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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.

Pulsed KrF (248 nm) laser ablation has been used for in situ growth of smooth, high‐quality YBa2Cu3O7‐x epitaxial films of variable thickness on SrTiO3, KTaO3, LaGaO3, LaA1O3, cubic ZrO2, and MgO substrates, at temperatures of ∼60O‐730°C, without higher temperature post‐annealing. A rotating target pellet, fine focusing by a single cylindrical lens, laser‐beam scanning over the target, and laser energy densities ∼2.5‐3 J/cm2 can be combined to yield films of completely uniform composition and with ∼25% thickness variation over areas ∼8 cm2. The best films have Tc > 92 K and JC(H = 0, T = 77 K) > 2 MA/cm2. Film‐growth procedures are described, together with results of superconducting and normal‐state transport measurements.

Magnetic properties have been investigated for several rare-earth based, polycrystalline samples of high Tc superconductive “123” compounds with magnetic onset temperatures between 90 and 95 K. Analysis of the susceptibility × of samples based on Gd, Ho, and Dy indicates that the superconductive and magnetic properties are independent of one another to a substantial degree. Studies of the critical current density Jc are reported.

Fractal analysis is used to interpret small-angle X-ray and neutron scattering data on commercial fumed silica powders. Rough primary particles are found in high surface area powders. A model based on ballistic polymerization, sintering, and diffusion-limited aggregation is proposed to explain the observed powder structure.

The magnetic hysteresis was studied for YBa2Cu3O7 films of different epitaxial orientations on single-crystal SrTiO3 and KTaO3 substrates. Deposition by coevaporation of Y, BaF2, and Cu was followed by annealing in flowing, wet oxygen at 800-850°C. The critical current density Jc deduced from magnetic hysteresis loops was compared with four-terminal transport-current results. Thermally activated magnetic flux flow was manifest in the audio-frequency data. Jc fits a scaling law similar to one used for describing Nb3Sn and other A15 materials.

The electrical transport properties of a series of Y1Ba2Cu307.x thin films deposited onto single crystal substrates by thermal coevaporation and laser ablation were investigated. For fully epitaxial, c‐oriented films on (001) substrate surfaces, the critical current density Jc showed large high‐field enhancements for the film aligned with H parallel to the copper‐oxygen planes. With H||c, a precipitous decay of Jc with increasing field is described by thermally activated flux motion. Films on (110) SrTiO3 substrates were comprised of finely‐divided arrays of grains having [110], and ‐type orientations, and exhibited granular behavior. For these “triaxial” films, the transport dissipation was also thermally activated but with much smaller energy barriers.

Although high critical current density (J c ) YBCO can be deposited on rolling assisted biaxially-textured substrates (RABiTS) with the YSZ/CeO2/Ni architecture, improvement in uniformity is needed due to the presence of two-component YBCO epitaxy and cracking in the CeO2 buffer. We have determined that Yb2O3 is an excellent buffer material that provides a single-component YBCO epitaxy. In addition, crack-free epitaxial Y2O3 can be consistently deposited onto textured Ni substrates. High quality YBCO films have been deposited, and J c as high as 1.8 ×106 A/cm2 at 77 K has been obtained on this Yb2O3/Y2O3/Ni alternative RABiTS architecture.

The basal plane transport critical current density J c of YBCO epitaxial thin films is strongly anisotropic, leading to large enhancements of J c when H is precisely parallel to the copper-oxygen planes. Experimental evidence shows that the enhancement is a bulk phenomenon, and the orientation dependence is compared with a model of “intrinsic flux pinning” by the layered crystal structure.

Reported here is a new epitaxial buffer layer configuration on biaxially textured Ni substrates for high temperature superconducting films. The hetero-epitaxial LaAlO 3 /SrTiO 3 /CeO 2 /Ni structure was grown using pulsed laser deposition and is the first demonstrated epitaxial deposition of LaAlO 3 on a metal substrate. This buffer configuration was designed specifically for, but is not limited to, the Tl-based superconducting materials for which LaAlO 3 has been shown to be the optimum substrate to date. The epitaxy and crystal quality of these layers were investigated using X-ray diffraction including θ /2 θ and pole figure analysis, which showed that the consistency of the SrTiO 3 orientation requires further optimization. Atomic force microscopy measurements revealed initial films that, although epitaxial, have a cracked morphology. The formation mechanism of these cracks and their subsequent elimination are discussed.

