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18 results on '"Lechter, W. L."'

4. The color of polarization in cuprate superconductors

Author

Hoff, H. A, Osofsky, M. S, Lechter, W. L, and Pande, C. S

Subjects
Solid-State Physics
Abstract

A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in reflected light through crossed polarizers (color of polarization). Such colors are generally characteristic of particular phases. When grains of many members of the class of hole carrier cuprate superconductors are so viewed at room temperature with a 'daylight' source, a characteristic color of polarization is observed. This color was studied in many of these cuprate superconductors and a strong correlation was found between color and the existence of superconductivity. Two members were also examined of the electron cuprate superconductors and it was found that they possess the same color of polarization as the hole carrier cuprate superconductors so far examined. The commonality of the characteristic color regardless of charge carrier indicates that the presence of this color is independent of carrier type. The correlation of this color with the existence of superconductivity in the cuprate superconductors suggests that the origin of the color relates to the origin of superconductivity. Photometric techniques are also discussed.

Published
1991

5. The color of polarization in cuprate superconductors

Author

Hoff, H. A, Osofsky, M. S, Pande, C. S, and Lechter, W. L

Subjects
Solid-State Physics
Abstract

A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in reflected light through crossed polarizers (color of polarization). Such colors are generally characteristic of particular phases. When grains of many members of the class of hole carrier cuprate superconductors are so viewed, using a xenon light source (600 K color temperature), a characteristic color of polarization is observed. This color was studied in many of these cuprate superconductors and a strong correlation was found between color and the existence of superconductivity. One of the members of the electron carrier cuprate superconductors (Nd(1.85)Ce(.15)CuO(4-x) was examined and found that it possesses the same color of polarization as all the electron hole carrier cuprate superconductors so far examined. The commonality of the characteristic color in the cuprate superconductors indicated that the presence of this color is independent of the nature of charge carriers. The correlation of this color with existence of superconductivity suggests that the origin of the color relates to the origin of superconductivity in the cuprate superconductors. Photometric techniques are also discussed.

Published
1990

10. Properties of electrodeposited Co-Cu multilayer structures.

Author

Dariel, M., Bennett, L. H., Lashmore, D. S., Lubitz, P., Rubinstein, M., Lechter, W. L., and Harford, M. Z.

Subjects
ALLOY plating, COBALT plating, COPPER plating, ELECTROLYTES, SURFACE roughness
Abstract

Reports on the electroplating of alternate layers of cobalt (Co) and copper (Cu) of individual thicknesses from an electrolyte having a low concentration of Cu and a high concentration of Co atoms. Electrodeposition technique used to prepare the Co-Cu composition modulated alloys; Investigation of the effects of surface roughness and layer interactions.

Published
1987
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13. Casting high-Tcsuperconducting BiSCCO

Author

Das, B. N., Toth, L. E., Rayne, R. J., Bender, B. A., Osofsky, M. S., Soulen, R. J., Lechter, W. L., Koon, N. C., and Wolf, S. A.

Abstract

Bi-Sr-Ca-Cu-O (BiSCCO) was melted and cast into molds in order to render the superconductor into fully dense and useful shapes. Special conditions for casting and subsequent heat treatments were required to ensure structural integrity and a high transition temperature,Tc.The history of the castings during heat treatments was studied by thermal analysis, X-ray diffraction, and microscopy.

Published
1989
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14. Novel technique for crystal growth of superconducting ErBa2Cu3O7

Author

Lechter, W. L., Das, B. N., Skelton, E. F., Osofsky, M. S., Toth, L. E., Hoff, H. A., Kamm, G. N., Singh, A. K., LeTourneau, V., Pande, C. S., and Wolf, S. A.

Abstract

Millimeter-sized crystals of ErBa2Cu3O7 were fortuitously grown while sintering a flat disk. It was possible to separate individual crystals from the sintered mass and measure their properties. The resistive transition and onset of magnetic transition of a single crystal was 93 K and the resistive transition width was < 1 K. Flux expulsion was observed and individual crystals could be levitated by a magnetic field. Crystals showed unusual growth features. They were heavily corrugated along the part of the crystal that grew parallel to the top surface of the disk and that coincided with thec axis of the unit cell. Crystals were characterized by X-rays, electron microscopy, and optical microscopy.

Published
1988
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15. Optical differentiation of orthorhombic superconductors such as YBa2Cu3O7 from their tetragonal precursor material

Author

Hoff, H. A., Singh, A. K., Wallace, J. S., Lechter, W. L., and Pande, C. S.

Abstract

The orthorhombic superconducting phase of YBa2Cu3O7 is shown to be differentiable from its tetragonal precursor by optical microscopy. Individual grains 1 µm in diameter or larger are found to either exhibit the color of the compensator in reflected polarized light (tetragonal material) or to change colors from the compensator (orthorhombic material). By using color differences, retained tetragonal material and the orthorhombic nature of untwinned areas of grains are identified. The advantage to producing better superconducting single crystals and sintered polycrystalline materials is discussed.

Published
1988
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17. Thin-film high Tc superconductors prepared by a simple flash evaporation technique.

Author

Osofsky, M. S., Lubitz, P., Harford, M. Z., Singh, A. K., Qadri, S. B., Skelton, E. F., Elam, W. T., Soulen, R. J., Lechter, W. L., and Wolf, S. A.

Subjects
HIGH temperature superconductors, THIN films
Abstract

Thin films of Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O have been deposited on single-crystal MgO substrates by a simple flash evaporation technique. Small pellets of the superconducting compound were formed by standard techniques, then evaporated to completion on the MgO substrates using an electron beam. The best films show an onset of superconductivity at approximately 110 K and zero resistance by 78 K. X-ray diffraction measurements show the films to be tetragonal with nominal lattice parameters of a=3.85 Å and c=30.66 Å. The x-ray data also show the films to be highly textured with the metal-oxide planes parallel to the substrate surface. [ABSTRACT FROM AUTHOR]

Published
1988
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