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Articles 1 - 21 of 21
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Intrinsic Nanostructural Domains: Possible Origin Of Weaklinkless Superconductivity In The Quenched Reaction Product Of Mg And Amorphous B, S. Li, O. Prabhakar, T. T. Tan, C. Q. Sun, Xiaolin Wang, Saeid Soltanian, J. Horvat, S. X. Dou
Intrinsic Nanostructural Domains: Possible Origin Of Weaklinkless Superconductivity In The Quenched Reaction Product Of Mg And Amorphous B, S. Li, O. Prabhakar, T. T. Tan, C. Q. Sun, Xiaolin Wang, Saeid Soltanian, J. Horvat, S. X. Dou
Josip Horvat
Smooth modulation structure of Mg–B alloy in the quenched reaction product of Mg and amorphous B was studied. It indicates that the MgB2 formed possibly in spinodal decomposition, thus resulting in MgB2 nanodomains. It was found that the nanodomains with small angle boundaries of atomic-scale width were distributed within the subgrains that constitute the clusters in MgB2 grains. This nanostructural characteristic may be intrinsic in the quenched reaction product of Mg and amorphous B. It makes the nanodomain boundaries not act as barriers to the current percolation path, thus exhibiting no weak-link problem in the MgB2.
Order-Disorder Transition In Bi2.1sr1.9cacu2o8 + Delta Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Order-Disorder Transition In Bi2.1sr1.9cacu2o8 + Delta Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Josip Horvat
The magnetic field Hdis(T) where an order-disorder transition of the vortex lattice in high-Tc superconductors occurs, is investigated by measurements of the magnetization M(H) in Bi2.1Sr1.9CaCu2O8 + delta (Bi2212) single crystals doped with iron and lead. Comparative studies are made of the temperature dependences of the field Hpeak(T), where the second peak occurs in |M(H)|, and the fields Hmin(T), and Hinfl(T) where a minimum and an inflection point occur at the low-field side of this peak. It is proposed that Hdis(T) lies close to Hinfl. In Bi2.1Sr1.9Ca1.0(Cu1–yFey)2O8 + delta single crystals with Fe concentration y = 0, 0.005, 0.016, and …
Effect Of Carbon Nanotube Doping On Critical Current Density Of Mgb2 Superconductor, S X. Dou, W. K. Yeoh, J. Horvat, M. Ionescu
Effect Of Carbon Nanotube Doping On Critical Current Density Of Mgb2 Superconductor, S X. Dou, W. K. Yeoh, J. Horvat, M. Ionescu
Josip Horvat
The effect of doping MgB2 with carbon nanotubes on transition temperature, lattice parameters, critical current density and flux pinning was studied for MgB2–xCx with x = 0, 0.05, 0.1, 0.2, and 0.3. The carbon substitution for B was found to enhance Jc in magnetic fields but depress Tc. The depression of Tc, which is caused by the carbon substitution for B, increases with an increasing doping level, sintering temperature, and duration. By controlling the extent of the substitution and addition of carbon nanotubes we can achieve the optimal improvement on critical current density and flux pinning in magnetic fields while …
Superconducting Screening On Different Length Scales In High-Quality Bulk Mgb2 Superconductor, J. Horvat, Saeid Soltanian, Alexey Pan, Xiaolin Wang
Superconducting Screening On Different Length Scales In High-Quality Bulk Mgb2 Superconductor, J. Horvat, Saeid Soltanian, Alexey Pan, Xiaolin Wang
Josip Horvat
High-quality bulk MgB2 exhibits a structure of voids and agglomeration of crystals on different length scales. Because of this, the superconducting currents percolate between the voids in the ensuing structure. Magnetic measurements reveal that the superconducting currents circulate on at least three different length scales, of ∼1 μm, ∼10 μm, and whole of the sample (∼millimeter). Each of these screenings contributes to the measured irreversible magnetic moment (Δm). The analysis of the field dependence of Δm for samples of subsequently decreasing size showed that the critical current obtained using the simple critical state model is erroneous. This leads to the …
