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Nanocomposite Y?Ba?Cu?O superconductors containing a wide range of Y2Ba4CuMOy (Y-2411), where M = Nb, Ta, Mo, W, Zr, Hf, Ru, Ag, Sb, Sn?and?Bi, embedded in the YBa2Cu3O7?? matrix, have been fabricated successfully. The Y-2411 phase typically has dimensions in the range 20?50?nm and it is observed to form effective flux pinning sites even at higher magnetic fields. A direct correlation between the Y2Ba4CuMOy phase inclusion content in the YBa2Cu3O7?? matrix and increased magnetic flux pinning has been observed. The critical current density increases by an order of magnitude for a nanocomposite compared to that of Y-123 without inclusions.

FeSe film is successfully fabricated onto Rolling Assisted Biaxially Textured Substrate (RABiTS) tapes by an electrochemical deposition technique. The deposited FeSe films tend to become high crystallinity with a decrease in the applied voltage to -1.0 V, and the compositional ratio of Fe to Se approaches 1:1. The sample deposited at -1.0 V shows a superconducting transition approximately 8.0 K in the magnetic susceptibility., 10 pages, 1 figure

Highly textured NdFeAs(O,F) thin films have been grown on ion beam assisted deposition (IBAD)-MgO/Y2O3/Hastelloy substrates by molecular beam epitaxy. The oxypnictide coated conductors showed a superconducting transition temperature (Tc) of 43 K with a self-field critical current density (Jc) of 7.0 x 104 A/cm2 at 5 K, more than 20 times higher than powder-in-tube processed SmFeAs(O,F) wires. Albeit higher Tc as well as better crystalline quality than Co-doped BaFe2As2 coated conductors, in-field Jc of NdFeAs(O,F) was lower than that of Co-doped BaFe2As2. These results suggest that grain boundaries in oxypnictides reduce Jc significantly compared to that in Co-doped BaFe2As2 and, hence biaxial texture is necessary for high Jc., 4 pages, 4 figures

YBa 2 Cu 3 O 7− δ /Y 2 O 3 /Y 2 BaCuO 5 (Y-123/Y 2 O 3 /Y-211) precursor powders enriched with various amounts of Nb 2 O 5 and Y 2 Ba 4 NbCuO y have been fabricated successfully in the form of large, single grain superconductors. Microstructural studies of these composites reveal the presence of nanometer-sized (as small as 10–20 nm) Y 2 Ba 4 NbCuO y phase particles and relatively larger sized Y-211 phase particles (about a micron) embedded in the YBa 2 Cu 3 O 7− δ phase matrix. The field trapping ability of these nano-composites is observed to increase significantly compared to undoped YBCO.

Single domain Y?Ba?Cu?O (YBCO) composed of a YBa2Cu3Oy (Y-123) superconducting bulk matrix with discrete, non-superconducting Y2BaCuO5 (Y-211) phase inclusions has been fabricated by a seeded infiltration and growth (IG) technique in the form of cylindrical pellets up to 32?mm in diameter. Sample shrinkage in the radial direction for single domains prepared by this technique is relatively low at 5% and independent of sample size, in contrast to the shrinkage observed in samples grown by conventional melt processing, which increases significantly with increasing sample diameter. Furthermore, samples grown by the IG technique exhibit low porosity of typically 0.9% of the bulk volume fraction, compared with a corresponding value of around 4.9% observed in samples fabricated by conventional melt processing. Fine Y-211 particles were observed to be embedded within the Y-123 superconducting matrix for the IG processed samples, leading to a high critical current density, Jc, of over 100?000?A?cm?2 at 77.3?K in self-field. The distribution of Y-211 particles in the IG sample microstructure, however, was inhomogeneous (unlike in previous reports), which leads to a variation in the spatial distribution of Jc. The volume fraction of Y-211 in the vicinity of the seed crystal (i.e.?corresponding to the initial c-sector growth stage), in particular, is typically around 5%, compared with a value of up to 30% in the a growth sectors more distant from the seed crystal (which corresponds well to the theoretical value for the sample composition studied here). The volume fraction of Y-211 inclusions in the c growth sector more distant from the seed was around 22%. Finally, a trend of the variation in the distribution of Y-211 particles in the Y-123 matrix grown by the IG technique was similar to that in sample grown by conventional melt processing.

