Improved trapped field performance of single grain Y‐Ba‐Cu‐O bulk superconductors containing artificial holes

Abstract: The intrinsic mechanical properties of single‐grain RE‐Ba‐Cu‐O bulk high‐temperature superconductors can be improved by employing a thin‐wall geometry. This is where the samples are melt‐processed with a predefined network of artificial holes to decrease the effective wall thickness. In this study, the tensile strengths of thin‐wall YBCO disks were determined using the Brazilian test at room temperature. Compared with conventional single grain YBCO disks, the thin‐wall YBCO disks displayed an average tensile strength that is 93% higher when the holes were filled with Stycast epoxy resin. This implies a thin‐wall sample should, in theory, be able to sustain a trapped field that is 39% higher without exceeding the mechanical limit of the sample. High‐field magnetization experiments were performed by applying magnetization fields of up to 11.5 T, specifically to break the samples in order to verify the effect of increased mechanical strength (and improved cooling) on the ability of bulk (RE)BCO to trap field successfully. The standard YBCO sample failed when it was magnetized with a field of 10 T at 35 K, suffering permanent damage. As a result, the standard sample could only trap a maximum surface field of 7.6 T without failure. On the other hand, the thin‐wall YBCO sample survived all magnetization cycles, including a maximum magnetization field of 11.5 T at 35 K, demonstrating a greater intrinsic ability to withstand significantly higher electromagnetic stresses. By subsequently field‐cooling the thin‐wall sample with 11 T at 30 K, a surface field of 8.8 T was trapped successfully without requiring any external ring reinforcement

Study of Composites Consisting of High-Tc\text{}_{c} Superconductor and Fine Magnetic Particles

The composite systems as a mixture of fine magnetic particles of Fe$\text{}_{3}$O$\text{}_{4}$ and superconducting powder such as Bi$\text{}_{1.8}$Pb$\text{}_{0.2}$Sr$\text{}_{2}$Ca$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{10+x}$ were prepared. The influence of internal magnetic field (generated by magnetic particles) on the superconducting properties of prepared composites were studied as a function of concentration of magnetic particles and their magnetic state. The observed data both of the shielding and the Meissner effect were compared with corresponding linear combination of pure signals of magnetite and superconductor, respectively. The large differences were observed for demagnetized samples. It means that result must be discussed in the frame of the distribution of internal magnetic field created by the magnetic particles

Dataset for 'Improved trapped field performance of single grain Y-Ba-Cu-O bulk superconductors containing artificial holes'

Dataset accompanying the paper entitled ‘Improved trapped field performance of single grain Y-Ba-Cu-O bulk superconductors containing artificial holes’, which measured the tensile strength of standard and thin-wall (i.e., with artificial holes) YBCO samples then subsequently confirmed the effect of the strength improvement on the trapped field capability of the different sample types. The dataset contains results obtained using the following techniques: (i) the Brazilian test to measure tensile strength of cylindrical samples, (ii) optical microscopy to measure sample porosity and (iii) a 12-tesla high-field magnet to magnetise and break the samples when they were superconducting. Explanations of figures containing experimental results: Fig. 3b shows the ramp rates used to magnetize the samples. The rates were fixed for each field range. Fig. 4 shows the strength of various sample types (i.e. standard, thin-wall) measured using the Brazilian test. Fig. 5a shows the optical images taken at half height across each sample, and Fig. 5b shows the porosity analysis on these images using ImageJ software. Fig. 6a and 6b show the performance of the two sample types, i.e. field trapped by the sample as a function of the applied field, showing where the sample failed. The samples were magnetized using the 12-tesla magnet. Fig. 7b shows the 2D field profile measured on the surface of the thin-wall sample using an array of hall sensors. Fig. 8 shows the field measured along the diameter of the thin-wall sample when magnetised using 11 T at 30 K

Improved trapped field performance of single grain Y-Ba-Cu-O bulk superconductors containing artificial holes

