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Materials Science and Engineering Faculty Research & Creative Works

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Articles 751 - 780 of 1006

Full-Text Articles in Materials Science and Engineering

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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Incommensurate Magnetic Fluctuations In Yba₂Cu₃O₆.₆, Pengcheng Dai, Herbert A. Mook, Fatih Dogan Feb 1998

Incommensurate Magnetic Fluctuations In Yba₂Cu₃O₆.₆, 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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Maskless, Direct Deposition Of Copper Onto Aluminum Bond Pads For Flip Chip Applications, M. Fang, Thomas J. O'Keefe, M. Stroder, W. Shih, Matthew O'Keefe, R. Strawser, D. Via Jan 1998

Maskless, Direct Deposition Of Copper Onto Aluminum Bond Pads For Flip Chip Applications, M. Fang, Thomas J. O'Keefe, M. Stroder, W. Shih, Matthew O'Keefe, R. Strawser, D. Via

Materials Science and Engineering Faculty Research & Creative Works

Flip chip interconnection of integrated circuits (IC) for packaging applications such as direct chip attachment use Pb-Sn solders as the connection between the die and the substrate. Under bump metallization is typically used to transition from the non-solderable Al bond pad on the IC to a solderable surface such as copper using traditional blanket metal deposition, photolithography and etching procedures. In this study, we report for the first time the use of a novel process for selectively depositing adherent copper directly onto aluminum thin films, eliminating the need for adhesion promoting transition layers and additional patterning steps. Utilizing copper bearing …

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Magnetoresistance Of Magnetic Tunnel Junctions In The Presence Of A Nonmagnetic Layer, Shi C. Zhang, P. M. Levy Jan 1998

Magnetoresistance Of Magnetic Tunnel Junctions In The Presence Of A Nonmagnetic Layer, Shi C. Zhang, P. M. Levy

Materials Science and Engineering Faculty Research & Creative Works

We find that electron propagation across a uniform nonmagnetic metallic layer di in a magnetically layered structure is coherent up to a critical length dc. This provides a possible explanation for the slow decay of the magnetoresistance of magnetic tunnel junctions when a layer of Cu or Ag is inserted between the magnetic electrode and the barrier. However, for many (most) structures the roughness of the interfaces breaks the coherence for di ≪ dc. While the loss of coherence is not fatal for the magnetoresistance of metallic multilayers, it is for tunnel junctions. The quantum well states arising from the …

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Analysis Of The Value Of The Fe Examination For The Assessment Of Student Learning In Engineering And Science Topics, John L. Watson Jan 1998

Analysis Of The Value Of The Fe Examination For The Assessment Of Student Learning In Engineering And Science Topics, John L. Watson

Materials Science and Engineering Faculty Research & Creative Works

This paper presents the results of a project, which investigated the potential of fully using previously unreleased data from the nationally normed Fundamentals of Engineering (FE) examination to assess learning in key engineering and science topics. In the past, very limited information was released by the National Council of Examiners for Engineers and Surveyors (NCEES) for the eight hour FE examination, which is composed of 150-200 questions in ten morning and five afternoon topics. For the purposes of this project the NCEES agreed to release information to the University of Missouri-Rolla (UMR) to permit the value of the FE data …

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Electrodeposition Of Copper On Thermally Oxidized 316 L Stainless Steel Substrates, Z. Zhou, Thomas J. O'Keefe Jan 1998

Electrodeposition Of Copper On Thermally Oxidized 316 L Stainless Steel Substrates, Z. Zhou, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

The effect of thermal oxidation of 316 L stainless steel cathode blanks used in copper electrodeposition was studied. Current and potential step experiments were performed to evaluate electrochemical changes caused by the oxidation treatments. SEM and AES were used to characterize the stainless-steel substrates and the deposited copper films. Particular emphasis was given to the initial stages of copper nucleation and growth. The copper electro crystallization process was strongly influenced by the temperature employed in oxidizing the stainless steel. Dense, uniform and fine copper nuclei were obtained on the stainless-steel substrate oxidized in air at 200°C and 300°C for 3 …

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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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Organically Deposited Metallic Films For Device Fabrication, Thomas J. O'Keefe, M. Stroder, Matthew O'Keefe Jan 1998

Organically Deposited Metallic Films For Device Fabrication, Thomas J. O'Keefe, M. Stroder, Matthew O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