Nano-phase (5-20 nm) particles of YBa/sub 2/(Cu/sub 0.5/M/sub 0.5/)O/sub 6/ [where M=Nb, Ta, Mo, W, Zr and Hf] have been introduced successfully into RE-Ba-Cu-O single grain superconductors. A study to enlarge the size of a single grain containing these particles has been carried out involving measurement of the growth rate as a function of YBa/sub 2/(Cu/sub 0.5/M/sub 0.5/)O/sub 6/ phase concentration and degree of undercooling. The influence of the change in YBa/sub 2/(Cu/sub 0.5/M/sub 0.5/)O/sub 6/ concentration on microstructural features is also investigated and the superconducting properties of these large grain superconductors are presented.

The effect of the addition of BaZrO3 and Y Ba2ZrO5.5 zirconium-containing compounds on the microstructure and superconducting properties of single-domain Y–Ba–Cu–O (YBCO) bulk superconductors has been investigated for various levels of Zr content. The distribution of Y2BaCuO5 (Y-211) particles along both the crystallographic a and c axes of the Y Ba2Cu3Oy (Y-123) superconducting matrix is observed to be rather discontinuous in Zr-containing samples, even with a small amount of secondary phase addition. The YBCO microstructure is observed to separate into regions of high and low concentrations of Y-211 particles when Zr-containing compounds are added to the precursor powder. Furthermore, Y-211 particles are observed to accumulate along the growth sector boundaries in the Y-211 free region of the Y-123 matrix. The extent of the Y-211 free region increases with increasing zirconium content. Increased concentrations of zirconium-containing compounds in the precursor powder trigger an undesirable segregation within the melt-processed microstructure of a band consisting of a liquid channel and a high concentration of Y-211 particles in both a and c axis growth sectors. The addition of BaZrO3 and Y Ba2ZrO5.5 to the precursor powders does not affect the superconducting transition temperature, Tc, of the bulk material. Critical current densities, Jc, of around 60 000 and 47 000 A cm−2 in self-field at 77.3 K were recorded for the samples containing 0.329 mol% BaZrO3 and 0.658 mol% Y Ba2ZrO5.5, respectively.

The effect of nano-size ZrO2 powder addition on the microstructure and superconducting properties of Y–Ba–Cu–O single grain bulk superconductors has been investigated. Significant pushing phenomena of Y2BaCuO5 (Y-211) particles, particularly in the c growth sector, were observed even with a small amount of ZrO2 added to the precursor powder. An increase in Y-211 particle pushing was observed with increasing ZrO2 content, leading to an inhomogeneous bulk microstructure. In addition, a growth cycle consisting of a Y-211 free layer–porous narrow layer–Y-211 high concentration layer was observed for samples prepared with 0.25 wt% ZrO2 in both the a and c growth sectors. The extent of the growth of single grain Y–Ba–Cu–O (YBCO) decreased with increasing ZrO2 content due to increased pushing of Y-211 particles towards molten liquid. The superconducting transition temperature, Tc, of the ZrO2 containing YBCO samples was sharp but depressed slightly (by up to 1 K) compared with an undoped YBCO grain, indicating a relative insensitivity of Tc to ZrO2 content. Finally, the sensitivity of critical current density, Jc, to applied magnetic field in large grain bulk YBCO containing ZrO2 was observed to depend critically on position due to the inhomogeneous sample microstructure.

Irreversible fields Birr of melt-processed (Sm,Eu,Gd)Ba2Cu3O7−δ bulk superconductors with varying (Sm,Eu,Gd)2BaCuO5 concentrations have been measured with pulsed magnetic fields up to 28 T in a temperature range from 55 to 85 K. The temperature dependence of Birr was studied by taking account of the effect of heat generation. In comparison with that including 5 mol% (Sm,Eu,Gd)2BaCuO5 phase the samples with 40 mol% (Sm,Eu,Gd)2BaCuO5 inclusion displayed a lower Birr value for temperatures above 75 K, while Birr was enhanced below 75 K. TEM observation unveiled a sharp contrast between a uniform nano-scaled compositional modulation in compositions with 40% (Sm,Eu,Gd)2BaCuO5 inclusion and an inhomogeneous distribution with very low (Sm,Eu,Gd)2BaCuO5 concentration. The present result could thus be understood in the context of different defect states induced by locally compositional fluctuation.

