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Study of the structure of ferroelectric domain walls in barium titanate ceramics

Description: Structure of 90{degree} ferroelectric domain boundaries in barium titanate ceramics has been studied by means of Transmission Electron Microscopy and High Resolution TEM. Tilts of specific fringes across domain walls are measured on HREM images and Selected Area Diffraction Patterns. They are in a good agreement with the twin model admitted for these domain boundaries. A computerized method has been developed to give access to quantitative information about atomic displacements across these ferroelectric domain walls. The so calculated displacement field is then compared with Landau-Ginzburg based theoretical predictions.
Date: February 1, 1995
Creator: Normand, L.; Thorel, A.; Kilaas, R. & Montardi, Y.
Partner: UNT Libraries Government Documents Department

Array automated assembly: Phase 2. Quarterly report

Description: An analysis was made of cost trade-offs for shaping modified square wafers from cylindrical crystals. For reasonably expectable silicon and sheet costs, the optimum shape will be nearer a circle than a square. Tests were conducted of the effectiveness of texture etching for removal of surface damage on sawed wafers. Four glass systems have survived preliminary screening tests for use as edge masking dielectrics. These include beta-spodumen, MgO-Al/sub 2/O/sub 3/ borosilicate, baria and titania glasses. Aluminum contact metallization does not appear promising, and six silver screen printing inks have been selected for detailed investigation. Screening tests are underway for the selection of adhesive and coating materials for the superstrate fabrication. Three adhesive candidate materials have been identified for detailed investigation.
Date: February 1, 1978
Creator: Taylor, W.E.
Partner: UNT Libraries Government Documents Department

Studies of the dissolution of geothermal scale

Description: Samples of geothermal scale formed from Magmamax No. 1 and Woolsey No. 1 wells in the Imperial Valley, Calif., were exposed to concentrated and dilute solutions of common laboratory reagents. The time of exposure and temperature of the reagent were also varied. Several reagents easily dissolved significant amounts of the scale. An in situ test was performed with marginal success.
Date: February 4, 1980
Creator: Deutscher, S.B.; Ross, D.M.; Quong, R. & Harrar, J.E.
Partner: UNT Libraries Government Documents Department

ERDA/NASA advanced thermionic technology program. Progress report No. 20

Description: Progress is reported in the areas of surface studies (surface theory and activation chamber experiments), plasma studies (converter theory and enhanced mode conversion experiments), converter development (low temperature conversion experiments and high efficiency conversion experiments), and component hardware (hot shell development). (WHK)
Date: February 1, 1977
Partner: UNT Libraries Government Documents Department

The oxidation state and magnetic behaviour of Tb in high-{Tc} related materials

Description: L{sub 3}-X-ray absorption spectroscopy is used together with inelastic neutron scattering and magnetic susceptibility measurements to characterize the Tb oxidation state and bonding in the high-{Tc} related materials Y{sub 1-x}Tb{sub x}Ba{sub 2}Cu{sub 3}O{sub 7} and Pb{sub 2}Sr{sub 2}TbCu{sub 3}O{sub 8}. The Tb is found to be essentially trivalent in both compounds with no indications of significant hybridization. However, there is evidence of significant Tb-Tb magnetic interactions in Pb{sub 2}Sr{sub 2}TbCu{sub 3}O{sub 8} that persist to temperatures much higher than the Tb long-range ordering temperature.
Date: February 1, 1995
Creator: Soderholm, L.; Staub, U.; Skanthakumar, S. & Antonio, M. R.
Partner: UNT Libraries Government Documents Department

Direct imaging of the atomic structure and chemistry of defects and interfaces by Z-contrast STEM (scanning transmission electron microscopy)