Effect Of Uranium Doping And Thermal Neutron Irradiation On The Flux-Pinning Of Silver-Clad Bi-Sr-Ca-Cu-O Tapes, D. Marinaro, S X. Dou, J. Horvat, J. Boldeman, R. Weinstein, R. Sawh
Effect Of Uranium Doping And Thermal Neutron Irradiation On The Flux-Pinning Of Silver-Clad Bi-Sr-Ca-Cu-O Tapes, D. Marinaro, S X. Dou, J. Horvat, J. Boldeman, R. Weinstein, R. Sawh
Josip Horvat
Ag/Bi-2223 tapes doped with small quantities of 235UO 4 powder were prepared by the powder-in-tube process and irradiated in a thermal neutron environment. Substantial improvements in critical current density (Jc)-applied field (H) performance and anisotropy have been previously reported. However, the radioactivity of the silver sheath is a limiting factor for commercial and industrial applications of this technique. Here we report the performance of the technique using various doping levels (from 0.15 to 2 percent by weight (wt.%) UO4) and thermal neutron fluences (Φn), in order to further reduce the silver radioactivity. Optimum fluence levels are identified and an optimum …
Effect Of Grain Size And Doping Level Of Sic On The Superconductivity And Critical Current Density In Mgb/Sub 2/ Superconductor, Saeid Soltanian, Xiaolin Wang, J. Horvat, M. J. Qin, Hua-Kun Liu, P. R. Munroe, S. X. Dou
Effect Of Grain Size And Doping Level Of Sic On The Superconductivity And Critical Current Density In Mgb/Sub 2/ Superconductor, Saeid Soltanian, Xiaolin Wang, J. Horvat, M. J. Qin, Hua-Kun Liu, P. R. Munroe, S. X. Dou
Josip Horvat
SiC doped MgB/sub 2/ polycrystalline samples were fabricated by in-situ reaction using different grain sizes (20 nm, 100 nm, and 37 /spl mu/m) of SiC and different doping levels (0, 8, 10, 12, 15 wt%). Phases, microstructures, superconductivity, critical current density and flux pinning have been systematically investigated using XRD, SEM, TEM, and magnetic measurements. Results show that grain sizes of the starting precursors of SiC have a strong effect on the critical current density and its field dependence. The smaller the SiC grains are, the better the J/sub c/ field performance is. Significant enhancement of J/sub c/ and the …
Uranium Doping And Thermal Neutron Irradiation Flux Pinning Effects In Mgb2, Tania M. Silver, J. Horvat, M. Reinhard, P. Yao, S. Keshavarzi, P. Munroe, S. X. Dou
Uranium Doping And Thermal Neutron Irradiation Flux Pinning Effects In Mgb2, Tania M. Silver, J. Horvat, M. Reinhard, P. Yao, S. Keshavarzi, P. Munroe, S. X. Dou
Josip Horvat
The U/n method is a well-established means of improving flux pinning and critical current performance in cuprate superconductors. The method involves the doping of the superconductor with 235U followed by irradiation with thermal neutrons to promote fission. The resultant columnar damage tracks produced by the energetic fission products pin flux vortices and improve critical current performance in magnetic fields. No such improvement could be observed when the U/n method was applied to the MgB2 superconductor. No fission tracks could be observed in TEM, even for samples that were irradiated at the highest fluence. Gamma-ray spectroscopy indicated that fission had occurred …
An Alternative Method For Determination Of The Lock-In Angle In Twinned Superconductors, S. Keshavarzi, J. Horvat, Alexey Pan, M. J. Qin, S. X. Dou, X. Yao, P. Munroe
An Alternative Method For Determination Of The Lock-In Angle In Twinned Superconductors, S. Keshavarzi, J. Horvat, Alexey Pan, M. J. Qin, S. X. Dou, X. Yao, P. Munroe
Josip Horvat