The effect of size, morphology and crystallinity of seed crystals on the nucleation and growth of melt processed Y–Ba–Cu–O (YBCO) during top seeded melt growth (TSMG) has been investigated. Conventional seeding of bulk YBCO with a small seed crystal of square planar or irregular geometry leads to point nucleation of the YBa2Cu3O7−δ (Y-123) phase and a subsequent square planar c-sector growth habit. The use of seeds of triangular and round geometries, however, results in a deviation from this growth habit symmetry. The use of large surface area seed crystals of dimensions 20 mm × 10 mm, on the other hand, influences the growth of bulk YBCO in two significant ways. Firstly, rapid epitaxial nucleation of the Y-123 phase occurs beneath the seed crystal, followed by grain growth via the usual peritectic solidification in the incongruent melt. Secondly, a large area seed reduces the processing time of large single grains compared to that achieved by TSMG with small area seeds. The present study is particularly relevant to the fabrication of single-grain samples with controlled growth sectors, reduced processing times and the multiple seeding of large area bulk materials containing good grain boundaries.

We have performed tensile tests at room temperature for Y–Ba–Cu–O bulk superconductors with artificial grain boundaries, which were fabricated by a joining technique using Ag added Y–Ba–Cu–O solder. The tensile strength of the joint was lower than that of the mother block Y–Ba–Cu–O. Microstructural analyses revealed that a residual liquid phase was observed in the vicinity of the interface between the mother block and the solder in the ac -plane. Cross-sectional observation for the samples after the tensile tests showed that the fracture occurred along the residual liquid phase. Hence, the residual liquid phase was responsible for the lower tensile strength.

Two Y–Ba–Cu–O bulk superconductors were joined by using Ag-added Y–Ba–Cu–O as a joining reagent. Two different Y–Ba–Cu–O blocks were prepared individually and subjected to the joining process. Here the joined surfaces were aligned parallel to the (1 1 0) plane. A Y–Ba–Cu–O/Ag plate was prepared via a solid state reaction. The plate was sandwiched by two Y–Ba–Cu–O blocks and heated to a temperature between the decomposition temperatures of Y–Ba–Cu–O and Y–Ba–Cu–O/Ag, and further annealed in flowing oxygen. The trapped field distribution of the joint using a Y–Ba–Cu–O/Ag solder with Y211 powders that were not refined by ball milling showed a small dip, corresponding to a decrease of the maximum trapped field values by 15%, while a single peak with no dip was obtained at the joint using a Y–Ba–Cu–O/Ag solder with finely refined Y211.

Ag-added Y–Ba–Cu–O bulk superconductors were joined using Ag-added Er–Ba–Cu–O solder and different Er211 contents. Microstructural analysis revealed that the volume fraction of Er211 at the joint with a composition of Er123:Er211 = 4:1 was the same as that for the expected volume fraction of the initial composition. That is, this composition seems to be optimum, since the mass balance was maintained during the crystal growth from the initial growth stage to the final stage. The trapped-field distribution for the joint using this composition was uniform and the only single peak indicated that strong coupling was achieved.

Joining of different Y–Ba–Cu–O bulk samples was performed using Er–Ba–Cu–O and Ag added Y–Ba–Cu–O sintered plates. In both cases, a small dip in the trapped field distribution was observed at the joint region due to the poor superconducting properties. However, the trapped field distribution of the sample joined with Ag added Y–Ba–Cu–O using refined Y 2 BaCuO 5 powders showed a single peak, which was similar to that of a single grain bulk superconductor.

In this study, we have performed the tensile tests of Y–Ba–Cu–O blocks welded by Er–Ba–Cu–O superconducting solder at room temperature. For comparative study, melt-textured Y–Ba–Cu–O and Er–Ba–Cu–O fabricated by the top-seeded melt growth are also tested. Most welded samples fractured at the joined region and the average strength was lower than those of bulk samples. This is due to the segregation of foreign phases at the joint.

The growth rate of Er–Ba–Cu–O bulk superconductor as a function of undercooling was investigated using an isothermal solidification technique. The behaviour of the growth rate of Er–Ba–Cu–O under various undercooling was similar to that of Y–Ba–Cu–O. Furthermore, macro-segregation of Er211 was also observed in the a and c growth regions. However, macro-segregation of Er211 was not observed in the Er123 crystal fabricated by a continual slow cooling method far from the seed crystal. The optimum concentration of Er211 was determined to be Er123:Er211 = 3:1 on the basis of microstructure analysis and SQUID measurements. Furthermore, the trapped field capability as well as the critical current density of Er–Ba–Cu–O bulk superconductor with an optimum composition fabricated by a continual slow cooling method employing very small particles of Er211 was dramatically improved.

