Publications on the project |
061 Higher borides and oxygen-enriched Mg–B–O inclusions as possible pinning centers in nanostructural magnesium diboride and the influence of additives on their formation |
Authors: | T.A. Prikhna, W. Gawalek, Ya.M. Savchuk, V.M. Tkach, N.I. Danilenko, M. Wendt, J. Dellith, H. Weber, M. Eisterer, V.E. Moshchil, N.V. Sergienko, A.V. Kozyrev, P.A. Nagorny, A.P. Shapovalov, V.S. Melnikov, S.N. Dub, D. Litzkendorf, T. Habisreuther, Ch. Schmidt, A. Mamalis, V. Sokolovsky, V.B. Sverdun, F. Karau, A.V. Starostina | |
Summary: | The study of high pressure (2 GPa) synthesized MgB2-based materials allows us to conclude that higher borides (with near MgB12 stoichiometry) and oxygen-enriched Mg–B–O inclusions can be pinning centers in nanostructural magnesium diboride matrix (with average grain sizes of 15–37 nm). It has been established that additions of Ti or SiC as well as manufacturing temperature can affect the size, amount and distribution of these inclusions in the material structure and thus, influence critical current density. The superconducting behavior of materials with near MgB12 stoichiometry of matrix is discussed. | |
Keywords: | MgB2-based bulk superconductor, MgB12, high-pressure synthesis, Mg–B–O pinning centers, critical current density | |
Edition: | Physica C | | | 2010,
- 470. - p.935–938 ,English |
061 Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines |
Authors: | T.A. Prikhna; W. Gawalek, Ya.M. Savchuk, N.V. Sergienko, V.E. Moshchil, V. Sokolovsky, J. Vajda, V.N. Tkach, F. Karau, H. Weber , M. Eisterer, A. Joulain, J. Rabier, X. Chaud, M. Wendt, J. Dellith, N.I. Danilenko, T. Habisreuther, S.N. Dub, V. Meerovich, D. Litzkendorf, P.A. Nagorny, L.K. Kovalev, Ch. Schmidt, V.S. Melnikov, A.P. Shapovalov, A.V. Kozyrev, V.B. Sverdun, J. Kosa, and A.V. Vlasenko. | |
Summary: | Materials of the Y–Ba–Cu–O (melt-textured YBa2Cu3O7-x-based materials or MT-YBCO) and Mg–B–O (MgB2-based materials) systems with high superconducting performance, which can be attained due to the formation of regularly distributed nanostructural defects and inhomogeneities in their structure can be effectively used in cryogenic technique, in particular in fault current limiters and electrical machines (electromotors, generators, pumps for liquid gases, etc.). The developed processes of high-temperature (900–800 °C) oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2 GPa) synthesis of MgB2-based materials allowed us to attain high superconductive (critical current densities, upper critical fields, fields of irreversibility, trapped magnetic fields) and mechanical (hardness, fracture toughness, Young modulus) characteristics. It has been shown that the effect of materials properties improvement in the case of MT-YBCO was attained due to the formation of high twin density (20–22 um-1), prevention of macrocracking and reduction (by a factor of 4.5) of microcrack density, and in the case of MgB2-based materials due to the formation of oxygen-enriched as compared to the matrix phase fine-dispersed Mg–B–O inhomogeneities as well as inclusions of higher borides with near-MgB12 stoichiometry in the Mg–B–O matrix (with 15–37 nm average grain sizes). The possibility is shown to obtain the rather high Tc (37 K) and critical current densities in materials with MgB12 matrix (with 95% of shielding fraction as calculated from the resistant curve). | |
Keywords: | | |
Edition: | Acta Physica Polonica A. | | | 2010,
– Vol. 117. – p.7-14.,English |
061 Measuring AC losses and critical current of high pressure synthesized MgB2 bulk rings by the transformer method |
Authors: | V. Meerovich, V. Sokolovsky, T. Prikhna and W. Gawalek | |
Summary: | The results of experimental study of the critical current and AC losses in high pressuresynthesized MgB2 bulk superconductors are presented. The method is based on the use of the transformer configuration and suitable for samples in the form of hollow superconducting cylinders and rings. It was shown that the critical current measured by the transformer method is an order of magnitude lower than the value given by the magnetization technique. The obtained dependencies of the losses on current and frequency reveal the deviations from the critical state model behavior and reflect structural peculiarities of the investigated MgB2 samples. | |
