摘要:

High quality Y‐Ba‐Cu‐O thin films were produced on single‐crystal Mgo and SrTiO3by metal‐organic chemical vapor deposition (MOVD) using metal chelates of &bgr;‐diketonate ligands. The films were grown in a cold‐wall CVD reactor at a reactor pressure of 10 torr and substrate temperature in the range 700–900 °C. Characterization studies were performed using Rutherford Backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDXS). The studies showed that the films were uniform, continuous, adherent and highly pure. Four point resistivity measurements showed that films had a sharp superconducting transition at 92 K and exhibited critical current densities of ∼5–106A/Cm2(B=0, T=77K).

ISSN:0094-243X    

DOI:10.1063/1.40280

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In ongoing research on the properties and fabrication of cuprate superconductors, we report here: experimental details on their magnetic alignment and its determination; a study of the ‘‘crossing over’’ from parallel to normal alignment (or failure to do so completely) in Gd‐containing Bi‐2212 and 123, respectively; and data on the complex magnetic field alignement of the non‐superconducting 211 phase RE2BaCuO5as a function of the rare earth (RE).

ISSN:0094-243X    

DOI:10.1063/1.40245

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The substantial variation in the melting behavior of the 123 (RE) high‐Tcsuperconductor (HTSC) phase Re1Ba2Cu3O6.5+&dgr;with substitution of different RE’s has been noted and partially studied before. Because of the enormous practical importance of the melting points in the processing of this major HTSC compound (e.g., in melt growth or regrowth, use as crucibles or melt substrates, non‐melting dispersoids, etc.), we have undertaken an operational study of the softening and melting behavior for all accessible RE elements forming a superconducting 123 phase; we report this study here.

ISSN:0094-243X    

DOI:10.1063/1.40246

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Preparation of YBa2Cu3Oxby solid state reaction of constituent oxides or carbonates results in a powder that is normally coarse and has a wide size distribution. Preparation of the fine powder is of utmost importance in the processing of the material into wires and tapes. The grinding media used seem to exert considerable influence on the morphology of the powders. Generally long exposure to liquid media results in the degradation of the material.The size, shape and distribution of powders ground in hexane, ethanol, xylene and deodorized kerosene for different time intervals up to 300 hours were studied. The degradation caused by exposure to the liquid media used for grinding and the effect of long term grinding on the crystal structure are also discussed.

ISSN:0094-243X    

DOI:10.1063/1.40247

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Ca‐free T1PbSrRCuO samples (R=rare earths) with Tc up to above 100 K were prepared, and studied by resistance and ac susceptibility measurements and by powder x‐ray diffraction analyses. A 1212‐type phase (Tl1−xPbx)Sr2(Sr1−yRy)Cu2Ozis responsible for the observed supercondcutivity. A rare‐earth is required for the formation of the 1212 phase. Pb‐dopping is necessary to increase the Tc of the 1212 phase from 90 K to above 100 K.

ISSN:0094-243X    

DOI:10.1063/1.40248

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Yttrium, barium and copper nitrates are dissolved in de‐ionized water to form a 0.038M: 0.078M: 0.1o5M solution, which is used to generate,in‐situY1Ba2Cu3O7−xsuperconducting films in an argon‐oxygen rf plasma. rf power is operated at 4.5 kW, 13.56 MHz and 760 Torr pressure. The best zero resistance temperature, onset critical temperature and current density measured by the four probe transport method are 86 K, 92 K and 4×105A/cm2at 77 K and zero field. X‐ray diffraction shows the films to be oriented withc‐axis perpendicular to the substrate surface. Variations in the critical temperatures of the films and their microstructure depend on rf power, solution composition, solution concentration, plasma gas and aerosol carrier gas. It has been seen that the concentration of barium in the solution is more critical than that of copper. The concentration of the solution is related to the rf power, to prepare the best film, the concentration and the power levels have to be matched. While the variation of both aerosol carrier gas flow rate and the plasma gas flow rate causes a change in the structure and critical temperature of the film, the control of the former is more critical than the plasma gas flow rate.

ISSN:0094-243X    

DOI:10.1063/1.40249

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Electrical properties of the contacts with different contact materials on superconducting YBCO thin films were extensively investigated. The different contact materials including Au, Pd/Au, Ag, Yb/Cr/Al, RuO2, RuO2/Au, and RuO2/Ag were chosen to explore the possibility of fabricating low resistance contacts on superconducting YBCO films with processes and materials compatible with semiconductor technology. Experimental results demonstrated the surface condition dependent contact properties regardless of the contact materials. Reproducible and controllable contacts were realized by using RuO2or the combination of RuO2with other metals.

ISSN:0094-243X    

DOI:10.1063/1.40250

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Brush‐on‐method with partial‐melt growth has been used to fabricate Bi‐based 2212 superconducting thick films on silver. Transport properties show critical currents of 10–20 amperes (or equivalentlyJcof 105A/cm2below 20K and zero field), with a 50 percent degradation at 9 tesla field parallel to the film surface. Electron microscopy reveals the film to be layered, consisting of platelets with large aspect ratios and with thec‐axis perpendicular to the substrate. Transport and microstructural properties of the films has been found to depend on the structural integrity of the substrate. Silver foil, 25 microns thick, has resulted in poor films with microcracks, whereas 75 micron thick silver foil have resulted in sturdy high quality superconducting films. Sputter deposited silver on polycrystalline MgO results in the total diffusion of the silver into the film with a corresponding degradation in film properties. Film processing and corresponding characterization results will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.40251

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Superconducting Y1Ba2Cu3O7−&dgr;films were produced by a radio frequency (RF) plasma aerosol evaporation technique at atmospheric pressure without post‐annealing. Aqueous solutions containing Y, Ba, and Cu were genertaed as an aerosol which was then injected into the plasma region. The ionized species were deposited onto substrates outside of both the plasma and flame regions. The substrate temperature was 400–600°C. The deposition rate is 0.01–100 &mgr;m/ (min cm2), and the film thickness is 1–200 &mgr;m. For an ‘‘as deposited’’ film on a single crystalline MgO substrate (100) with substrate temperature of 600 °C, the onset temperature of the superconducting transition is 100 K with a transition width (10%–90%) of 3 K, and zero resistance at 93 K. The critical current density of the film is 0.8–104A/cm2at 77 K. An optimum substrate temperature for this technique is discussed. The as‐deposited films are compared with other post‐annealed films (850°C, 1 hour). Since this technique does not require a vacuum environment it has potential for large scale production of thin films.

ISSN:0094-243X    

DOI:10.1063/1.40252

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Some problems of the controlled growth of the HTSC layered crystals and textured Bi‐Sr‐Ca‐Cu‐O films by the Czochralski technique and liquid and epitaxy are considered in the present paper. Layered crystals of the diameter 30 mm, thickness 5 2m and epitaxial films on YA1O3substrate were obtained.

ISSN:0094-243X    

DOI:10.1063/1.40253

出版商:AIP    

年代:1991

数据来源: AIP