We have studied the effect of crystal orientation on the microstructure at joining regions between two blocks of Y–Ba–Cu–O bulk superconductors using Er–Ba–Cu–O sintering plate. The (1 0 0)/(1 0 0) joint suffered from the segregation of second phase and residual liquid phase, which reduced the critical current. In contrast, the (1 1 0)/(1 1 0) joint was free from the segregation of second phase and residual liquid phase. Microstructural observation showed that many triangular crystals were formed from the back melt zone in the (1 1 0)/(1 1 0) joint. On the other hand, the growth front was parallel to the (1 0 0) surfaces in the (1 0 0)/(1 0 0) joint. Such a difference in the growth morphology was responsible for the difference in the superconducting properties of the joints.

For the development of superconducting electronic devices made from iron-arsenide superconductors, thin films have to be patterned into sub-micrometer sized structures while retaining high superconducting transition temperature ( T C ) and critical current ( I C ) values. To investigate current transport properties, we structure Ba(Fe,Co) 2 As 2 thin films with and without Fe buffer layers into μm- and sub-μm-bridges and measure the temperature- and field-dependent I C . The process of penetration and de-pinning of self-generated and externally excited magnetic vortices in such bridges is discussed.

A skilful combination of different types of pinning centers with the aim to optimize J c ( B ) performance of bulk superconductors in a wide range of magnetic fields is demonstrated on melt-textured (Nd,Eu,Gd)Ba 2 Cu 3 O 7− δ and NdBa 2 Cu 3 O 7− δ materials. In this contribution we show (i) the distinct effect of different types of micrometer-size secondary phase particles on J c ( B ) dependence at low fields; (ii) possibility to produce materials with either high-current densities at moderate fields or with a flat J c ( B ) curve extending to high fields, via appropriate choice of Nd:Eu:Gd ratio in NEG-123 matrix; (iii) extremely high-irreversibility field (≈9 T at 77 K) in NEG-123 samples Eu/Gd>1 and a small content of NEG-211; (iv) twin structure effect in melt-textured Nd-123 doped by micron-sized Nd-211 particles resulting at low temperatures in a field independent J c ( B ) extending to very high fields (at 40 K above 10 T). Vast majority of the data could be interpreted in terms of additive contributions of pinning on point-like and large defects.

Two monoliths of single grain Y–Ba–Cu–O superconductors were successfully joined with Er–Ba–Cu–O superconductor, which was sandwiched by two Y–Ba–Cu–O plates. Microstructural analyses revealed that no segregation of the secondary phase and/or the residual liquid phase was observed at the joint with two (1 1 0) surfaces. We also found that we can produce a strongly coupled joint for Ag added Y–Ba–Cu–O blocks using a sintered Er–Ba–Cu–O/Ag bar as a welding reagent.

We constructed a model superconducting magnetic bearing (SMB) module which will be installed for the 10 kW h class flywheel. The bearing is a radial type in that YBCO bulks are installed in the inner-stator and permanent magnet (PM) circuit in the outer-rotor. The PM circuit consists of NdFeB magnets and SPCC yokes. The maximum levitation force density of the superconducting bearing was 9.0 N/cm 2 at 77 K. The rotational loss of the SMB was 8.03 W at 6000 rpm with the load of 838 N, which was mainly caused by an inhomogeneity in magnetic field generated from the PM circuit.

Microstructural studies were performed at the joining area between two blocks of Y–Ba–Cu–O bulk superconductors using sintered ErBa 2 Cu 3 O y (Er123) welding solder when the joined surfaces were parallel to the (1 0 0) and (1 1 0) crystallographic planes. The residual liquid phase and the segregation of second phase particles were always observed in the joint with (1 0 0)/(1 0 0) surfaces, while no such defects were observed in the joint with (1 1 0)/(1 1 0) surfaces. Microstructural observations of the joint at several stages of the joining process showed that the growth front was always parallel to the (1 0 0) joined surfaces for the (1 0 0)/(1 0 0) joint, leading to the segregation of liquid phase and second phase particles. In contrast, many triangular crystals were observed at the (1 1 0)/(1 1 0) joint in that the (1 0 0) facet was tilted about 45° from the (1 1 0) joined surfaces, and thus allowing the complete reaction of the Er123 phase at the joint. Such growth morphology was the source of joint free from residual liquid phase and segregation of second phase that reduce the critical current in the (1 1 0)/(1 1 0) joint.