Advances in integrated circuit density, speed and complexity are dependent on lower resistance, finer line width on-chip interconnections. Methods for incorporating copper interconnects into IC fabrication processes have been developed which accomplish this objective but most of these methods use some form of blanket metal deposition that requires mechanical and/or chemical removal of excess material. To date, investigations into the selective deposition of conductor materials for device fabrication have met with limited success. A new process for selectively depositing metallic conductors using inexpensive, organic-based chemical solutions could potentially force a paradigm shift in the deposition of metals for microelectronic applications. …

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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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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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Increased Radiative Lifetime Of Rare Earth-Doped Zinc Oxyhalide Tellurite Glasses, David L. Sidebottom, Michael A. Hruschka, B. G. Potter, Richard K. Brow Oct 1997

Increased Radiative Lifetime Of Rare Earth-Doped Zinc Oxyhalide Tellurite Glasses, David L. Sidebottom, Michael A. Hruschka, B. G. Potter, Richard K. Brow

Materials Science and Engineering Faculty Research & Creative Works

We have investigated the structural and optical properties of rare earth-doped zinc tellurite glasses modified by the substitution of ZnF2. Raman and phonon sideband spectroscopies were employed to characterize changes in the glass structure as well as to probe vibrational behavior in the immediate vicinity of the rare earth ion. These measurements are combined with photoluminescence and optical absorption to monitor the effect of halide substitution upon the optical behavior of the rare earth dopant. A substantial increase in the intrinsic radiative lifetime of Nd3+ is observed with increasing halide concentration.

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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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Strip Casting With Fluxing Agent Applied To Casting Roll, Robert S. Williams, Ronald J. O'Malley, Richard C. Sussman Jul 1997

Strip Casting With Fluxing Agent Applied To Casting Roll, Robert S. Williams, Ronald J. O'Malley, Richard C. Sussman

Materials Science and Engineering Faculty Research & Creative Works

A strip caster (10) for producing a continuous strip (24) includes a tundish (12) for containing a melt (14), a pair of horizontally disposed water cooled casting rolls (22) and devices (29) for electrostatically coating the outer peripheral chill surfaces (44) of the casting rolls with a powder flux material (56). The casting rolls are juxtaposed relative to one another for forming a pouting basin (18) for receiving the melt through a teeming tube (16) thereby establishing a meniscus (20) between the rolls for forming the strip. The melt is protected from the outside air by a non-oxidizing gas passed …

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Aluminum Nitride-Compatible Thick-Film Binder Glass And Thick-Film Paste Composition, Douglas M. Mattox Jun 1997

Aluminum Nitride-Compatible Thick-Film Binder Glass And Thick-Film Paste Composition, Douglas M. Mattox

Materials Science and Engineering Faculty Research & Creative Works

Mixed alkaline earth boroaluminate glasses comprising BaO combined with at least one of CaO, SrO and MgO. The glasses are useful as frit binders in aluminum nitride- compatible, thick-film paste compositions used in thick-film printing of hybrid microelectronic circuits on aluminum nitride substrates.

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The Structure And Electrical Properties Of Srce0.95yb0.05o3 Thin Film Protonic Conductors, Igor Kosacki, Harlan U. Anderson May 1997

The Structure And Electrical Properties Of Srce0.95yb0.05o3 Thin Film Protonic Conductors, Igor Kosacki, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The results of a study of the structure and electrical properties of SrCe0.95Yb0.05O3 thin film protonic conductors are presented. Dense SrCe0.95Yb0.05O3 thin films (∼1000 nm) with grain size in the 30-70 nm range were obtained on Si- and Al2O3-substrates using a polymeric precursor spin coating technique. The electrical conductivity of these thin films has been studied as a function of temperature and correlated with the microstructure. The thin films showed higher electrical conductivity than dense sintered polycrystalline SrCe0.95Yb0.05O3 specimens which had grain size in the micrometer range. This electrical conductivity enhancement has been attributed to the influence of interfacial grain …

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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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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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The Effect Of Casting Shape And Size On Solidification Time: A New Approach, Murat Tiryakioǧlu, Ergin Tiryakioǧlu, Donald R. Askeland Jan 1997

The Effect Of Casting Shape And Size On Solidification Time: A New Approach, Murat Tiryakioǧlu, Ergin Tiryakioǧlu, Donald R. Askeland

Materials Science and Engineering Faculty Research & Creative Works

The limitations of Chvorinov's Rule for predicting the solidification time of a casting are discussed and previous studies intended to modify Chvorinov's Rule in order to express the effect of the size and shape of castings on solidification time are reviewed. A new model that introduces a shape factor is presented that predicts the solidification times of castings as well as or better than Chvorinov's Rule, particularly for more complex shapes. The validity of the new model is compared with the conventional Chvorinov's Rule by a statistical analysis of twelve sets of data obtained from the literature.