Keywords: | bulk MgB2 superconductor, AC losses, critical current | |
Edition: | Materials Science Forum | | | 2012,
– Vol. 721. – p.27-32,English |
061 Universal character of tunnel conductivity of metalinsulator-metal heterostructures with nanosized oxide barriers |
Authors: | V.Shaternik, M. Belogolovskii, T.Prikhna, A.Shapovalov, O.Prokopenko, D. Jabko, O.Kudrja, O.Suvorov, V. Noskov | |
Summary: | We discuss an universal effect in tunnel characteristics of layered metal - insulator – metal structures, where the dielectric barrier is formed by a nanoscale disordered oxide film: a universal distribution of the insulator layer transparencies, which does not depend on specific microscopic characteristics of it. Experimental results for superconducting three- and four-layered structures with inhomogeneous tunnel barriers, confirming the existence of a universal distribution of transparencies, are given jointly with a simple theoretical interpretation, based on the equipartition hypothesis of a product of the barrier height on the way which an electron passes within it. | |
Keywords: | Josephson junction; multiple Andreev reflection; transparency distribution; quasiparticle, I-V curve, barrier | |
Edition: | Physics Procedia | | | 2012,
– Vol. 36. – p. 94–99,English |
061 Superconductivity in multi-phase Mg-B-O compounds |
Authors: | T. Prikhna, W. Gawalek, M. Eisterer, H. W. Weber, J. Noudem, V. Sokolovsky, X. Chaud, V. Moshchil,M. Karpets, V. Kovylaev, A. Borimskiy, V. Tkach,A. Kozyrev, R. Kuznietsov, J. Dellith, C. Shmidt, T. Basyuk, D. Litzkendorf, F. Karau, U. Dittrich, M. Tomsic | |
Summary: | Structures of MgB2-based materials manufactured under pressure (up to 2 GPa) by different methods having high superconducting performance and connectivity are multiphase and contain different Mg-B-O compounds. Some oxygen can be incorporated into MgB2 and boron into MgO structures, MgBx (X=4-20) inclusions contain practically no oxygen. Regulating manufacturing temperature, pressure, introducing additions one can influence oxygen and boron distribution in the materials and thus, affect the formation, amount and sizes of Mg-B-O and MgBx inclusions and changing type of pinning, pinning force and so affect critical current density jc. The boron concentration increase in initial Mg and B mixture allows obtaining sample containing 88.5 wt% of MgB12 with TC of 37.4 K (estimated magnetically). | |
Keywords: | magnesium diboride; higher magnesium borides; nanostructure; critical current density, pinning force. | |
Edition: | Physics Procedia | | | 2012,
– Vol. 36. – p.475–478,English |
061 Synthesis pressure–temperature effect on pinning in MgB2-based superconductors |
Authors: | T. Prikhna, M. Eisterer, W. Gawalek, A. Kozyrev, H.W. Weber, V. Sokolovsky, X. Chaud, J. Noudem, T. Habisreuther, V. Moshchil, M. Karpets, T. Basyuk, V. Kovylaev, J. Dellith, V. Sverdun, R. Kuznietsov, C. Shmidt, T. Vitovetskaya, L. Polikarpova | |
Summary: | The volume pinning force, Fp(max), increases with increasing synthesis or sintering pressure (0.1 MPa–2 GPa) in materials prepared at high temperature (1050 °C) while it stays practically unchanged in those prepared at low temperature (800 °C). The position of Fp(max) can be shifted to higher magnetic fields by: (1) increasing the manufacturing pressure or decreasing the temperature (2) additions (Ti, SiC, or C, for example), and (3) in-situ preparation. Grain boundary pinning (GBP) dominates in materials prepared at low temperatures (600–800 °C), while high-temperature preparation induces strong point pinning (PP) or mixed pinning (MP) leading to outstanding properties. In materials produced by spark plasma sintering (SPS), the position of Fp(max) is higher than expected for both grain boundary and point pinning. The distribution of boron and oxygen in MgB2 based material, which can changed by additions or the preparation conditions, significantly affects the type and strength of pining. Materials prepared under a pressure of 2 GPa with a nominal composition of Mg:7B or Mg:12B consist of 88.5 wt % MgB12, 2.5 wt% MgB2, 9 wt % MgO or 53 wt % MgB12, 31 wt %MgB20 16 wt %MgO, respectively. Their magnetic shielding fractions at low temperatures are 10 % and 1.5 %, with a transition temperature, Tc of 37.4–37.6 K. Although their magnetic critical current density at zero field and 20 K was 2–5 × 100 A/cm2, they were found to be insulating on the macroscopic level. | |
