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1
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Trapped Field of YBCO Bulk Superconductors Prepared by Infiltration Growth Process

100%
Vojtkova L., Diko P., Piovarči S.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1048-1050
EN
Single grain Y₁Ba₂Cu₃O_{7-x} (YBCO) bulk superconductors were prepared from different starting precursors. In the first case, Y₂Ba₁Cu₁O₅ (Y211) powder as the solid phase and the liquid phase of mixture of YBa₂Cu₃O_{7-x}+BaCuO₂+CuO powders were used. In the second case, the solid phase was prepared from the mixture of Y₂O₃+BaCuO₂ instead of the conventionally used Y211, and as the liquid phase a mixture of Y₂O₃+BaCuO₂+CuO powders was used. The trapped field measurements at 77 K were performed and microstructure of samples was studied by polarized light microscopy. The positive influence of Y₂O₃+BaCuO₂ starting precursor on the oxygenation, Y211 particle refinement and measured trapped field is shown.
2
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Changes in YBCO Single Grain Bulk Superconductor Exposed to Air Moisture

88%
Piovarči S., Antal V., Kaňuchová M., Radušovská M., Diko P.
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vol. 126
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issue 1
364-365
EN
Changes in bulk single grain YBCO superconductor at exposition to air were studied. The increase of the sample weight caused by reaction with air moisture was observed by weighing the samples over two months period. Thermal analyses and mass spectrometry of the exposed samples has shown evolution of water and oxygen during sample heating. Observation with scanning electron microscope confirmed the formation of some nanosize phases at the inner sample surfaces. XPS spectra done on the freshly cleaved and on the air exposed (001) surfaces confirmed changes in Ba and Cu bonds. Observed structural changes did not caused systematic changes in measured trapped field.
3
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The Effect of Sm Addition on the Microstructure and Superconducting Properties of YBCO Bulk Superconductors

76%
Volochová D., Diko P., Piovarči S., Antal V., Kováč J., Jirsa M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1009-1011
EN
The effect of Sm addition on the microstructure and superconducting properties of Y-Ba-Cu-O (YBCO) bulk superconductors has been studied. Nominal composition: 1 mol YBa₂Cu₃O_{7-δ} + 0.25 mol Y₂O₃ + 1 wt% CeO₂ was enriched with different amounts of SmBa₂Cu₃O_y powder with the aim to increase critical current density, J_c, especially in higher magnetic fields by introducing additional pinning centers. Single grain YBCO bulk superconductors with SmBa₂Cu₃O_y (Y123-Sm) addition were prepared by the optimized top seeded melt growth process. Microstructure analysis, performed by polarized light microscope, revealed that SmBa₂Cu₃O_y addition leads to a higher amount of slightly coarser Y₂BaCuO₅ particles, which is related to lower critical current densities (J_c ≈ 6×10⁴ A/cm²) of the YBCO samples with SmBa₂Cu₃O_y addition in low magnetic fields. On the other hand, an enhancement of critical current density, J_c, in higher magnetic fields was observed for Y123-Sm samples. Moreover, a maximum trapped magnetic field, B_{tmax}, of 564 mT at 77 K in Y123-Sm, x=0.0025 sample (Ø 17.2 mm) was 43% higher than that for YBCO sample without any addition.
4
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Structure of Melt-Spun Co₂MnAl Heusler Alloy

76%
Piovarči S., Diko P., Kavečanský V., Ryba T., Vargová Z., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
881-883
EN
The growth-related microstructure and texture of the Co₂MnAl-type Heusler alloy in the form of a melt-spun ribbon was studied by electron microscopy, electron backscattered diffraction and X-ray diffraction. It is shown that melt spinning produces a single-phase disordered Heusler alloy. The fine grain structure at the wheel side of the ribbon exhibits no texture, while dominant columnar grain structure formed on the free surface side exhibits the ⟨111⟩ fibre texture with a declination by about 10 degrees in the spinning direction. The dendritic growth of columnar crystals causes inhomogeneity of the chemical composition on a micrometre scale with a higher Co and Al concentration in the centre of dendritic arms and a higher concentration of Mn at the dendrite arm boundaries.
5
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Growth Rate of YBa_2Cu_3O_7 Bulk Crystals in Y_{1.5}Ba_2Cu_3 System with CeO_2 Addition

76%
Zmorayová K., Šefčiková M., Volochová D., Kalmanová M., Piovarči S., Diko P.
Acta Physica Polonica A
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2012
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vol. 122
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issue 4
725-727
EN
The growth rate of Y_1Ba_2Cu_3O_{x} bulk single grain (in fact single crystal) superconductors in the system with composition Y_{1.5}Ba_2Cu_3O_{x} and CeO_2 addition was studied in the temperature range 991-1001°C. It is shown that the growth rate of bulk crystal is different for a- and c-growth direction. Slower measured growth rate in studied system than in pure Y_1Ba_2Cu_3O_{x} is related to the composition shift to the three-phase field containing CuO.
6
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Influence of Sm and Yb Pollution on Superconducting Properties of YBCO Bulk Superconductors

64%
Volochová D., Jurek K., Radušovská M., Piovarči S., Antal V., Kováč J., Jirsa M., Diko P.
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vol. 126
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issue 1
358-359
EN
YBa_{2}Cu_{3}O_{7-δ } (YBCO, Y-123) bulk superconductors with a nominal composition Y_{1.5}Ba_{2}Cu_{3}O_{x} and 1 wt% CeO_{2} addition were prepared by the Top Seeded Melt Growth (TSMG) process. Small single-crystalline pieces, cut from the SmBa_{2}Cu_{3}O_{y} (Sm-123) bulk, were used for seeding of epitaxial growth. Wavelength-dispersive spectrometry (WDS) confirmed the presence of 0.1 wt% Sm from the seed and 0.25 wt% Yb from the substrate, practically in the whole sample volume. The influence of this Sm and Yb contamination on superconducting properties of grown bulk materials is reported.
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