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The dependence of properties in YBa2Cu3O7 (YBCO) films grown by pulsed laser deposition at different distances from the target to a substrate has been systematically studied. The target to substrate distance DTS is shown to enable simple means for tunability of the critical current density and microstructure of the YBCO films. The variation of structural and electromagnetic properties in the films as a function of DTS has been explained in terms of laser plume propagation model and thin film formation mechanism. [ABSTRACT FROM AUTHOR]

Application of Josephson effect in sensors, electronic and metrological devices working at temperature of 77 K requires fabrication of efficient and reproducible high temperature superconducting (HTS) Josephson junctions. In order to enhance the performance of HTS junctions, we introduce multilayered approach to YBCO-based step-edge Josephson junction manufacture. Thin YBCO and multilayered YBCO/NdBCO/YBCO films of a similar thickness (\sim210 nm) were grown by a pulsed-laser deposition technique on MgO (100) substrates with artificially created step edge. Large discrepancies of Ic and Rn values were found between these two types of junction. Results of their structural and electrical properties are reported. [ABSTRACT FROM AUTHOR]

The vortex pinning model based on the presence of the large number of edge dislocations in high quality YBa2Cu3O7 (YBCO) films and multilayers has been refined. By introducing the pinning potential of a chain of individual edge dislocations, we have been able not only to describe the critical current density dependence on the applied magnetic field over its entire range, but also to extract the microstructural parameters in the films, such as interdislocation spacing and average domain size, without employing sophisticated microstructural analysis. The model applicability and its results have been verified with the help of microstructural characterization combined with magneto-optical imaging in YBCO films and multilayers with different properties. [ABSTRACT FROM AUTHOR]

MgB2 superconductors were made with two processes in this work. In one case, the SiC doped MgB2 pellets were sintered in excessive Mg medium. It is found that the samples sintered in excessive Mg medium present Mg-rich composition comparing with the one sintered in Ar gas. The density is higher and the resistance is lower due to the penetration of the Mg into the pores and grain boundary of MgB2, which is beneficial to the Jc improvement. In the other case, a two-step process was employed to make MgB2. Jc, of the sample with the composition of MgB4 is very low after the first sintering. The Jc. was dramatically improved after the second sintering, but J. of the two-step made sample is still poorer than the MgB2 made with general one step sintering due to the connectivity deterioration caused by the pulverization prior to the second sintering. [ABSTRACT FROM AUTHOR]

Much denser YBa2Cu3O7 (YBCO) superconducting films at least 1 μm thick with smooth surfaces have been obtained after introducing (Y/Nd)BCO multilayered structures. A significant enhancement of current carrying abilities has been achieved in these pulsed laser deposited films. The critical current density (Jc) has been increased by a factor of up to three in the entire field range. The imitation of the (Y/Nd)BCO multilayered structure by using YBCO ‘interlayers’ has also exhibited a considerable improvement in the current carrying ability. Similarities and differences between these two ‘multilayering’ approaches, leading to the observed effects, are discussed. The presence of interfaces even without element variation is likely to be the key to the improvements observed. In order to further promote Jc enhancement, small ‘multilayered’ additions of silver (Ag) to the films and multilayers provide various results: (i) rather strong enhancement for rather thin films and low addition levels, (ii) considerable degradation for large addition levels, and (iii) much less pronounced effect for thicker films. The enhancement of Jc is observed in zero and low magnetic fields, but has almost no effect at higher fields. All these experimental observations are discussed in terms of pinning, transparency and structural modifications introduced during the deposition of the film structures. [ABSTRACT FROM AUTHOR]

Significant differences in superconducting and microstructural properties between two types of MgB2 films prepared by pulsed laser deposition were determined. A very high Hc2 — T slope of 1.1 T/K was achieved in the in situ film. The Jc — H curves of the in situ film also show a much weaker field dependence than that of the ex situ film. The magneto-optical (MO) images show that at 4 K the flux penetrates the in situ MgB2 film through random paths, while for the ex situ film, the flux penetration pattern is mostly repeatable, indicating a defect-controlled flux penetration. Microstructural study (transmission electron microscopy and atomic force microscopy) revealed a relatively big grain size in the ex situ film. The correlation between the super- conducting properties, microstructure and preparation conditions is discussed with regard to the two types of films. [ABSTRACT FROM AUTHOR]

Magnetic field and temperature dependencies of the critical current density, J[sub c](Hc, T) were measured by SQUIDmagnetometry, ac magnetic susceptibility, and dc transport current techniques in the single-crystalline epitaxially-grown by offaxis dc magnetron sputtering YBa[sub 2]Cu[sub 3]O[sub 7-δ] (YBCO) films with J[sub c](Hc, 77 K) ≥ 2 · 10[sup 6] A/cm². The mechanism of vortex depinning from growth-induced linear defects, i.e., out-of-plane edge dislocations in low-angle tilt domain boundaries, is shown to describe quantitatively measured J[sub c](Hc, T). The developed model takes into account a statistical distribution of the dislocation domain boundaries ordered in a network as well as the interdislocation spacing within boundaries. Actual structural features of YBCO film known from HREM data turn out to be extracted from J[sub c](Hc, T)-curves by a fitting procedure within the proposed model. [ABSTRACT FROM AUTHOR]