Wires were fabricated from the high-Tc superconductor Bi0.7Pb0.3SrCaCu1.8Ox (Pb-BSCCO) by an extrusion process. The specimens were sintered for periods up to 14 days, and density was found to decrease with longer sintering times. Rf surface resistance data revealed that the onset of superconductivity occurred at 105 K and that the transition was very broad.

We have measured the surface resistance R, in polycrystalline films of YBCO and BSCCO deposited in our laboratory as well as oriented films made by other laboratories by codepostion techniques. The R, of YBCO and BSCCO has been measured in the frequency range between 0.5 and 40 GHz using a stripline resonator technique. R, for the films is nearly proportional to the square of the applied frequency over the entire measurement range. The magnitude of R, is, however, strongly dependent on the film microstructure. Our measurements at 1 GHz and 4 K show that randomly oriented films have R, ~ 10~3 Ω (close to Cu) while oriented large-grain films have markedly lower R, ~ 2 x 10-6 Ω, approaching the R, of superconducting Nb. The magnitude of R, rises to ~ 2 Ω and ~ 10-3 Ω at 40 GHz for the randomly oriented and preferentially oriented films, respectively. An effective penetration depth, λeff, has been determined from R, using local electrodynamics. We find that λeff is dependent on film microstructure and is ~ 5 µm for high-R, films, decreasing to ~ 5000 Å for low-R, films. The smaller values of Ωeff calculated for oriented films are of similar magnitude to values of the YBCO penetration depth (~ 2000 Å) reported in the literature. The use of the stripline resonator technique for temperature and magnetic field dependent i Measurements of R, will also be discussed.

The cuprate superconductors rapidly degrade in moisture and in the presence of organic compounds. A protection method has been developed with a coating process using sol/gel routes to the low temperature formation of oxide films. In contrast to traditional protective films, amorphous silica films formed from a solution precursors gave excellent protection and caused little degradation of the superconductors.

The protective abilities of the films were assessed by monitoring the degradation of Y1Ba2Cu307-d in the presence of 85% relative humidity at 85 C. Volume magnetic susceptibility, four-point probe resistivity, current density measurements and x-ray diffraction were performed. Without protection, degradation was almost complete within 30 minutes of exposure. With protection, superconducting properties were maintained even after 48 hours of exposure.

If useful electronic devices are to be fabricated from thin films of the high critical temperature oxide superconductors, such as yttrium barium copper oxide (YBCO), then films must be formed on substrates with dielectric properties which permit device operation at high frequencies, such as sapphire. It is, however, difficult to form high quality YBCO on sapphire because of reaction with the substrate and because epitaxy is not readily achieved.

We report the deposition of epitaxial thin films of magnesium oxide, by UHV reactive d.c. magnetron sputtering, on variously orientated substrates of sapphire, and the characterisation of the MgO/sapphire system by x-ray and TEM techniques.

Onto such films of MgO on sapphire we have deposited films of YBCO which were strongly textured with the c-axis perpendicular to the plane of the substrate and which were superconducting without the need for a high temperature post deposition anneal.

Thin films of ZrO2, BaF2, and noble metals on TiN have been examined by RBS as potential diffusion barriers between Si(100) substrates and high-temperature superconductors. As best result so far, a buffer layer of 260 nm ZrO2 enabled the growth of a 230 nm film of YBa2Cu3O7-x, which had been deposited by laser ablation. The relatively low zero resistance temperature of about 60 K may result from some interdiffusion between YBaCuO components and the ZrO2 layer or from holes in the film. A 520 nm BaF2 layer was able to prevent Si outdiffusion towards the surface, when exposed to an oxidizing ambient at typical YBa2Cu3O7-x deposition temperatures between 750 and 800°C. A strong reaction between YBaCuO components and BaF2, however, resulted in non-superconducting films. At high temperatures in oxidizing ambient the noble metal/TiN/Si samples suffered severely from oxidation and surface roughening.

Different materials were investigated for use as diffusion barriers between silicon and yttrium barium copper oxide (YBCO). Ion beam assisted deposition (IBAD) of 300nm zirconia films at room temperature prevented interdiffusion at sintering temperatures over 800°C. Similar MgO and indium-tin oxide films did not prevent degradation at elevated temperatures. All films deposited on top of YBCO reduced the effects of extended atmospheric exposure.

The quality of epitaxially grown superconducting thin films is dependent on the nature of the substrate surface. In this study, the surface of <100> oriented SrTiO3 single crystals was modified by mechanical polishing, thermal annealing and chemical etching. A study of the YBa2Cu3O7-x thin films grown on these substrates showed that high quality superconducting films were obtained when the substrate surface was highly oriented in the <100> direction and was also microscopically smooth.

Substrate temperature during film growth is an important processing parameter for vapor deposited films of the high Tc superconductors. In this paper we describe a novel, non-contact optical thermometry technique in which the temperature of a transparent substrate or “temperature sensor” is determined from its thermal expansion and refractive index change measured by laser interferometry. The technique is easy to implement and extremely accurate. Temperatures measured with this technique are reported for MgO substrates in varying degrees of thermal contact with a heated backing plate and compared to those measured conventionally by optical pyrometry or thermocouples in close proximity to the sample. The effect of the deposited film on the temperature of radiatively heated substrates will also be discussed.

Joining technology for ceramic superconductors is currently a major problem. The possible reactions which occur at ceramic superconductors/metal interfaces are discussed and examples are shown of interfaces between YBa2Cu3Ox and Nd1.85Ce0.15CuO4-x vs. a series of metals (Ag, Ni, Fe) now being considered for joining and cladding applications. Various characterization techniques, including EPMA and x-ray mapping, are utilized for analyzing the spatial distribution of reaction products. In a composite configuration, Ag interlayer is found to promote interfacial reactions.