Description: Z-contrast scanning transmission electron microscopy (STEM) is a fundamentally new approach to high-resolution imaging which provides unambiguous, compositionally sensitive images on the atomic scale. Such images are intuitively interpretable, even in thick regions of the sample, tremendously simplifying determination of the structure and chemistry of defects and interfaces. To illustrate this, examples are presented of commonly observed planar defects in laser-ablated thin films of YBa{sub 2}Cu{sub 3}O{sub 7-x}. Film/substrate interfaces are shown to be chemically diffuse on the atomic scale and steps or undulations in the substrate need not result in defects in the film. Low-angle grain boundaries are found to be chemically clean, the drastic reductions in critical currents with tilt angle being due to the array of intrinsic structural defects comprising the boundary. 20 refs., 10 figs.
Date: February 1, 1990
Creator: Pennycook, S. J.; Chisholm, M. F.; Jesson, D. E.; Norton, D. P.; McCamy, J. W. & Lowndes, D. H.
Partner: UNT Libraries Government Documents Department

Infrared phonon structure in epitaxial films of Tl sub 2 Ca sub 2 Ba sub 2 Cu sub 3 O sub 10 at low temperatures

Description: We have used both bolometric and cavity techniques to obtain accurate submillimeter and microwave loss data for epitaxial thin films of Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10} at low temperatures. These films have {Tc}=121.5 K, are c-axis oriented, contain some volume fraction of the 2:1:2:2 phase, and are characterized by excellent in-plane epitaxy. The absorptivity of these films at 100 cm{sup {minus}1} is a factor of five lower than that obtained by others from a reflectivity measurement on a ceramic sample. We observe strong phonon structure for frequencies between 70 and 600 cm{sup {minus}1}, which are in agreement with a lattice dynamical calculation. Our results show remarkably similar phonon structure to that observed in the ceramic sample. This is in strong contrast to the case for other high {Tc} superconductors such as YBa{sub 2}Cu{sub 3}O{sub 7}, where phonon structure observed in ceramic samples in absent in epitaxial oriented films and crystals because of the electronic screening due to the high conductivity of the a-b planes. At microwave frequencies the absorptivity follows a frequency squared dependence, and is consistent with the submillimeter results. 6 refs.
Date: February 1, 1992
Creator: Miller, D.; Richards, P.L. (Lawrence Berkeley Lab., CA (United States)); Lee, W.Y. (IBM Research Div., San Jose, CA (United States). Almaden Research Center); Newman, N.; Garrison, S.M. (Conductus, Inc., Sunnyvale, CA (United States)) & Martens, J.S. (Sandia National Labs., Albuquerque, NM (United States))
Partner: UNT Libraries Government Documents Department

[Development of a semi-autonomous mobile robot for reactor containments]

Description: The University of Michigan reports its progress on this project on a bimonthly or quarterly reporting frequency. As a result, the detailed annual summary of activity is derived from the integration of these progress reports. They are attached here to form a permanent record of the University's contribution to this program.
Date: February 10, 1993
Creator: Wehe, D.K.
Partner: UNT Libraries Government Documents Department

High-temperature superconductor applications development at Argonne National Laboratory

Description: Developments at Argonne National Laboratory of near and intermediate term applications using high-temperature superconductors are discussed. Near-term applications of liquid-nitrogen depth sensors, current leads, and magnetic bearings are discussed in detail.
Date: February 9, 1992
Creator: Hull, J.R. & Poeppel, R.B.
Partner: UNT Libraries Government Documents Department

Influence of oxygen partial pressure and silver additions on microstructure and related properties of YBCO superconductors

Description: Microstructure has a great influence on the mechanical and superconducting properties of YBCO. Mechanical properties of YBCO can be improved by both modifying the monolithic microstructure and developing composites of YBCO with silver (Ag). When monolithic YBCO was sintered to high densities ({approx} 91%) at a relatively low temperature ({approx} 910{degrees}C) by controlling oxygen partial pressure during sintering, the result was a small-grain microstructure (average grain size {approx} 5 {mu}m) and hence a high strength of 191 {plus minus} 7 MPa. Addition of Ag as a second phase further improved the strength of YBCO. Composites of YBCO with 10 to 15 vol % Ag has a strength of 225 {plus minus} 6 MPa and a fracture toughness of 3.3 {plus minus} 0.2 MPa{radical}m. These improvements are believed to be due to compressive stresses in the YBCO matrix as a result of thermal mismatch between the YBCO and Ag phases. Furthermore, the Ag particles may provide increased resistance to crack propagation by pinning the crack. On the other hand, addition of Ag as a dopant to substitute for Cu sites in YBCO has a profound but nonmonotonic effect on grain microstructure and the resulting critical current density.
Date: February 1, 1992
Creator: Singh, J.P.; Joo, J.; Guttschow, R. & Poeppel, R.B.
Partner: UNT Libraries Government Documents Department

