Sponsored by: Jt. EMPMD/SMD Superconducting Materials Committee, MSD Electronic, Magnetic and Optical Phenomena Committee, and FEMS (Federation of European Materials Societies)
Program Organizers: U. Balachandran, Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439; Paul J. McGinn, University of Notre Dame, Notre Dame, IN 46556; and Stuart Abell, University of Birmingham, Edgbaston, Birmingham B152TT, UK
Wednesday, PM Room: B8
February 7, 1996 Location: Anaheim Convention Center
Session Chairpersons: S. Abell, University of Birmingham, Edgbaston, UK; M. Dhalle, Imperial College, London, UK
2:00 pm
HYSTERESIS MOTOR AND LINEAR CARRIER SYSTEM CONSTRUCTED WITH BULK MELT TEXTURED YBCO: W. Gawalek, T. Habisreuther, T. Straer, M. Wu, D. Litzkendorf, P. Görnert, Institut für Physikalische Hochtechnologie e.V., Helmholtzweg 4, D-07743 Jena, Germany; K. V. Ilushin, L. K. Kovalev, Moscow State Aviation Institute, Volokolamskoe shosse, 125871 Moscow, Russia
Bulk cylindrical blocks of YBCO are prepared by a modified Melt Textured Growth batch process. Multi-grain samples are characterized by integral levitation force measurements at 77 K and 18 K in the zero field cooled and field cooled state. Field mapping of the frozen flux distribution was carried out at 77 K using an axial Hall probe. In maximum the blocks trap 0.4 T (extrapolated to the surface). With blocks of our melt textured material the rotor of a hysteresis motor was constructed. The motor was tested in liquid nitrogen for some hours with 3.000 rpm and an output power of about 80 W is reached. With the material also a linear carrier system for application relevant investigations at 77 K was constructed. The carrier equiped with 4 permanent magnet rails is placed below the dewar containing the HTSC blocks before the system was field cooled. The carrier can be moved parallel to the rails with very low friction, for the remaining five degrees of freedom we found high stiffness and damping.
2:20 pm
THE EFFECT OF BUFFER LAYERS ON SLOW WAVE PROPAGATION IN SUPERCONDUCTING PLANAR TRANSMISSION LINES: Farhat Abbas, L. E. Davis, Dept. Elec. Eng. & Elec, UMIST P O Box 88 Manchester M60 lQD UK; J. C. Gallop, National Physical Labortory, Teddington Middlesex TW11 OLW UK
Attempts to grow YBCO films on both sapphire and Si directly have encountered some serious problems due to large mismatches of both lattice constants and thermal expansion coefficients of the YBCO films and sapphire, and Si. For cryogenic microwave microelectronics application it is necessary to seek proper buffer layers which, prevent the interdiffusion, better thermal expansion coefficient matching, better lattice matching, confinement of the field into substrate and enhance the fact that a wave in a superconducting transmission line would be slowed due to the penetration of the magnetic field into the superconductor. In this study an analysis has been completed to explore the slow mode of propagation which is dependent on the material properties and thicknesses of the superconductors, substrate, and buffer layers. Relative velocity with respect to that in vacuo is computed for various combinations of material properties. The dependence on the dielectric constant of the buffer layers is discussed.
2:40 pm
CURRENT-VOLTAGE CHARACTERISTICS OF BSCCO CONDUCTORS: M. Dhalle, J. Everett, M. Johnston, J. V. Thomas, A. D. Caplin, Centre for High Temperature Superconductivity, Blackett Laboratory, Imperial College, London SW7 2BZ, UK
Transport and magnetization measurements of current-voltage (I-V) characteristics of conductors complement each other in two important respects: The magnetic studies extend the characteristics downward by several orders of magnitude in electric field, and the topology of the important current paths is very different in the two cases. Furthermore, current paths that are associated with weak-links are suppressed in rather low magnetic fields. We report detailed transport and magnetic studies of a range of BSCCO-phase conductors, and interpret the data within a model that incorporates a spectrum of current paths, and includes both inter- and intra-granular current limitation.
3:00 pm
CRYOGENIC MICROCALORIMETER FOR MEASUREMENT OF MICROWAVE SURFACE IMPEDANCE OF HTS-THIN FILMS: L. Brunetti, M. Petrizzelli, Isituto Electrotecnico Nazionale "G Ferraris" Strada delle Cacce 91, 10135 Torino, Italy
Since the discovery of superconductivity, the measurement of the surface impedance Z of thin films represents one of the most important paces for the application of the materials at microwave frequencies. In this paper we describe a cryogenic microcalorimeter for measurements of microwave surface impedance in HTS thin films. The microcalorimeter technique, that is an alternative approach to other methods, is based on the temperature rise measurement produced by microwave power dissipation in a thermally isolated thin film. Basically, the HTS thin film is the dissipative element of a self-resonant microwave structure, that is a tuned bolometer mount. It is placed inside an undervacuum container and supplied with microwave power through a thermal insulating waveguide section while a copper-constantan thermopile senses its temperature. This structure allows to know the real power dissipated in the film and then the related quantities, like R.
