Systematic studies have been performed on 1000 Å YBa2Cu3O7−δ films produced by the BaF2 process and annealed in an oxygen partial pressure (Po2) range from 740 Torr to 10 mTorr as well as a temperature range from 600 to 1050 °C. The results show that while high quality films can be annealed in a wide range of oxygen partial pressure, they have different characteristics. In general, crystalline quality and Tc are optimized at high Po2 and high annealing temperature, while strong flux pinning and low normal state resistivity are achieved at lower values of both variables. Under optimized low Po2 conditions, an ion channeling Xmin of 6% is obtained on films as thick as 5000 Å. This study will serve as a useful guide to tailoring film properties to the application at hand.

Rare-earth huntite-borates R(Al, Ga)3(BO3)4, where R = Yb, Er, and/or Nd, were grown by spontaneous crystallization from fluxes based on Bi2O3-B2O3. Crystals were removed from the melts and selected to different size fractions using meshes. It was found that dependence of weight for each size fraction on size in double logarithm coordinates was close to a symmetrical function. The dependence of logarithm of crystal amount on size was almost linear.

Heteroepitaxial growth of Ba2YCu3O7−x (BYC) thin films prepared by postdeposition annealing on (001) LaAlO3 was characterized by TEM and x-ray diffraction studies of specimens rapidly cooled from various points in the growth heat treatment. Heteroepitaxial nucleation of BYC occurred between 720 and 770 °C during heating at 25 °C/min to the annealing temperature of 830 °C. The c-axis normal BYC rapidly coalesced into a continuous film with nearly complete coverage of the substrate surface after growth of a film of several unit cells thickness. The experimental results were not consistent with purely solid phase heteroepitaxial nucleation and growth or epitaxial grain growth, mechanisms for microstructural evolution of other chemically derived epitaxial oxide thin films. The nature of the transformation and the microstructure of the final superconducting films were consistent, instead, with growth of epitaxial BYC from a liquid phase that is present transiently during the anneal. This hypothesis was supported by thermal analysis results obtained from the precursor material of which the films are composed prior to transformation to BYC.

Dense polycrystalline Bi2Sr2Cu2Ox (2201), Bi2Sr2CaCu2Ox (2212), and (Bi, Pb)2Sr2Ca2Cu3Ox (2223) specimens were compressed in air at 730–835 °C. All of the materials exhibited an apparent steady-state creep response. Strain rate was proportional to stress to the 3.1–3.8 power. Apparent activation energies for the deformation processes were 520 ± 50 kJ/mole for the 2201, 630 ± 210 kJ/mole for the 2212, and 960 ± 210 kJ/mole for the 2223. Transmission electron microscopy revealed substantial generation and propagation of basal-plane dislocations during deformation. Few nonbasal-plane dislocations were observed. Intergranular fracture was evident in all deformed samples, and intragianular fracture was evident along the basal planes of some grains. It is suggested that the kinetics of fracture were determined by dislocation motion within the grains.

Optical emission spectroscopic studies of dc-94.92 MHz hybrid plasma generated in the newly developed magnetron sputtering system were performed during the growth of YBa2Cu3O7−δ (YBCO) thin films. All the detectable species showed uniform spatial distribution along the radial direction of the target more than 8 mm above the target surface. High cathode current conditions in the hybrid plasma were found to make the plasma with high ion density. The high ionizing efficiency was concluded to be essential in obtaining an excellent crystalline film. This result is explained by the ion acceleration mechanism through the ion sheath formed near the substrate surface. Oxygen gas introduced into the growing chamber during deposition was found to be responsible for the oxidation of the target surface.

Ion-beam sputter deposition (IBS) has been developed to a fully oxygen-compatible technology for growth of complex oxides, such as Y1Ba2Cu3O7−δ (YBCO) thin films. The IBS system consists of an rf-plasma ion source with molybdenum grids for sputtering, a dc-plasma electron source for space charge compensation, stoichiometric YBCO and NGO targets, a beam chopper with BaO2, Cu, and Nd blades for stoichiometry control, and an ECR-oxygen-plasma source for in situ film oxidation and photoresist removal. Due to its complexity the IBS process is fully computer-controlled. A salient feature of IBS is the excellent crystallographic and morphological properties of thin (100)/(010)- and (103)-oriented YBCO films on SrTiO3 (STO) and NdGaO3 (NGO) substrates. Sharp interfaces and good superconducting properties render this technology feasible for the fabrication of SIS-ramp-junction SQUID's.

