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

Much smoother surfaces and significantly improved superconducting properties of relatively thick YBa2Cu3O7 (YBCO) films have been achieved by introducing a multilayered structure with alternating main YBCO and additional NdBCO layers. The surface of thick (1 microm) multilayers has almost no holes compared to YBCO films. Critical current density (Jc) have been drastically increased up to a factor > 3 in 1 microm multilayered structures compared to YBCO films over entire temperature and applied magnetic filed range. Moreover, Jc values measured in thick multilayers are even larger than in much thinner YBCO films. The Jc and surface improvement have been analysed and attributed to growth conditions and corresponding structural peculiarities.Comment: Accepted to Appl. Phys. Lett. 88, June (2006), in press 4 pages, 3 figure

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

Much smoother surfaces and significantly improved superconducting properties of relatively thick YBa2Cu3O7 (YBCO) films have been achieved by introducing a multilayered structure with alternating main YBCO and additional NdBCO layers. The surface of thick (1 µm) multilayers has almost no holes compared to YBCO films. Critical current density (Jc) has been drastically increased up to a factor \u3e3 in 1 µm multilayered structures compared to YBCO films over entire temperature and applied magnetic field range. Moreover, Jc values measured in thick multilayers are even larger than in much thinner YBCO films. The Jc and surface improvement have been analyzed and attributed to growth conditions and corresponding structural peculiarities

Microbial remediation of petroleum polluted soil

Saabunud / Received 10.05.2022 ; Aktsepteeritud / Accepted 28.07.2022 ; Avaldatud veebis / Published online 28.07.2022 ; Vastutav autor / Corresponding author: Anna Taranenko ; [email protected] issues of land pollution, restoration, and return of land to agricultural cultivation are today. Especially, this is gaining new relevance in modern conditions of military action on the territory of Ukraine and other countries, which causes the reduction of cultivation areas. Therefore, there is a need for maximum cleaning and restoration of polluted soils to ensure environmental and food security. Petroleum hydrocarbons are classified as major environmental pollutants due to their stability and durability in the environment. The influence of petroleum hydrocarbons is caused by direct toxic activity and by the soil environment transformation. The research aimed: to study the effectiveness of probiotics in the technology of soil cleaning and remediation; evaluate the phytotoxic effect of oil-contaminated soil before and after the application of probiotics; to find the optimal concentration of probiotics for the effective cleaning and remediation of soil. The seedling method was used to evaluate the phytotoxic effect of contaminated soil before and after the application of probiotics. Research results showed an ambiguous impact on Pisum sativum and Avéna satíva at different times after pollution. In the initial phase, polluted soil has no significant influence on Pisum sativum. For Avéna satíva soil, become toxic right away after pollution. Phytotoxic effect of Pisum sativum and Avéna sativa decrease by the indexes of seed emergence, roots length, roots weight, underground part length and ground part weight due to probiotics treatment. The high efficiency of biological remediation by probiotics in comparison with soil cleaning in natural conditions is determined in the experiment. Probiotic concentration 1:10 is the most effective of all studied initial concentrations of pollutants. Reducing probiotic concentration leads to a decrease in the efficiency of soil cleaning from petroleum products

Structure, pinning and supercurrent in YBa2Cu307 films and ReBa2Cu307 multilayers

