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Materials Science and Engineering Faculty Research & Creative Works

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Full-Text Articles in Ceramic Materials

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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Influence Of Chemical Reactions In Magnesia-Graphite Refractories: I, Effects On Texture And High-Temperature Mechanical Properties, Carmen Baudín, Carlos Alvarez, Robert E. Moore Jan 1999

Influence Of Chemical Reactions In Magnesia-Graphite Refractories: I, Effects On Texture And High-Temperature Mechanical Properties, Carmen Baudín, Carlos Alvarez, Robert E. Moore

Materials Science and Engineering Faculty Research & Creative Works

Four formulations of magnesia-graphite-aluminum metal (antioxidant) bricks were prepared from the same raw materials, using the standard commercial practices. Chemical analysis and determination of room-temperature modulus of rupture and Young's modulus, as well as a complete microstructural characterization of the as-received materials, were performed. For high-temperature modulus-of-rupture and Young's modulus data, test samples of the four brick compositions were heated to 1000°, 1200°, and 1450 °C in flowing argon (< 1000 ppm oxygen at 1000 °C) and then loaded mechanically in flexure. Modulus-of-elasticity values ranged from 3.7 to 16.2 GPa and reflected strong effects of aluminum-metal concentration and treatment temperature. Young's modulus evolution with temperature was determined by the evolution of the micro-structure in the bulk of the specimens. Modulus-of-rupture values ranged from 6 to 21 MPa, and their evolution with temperature was determined by the evolution of the micro-structure in the bulk of the specimens at the lower testing temperatures (T≤1200 °C) and by phase assemblages in the surface regions of the specimens - essentially by the presence of the dense MgO zone - at 1450 °C.

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Influence Of Chemical Reactions In Magnesia-Graphite Refractories: Ii, Effects Of Aluminum And Graphite Contents In Generic Products, Carmen Baudín, Carlos Alvarez, Robert E. Moore Jan 1999

Influence Of Chemical Reactions In Magnesia-Graphite Refractories: Ii, Effects Of Aluminum And Graphite Contents In Generic Products, Carmen Baudín, Carlos Alvarez, Robert E. Moore

Materials Science and Engineering Faculty Research & Creative Works

A group of magnesia-graphite and magnesia-graphite-aluminum materials, the compositions of which represent a wide range of graphite contents (approximately 10-16.4 wt.%), aluminum contents (0-5.2 wt.%), and MgO and graphite qualities, were fabricated, using standard commercial practices. Chemical analysis and determination of room-temperature modulus of rupture (MOR) and Young's modulus, as well as a complete microstructural characterization of the as-received materials, were performed. Mechanical characterization at high temperature (1000°, 1200°, and 1450 °C) was done in terms of Young's modulus and MOR in an argon atmosphere (°C). Modulus-of-elasticity values ranged from 4 to 16 GPa, and their evolution with temperature was …

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Neuron Scattering Studies Of The Magnetic Fluctuations In Yba2cu3o7−Δ, Herbert A. Mook, Pengcheng Dai, Rodney Dale Hunt, Fatih Dogan Oct 1998

Neuron Scattering Studies Of The Magnetic Fluctuations In Yba2cu3o7−Δ, Herbert A. Mook, Pengcheng Dai, Rodney Dale Hunt, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering measurements were made on the spin fluctuations in YBa2Cu3O7−δ for different oxygen doping levels. Incommensurability is clearly observed for oxygen concentrations of 6.6 and 6.7 and is suggested for the 6.93. Measurements of the resonance for the O6.6 concentration show that it exists in a broadened and less intense form at temperatures much higher than Tc.

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Iron Phosphate Compositions For Containment Of Hazardous Metal Waste, D. E. Day May 1998

Iron Phosphate Compositions For Containment Of Hazardous Metal Waste, D. E. Day

Materials Science and Engineering Faculty Research & Creative Works

An improved iron phosphate waste form for the vitrification, containment and long-term disposition of hazardous metal waste such as radioactive nuclear waste is provided. The waste form comprises a rigid iron phosphate matrix resulting from the cooling of a melt formed by heating a batch mixture comprising the metal waste and a matrix-forming component. The waste form comprises from about 30 to about 70 weight percent P205 and from about 25 to about 50 weight percent iron oxide and has metals present in the metal waste chemically dissolved therein. The concentration of iron oxide in the waste form along with …

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Incommensurate Magnetic Fluctuations In Yba2⁢Cu3⁢O6.6, Pengcheng Dai, Herbert A. Mook, Fatih Dogan Feb 1998

Incommensurate Magnetic Fluctuations In Yba2⁢Cu3⁢O6.6, Pengcheng Dai, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

We use inelastic neutron scattering to demonstrate that the low-frequency magnetic fluctuations in YBa2Cu3O6.6 (Tc= 62.7 K) change from commensurate to incommensurate on cooling with the incommensurability first appearing at temperatures above Tc. For the energies studied, the susceptibility at incommensurate positions increases on cooling below Tc, accompanied by a suppression of the spin fluctuations at the commensurate points. These results suggest that incommensurate spin fluctuations may be a common feature for all cuprate superconductors.