SiC whisker/calcium phosphate and C fiber/calcium phosphate composites were fabricated by hot-pressing at 1185 °C and 7.6 MPa in vacuum. The microstructural characteristics, especially interfaces, of these composites were studied using transmission electron microscopy. The mechanical properties of these composites were measured by four-point bending tests. It was found that the mechanical properties of these calcium phosphate-based composites were strongly dependent on their microstructural characteristics.

The unidirectional solidification by a zone-melting method was performed to investigate the growth anisotropy of YBa2Cu3O6+x (123) superconductive oxides. Large faceted interfaces were obtained at growth rates lower than 2 mm/h. The three-dimensional interface morphology and the onset of growth were observed. The crystal faces toward the growth direction were revealed to be close to the {112} face, which was selected as the result of the preferential growth. The growth rate of the {100} faces was evaluated to be about 1.5 times faster than that of the {001} faces from the steady growth condition.

Nanometer-sized silver particles with diameters in the range 4.3 to 11.5 nm have been grown within a glass-ceramic containing BaTiO3 by just subjecting the former to an alkali/silver ion exchange reaction. A reduction treatment in hydrogen is, however, shown to be necessary for such growth in glass-ceramics having crystalline phases such as BaTiSiO5, Zn2SiO4, and Li4P2O7, respectively. The possible presence of Ti3+ ions in the BaTiO3 phase is believed to cause such a difference in the reduction behavior of these composites.

Following our recent report on the successful fabrication of “stationary” MTG Bi1.6Pb0.4Sr2Ca2Cu3Oy pellets in a simple tube furnace, we have tried many heating programs with various “crystal growth starting temperatures”, Ts, and sintering temperatures, Te; the samples are sintered for 20–40 h before quenching in air. It is found that Ts-Te should be rather narrow to produce good MTG samples, and the typical value of Jc is enhanced from 100 A cm−2 (for a polycrystalline sample) to about 3 × 103 A cm−2 for our good ones. SEM and TEM results indicate that the samples are full of packs which contain highly oriented mica-like layers.

A simple method for the bulk synthesis of 80 K bismuth-based superconducting phase (2212) is described. It employs a modified citrate gel route giving rise to an auto-ignited combustion process. The precursor ash obtained after combustion is further calcined at 800 °C to produce the desired superconducting powder with excellent homogeneity and fineness, leading to good sinterability and fairly sharp transition temperature. For a particular citrate-nitrate ratio, the nature of combustion of the gels containing two different bases has been compared. The thermal decomposition characteristics of the gels and the plausible mechanism of formation of the superconducting phase are also described.

The angular magnetic field dependence of the critical current density JC(θ) of epitaxial YBa2Cu3O7 thin films is presented in the temperature regime close to Tc. The high temperature behavior of Jc(θ) shows features that are significantly different from the earlier observations at lower temperatures. A comparison between the films on (100) LaAlO3 and (100) yttria stabilized zirconia (YSZ) indicates significant differences that may be attributed to the differences in the microstructure of the films on the two substrates. In particular, the observation of enhanced pinning in the films on YSZ may be due to the pinning effects of the low angle grain boundaries present in these films.