We have fabricated the stator of a superconducting bearing module for a 10 kWh class flywheel system. The bearing is of radial type in that YBCO bulks are installed in the inner stator and ring-shaped permanent magnets in the outer rotor. YBCO bulk superconductors have a Japanese roof tile shape with epoxy resin impregnation for reinforcement and surface protection. The inner stator is a cylinder (OD = 123 mm, ID = 93 mm, height = 60 mm) that consists of eight YBCO blocks. The c-axis of the YBCO blocks was parallel to the radial direction of the cylinder. The cylindrical set of the YBCO bulks was fixed in a cryostat with epoxy resin. Before installment, we measured the trapped magnetic field distribution of the individual YBCO bulks by using Hall probes at 77 K after field-cooled in the presence of 1 T. The peak field values ranged from 0.4 to 0.7 T. For some samples, the field distribution was not symmetrical, suggesting the presence of some cracks or defects. We also measured the repulsive force between the YBCO bulk at 77 K and a permanent magnet using a tensile machine with a permanent magnet 25 mm in diameter and 5 mm in thickness having surface induction of 0.3 T. Unlike the trapped field, the repulsive force was almost constant for all the samples and was about 50 N at a 0.5 mm gap.

We have succeeded in joining Y–Ba–Cu–O bulk superconductors using sintered Yb–Ba–Cu–O and Er–Ba–Cu–O bars as welding solders. The key to the fabrication of strongly coupled joints was the control of the welded surfaces such that both of the joined surfaces are parallel to the (110) plane. Another key was the use of highly dense sintered Yb–Ba–Cu–O and Er–Ba–Cu–O bars as welding solders. Microstructural observations have shown that welded regions were free from voids, residual liquid phase, and the segregation of second phase particles. The joint made with the Er–Ba–Cu–O solder was superior to that with Yb–Ba–Cu–O, presumably due to the inherently superior superconducting properties of Er–Ba–Cu–O.

Two melt-textured Y–Ba–Cu–O superconductor blocks were successfully welded with Er–Ba–Cu–O solder having a lower peritectic temperature than that of Y–Ba–Cu–O. The key to a strongly coupled joint was a combination of the control of crystal growth along 〈1 1 0〉 direction and the employment of a highly dense sintered Er–Ba–Cu–O bar as a solder material. Microstructural analyses revealed that no segregation of secondary phase and/or residual liquid phase was observed at the joint interface. Furthermore, it was found through magneto-optical observations that magnetic field could not penetrate into the joint, indicating that the two superconductors were strongly connected with this method.

An important step forward for the understanding of high-temperature superconductivity has been the discovery of iron-based superconductors. Among these compounds, iron pnictides could be used for high-field magnet applications, resulting more advantageous over conventional superconductors, due to a high upper critical field as well as its low anisotropy at low temperatures. However, the principal obstacle in fabricating high quality superconducting wires and tapes is given by grain boundaries. In order to study these effects, the dc transport and voltage-noise properties of Co-doped BaFe₂As₂ superconducting films with artificial grain boundary junctions have been investigated. A specific procedure allows the separation of the film noise from that of the junction. While the former shows a standard 1/f behaviour, the latter is characterized by an unconventional temperature-dependent multi-Lorentzian voltage-spectral density. Moreover, below the film superconducting critical temperature, a peculiar noise spectrum is found for the grain boundary junction. Possible theoretical interpretation of these phenomena is proposed.

A detailed characterization of the voltage-noise properties has been performed in FeTe0.5Se0.5 epitaxial thin films and Co-doped BaFe2As2 bilayers, deposited by pulsed laser deposition. In all the samples analyzed, the experimental voltage-spectral density has a 1/f noise component. Different behaviors are observed for the bias current and temperature dependencies of this 1/f noise, and are related to specific structural and electric transport properties of the two materials.

Angle-resolved transport measurements revealed that planar defects dominate flux pinning in the investigated Co-doped BaFe2As2 thin film. For any given field and temperature, the critical current depends only on the angle between the crystallographic c-axis and the applied magnetic field but not on the angle between the current and the field. The critical current is therefore limited only by the in-plane component of the Lorentz force but independent of the out-of-plane component, which is entirely balanced by the pinning force exerted by the planar defects. This one-dimensional pinning behavior shows similarities and differences to intrinsic pinning in layered superconductors., Comment: 8 pages, 6 figures

We have investigated the effect of undercooling on the growth rate and Nd–Ba substitution for the Nd–Ba–Cu–O/Ag system in air. It was found that the growth rate along the c-axis was larger than that along the ab-axis. The range of Nd–Ba solid solution was also affected by undercooling such that Nd substitution was suppressed with large undercooling. A high Tc of around 94 K with sharp superconducting transition was achieved in the sample melt grown with large undercooling in air.

