Reactive YBa2Cu3O7-δ powders have been produced via freeze-drying, carbonate- and oxalate-coprecipitating methods. In the coprecipitating methods, sodium carbonate and sodium oxalate were used as precipitants. These powders were characterized by TGA, XRD, and SEM. The morphologies of the YBa2Cu3O7-δ powders produced from these methods are different from each other. The influence of hot-press process on the bulk density, micro-structure development and superconducting properties of YBa2Cu3O7-δ samples was also studied.

The formation of Y-Ba-Cu-O phases, including the high Tc superconducting YBa2Cu3O7−x (Y123) phase, during solid state reaction of the mixture of Y2O3: BacO3: CuO, in molar ratio of 0.2:0.6:1 to conform the formula of the perovskite (Y0.4 Ba0.6)CuO3 composition was studied by means of DTA, DTG and X-ray difractometry(XRD). For continuous heating at 10 C/min, it was found that the Y123 phase exists at 790–995 C, and gradually disappears at higher temperatures. The insulating Y2BaCuO5 (Y211) phase exists at 985 to 1190 C, the maximum experiment temperature. While the semiconducting YBa3Cu2O7-y, (Y132) phase coexists with the Y123 phase. For isothermal heating, it was found that the most appropriate temperature and time for the formation of the Y123 phase is 900 C and 16 hours. Semiquantitative data on the amount of phases presented, including the above mentioned phases and other binary Ba-Y-O or Ba-Cu-O phases, during heating are also given. High temperature superconductor with a Tc of around 93 K can be synthesized reproducibly by the processes based on this study.

The effect of thermal processing in the sample preparation of YBa2Cu3Oy has been investigated systematically on microstructures and electrical properties. The grain size was found to grow preferably during the cooling process rather than during the sintering process. The high Tc superconducting phase appears around 500 C in this thermal processing. The annealing experiment shows that the grains still grow at low temperature such as 300 °C.

Processing of YBa2Cu3O6+x superconducting samples by employing different precursor powder preparation techniques such as ball milling, attrition milling and also narrow particle size distribution powder preparation through coprecipitation by spraying will be discussed. CuO coated with oxalates shows the lowest resistance above T up to room temperature. The extent of corrosion by water has been studied by employing magnetic susceptibility, XPS and X-ray diffraction. Superconducting samples are affected to a considerable extent when treated in water at 60° C and the severity of the attack increases with time.

We describe here the deposition of the YBCO superconducting thin films by the laser evaporation technique. The characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discussed.

Single crystals of pure and Sr doped La2CuO4 have been grown with a top seeded solution growth technique. Crystals grown from a lithium borate flux incorporate impurities detrimental to superconductive properties while those grown from excess copper oxide are free from this difficulty.

A method for making low resistivity contacts to high-Tc superconductors has been developed, consisting of depositing noble metal contact pads (silver or gold) on a clean superconductor surface at low temperatures (<150°C). After annealing the silver contact pads in oxygen at intermediate temperatures (<500°C) for one hour, contact resistivities less than 2 × 10'° Ω-cm2 at 76 K are obtained, about six orders of magnitude less than for indium-solder contacts. Before annealing, the contact resistivities are still very low, in the 10-6 to 10-5 Ω-cm range at 76 K, which would be useful when contacts with low fabrication temperatures are required. The voltage-current characteristics of the contacts are strongly nonlinear after annealing, having a superconducting transition character. This is ascribed to the critical current of the superconducting material being exceeded at the contact interface. External connections to the contact pads have been made using both solder and thermosonic wire-bonding techniques.

High Tc superconducting films of heavy metal soaps (derived from carboxylic acid precursors) have been prepared on Si and other substrates. The precursors were synthesized and mixed in appropriate molar ratios to form the high Tc compound YBa2Cu3O7−x, using a high boiling point common solvent base. The precursor solution was deposited by a spin casting technique on the substrates. Film thicknesses of 0.1–1.0μm were achieved after heat treatment at 550°-850°C ≤4 hours. Films were analyzed as to orientation, appropriate phase, interfacial reaction and superconducting properties.

Since the discovery of high Tc superconducting oxide such as Ln-Ba-Cu-O system which shows superconductivity above liquid nitrogen temperature, intensive study has been carried out to investigate its intrinsic properties[l-4]. Superconducting wire which operates in liquid nitrogen is one of the emerging products among application, however, there are many factors to be investigated for practical use. Critical current density, Jc, is one of the most important characteristics of superconductor, although, only few report describing Jc measurement ever published[5]. In this paper, fabrication procedure of silver sheathed Y-Ba-Cu-O wire by powder metallurgical technique and its superconducting properties have been reported. Other factors which may influence superconductivity such as microstructure of the oxide, configuration of wires, etc. are also discussed.

Most thin film processes developed for the formation of the new cuprate superconductors involve admixture of oxygen during film growth, followed by a subsequent anneal in O2 at high temperatures in order to form the correct phase. We completely separated the two processes by first depositing a metallic alloy of YBa2Cu3 by DC magnetron sputtering, taking full advantage of the ease of calibration and high rates of deposition typical of metals, and then performing a second oxidation and annealing step in an Oo furnace. A potential problem of the attack by ambient moisture on the highly reactive metallic alloy was handled by use of thin Y overlayers. We examined substrate interactions of our films and identified several favorable combinations of substrates and protective buffer layers, such as ZrO2 /Ag and MgO/Nb.