Formation and coarsening behavior of the Y2BaCuO5 (211) phase has been examined in samples produced by peritectic decomposition of pure YBa2Cu3O7−x (123), resulting in 211 crystals and the liquid phase [BaCuO2-CuO]. Through various temperature (1020 °C-1060 °C) and time (0.25 h-10 h) studies, the fundamental coarsening behavior was determined. At 1040 °C, 211 crystals coarsen significantly over a 10 h period. The acicular crystals can be modeled by the diffusional ripening law, r–r0 = (Kt)1/3, where r=V1/3. However, the log-normal distributions of the lengths, widths, and volumes for each coarsening run are much wider than general ripening theory would predict. Results from coarsening studies at 1020 °C and 1060 °C for 3 h reveal that the 211 crystal volume increases with increasing superheat. Prior coarsening of the 123 grain size yields much larger 211 particles, suggesting that the 211 crystals must nucleate at the 123 grain boundaries during peritectic decomposition, and this nucleation governs the size of the 211 crystals for short coarsening times. Addition of properitectic 211 (15 mole %) to pure 123 before peritectic decomposition strongly influences the particle habit of the resulting 211 crystals. Without any additions, acicular or needle-like 211 crystals result from the melting of 123. However, when equiaxed properitectic 211 is added to the 123, the resulting 211 is faceted, but still equiaxed. If acicular 211 is added to the starting composition, the resulting 211 is needle shaped. These results will be discussed in terms of 123 melt-texturing and directional solidification processing.

The effects of annealing temperature and oxygen partial pressure [p(O2)] were investigated on the crystallization and orientation of superconducting YBa2Cu3O7-y (YBCO) films on SrTiO3(100) prepared by the dipping-pyrolysis process. Annealing conditions for precursor films consisting of a Y2O3—BaCO3—CuO mixture were varied in the temperature range 700–850 °C and initial p(O2) range 2 × 10-4-10-2 atm followed by pure O2 treatment. Three different types of crystallization behavior were observed. The c-axis-oriented epitaxial YBCO films were obtained on the lower p(O2) and higher temperature side in the p(O2)-T diagram. The c/a-axis-oriented growth was observed in films heat-treated at 750–800 °C under p(O2) of 10-3 atm. In addition, mixtures of YBCO and YBa2Cu4O8 resulted when the films were annealed at 700 °C.

Using molecular dynamics computer simulations and interatomic potentials derived partly by Voter and Chen1 and Rifkin et al.,2 we studied the surface reconstruction taking place on free surfaces of arrays of RuAl. Surface reconstruction appears to be very important on {111} and {110} types of planes and almost nonexistent on {100} type of planes. Cracks oriented so that their crack planes were either {111} types or {110} types exhibit on their internal free surface important surface reconstruction. It is believed that this effect may have some contribution in the brittle versus ductile behavior of the crack.

A fully oxygen-compatible ion-beam sputter deposition process (IBS) has been implemented for investigation of four film/substrate couples: (103)/(110)YBCO on (110)SrTiO3 (STO) and on (100)NdGaO3 (NGO), and (100)/(010)YBCO on (110)NGO and on (100)STO. For comparison, some (103)/(110)YBCO films have also been prepared by off-axis rf-magnetron sputtering. Below about 600 °C semiconducting, sub-nm flat, and perfectly single-crystalline YBCO films crystallize on these substrates with a crystallographic unit cell of about 1/3 of the Cu-O subcell of YBCO and perfect registration with the Ti4+-O and Ga3+-O sublattice of STO and NGO, respectively. At higher temperature superconducting YBCO films grow coherently epitaxially in the first ∼100 nm thickness; in thicker films the lattice-misfit strain relaxes to the “free” lattice constants. Above ∼680 °C a faceted (103)YBCO orientation grows on (110)STO and (100)NGO substrates with uniform in-plane orientation of the [010]YBCO direction parallel to [001]STO and [001]NGO. Along [010]YBCO the (103)YBCO films exhibit high crystalline perfection and intrinsic superconducting properties approaching those of (001)YBCO films in the plane; i.e., Tc,0 > 88 K, ΔTc,0 < 0.6 K, R300/R100 > 2.9, ρ100 > 250 μ°Cm, and jc (77 K) ⋚106 A/cm2. Practical use of (103)YBCO films is hampered by the large surface roughness. Above ∼680 °C a mixed (100)/(010)YBCO orientation grows on (110)NGO substrates, exhibiting a very smooth surface but less attractive superconducting properties; typically, Tc,0 ⋚ 80 K, ΔTc,0 ∼ 1 K, R300/R100 ∼ 1.2, ρ100 > 3 m°Cm, and jc (77 K) ⋚105 A/cm2. On (100)STO substrates the YBCO film orientation varies from pure (100)YBCO between ∼580 and ∼630 °C and mixed (100)/(010)YBCO below ∼660 °C to pure (001) YBCO above ∼670 °C. With rising temperature the surface roughness increases from <2 to ∼6 nm-rms, while the other parameters continuously improve to state-of-the-art values for c⊥-oriented films. Specifically, mixed (100)/(010)YBCO films reach Tc,0 > 86 K, δc,0 ∼ 1 K, R300/R100 > 2.8, ρ100 < 3 m°Cm, and jc (77 K) > 105 A/cm2. (100)/(010)YBCO films on (100)STO are a promising candidate for sandwich-type SIS-JJ.

