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1
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Synthesis of Nanocrystalline BaCeO₃ by Oxalate Coprecipitation for YBa₂Cu₃O₇ Bulk Superconductors

100%
Verbová R., Kavečanský V., Diko P., Antal V.
Acta Physica Polonica A
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2018
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vol. 133
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issue 1
82-85
EN
Barium cerate (BaCeO₃) is one of the preferred additions to bulk YBa₂Cu₃O₇ single-grain superconductors to inhibit the growth of Y₂BaCuO₅ particles. The present paper investigates synthesis of very fine barium cerate powder and its use in YBa₂Cu₃O₇ bulk superconductor growth. The crystalline barium cerate was synthesized by oxalate co-precipitation from barium and cerium nitrates. X-ray diffraction in air and vacuum was performed to understand the formation of barium cerate as well as to determinate its crystal structure. Size and shape of BaCeO₃ particles were studied by scanning electron microscopy. The BaCeO₃ was used to grow YBa₂Cu₃O₇ bulk superconductor. Microstructure of prepared YBa₂Cu₃O₇ crystal shows that the barium cerate in the final product is very fine and uniformly distributed throughout the whole YBa₂Cu₃O₇ crystal.
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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Influence of Spark Plasma Sintering on Microstructure and Properties of Bulk LaCaSrMnO Magnetocaloric Materials

88%
Zmorayová K., Antal V., Kováč J., Diko P., Noudem J.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
804-806
EN
Polycrystalline La_{0.67}Ca_{0.33-x}Sr_xMnO₃ (x=0.33, 0.03, 0) (LCSM) perovskite samples treated by spark plasma sintering technique were investigated. This study proved influence of the sintering temperature on microstructure of these perovskite ceramics. The thermogravimetric measurements revealed the possibility of increase of oxygen content in studied LCSM samples by additional annealing under oxygen atmosphere and low temperature. Finally, the effect of this annealing on magnetic properties was demonstrated.
4
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Critical Current Density and Microstructure of NdBa_2Cu_3O_7 Single Crystal

76%
Diko P., Zmorayová K., Šefčiková M., Antal V., Kováč J., Yao X.
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issue 5
1028-1030
EN
The top-seeded solution growth method was used to grow NdBCOss single crystals in air. The microstructure of the samples has shown that the oxygenation crack structure developed in the single crystals. The intrinsic critical current density was estimated to be at least twice higher than the value of volume critical current density determined from the magnetization measurements.
5
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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.
6
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Microstructure and Magnetic Properties of La-Ca-Sr-Mn-O Perovskite Ceramics

76%
Zmorayova K., Antal V., Radusovska M., Piovarci S., Kováč J., Kavecansky V., Diko P.
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vol. 126
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issue 1
168-169
EN
La_{0.67}Ca_{0.33-x}Sr_{x}MnO_{3} (x=0.33; 0.03; 0) (LCSM) perovskite magnetocaloric ceramics were prepared by solid state synthesis in air and sintering at 1520°. The phase composition was checked by x-ray powder diffraction. Microstructure analyses were done by scanning electron microscopy. The influence of high pressure oxygenation on magnetisation behaviour is shown.
7
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Microstructure and Properties of Y-123/Y-211 Bulk Superconductors with BaCeO_{3} and BaO_{2} Addition

76%
Zmorayova K., Antal V., Radusovska M., Piovarci S., Volochova D., Diko P.
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vol. 126
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issue 1
366-367
EN
YBa_{2}Cu_{3}O_{7-δ} (YBCO) bulk single-grain superconductors were prepared by a TSMG process. CeO_{2}, BaCeO_{3} and BaO_{2} powders were added to nominal composition Y_{1.5}Ba_{2}Cu_{3}O_{7} with the aim to refine Y_{2}BaCuO_{5} (Y-211) secondary particles. Added powders were refined by milling in a friction milling and characterized by X-ray powder difractometry. Thermal properties of the systems were characterized by DTA. Microstructure of samples was studied by PLM. Successful refinement of Y-211 particles size was confirmed by IP measurements. Transition temperatures and field dependences of the magnetic moment for further determination of the critical current densities were obtained using a VSM.
8
Content available remote

Time Dependent Changes in Ag Doped YBCO Superconductors

64%
Volochová D., Antal V., Diko P., Šefčiková M., Zmorayová K., Kováč J., Weber H., Chaud X.
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issue 5
1047-1048
EN
Magnetization measurements at 77 K were conducted on the single-crystalline samples of YBCO superconductor doped with Ag prepared by the top-seeded melt-growth process. The single-grain samples had a nominal composition Y_{1.5}Ba_2(Cu,Ag)_3O_{y}. Magnetization measurements on the samples, oxygenated by two different processes: by standard oxygenation and by high pressure oxygenation, repeated after 24 months, revealed time dependent changes in magnetization behaviour and critical transition temperatures, T_{c}, which could be associated with redistribution of oxygen vacancies and their interaction with Ag dopant atoms.
9
Content available remote

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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