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Incommensurate Magnetic Fluctuations In Yba2cu3o6.6, Pengcheng Dai, Hernert A. Mook, Fatih Dogan Feb 1998

Incommensurate Magnetic Fluctuations In Yba2cu3o6.6, Pengcheng Dai, Hernert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

We use inelastic neutron scattering to demonstrate that the low-frequency magnetic fluctuations in YBa2Cu 3O6.6 (Tc=62.7 K) change from commensurate to incommensurate on cooling with the incommensurability first appearing at temperatures above Tc. For the energies studied, the susceptibility at incommensurate positions increases on cooling below Tc, accompanied by a suppression of the spin fluctuations at the commensurate points. These results suggest that incommensurate spin fluctuations may be a common feature for all cuprate superconductors.

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Dai Et Al. Reply:, Pengcheng Dai, Mohana Yethiraj, Herbert A. Mook, Terrence B. Lindemer, Fatih Dogan Feb 1998

Dai Et Al. Reply:, Pengcheng Dai, Mohana Yethiraj, Herbert A. Mook, Terrence B. Lindemer, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

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Evolution Of In Situ Refractories In The 20th Century, William E. Lee, Robert E. Moore Jan 1998

Evolution Of In Situ Refractories In The 20th Century, William E. Lee, Robert E. Moore

Materials Science and Engineering Faculty Research & Creative Works

A common theme over the past 100 years in refractories science and technology has been to generate a protective refractories layer in a high-temperature container, often by reaction of the refractory materials with the contents (glass, slag, or atmosphere). The history of refractories during the 20th century is used in this review to illustrate how techniques - such as slag splashing, in situ spinel generation in castables, magnesia dense layer formation in magnesia-carbon brick in steelmaking, clinker adhesion in cement kilns, and viscous boundary layer generation in glass tanks - have evolved to their present status.

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Absolute Measurements Of The High-Frequency Magnetic Dynamics In Hihg-Tc Superconductors, Stephen M. Hayden, Gabriel Aeppli, Pengcheng Dai, Herbert A. Mook, Toby G. Perring, S-W Cheong, Zachary Fisk, Fatih Dogan, Thomas E. Mason Dec 1997

Absolute Measurements Of The High-Frequency Magnetic Dynamics In Hihg-Tc Superconductors, Stephen M. Hayden, Gabriel Aeppli, Pengcheng Dai, Herbert A. Mook, Toby G. Perring, S-W Cheong, Zachary Fisk, Fatih Dogan, Thomas E. Mason

Materials Science and Engineering Faculty Research & Creative Works

We review recent measurements of the high-frequency dynamic magnetic susceptibility in the high-T~ superconducting systems La2-xSrxCuO4 and YBa2Cu3O6+x. Experiments were performed using the chopper spectrometers HET and MARI at the ISIS spallation source. We have placed our measurements on an absolute intensity scale; this allows systematic trends to be seen and comparisons with theory to be made. We find that the insulating S = ½ antiferromagnetic parent compounds show a dramatic renormalization of the spin wave intensity. The effect of doping on the response is to cause broadenings in …

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Pseudogap And Incommensurate Magnetic Fluctuations In Yba2cu3o6.6, Pengcheng Dai, Herbert A. Mook, Fatih Dogan Dec 1997

Pseudogap And Incommensurate Magnetic Fluctuations In Yba2cu3o6.6, Pengcheng Dai, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Unpolarized inelastic neutron scattering is used to study the temperature and wave vector dependence of the dynamical magnetic susceptibility, X"(q, w), of a well-characterized single-crystal YBa2Cu3O6.6 (Tc = 62.7 K). We find that a pseudo gap opens in the spin-fluctuation spectrum at temperatures well above Tc. We speculate that the appearance of the low-frequency incommensurate fluctuations is associated with the opening of the pseudo gap. To within the error of the measurements, a gap in the spin-fluctuation spectrum is found in the superconducting state.

