Improvement Of Critical Current Density Research Articles

Determinant for Self-Organization of BaMO<sub>3</sub> Nanorods Included in Vapor-Phase-Grown <inline-formula> <tex-math notation="LaTeX">$\mbox{REBa}_{2}\mbox{Cu}_{3}\mbox{O}_{y}$</tex-math></inline-formula> Films

BaMO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BMO; M = Zr, Sn, and Hf) self-organizes into nanorod shape within REBCO films grown by vapor phase epitaxy. Controlling the number density of the BMO nanorods is effective for an improvement of critical current density of the REBCO films in magnetic fields. We focused on the growth mechanism of the BMO nanorods in this paper. BaHfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BHO)-doped REBCO films were fabricated under various conditions such as volume fraction of BHO and substrate temperature. We checked the number density and diameter of the BHO nanorods. We found that the volume fraction of BHO increased the number density, whereas the diameter was not affected by the volume fraction so much. The low substrate temperature contributed to the high number density in the films. Additionally, we carried out the 2-D Monte Carlo simulations for the nucleation and the selforganization of the BMO. The REBCO and BMO nuclei occurred randomly. However, due to small amount of BMO relative to REBCO, it was difficult for the BMO nuclei to get fat. We changed the molar fraction of the BMO and the substrate temperature in the simulations and evaluated the number density and the diameter of the resulting BMO nanorods.

Optimization of a 10 MW Direct Drive HTS Generator for Minimum Levelized Cost of Energy

High Temperature Superconducting (HTS) tapes based on YBCO are expected to reach a 4-fold critical current density improvement at 30 K and 3 T through developments currently underway at the University of Houston as part of an ARPA-e sponsored project. The major objective of this undertaking is to enable the deployment of cost effective direct drive HTS generators for large off-shore wind turbines. The improved conductor performance allows for a significant reduction of the length of HTS tapes required to generate the excitation field and thus to a reduction of the overall generator cost. This paper presents design and optimization work to find the best generator topology based on the 4X conductor to minimize the levelized cost of energy. The electromagnetic model uses the commercial package FlexPDE as the Finite Element Analysis (FEA) solver. The model takes the power and RPM requirements as inputs, and outputs the Levelized Cost of Energy (LCOE) for the turbine. The model estimates the actual mass and cost of the generator assuming mass production of multiple units per year. The paper presents the model developed in detail as well as the results obtained from the analysis through Monte-Carlo design space exploration.

Significantly enhanced critical current density in nano-MgB2 grains rapidly formed at low temperature with homogeneous carbon doping

High performance MgB2 bulks using carbon-coated amorphous boron as a boron precursor were fabricated by Cu-activated sintering at low temperature (600 °C, below the Mg melting point). Dense nano-MgB2 grains with a high level of homogeneous carbon doping were formed in these MgB2 samples. This type of microstructure can provide a stronger flux pinning force, together with depressed volatility and oxidation of Mg owing to the low-temperature Cu-activated sintering, leading to a significant improvement of critical current density (Jc) in the as-prepared samples. In particular, the value of Jc for the carbon-coated (Mg1.1B2)Cu0.05 sample prepared here is even above 1 × 105 A cm−2 at 20 K, 2 T. The results herein suggest that the combination of low-temperature Cu-activated sintering and employment of carbon-coated amorphous boron as a precursor could be a promising technique for the industrial production of practical MgB2 bulks or wires with excellent Jc, as the carbon-coated amorphous boron powder can be produced commercially at low cost, while the addition of Cu is very convenient and inexpensive.

Optimization of Bi-2212 high temperature superconductors by potassium substitution

Polycrystalline bulks of Bi2Sr2Ca1−xKxCu2.0O8+δ (Bi-2212) with x = 0, 0.05, 0.10 and 0.15 were fabricated by the spark plasma sintering technique. The influences of K doping on the microstructures, electronic structures, as well as the related superconducting properties, were systematically investigated. The XRD analyses confirmed that K+ ions have successfully substituted into the matrix of Bi-2212, and lead to a systematical change of lattice parameters. Due to the change of thermodynamic properties, bulks with higher density, larger grain size and better texture structures were obtained after doping. Therefore, ac susceptibility measurement revealed the optimization of intergrain connections, which lead to the optimization of both self- and in-field critical current density, Jc of this system. The optimization of microstructures also caused the enhancement of surface pinning. Based on the enhancements of both intergrain connections and flux pinning properties, an obvious improvement of critical current density was obtained with the optimal doping content of K = 0.05. Meanwhile, Bi-2212 single filament tapes with K doping content of 0 and 0.05 were also fabricated by the powder-in-tube process. The XRD patterns also proved the successful doping of K ions in the Bi-2212 matrix. The critical current density Jc, measured by the transport method under the magnetic field from 0 to 20 T at 4.2 K, proved the effectiveness of K doping on the enhancement of flux pinning properties of Bi-2212.