Thermal conductivity of OCMG processed NEG123 bulk samples including 5, 10, 20, 30, and 40 mol% NEG211 second phase (SP) have been measured in the temperature range between 15 and 150 K. Thermal conductivity enhancement below Tc was observed in all samples. Magnitude of both thermal conductivity and its enhancement become smaller with increasing SP amount. It turned out that electronic contribution is smaller than 1% of total thermal conductivity. We found a very strong correlation between magnitude of thermal conductivity and the average distance between SP grains. Therefore, we can control the magnitude of thermal conductivity by added amount of SP. Critical current density Jc measured by SQUID magnetometer is larger than 2×104 A/cm2 up to 3–4 T for the samples with 5, 10, 20, 30, and 40 mol% SP. From these results, these materials have very good characteristics for high current power leads in relatively large stray field environment.

Morphology of Gd 2 BaCuO 5 (Gd-211) secondary phase particles in an oxygen-controlled-melt-growth processed (Nd 0.33 Eu 0.33 Gd 0.33 ) Ba 2 Cu 3 O y +0.5 mol % of Pt (NEG-123) was studied as a function of varying amount (0–3 mol%) of CeO 2 . Optical and scanning electron microscopy revealed that sub-micron Gd-211 particles were distributed uniformly throughout the NEG-123 matrix for additions of up to 2 mol% of CeO 2 . With increasing CeO 2 content the critical current density, J c , increased particularly at low magnetic fields. The maximum value of J c was achieved for 1 mol% CeO 2 and reached 100 kA cm −2 at zero field and 77 K. The improved low-field critical current density is attributed to the refinement of Gd-211 particles.

We have fabricated (Nd,Sm)–Ba–Cu–O bulk superconductor using Ba-rich (Nd 1− x ,Sm x ) 4−2 y Ba 2+2 y Cu 2− y O 10− δ powder in air. The magnetic property of bulk (Nd,Sm)–Ba–Cu–O melt textured in air was similar in T c and superconducting transition to the bulk with the same nominal composition melt textured in low P O 2 . This is due to the fact that the presence of Ba-rich second phase in the liquid suppressed (Nd,Sm) enrichment in (Nd,Sm)Ba 2 Cu 3 O y phase.

We have studied the range of Nd–Sm solid solution in the (Nd1−x,Smx)4−2yBa2+2yCu2−yOz system in the Nd123 matrix. X-ray diffraction studies for the sintered (Nd1−x,Smx)4−2yBa2+2yCu2−yOz powders in air showed that the samples were a single phase 422 in the range of x=0–0.3, showing that Sm substituted on Nd site in Nd422. It was also found that Sm is soluble up to x=0.3 in (Nd1−x,Smx)3.6Ba2.4Cu1.8Oz. We then fabricated Nd123/Nd422 bulk superconductors by melt processing, in which Nd123 powder is mixed with 20 mol% (Nd0.8,Sm0.2)3.6Ba2.4Cu1.8Oz and 1 wt.% CeO2. The sample exhibited high Tc of 97 K and sharp superconducting transition when melt-processed under controlled oxygen partial pressure (PO2) of 0.01 atm.

We have investigated the effect of oxygen partial pressure, the initial composition, and the addition of CeO/sub 2/ and/or Pt on the grain growth of Nd/sub 4/Ba/sub 2/Cu/sub 2/O/sub 10/ (Nd-422) in the Ba-Cu-O liquid. Logarithmic plots of the mean diameter of Nd-422 under various oxygen levels as a function of the holding time showed the power law behavior with the slope of 1/3, which suggested that the grain growth of Nd-422 could be explained in terms of the Ostwald ripening theory. A reduction of oxygen partial pressure, the shift of the initial composition toward Ba-rich direction, and a combined addition of Pt and CeO/sub 2/ could suppress the coarsening of Nd-422. Furthermore, a combination of these techniques was found to be effective in refining the Nd-422 in the Nd-123 matrix, which led to an enhancement of J/sub c/ values.

We have investigated the effect of oxygen partial pressure, initial composition and CeO 2 addition on the coarsening of Nd 4 Ba 2 Cu 2 O 10 (Nd422) in a Ba–Cu–O melt. It was found that the size of Nd422 decreased in the liquid when the initial composition was shifted toward Ba-rich direction. Reduction of the partial pressure of oxygen and addition of CeO 2 were also found to be effective for the refinement of Nd422. Fine dispersion of Nd422 led to an enhancement of the critical current density ( J c ) in a low field region for melt-textured Nd–Ba–Cu–O.