An alternative method for determining the lock-in angle phiL for pinning of the vortices on extended defects has been developed. This method does not require any preassumed criterion for defining phiL. Highly twinned Sm1+xBa2–xCu3O6+y single crystal was used for demonstrating the method. Appropriate scaling of the hysteresis loops measured for different angles between the field and twin planes in highly twinned SmBaCuO single crystal led to a clear discrimination between two vortex dynamics regimes. From this scaling, the lock-in angle was determined to be 6°±0.1° for the single crystal investigated. This method significantly reduces the uncertainty in determining the lock-in …
Thermal Activation And Ac-Field-Induced Discontinuous Domain Jumps In Perovskite La0.7ca0.3mno3, Xiaolin Wang, J. Horvat, Hua-Kun Liu, S. X. Dou
Thermal Activation And Ac-Field-Induced Discontinuous Domain Jumps In Perovskite La0.7ca0.3mno3, Xiaolin Wang, J. Horvat, Hua-Kun Liu, S. X. Dou
Josip Horvat
Low-field ac susceptibility was measured on bulk La0.7Ca0.3MnO3 prepared by a partial melting technique. Discontinuous jumps with heights of (1 - 2)105 emu at temperature intervals of 3-5 K were observed in the ac susceptibility. 28 jumps were observed in the temperature range between 4.2 K and the Curie temperature of 250 K, with an ac field amplitude of 1 Oe, a frequency of 117 Hz, and a dc bias field of 5 and 20 Oe. Upon increasing the frequency up to 5000 Hz, the jumps shifted to lower temperature. For a dc bias field of 50 Oe and an …
The Relevance Of The Self-Field For The 'Peak Effect' In The Transport Jc(H) Of Iron-Sheathed Mgb2 Wires, J. Horvat, Saeid Soltanian, W. K. Yeoh
The Relevance Of The Self-Field For The 'Peak Effect' In The Transport Jc(H) Of Iron-Sheathed Mgb2 Wires, J. Horvat, Saeid Soltanian, W. K. Yeoh
Josip Horvat
Ferromagnetic sheath around a superconducting wire results in an unusual transport Jc(H). For the field perpendicular to the current, there is a plateau in Jc(H) at high temperatures and intermediate fields. This plateau develops into a peak at lower temperatures, resembling a “peak effect”. A model based on cancellation of the self-field of the current and external field within the iron sheath was proposed for the explanation of the plateau in Jc(H). We test this model in three key experiments. Firstly, we show that the form of Jc(H) for round MgB2/Fe wires is strongly temperature dependent. This is in contradiction …
Transport Critical Current Density In Fe-Sheathed Nano-Sic Doped Mgb/Sub 2/ Wires, S X. Dou, J. Horvat, Saeid Soltanian, Xiaolin Wang, M. J. Qin, S. H. Zhou, Hua-Kun Liu, P. G. Munroe
Transport Critical Current Density In Fe-Sheathed Nano-Sic Doped Mgb/Sub 2/ Wires, S X. Dou, J. Horvat, Saeid Soltanian, Xiaolin Wang, M. J. Qin, S. H. Zhou, Hua-Kun Liu, P. G. Munroe
Josip Horvat
The nano-SiC doped MgB/sub 2//Fe wires were fabricated using a powder-in-tube method and an in-situ reaction process. The depression of T/sub c/ with increasing SiC doping level remained rather small due to the counterbalanced effect of Si and C co-doping. The high level SiC co-doping allowed creation of the intra-grain defects and nano-inclusions, which act as effective pinning centers, resulting in a substantial enhancement in the J/sub c/(H) performance. The transport J/sub c/ for all the wires is comparable to the magnetic J/sub c/ at higher fields despite the low density of the samples and percolative nature of current. The …
Superconductivity And Flux Pinning In Y And Heavily Pb Codoped Bi-2212 Single Crystals, Xiaolin Wang, Hua-Kun Liu, S X. Dou, J. Horvat, D. Millikon, G. Heine, W. Lang, H. M. Luo, Shichao Ding
Superconductivity And Flux Pinning In Y And Heavily Pb Codoped Bi-2212 Single Crystals, Xiaolin Wang, Hua-Kun Liu, S X. Dou, J. Horvat, D. Millikon, G. Heine, W. Lang, H. M. Luo, Shichao Ding
Josip Horvat