Influences of Yb substitution on the intergrain connections and flux pinning properties of Bi-2212 superconductors

Polycrystalline bulks Bi2Sr2−xYbxCaCu2.0O8+δ (Bi-2212) with Yb doping content of x=0, 0.01, 0.02 and 0.05) were fabricated by solid state sintering process. Bi-2212 precursor powders were synthesized by modified co-precipitation process, and Yb2O3 powders were added into the precursor powders during the calcination process as dopants. The influences of Yb substitution on the lattice parameter, microstructure and related superconducting properties were systematically investigated. The amorphous components within the grain boundaries were observed with HRTEM, which contributed to the formation of weak links. Therefore, both the decreasing number of porosity and better crystallized grain boundary structure after Yb doping obviously enhanced the intergrain connections. Meanwhile, doping of Yb ions into Bi-2212 matrix also contributed to the enhancement of point pining, thus lead to the improvement of in-field critical current density. Based on the enhancements of both intergrain connections and flux pinning properties, improvement of critical current density was obtained with the optimal doping content of x=0.02.

Optimized Intergrain Connection and Transport Properties of Bi-2212 High-Temperature Superconductors by Ag Nanoparticles Inclusions

Bi2Sr2CaCu2.0 O 8+δ (Bi-2212) polycrystalline bulks with Ag nanoparticles inclusion content of x = 0, 0.125, 0.250 and 0.500 wt% were fabricated by spark plasma sintering process. Bi-2212 precursor powders were synthesized by modified coprecipitation process Ag nanoparticles with the particle size of 5 ∼ 20 nm were synthesized by a microplasma reduction method. The influences of Ag inclusions on the textural structures and related superconducting properties were systematically investigated. Both XRD and XPS results revealed the elemental state of Ag in the bulks. Therefore, no doping effect was observed on the lattice parameters, as well as the critical temperature of Bi-2212 phase. Obvious enhancements of texture structures and increase of average grain size were obtained due to the change of crystallization behavior of Bi-2212 with Ag doping. Thus, intergrain connections were obviously improved, which contributed to the increase of self-field critical current density. Besides, the formation of better crystallized grain boundaries increased the number of effective pinning centers, thus enhanced the flux pinning properties and the in-field transport properties. Based on the influences mentioned above, improvement of critical current density of over 60 % was obtained with the optimal Ag content of 0.250 wt %.

Improvement of Critical Current Density in YBa2Cu3O7-δ Superconductor with Nano TiO2 Addition

The optimization of flux line pinning in superconductors is one of the most efficient ways to improve the transport properties of these materials. In this work, we have examined the effectiveness of an insulating nano particle inclusion in a type II superconductor as a pinning center with a size close to the coherence length, ξ. We report on measurements of the superconducting properties of YBa2Cu3O7-δ bulk superconductors with different weight % of nano particles of TiO2 contents (x = 0–3wt %) prepared by the modified combustion route. The microstructure of bulk YBCO added with nano particles was characterized by scanning electron microscopy. Sub-micron, randomly oriented particles of this phase were found to form around grain boundaries and within YBCO grains in bulk sintered pellets. It is observed that the critical current density is higher by a factor of 3 and the Jc–B behavior is remarkably improved in samples with nano additions. However, the superconductor transition temperature (Tc) slightly decreases from 92K to 90.5K. The flux pinning force is enhanced by 8 times that of pure YBCO sample. Thus these nano particles are effective flux pinning centers and enhance the transport critical current density at liquid nitrogen temperature for an applied magnetic field. The experimental results suggest that the added nano-sized TiO2 particle may have high pinning efficiency at a temperature around 77K.

