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The main objective of the investigation is to establish optimum processing conditions of YBCO large grains by studying the effects of top and bottom seeding on microstructure, crystal orientation and its superconducting properties is discussed. It is concluded that the use of technique in improving the superconducting properties in bulk textured YBCO.

Having investigated a powerful experimental technique for measuring the properties of YBa2Cu3O(sub 7-delta) grain boundaries in the normal state are discussed. It is concluded that the technique provides a useful way to assess the effects of doping the boundary.

Research is presented concerning the development of a technique for the measurement of the YBa2Cu3O7-delta grain boundary junction through the use of an SalphaSbetaISbetaSalpha tunneling/proximity-effect model.

Research is presented concerning the investigation of Andreev reflection, high temperature superconductors and Josephson structures within layered anisotropic normal metal/superconductor systems.

Research is presented concerning the use of laser scanning microscopy to investigate critical current spread within a series array containing up to 100 YBa2Cu3O7-x bicrystal junction junctions.

A study was conducted to analyze the transport properties of electron-doped, s-wave Nd1.85Ce0.15CuO(sub 4-y) bicrystal grain boundary Josephson junctions (NCCO-GBJs) and compare them with those of hole-doped, d-wave high-temperature-superconducting-GBJs (HTS-GBJs). Results indicate that the universal properties observed for HTS-GBJs are also exhibited by NCCO-GBJs. It was also noted the NCCO-GBJs' grain boundary properties appear to be dominated by structural characteristics such as strain disorder and oxygen stoichiometry.

Yttrium barium copper oxide (YBCO) junctions and direct current (dc) superconducting quantum interference devices (SQUIDs) based on 45 degree a-axis tilt grain boundaries were realized and fully characterized in terms of transport characteristics. The realized SQUIDs are among the first that employ such grain boundaries. High values of the I(sub C)R(sub N) quality factor and of the magnetic flux-to-voltage transfer parameter were derived.

Research was conducted to examine (Hg,Re)-1212 bicrystal grain boundary Josephson junctions and direct current (dc) superconducting quantum interference devices (SQUIDs). The junctions reveal RSJ-like current-voltage characteristics even at 113 K and I(sub c)R(sub n) products of 400-460 microV at 77 K which is the highest recorded value reported so far. The dc SQUIDs show a field-induced periodic voltage of up to 111 K.

Interesting behavior in substantial magnetic fields is exhibited by superconducting electrical transport across single grain boundaries in YBCO. Measurements taken on (001) tilt bicrystal YBCO thin films in strong magnetic fields were consistent with the following: large angle grain boundaries exhibit weak coupling behavior that retained a well defined critical current even at high field while low angle grain boundaries are composed of well-ordered bridges that act as strong superconducting inter-granular links.

A study of the effect of vortex pinning along a grain boundary on dissipation was conducted using single grain boundary studies done on bulk bicrystals and YBCO thin films. The results point to the existence of significant differences in the critical current density across boundaries in the case of thin YBCO films compared to bulk bicrystals. This difference can be adequately explained when vortex pinning along the boundary is taken into consideration.

A procedure for joining large-grain YBCO to produce bulk-bicrystal grain boundaries that exhibit different orientations has been developed. The boundaries show a normal metallic state coupled with a superconducting transition that widens with an increasing field that features an irreversibility line that closely resembles the adjacent grains. The results indicate that the joining technique can be applied in bulk-scale engineering operations.

Analytical studies of the effects of 2.2 GeV Au-ions irradiation on the transport properties of the bicrystals of Bi2Sr2CaCu2O8+delta bicrystals with (001) twist grain boundaries were conducted. The studies involved measuring the critical current and irreversibility line within the single crystals and across the twin grain boundaries prior to and after irradiation. The results indicate that the columnar defects from the irradiation increased the irreversible temperatures by a large factor.

The study of the transport properties of the grain boundary was undertaken using more than a dozen successfully isolated, naturally-grown (100) tilt Bi2Sr2CaCu2O8+delta bicrystals. The bicrystals are characterized by a single clean (100) non-basal-plane-faced tilt grain boundary with various degrees of misorientation. The results showed that almost all the (100) non-basal-plane-faced tilt grain boundary had a T(sub c) depression as compared to the constituent single crystals. However, these grain boundaries did not behave like weak-links at low temperatures.

A study was conducted on the current transition of voltage-fed high temperature superconducting materials for resistive limiters. The quench properties of textured and sintered Bi compounds were also examined and compared. Results demonstrate the importance of grain boundaries in the limitation process. Results also reveal that the complete resistive transition of the sample materials are very low.

A study was conducted on powder-in-tube Bi(Pb)-2223/Ag high temperature superconducting tapes using transmission electron microscopy. Results reveal reveal several fine-scale, current-limiting features. These features include amorphous phases at twist grain boundaries, secondary phase, grain boundary structure variation, residual 2212 layers at grain boundaries and inside grains.

A study was conducted on the critical current density distribution in large YBa2Cu3O7-delta grains developed through seeded peritectic solidification. The critical current density derived from magnetic characterization was correlated with the grains' microstructural features. The irreversibility line as well as the critical current density's field, temperature and positional dependence were determined.

The barrier properties of grain boundary junctions in high temperature superconductors were measured. An insulating barrier with a high density of localized states was observed through an examination of the quasiparticle tunneling's temperature and voltage dependence in various applied magnetic fields over a wide voltage range. A zero-bias conductance peak was also seen in the low voltage regime.

Magneto-optic and current transport methods were employed to investigate the electromagnetic coupling inhomogeneity across the high angle grain boundaries of YBa2Cu3O(6+x) bicrystals fabricated via melt texturing and liquid phase removal. Specifically, it was proven that the grain boundary plane orientation has no effect on the coupling behavior across such boundaries. Moreover, it was shown that inter- and intra-grain zones contain 'a strong coupled component to the boundary.'

A process for reproducibly creating 45-degree grain boundary junctions in YBa2cu3O(7-x) (YBCO) thin films grown on magnesium oxide substrates is implemented. It requires the use of a low-energy Argon ion source to pre-treat the substrate to induce a 45-degree rotation about the c-axis while YBCO is being deposited on the film via pulsed organo metallic beam epitaxy. This results in uniform grain boundaries without amorphous phases.

The electrical properties of step-edge Josephson junctions and direct current superconducting quantum interference devices (DC SQUIDs) were investigated. The junctions and the SQUIDs were fabricated by laser ablated deposition of YBaCu films onto polycrystalline TiBaCaCuO films. The devices' current-voltage characteristics were then measured at different temperatures. The results were found to be in good agreement with those predicted by a resistively shunted junction model.

The linewidth of the Josephson radiation in YBa2Cu3O7-x (YBCO) grain boundary junctions was studied. Grain boundary junctions were fabricated by the laser ablated deposition of YBCO films on SrTiO3 and Y-ZrO2 bicrystals. The devices were then subjected to millimeter wave radiation and their self-detector direct current response was measured at different temperatures using the lock-in technique. Results show that the effective noise temperature of the junctions may be as low as the physical temperature in the range of 4.5 to 90 degrees Kelvin.

Ten years ago in November, an innocuously entitled paper about superconductivity at record-breaking temperatures was published in Zeitschrift fur Physik (1). Although it took a few months for the field [...]