Materials Science and Engineering Commons^™

Optical Properties Of Ceo2 Films Prepared From Colloidal Suspension, V. Petrovsky, B. P. Gorman, Harlan U. Anderson, T. Petrovsky

Materials Science and Engineering Faculty Research & Creative Works

Electronic Materials Applied Research Center, University of Missouri-Rolla, Rolla, Missouri 65409-1170 Optical absorption of nanocrystalline thin films can be influenced by the presence of both porosity and grain size effects. If both are present simultaneously, their effects are difficult to separate. In this study it is shown that the combination of uv-vis transmittance and reflectance measurements on porous CeO₂ films provides enough data to make this separation. The CeO₂ films were prepared by deposition of nanosized (∼5 nm) particles from a water colloidal suspension onto sapphire and subjecting these films to sintering temperatures sufficiently high to provide a …

Electrochemical Characterization Of The Effects Of Impurities And Organic Additives In Lead Electrowinning From Fluoborate Electrolyte, Puqiang Zhang, Thomas J. O'Keefe, Pu Yu

Materials Science and Engineering Faculty Research & Creative Works

The effects of glue and calcium lignin sulfonate additives, and chloride and antimony impurities on the lead electrowinning process, using a fluoborate electrolyte, were studied. Short-term deposition tests, voltammetry, electrochemical impedance spectroscopy (EIS) and SEM techniques were used for the evaluation. The interactions among additives and impurities were also evaluated. The presence of antimony or chloride ion in the range of 50 to 200 mg/L was shown to cause a more dendritic and powdery lead deposit. Additions of glue and calcium lignin sulfonate at selected concentrations helped to level the deposit and counteracted the detrimental effects of chloride and antimony. …

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 YBa_2⁢Cu_3⁢O_6.6 have identified small magnetic moments that increase in strength as the temperature is reduced below T* and further increase below T_c. 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.

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 YBa₂Cu₃O_6.95 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 …

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 YBa_2⁢Cu_3⁢O_6.6 have identified small magnetic moments that increase in strength as the temperature is reduced below T* and further increase below T_c. 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.

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 YBa₂Cu₃0_7-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 % Er_{2 …}

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 YBa₂Cu₃O_7-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 …

Dopant Structural Distortions In High-Temperature Superconductors: An Active Or A Passive Role?, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh

Materials Science and Engineering Faculty Research & Creative Works

The parent compounds of high-temperature superconductors, such as YBa2Cu3O6 and La2CuO4, are strongly interacting electron systems, rendering them insulators with Mott-Hubbard gaps of a few electronvolts. Charge carriers (holes) are introduced by chemical doping, causing an insulator-metal (IM) transition and, at low temperatures, superconductivity. the role of dopants is widely seen as limited to the introduction of holes into the CuO2 planes (i.e. occupying electronic states derived from Cu and O 2px,y atomic orbitals). Most theories of high-Tc superconductivity deal with pairing interactions between these planar holes. Local distortions around dopants are poorly understood, because of the experimental difficulty in …

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⁢O_6+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 …

Characterization And Soldering Of Organic Modified Aluminum Thin Films And Bond Pads, Rui Fang, Eric Dahlgren, Matthew O'Keefe, Thomas J. O'Keefe, Wu Sheng Shih, Daniel R. Gamota, Jie Zhang

Materials Science and Engineering Faculty Research & Creative Works

An immersion plating process using organic solutions was used to deposit a seed layer of copper and to activate the surface of thin film aluminum surfaces and bond pads. The seeded surfaces were subsequently electroless copper plated and tested for compatibility with soldering assembly. It was demonstrated that the copper particles deposited from the organic solution onto sputter deposited aluminum thin films were able to act as nucleation sites for the subsequent buildup of adherent, continuous copper films from conventional electroless plating baths. In addition, the metal deposition from organic solution process was found to be very selective on patterned …

Rms Titanic: A Metallurgical Problem, Hollis P. Leighly, B. L. Bramfitt, S. J. Lawrence

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

Electrical Conductivity And Lattice Defects In Nanocrystalline Cerium Oxide Thin Films, Toshio Suzuki, Igor Kosacki, Harlan U. Anderson, Philippe Colomban

Materials Science and Engineering Faculty Research & Creative Works

The results of the electrical conductivity and Raman scattering measurements of CeO₂ thin films obtained by a polymeric precursor spin-coating technique are presented. The electrical conductivity has been studied as a function of temperature and oxygen activity and correlated with the grain size. When compared with microcrystalline samples, nanocrystalline materials show enhanced electronic conductivity. The transition from extrinsic to intrinsic type of conductivity has been observed as the grain size decreases to < 100 nm, which appears to be related to a decrease in the enthalpy of oxygen vacancy formation in CeO₂. Raman spectroscopy has been used to analyze the crystalline quality as a function of grain size. A direct comparison has been made between the defect …

