Showing papers by "Masato Murakami published in 2006"

Effect of RE2BaCuO5 refinement on the critical current density and trapped field of melt-textured (Gd, Y)–Ba–Cu–O bulk superconductors

Abstract: We have investigated the superconducting properties of (Gd, Y)–Ba–Cu–O bulk superconductors fabricated from precursors of the Gd123–Y211 with small additions of Pt and CeO 2 in a reduced oxygen atmosphere. The employment of ball-milled ultra-fine Y211 powder as a precursor material was very effective in enhancing critical current density ( J c ), since RE211 inclusions in the melt-textured samples could be drastically refined with decreasing the particle size of Y211 starting powder. The maximum J c value reached an extremely high value of 380 kA/cm 2 at 77 K in self-field. However, size reduction of RE211 led to inhomogeneous distribution of RE211 inclusions. The amount of RE211 was extremely small in the vicinity of a seed crystal, when the ultra-fine Y211 powder was employed. The trapped magnetic fields of Ag-added single-grain samples 25 and 33 mm in diameters were 1.5 and 2.0 T at 77 K, respectively.

Field trapping property of Gd–Ba–Cu–O bulk superconductor 140 mm in diameter

Abstract: We have studied field trapping ability of single grain Gd–Ba–Cu–O bulk superconductor 140 mm in diameter, which was fabricated by using Gd2BaO4 and Ba–Cu–O phase as raw materials. The distribution of the trapped magnetic field showed single domain without serious weak links, when the bulk was field-cooled in 1 T at liquid nitrogen temperature. The maximum trapped magnetic field at 77 K and 65 K were 2.30 T and 3.66 T respectively, when a field of 4 T was applied. From the distribution measurements of magnetic field, it was confirmed that a large amount of flux can be trapped in this large bulk. It was also confirmed that magnetic field can reach a longer distance in a larger bulk than smaller diameter samples.

Developments of superconducting mixers for medical applications

Abstract: We have designed non-contact mixers for mixing various solutions for medical and biotechnological applications. A new type of superconducting mixer is composed of three parts: top permanent magnet, bulk superconductor, and bottom permanent magnet. Here the bulk superconductor is inserted into a liquid nitrogen bath and is free to rotate. The top magnet component is immersed in a solution with the rotating wing on top. The component has a multi-pole configuration and is coupled with the bulk superconductor by flux pinning. The bottom magnet component is laid outside the system, and also has a multi-pole configuration and is coupled with the bulk superconductor by flux pinning. When the bottom component was rotated with the outer rotation device, the top magnet component rotated without contact by virtue of flux pinning, which shows that one can make non-contact mixers.

Advances in enlargement of melt-textured Gd-Ba-Cu-O superconductors

Abstract: We investigated the fabrication of melt-textured Gd–Ba–Cu–O bulk superconductors with the employment of a Gd2BaO4 (Gd210)–BaCuO2–CuO precursor. This enabled us to synthesize a very large Gd–Ba–Cu–O bulk superconductor, 140 mm in diameter. The trapped field distribution measured at 77 K revealed that the sample had no serious cracks, and the maximum field was 2.3 T. The formation behaviour and depressing mechanism of cracking were studied using sintered Gd210-containing precursors. The Ba–Cu–O component in the precursor melted at around 900 °C. The formation of such a liquid phase enhanced the densification of the precursor by liquid phase sintering. The mechanical strength of the sintered precursor was increased compared to the conventional Gd123–Gd211 precursor. This will be effective in preventing crack formation in the texturing process of large single-grain samples. The superconducting properties of the bulk sample fabricated from Gd210-containing precursor have been discussed.

Gd Ba Cu O bulk superconductors fabricated by a seeded infiltration growth technique under reduced oxygen partial pressure

Abstract: Single-grain Gd–Ba–Cu–O (GdBCO) bulk superconductors have been grown by a seeded infiltration and growth (SIG) technique under a 1% O2+N2 atmosphere using a generic MgO-doped Nd–Ba–Cu–O (MgO–NdBCO) seed placed on the sample surface at room temperature (the so-called the cold-seeding method). Partial melting of the MgO–NdBCO seeds fabricated in air under notionally identical thermal processing conditions, however, limited the reliability of this bulk GdBCO single-grain process. The observed seed decomposition is attributed to the dependence of the peritectic temperature Tp of MgO-doped Nd1+xBa2−xCu3Oy solid solution (MgO-doped Nd-123ss, where ss indicates solid solution) compounds on both oxygen partial pressure during the melt process and the level of solid solution (x). The peritectic decomposition temperature of MgO-doped Nd-123ss, with x ranging from 0 to 0.5 under p(O2) = 1.00 atm, was observed to remain constant at 1120 °C. Tp was observed to decrease linearly as a function of solid solution level, on the other hand, under oxygen partial pressures of both p(O2) = 0.21 and 0.01 atm. Based on these results, MgO-doped NdBCO seed crystals should be grown under reduced oxygen partial pressure in order to obtain a stable MgO-doped NdBCO seed crystal suitable for cold-seeding processes of large-grain (RE)BCO bulk superconductors (where RE is a rare earth element).