[Aspects of photoionization of impurities and electron transfer in ionic crystals]

Description: Spectral evidence was found for photoionization in spectra of Eu[sup 2+] and Sm[sup 3+] in BaF[sub 2]; Ce[sup 3+] was also studied in BaF[sub 2], CaF[sub 2], and SrF[sub 2]. Two-photon spectroscopy of forbidden transitions (zero-phonon lines) was extended from NaF: Cu[sup +] to Mn[sup 4+] in Cs[sub 2]GeF[sub 6] and to MgO:Ni[sup 2+].
Date: February 10, 1993
Creator: McClure, D.S.
Partner: UNT Libraries Government Documents Department

Direct conversion of methane to C sub 2 's and liquid fuels

Description: Research on promoted metal oxide catalysts has continued with the study of alkaline earth/metal oxide halide catalysts. A barium bromide/alumina catalyst was comparable in methane conversion and selectivity to C{sub 2}'s to barium chloride/alumina catalysts. The effects of varying methane to oxygen feed ratios were explored for one of the best alkaline earth catalysts and one of the best literature catalysts (Li/MgO). A significant decrease in the selectivity to C{sub 2}'s is observed upon addition of ethane to the feed gas (feed gas methane/ethane ratio of 3). This observation demonstrates that a significant amount of ethane should not be recycled during methane oxidation over these types of catalysts under process conditions used. Methane oxidation over barium carbonate alone results in high enough selectivities and methane conversions to suggest an oxidized barium species may be responsible for methane oxidation on barium/metal oxide catalysts. Methane coupling studies have continued using layered perovskite catalysts in the cofeed mode and double perovskite catalysts in the sequential mode. Addition of sodium to the double perovskite LaCaMnCoO{sub 6} resulted in a catalyst with improved selectivity over the one without sodium. A reactor system containing two reactors in under construction. These reactors will be used to study different feed diluents, including steam. One reactor will be used to study the effects of pressure on the reaction. Process economics were explored for a hypothetical methane coupling scheme employing a feed mixture of 7/2/1 nitrogen/methane/oxygen. Economic evaluations of the first two of a series of cases based on extrapolations of Union Carbide methane coupling results have been completed. 33 refs., 17 figs., 2 tabs.
Date: February 14, 1990
Creator: Warren, B.K.; Campbell, K.D. & Matherne, J.L.
Partner: UNT Libraries Government Documents Department

[Development of a semi-autonomous mobile robot for reactor containments]. 1992 annual summary of activity

Description: The University of Michigan reports its progress on this project on a bimonthly or quarterly reporting frequency. As a result, the detailed annual summary of activity is derived from the integration of these progress reports. They are attached here to form a permanent record of the University`s contribution to this program.
Date: February 10, 1993
Creator: Wehe, D. K.
Partner: UNT Libraries Government Documents Department

