摘要:

Y1Ba2Cu3O7−&dgr;films prepared by chemical vapor deposition indicate very strong anisotropic behavior of the upper critical field and the critical current density. It is found that the angular dependence of the critical current density predominantly comes from the anistropy of the upper critical field.

ISSN:0094-243X    

DOI:10.1063/1.40233

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Superconducting YBCO thin films with a zero resistance temperature of around 80 K and very sharp transitions were obtained on Si substrates by RF magnetron sputtering from a stoichiometric oxide target. Metallic ruthenium oxide was used as a buffer layer to reduce the interdiffusion between YBCO and Si and to nucleate YBCO. The stoichiometry of the YBCO films was well controlled by arranging the substrates perpendicular with respect to the target. The introduction of oxygen into the sputtering chamber immediately after YBCO film deposition was very important to obtain such superconducting films as indicated by thein situfilm resistance measurement.

ISSN:0094-243X    

DOI:10.1063/1.40235

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

96 Sn‐4 Ag was superior to Sn or 63 Sn‐37 Pb as the binder for continous carbon fiber reinforced superconductor. It allowed diffusion bonding to YBa2Cu3O7−&dgr;superconductor to take place at 85 °C. By using 96 Sn‐4 Ag as the binder and YBa2Cu3O7−&dgr;powder prepared by vacuum calcination, carbon fiber reinforced superconductor ofJcaround 400 A/cm2at 77 K was obtained. The composite processing had negligible effect on theJcof the superconductor.

ISSN:0094-243X    

DOI:10.1063/1.40236

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of particle size and shape on the orientation of bulk forms YBa2Cu3O7−xhas been studied. Orientation was found in the green pressed sample made of relatively coarse powder (consisted of 50%–200 mesh and 50% −325 mesh), while there was no such orientation found in sample prepared by shaker mill which consisted of fine particles (1.10 &mgr;m). However, after melt processing including a 100 hr anneal at 980 °C in O2, highly oriented surface layers developed on both type of samples.

ISSN:0094-243X    

DOI:10.1063/1.40237

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

One important requirement for large scale applications of highTcsuperconducting films as well as for some very interesting experiments in the field of microwave properties is the successful deposition of high quality large area thin films. The utilization of a multitarget magnetron sputtering system, especially designed for preparing film sizes up to two inches in diameter, allows a variety of different film compositions in the YBCO system. To avoid problems arising from the chemical properties of many barium compounds, we used targets of the intermetallic compounds BaCu and YCu, respectively. Argon is used as sputtering gas. Beside this, we let a flow of oxygen direct to the growing film to form the superconducting oxide. The substrate holder can be heated up by quartz lamps over 900 °C. We are using two different ways to prepare thin supercondcuting films. The first way is an ‘ex‐situ’ process. The oxygen partial pressure during depoistion is very low due to the metallic surface of the targets. The superconducting phase is formed during a short high temperature post annealing in the deposition chamber at a pressure of 10mbar of pure oxygen without breaking the vacuum. The other way uses oxidized targets, where higher oxygen partial pressures are possible. Utilization of a suitable substrate temperature during deposition and omission of the high temperature post annealing lead to an ‘in‐situ’ process. In this work we discuss both ways of sputter deposition and compare the properties of ‘‘ex‐situ’’ and ‘in‐situ’ grown films. Our best films so far show metallic behavior and a critical temperature (R=0) above 85 K.

ISSN:0094-243X    

DOI:10.1063/1.40238

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The development of a commercial‐scale sputtering process for deposition of superconducitng YBa2Cu3O7(YBCO) thin films is described.YBCO films are sputter deposited from a single 20 cm diameter powder target onto 2 inch substrates of MgO and LaAlO3usingin‐situheating to produce high quality, c‐axis oriented films without post annealing. By locating the substrate above the center of the magnetron erosion ring and by placing a ‘‘negative ion shield’’ between the target and the substrate, negative ion resputtering is avoided. Small shifts in composition are corrected by using a slightly Y‐ and Cu‐rich target to produce films within 1% of stoichiometric composition. Films on LaAlO3and MgO have critical temperatures up to 88 K and critical currents above 5×105A/cm2at 77 K. Uniformity is ±5% in thickness and ±7% in resistivity across at 2‐inch diameter substrate. Microwave surface resistance meaurements at 1.2 GHz and 4 K showRS≊0.1 m&OHgr; for YBCO ground planes and ≊0.3 m&OHgr; for patterned YBCO striplines on MgO.

ISSN:0094-243X    

DOI:10.1063/1.40239

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Stability of the YBa2Cu3Ox(YBCO) superconductor in reacting with CO2in CO2/O2gas mixtures during sintering was investigated as a function of the partial pressure of CO2and temperature. The transport critical current density,Jc, of the superconductor decreased drastically with increasing partial pressure of CO2in the gas mixture. As the partial pressure of CO2was increased,Jcbecame zero (at 77 K) even though the major phase of the sample was still a superconductor according to magnetic susceptibility measurements. Microstructures and compositions of the samples were investigated by transmission electron microscopy in conjunction with energy‐dispersive X‐ray spectroscopy. Two types of grain boundaries were observed: ≊10% of the grain boundaries contained a second phase, and the regions near the remaining grain boundaries were tetragonal. At high partial pressures of CO2, the YBCO completely decomposed to BaCO3, Y2BaCuO5, and CuO.

ISSN:0094-243X    

DOI:10.1063/1.40240

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The degree of texturing of the grains in epitaxial Y‐Ba‐Cu‐O films was studied by x‐ray measurements. These high quality laser deposited films were all aligned with thec‐axis perpendicular to the substrate surface, with a spread angle ranging from 0.3° to 4°, depending on the substrate quality. It was found that films on SiTiO3(100) and LaAlO3(100) were totally aligned with the a‐axis either parallel or pependicular to the [100] direction of substrate. On MgO(100) there was a small fraction of the grains in the ⟨110⟩ direction. For yttria‐stabilized‐zirconia, the a‐axes of the YBCO grains were distributed in the ⟨100⟩ of the substrate. These observations are consistent with the degree of lattice mismatch in the various directions. For a polycrystalline substrate such as hastelloy, the in‐plane texturing was found to be completely random, consistent with the random nature of the substrate. The correlation of these texturing results with theJcvalues was found to be excellent.

ISSN:0094-243X    

DOI:10.1063/1.40241

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Anisotropies in both critical current carrying capacity and in fluxoid pinning from single‐crystal high temperature superconductors determine optimum orientations for directionally solidified (from the partial melt) microcrystals in material for coil applications. Optimization depends partly on the selected coil diameter. In melt texturing, crystal growth is accompanied by liquid flow which generally leads to the production of second phases by segregational effects except where careful procedures are adopted to prevent these. These segregational effects tend to reduce potential current carrying capacities even though they can in principle be used to increase flux pinning. Texturing of coils imposes special difficulties because of the mechanical weakness of the partially melted region. Process in overcoming these difficulties is of great importance to a significant range of applications requiring either higher magnetic fields than are attainable with conventional superconductors or the economy of superconduction at higher temperatures.

ISSN:0094-243X    

DOI:10.1063/1.40242

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High quality YBCO films on LiNbO3substrate through in‐situ deposition without post annealing have been reported. We have grown fine quality thin films withTc≊90°K on Y‐cut LiNbO3substrate utilizing a sputter S‐gun and a special post annealing process. The technique of thin film processing, interfacial studies, characterization by ultrasonics as well as film quality enhancement by ion implantation will be discussed in this paper.

ISSN:0094-243X    

DOI:10.1063/1.40243

出版商:AIP    

年代:1991

数据来源: AIP