Search

Your search keyword '"Rubešová, K."' showing total 98 results
Start Over Author "Rubešová, K."
98 results on '"Rubešová, K."'

26. Increase of the critical current density of MgB2 superconducting bulk samples by means of methylene blue dye additions

Author

Grivel, Jean-Claude, Rubešová, K., Grivel, Jean-Claude, and Rubešová, K.

Abstract

MgB2 bulk samples were made by means of reaction of elemental Mg and B powders with or without additions of methylene blue trihydrate, a carbon source, which melts at high temperature upon decomposition. The Tc of the MgB2 phase as well as its a-axis parameter were decreased as a result of carbon doping, whereas the c-axis parameter only shows a weak tendency for increasing. The critical current density of MgB2 was improved both in self-field and under applied magnetic field for T ≤ 25 K, the best results being obtained for 0.5–1.0 wt.% methylene blue trihydrate addition. Based on normalized flux pinning force (f(b)) versus reduced field (b) plots, it was found that the flux pinning mechanism at low reduced field is similar for all samples, with a behavior close to the predictions of the point pinning model. However, for b larger than 1, the behavior of f(b) is significantly altered in the methylene blue trihydrate added samples and tends towards the surface pinning model. Methylene blue trihydrate is an efficient carbon source and furthermore provides a liquid phase between 200 °C and 450 °C, which may have some influence on the critical current density improvements at low field.

Published
2019

38. Water-soluble polymers as chelating agents for the deposition of Er3+/Yb3+:LiNbO3 waveguiding films.

Author

Mikolášová, D., Rubešová, K., Jakeš, V., Nekvindová, P., Cílová, Z. Zlámalová, and Oswald, J.

Abstract

Compared to other oxide materials, the sol-gel deposition of an optically transparent LiNbO3 waveguiding film of sufficient thickness (approx. 1 μm) is complicated by the presence of a highly hydrolyzing Nb(V) in the starting solution. Thicker films require more concentrated solutions that are not easily achieved for such ions. This problem may be solved using strong chelating agents such as water-soluble polymers. To prepare a stable Er(III)/Yb(III)/Li(I)/Nb(V)/2-methoxyethanol solution with high metal concentration, we tested three such polymers: polyethylene glycol (PEG), polyacrylic acid (PAA) and polyvinyl alcohol (PVA), and compared them with already used polyvinylpyrrolidone (PVP). The solutions were spin-coated on crystalline sapphire substrates under a multi-step heating-deposition regime. Apart from Er3+/Yb3+ photoluminescence properties, we evaluated the influence of the film microstructure (SEM, AFM) on optical transparency and waveguiding ability in the UV/Vis/NIR region (transmission and m-line spectroscopy). Among the newly tested polymers, only PEG was able to prevent Nb(V) hydrolysis up to a maximum metal concentration of 0.6 mol/L. For PEG and PVP, the crystallization temperature of the deposited films (between 700 °C and 1000 °C) was compared. After further optimization of the heating-deposition process, we were able to prepare a transparent Er3+/Yb3+:LiNbO3 film thick enough to guide an optical signal in the NIR region. Thus, the use of PEG results is one of the very few non-hydrolytic sol-gel methods suitable for the preparation of not only luminescent, but also waveguiding Er3+/Yb3+:LiNbO3 structures. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

39. Manufacture of Bi-cuprate thin films on MgO single crystal substrates by chemical solution deposition

Author

Grivel, Jean-Claude, Bertelsen, Christian Vinther, Andersen, Niels Hessel, Kepa, Katarzyna, Hlásek, T., Rubešová, K., Huhtinen, H., Paturi, P., Grivel, Jean-Claude, Bertelsen, Christian Vinther, Andersen, Niels Hessel, Kepa, Katarzyna, Hlásek, T., Rubešová, K., Huhtinen, H., and Paturi, P.

Abstract

Bi2Sr2CaCu2O8 thin films have been deposited on MgO single crystal substrates by spin-coating a solution based on 2-ethylhexanoate precursors dissolved in xylene. Pyrolysis takes place between 200°C and 450°C and is accompanied by the release of 2-ethylhexanoic acid, CO2 and H2O vapour. Highly c-axis oriented Bi2Sr2CaCu2O8 as well as Er- or Ho-doped Bi2Sr2(Ca,Ln)Cu2O8 (Ln = Er, Ho) films were obtained after heat treatment at 840°C in air.

Published
2014

47. Preparation and Characterization of MgB Bulk Samples and Cu/Nb Sheathed Wires with Low Grade Amorphous Boron Powder.

Author

Grivel, J.-C., Alexiou, A., Rubešová, K., Tang, X., Andersen, N., Zimmermann, M., and Watenphul, A.

Subjects
BORON, SYNCHROTRONS, STOICHIOMETRY, SUPERCONDUCTIVITY, BULK solids, PHASE transitions
Abstract

MgB bulk and wire samples were prepared using cheap, low grade amorphous boron powders. Based on chemical analysis performed on the starting reagents, three nominal stoichiometries were studied. It was found that the structural and superconducting properties of the bulk samples were not affected by the composition, but that residual Mg was left in the wires for the nominal MgB composition. In contrast, slightly Mg-deficient compositions were free from residual Mg and exhibited higher critical current densities. The MgB phase formation kinetics was not influenced by the variations in the nominal powder composition. [ABSTRACT FROM AUTHOR]

Published
2014
Full Text
View/download PDF

48. Modified sol–gel preparation of LiNbO3 target for PLD.

Author

Jakeš, V., Rubešová, K., Erben, J., Nekvindová, P., and Jelínek, M.

Subjects
*SOL-gel processes, *LITHIUM compounds, *PULSED laser deposition, *ESTERIFICATION, *TEMPERATURE effect, *SINGLE crystals
Abstract

Highlights: [•] LiNbO3 target for pulsed laser deposition (PLD) was prepared by Pechini polyesterification. [•] Precursor powders were decomposed in various temperature/atmosphere regimes. [•] We report an enhanced processing of the precursor powder with respect to the minimal porosity of the prepared PLD target. [•] Layers prepared by PLD from our targets were compared with layers prepared from commercial monocrystal target. [ABSTRACT FROM AUTHOR]

Published
2013
Full Text
View/download PDF

50. Preparation of Strontium Vanadate Sr3V2O8 as Additive to Bi-Based Superconductors

Author

Rubešová, K. and Sýkorová, Dagmar

Abstract

The phase evolution and properties of strontium vanadate Sr3V2O8 were investigated using different method of preparation: solid state reaction and two wet-route techniques (colloidal route and sol-gel method - polymerized complex route). DTA/TG study showed decomposition temperatures of starting materials and helped to choose processing temperatures. XRD analysis was used to determine phase evolution. Solid state reaction sample contained a small amount of Sr3V2O8 as soon as after the first calcinations, but 100% of Sr3V2O8 did not appear until whole procedure was finished. Colloidal route turned out as an inconvenient method for preparation of pure phase. The final colloidal route sample contained 80% of Sr3V2O8, residual volume corresponded to Sr10V6O25. The most progressive phase evolution was detected in the sol-gel route. Raman an FTIR spectroscopy detected evolution of the first amount of Sr3V2O8 after gel heating at 250°C for 2 hours. The pure strontium vanadate was prepared after heating at 800°C for 2 hours.

Published
2006
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results