Improvement of critical current densities in SmBa2Cu3Oy, films with BaHfO3 nano-rods using low temperature growth technique

We studied growth substrate temperature dependent morphologies of BaHfO3 (BHO) nano-rods for SmBa2Cu3Oy, (SmBCO) films with BHO fabricated by pulsed laser deposition (PLD) method. The morphology of BHO nano-rods within the SmBCO matrix could be controlled by changing substrate temperatures adoping a Low Temperature Growth (LTG) technique. Using the LTG technique, we could fabricate SmBCO films showed c-axis orientation even at low substrate temperature during deposition without a degradation of superconducting properties, which is one of the most advantages of the LTG technique. In this study, we found an optimal morphology of the BHO nano-rods and the morphology was fine, straight and various growth directions. The BHO nano-rods were more effective to improve the Jc in a magnetic field than other morphologies of the BHO nano-rods.

Critical current density improvement by intermediate deformation for the fabrication of Bi&lt;SUB&gt;2&lt;/SUB&gt;Sr&lt;SUB&gt;2&lt;/SUB&gt;Ca&lt;SUB&gt;2&lt;/SUB&gt;Cu&lt;SUB&gt;3&lt;/SUB&gt;O&lt;SUB&gt;10+δ&lt;/SUB&gt;/Ag round wires

Critical current density improvement by intermediate deformation for the fabrication of Bi&lt;SUB&gt;2&lt;/SUB&gt;Sr&lt;SUB&gt;2&lt;/SUB&gt;Ca&lt;SUB&gt;2&lt;/SUB&gt;Cu&lt;SUB&gt;3&lt;/SUB&gt;O&lt;SUB&gt;10+δ&lt;/SUB&gt;/Ag round wires

Cu diffusion in Nb3Sn internal tin superconductors during heat treatment

Heat treatments and phase formation of Nb3Sn internal tin superconductors are more complicated than bronze route conductors due to the need to convert low melting/low decomposition temperature Sn-rich phases to higher temperature Cu-rich Cu–Sn phases. Conventionally, the Cu–Sn phase development in internal tin wires and hence heat treatment optimization and microstructure control are typically interpreted as a matter of outward Sn diffusion from the Sn core towards the Nb filaments, and Cu diffusion in the opposite direction is simply assumed. In this paper, we present a perspective of Cu diffusion, based on our investigation of phase development. We shall show that the conventional Sn diffusion perspective cannot explain some of our observations, in particular the subelement core phase development. We shall also show that the distribution of Kirkendall pores is opposite to that of the coarse Nb3Sn grains, thus establishing a direct relationship between copper diffusion and coarse Nb3Sn grain formation and distribution. We shall compare wires of different local Cu:Nb area ratio (LAR) and show how Cu diffusion appears to control the Cu–Sn phase formation across the subelement and the final Nb3Sn microstructure (and hence influences the critical current density). Drawing from what we learnt from our observation, we managed to modify a standard heat treatment and obtained up to over 20% improvement in critical current density in some of the wire designs we investigated.

Large critical current density improvement in Bi-2212 wires through the groove-rolling process

Recently there has been a growing interest in Bi-2212 superconductor round wire for high magnetic field use despite the fact that an increase of the critical current is still needed to boost its successful use in such applications. Recent studies have demonstrated that the main obstacle to current flow, especially in long wires, is the residual porosity inside these powder-in-tube processed conductors that develops from bubble agglomeration when the Bi-2212 melts. In this work we tried to overcome this issue affecting the wire densification by changing the deformation process. Here we show the effects of groove rolling versus the drawing process on the critical current density JC and on the microstructure. In particular, groove-rolled multifilamentary wires show a JC increased by a factor of about 3 with respect to drawn wires prepared with the same Bi-2212 powder and architecture. We think that this approach in the deformation process is able to produce the required improvements both because the superconducting properties are enhanced and because it makes the fabrication process faster and cheaper.

Significant improvement in critical current densities of C-doped MgB2 tapes made by high-energy ball milling

C-doped MgB2 tapes were fabricated using crystalline boron as one of the ball milled precursor powders. It was found that the ball milling process can strongly enhance the Jc values of MgB2 tapes and reduce the anisotropy of the Jc. At 4.2 K, the transport Jc of the 80 h milled C-doped MgB2 tapes sintered at 800 °C reaches 4.3 × 104 A cm−2 at 10 T and 2.2 × 104 A cm−2 at 12 T, respectively. These values are even higher than for tapes made from amorphous B powders. Ball milling can improve not only the upper critical field, by increasing the C substitution level in the MgB2 lattice, but also the flux pinning, by increasing grain boundaries, both of which result in the enhancement of Jc performance. Moreover, the high MgB2 phase fraction and large density of milled MgB2 tapes are beneficial to the active area. These results indicate that the use of crystalline B in combination with a ball milling process may be an economic method to harness the excellent properties of MgB2 for practical applications.