We discuss our results on the growth of YBCO thin films on ultrathin (1-10 nm) Ag underlayers. Substrates were LaAlO3. YBCO was sputter deposited and Ag thermally evaporated. It was observed that Tc remained relatively unaffected by the Ag underlayers, ranging from 86-88 K. Critical currents were found to be consistent with YBCO grown on bulk Ag when the Ag underlayer film reached complete coverage (∼9 nm). Films grown on Ag showed a marked tendency for microcrystalline growth on the basis of atomic-force microscopy (AFM) results.

As-grown YBa2Cu3Ox films prepared on single crystal (100)MgO substrates by rf thermal plasma evaporation have the advantages of a high deposition rate of 730 nm/min, a large area deposition over 300 cm2, and a high Jc of 6.8 × 105 A/cm2 (77 K, O T), as reported in previous papers.1,2 We report in this paper about the preparation of YBa2Cu3Ox films on yttria-stabilized zirconia (YSZ) polycrystalline substrates for a practical application using this technique to synthesize these films on flexible (metal or flexible polycrystal) substrates. Films prepared on YSZ polycrystalline substrates grew with a c-axis orientation at a relatively high deposition rate and exhibited a zero resistance temperature (TcO) of 88 K and a critical current density Jc of 3500 A/cm2 (77 K, O T). Films prepared on flexible YSZ polycrystalline tapes with a length of 100 mm were also grown with a c-axis orientation and exhibited TcO) over 77 K.

Analysis and sample preparation techniques for the bulge test have been improved to the point where the test can provide reliable and accurate measurements of the mechanical properties of thin films. Ag-Pd multilayer films of variable bilayer period were prepared for this study and characterized by cross-section transmission electron microscopy and by x-ray methods. The films were tested in the bulge test to determine their biaxial moduli. The data show no peak in biaxial modulus at a critical composition wavelength and no nonlinear elastic behavior. They do show a slight trend toward increasing elastic modulus with increasing strength of (111) crystallographic texture. These findings refute a previous report of the “supermodulus” effect in this system and add to the evidence that the effect is caused by artifacts of the mechanical testing technique. Methods for eliminating such artifacts are discussed.

Single crystals of YBa2Cu3O7−x (Y123) were grown by a modified top-seeded crystal pulling method using a BaO-CuO solution with the solid Y2BaCuO5 (Y211) as a solute in an yttria crucible [the so-called solute-rich liquid crystal pulling (SRL-CP) method] under 2% oxygen partial pressure atmosphere [P(O2) = 0.02 atm]. According to the pseudo-binary phase diagrams of Lee and Lee,1 the temperature of Y123 crystal growth was expected to be lower for 0.02 atm oxygen pressure than for 0.21 atm oxygen pressure. The single crystals grown under P(O2) = 0.02 atm and cooled under the same atmosphere after the separation of crystal from a solution had twins near the microcracks on the crystal surface. On the other hand, the single crystals grown under P(O2) = 0.02 atm and cooled under pure nitrogen atmosphere (6N) showed no twin structure. These results indicate that twins did not form during crystal growth but formed due to tetragonal-orthorhombic transition as a consequence of oxygenation at cooling under low oxygen partial pressure.