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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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Ferroelectric Films As A Fashion Object For Polycrystalline Film Investigation, V. Petrovsky, Harlan U. Anderson, M. Shumsky Jan 1997

Ferroelectric Films As A Fashion Object For Polycrystalline Film Investigation, V. Petrovsky, Harlan U. Anderson, M. Shumsky

Materials Science and Engineering Faculty Research & Creative Works

BaxSr1-xTiO3 (BST), PbZrxTi1-xO3 (PZT) and two-layer PZT-BST films were prepared on Pt, Si(100) and Si(111) substrates by a sol-gel method. XRD analysis shows that the PZT films on the Si(111) substrates tended to be preferentially oriented in the (110) direction. The nondestructive readout of the state of ferroelectric polarization was investigated by three methods: the pyroelectric effect, the non-linearity of the capacitance and the field effect in MOS structures. It is shown that all three methods provide nondestructive readout, and the choice between them depends on the intended use.

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Scaling Parallels In The Non-Debye Dielectric Relaxation Of Ionic Glasses And Dipolar Supercooled Liquids, David L. Sidebottom, Peter F. Green, Richard K. Brow Jan 1997

Scaling Parallels In The Non-Debye Dielectric Relaxation Of Ionic Glasses And Dipolar Supercooled Liquids, David L. Sidebottom, Peter F. Green, Richard K. Brow

Materials Science and Engineering Faculty Research & Creative Works

We compare the dielectric response of ionic glasses and dipolar liquids near the glass transition. Our work is divided into two parts. In the first section we examine ionic glasses and the two prominent approaches to analyzing the dielectric response. The conductivity of ion-conducting glasses displays a power law dispersion σ(ω)∞ωn, where n≈0.67, but frequently the dielectric response is analyzed using the electrical modulus M*(ω) = 1/ε*(ω), where ε*(ω) = ε(ω) - iσ(ω)/ω is the complex permittivity. We reexamine two specific examples where the shape of M*(ω) changes in response to changes in (a) temperature and (b) ion concentration, to …

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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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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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The Transport Properties Of Nanocrystalline Srce0.95yb0.05o3 Thin Films, Igor Kosacki, Harlan U. Anderson Dec 1996

The Transport Properties Of Nanocrystalline Srce0.95yb0.05o3 Thin Films, Igor Kosacki, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The results of electrical transport measurements on nanocrystalline SrCe0.95Yb0.05O3 thin films are presented. Dense SrCe0.95Yb0.05O3 thin films with 30-70 nm grain size have been obtained using a spin-coating technique. These films exhibit about 103 higher electrical conductivity when compared with the bulk polycrystalline material. The grain size of thin films is stable to temperatures as high as 1000 °C since no grain-coarsening was observed. These unique electrical properties of nanocrystalline SrCe0.09Yb0.05O3 thin films are attributed to a dominant role of grain boundaries and/or interfaces. © 1996 American Institute of Physics.

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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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Incommensurate One-Dimensional Fluctuations In Yba2⁢Cu3⁢O6.93, Herbert A. Mook, Pengcheng Dai, Kamel Salama, Dominic Lee, Fatih Dogan, Gabriel Aeppli, Andrew T. Boothroyd, Mark E. Mostoller Jul 1996

Incommensurate One-Dimensional Fluctuations In Yba2⁢Cu3⁢O6.93, Herbert A. Mook, Pengcheng Dai, Kamel Salama, Dominic Lee, Fatih Dogan, Gabriel Aeppli, Andrew T. Boothroyd, Mark E. Mostoller

Materials Science and Engineering Faculty Research & Creative Works

A novel neutron scattering technique has been utilized to discover one-dimensional fluctuations with a very sharply defined modulation period of 16.65⁢Å along the b⁡(a) direction in YBa2⁢Cu3⁢O6.93. The fluctuations are found to be absent in the reduced oxygen compound YBa2⁢Cu3⁢O6.15. The wave vector of the fluctuations is consistent with accepted values of 2⁢kF for the Cu-O chains.

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