The influence of post-growth thermal treatments on the critical current density of TSMG YBCO bulk superconductors

Diko, P.; Antal, V.; Zmorayová, K.; Šefčiková, M.; Chaud, X.; Kováč, J.; Yao, Xin; Chen, I; Eisterer, M.; Weber, H.W.

doi:10.1088/0953-2048/23/12/124002

Cited by 18 publications

(4 citation statements)

References 22 publications

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“…The observed macroscopic cracks are then simply the largest members of these fissure families, as shown in the figure where the two micro-fissure families appear close to a crack: it is easy to verify that all fissures are only directed either parallel or perpendicular to the crack. This well-defined pattern shown by the a-b plane cracks observed in the bulk of oxygenated orthorhombic TSG Nd123 samples, is completely different from the irregular structure characterizing the similarly oriented cracks reported in analogous Y123 samples [16,17,27]. These are apparently due to a high precipitate density, but the only analogous structures found in Nd123 samples are the irregular cracks that can be observed in the peripheral growth bands of samples obtained by high initial Nd210 content precursor powders [25], which are clearly due to a very high local density of 422 particles (figure 2(a)) as well.…”

Section: D1 Pellet Characterizationcontrasting

confidence: 64%

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa₂Cu₃O_7−δbulk samples fragmentation process

Gombos

Gomis

Ciancio

et al. 2012

Supercond. Sci. Technol.

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Here we report on a detailed investigation on NdBa 2 Cu 3 O 7−δ (Nd123) crack generation achieved by an extensive morphological and structural study on 1 cm diameter top-seeded melt-textured grown pellets, where crack development stops at an earlier stage, and on the parallelepiped fragments resulting from the spontaneous breaking of larger (3 and 5 cm diameter) pellets. In this way complementary information on the process is obtained.Sample morphology was investigated by polarized light optical microscopy, scanning electron microscopy, and atomic force microscopy, confirming that microscopic fissures and macroscopic cracks act as preferential oxygenating channels. This fact suggests that mechanical stress, generated locally by an oxygenation induced tetragonal-orthorhombic transition, is the driving mechanism for fissure evolution into cracks and their further growth. Our observations reveal that Nd123 fissure bundles have a tri-dimensional character, lying not only along the a-b plane, but also along two a-b out-of-plane perpendicular directions. Twin and fissure bundle orientations appear to differ by 45 • , thus suggesting that fissures lie along a-c and/or b-c crystallographic planes.This observation was confirmed by θ -2θ x-ray diffraction and x-ray pole figure analysis (XPFA) performed on the parallelepiped fragments, which revealed that samples are single domain, with edges oriented along the principal crystallographic planes. XPFA detected a-b axes twinning in the domain on the global scale.A remarkable result achieved by electron backscattered diffraction (EBSD) is the evidence that cracking along b-c plane is preferred with respect to a-c, acting in this way as a second preferential cleavage direction. Indeed EBSD measurements show long-range ordering of a and b axes, suggesting that twinning is less effective in releasing in-plane mechanical stress in Nd123 than in parent compounds. Results are discussed on the basis of the identification of Nd-Ba cationic substitutions as the main competing relaxation mechanism.The superconducting properties of the analysed samples were studied by measuring the fragments superconducting parameters by vibrating sample magnetometry.

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Section: D1 Pellet Characterizationcontrasting

confidence: 64%

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa₂Cu₃O_7−δbulk samples fragmentation process

Gombos

Gomis

Ciancio

et al. 2012

Supercond. Sci. Technol.

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“…The formation of micro-and macro-cracks, mainly during oxygenation process, can significantly reduce the effective cross section of the bulks. The cracks can be partially eliminated by post-growth heat treatments [15][16][17], and the mechanical properties of the bulks can be improved by the addition of silver [18]. Subgrain boundaries are weak links in the bulks that reduce the current flow within the bulk.…”

Section: Introductionmentioning

confidence: 99%

Relationship between local microstructure and superconducting properties of commercial YBa₂Cu₃O_7−δ bulk

Antal

Zmorayová

Rajňák

et al. 2020

Supercond. Sci. Technol.

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The relationship between local microstructure and superconducting properties of commercially prepared YBa 2 Cu 3 O 7−δ single-grain bulk superconductor was investigated. The small samples for magnetization measurements were taken from the beginning and end of the a-growth sector and the c-growth sector as well as from the beginning and end of a/a-growth sector boundary. The field dependence of the magnetic moment was measured at temperatures starting from liquid helium (4.2 K) to liquid nitrogen (77 K) using the commercial Magnetic Property Measurement System with a magnetic field of up to 7 and 18 T. The microstructure was analysed using polarised light optical microscopy and scanning electron microscopy. The quantitative microstructural data were determined using an image processing software package. Microstructure analysis was focused on the size and volume fraction of Y 2 BaCuO 5 particles as well as on the characterisation of subgrain structure. These measurements showed that not only inhomogeneous distribution of Y 2 BaCuO 5 particles had influence on the critical current density but it can also be significantly affected by the subgrain structure within the bulk or by local contamination of YBa 2 Cu 3 O 7−δ from the seed during fabrication process. It was observed that the critical current density along the a/a-growth sector boundary could be substantially higher in comparison to the other parts of the bulk and this behaviour can be related to the subgrain structure in the sample.

