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Materials Science and Engineering Faculty Research & Creative Works

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Articles 211 - 240 of 326

Full-Text Articles in Ceramic Materials

In-Plane Anisotropy And Temperature Dependence Of Oxygen Phonon Modes In Yba2⁢Cu3⁢O6.95, J-H Chung, Takeshi Egami, Rj Mcqueeney, Mohana Yethiraj, Masatoshi Arai, Tetsuya Yokoo, Y. Petrov, Herbert A. Mook, Yasuo Endoh, Setsuko Tajima, C. Frost, Fatih Dogan Jan 2003

In-Plane Anisotropy And Temperature Dependence Of Oxygen Phonon Modes In Yba2⁢Cu3⁢O6.95, J-H Chung, Takeshi Egami, Rj Mcqueeney, Mohana Yethiraj, Masatoshi Arai, Tetsuya Yokoo, Y. Petrov, Herbert A. Mook, Yasuo Endoh, Setsuko Tajima, C. Frost, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Inelastic pulsed neutron scattering measurements on YBa2⁢Cu3⁢O6.95 single crystals indicate that the sample has a distinct a-b plane anisotropy in the oxygen vibrations. The Cu-O bond-stretching-type phonons, which are suspected to interact strongly with charge, are simultaneously observed along the a and b directions due to a 7-meV splitting arising from the orthorhombicity, even though the sample is twinned. The bond-stretching LO branch with the polarization along a (perpendicular to the chain) loses intensity beyond the middle of the zone, indicating branch splitting as seen in doped nickelates, with the second branch being located at …

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Comparison Of Anode And Electrolyte Support Configuration Of Single-Chamber Sofc, Piotr Jasinski, Toshio Suzuki, Zach Byars, Fatih Dogan, Harlan A. Anderson Jan 2003

Comparison Of Anode And Electrolyte Support Configuration Of Single-Chamber Sofc, Piotr Jasinski, Toshio Suzuki, Zach Byars, Fatih Dogan, Harlan A. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The single-chamber solid oxide fuel cell (SOFC) has recently received considerable attention. This type of fuel cell operates in the mixed reactant gas and therefore does not require separation of the fuel and oxidant gases. In this paper we report the anode- and electrolyte-supported configurations of the single chamber SOFC that we have studied. The system based on typical fuel cell composition has been examined: yttrium stabilized zirconia (YSZ) as an electrolyte, nickel/YSZ cermet as an anode, lanthanum strontium manganese oxide (LSM) as a cathode. The cells were prepared by tape-casting and screen-printing techniques. The cathode processing parameters have been …

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Phase Diagram For Stripes In Yba2cu3o6+X Superconductors, Herbert A. Mook, Fatih Dogan Dec 2002

Phase Diagram For Stripes In Yba2cu3o6+X Superconductors, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering has been used to measure the charge and spin structure in the YBa2Cu3O6+x superconductors. Incommensurate static charge ordering is found at low doping levels while only charge fluctuations are found at higher doping. The spin structure is complex with both a commensurate resonance and incommensurate structure observed at low temperatures. The scattering results are used to construct a phase diagram for stripes in the YBa2Cu3O6+x system.

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Magnetic Order In Yba2⁢Cu3⁢O6+X Superconductors, Herbert A. Mook, Pengcheng Dai, Stephen M. Hayden, Arno Hiess, Jw Lynn, S-H Lee, Fatih Dogan Oct 2002

Magnetic Order In Yba2⁢Cu3⁢O6+X Superconductors, Herbert A. Mook, Pengcheng Dai, Stephen M. Hayden, Arno Hiess, Jw Lynn, S-H Lee, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Polarized and unpolarized neutron diffraction has been used to search for magnetic order in YBa2⁢Cu3⁢O6+x superconductors. Most of the measurements were made on a high-quality crystal of YBa2⁢Cu3⁢O6.6. It is shown that this crystal has highly ordered ortho-II chain order, and a sharp superconducting transition. Inelastic scattering measurements display a very clean spin-gap and pseudo gap with any intensity at 10 meV being 50 times smaller than the resonance intensity. The crystal shows a complicated magnetic order that appears to have three components. A magnetic phase is found at …