Studies of superconductivity and flux pinning were carried out on (Bi1.64Pb0.36)Sr2Ca1–xYxCu2O8 + y (x = 0, 0.05, 0.11, 0.33) single crystals grown by the self-flux method. X-ray diffraction, transport, and magnetic measurements were performed for purposes of characterization. X-ray analysis revealed that the c lattice parameter systemically decreases as the Y doping level increases. The superconducting transition temperature Tc decreases from 80 to 30 K as x increases. A strong annealing effect on Tc and superconducting volume has been observed. Resistance measurements show that x = 0.33 samples are semiconductive over a wide temperature range between 4.2 and 300 K …
Effect Of Heating Rates On Superconducting Properties Of Pure Mgb2, Carbon Nanotube- And Nano-Sic-Doped In Situ Mgb2/Fe Wires, S. K. Chen, K. S. Tan, B. A. Glowacki, W. K. Yeoh, Saeid Soltanian, J. Horvat, S. X. Dou
Effect Of Heating Rates On Superconducting Properties Of Pure Mgb2, Carbon Nanotube- And Nano-Sic-Doped In Situ Mgb2/Fe Wires, S. K. Chen, K. S. Tan, B. A. Glowacki, W. K. Yeoh, Saeid Soltanian, J. Horvat, S. X. Dou
Josip Horvat
The influence of heating rates and annealing temperatures on the transition temperatures (Tc) and critical current densities (Jc) of pure MgB2, carbon nanotube- and nano-SiC-doped in situ monofilamentary MgB2/Fe wires was investigated. It was found that higher Jc was obtained for pure MgB2 samples when heat treated with slower heating rates. SiC-doped samples also have higher Jc with slower heating rates, but the Jc is less sensitive to annealing temperatures. However, the Jc of the carbon nanotube-doped wire was found to be insensitive to heating rates. The variation in Tc and Jc with heating rate, and the different behaviors of …
Intense Vortex Pinning Enhanced By Semicrystalline Defect Traps In Self-Aligned Nanostructured Mgb2, S. Li, T. White, K. Laursen, T. T. Tan, C. Q. Sun, Z. L. Dong, Y. Li, S. H. Zho, J. Horvat, S. X. Dou
Intense Vortex Pinning Enhanced By Semicrystalline Defect Traps In Self-Aligned Nanostructured Mgb2, S. Li, T. White, K. Laursen, T. T. Tan, C. Q. Sun, Z. L. Dong, Y. Li, S. H. Zho, J. Horvat, S. X. Dou
Josip Horvat
In this work, we report the discovery of a vortex pinning source: semicrystalline defect wells in self-aligned nanostructured MgB2. It is demonstrated that these aperiodic regions trap numerous crystal defects migrating along nanodomain boundaries during self-alignment and act as intense vortex pinning centers that significantly enhance the high-field performance of MgB2. This suggests that the density of trapped defects in the wells is much greater than that found in other vortex pinning sources.
Superconductivity, Critical Current Density, And Flux Pinning In Mgb2–X(Sic)X/2 Superconductor After Sic Nanoparticle Doping, S X. Dou, A. V. Pan, S. Zhou, M. Ionescu, Xiaolin Wang, J. Horvat, Hua-Kun Liu, P. R. Munroe
Superconductivity, Critical Current Density, And Flux Pinning In Mgb2–X(Sic)X/2 Superconductor After Sic Nanoparticle Doping, S X. Dou, A. V. Pan, S. Zhou, M. Ionescu, Xiaolin Wang, J. Horvat, Hua-Kun Liu, P. R. Munroe
Josip Horvat
We investigated the effect of SiC nanoparticle doping on the crystal lattice structure, critical temperature Tc, critical current density Jc, and flux pinning in MgB2 superconductor. A series of MgB2–x(SiC)x/2 samples with x = 0–1.0 were fabricated using an in situ reaction process. The contraction of the lattice and depression of Tc with increasing SiC doping level remained rather small most likely due to the counterbalancing effect of Si and C co-doping. The high level Si and C co-doping allowed the creation of intragrain defects and highly dispersed nanoinclusions within the grains which can act as effective pinning centers for …
Effect Of Carbon Substitution On The Superconducting Properties Of Mgb2 Doped With Multi-Walled Carbon Nanotubes And Nano Carbon, W. K. Yeoh, J. Horvat, J. H. Kim, X. Xu, S. X. Dou
