-Ni Composites With High Strength And Fracture Toughness, William Fahrenholtz, Donald T. Ellerby, Ronald E. Loehman Jan 2000

Al2o3-Ni Composites With High Strength And Fracture Toughness, William Fahrenholtz, Donald T. Ellerby, Ronald E. Loehman

Materials Science and Engineering Faculty Research & Creative Works

Al2O3-Ni Composites Were Prepared by the Reactive Hot Pressing of Al and NiO. the Composites Had a Two-Phase, Interpenetrating Microstructure and Contained Approx. 35 Vol% Ni. They Exhibited an Impressively High Combination of Strength and Toughness at Room Temperature; the Four-Point Bending Strength Was in Excess of 600 MPa with a Fracture Toughness of More Than 12 MPa·m1/2 . Examination of Fracture Surfaces Showed that Ni Ligaments Underwent Ductile Deformation during Fracture. SEM Analysis Revealed Knife-Edge Ni Ligaments with a Limited Amount of Debonding Around their Periphery (I.e., at the Ni-Al2O3 Interface), …

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Structural Disorder And The Origin Of High-Tc Suppression In La1.875ba0.125cuo4, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh Nov 1999

Structural Disorder And The Origin Of High-Tc Suppression In La1.875ba0.125cuo4, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh

Materials Science and Engineering Faculty Research & Creative Works

Polarized x-ray absorption fine structure (XAFS) measurements at all La, Pa and Cu sites were used to study local structural features that accompany the strong Tc suppression at x similar to 1/8 in La2-xBaxCuO6. Two critical parameters regulating the strength of hole-lattice coupling in this material were determined, i.e., the direction and magnitude of CuO6 octahedra local tilts. Our findings include the existence of large disorder in the magnitude of the tilt angle about its average value {theta}, with an rms {radical}{delta} {theta}{sup 2}] {approx_equal} 2{theta}. We suggest that this large disorder …

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Charge Fluctuations In Yba2cu3o7-X High-Temperature Superconductors, Herbert A. Mook, Fatih Dogan Sep 1999

Charge Fluctuations In Yba2cu3o7-X High-Temperature Superconductors, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Understanding the behavior of the electrons in the high-temperature copper oxide superconductors remains a challenging problem. An important class of models1,2,3,4,5 argues that the distribution of electronic charge and spin is not homogeneous: rather, spin and charge adopt a dynamic arrangement in which the spins on the copper form antiferromagnetic stripes, separated by domain walls containing the charge1,2,3,4,5. The dynamic behavior of the spins has been extensively studied by neutron scattering, and recent results have shown that the low-frequency fluctuations for different classes of materials display a universal spatial behavior that is consistent with the stripe picture. But arguments for …

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The Weights Of Various Features In The Magnetic Spectra Of Cuprates, G. Aeppli, S. M. Hayden, Pengcheng Dai, Herbert A. Mook, R. D. Hunt, T. G. Perring, Fatih Dogan Sep 1999

The Weights Of Various Features In The Magnetic Spectra Of Cuprates, G. Aeppli, S. M. Hayden, Pengcheng Dai, Herbert A. Mook, R. D. Hunt, T. G. Perring, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

We review briefly the magnetic fluctuation spectra, obtained by neutron scattering, of the high temperature superconductor YBa2Cu3O6.6 (Tc = 62.7 K). The resonance at 34 meV is the most prominent spectral feature in the superconducting state. Even so, its net weight accounts for a mere 1% of the total squared moment expected for planar Cu2+ ions. For context, we also provide a discussion of the spectral weights associated with the magnetic order and spin waves in two-dimensional S = 1/2 Heisenberg antiferromagnets.