Comment On "Influence Of Fe³⁺/Fe2+ Ratio On The Crystallization Of Iron-Rich Glasses Made With Industrial Wastes", Chandra S. Ray, Mario Pelino, Alexander Karamanov

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

Spontaneous, Non-Aqueous Electrochemical Deposition Of Copper And Palladium On Al And Al(Cu) Thin Films, R. Fang, H. Gu, Matthew O'Keefe, Thomas J. O'Keefe, W. S. Shih, K. D. Leedy, R. Cortez

Materials Science and Engineering Faculty Research & Creative Works

Copper and palladium seed layers have been successfully deposited from organic solutions onto patterned and unpatterned pure aluminum and Al (0.5%Cu) thin films using an immersion displacement process. The reaction occurs at ambient temperature and pressure by a spontaneous electrochemical mechanism. Copper and palladium deposition using the organic solution was studied as a function of reaction time and Cu or Pd concentration in the solution. It was found that both time and the initial ionic metal concentration significantly influence deposit morphology, particle size and shape, and adherence. Nucleation of Cu or Pd sub-micron particles on both Al and Al (Cu) …

Properties Of Sputtered Bilayer Wnx/W Diffusion Barriers Between Si And Cu, K. D. Leedy, Matthew O'Keefe, E. J. Dahlgren, J. T. Grant

Materials Science and Engineering Faculty Research & Creative Works

Copper interconnect metallizations in next generation integrated circuits will require thin diffusion barrier layers (< 20 nm) between the Cu and low-k dielectric which may also function as seed layers for subsequent material depositions. One possible structure entails a multicomponent diffusion barrier with a lower resistivity component, such as W on WNx. In this study, sputtered WNx/W bilayer thin films were investigated as diffusion barriers between Si and Cu. The total thickness of the WNx/W bilayer was fixed at 20 nm while the WNx thickness was varied from 0 to 20 nm. After deposition of the barrier films, a 100 nm thick Cu film was sputtered over the top of the ct-W and amorphous WNx bilayer. The as-deposited WNx/W film stress was found to be strongly dependent on the relative amount of WNx and W present and the addition of a Cu overlayer was found to mitigate the stress levels. The WNx/W barriers remained stable after 650°C anneals and exhibited phase transformations to W 2N. Microstructural characterization using transmission electron microscopy and x-ray diffraction and chemical analysis by x-ray photoelectron spectroscopy of the films were used to identify the as deposited and transformed phases. © 2001 Materials Research Society.

Agglomerated Die Casting Lubricant, Mary R. Reidmeyer

Materials Science and Engineering Faculty Research & Creative Works

A lubricant for use in lubricating the shot sleeve of a machine for die casting molten metals is in the form of agglomerated particles. The particles have an inorganic high pressure lubricant agglomerated, with a binder material and with an organic material. The solid lubricant is resistant to dusting, caking and breakage, can be fed through an automatic dispensing machine, and combines inorganic and organic materials to achieve excellent lubrication properties. The product has low flash and low smoke release into the environment.

Chemical Plating Method, Electrolytic Cell And Automotive Oxygen Sensor Using It, Mary R. Reidmeyer, Matthew J. Donelon, Robert F. Killion

Materials Science and Engineering Faculty Research & Creative Works

An automotive lambda oxygen sensor is formed by electroless plating of a thin, catalytically active, conductive electrode uniformly on the outer surface of a zirconia thimble. The process includes forming a pristine zirconia solid electrolyte thimble and drilling out a cylindrical cavity in it. A porous outer surface suitable for producing crystallization sites is formed by dipping the unfired thimble in a zirconia slurry containing spray-dried microspheres and firing the coated thimble to densify the thimble and the microspheres and to produce cavities on the surface of the thimble. An inner platinum electrode is formed by conventional conductive ink painting …

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 …

Electrical Conductivity Of Nanocrystalline Ceria And Zirconia Thin Films, Igor Kosacki, Toshio Suzuki, Vladimir Petrovsky, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The results of studies of the preparation, structure and electrical conductivity of ZrO₂:16% Y and CeO₂ thin films are presented. Dense films with grain size controlled in the region of 1-400 nm have been obtained on monocrystalline sapphire and polycrystalline Al₂O₃ substrates using a polymeric precursor spin coating method. The electrical conductivity of nanocrystalline thin films has been studied as a function of oxygen activity and temperature and correlated with the microstructure. Nanocrystalline specimens are characterized by enhanced electrical conductivity and different stoichiometry compared with microcrystalline material.