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Phonon Dispersion Measurements Of Yba2cu3o6.15 And Yba2cu3o6.95 By Time-Of-Flight Neutron Spectroscopy, J-H Chung, T. Egami, R. J. Mcqueeney, M. Yethiraj, M. Arai, T. Yokoo, Herbert A. Mook, Y. Endoh, S. Tajima, C. Frost, Fatih Dogan Oct 2002

Phonon Dispersion Measurements Of Yba2cu3o6.15 And Yba2cu3o6.95 By Time-Of-Flight Neutron Spectroscopy, J-H Chung, T. Egami, R. J. Mcqueeney, M. Yethiraj, M. Arai, T. Yokoo, Herbert A. Mook, Y. Endoh, S. Tajima, C. Frost, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

We measured the phonon dispersions of YBa2Cu3O6.15 and YBa2Cu3O6.95 by time-of-flight inelastic neutron scattering. The in-plane bond-stretching modes in the metallic phase showed a distinct a-b plane an isotropy beyond what is expected for structural origin. Such an isotropy in the longitudinal optical modes, which is absent in the TO, suggests strong in-plane anisotropy in the underlying electronic structure. Apical oxygen bond-stretching modes showed a large frequency change between the insulating and the metallic phases. This large softening also is beyond structural origin, and suggests the effect of local electronic …

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Method For Sintering Ceramic Tapes, Fatih Dogan, Jian-Huei Feng, Lucian G. Ferguson Sep 2002

Method For Sintering Ceramic Tapes, Fatih Dogan, Jian-Huei Feng, Lucian G. Ferguson

Materials Science and Engineering Faculty Research & Creative Works

Flexible Setter powder deposition sheets containing Setter powders were developed for Sintering of ceramic articles including tapes by an economical, fast and Simple method. The sheets provide for deposition of a thin and uniform layer of Setter powders on a green ceramic article after burnout of a binder in the sheet. Because of high Strength and low burnout temperature, hydroxypropyl methylcellulose binder is preferred for production of these sheets. Tape cast sheets with low Solids loading can be obtained by optimizing the wetting behavior of aqueous slurries on tape carrier. Setter, powder deposition sheets are of particular benefit in processing …

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Dopant Effect On Local Dielectric Properties In Barium Titanate Based Electroceramics Determined By Transmission Eels, Kalpana S. Katti, Maoxu Quian, Fatih Dogan, Mehmet Sarikaya Sep 2002

Dopant Effect On Local Dielectric Properties In Barium Titanate Based Electroceramics Determined By Transmission Eels, Kalpana S. Katti, Maoxu Quian, Fatih Dogan, Mehmet Sarikaya

Materials Science and Engineering Faculty Research & Creative Works

Investigates the local electronic excitations of barium titanate electro ceramic using low-loss electron energy loss spectroscopy. Process for monitoring of electronic structure of titanate; Changes in valence and conduction band states by valence state of barium; Shift of oscillator strengths of excitations in local regions.

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Electron–Phonon Interactions In Htsc Cuprates, Takeshi Egami, J-H Chung, Rj Mcqueeney, Mohana Yethiraj, Herbert A. Mook, C. Frost, Y. Petrov, Fatih Dogan, Yasuhiro Inamura, Masatoshi Arai, Setsuuko Tajima, Yasuo Endoh May 2002

Electron–Phonon Interactions In Htsc Cuprates, Takeshi Egami, J-H Chung, Rj Mcqueeney, Mohana Yethiraj, Herbert A. Mook, C. Frost, Y. Petrov, Fatih Dogan, Yasuhiro Inamura, Masatoshi Arai, Setsuuko Tajima, Yasuo Endoh

