Serhiy Pysarenko

Drastic improvement of surface structure and current-carrying ability in YBa2Cu3O7 films by introducing multilayered structure

Various superconducting applications demand different forms of the high temperature superconducting HTS films in terms of thickness, composition e.g, multilayers, properties, and performance. To establish a technology for growth of high quality YBa2Cu3O7 YBCO films with a singlecrystal structure, an enormous effort has been made. However, a clear solution to some important problems has not been found. For example, properties of thick YBCO films for coated conductors significantly degrade as the thickness of the films is increased over about 400 nm; considerable surface roughness of YBCO films and their growth problems over large-angle boundaries on bicrystals obstruct the development of reproducible Josephson junctions JJs of different types. In this work, we show that films with relatively large

Quantitative Description of Critical Current Density in YBCO Films and Multilayers

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 inter-dislocation 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.

Extended dislocation-based pinning mechanism in superconducting YBa2Cu3O7 films

To describe the critical current density (Jc) as the function of applied magnetic field (Ba) in high quality YBa2Cu3O7 (YBCO) superconducting films, the vortex pinning mechanism along the structural domain boundaries of the films is developed. The boundaries, assumed to have low misorientation angles, are quantitatively considered to consist of individual edge dislocations acting as pinning wells, rather than a continuous boundary. This extended model accurately describes the experimental Jc(Ba) over the wide field and temperature ranges. Marginal deviations of the model from the experimental Jc(Ba) curves are observed at high fields and temperatures where thermally activated depinning is significant. This pinning model is verified to provide precise structural properties of the films which can be obtained by other considerations.

Origin of Surface Morphology Variation During Pulsed Laser Deposition of

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.

{\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7}

The quality superconducting YBa2Cu3O7 films and YBa2Cu3O7/NdBa2Cu3O7 multilayered film structures have been grown by pulsed laser deposition on metallic templates with magnesium oxide (MgO) buffer layer grown by incline substrate deposition. Different supplementary buffer layers have been deposited between the superconductor and MgO buffer layer. This additional buffer layer reduces the crystal structure misalignment of the superconducting layers. The critical current density has been observed to be higher in the multilayered structures in comparison with the same thickness of monolayer YBa2Cu3O7 films. The origin of this enhancement is the improved microstructure of the multilayered systems obtained.

Superconducting Films

High temperature superconducting YBa2Cu3O7 films have been prepared by pulsed laser deposition on top of single crystal substrates and metallic templates. Films have been investigated in order to determine the influence of microstructural peculiarities on the critical current density. It has been found that there is an inherent mechanism limiting the superconductive current flow in YBa2Cu3O7 film deposited on metallic template. This mechanism is associated with YBa2Cu3O7 film architecture, fabrication procedure and following low temperature usage.

Development of multilayer coated conductors with simplified buffer structure

High quality YBa2Cu3O7 (YBCO) films and multilayers of ReBa2Cu3O7 superconductors, where Re is rare earth elements (Y and Nd), have been prepared by pulsed laser deposition. Pinning characteristics of the structures obtained have been analysed and attributed to growth conditions and corresponding structural peculiarities. Relatively thick (~1 µm) multilayers exhibit better performance than mono-layer YBCO films having arbitrary thickness. differences in the films and multilayers are discussed in terms of their structure homogeneity and defects induced by the growth of the layers.