A series of ceramic oxides were prepared by adding alumina to the superconductor YBaCuO. The solids were characterized by X-ray diffraction, transmission (TEM) and scanning electron microscopy (SEM) with EDS and electrical measurements. Partial drops in electrical resistance (R ≠ 0) indicate the presence of superconducting phases trapped in ceramic masses. Additionally, the systematic diminution of Tc could indicate a partial substitution of Cu by Al.

Resistivity measurements of YBCO thin films on MgO substrates show that the transition to the superconducting state depends on film thickness. TEM investigations of the films revealed interdiffusion of Cu and Mg. The concentrations of the cations at the interface were quantitatively measured. These data show that their diffusion rates are much different (MgODCu/YBCODMg=30); this indicates that the diffusion mechanism is complicated by the layered structure of the perovskite-like films. No impurity segregation was detected at the interface. Diffraction study of several YBCO grains confirms that the film c-axis is oriented perpendicular to the substrate, but that the a/b plane has no fixed orientation, indicating that no epitaxial relationship exists.

Potential substrate and buffer layer materials for Bi2Sr2CaCu2Ox (BSCCO) were surveyed using bulk ceramic processing techniques. Of the materials tested, only Ag was inert with respect to BSCCO. MgO slightly degrades the superconducting onset temperature and volume fraction. LaGa03 may be a feasible ceramic substrate for BSCCO, although some reaction appears to occur.

We fabricated the multi layered structure with Au gate electrode/polymer film/Bi-Sr-Ca-Cu-O film to study the electric-field control of high Tc superconductor. A Bi-Sr-Ca-Cu-O(BSCCO) film was fabricated using an ion beam sputtering technique. The plasma polymerization using trif luoroethane gas was used to make the gate insulator. The patterning of the BSCCO film was carried out using an ion beam etching technique. The supercurrent of the structure decreased when the gate voltage was applied to the gate electrode.

The effects of low magnetic field (0–40 Gauss) on electrical properties of gold-YBCO contacts are investigated. The contact resistance increases significantly with applied magnetic fields. For high magnetic field or when high current is flowing through the contact, the contact resistance decays after removing the magnetic field to a finite value greater than that is measured before the contact is exposed to the magnetic field and stays there for long time as long as the sample is kept below the superconductivity critical temperature.

A Si-YBaCuO intermixed system has been formed using rapid thermal annealing (RTA) of Cu/BaO/Y2O2/Si layered structures, which were deposited on MgO substrates by electron-beam evaporation. The electrical and structural properties of the Si-YBaCuO system have been analyzed by resistivity, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy and Auger depth profiling measurements. It was found that Si mixed with YBaCuO during annealing, thus creating an insulating film. This effect has been used to pattern YBaCuO films. The patterning process was carried out on an underlying silicon layer, rather than the YBaCuO film itself, using conventional photolithography or laser etching. After YBaCuO film deposition and RTA, the patterned region became superconducting separated by Si-YBaCuO intermixed areas. Micron-sized line features with Tc's above 77 K have been demonstrated.

Critical current densities, magnetic field response, and microwave response have been measured for laser ablated YBa2Cu3O7-δ thin film lines on MgO and SrTiO3 substrates. Films on SrTiO3 have critical current densities > 1 x 106 A/cm2 at 77K and show uniform transport properties in lines of all sizes. Films on MgO have critical current densities which range between 102 and 106 A/cm2 at 77K and show considerable variation from device to device on the same chip. Narrow lines on MgO with low critical current densities show Josephson weak link structure which includes RSJ-like IV curves, microwave induced constant voltage steps, and a high sensitivity to magnetic field. The presence of the Josephson weak links is correlated with small amounts of misaligned grains in films on MgO.

The feasibility of preparing YBaCuO films on metallic substrates is discussed in an attempt to fabricate a superconducting tape. Deposition method employed was an rf magnetron sputtering. An amorphous MgO thin layer was found to be a promising buffer layer. The highest zero resistance temperature was 84.0 K in its as grown state, and a critical current density was 4.8x10 A/cm2 at zero field and 77.4 K. Preliminary experiments using laser ablation technique were also carried out to obtain YBaCuO films at a rather high deposition rate.

Y1Ba2Cu3O7-x superconducting composites have been prepared on metallic substrate by rf magnetron sputtering method. Buffer layer of thin SrTiO3 layer between superconducting film and the substrate was found to be effective to realize superconductivity. Preferable grain alignment of c-axis was also obtained. The critical current density at 77K was 2.2x103 A/cm2 with Tc at 83K, and it was found that the thicker films had the higher Jc values.

Samples of a prototype composite tape conductor have been prepared consisting of a thick layer of Y Ba2 Cu3 O7 (123) on a metallic substrate. A thick coating of 123 precursor powder was applied to the substrate by a mechanical compaction process. A melt-quench-growth technique was then employed to effect a textured grain development and improved current density. The resulting melt processed structure showed a textured 123 orthorhombic matrix with a dispersion of the 211 phase. The orthorhombic 123 phase was highly developed with an onset temperature of 90K and current density near 104 A/cm2 at 4T and 50K measured by a steady-state magnetization method.

YBa2Cu3O7-x filaments, with a zero resistance Tc of 89.5 K and a Jc of 225 A/cm2 in zero field at 77 K, were prepared from precursor filaments fabricated by extrusion of a polymeric Cu-Ba-Y precursor. The precursor was prepared by reaction of linear a (CuO)n polymer with Y and Ba alkoxides in non-aqueous solvents. Characterization of the precursor and superconducting filaments, along with the optimum extrusion and pyrolysis conditions, are described.