Study of a new split-type magnetizing coil and pulsed field magnetization of Gd-Ba-Cu-O high-temperature superconducting bulk for rotating machinery application

Abstract: A new type of magnetization coil was designed to increase the maximum trapped magnetic flux density and the total flux associated with an appropriate trapped magnetic flux density distribution in a high-temperature superconducting bulk magnet. The coil is composed of an inner vortex-type coil wound with an outer solenoid coil. A pulsed current is applied to the inner or the outer coils. Successive applications of pulsed current from both the inner and the outer coils to only the inner coil provide a distribution of trapped magnetic flux density closer to being conical in addition to an increase of the maximum flux density and total integrated flux. The present magnetization technique, the controlled magnetic flux density distribution coil method, is useful for magnetized high-temperature superconducting bulk applications such as in rotating machines, generators and magnetic separation.

Levitation forces of bulk RE–Ba–Cu–O in high magnetic fields

Abstract: The levitation force of bulk RE–Ba–Cu–O (RE: rare earth elements) superconductors can be drastically increased by increasing the strength of the external field. We have studied the effects of the temperature and magnetic field on the levitation force and its time relaxation in the field range of 0–2 T by using a superconducting magnet as a magnetic field source. The samples we used were bulk Y–Ba–Cu–O and Sm–Ba–Cu–O superconductors 46 mm in diameter and 15 mm in thickness, which were fabricated with a top-seeded melt-growth process. The levitation forces were measured by applying the magnetic fields of 0–2 T at 10–80 K. It was found that the levitation force increased with decreasing temperature in both Y–Ba–Cu–O and Sm–Ba–Cu–O. The time relaxation of the levitation force was also reduced with lowering temperature. Sm–Ba–Cu–O exhibited better performance in the levitation force and its time relaxation only in a high temperature and high field region.

Thermal conductivity and thermoelectric power of DyBaCuO bulk superconductors

Abstract: The ab-plane thermal conductivity κ(T) and thermoelectric power S(T) have been investigated for DyBaCuO bulk superconductors for various contents of the Dy2BaCuO5 (Dy211) phase X. The absolute κ(T) value is pretty small compared with that of other REBaCuO bulks (RE = Y and rare earth elements). The S(T) value above the superconducting transition temperature Tc changes from negative to positive and κ(T) slightly decreases with increasing oxygen deficiency in the DyBa2Cu3O7−δ (Dy123) superconducting phase. The point-defect-type phonon scattering due to oxygen deficiency affects the κ(T) value, but is not a main origin for the low κ(T) even for the fully oxidized DyBaCuO bulk. Another type of powerful phonon scattering centre governs the thermal transport properties in the DyBaCuO bulk.

Stripe and criss-cross patterns in high-Tc superconductors revealed by atomic force microscopy and scanning tunnelling microscopy

Abstract: By using atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) at ambient conditions, we have investigated the topographies of various surfaces of bulk samples of YBa2Cu3Ox (YBCO), SmBa2Cu3Ox (SmBCO), and (Sm,Eu,Gd)Ba2Cu3Ox (SEG) oxidic high-Tc superconductors. We find that the last two systems exhibit microstructures on the nanometer scale which are remarkably different from those obtained in the YBCO system. The stripe-like growth structures observed in our topography measurements may be the key for the considerable improvements concerning the critical current densities especially at high magnetic fields and elevated operating temperature (77 K). The properties of the microstructures are discussed in detail.