Materials Science and Engineering Faculty Research & Creative Works

Phonons have been generally considered to be irrelevant to the high-temperature superconductivity in the cuprates. However, such a bias is usually based upon the assumption of conventional electron–phonon coupling, while in the cuprates the coupling can be rather unconventional because of strong electron correlation. We present the results of our recent measurements of phonon dispersion in YBa2Cu3O6+x by inelastic neutron scattering. These suggest certain phonon modes interact strongly with electrons and are closely involved in the superconductivity phenomenon with possible contribution to pairing.

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Biodegradable Glass Compositions And Methods For Radiation Therapy, D. E. Day, James E. White Apr 2002

Biodegradable Glass Compositions And Methods For Radiation Therapy, D. E. Day, James E. White

Materials Science and Engineering Faculty Research & Creative Works

A nonradioactive glass in particulate form adapted for radiation therapy in a mammal comprise a biodegradable rare earth-lithium borate glass material of a specified composition which, upon being subjected to an effective amount of neutron irradiation, will produce a beta or gamma emitting radioisotope, the radioisotope being distributed throughout the glass material, the glass upon being introduced into a body fluid for radiation therapy being adapted to react therewith causing the radioisotope to form an insoluble compound on the surface of the glass material which is retained in the glass material and thereby prevented from escaping from the treatment site. …

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Spectral Analysis Of Transition Metal-Doped Mgo “Matched Emitters” For Thermophotovoltaic Energy Conversion, Lucian G. Ferguson, Fatih Dogan Apr 2002

Spectral Analysis Of Transition Metal-Doped Mgo “Matched Emitters” For Thermophotovoltaic Energy Conversion, Lucian G. Ferguson, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

A new, thermally excited Co/Ni-doped MgO ceramic emitter for TPV energy conversion is described in this work and termed the “matched emitter” because its emissive power spectrum is very efficiently matched with the portion of the electromagnetic spectrum that can be converted directly into electrical energy by infrared responding GaSb photovoltaic cells. Ligand Field Theory calculations are used to estimate the crystal field splitting energies at high temperatures for Co and Ni-doped MgO matched emitters. Experimental measurements of the high temperature (1300–1400◦C) emissive power spectrums for Co and Ni-doped MgO emitters are compared with predictions obtained from ligand field calculations …

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Synthesis Of Pmma-Ceramics Nanocomposites By Spray Process, X.-D. Zhou, H. C. Gu Apr 2002

Synthesis Of Pmma-Ceramics Nanocomposites By Spray Process, X.-D. Zhou, H. C. Gu

Materials Science and Engineering Faculty Research & Creative Works

PMMA-ceramics nanocomposites particles were synthesized by a spray process. PMMA-ZnO compositions showed a higher homogeneous than PMMA-SiO2. The surface of PMMA-SiO2 composites was SiO2 rich. Donut shape particles were formed at high gas flow rate, which was due to the competition between surface tension and dragging force. The Zeta potential dramatically changed in PMMA-ZnO composites whereas there was a slight change in PMMA-SiO2 system.

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Method For Preparing Porous Shells Or Gels From Glass Particles, D. E. Day, Samuel D. Conzone Mar 2002

Method For Preparing Porous Shells Or Gels From Glass Particles, D. E. Day, Samuel D. Conzone

Materials Science and Engineering Faculty Research & Creative Works

A method is provided for preparing shells, concentric shells or porous, homogenous gels from alkali borate glass particles at low temperatures (i.e. room temperature or less than above 100° C.). The alkali borate glass particles contain one or more cations such as aluminum which react with an aqueous solution containing an anion such as hydroxide to form an aqueous insoluble material having a solubility limit of less than about 0.01 wt. percent. TTie resulting shells or gels may be used in many different applications such as a filler in resins, as filters, precursors for nano-sized powders, as thin surface films …

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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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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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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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