We describe single-target ion beam sputtering of superconducting YBaCuO thin films mainly onto R-sapphire and (100) SrTiO3 substrates. We discuss different thermal treatments and consequent X-ray and resistivity results and conclude with X-ray photoelectron spectroscopy data which indicate formation of hydroxydes on the surface of films exposed to atmosphere.

The effect of uniaxial strain e on superconducting transition temperature Tc of thin YBa2Cu3O7 film is presented. The value of TC increases linearly with compressional strain with a slope of -275K/e. Under tensile strain, Tc initially decreases to a value ∼ 0.3K below the zero-strain value and then remains constant with additional strain. In compression, the logarithmic strain derivative of Tc, (1/Tc)(dTc/de), is -3 per unit strain which is slightly less than 4–6 per unit strain observed in conventional superconductors.

Thick coatings of Y-Ba-Cu-oxide superconductors have been prepared by plasma spray processing. This paper reports a number of the important properties of coatings sprayed at two different power levels. The microstructure, porosity, and chemical composition of the coatings were studied in their as-sprayed and annealed states. Critical current and magnetic susceptibility measurements were made on the annealed coatings. X-ray diffraction was used to identify non-superconducting phases present in the coatings and to determine the superconducting phase's lattice constants.

A tape-shaped wire with Y1 Ba2Cu3, O7-δ, core and Ag sheath was fabricated by a drawing-rolling method. The critical current density of the wire with 0.1 mm thickness and 6 mm width was in 2 the range of 2000 A/cm at 77 K in the absence of external magnetic field. Presence of 20 m Tesla magnetic field reduced the J value to 1/100.

Thin superconducting films of YBa2Cu3O7 and HoBa2Cu3O7 have been obtained by ablating material from high-Tc bulk superconductor ceramics onto a nearby substrate using focused excimer laser radiation. Subsequent annealing in oxygen at elevated temperatures was necessary to achieve the superconducting phase. A range of deposition and annealing conditions was investigated to yield films of the desired stoi chiometry and phase.

Ba2YCu3O7 films produced by co-evaporation of BaF2, Cu and Y onto <100> S1TiO3 substrates in an O2 ambient followed by post-annealing were analyzed using RBS, X-ray diffraction and Auger microscopy. These films exhibit Tc's (R=0) of =90K and a best Jc of > 1.0×106 A/cm2 at 81K for a =2500A thick film. RBS and Auger depth profiling limit the level of F present in the post-annealed films to <5 at. %, although F is evident in the as-deposited material. RBS channeling experiments yield a Xmin=31%, demonstrating the epitaxial quality of the films. X-ray diffraction shows that the films are predominantly oriented with c-axis perpendicular to the substrate, with narrow mosaic spread in-plane. A small portion of the film is in the form of needles oriented with a-axis perpendicular to the substrate, whose areal density is dependent on annealing conditions and local film stoichiometry. Scanning Auger microscopy confirms that the needles and c-axis plateaus have the same metal and oxygen stoichiometry. Also present in the film are insulating balls which appear to nucleate terraces in the c-axis perpendicular structure. Scanning Auger shows that these features are also close to the metals stoichiometry, but are C rich compared to the needles. The plateaus are covered with =11 times more C than the needles, indicating that the basal plane surface is highly reactive. Auger depth profiling and RBS show little evidence for interdiffusion.

Thin films of (RE)-Ba-Cu-O perovkites containing silver were prepared by pulsed Nd:YAG (wavelength 1064 nm) laser ablation. Presence of the 1:2:3 phase was verified by scanning Auger microscopy. Onset of the d.c. resistive superconducting transition of 85 K was observed. Films with and without silver were compared and the potential benefits of silver inclusion are discussed.

Superconducting film of ternary copper oxides from the Y-Ba-Cu-O system has been prepared by screen printing on 96% A1203 substrate with onset temperature at 95K and zero resistance at 85K. X-ray diffraction patterns show that film will react with the A1203 substrate. With decreasing film thickness the superconductivity is destroyed and may become a semiconductor.

Grain boundaries in YBa2Cu3O7−x. thin films deposited on yttria-stabilized cubic zirconia have been characterized using selected-area diffraction. In addition to twin boundaries, several types of low-angle and high-angle grain boundaries are frequently found in these films. The high-angle boundaries include 23.5°, 29°, and 45° rotations about [001] and 90° rotations about [100] or [010]. These boundaries are compared to special high-angle grain boundaries in cubic materials.

The microstructure of thin films of the high Tc superconductor YBa2Cu3O7−x deposited on SrTiO3 and Y-stabilized cubic-zirconia (YSZ) single-crystal substrates has been characterized by transmission electron microscopy. Films on both substrates were polycrystalline. On {001 }-oriented SrTiO3, the grains are oriented with <110> normal to the substrate surface. On the same orientation of YSZ, two microstructures are observed: one in which grains have their c-axes normal to the substrate surface, the other in which grains have the a- (or b-) axis normal to the substrate surface. Both of these microstructures contain special grain boundaries. Annealing of ion-milled TEM specimens is presented as a means of removing ion-beam damage.

The high-Tc YBCO superconducting films have been prepared using a cw CO2 laser evaporation from a single bulk target. The adjustment of the target composition, especially the yttrium concentration, was found to be a key factor to achieve a desired film composition. After post-annealing at 930°C, the films deposited on YSZ substrate exhibited a zero resistance temperature of 85K. The deposition rate of the films was about lOOA/sec.