Pulsed field magnetization properties for Gd–Ba–Cu–O superconductors impregnated with Bi–Sn–Cd alloy

Abstract: We present a post-fabrication treatment that improves thermal conductivity of bulk Gd–Ba–Cu–O magnets for pulsed field magnetization (PFM). A small hole about 1 mm in diameter was artificially drilled into the center of bulk Gd–Ba–Cu–O 25 mm in diameter and 18 mm in thickness. An aluminum wire was inserted into the hole, and then the sample was subjected to the impregnation by using Bi–Sn–Cd alloy. We employed PFM to magnetize Gd–Ba–Cu–O bulk superconductors with and without the alloy impregnation treatment. The temperatures of the samples were monitored with thermocouples, and local magnetic field density was measured with a Hall sensor. It was found that the alloy impregnation was effective in suppressing the temperature rise by 4 K and in increasing the trapped field by 25% at 44 K. The present results show that the alloy impregnation treatment enhanced the thermal conductivity of bulk Gd–Ba–Cu–O, and thereby improved the field trapping ability.

Recent progress on compositional nanostripes of REBa2Cu3O7-δ (RE = Sm, Eu, Gd) superconductors

Abstract: We characterized ordered compositional fluctuation in high-quality SmBa2Cu3O7−δ, (Sm0.5Eu0.5)Ba2Cu3O7−δ, and (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ superconductors by atomic force microscopy, scanning tunnelling microscopy, and transmission electron microscopy. The presence of nanostripes along the crystalline c direction was confirmed in SmBa2Cu3O7−δ single crystals and in melt-processed (Sm0.5Eu0.5)Ba2Cu3O7−δ, (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ materials. Meanwhile, thickness fringes originating from the twin boundaries were also identified in some samples; these could be clearly separated from real nanostripes with sample tilting. Compositional nanostripes displayed spatial variation in both shape and wavelength over a large area of RE–Ba–Cu–O single domains. The origin of the nanostripe is discussed in the context of the competitive growth mechanism of RE1+xBa2−xCu3O7−δ solid solution.

Superconductive non-contact rotary device

Abstract: A superconductive non-contact rotary device comprising; a bulk superconductor having a pinning effect arranged in a heat insulating cryogenic vessel, a permanent magnet arranged at one side of the vessel so as to face one surface of the bulk superconductor across a wall, and a permanent magnet arranged at the other side of the vessel facing the other surface of the bulk superconductor across a wall, one permanent magnet being rotated to make the other permanent magnet rotate in a non-contact state.

ZnO doping effects in melt-textured (Nd0.33Eu0.39Gd0.27)Ba2Cu3Oy grown from MgO seed

Abstract: We successfully grew high-quality single-grain (Nd0.33Eu0.39Gd0.27)Ba2Cu3Oy pellets using MgO seed crystals, provided a small quantity of ZnO was added. Tc (onset) continuously decreased with growing Zn content. An optimum for ZnO, compromising good superconducting and electromagnetic properties, was 0.035 mol%. With this ZnO content, Tc>92 K, a critical current density of 100 kA cm−2 was achieved at 77 K and 3 T, and the irreversibility field was >7 T. Perfect facet lines up to the bottom of the sample with the c-axis reflection plane appeared after the melt growth, implying a high density of the material and practically no liquid loss. Very small difference in the trapped field distribution on the top and bottom surfaces confirmed a uniform crystallographic structure and the electromagnetic properties of the pellet.

RE-Ba2Cu3Oy formation mechanism via (RE)2BaO4

Abstract: We studied the mechanism of (RE)Ba 2 Cu 3 O y phase formation via (RE) 2 BaO 4 in the case of GdBa 2 Cu 3 O y + 40 mol% Gd-211 combination, using mixture of Gd 2 BaO 4 , BaCuO 2 and CuO. Pellets of this composite were sintered at various temperatures between 700 °C and 1100 °C and held for 1 h in Ar (100%), Ar–1% O 2 , Ar–0.1% O 2 atmospheres, then rapidly quenched in oil. The samples were characterized by XRD, SEM, and EPMA analyses. XRD and EPMA analyses indicated that Gd-123 phase forms at around 900 °C but the temperature depends on the chosen atmosphere. The samples quenched from high temperatures (>1000 °C) showed that final formation of a secondary phase depends on the temperature held before the quench.