Keywords: | Bulk magnesium diboride, pinning force, grain boundary, point and mixed pinning, pressure–temperature effect | |
Edition: | Journal of Superconductivity and Novel Magnetism | | | 2013,
– Vol. 26, Is. 5. – p.1569-1576. ,English |
061 Influence of oxygen and boron distrib ution on the superconducting characteristics of nanostructural Mg-B-O ceramics |
Authors: | T. Prikhna, M. Eisterer, W. Gawalek, H. W. Weber, V. Moshchil, A. Kozyrev, M. Karpets, T. Basyuk, T. Habisreuther, V. Kovylaev, A. Shaternik, V. Sverdun, X. Chaud | |
Summary: | The superconducting characteristics, such as the critical current density and the critical magnetic fields, of MgB2-based materials, which in fact belong to the Mg-B-O system because of the high concentration of admixed oxygen (up to 17wt.%), depend on the inhomogeneity of the oxygen and boron distribution, which can be controlled by the synthesis temperature (600-1200 °C) and pressure (up to 2 GPa) as well as by SiC and Ti additions (10wt%). With increasing manufacturing temperature grain boundary pinning transforms into point pinning, which is well correlated with the transformation of discontinuous oxygen enriched layers into separately located Mg-B-O inclusions in the MgB2 nanostructure and with a reduction of the size and amount of inclusions of higher magnesium borides MgBX (X>2). Ti or SiC additions can influence the oxygen and boron distribution as SEM and Auger structural studies showed. | |
Keywords: | Magnesium diboride, nanostructural Mg-B-O ceramics: oxygen and boron distribution, critical current density, pinning force | |
Edition: | Solid State Phenomena | | | 2013,
– Vol. 200. – p. 137-143,English |
061 AC losses in high pressure synthesized MgB2 bulk rings measured by a transformer method |
Authors: | V. Meerovich, V. Sokolovsky, T. Prikhna, W. Gawalek and T. Habisreuther | |
Summary: | Recently developed manufacturing technologies use high pressure and various doping additions to prepare bulk MgB2-based materials with a high critical current density measured by the magnetization method. We use a contactless transformer method, which is based on studying the superconductor response to an induced transport current, to measure AC losses in bulk MgB2 rings synthesized under high pressure. The obtained dependence of the losses on the primary current (applied magnetic field) is fitted by a power law with an exponent of 2.1 instead of the cubic dependence predicted by Bean’s model and power law electric field–current density (E–J) characteristics with a large exponent. An unusually strong dependence of the AC losses on the frequency is also observed. It is shown that the E–J characteristic of bulk MgB2 is well fitted by the dependence used in the extended critical state model based on account of the viscous vortex motion in the flux flow regime. Numerical simulation using this E–J characteristic gives current and frequency AC loss dependences that agree well with the experimental results. | |
Keywords: | | |
Edition: | Superconductor Science and Technology | | | 2013,
– Vol.26 – p.035015 ,English |
061 Charge transport under microwave irradiation in Josephson heterostrucrures superconductor – doped semiconductor – superconductor |
Authors: | V. Shaternik, A. Shapovalov, A. Suvorov, S. Doring, S. Schmidt, P. Seidel | |
Summary: | On the base of superconducting MoRe alloy superconductor – doped semiconductor – superconductor junctions have been fabricated. For the pure silicon barriers and silicon barriers doped by tungsten fabricated with small W concentration (3-4at.%) we observed the existence of an over-barrier direct tunneling effect and a direct tunneling effect through an impurity level within the barrier. At relatively high concentrations (6-9at.%) of tungsten in the silicon barriers an existence of a resonant tunneling effect is observed (if percolation limit is overcome) through localized levels of scattering centers (W atoms). Simultaneously, at some conditions in these junctions a superconducting Josephson current appears on the base of the resonant tunneling. It is experimentally observed that the sufficient excess quasiparticle currents flow through the investigated junctions at 6-9at.% of tungsten. This could be an evidence for two S/N interfaces with resonant tunneling according to BTK theory. The quasiparticle I-V curves of the fabricated junctions show a high differential resistance value and the same Josephson critical current compared to S-I-S Josephson junctions with direct tunneling. Thus, the ICRN product of the fabricated junctions is quite high. | |