Microstructure of (Nd, Eu, Gd)Ba2Cu3O7−δ (NEG-123) samples with (Nd, Eu, Gd)2BaCuO5 (NEG-211) particles were observed by transmission electron microscopy. High-resolution electron microscopy observation demonstrated that the density of microstructural defects was small around the NEG-211 secondary phase particles. Furthermore, the 123/211 interfaces were found to be very clean and sharp. Chemical compositional analysis of the submicron secondary phase particles revealed that these fine particles are not composed of NEG-211 but Eu2BaCuO5 (Eu-211) or Gd2BaCuO5 (Gd-211).

The discovery of superconductivity (SC) with a transition temperature, Tc, up to 65K in single-layer FeSe (bulk Tc =8K) films grown on SrTiO3 substrates has attracted special attention to Fe-based thin films. The high Tc is a consequence of the combined effect of electron transfer from the oxygen-vacant substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate the realization of SC in the parent compound BaFe2As2 (no bulk Tc) just by tensile lattice strain without charge doping. We investigate the interplay between strain and SC in epitaxial BaFe2As2 thin films on Fe-buffered MgAl2O4 single crystalline substrates. The strong interfacial bonding between Fe and the FeAs sublattice increases the Fe-Fe distance due to the lattice misfit which leads to a suppression of the antiferromagnetic spin density wave and induces SC with bulk-Tc ?10K. These results highlight the role of structural changes in controlling the phase diagram of Fe-based superconductors., http://www.nature.com/ncomms/2013/131206/ncomms3877/full/ncomms3877.html

The dependence of the superconducting gaps in epitaxial Ba(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$ thin films on the nominal doping $x$ ($0.04\ensuremath{\leqslant}x\ensuremath{\leqslant}0.15$) was studied by means of point-contact Andreev-reflection spectroscopy. The normalized conductance curves were well fitted by using the two-dimensional Blonder-Tinkham-Klapwijk model with two nodeless, isotropic gaps---although the possible presence of gap anisotropies cannot be completely excluded. The amplitudes of the two gaps ${\ensuremath{\Delta}}_{\mathrm{S}}$ and ${\ensuremath{\Delta}}_{\mathrm{L}}$ show similar monotonic trends as a function of the local critical temperature ${T}_{\mathrm{c}}^{\mathrm{A}}$ (measured in the same point contacts) from 25 K down to 8 K. The dependence of the gaps on $x$ is well correlated to the trend of the critical temperature, i.e., to the shape of the superconducting region in the phase diagram. When analyzed within a simple three-band Eliashberg model, this trend turns out to be compatible with a mechanism of superconducting coupling mediated by spin fluctuations, whose characteristic energy scales with ${T}_{\mathrm{c}}$ according to the empirical law ${\ensuremath{\Omega}}_{0}=4.65{k}_{\mathrm{B}}{T}_{\mathrm{c}}$, and with a total electron-boson coupling strength ${\ensuremath{\lambda}}_{\mathrm{tot}}=2.22$ for $x\ensuremath{\leqslant}0.10$ (i.e., up to optimal doping) that slightly decreases to ${\ensuremath{\lambda}}_{\mathrm{tot}}=1.82$ in the overdoped samples ($x=0.15$).

We report the NdBa2Cu3Oy (Nd123)-Ba3Cu5Oz(035) pseudo-binary section in the Nd2O3-BaO-CuO system under the oxygen partial pressure pO2 = 0.01 atm. We performed thermogravitational and differential thermal analysis (TG-DTA) and powder x-ray diffraction (XRD) measurements for quenched samples. We also performed high-temperature XRD for the determination of equilibrium solid phases at elevated temperatures. In situ observation of the primary solid phases with laser scanning microscopy was also performed for an accurate determination of the liquidus line. In comparison with the Nd123-035 pseudo-binary phase diagram in air, the liquidus line under pO2 = 0.01 atm shifts to a lower temperature.

We have studied the microstructure and the superconducting properties of NdxEu1-xBa2Cu3Oy compounds synthesized by the solid-state reaction and the melt process. NdxEu1-xBa2Cu3Oy formed a complete solid solution in a full range (0

We fabricated large grain (Sm, Gd)-Ba-Cu-O bulk superconductors with the top-seeded, melt-growth process in air and 1%O2-Ar. Ag addition was effective in suppressing the amount of cracking. Unlike Sm-Ba-Cu-O, the (Sm, Gd)-Ba-Cu-O bulk showed relatively high Tc and large Jc values even when melt-processed in air. The trapped field value of 0.83 T was recorded at 77 K for the sample melt processed in air.