Studies of Y-Ba-Cu-O single crystals by x-ray absorption spectroscopy

Description: The symmetry and density of unoccupied states of YBa{sub 2}Cu{sub 3}O{sub 7} YBa{sub 2}Cu{sub 4}O{sub 8} have been investigated by orientation dependent x-ray absorption spectroscopy on the O 1s edge using a bulk-sensitive fluorescence-yield-detection method. It has been found that the O 2p holes are distributed equally between the CuO{sub 2} planes and CuO chains and that the partial density of unoccupied O 2p states in the CuO{sub 2} planes are identical in both systems investigated. The upper Hubbard band has been observed in the planes but not in the chains in both systems. 18 refs.
Date: February 1, 1992
Creator: Krol, A.; Ming, Z.H.; Kao, Y.H. (State Univ. of New York, Buffalo, NY (United States). Dept. of Physics); Nuecker, N.; Roth, G.; Fink, J. (Kernforschungszentrum Karlsruhe GmbH (Germany). Inst. fuer Nukleare Festkoerperphysik) et al.
Partner: UNT Libraries Government Documents Department

Recent results in characterization of melt-grown and quench-melt- grown YBCO superconductors

Description: From the standpoint of applications, melt-grown (MG) and quench-melt-grown (QMG) bulk YBCO superconductors are of considerable interest. In this paper, we studied the intragranular critical current density (J{sub c}), the apparent pinning potential (U{sub o}), and the irreversibility temperature (T{sub irr}) of MG and QMG samples and compared the results to those for conventionally sintered YBCO. A systematic increase in U{sub o} and a slower drop in J{sub c} with temperature indicate a systematic improvement in flux-pinning properties in progressing from the sintered YBCO to QMG and MG samples. Weaker pinning is observed in the QMG YBCO than in the MG samples.
Date: February 1, 1992
Creator: Balachandran, U.; Poeppel, R.B. (Argonne National Lab., IL (United States)) & Gangopadhyay, A.K. (Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering)
Partner: UNT Libraries Government Documents Department

Local environment around the oxygen atoms in Y-Ba-Cu-O studied x-ray absorption fine structure (XAFS) spectroscopy

Description: The local environment about oxygen atoms in the CuO{sub 2} plane in YBa{sub 2}Cu{sub 3}O{sub 7} single crystals has been investigated by orientation-dependent x-ray absorption fine structure (XAFS) spectroscopy at the O ls edge using bulk-sensitive fluorescence-yield-detection method. Within experimental accuracy ({plus minus}0.03 {Angstrom}) no structural change in local ordering about oxygen atoms in the CuO{sub 2} plane at 90 K has been detected. 14 refs.
Date: February 1, 1992
Creator: Krol, A.; Soo, Y.L.; Huang, S.W.; Ming, Z.H.; Kao, Y.H. (State Univ. of New York, Buffalo, NY (United States). Dept. of Physics); Nuecker, N. et al.
Partner: UNT Libraries Government Documents Department

Control of toxic metallic emissions formed during the combustion of Ohio coals. Final report, September 1, 1993--August 31, 1994

Description: The objective of the project was to characterize metallic emissions from representative coals and develop strategies for their control. Though metallic emissions from coal combustors have been extensively studied, more studies need to be performed to better characterize the interaction of various species which is required for the selection and design of sorbents for effective control of these emissions. Some coals are rich in sulfur, and utilities using these coals will have to use some form of Flue Gas Desulfurization (FGD). A technique for FGD is the use of calcium based sorbents, and the degree of metals capture of these sorbents under different conditions will be researched. The objective of the first year of the study was to understand the evolution of metallic aerosol size distributions and the capture characteristics of various sorbents. Also, the metallic emissions resulting from the combustion of two seams of Ohio coals were to be characterized. Studies on the evolution of the metallic aerosol size distributions have been completed and the use of silicon and calcium based sorbents for capture of lead species has been examined. Co-injection of metallic compounds along with organometallic silicon indicated a high degree of capture of lead in a certain temperature regime. Preliminary results with calcium based sorbents also indicate capture of metallic species. To gain a further understanding of the capture processes, in situ optical diagnostic studies were performed in collaboration with researchers at the National Institute of Standards and Technology. Spectroscopic studies (laser induced fluorescence coupled with particle scattering) were performed to help understand the mechanisms of metallic species capture.
Date: February 1995
Creator: Biswas, Pratim; Owens, T. M. & Wu, Chang-Yu
Partner: UNT Libraries Government Documents Department