Fabrication and superconducting properties of Gd–Ba–Cu–O single-grain bulk with barium cerate addition

Abstract: We investigated processing, microstructure and superconducting properties of Gd123 single grain bulk superconductors with a large amount of BaCeO 3 . The melt-textured bulk samples with compositions of Gd123 : BaCeO 3 : Gd211 = 100 : 40− x : x ( x = 0–40) plus 20 wt.% of Ag 2 O and 0.5 wt.% of Pt were fabricated in Ar–1%O 2 gas. The single grain bulk samples 25 and 33 mm in diameters were obtained with the composition of x = 5–40. It was observed that BaCeO 3 particles of 1–2 μm in diameters and Gd211 particles of 0.5–1 μm in diameters were dispersed in the melt-textured samples. Magnetic trapped fields of the 25 mm-sized samples with x = 10–40 were around 1 T at 77 K and the 33 mm-sized sample with x = 20 was 1.4 T at 77 K.

Contact characteristics of mechanically mated Y–Ba–Cu–O bulks with a deposited metal layer

Abstract: We measured the contact resistance of a silver block with convex curvature and silver, a melt-textured Y–Ba–Cu–O sample (YBCO), and a silver-deposited YBCO sample (dAg/YBCO) to clarify the main source of the resistance. The study was performed with the development of a persistent current switch in mind. The contact resistance was largest in the Ag/YBCO contact. It decreased by increasing the thickness of the deposited-Ag layer for the Ag/dAg/YBCO contact. However, the smallest resistance of the Ag/dAg/YBCO contact was even larger than that of the Ag/Ag contact. This is probably due to the fact that the Ag/dAg/YBCO contact has two interfaces. The present result suggests that the contact area is dominant in controlling the contact resistance. A simulation study of the contact area with a finite element method (FEM) also supported this idea.

Grain orientations and distribution of Y2Ba4CuUOx phase in melt-textured YBCO with addition of depleted uranium oxide studied by EBSD

Abstract: The local grain orientations and the distribution of Y2Ba4CuUOx (U-2411) phase are measured within melt-textured YBCO samples by means of electron backscatter diffraction (EBSD). In this work, several samples with varying addition (0.1–0.8 wt%) of depleted uranium oxide (DU) were analysed by means of EBSD. The embedded U-2411 particles were found to have sizes around 200 nm, some large particles being present in the samples with a high DU concentration. Combined EBSD and EDX analysis enabled the identification of the Kikuchi patterns of the U-2411 phase, so that a true three-phase EBSD scan (YBCO, Y2BaCuO5 and U-2411) becomes possible.

Superconductive levitated stirrer

Abstract: A superconductive non-contact rotary device comprising; a bulk superconductor having a pinning effect arranged in a heat insulating cryogenic vessel, a permanent magnet arranged at one side of the vessel so as to face one surface of the bulk superconductor across a wall, and a permanent magnet arranged at the other side of the vessel facing the other surface of the bulk superconductor across a wall, one permanent magnet being rotated to make the other permanent magnet rotate in a non-contact state.

High Magnetic Field Transport Properties of NEG123 and Y123 Bulk Materials

Abstract: The bulk material comprised of (Nd, Eu, Gd)Ba2Cu3Ox(NEG123) shows a high irreversibility field over 14 T at 77.3 K. In order to study the origin of the high irreversibility field, transport measurements of NEG123 and Y123 bulk samples were performed as functions of temperature, high magnetic field and field angle, and transport properties were compared with each other. Dip structures for the angular dependence of resistivity are observed around B//c for all samples. These results indicate that c-axis correlated disorder exists. The NEG123 bulk sample with a larger dip shows a higher irreversibility temperature. In addition, we found that the differences of the irreversibility temperature between on and 12° off the dip are scaled universally as a function of the depth of the dip for NEG123 and Y123 bulk samples. It is considered that c-axis correlated disorder is important for high irreversibility fields.

Effect of potassium addition on YBa2Cu3Ox superconductors

Abstract: Long period post-annealing in the oxygen atmosphere is necessary for YBa 2 Cu 3 O x (Y123) bulk superconductors to impart superconductivity. We have investigated whether Y123 shows good superconductivity without oxygen annealing by potassium addition. If K + ion substitutes on Ba 2+ site since the size of K + ion is close to that of Ba 2+ ion, we can expect hole doping effect without additional oxygen annealing. We confirmed that the sample without potassium addition exhibited no superconductivity, while the sample with potassium addition had the onset T c of above 90 K. This implies that the potassium addition certainly promotes the superconductivity of Y123.