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The Effect Of Platinum And Excess 211 Phase On The Loss Of The Liquid Phase In Melt Textured Yba₂Cu₃O₇₋ₓ, William C. Hicks, Fatih Dogan, Michael Strasik, Arthur C. Day, Kevin E. Mccrary Jun 1999

The Effect Of Platinum And Excess 211 Phase On The Loss Of The Liquid Phase In Melt Textured Yba₂Cu₃O₇₋ₓ, William C. Hicks, Fatih Dogan, Michael Strasik, Arthur C. Day, Kevin E. Mccrary

Materials Science and Engineering Faculty Research & Creative Works

Platinum is an important additive in YBa2Cu3O7-x [123] powders for melt processing and growth of large, oriented crystals, but its role in liquid loss during the growth cycle is poorly understood. A series of experiments were conducted to determine how platinum effects liquid loss, and to study the solubility limit of platinum in 123. Both atomically mixed and solid state platinum sources were compared. Crystals were grown on a nonreactive setter so that liquid loss could be clearly distinguished by weight from reaction products with the setter. Based on weight loss studies there was little …

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The Effect Of Platinum And Excess 211 Phase On The Loss Of The Liquid Phase In Melt Textured Yba2cu3o7-X, William C. Hicks, Fatih Dogan, M. Strasik, A. C. Day, Kevin E. Mccrary Jun 1999

The Effect Of Platinum And Excess 211 Phase On The Loss Of The Liquid Phase In Melt Textured Yba2cu3o7-X, William C. Hicks, Fatih Dogan, M. Strasik, A. C. Day, Kevin E. Mccrary

Materials Science and Engineering Faculty Research & Creative Works

Platinum is an important additive in YBa2Cu3O7-x [123] powders for melt processing and growth of large, oriented crystals, but its role in liquid loss during the growth cycle is poorly understood. A series of experiments were conducted to determine how platinum effects liquid loss, and to study the solubility limit of platinum in 123. Both atomically mixed and solid state platinum sources were compared. Crystals were grown on a nonreactive setter so that liquid loss could be clearly distinguished by weight from reaction products with the setter. Based on weight loss studies there was little …

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The Magnetic Excitation Spectrum And Thermodynamics Of High-Tc Superconductors, Pengcheng Dai, Herbert A. Mook, Stephen M. Hayden, Gabriel Aeppli, Toby G. Perring, Rodney Dale Hunt, Fatih Dogan May 1999

The Magnetic Excitation Spectrum And Thermodynamics Of High-Tc Superconductors, Pengcheng Dai, Herbert A. Mook, Stephen M. Hayden, Gabriel Aeppli, Toby G. Perring, Rodney Dale Hunt, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Inelastic neutron scattering was used to study the wave vector– and frequency dependent magnetic fluctuations in single crystals of superconducting YBa2Cu3O6+x. The spectra contain several important features, including a gap in the superconducting state, a pseudo gap in the normal state, and the much-discussed resonance peak. The appearance of the pseudo gap determined from transport and nuclear resonance coincides with formation of the resonance in the magnetic excitations. The exchange energy associated with the resonance has the temperature and doping dependences as well as the magnitude to describe approximately the electronic specific heat near …

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The Magnetic Excitation Spectrum And Thermodynamics Of High-Tc Superconductors, Pengcheng Dai, Herbert A. Mook, Stephen M. Hayden, Toby G. Perring, Gabriel Aeppli, Rodney Dale Hunt, Fatih Dogan May 1999

The Magnetic Excitation Spectrum And Thermodynamics Of High-Tc Superconductors, Pengcheng Dai, Herbert A. Mook, Stephen M. Hayden, Toby G. Perring, Gabriel Aeppli, Rodney Dale Hunt, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Inelastic neutron scattering was used to study the wave vector– and frequency dependent magnetic fluctuations in single crystals of superconducting YBa2Cu3O6+x. The spectra contain several important features, including a gap in the superconducting state, a pseudo gap in the normal state, and the much-discussed resonance peak. The appearance of the pseudo gap determined from transport and nuclear resonance coincides with formation of the resonance in the magnetic excitations. The exchange energy associated with the resonance has the temperature and doping dependences as well as the magnitude to describe approximately the electronic specific heat near …