Since discovery of the Y-Ba-Cu oxide compound showing superconductivity above liquid nitrogen temperature, intensive study has been under way to clarify nature of the high Tc oxides[l-4]. Much efforts were also made in the field of superconductor applications. A number of studies have been carried out by a powder metallurgical process of Y-Ba-Cu oxide compound wires, although, obtained critical current densities were still low at liquid nitrogen temperature[5–6]. Other techniques for wire fabrication is also being attempted[7–9]. In this study, Y-Ba-Cu oxide superconducting composite tapes were prepared by a diffusion process, which is one of the promising methods to obtain a high critical current density.

A new metallo-organic spin-on technique is described for producing thin films of the high temperature perovskite superconductors, LnBa2Cu3O7−x, where Ln represents a rare earth element. Pyrolysis of the spin-coated films leads to black films up to several microns thick whose degree of orientation is a function of the processing temperature and duration. Representative films of YBa2Cu3O7−x on MgO begin to exhibit orientation with the c-axis perpendicular to the film at heat treatments above 900 'C. The superconducting behavior of a highly oriented film produced at 990 ° C is characterized by Tc (onset) = 89 K, Tc (R=0) = 77 K and Jc = 104 amp cm-2 at 65 K.

We describe here the deposition of the YBaCuO 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 discus sed.

We report a systematic investigation of the critical current at 77K for a number of different composite conductors based on the high critical temperature superconductor YBa2 Cu3 O7. Results are reported for an ‘external’ diffusion composite where the oxygen diffuses through an outer cladding of silver, and for an ‘internal’ diffusion design where the composite is clad externally with an oxygen impermeable layer and oxygen diffuses internally from a channel within the conductor. Measurements are reported of the dependence of the critical current on i) the preparation route for the superconducting powder, ii) the preform particle size, iii) the presence of air or vacuum during compaction, iv) the time of the sintering anneal and v) the applied load on the conductor during a critical current test.

The thermal conductivity k of micro-twinned single crystals of YBa2Cu3O7 and HoBa2Cu3O7 and a sintered sample of YBa2Cu3O7 has been measured for temperatures 0.03<T<5K. For the single crystals, k is small and varies as T1.8-1.9 This behavior resembles k for glassy insulators except for the lack of a plateau above IK. It is concluded that the thermal carriers are phonons with their mean free path limited by resonant scattering from tunneling entities, as in glasses. Suggestions for the location of tunneling systems are given. For the sinter, k is still smaller but does not follow a power law T-dependence. It is similar to other sintered ceramics with the same particle size, where the phonon mean free path is dominated by Rayleigh scattering from the particles. This strong scattering from the microstructure presumably masks the scattering from TS within each particle.

Members of the solid solution system La1.5−xBa1.5+Cu7+ywith x = 0, 0.125, 0.25. 0.375 and 0.5 have been prepared both in air and under one atmosphere of flowing oxygen. In general, except for x =0, the oxygen annealed compounds are superconducting while the air-annealed samples are semiconductors. Tc's measured by Meissner effect and resistivity data range to 70K. The crystal symmetry in all cases is apparently tetragonal as verified for x = 0.375 by variable temperature Guinier x-ray experiments at temperatures down to 8K. Crystal structures have been refined from neutron powder diffraction data. A correlation is noted between Cu-0 distances which connect adjacent Cu planes - the average copper valence and the occurrence of superconductivity.

Nonstoichiometry in YBa2Cu3Ox has been studied by means of equilibrium electrical conductivity and thermogravimetric method. We have observed a strong correlation between electrical resistivity and oxygen stoichiometry (x) at high temperature. Electrical resistivities increase linearly from the superconducting onset tcmperature(100 K) to 450 C where oxygen starts to evolve from this material, and then begin to deviate from linear temperature dependence. The experimental results indicate that electrical resistivity in this material is associated with the defect species (charge carrier) population due to oxygen stoichiometry. Electrical conductivities were also measured as a function of oxygen partial pressure (1 to 10−4 atm) at various temperatures. At P(OI) > 101 atm the conductivity shows a l/4th slope dependence on oxygen partial pressure while at P(0;) < 10 f atm the conductivity is proportional to P(O2)1/2- The conductivity behavior with oxygen stoichiometry suggests that the electron holes associated with Cu+ play an important role as charge carriers in this material, and even at x < 6.5 p-typc conduction is predominant.

X-ray absorption measurements have been made on powder samples of YBa2Cu3O7 and La1.85sr0.15CuO4 oriented in a magnetic field. Measurements made at the Cu K edge with the x-ray polarization oriented perpendicular and parallel to the c-axis show distinct differences for both materials, indicating a strong anisotropy of the electronic states about the Cu atoms. The Y edge measurements show a much smaller anisotropy as expected due to its more symmetric environment. Preliminary analysis indicates these measurements should be useful in choosing between the conflicting interpretations of the near edge structure in these materials.

Measurements of the thermal conductivity of rare earth-barium-copper-oxide superconductors are presented. Heat conduction occurs principally by phonons, and increases below the transition temperature due to a decrease in electron scattering. This implies a strong electron-phonon coupling, and estimates for the coupling constant and transition temperatures are obtained within the framework of BCS theory.