Cooperative doping effects of Ti and nano-SiC on transport critical current density and grain connectivity of in situ MgB2 tapes

By now, nano-SiC powder (20–30nm) is still the most effective additive for improving upper critical field and critical current density of MgB2-based superconducting materials. However, some decomposed carbon aggregates at grain boundaries and results in serious weak-links of MgB2 grains, and these weak-links limit the further improvement of critical current density, Jc of MgB2, especially at lower fields. Ti doping is reported to increase the compactness of MgB2, and modify its intergranular coupling by forming ultrathin TiB2 layer at grain boundaries. In this work, we studied the cooperative doping effects of Ti and nano-SiC on transport Jc and grain connectivity of MgB2 and the possibility to improve transport Jc of SiC doped MgB2 by introducing Ti additive. The results suggest the Ti addition can obviously improve Jc of MgB2 at lower fields and also enhance the Jc of SiC doped MgB2 by improving their grain connectivity which shows serious intergranular weak-links.

Influences of Y 2O 3 nanoparticle additions on the microstructure and superconductivity of YBCO films derived from low-fluorine solution

Low-fluorine YBCO precursor solutions with metallic ion molar ratio of Y 3+:Ba 2+:Cu 2+ = (1 + λ):2:3 ( λ = 0, 0.05, 0.1, 0.15, 0.2, 0.3) were prepared using fluorine-free yttrium acetate, copper acetate and fluorinated Ba-TFA as starting materials. Using the yttrium-excess YBCO solutions, YBCO–Y 2O 3 nanocomposite films were prepared on (0 0 1)-oriented LaAlO 3 single-crystal substrates by dip-coating process. The growth orientation and microstructure of the as-prepared YBCO–Y 2O 3 nanocomposite films were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Both the electrical transport and magnetization methods were used to measure the superconducting performance of the films. The results show that Y 2O 3 nanoparticles with the diameter of 5–6 nm are formed and well dispersed in YBCO matrix. These nanoscaled Y 2O 3 nanoparticles and the induced nano-sized crystal defects can act as the flux pinning centers, thus leading to the improvement of critical current density J c of YBCO films at all magnetic field orientations.

The effect of Pr6O11 doping on superconducting properties of MgB2

AbstractIn this paper we report the effect of Pr6O11 doping on the structural and superconducting properties of MgB2. The bulk samples of Pr6O11‐doped MgB2 have been prepared with nominal compositions Mg1−x(Pr6O11)x/6B2 (where x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) via a standard solid‐state reaction route by sintering in a reducing atmosphere of Ar/H2. The superconducting transition temperature Tc of MgB2 is found to decrease from 39 to 37 K when x increases from 0 to 0.05. The XRD results show the presence of MgO and PrB6 secondary phases in the doped samples besides the main hexagonal phase of MgB2. Improvement in critical current density (Jc), irreversibility field (Hirr), and upper critical field (Hc2) of doped samples has been observed. The Jc values at 10 and 20 K of the x = 0.03 sample are higher in the entire field region (0–6 T). At 10 K and 2 T field the Jc values of undoped and 0.03 Pr6O11‐doped samples are 1.09 × 105 and 2.21 × 105 A/cm2, respectively. Variations of Hc2, Jc, Hirr, and flux‐pinning force (Fp) with doping concentrations have been studied in this paper and a correlation between these superconducting properties and structural characteristics of the samples has been found in the present work.