Orientation degree of strontium ferrite particles in a magnetic field at water-based wet-pressing stage was investigated from the viewpoint of calcining temperature and dispersant addition. In the case of no dispersant addition, the orientation degree was low especially at low calcining temperature (1150°C and 1200°C), at which the particle size was under micron. Increasing the calcining temperature, the orientation degree noticeably increased. On the other hand, we found that the orientation of the submicron sized particles was much improved by addition of calcium gluconate as a dispersant and then the orientation degree was almost independent of calcining temperature. It was predicted that calcium gluconate effectively deagglomerated submicron sized particles of strontium ferrite. Therefore addition of calcium gluconate enabled to produce high-performance ferrite magnets with both high coercivity and high remanence.

The magnetic anisotropy constant K1 and anisotropy field HA of M-type Sr-ferrite containing La and Co (Sr0.7La0.3Fe11.7Co0.3O19) were investigated by the singular-point detection (SPD) method using a pulsed field and SQUID magnetometers, and also by torque measurements. The value of HA=22.2 kOe was obtained by the SPD method at 298 K. The K1 value was 4.2 × 106 erg/cm3 at 298 K, which was determined by extrapolation to the high field of the coefficient of the sin(2 φ) term calculated by Fourier analysis of unsaturated torque curves. This value was 15% larger than that of conventional Sr-ferrite (SrFe12O19) in the temperature range from 77 to 373 K.

Magnetic properties of anisotropic M-type Sr-ferrite containing La and Co (Sr1-xLaxCoxFe12-xO19) was investigated in detail. At a composition of x = 0.3, the magnetic properties for permanent magnets were much improved, with the highest values of Br = 4.45 kG, HcJ = 4.82 kOe, and (BH)max = 4.86 MGOe. The temperature dependence of the coercivity was also much improved, with ΔHcJ/HcJ/ΔT = 0.1 %/°C.

We have reported previously the successful fabrication of single grain Gd–Ba–Cu–O (GdBCO) bulk superconductors in air by top seeded melt growth (TSMG) using a generic Mg–Nd–Ba–Cu–O (Mg–NdBCO) seed crystal. Here, we report a new processing route that enables the fabrication of bulk GdBCO single grains in air using precursors with higher Ba content than has been achieved in previous studies. In particular, the composition of the superconducting matrix of single grains prepared with high, but varying, levels of Ba is analyzed by EPMA. The degree of substitution Ba for Gd (corresponding to a negative value of x in the composition formulation), in GdBCO is proposed for the first time based on the superconducting, compositional, chemical and structural properties of the Gd-123ss (Gd 1+ x Ba 2− x Cu 3 O 7− δ ) phase matrix observed this study.

We have measured the temperature dependences of the thermal conductivity in the ab -plane, κ ab ( T ), and along the c -axis, κ c ( T ), respectively, for the Er–Ba–Cu–O bulk superconductors, which were fabricated by a method of the melt texture growth. Above the critical temperature T c , the κ ab decreases quite moderately as increasing temperature or is almost independent of the temperature. Below the T c , the well-known enhancement is observed but is relatively small. The κ c ( T ) shows the small absolute values and we found that the anisotropy of the thermal conductivity ( κ ab / κ c ) for Er–Ba–Cu–O bulks is of about 2–6.

The anisotropy of the critical current density Jc depends in general on both the properties of the flux lines (such as line tension, coherence length and penetration depth) and the properties of the defects (such as density, shape, orientation etc.). Whereas the Jc anisotropy in microstructurally clean films can be scaled to an effective magnetic field containing the Ginzburg-Landau anisotropy term, it is in general not possible (or only in a limited field range) for samples containing extended defects. Here, the Jc anisotropy of a Co-doped BaFe2As2 sample with 45{\deg} [001] tilt grain boundaries (GBs), i.e. grain boundaries created by 45{\deg} in-plane rotated grains, as well as extended Fe particles is investigated. This microstructure leads to c-axis correlated pinning, both due to the GBs and the Fe particles and manifests in a c-axis peak in the Jc anisotropy at low magnetic fields and a deviation from the anisotropic Ginzburg-Landau scaling at higher fields. Strong pinning at ellipsoidal extended defects, i.e. the Fe particles, is discussed, and the full Jc anisotropy is fitted successfully with the vortex path model. The results are compared to a sample without GBs and Fe particles. 45{\deg} GBs seem to be good pinning centers rather than detrimental to current flow., Comment: 8 pages, 7 figures, CEC-ICMC 2013 proceeding, accepted for publication in Advances in Cryogenic Engineering (Materials)