Superior growth orientation control via ZnO doping of large-grain LRE-Ba2Cu3Oy compounds grown with MgO seeds

Abstract: MgO seeds proved to be efficient in the growth orientation control of large grain LREBa2Cu3Oy 'LRE-123' pellets when a small quantity of ZnO was added, accompanied by a substantial reduction of liquid phase loss Perfect facet lines grown up to the pellet bottom demonstrated excellent melt growth Field distribution contour maps at the top and bottom surfaces were nearly identical Magnetization measurements indicated that flux pinning performance continuously improved with increasing ZnO content up to 0035 mol%, with critical current density reaching 100 kA cm−2 at 3 T (77 K) Microstructure analysis by scanning tunnelling microscopy and dynamic force microscopy proved the superior microstructure of the material, consistent with the other characteristics

Improvement of the field-trapping capabilities of bulk Nd-Ba-Cu-O superconductors using Ba-Cu-O substrates

Abstract: We used Ba–Cu–O substrates to fabricate bulk Nd–Ba–Cu–O superconductors using a top-seeded melt-growth method. There were several advantages for the use of Ba–Cu–O substrate compared to conventional substrate materials such as MgO, ZrO2, Al2O3, RE123 and RE211 (RE = rare earth). The Ba–Cu–O did not react with the precursor and minimized liquid loss. Accordingly, the introduction of large-sized cracks was suppressed. We also found that Tc values were high at the bottom regions, which was ascribed to the beneficial effect of Ba–Cu–O in suppressing Nd/Ba substitution. As a result, we obtained bulk Nd–Ba–Cu–O superconductors that exhibited fairly good field-trapping capabilities, even at the bottom surfaces.

Nuclear power plant and method of operation control for the same

Abstract: PROBLEM TO BE SOLVED: To provide a nuclear power plant easily adjustable to meet the requirement for maintaining the output of a nuclear reactor constant even if the pressure of steam from a nuclear reactor pressure vessel varies up and down from a rated pressure by reducing an energy loss by utilizing a steam increasing/decreasing valve with less pressure loss and a method of operation control for the nuclear power plant. SOLUTION: In this nuclear power plant, a pressure header 27, a main steam stop valve 29, and the steam increasing/decreasing valve 30 are interposed in a main steam pipe 25 connecting the nuclear reactor pressure vessel 20 to a steam turbine, and the flow of the steam from the nuclear reactor pressure vessel is fed to the steam turbine after being controlled by the steam increasing/decreasing valve. A power is generated in the steam turbine, turbine exhaust gases are condensed in a condenser 24 and returned to the nuclear reactor pressure vessel. Then, the pressure header is connected to the condenser through a turbine bypass pipe 32 for escaping the steam from the nuclear reactor pressure vessel to the condenser. The nuclear power plant also comprises a steam pressure regulating device 34 having an input side connected to the main steam pipe between the downstream side of the pressure header and the upstream side of the steam increasing/decreasing valve and regulating the pressure of the steam from the nuclear reactor pressure vessel. COPYRIGHT: (C)2006,JPO&NCIPI

Elastic behavior of oxygen controlled melt growth processed neg-123 htsc materials

Abstract: A series of superconducting materials having compositional formula, (Nd-Eu-Gd)-Ba-Cu-O (123) + x%(Nd-Eu-Gd)Ba-Cu-O (211) or NEG-123 + NEG-211 (where x ranges from 0–50%) were prepared by the Oxygen Controlled Melt Growth (OCMG) process. After characterizing the materials by studying their microstructure, measuring Jc and Tc values, the ultrasonic longitudinal velocity (Vl) measurements were carried out both as a function of composition (x% of 211 phase) as well as the temperature, over a temperature range 80–300 K. It has been found that the variation of ultrasonic longitudinal velocity is similar to that of Jc with increasing x values (concentration of NEG-211). These results indicate that by dispersing 40% fine NEG-211 particles in the superconducting matrix of NEG-123, both the critical current densities as well as the ultrasonic velocity values are found to exhibit highest values. It is known that the lattice defects of ceramic superconductors are manifested in the form of elastic anomalies, especially in the normal temperature region (100–250 K). In order to understand the complete scenario of elastic anomalies of HTSC materials, a systematic investigation of the ultrasonic velocities of HTSC materials prepared by the OCMG technique has been undertaken and using the results an attempt has been made to generalize the scenario of the elastic anomalies in HTSC materials.