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Pseudogap And Incommensurate Magnetic Fluctuations In Yba2cu3o6.6, Pengcheng Dai, Herbert A. Mook, Fatih Dogan Dec 1997

Pseudogap And Incommensurate Magnetic Fluctuations In Yba2cu3o6.6, Pengcheng Dai, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Unpolarized inelastic neutron scattering is used to study the temperature and wave vector dependence of the dynamical magnetic susceptibility X"(q,w) of a well-characterized single-crystal YBa2Cu3O6.6 (Tc = 62.7 K). We find that a pseudogap opens in the spin-fluctuation spectrum at temperatures well above Tc. We speculate that the appearance of the low-frequency incommensurate fluctuations is associated with the opening of the pseudogap. To within the error of the measurements, a gap in the spin-fluctuation spectrum is found in the superconducting state.

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Optically Transparent Composite Material And Process For Preparing Same, D. E. Day, James O. Stoffer, John M. Barr Sep 1997

Optically Transparent Composite Material And Process For Preparing Same, D. E. Day, James O. Stoffer, John M. Barr

Materials Science and Engineering Faculty Research & Creative Works

Glass ribbon-reinforced transparent polymer composites which provide excellent optical transparency and a low distortion level over a wide temperature range while exhibiting superior mechanical properties as compared to non- reinforced polymer counterparts, and equivalent properties as compared to glass fiber-reinforced counterparts.

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Spin Dynamics Of Er3+ In Erba2cu3o7−Δ, S. Skanthkumar, J. W. Lynn, Fatih Dogan Apr 1997

Spin Dynamics Of Er3+ In Erba2cu3o7−Δ, S. Skanthkumar, J. W. Lynn, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering techniques are used to study the magnetic excitations of the Er ions in superconducting ErBa2Cu3O7, a system where the Er ions order antiferromagnetically at TN=0.62 K and the sublattice magnetization obeys the relation for a 2D S=1/2 Ising model. Our data, which were taken on a cold neutron triple axis spectrometer using a horizontally focusing analyzer, reveal that there is a large gap of about 0.20 meV in the excitation spectrum, about four times the thermal energy kTN, as expected for an Ising system. However, we also observe dispersion of the spin …

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Spin Dynamics Of Er3+ In Erba2cu3o7−Δ, Suntharalingam Skanthakumar, Jeffrey W. Lynn, Fatih Dogan Apr 1997

Spin Dynamics Of Er3+ In Erba2cu3o7−Δ, Suntharalingam Skanthakumar, Jeffrey W. Lynn, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Neutron scattering techniques are used to study the magnetic excitations of the Er ions in superconducting ErBa2Cu3O7, a system where the Er ions order antiferromagnetically at TN=0.62 K and the sublattice magnetization obeys the relation for a 2D S=1/2 Ising model. Our data, which were taken on a cold neutron triple axis spectrometer using a horizontally focusing analyzer, reveal that there is a large gap of about 0.20 meV in the excitation spectrum, about four times the thermal energy kTN, as expected for an Ising system. However, we also observe …

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Evaluation Of Unified Interaction Parameter Model Parameters For Calculating Activities Of Ferromanganese Alloys: Mn-Fe-C, Mn-Fe-Si, Mn-C-Si, And Mn-Fe-C-Si Systems, L. I. Hongjie, Arthur E. Morris Jan 1997

Evaluation Of Unified Interaction Parameter Model Parameters For Calculating Activities Of Ferromanganese Alloys: Mn-Fe-C, Mn-Fe-Si, Mn-C-Si, And Mn-Fe-C-Si Systems, L. I. Hongjie, Arthur E. Morris

Materials Science and Engineering Faculty Research & Creative Works

Interaction parameters for Mn-based alloys were evaluated using both carbon solubility and activity data for species in binary and ternary manganese alloys. The parameters at 1400 °C are the following εcc = -4.5; εccc = 58.8; εFeCC = 1.5; εFeCC = 2.5; In γC0 = -1.15 . εsisi = 15.5; εsisisi = 2.69; εFeSi = 2.5; εcsi = 12.4; εccsi = 27.5; In γSi0 = -7.46 The unified interaction parameter model (UIPM) was used to calculate the activity coefficients of species and the solubility of carbon in ferromanganese alloys (up to quaternary Mn-Fe-C-Si). The results were in good agreement with …

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Chemical Durability Of Lead-Oxide-Based, Thick-Film Binder Glasses, Douglas M. Mattox, Joshua H. Robinson Jan 1997

Chemical Durability Of Lead-Oxide-Based, Thick-Film Binder Glasses, Douglas M. Mattox, Joshua H. Robinson

Materials Science and Engineering Faculty Research & Creative Works

Lead-oxide-bearing glasses are incompatible with aluminum nitride metallization's, and federal legislation is recommending their replacement in thick-film electronics and labeling. To evaluate alternatives, the benchmark chemical durability's of the lead borosilicate and lead aluminate thick-film binder glasses have been determined. Aluminum oxide (Al2O3) benefits water durability moderately, acid durability substantially, and basic durability indistinguishably. The rate of attack in water is approximately two orders of magnitude greater than for soda-lime glass. The thermal contractions of the glasses are compatible. An apparent, spontaneous phase separation in the Al2O3-free glass is suppressed by Al2O3 that is included as a batch component.