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

Multilayering approach to enhance current carrying capability of YBa2Cu3O7 films

High temperature superconducting (HTS) thin films deposited onto metallic substrates are known as coated conductors (CC) and are currently the most promising HTS candidates for wide-scale industrial applications. These films are fabricated from ReBa2Cu3O7 (where Re is a rare earth element) ceramics and have very specific requirements with regard to their manufacturing and maintenance, due to their complex stoichiometry and large anisotropy. One of the most important problems studied by many researchers around the world is the improvement of critical current capability in such superconducting films. Structures consisting, for example, of both YBa2Cu3O7 (YBCO) layers and layers of different superconductive or non-superconductive materials having a similar crystal structure are likely to have enhanced microstructural properties, and they are able to carry larger critical currents as compared to their monolayer counterparts. Such sandwich-like films are called multilayer structures. Usually, in order to increase the amount of electrical current being transported through a coated conductor, one needs to make necessary adjustments to the superconducting layer. An obvious way to enhance transport electrical current is to increase the thickness of the superconducting film. However, this approach has one very significant flaw: the fact that critical current density degrades with increasing thickness of the film. This phenomenon is widely observed in coated conductors, which are already used for transmission of electricity in electric motors and high-field magnets around the globe. The present work involves fundamental studies of the fabrication of multilayered structures on single crystal and metallic substrates with the emphasis on improvement of the critical current density and understanding the mechanisms responsible for the behaviour of the critical current in such superconducting multilayer thin films. Enhancement of the critical current density has been achieved, reaching 3.4 MAcm¡2 at 77 K in YBa2Cu3O7/NdBa2Cu3O7 based multilayers about 1 µm thick. This critical current density is higher than that for the best quality and optimal thickness YBa2Cu3O7 monolayer films. Investigation of the crystal structure and electromagnetic properties of mono- and sandwich-like structures has been performed to clarify the origin of the critical current enhancement in the multilayer structures. It was found that, from the structural point of view, the multilayer films have much better microstructure and surface quality (i.e. the smoothness of the surface) than is the case for monolayer films. This is due to the increased filling factor in the multilayered structures, because the holes which are usually observed in the film have been successfully eliminated. With one of the critical problems being solved, which is degradation of critical current due to thickness of the superconducting film, multilayer structures offer great potential to be utilized not only for electrical power transmission, but also, for example, in fabrication of superconducting electronic components, such as magnetic detectors, superconducting quantum interference devices, etc. Enhancement of the critical current capability of multilayer structures was investigated using a newly developed theoretical model. Mathematical modelling of critical current behaviour in thin superconducting films is one of the most complicated tasks of modern solid state physics. Theoretical investigation of multilayering is crucial for understanding the superconductivity and for further improvement of the superconducting properties of such structures. The qualitative analysis of electric current properties in superconductors can uncover the nature of the coexistence and interaction of two states: the solid state and the field state of the matter. The existing theory of vortex lattice behaviour in superconducting thin films in the field state of matter is an intriguing part of the research, as parameters controlling such a lattice are controllable. By changing these parameters, a variety of structural defects and crystal characteristics on macroscopic and microscopic scales can be investigated. One of the major objectives of this PhD project was to develop a theoretical model that would allow modelling of critical current behaviour in superconducting films. The constraints and applicability of the model are discussed in accordance with experimental data and fitting procedures. Calculation results, obtained within reasonable approximations, can well describe various properties of the crystal struc-tures of monolayer and multilayer thin films. An automated computer program was successfully designed on the basis of the statistical theory for the quantification of the crystal structure parameters in superconducting thin films. Observed data showed that multilayering is crucial to enhance the quality of the upper layers of the films and to increase the amount of dislocations that act as effective pinning centres, resulting in improved critical current carrying capability. During this work, a few additional related research problems have been addressed. An emphasis was put onto development of the pulsed laser deposition method (to prepare thin film samples of the highest quality) and investigation of the effect of Ag doping, which has a positive influence on the critical current carrying capability of YBCO superconducting films. Fabrication of high quality YBCO thin films implies usage of very reactive oxygen atmosphere and high temperature. These peculiarities make the process very sensitive to a number of various deposition parameters. Optimal deposition conditions were verified and, as a consequence, a new heater was designed and fabricated. As a result of this work, the amount of time required to be spent on optimization of deposition conditions has been considerably reduced. This, in fact, significantly increased the productivity of the pulsed laser deposition system. A comprehensive study of one deposition parameter, the target to substrate distance was performed. The obtained results showed that the target to substrate distance plays a crucial role in pulsed laser deposition of monolayer and multilayer structures. Special efforts were also dedicated to the investigation of Ag doping of the YBCO superconducting thin films. It was found that doping strongly improves critical current at low applied magnetic fields. Research was directed towards uncovering the nature of advanced critical current carrying capabilities in Ag doped films. Microstructural analysis revealed that Ag doping leads to the enhancement of transparency for electrical current flow in the films. This is achieved in the process of deposition of the YBa2Cu3O7 films, in which silver particles transfer extra energy to the YBa2Cu3O7 ablated adatoms, thus ordering the microstructure during growth of the film. Moreover, the amount of silver which remains in the intergrain boundaries increases the transparency of films to the supercurrent flow and presumably plays a role as a barrier against oxygen depletion

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

Constrains of super-current flow in YBCO coated conductors

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

A pinning model and universal pinning regimes in YBa2Cu 3O7 superconducting films

A model for vortex pinning at boundaries with modulated pinning potentials is developed for high-quality YBa2Cu3O7 superconducting films and multilayers. This model accurately describes the experimentally obtained Jc(Ba) behavior in different films over the entire field and temperature (T) ranges. Deviations are observed at high fields and temperatures due to the thermally activated depinning which is not accounted for by the model. A supplementary “model-free” analysis of the temperature dependent Jc curves leads to the four regions in the field-temperature phase diagram which are attributable to the well-known pinning regimes of collective pinning theory. The results obtained indicate the universality of the pinning model developed, which incorporates the universal pinning regimes and the ability to describe Jc(Ba,T) dependences