Effect of rare-earth doping on the superconducting properties of MgB2

The bulk polycrystalline samples with nominal compositions Mg1−x(Eu2O3)x/2B2 and Mg1−x(Pr6O11)x/6B2 (where x=0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) have been prepared via standard solid-state reaction route. The x-ray diffraction (XRD) results of both series of materials reveal the presence of secondary phases MgO and REB6(RE=Eu/Pr) besides the main hexagonal phase of MgB2. The magnetic and electrical measurements show that transition temperatures (Tc) of both Eu2O3 and Pr6O11-doped MgB2 samples decrease from 39 to 37 K when values of x increase from 0.0 to 0.05. Improvement in critical current density (Jc) at 10 K has been observed at higher fields (&amp;gt;4 T) for Eu2O3-doped samples of composition x=0.04 and in entire field range (0–5 T) in the case of Pr6O11-doped samples of composition x=0.03 as compared to the Jc values of other compositions. The Jc values at 5 T field and 10 K of undoped, x=0.03 for Pr6O11-doped and x=0.04 for Eu2O3-doped MgB2 samples are 2.21×103, 1.15×104, and 1.10×104 A/cm2, respectively. Improvement in Hc2 and Hirr has also been observed in doped samples.

Superconducting properties of MgB2 prepared from attrition ball-milled boron powder

Abstract We report superconducting properties of the MgB 2 pellets prepared from the attrition ball-milled boron, in order to control the grain size of the MgB 2 that is formed from it. We observed that the semi-crystalline peaks in the ball-milled boron became broader when the ball-milling time was further increased, indicating that the boron powders had lost their crystalline. In addition, the B 2 O 3 peak was appeared in the ball-milled powders, resulting in an increase in the amount of MgO. However, the sample prepared from boron that was ball milled for 5 h showed an improvement of critical current density ( J c ), even with increased MgO phase, under an external magnetic field at 5 K and 20 K.

Improvement of the High-Magnetic-Field Critical Current Density of the Ex-Situ Annealed MgB2 Thick Films by Oxygen Doping

This paper presents a very simple way to synthesis MgB2 thick films with high critical current density in a magnetic field by ex-situ annealing precursor B films in air with excessive Mg in a sealed quartz tube. The films show a significant improvement of critical current density in a magnetic field compared to the high purity films annealed in vacuum, while its zero-resistance transition temperature Tczero and normal state resistivity still maintain about 38 K and 17 μΩcm. The results demonstrate MgB2 thick films have great potential applications in superconducting coated conductors.

마그네슘과 글리세린 처리한 붕소 분말로 합성한 Mg(B1-xCx)2의 초전도 특성

Carbon was known to be one of effective additives which can improve the flux pinning of <TEX>$MgB_2$</TEX> at high magnetic fields. In this study, glycerin <TEX>$(C_3H_8O_3)$</TEX> was selected as a chemical carbon source for the improvement of critical current density of <TEX>$MgB_2$</TEX>. In order to replace some of boron atoms by carbon atoms, the boron powder was heat-treated with liquid glycerin. The glycerin-treated boron powder was mixed with an appropriate amount of magnesium powder to <TEX>$MgB_2$</TEX> composition and the powder pallets were heat treated at <TEX>$650^{\circ}C\;and\;900^{\circ}C$</TEX> for 30 min in a flowing argon gas. It was found that the superconducting transition temperature <TEX>$(T_c)$</TEX> of <TEX>$Mg(B_{1-x}C_x)_2$</TEX> prepared using glycerin-treated boron powder was 36.6 K, which is slightly smaller than <TEX>$T_c$</TEX>(37.1 K) of undoped <TEX>$MgB_2$</TEX>. The critical current density <TEX>$(J_c)$</TEX> of <TEX>$Mg(B_{1-x}C_x)_2$</TEX> was higher than that of undoped <TEX>$MgB_2$</TEX> and the <TEX>$T_c$</TEX> improvement effect was more remarkable at higher magnetic fields. The <TEX>$T_c$</TEX>, decrease and <TEX>$J_c$</TEX> increase associated with the glycerin treatment for boron powder was explained in terms of the carbon substitution to boron site.

Comparative study of different chemical doping effect on the Jc-B properties of MgB2 tapes

The effect of chemical doping on the critical current density of MgB2 tapes is studied. As impurities, we tried silicides, carbon and organic compound. Most of them lead to an obviously improvement of critical current density (Jc), and weaken its field dependence. For the silicides addition, the reaction products, such as Mg2Si play an important role in the enhancement of flux pinning ability. For the doping of carbon containing impurities, carbon substitution to boron contributes significantly to the enhancement of flux pinning ability and upper critical field, and eventually improves the Jc-B performance of MgB2 tapes. By modifying starting materials preparation process and optimizing carbon source, further improvement of in-filed Jc is expected.