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Why Does Ni Suppress Superconductivity In La1.85sr0.15cu1−Yniyo4?, Daniel Haskel, Edward A. Stern, V. Polinger, Fatih Dogan May 1999

Why Does Ni Suppress Superconductivity In La1.85sr0.15cu1−Yniyo4?, Daniel Haskel, Edward A. Stern, V. Polinger, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

The role played by Ni impurities in destroying the superconducting state of La2-xSrxCuO4 is still unclear. This is partly due to the lack of clear experimental evidence on the effect of Ni substitution upon the atomic and electronic structure of this cuprate. To provide this information, we performed Ni /(-edge polarized XAFS measure-ments on oriented powder. A special magnetic alignment geometry allowed us to measure pure ~ and aAb-polarized XAFS in identical experimental conditions. We found that the NiO6 octahedra are contracted along the t-axis by 0.16(A) relative to the CuO6 octahedra in Lal.~sSro.~sCuO4, …

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Structural Disorder And The Origin Of High-Tc Suppression In La1.875ba0.125cuo4−Δ, Daniel Haskins, Edward A. Sterns, Fatih Dogan, Arnie R. Moodenbaugh May 1999

Structural Disorder And The Origin Of High-Tc Suppression In La1.875ba0.125cuo4−Δ, Daniel Haskins, Edward A. Sterns, Fatih Dogan, Arnie R. Moodenbaugh

Materials Science and Engineering Faculty Research & Creative Works

Polarized x-ray absorption fine structure (XAFS) measurements at all La, Ba and Cu sites were used to study local structural features that accompany the strong Tc suppression at x ~ 1/8 in La2-xBaxCuO4. Two critical parameters regulating the strength of hole-lattice coupling in this material were determined, i.e., the di- rection and magnitude of CuO6 octahedra local tilts. Our findings include the existence of large disorder in the magnitude of the tilt angle about its average value < 0>, with a rms (formula presented) ≈2< 0>. We suggest that this large disorder strongly …

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Modeling The Dielectric Response And Relaxation Spectra Of Relaxor Ferroelectrics, Huh Tswen Lin, David C. Van Aken, Wayne Huebner Jan 1999

Modeling The Dielectric Response And Relaxation Spectra Of Relaxor Ferroelectrics, Huh Tswen Lin, David C. Van Aken, Wayne Huebner

Materials Science and Engineering Faculty Research & Creative Works

A multi-Debye relaxation model that is based upon the Boltzmann superposition principle has been used to determine the frequency-dispersion behavior of Pb (Mg1/3-Nb2/3)O3 (PMN) and Pb0.88La0.08 (Zr0.65Ti0.35) O3 (PLZT 8/65/35) relaxor ferroelectrics. For PMN, relaxation times on the order of seconds contribute to the dispersive character of the dielectric properties. A defect-relaxation mechanism that involves Mg cation hopping in a structure that is composed of interpenetrating 〈111〉 chains of ordered Pb (Mg1/2Nb1/2) O3 is proposed for PMN. Motion of the Mg cations …

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Structural Disorder And The Origin Of High-Tc Suppression In La₁.₈₇₅Ba₀.₁₂₅ Cuo4−Δ, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh Jan 1999

Structural Disorder And The Origin Of High-Tc Suppression In La₁.₈₇₅Ba₀.₁₂₅ Cuo4−Δ, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh

Materials Science and Engineering Faculty Research & Creative Works

Polarized x-ray absorption fine structure (XAFS) measurements at all La, Ba and Cu sites were used to study local structural features that accompany the strong Tc suppression at: r,,, 1/8 in La2BaCuO4. Two critical parameters regulating the strength of hole-lattice coupling in this material were determined, ie, the direction and magnitude of CuO6 octahedra local tilts. Our findings include the existence of large disorder in the magnitude of the tilt angle about its average value (0), with an rms~~ 2 (0). We suggest that this large disorder strongly scatters a large fraction of states at …

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