Flux pinning and orientation control of large grain LREBa2Cu3Oy

Abstract: The ternary high-Tc superconductor (Nd0.33, Eu0.39, Gd0.27)Ba2Cu3Oy ''NEG-123'' doped by 5 mol% of the nonsuperconducting secondary phase (Nd0.33, Eu0.33, Gd0.33)2BaCuO5 ''NEG-211'' was prepared by oxygen controlled melt growth (OCMG) process using MgO seeds. Various contents of ZnO up to 0.07 mol% were added. At the ZnO concentration around 0.035 mol%, a substantial reduction of liquid phase loss was observed, accompanied with a perfect facet line up to the bottom of the sample, with c-axis reflection plane. Magnetization measurements showed that at this optimum ZnO addition the superconducting transition temperature was slightly depressed. On the other hand, flux pinning performance around the secondary peak, observed at liquid nitrogen temperature, was continually improved with increasing ZnO content up to 0.035 mol%. It was found that the optimum content of ZnO is crucial for flux pining enhancement and orientation control of MgO seeded melt-textured NEG-123 system.

Improvement of Thermal Stability with Alloy Impregnation in Gd-Ba-Cu-O Superconductors for Pulsed Field Magnetization

Abstract: We present a post-fabrication treatment that improves thermal conductivity of bulk Gd-Ba-Cu-O magnets. A small hole about 1 mm in diameter was artificially drilled into the centre of bulk Gd-Ba-Cu-O 25 mm in diameter and 18 mm in thickness. An aluminium wire was inserted into the hole, and then the sample was subjected to the impregnation by using Bi- Su-Cd alloy. A pulsed-field magnetization was performed for Gd-Ba-Cu-O bulk with and without the alloy impregnation treatment. The temperature of samples was monitored with thermocouples and local magnetic field density was measured with a Hall sensor at several positions. The maximum temperature rise was depressed by 4 K and the trapped field was increased by 25 % at 44 K. The result shows that the alloy impregnation is very effective in enhancing the thermal conductivity and thereby improving the field trapping ability.

Flux pinning and superconducting properties of ZnO added (Nd,Eu,Gd)Ba2Cu3Oy

Abstract: The paper provides an experimental basis for preparing large grain (Nd0.33Eu0.27Gd0.39)Ba2Cu3Oy “NEG-123”. MgO seeds proved to be efficient in controlling growth orientation when a small quantity of ZnO of around 0.035 wt.% was added to the NEG-123 matrix. A substantial reduction of liquid phase loss was observed for a proper ZnO concentration. A perfect facet line up to the bottom of the sample with c-axis reflection plane was observed after the melt-growth implying high density of the material and practically no liquid loss. The magnetization measurements suggested that the superconducting transition temperatures were not affected up to 0.035 wt.% ZnO addition. Critical current density Jc, measured at 3 T and 77 K (Ha∥c-axis), increased with increasing ZnO content up to 0.035 wt.%, where it reached maximum value of 100 kA/cm2 and decreased thereafter. The scalling analysis of the pinning force density as a function of the reduced field h = Ha/Hirr (Hirr is the irreversibility field) showed a peak at relatively high position as expected for an optimized pinning structure. The present results indicate high potential of ZnO particles for further enhancement of the material performance.

Deformation analysis of electrical contact using YBaCuO bulk superconductors

Abstract: A persistent current switch (PCS) is used for superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of YBCO bulk as a mechanical PCS. From the previous research, it turned out that there were improvements of reducing contact resistance and load in the YBCO switch. In this paper, the phenomenon of the YBCO-deposited metal interface was reported. The authors experimentally investigated as one side curvature silver sample (above contactor), other side YBCO sample deposited silver layers (below contactor). Additionally, the contact area of the sample was analyzed with finite element method (FEM). This analysis result may lead to the elucidation of a contact mechanism with the contact surfaces deposited metal.

Nanoscale stripe structures in SmBCO superconductors

Abstract: AFM and STM scans on SmBa2Cu3Ox (SmBCO) melt processed samples revealed nanoscale stripe-like structures, sometimes parallel over several micrometers, sometimes wavy. These structures consist of chemical compositional fluctuations and act as effective δTc pinning centres due to their wavelength of typically 10-60 nm which is comparable to the ideal pinning center size 2ξ (~10 nm for YBa2Cu3Ox in the ab-plane). Compared to similar structures in ternary (Sm, Eu, Gd)Ba2Cu3Ox (SEG) and (Nd, Eu, Gd)Ba2Cu3Ox (NEG) systems, where the stripes appear either as plateau-like stripes or as chains of aligned clusters, the stripes in SmBCO always appear as plateau-like stripes with a height of 1A–8A. These pinning structures throughout the whole sample volume may be a key to improve critical current densities especially at high external magnetic fields.