Conductive multilayers of YBa2Cu3O7−δ/SrRuO3/LaNiO3 (YBCO/SRO/LNO), YBCO/SRO, and YBCO/LNO were grown epitaxially on single-crystal LaAlO3 and SrTiO3 substrates. Property characterizations revealed that the YBCO films on SRO and SRO/LNO buffer structures have excellent structural and superconducting properties. The YBCO/LNO, however, suffers degradation in superconducting transition temperatures and critical current densities, despite a good crystalline structure. The SRO/LNO bilayer showed excellent electrical contact with YBCO. These results have demonstrated the structural and chemical compatibility of SRO/LNO multilayers with YBCO and their potential use as conductive buffer layers for YBCO-based coated conductors as well as for other high-temperature superconducting applications.

A small-angle neutron-diffraction technique has been used to obtain the first direct observations of a well-defined flux-line lattice (FLL) in the mixed state of a single-crystal sample of the A-15 compound V 3 Si. From the measurements made at 4.85 K, the form factor of the FLL was deduced, and found to be nearly London-like. For a scattering geometry employing the neutron beam parallel to the flux lines, the sample rocking-curve widths reveal that there is no significant correlated bending of the flux lines greater than ± 0.3° from the mean direction of their axes. With the neutron beam orthogonal to the flux lines, the FLL morphology was determined, and found to be strongly correlated with the symmetry properties of the crystal axis parallel to the applied magnetic field.

The dc magnetic hysteresis and audio-frequency ac susceptibility were studied for YBa 2 Cu 3 O x films of different epitaxial orientations on SiTiO 3 . The apparent critical current density deduced from the ac susceptibility is in reasonable agreement with that deduced from the slowly-swept-field dc result, but not with the quasistatic dc hysteresis. Both the ac-voltage waveform from the mutual inductance bridge and the slow decay of magnetic moment in a static applied field show magnetic flux creep.

The epitaxial orientation of coevaporated Y 1 Ba 2 Cu 3 O 7−x thin films was identified and the transport critical current density J c characterized. The best c-axis oriented films deposited on (100) SrTiO 3 substrate surfaces had properties that approached estimated material limits, with J c > 1 MA/cm 2 in zero magnetic field at 85K, and showed a large dependence on magnetic field orientation, such that J c ( H ⊥ c ) J c ( H ∥ c ) ⋍ 100 at H=60 kOe and 77 K. Triaxial [110]- and [103]-oriented films deposited on (110) substrate surfaces had significantly lower T c and J c values, and exhibited temperature dependencies indicative of normal weak-link arrays.

The effect of fast neutron damage on the superconducting transition temperature Tc and the critical current density jc of the compound La1.85Sr0.15CuO4 has been investigated. Irradiation to a fluence of 1.3×1018 n/cm2 (E > 0.1 MeV) resulted in a decrease of Tc of about 3 K while jc at 4.2 K and H = 2 T increased by a factor of two to 1.2×104 A/cm2.

The influence of disorder on the properties of the B1 phase superconductive compound titanium nitride has been investigated. Following synthesis and characterization of thin films of TiN, the materials were disordered progressively and uniformly by irradiation with nitrogen ions. The superconducting transition temperature Tc decreased and the low temperature electrical resistivity ρ increased as lattice damage was introduced. The dependence of both Tc and ρ on N-ion fluence φ could be described by exponentially saturating functions of φ with similar rate constants. These constants correspond to characteristic damage energy densities of 14 and 12 eV/atom, respectively.

For various thermal processing conditions, measurements of the electrical transport and superconducting magnetic properties have been correlated with the microstructure as determined by X-ray diffraction and transmission electron microscopy. We find the largest critical current densities Jc are associated with the presence of coherent second-phase precipitates, and are significatly higher than for materials containing only grain boundaries or dislocations as flux pinning sites. Low-temperature annealing in oxygen results in nearly perfect, defect-free grains, separated by clean, planar grain boundaries. We conclude that the temperature-dependent diamagnetic response below Tc cannot be explained by the observed gross microstructure.