The intrinsic mechanical properties of single-grain RE-Ba-Cu-O bulk high temperature superconductors can be improved by employing a thin-wall geometry. This is where the samples are melt-processed with a pre-defined network of artificial holes to decrease the effective wall thickness. In this study, the tensile strengths of thin-wall YBCO discs were determined using the Brazilian test at room temperature. Compared with conventional single grain YBCO discs, the thin-wall YBCO discs displayed an average tensile strength that is 93 % higher when the holes were filled with Stycast epoxy resin. This implies a thin-wall sample should, in theory, be able to sustain a trapped field that is 39 % higher without exceeding the mechanical limit of the sample. High-field magnetisation experiments were performed by applying magnetisation fields of up to 11.5 T, specifically to break the samples in order to verify the effect of increased mechanical strength (and improved cooling) on the ability of bulk (RE)BCO to trap field successfully. The standard YBCO sample failed when it was magnetised with a field of 10 T at 35 K, suffering permanent damage. As a result, the standard sample could only trap a maximum surface field of 7.6 T without failure. On the other hand, the thin-wall YBCO sample survived all magnetisation cycles, including a maximum magnetisation field of 11.5 T at 35 K, demonstrating a greater intrinsic ability to withstand significantly higher electromagnetic stresses. By subsequently field-cooling the thin-wall sample with 11 T at 30 K, a surface field of 8.8 T was trapped successfully without requiring any external ring reinforcement

Cost-effective isothermal top-seeded melt-growth of single-domain YBCO superconducting ceramics

Abstract In this work, a series of melt processed YBaCuO (YBCO) single-grains have been fabricated by the top-seeded melt growth (TSMG) technique. The melt processing is accepted widely as an effective way to grow bulk, single grain YBCO superconductors; however, this process is extremely complex and every step can affect the final properties of prepared bulk. Therefore, the impact of precursor powder preparation and growth conditions was studied for the first time. Cost-effective in-house made powder and commercially available precursor powders were employed and samples were grown employing top seeded melt growth, following the isothermal and the under-cooling growth techniques. The bulk microstructure including Y2BaCuO5 (Y-211) particle size and distribution, superconducting properties (Tc, Jc) and field trapping potential were investigated. The cost-effective high performance batch processing methodology was optimized. The fabricated YBCO bulks (diameter of 28 mm) exhibited average trapped field of 0.85 T at 77 K. Furthermore, other possibilities to achieve advancement in processing (RE)BCO bulks, are proposed.Czech Ministry of Industry and Trade, project TIP (FR-TI4/184)

Cost-effective isothermal top-seeded melt-growth of single-domain YBCO superconducting ceramics

In this work, a series of melt processed Y–Ba–Cu–O (YBCO) single-grains have been fabricated by the top-seeded melt growth (TSMG) technique. The melt processing is accepted widely as an effective way to grow bulk, single grain YBCO superconductors; however, this process is extremely complex and every step can affect the final properties of prepared bulk. Therefore, the impact of precursor powder preparation and growth conditions was studied for the first time. Cost-effective in-house made powder and commercially available precursor powders were employed and samples were grown employing top seeded melt growth, following the isothermal and the under-cooling growth techniques. The bulk microstructure including Y 2 BaCuO 5 (Y-211) particle size and distribution, superconducting properties (T c , J c ) and field trapping potential were investigated. The cost-effective high performance batch processing methodology was optimized. The fabricated YBCO bulks (diameter of 28 mm) exhibited average trapped field of 0.85 T at 77 K. Furthermore, other possibilities to achieve advancement in processing (RE)BCO bulks, are proposed

Monokrystaly SnSe dopované arsenem: Ambivalentní dopování a interakce s intrinsickými defekty