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“…This gives a J c (0.36 T) of 6.13 × 10 7 A/m 2 which is in close agreement with the inferred J c of 6.46 × 10 7 A/m 2 . A similar J c (B) behaviour has also been reported for GdBCO [150,151] and YBCO [152,153] bulks. Some discrepancies might be due to differences in the J c (B) behaviour between bulks and wires, the impact of surface degradation of the bulk on the trapped field characteristics, and the angle of the applied magnetic field with respect to the surface of the superconductor.…”

Section: A Non-destructive Methods For Estimating E-j Power Law Param...supporting

confidence: 83%

AC Losses in Superconducting Magnetic Bearings

Siamaki¹

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Since the discovery of high-temperature superconductors, superconducting magnetic bearings have become an icon of applied superconductivity. Their ability to provide passive stable levitation/suspension has attracted much attention for industrial applications such as maglev trains, flywheel energy storage systems, and high speed electrical machines. Paihau-Robinson Research Institute has been working on the design and construction of a 22 kW, 30000 rpm homopolar superconducting motor for a hybrid aircraft propulsion system. Superconducting magnetic bearings seem to be a potential solution to overcome the speed limits imposed by friction and heat in mechanical bearings. Considering the lack of commercial availability of superconducting bearings, the Institute has decided to investigate the challenges involved in developing suitable bearings for ongoing and future projects. The focus of this thesis is to explore the development of suitable low-loss bearings from bulk high-temperature superconductors, and to develop suitable test methodologies that allow the properties and behaviour of high-temperature superconducting bearings to be explored. In order to accurately predict the behaviour of superconducting magnetic bearings, a precise knowledge about the non-linear voltage-current (E-J) relationshipis required for input to simulations. Unlike coated conductors, this cannot be achieved by transport measurements in superconducting bulks. In this thesis, a convenient non-destructive method based on levitation force decay in superconducting bearings is introduced and evaluated to map the non-linear electrical properties in superconducting bulks. Furthermore, fibre Bragg grating sensors are employed in an actual superconducting bearing environment to monitor temperature at the bearing surface. Accurate cryogenic temperature monitoring with large electromagnetic fields present is of great importance in practical applications, and is problematic with conventional electronic sensors. A barrier to commercial application is suspected to be the effects of inhomogeneous magnet, or superconducting, properties on the efficiency of bearings. The key drivers of this, AC loss mechanisms in superconducting bearings are investigated and a new analytical expression is proposed for hysteresis loss in superconducting bearings which takes magnetic field inhomogeneity, magnetic field periodicity, and loss surface distribution into account. This new expression is tested by performing spin-down experiments, and the results are found to be in good agreement. Lastly, a high-speed superconducting motor/generator demonstration is built, which sets a record for the fastest superconducting bearing made in New Zealand. This will enable applications such as flywheel energy storage systems, direct-drive generators and high speed microfans to be explored whilst also providing the opportunity to demonstrate key technology elements such as flux-pumped hightemperature superconducting field windings and low-loss high-speed bearings. AC loss mechanisms at kHz-rated rotational frequencies are also studied with this prototype. The results show that at high rotational frequencies the superconducting bulks are pushed into a resistive flux-flow regime, where AC losses are createdby an eddy-current-like mechanism. This thesis explores two phenomena of practical importance in superconducting bearings, and proves the principle of the application of superconducting bearings for ongoing and future projects in New Zealand.

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The influence of post-growth thermal treatments on the critical current density of TSMG YBCO bulk superconductors

Cited by 18 publications

References 22 publications

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa₂Cu₃O_7−δbulk samples fragmentation process

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa₂Cu₃O_7−δbulk samples fragmentation process

Relationship between local microstructure and superconducting properties of commercial YBa₂Cu₃O_7−δ bulk

AC Losses in Superconducting Magnetic Bearings

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The influence of post-growth thermal treatments on the critical current density of TSMG YBCO bulk superconductors

Cited by 18 publications

References 22 publications

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa2Cu3O7−δbulk samples fragmentation process

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa2Cu3O7−δbulk samples fragmentation process

Relationship between local microstructure and superconducting properties of commercial YBa2Cu3O7−δ bulk

AC Losses in Superconducting Magnetic Bearings

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Product

Resources

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Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa₂Cu₃O_7−δbulk samples fragmentation process

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa₂Cu₃O_7−δbulk samples fragmentation process

Relationship between local microstructure and superconducting properties of commercial YBa₂Cu₃O_7−δ bulk