High Strain Rate Superplasticity In Microcrystalline And Nanocrystalline Materials, S. X. Mcfadden, A. V. Sergueeva, Rajiv S. Mishra, A. K. Mukherjee

Materials Science and Engineering Faculty Research & Creative Works

Superplasticity has evolved to become a significant industrial forming process. The phenomenon of superplasticity is explored at high strain rates where it is economically more attractive. True tensile superplasticity has been demonstrated in nanocrystalline materials. The difference in the details of superplasticity between the nanocrystalline and microcrystalline state is emphasised.

An Exafs Study Of Nanocrystalline Yttrium Stabilized Cubic Zirconia Films And Pure Zirconia Powders, Georgina E. Rush, Alan V. Chadwick, Igor Kosacki, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

Detailed EXAFS (extended X-ray absorption fine structure spectroscopy) measurements have been collected for two nanocrystalline forms of zirconia, namely, dense films of yttria-stabilized cubic zirconia (YSZ) and tetragonal phase powders of pure ZrO2. Zr and Y K edge EXAFS spectra for the YSZ films with grain sizes of 6, 15, and 240 nm showed no major differences with the corresponding spectra of the bulk counterpart. This is clear proof that these nanocrystalline films exhibit similar levels of disorder to that of large crystals. In particular, there is no support for the view that the intergrain regions are highly disordered, and …

Evaluation Of Nickel Deposition By Electrochemical Impedance Spectroscopy, M. Holm, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

Electrochemical impedance spectroscopy was used to characterize the deposition of nickel from unbuffered acid sulfate electrolytes, from which a wide range of deposit morphologies and current efficiencies are possible. The operating parameters were in the range of 40 to 60 g L-1 Ni2+, 40 to 60 °C, and the pH from 2.0 to 3.5. The resulting impedance spectra for nickel deposition at 20 mA cm-2 consisted of one or two characteristic loops whose frequency and capacitance were dependent upon the electrowinning conditions and indicative of the resultant deposit morphology. A single high frequency capacitive loop, on the order of 1 …

High Energy Density Dielectrics For Symmetric Blumleins, Wayne Huebner, Shi C. Zhang

Materials Science and Engineering Faculty Research & Creative Works

Multilayer, tape cast ceramics are being developed for use in large area, high voltage devices in order to achieve high specific energy densities (>10⁶ J/m³) and physical size reduction. In particular, symmetric Blumleins are desired with the following properties:

• High voltage hold off (≥ 300 kV)
• High, nondispersive permittivity: ≈100 to 900
• Ability to be fabricated into various shapes and sizes
• Surface flashover inhibition at the edge
• Ability to be triggered by surface flashover switching

The compositions being pursued are based on pure BaTiO₃ dielectrics. Our approach is to add glass phase additions which result …

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 …

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 …

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 YBa₂Cu₃O_7-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 …

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. …

A High Energy X-Ray And Neutron Scattering Study Of Iron Phosphate Glasses Containing Uranium, Mevlüt Karabulut, G. K. Marasinghe, C. S. Ray, Y. S. Badyal, M.-L. Saboungi, S. Shastri, D. Haeffner, George Daniel Waddill, D. E. Day

Materials Science and Engineering Faculty Research & Creative Works

The atomic structure of iron phosphate glasses containing uranium has been studied by complementary neutron and x-ray scattering techniques. by combining x-ray and neutron structure factors, detailed information about different pair interactions has been obtained. Most of the basic structural features such as coordination numbers and O-O and P-O distances in uranium containing glasses are the same as those in the base glass of batch composition 40Fe2O3-60P2O5 (mol %). However, the Fe-O distances change slightly with the addition of uranium. The observed structural parameters support a structural model in which the waste elements occupy voids in the Fe-O-P network, hence, …

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 La_2−x⁢Ba_x⁢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 …

Influence Of Gas Flow Rate On Oxygen Flux Measurements For Dense Oxygen Conducting Ceramic Membranes, W. T. Stephens, T. J. Mazanec, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

Oxygen transport through a dense oxygen conducting ceramic membrane is driven by an oxygen activity gradient imposed by the gas streams on either side of the membrane. The oxygen activity on each side of the membrane is altered as oxygen is transported across the membrane. Thus, the oxygen activity gradient will not be the same in each region of a membrane and will generate a different oxygen flux. This interaction between the oxygen gradient and the oxygen flux can produce a lower average oxygen flux across the membrane, can mask differences between materials, and can explain the dependence of oxygen …