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Magnetic Dynamics In Underdoped Yba2⁢Cu3⁢O7−X: Direct Observation Of A Superconducting Gap, Pengcheng Dai, Mohana Yethiraj, Herbert A. Mook, Terrence B. Lindemer, Fatih Dogan Dec 1996

Magnetic Dynamics In Underdoped Yba2⁢Cu3⁢O7−X: Direct Observation Of A Superconducting Gap, Pengcheng Dai, Mohana Yethiraj, Herbert A. Mook, Terrence B. Lindemer, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Polarized and unpolarized triple-axis neutron measurements were performed on an underdoped crystal of YBa2⁢Cu3⁢O7−x (x = 0.4 ±0.02, Tc = 62.7⁢K). Our results indicate, contrary to earlier evidence, that the spin excitations in the superconducting state are essentially the same as those in the fully doped material except that the unusual 41 meV resonance is observed at 34.8 meV. The normal state spin excitations are characterized by a weakly energy-dependent continuum whose temperature dependence shows the clear signature of a superconducting gap at Tc. The enhancement at the resonance is accompanied by …

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Low Temperature Hydrothermal Synthesis Of Nanophase Batio3 And Bafe12019 Powders, Fatih Dogan, Shawn O'Rourke, Mao-Xu Qian, Mehmet Sarikaya Dec 1996

Low Temperature Hydrothermal Synthesis Of Nanophase Batio3 And Bafe12019 Powders, Fatih Dogan, Shawn O'Rourke, Mao-Xu Qian, Mehmet Sarikaya

Materials Science and Engineering Faculty Research & Creative Works

Nanocrystalline powders with an average particle size of 50 nm have been synthesized in two materials systems under hydrothermal conditions below 100°C. Processing variables, such as temperature, concentration and molar ratio of reactants and reaction time were optimized to obtain particles of reduced size and stoichiometric compositions. Hydrothermal reaction takes place between Ba (OH)2 solution and titanium/iron precursors in sealed polyethylene bottles in the BaTiO3 and BaFe12019 systems, respectively. While crystalline BaTiO3 forms relatively fast within a few hours, formation of fully crystalline and stoichiometric BaFe12019 require considerably longer reaction times up to several weeks and strongly …

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Magnetic Dynamics In Underdoped Yba2cu3o72x: Direct Observation Of A Superconducting Gap, Pengcheng Dai, Mehmet Yethiraj, Herbert A. Mook, T. B. Lindemer, Fatih Dogan Nov 1996

Magnetic Dynamics In Underdoped Yba2cu3o72x: Direct Observation Of A Superconducting Gap, Pengcheng Dai, Mehmet Yethiraj, Herbert A. Mook, T. B. Lindemer, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Polarized and unpolarized triple-axis neutron measurements were performed on an underdoped crystal of YBa2Cu3O7-x (x 0.4 6 0.02, Tc 62.7 K). Our results indicate, contrary to earlier evidence, that the spin excitations in the superconducting state are essentially the same as those in the fully doped material except that the unusual 41 meV resonance is observed at 34.8 meV. The normal state spin excitations are characterized by a weakly energy-dependent continuum whose temperature dependence shows the clear signature of a superconducting gap at Tc. The enhancement at the resonance is accompanied by …

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Recent Developments In Extrusion Freeform Fabrication (Eff) Utilizing Non-Aqueous Gel Casting Formulations, Greg Hilmas, John L. Lombardi, Robert A. Hoffman, Kevin Stuffle Aug 1996

Recent Developments In Extrusion Freeform Fabrication (Eff) Utilizing Non-Aqueous Gel Casting Formulations, Greg Hilmas, John L. Lombardi, Robert A. Hoffman, Kevin Stuffle

Materials Science and Engineering Faculty Research & Creative Works

Extrusion Freeform Fabrication (EFF) was shown to be an extremely versatile method for fabricating Functionally Graded Materials (FGMs) The approach is inexpensive and potentially feasible for grading between any thermodynamically compatible ceramic-metal, ceramic-ceramic, or metal-metal material combination. Several material systems were investigated in this study including alumina-304 stainless steel, zirconia-304 stainless steel, alumina-Inconel 625, zirconiaInconel625, alumina-nickel aluminide, zirconia-nickel aluminide, titanium carbide-InconeI625, titanium diboride-nickel aluminide, and tungsten carbide-nickel aluminide. A controlled gradient was demonstrated between the end members for all of the above compositions. The FGMs were hot pressed to achieve near theoretical densities, providing flexural strengths as high as 1000 …

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