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1
Content available remote

The Doped YBCO Superconductor Crystal Structure Simulation

100%
Kavečanský V., Diko P.
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issue 5
1034-1035
EN
Pinning process plays an important role in improving utility properties of YBa_2Cu_3O_{7-δ} (YBCO) superconductors. As a consequence of the low coherent length, the most effective pinning centers in such type of materials should have nanometer size dimensions. An efficient way of introducing such centers can be a chemical substitution in the YBCO lattice. Computer simulation of locally distorted YBCO crystal structure due to the substitutions has been performed.
2
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Clean Bulk YBaCuO Superconductors Doped by Paramagnetic Ions of Sm and Yb

81%
Jirsa M., Volochová D., Kováč J., Diko P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1027-1029
EN
The recently developed clean cuprate technology was employed to study the effect of tiny amounts of paramagnetic Yb and Sm ions on electromagnetic properties of bulk YBaCuO. Small samples of about 1.5×1.5×0.5 mm³ were measured by vibrating sample magnetometer in the field range ±9 T and temperatures 30 K to 10 K in the non-superconducting tetragonal state and 300 K to 70 K in the orthorhombic, superconducting state. In the latter case, we observed the reversible paramagnetic moment above T_{C}, similar as in the tetragonal state. Below T_{C} an irreversible magnetic moment was observed from which critical current density, J_c, was evaluated using the extended Bean model. The effect of doping by Yb and Sm ions on J_c was studied and a correlation between J_c and the total paramagnetic moment was found. Both J_c(B) and the normalized pinning force density as a function of the reduced magnetic field were analyzed in terms of the classical model and discussed with respect to the material anisotropy, giving us at least a rough idea on the type of the effective pinning type and mechanism.
3
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Synthesis of Nanocrystalline BaCeO₃ by Oxalate Coprecipitation for YBa₂Cu₃O₇ Bulk Superconductors

81%
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.
4
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Trapped Field of YBCO Bulk Superconductors Prepared by Infiltration Growth Process

81%
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.
5
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Electromagnetic Properties of Melt-Grown YBaCuO Superconductors Doped by Gd and Sm

71%
Jirsa M., Rameš M., Volochová D., Radušovská M., Diko P.
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vol. 126
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issue 1
326-327
EN
Electromagnetic properties of YBa_{2}Cu_{3}O_{y} samples melt-grown in air and doped with small amounts of light rare earth (LRE) ions Gd and Sm were studied. The LRE doping creates a point-like disorder contributing to the second peak on the magnetization curve. In the field range of the second peak the average magnetic moment, M_{av}, deduced from the magnetization curves exhibited strong fluctuations. M_{av} is commonly regarded as an equilibrium moment close to the thermodynamic reversible one, obeying in intermediate fields a logarithmic field dependence. However, in our experiments M_{av}(B) curves failed to follow such a dependence below irreversibility line. M_{av}(B) curves deduced from rather static measurements, done by SQUID magnetometer still showed the disturbance but significantly weaker. It indicates that this feature reflects the vortex dynamics in the second peak region. Its scaling with temperature was found to coincide with that of the pinning force.
6
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Crystalline Structure, Stoichiometry and Magnetic Properties of the Morasko Meteorite

71%
Idzikowski B., Kováč J., Diko P., Stankowski W., Muszyński A.
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issue 5
1071-1073
EN
The composition and structure of iron-nickel alloys smithereens extracted from the Morasko (Poland) Meteorite (fell ∿ 5 ka BP) were investigated by optical metallographic techniques, scanning electron microscopy and electron microprobe analysis, thermal analyses, magnetic measurements and X-ray diffraction. Microstructural analysis by scanning electron microscopy and optical microscopy has shown that the sample is composed from large grains of Fe-Ni alloy in which secondary phase crystals with well developed crystal habits and the size about 10 micrometers are distributed. Thermal analyses confirmed that the transformation from alpha to gamma Fe-Ni solid solution appearing as a function of temperature corresponds to about 5 wt% Ni in the Fe-Ni alloy. Possible scenario of the extraterrestrial sample solidification is related to the microstructural and magnetic behavior.
7
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Changes in YBCO Single Grain Bulk Superconductor Exposed to Air Moisture

71%
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.
8
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Influence of Spark Plasma Sintering on Microstructure and Properties of Bulk LaCaSrMnO Magnetocaloric Materials

71%
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.
9
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Critical Current Density and Microstructure of NdBa_2Cu_3O_7 Single Crystal

62%
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.
10
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The Effect of Sm Addition on the Microstructure and Superconducting Properties of YBCO Bulk Superconductors

62%
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.
11
Content available remote

Structure of Melt-Spun Co₂MnAl Heusler Alloy

62%
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.
12
Content available remote

Microstructure and Magnetic Properties of La-Ca-Sr-Mn-O Perovskite Ceramics

62%
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.
13
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Microstructure and Properties of Y-123/Y-211 Bulk Superconductors with BaCeO_{3} and BaO_{2} Addition

62%
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.
14
Content available remote

Growth Rate of YBa_2Cu_3O_7 Bulk Crystals in Y_{1.5}Ba_2Cu_3 System with CeO_2 Addition

62%
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.
15
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Influence of Pressure on the Electrical Transport Properties of Carbon-Doped EuB₆

52%
Pristáš G., Gabáni S., Baťko I., Baťková M., Orendáč M., Gažo E., Filipov V., Konovalova E., Diko P., Flachbart K.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
982-984
EN
We have studied the influence of hydrostatic pressure on the electrical resistivity of carbon-doped semimetal EuB₆ which orders ferromagnetically at T_{C}=3.9 K and is intrinsically inhomogeneous due to fluctuations of carbon content. We observed a shift of the low-temperature resistivity maximum from 4.6 K (at 1 bar) to 5.2 K (at 30.3 kbar) with increasing pressure. However, the maximum of the derivative dρ/dT(T), which reveals the temperature of ferromagnetic ordering, does not change its position with increasing pressure. This behaviour is different from stoichiometric EuB₆, where pressure increases the ferromagnetic ordering temperature. The origin of this discrepancy may lie in the increase of volume fraction of the non-ferromagnetic phase with increase of pressure. Additional magnetoresistance measurements at various pressures between 1.5 K and 30 K have shown that with increase of magnetic field the resistivity is monotonically decreasing, and above 1 T a transition to a monotonic resistivity behaviour (dρ/dT(T)>0) is observed. Our results support the picture that carbon-rich regions play a role of "spacers", which prevent the percolation of the ferromagnetic phase.
16
Content available remote

Time Dependent Changes in Ag Doped YBCO Superconductors

52%
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.
17
Content available remote

Influence of Sm and Yb Pollution on Superconducting Properties of YBCO Bulk Superconductors

52%
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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