Keywords: | Mo-Re alloy superconductor, Josephson junctions | |
Edition: | Proceedings of 8th International Kharkov Symposium on Physics and Engineering of Microwaves, Millimeter and Submillimeter Waves (MSMW 2013). | | | 2013,
p.655-657,English |
061 Temperature-pressure induced nano-structural inhomogenities for vortex pinning in bulk MgB2 of different connectivity |
Authors: | T. Prikhna, M. Eisterer, H. W. Weber, W. Gawalek, V. Kovylaev, M. Karpets, V. Moshchil, A. Kozyrev, T. Basyuk, X. Chaud, W. Goldacker, V. Sokolovsky, J. Noudem, A. Borimskiy, V. Sverdun, E. Prisyazhnaya | |
Summary: | Higher critical current densities, jc, (up to 1.6–0.15 MA/cm2 at 10–35 K) at low magnetic fields can be attained in MgB2-based materials, if a high manufacturing temperature (1050 °C) is used, while low temperatures (600–800 °C) usually lead to higher critical currents in high magnetic fields (0.0001 kA/cm2 in 6–10 T at 10 K). This tendency was observed for MgB2-based materials having 55-99% density and 17-98% connectivity, which were prepared by different methods from different precursors in a wide range of pressure (0.1 MPa–2 GPa). The variation of the manufacturing temperature led to a redistribution of the magnesium, boron, and impurity oxygen. At 2 GPa, its increase results in the segregation of the oxygen in MgB2 and the transformation of 15–20 nm thick layers of MgB0.6-0.8O0.8-0.9 into separate MgB0.9-3.5O1.6-2 grains and to a reduction of the size of MgB11-13O0.2-0.3 inclusions located in the MgB2 (MgB2.2-1.7O0.4-0.6) matrix. The size reduction of B-enriched inclusions and the localization of O in MgB2 seem to be the reason for the increase of jc in low fields and for the shift from grain boundary to point pinning of vortices witnessed by an increase of the k-ratio. | |
Keywords: | Magnesium diboride, critical current density, connectivity, pinning centres, higher magnesium borides, nanostructure | |
Edition: | Physica C | | | 2014,
- Vol.503. – p.109-112,English |
061 Transition from Coulomb blockade to resonant transmission regime in superconducting tunnel junctions woth W-doped Si barriers |
Authors: | V. Shaternik, A. Shapovalov, M. Belogolovskii, O. Suvorov, S. Döring, S. Schmidt, P. Seidel | |
Summary: | We have fabricated trilayered sandwiches consisting of superconducting electrodes made of MoRe alloy with a critical temperature of about 10K and a silicon interlayer of thicknesses up to 20 nm doped by tungsten with atomic concentrations up to 10 at%. For concentrations below 5 at%, measurements of transport characteristics have revealed the presence of charging energy in ultrasmall dopant granules (the Coulomb-blockade effect) without any supercurrent through the junction. Unexpectedly, a persistent current at zero voltage bias has exposed itself at higher W concentrations and even for the thickest W:Si layers. Microwave-radiation experiments have proven that in this case we are dealing with a Josephson current. The observation is explained as the fingerprint of ‘open’ channels in the charge transmission due to resonance-percolating trajectories inside the strongly inhomogeneous silicon interlayer with metallic nanoclusters. We have calculated the ratio of super- and excess currents using a universal distribution function for randomly arranged localized states and found good agreement with our experimental data without any adjustable parameters. The novel functionalities due to the disorder in doped semiconducting films make it possible to fabricate trilayered junctions with enhanced conductance properties and, at the same time, with well separated metallic electrodes. | |
Keywords: | superconducting trilayered junctions, doped semiconducting interlayers,
charge transport, Coulomb blockade, resonance tunnelling | |
Edition: | Materials Research Express | | | 2014,
026001,English |
The events in the framework of the project |
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061 4. Nanomaterials Purpose: Expected results:Release of new product: technology Stage 1: Stage 2: Stage 3: Stage 4: Stage 5:
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