High Tc superconducting thin films were prepared by DC triode sputtering and laser ablation. With both deposition methods we were able to fabricate thin films on SrTiO3 which show an onset at Tcf=92 K. The superconductive transition is complete at Tcf=86 K. On other substrates like Al2O3, MgO and ZrO2 relatively poor results were obtained.

Thin films of La2−xSrxCuO4 and YBa2Cu3O7-y superconductors have been prepared from citrate-polymer precursors. By a simple spin-coating and pyrolysis process, films which are dense and continuous at greater than 0.5 μm thickness have been prepared. For YBa2Cu3O7-y films deposited on SrTiO3, a large degree of epitaxial orientation has been observed, with the a-b plane of the superconductor parallel to the (100) plane of the substrate. Microstructural characterization and electrical properties measurements of these films are presented.

Superconducting YBa2Cu3O; thin films have been prepared by magnetron sputtering onto [100] single crystal MgO with and without an Au buffer layer. All samples show high transition temperatures (82–87 K). The use of an Au buffer layer significantly improves the superconducting properties, particularly the Meissner effect and critical current density (3.3×106A/cm2 at 2 K and 3.5×104A/cm2 at T=77 K). The Au buffer layers remain metallic after high temperature annealing in an oxygen atmosphere, and may thus serve as effective current shunts.

Thin film superconductors of the YBaCuO family have been fabricated using layer structures of Cu/BaO/Y2O3 deposited by electron-beam evaporation. Using layer thicknesses off the stoichiometric YBa2Cu3O7, we have formed superconducting films with zero resistance above 77°K using MgO and SrTiO3 substrates. The films were found to be composed of both the superconducting YBa2Cu3O7 phase, and the non-superconducting green Y2BaCuO7 phase. Dependence of transition temperatures on the annealing temperatures and the substrates has also been studied.

High Tc Y-Ba-Cu-O superconducting thin films have been successfully deposited by DC sputtering techniques with excellent adhesion properties. Onset temperature of 95K had been achieved without any heat treatment nor annealing. Typical deposition rate is 1–2A/sec. It is possible to fabricate the superconducting thin films on a variety of substrates with this techniques, i.e., SiO2, Si and MgO. Analysis indicated that the films were predominantly the orthorhombic perovskite structure with traces of copper oxide.

High Tc superconducting powders and thin films on silicon have been fabricated by the sol-gel process. Both powder and film preparation involved the synthesis of metal alkoxides, followed by the complexation of yttrium, barium, and copper alkoxides in a common solvent. Bulk gels were then vacuum dried and fired at 700 and 950 °C in flowing oxygen. Thin films on (100) silicon were fired at 700 °C in flowing oxygen. Susceptibility vs temperature measurements showed that the thin films on silicon had a Tc of 40 K while the bulk gels fired under the same conditions had a Tc of 75 K. The sample fired at 950 °C was superconducting at 90 K.

High Tc YBa2 Cu3 Oy and GdBa2 Cu3 Oy thin films can be made by a laser sputtering method using LnBa2 Cu3 Oy (Ln=Y and Gd) ceramics as targets and cubic zirconia as a substrate in a high vacuum system. The superconcucting onset temperature and the zero resistance temperature of the film are 95 and 80K, respectively. The surfaces of these films were subjected to an irradiation with a focused pulsed excimer laser. Scanning of the beam led to the etching of the surface to form a groove. Photochemical processes on these superconductor films were studied using dynamic mass-spectroscopic method.

An oriented film of YBa2Cu3O7−x superconductor was formed by a spray pyrolysis method. The temperature dependence of resistance showed the Tc-onset at 95K and Tc-zero at 83K with the film on a cubic zirconia single crystal surface. The X-ray diffraction pattern showed that the structure of the film was pure orthorhombic phase. Effect of the substrates and the modification of the substrates surface to form superconductive films are presented.

Thin films of Y-Ba-Cu-O have been prepared by rf diode sputtering from a single mixed-oxide powder target. The films were deposited on sapphire and cubic zirconia substrates, with the substrates either cooled, heated, or left to establish thermal equlibrium. The Cu content in the films decreased with increasing substrate temperature. Films having composition close to the desired 1–2–3 stoichiometry were fabricated either by enriching the target with CuO or by cooling the substrate. Using the latter approach, a single target was used for over 20 depositions yielding films that were uniform in composition (although slightly Cu-rich), and consistent from run to run. These films had as-deposited room temperature sheet resistances on the order of 100 kΩ. Subsequent annealing at temperatures up to 850 C resulted in films that were superconducting with an onset around 90 K and zero resistance at 50 K. The critical current was found to exceed 2000 A/cm2 at 4.2 K.

Orientation ordered high-Tc oxide films of Y1Ba2Cu3O7 were prepared by molecular beam epitaxy on SrTiO3 substrates. A combination of effusion cells and e-beam evaporators was used with the addition of an oxygen jet. The superconducting phase is formed by further O2 anneal at temperatures ≥800° C. For SrTiO3 (100), the Y1Ba2Cu3O7 films grow in the orientation of either the c-axis or the a-axis perpendicular to the film plane. Films with predominant “c⊥” orientation exhibit a high degree of crystalline order with a rocking curve 0.3° wide. The Jc is about two times higher than those with the “a⊥” orientation of a comparable Tc (R=0). For a typical film of 9000Å thickness, a Tc (R=O) of 87K, and a Jc of 7 × 104 A/cm2 at 77K were reproducibly achieved. For SrTiO3 (110), X-ray showed twinning of (110) and (103) orientations in Y1Ba2Cu3O7, thus precluding the observation of anisotropy expected for the in-plane axes of [001] and [110].