3:20 pm BREAK
3:30 pm
MICROSTRUCTURE OF 123-211 MELT-TEXTURED COMPOSITES STUDIED BY POLARIZED LIGHT MICROSCOPY: P. Diko, Institute of Experimental Physics, SAS, Watsonova 47, 04353 Kosice, Slovakia; W. Gawalek, T. Habisreuther, P. Görnert,IPHT, Helmholtzweg 4, 100239 Jena, D-07702, Germany; N. Pellerin, P. Odier, CCRPHT, CNRS, 4S071 Orleans Cedex 2, France; R. Cloots, M. Ausloos, SUPRAS, University of Liége, B-4000 Liége, Belgium
The microstructure features of melt-textured YBaCuO (123) such as observed phases, 123 domain and subgrain boundaries, macro and microcracking and twin structure have been characterized. The linear dependence between a-b microcrack spacing, Ic, and d21l, V123/V2ll(d2ll-mean 211 particle size, V123-123 volume fraction, V21l-211 volume fraction) was observed. Shorter mean free distance between 211 particles depresses the subgrain thickness, the twin complex size and twin spacing. The level of residual tensile stress in the 123 a-b plane (50-100 MPa) was estimated from detwinning observed around 211 particles. A maximum residual tensile stress of 290 MPa in the "c" direction was estimated on the basis of the 123 fracture toughness. Oxygenation of the melt-textured samples was shown to be a combination of oxygen volume diffusion, microcracking and penetration of oxygen through the cracks. A new secondary phase having a composition close to Ba2Cu5Ox has been found. The essential influence of gas bubbles, and uniformity of 211 particles in the melt, on the microstructure of 123 domains has been shown.
3:50 pm
XPS AND A.C. SUSCEPTIBILITY STUDY OF SURFACE DEGRADATION OF YBa2Cu307-x POWDERS: I. Sargánková, P. Diko, Institute of Experimental Physics, Slovak Academy of Science, Watsonova 47, 043 53 Kosice, Slovakia; J. D. Tweed,C. A. Anderson, N. M. D. Brown, Joint Ceramics Research Centre, Surface Science Laboratory, University of Ulster, Cromore Road, Coleraine, Co. Londonderry, Northern Ireland, BT52 lSA
The preparation of powder fractions of YBa2Cu3O7-x by sedimentation in 2-butanol raises questions of particle surface degradation of particles during the sedimentation and the possibility of regeneration by re-annealing. In this work we studied this behaviour by XPS and a.c. susceptibility measurements. Characteristic peaks for monitoring changes due to degradation and regeneration were found in the Y3d (c. 160 eV) and Cls (c. 282 eV) regions. Our results suggest that annealing close to the sintering temperature can regenerate the particle surfaces.
4:10 pm
MAGNETIC BEHAVIOR OF YBa2Cu307-x (123)-Y2BaCuO5 (211) SINTERED COMPOSITES PREPARED BY SOL-GEL: P. Diko, I. Sargánková, Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 04353 Kosice, Slovakia; M. Reissner, W. Steiner, Institut fur Angewandte und Technische Physik, Technische Universitat Wien Wiedner Hauptstrasse 8-10/137, a-1040 Wien, Austria
The grain growth at 980deg.C in 123-211 composites prepared by sol-gel technic is controlled by pinning of 123 grain boundaries by 211 particles. It produces a narrow 123 grain size distribution. The secondary grain growth in pure 123 leads to the structure composed by large and small grains (bimodal grain size distribution). The quality of contacts between 123 grains is related to the deviation from 123-211 line and to the grain size uniformity.
4:30 pm
IN SITU PREPARATION OF EXPITAXIAL TlBa2Ca2Cu3O9 FILMS BY LASER ABLATION IN THE PRESENCE OF Tl2O VAPOR: N. Reschauer, U. Spreitzer, W. Brozio, A. Piehler, K. F. Renk, Institut für Angewandte Physik, Universität Regensburg, 93040 Regensburg, Germany
We report an in situ growth method of epitaxial TlBa2Ca2Cu3O9 (Tl-1223)
high Tc films. By laser ablation from a BaCaCuO target we deposited Ba, Ca, and
Cu simultaneously with Tl in an oxygen atmosphere. The Tl was delivered as Tl2O
vapor by thermal evaporation of Tl2O3 powder. Typical film thicknesses were
80-400 nm. The films had transition temperatures near 100 K. X-ray diffraction
patterns of [[theta]] - 2[[theta]] scans indicated that the films were single
phase and highly oriented with the c axis perpendicular to the substrate
surfaces. Epitaxial growth of the films was proved by [[theta]] scan
measurements. Scanning electron microscope investigations showed smooth
surfaces without platelike structures.
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