We performed ambivalent doping study on single crystals of two sets, SnSe1-xAsx and Sn1-xAsxSe, with the aim to explore the interaction of doping species with intrinsic defects. We found that As atoms substitute preferentially for Se atoms in both sets forming the extrinsic substitutional point defect As-Se. In the first set, As lowers the concentration of Sn vacancies, V-Sn, by an order of magnitude compared to undoped stoichiometric SnSe crystal. The remaining Sn vacancies are preferentially coordinated with As atoms. Importantly, a very low concentration of As led to healing process of hosting structure in terms of intrinsic point defects and eventual SnSe2 inclusions. This is reflected in an increase of the Hall mobility and drop of the Hall concentration. In the second set, the concentration of Sn vacancies markedly increases upon doping in contrast to the first set. Additionally, the coordination of Sn vacancies by As atoms is less evident due to the high concentration of vacancies. The substitutional defect As-Se is a deep-level defect that produces no free carriers at room temperature. Moreover, the coupling of V-Sn to As-Se defects increases their activation energy. This results in an unprecedentedly low Hall concentration in SnSe which stays below 10(16) cm(-3) for x = 0.0075. The present study indicates that doping of SnSe is a rather complex process that generally includes a strong interaction of doping atoms with the hosting structure. On the other hand, such doping allows adjustment of the type and concentration of defects. The present study reveals a general tendency of point defects to clustering, which modifies the properties of point defects markedly.Byla provedena studie ambivalentního dopování na dvou sériích monokrystalů SnSe: SnSe1-xAsx a Sn1-xAsxSe, jejímž cílem bylo zkoumání interakce dopantu s intrinsickými defekty. Bylo zjištěno, že atomy As v obou sériích přednostně substituují atomy Se za vzniku extrinsických substitučních bodových defektů AsSe. V první sérii As řádově snižuje koncentraci cínových vakancí VSn v porovnání s nedopovaným stechiometrickým krystalem SnSe. Zbylé Sn vakance se přednostně obklopují atomy As. Důležitým poznatkem je, že velmi nízká koncentrace As vede k uzdravování struktury SnSe ve smyslu intrinsických bodových defektů a případných inkluzí SnSe2. To se odráží v nárůstu Hallovy pohyblivosti a poklesu Hallovy koncentrace. Na rozdíl od první série ve druhé sérii koncentrace Sn vakancí spolu se vzrůstajícím obsahem As znatelně narůstá. Navíc obklopení Sn vakancí As atomy je méně zřetelné díky vysoké koncentraci vakancí. Substituční defekt AsSe je hlubokým defektem, který za teploty místnosti neprodukuje volné nositele náboje. Navíc párování VSn s defekty AsSe zvyšuje aktivační energii vakancí. To má za následek bezprecedentně nízké hodnoty Hallovy koncentrace v SnSe, které se pohybují pod 1016 cm-3 pro x = 0,0075. Předkládaná studie ukazuje, že dopování SnSe je velmi komplexní proces, který obecně zahrnuje silnou interakci dopujících atomů s hostitelskou strukturou. Na druhou stranu takovýto doping dovoluje upravení typu a koncentrace defektů. Předkládaná studie odhaluje obecnou tendenci bodových defektů vytvářet klastry, které významně upravují vlastnosti bodových defekt

Termoelektrické vlastnosti a stabilita Tl-dopovaného SnS

Tin sulfide (SnS) is an analog of tin selenide (SnSe) and is a promising thermoelectric material. However, a stable and effective doping of this compound has still not been achieved. According to our observations, this is mainly due to the very low equilibrium solubility of dopants and formation of extraneous phases, which is also an important issue for photovoltaic (PV) applications. Achieving a reasonable (60%) doping efficiency of thallium (Tl) in a cation sublattice of SnSe, we explored the same doping for SnS. Hot-pressed polycrystalline (PC) samples were prepared along with their single-crystalline (SC) counterparts. Samples were examined for extraneous phases by X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). Thermal stability was determined by thermogravimetric analysis (TGA). Measurements of the Seebeck and Hall coefficient, and electrical and thermal conductivity were conducted over a temperature range of 80-775 K. The experiments suggested a very low solubility of Tl ( approximate to 0.1%). Slight Tl doping resulted in a substantial improvement of the thermoelectric efficiency (ZT) of SnS and enhanced crystal quality in terms of carrier mobility. We found, however, that attempts to prepare material with a high concentration of Tl or the examination of samples at temperatures above 600 K led to chemical instability. (C) 2019 Elsevier B.V. All rights reserved.Sulfid cínatý (SnS) je analogem selenidu cínatého (SnSe) a je slibným termoelektrickým materiálem. Stále však nebylo dosaženo stabilního a efektivního dopování této sloučeniny. Podle našich pozorování je tomu tak hlavně kvůli velmi nízké rovnovážné rozpustnosti dopantů a tvorbě cizích fází, což je také důležitý problém pro fotovoltaické (PV) aplikace. Dosažením rozumné (60%) dopovací účinnosti thalia (Tl) v kationtové podmřížce SnSe, zkoumali jsme stejné dopování v případě SnS. Byly připraveny za tepla lisované polykrystalické (PC) vzorky spolu s jejich monokrystalickými (SC) protějšky. Vzorky byly vyšetřeny na přítomnost cizích fází rentgenovou difrakcí (XRD) a energiově-dispersní spektroskopií (EDS). Termická stabilita byla stanovena termogravimetrickou analýzou (TGA). Měření Seebeckova a Hallova koeficientu a elektrické a tepelné vodivost byla provedena v teplotním rozsahu 80-775 K. Experimenty naznačily velmi nízkou rozpustnost Tl (≈0,1%). Mírné dopování Tl vedlo k podstatnému zlepšení termoelektrické účinnosti (ZT) SnS a ke zlepšení kvality krystalů z hlediska pohyblivosti nositelů. Zjistili jsme však, že pokusy připravit materiál a vysokou koncentrací Tl nebo vyšetření vzorků při teplotách nad 600 K vedly k chemické nestabilitě