Effect Of Carbon Substitution On The Superconducting Properties Of Mgb2 Doped With Multi-Walled Carbon Nanotubes And Nano Carbon, W. K. Yeoh, J. Horvat, J. H. Kim, X. Xu, S. X. Dou
Josip Horvat
We have fabricated the multiwalled carbon nanotube (MWCNT) and nano-C doped MgB2 bulk and wire to investigate the effect of carbon substitution in theMgB2. Carbon substitution into boron site was confirmed by the shrinkage of the lattice parameter with the increasing of the doping level. It was found that the lattice distortion and optimum doping level are different in the CNT and nano-C samples. This can be explained by carbon substitution, which is a more direct substitution process with the nano-C precursor. With CNT doping, carbon substitution only occurred after break out of carbon atoms from CNT. Both dopants showed …
Effects Of Fission-Fragment Damage On Vortex Dimensionality In Silver-Sheathed Bi2sr2ca2cu3ox Tapes, D. G. Marinaro, J. Horvat, S X. Dou
Effects Of Fission-Fragment Damage On Vortex Dimensionality In Silver-Sheathed Bi2sr2ca2cu3ox Tapes, D. G. Marinaro, J. Horvat, S X. Dou
Josip Horvat
We report on the vortex dimensionality of uranium-doped Ag/Bi2223 tapes, before and after irradiation to a thermal-neutron fluence. The effective activation energies, as a function of current density and applied field, were calculated from dynamic magnetization relaxation measurements. A dimensional crossover from a three-dimensional (3D) elastic creep regime to a 2D plastic creep was observed in the nonirradiated tape at an applied magnetic field µ0Hcr[approximate]0.37 T, with an associated change in the flux hop velocity and temperature dependence. After the introduction of the fission-fragment damage by irradiation, a shift in the crossover to µ0Hcr[approximate]0.65 T was observed. These results indicate …
Oxygen Vacancy Ordering And Magnetism In The Rare Earth Stabilised Perovskite Form Of “Srco3-D, M. James, D. Cassidy, K. F. Wilson, J. Horvat, R. L. Withers
Oxygen Vacancy Ordering And Magnetism In The Rare Earth Stabilised Perovskite Form Of “Srco3-D, M. James, D. Cassidy, K. F. Wilson, J. Horvat, R. L. Withers
Josip Horvat
We have demonstrated that SrCoO3-d can be stabilised into phase pure perovskite forms by the introduction of small amounts ~5% of certain rare earth ions (Sm3+ - Yb3+). At the same doping levels, La3+ and Pr3+ crystallise with the same isostructural trigonal structure as SrCoO3-d; while the Nd3+ composition shows a mixture of both structure types. Powder X-ray diffraction showed only a simple cubic perovskite structure, however a combination of electron and neutron diffraction has revealed a tetragonal (P4/mmm) ap x ap x 2ap superstructure. Strontium and the rare earth ions are disordered over a single site, while the oxygen …
Anomalous Magnetization Peak Effect In Spiral-Grown Bi2sr2cacu2oy Crystals, Xiaolin Wang, J. Horvat, Hua-Kun Liu, J. N. Li, S. X. Dou
Anomalous Magnetization Peak Effect In Spiral-Grown Bi2sr2cacu2oy Crystals, Xiaolin Wang, J. Horvat, Hua-Kun Liu, J. N. Li, S. X. Dou
Josip Horvat
Magnetic hysteresis loops were measured on spiral-grown Bi2Sr2CaCu2Oy (Bi-2212) crystals. An anomalous peak effect at a magnetic field of 1000–2000 Oe was observed both in high-Tc (86 K) and oxygen underdoped (Tc=76 K) spiral-grown crystals between 20 and 40 K. The peak effect was observed to be stronger than that induced by oxygen vacancies, defect dislocation networks reported in Bi-2212 crystals. Further, the anomalous peak almost completely disappeared after removing growth spiral patterns from the crystal surface. Edge barriers associated with the growth spirals are suggested to be responsible for the strong peak effect for the spiral-grown Bi-2212 crystals and …
Effect Of Sample Size On Magnetic Jc For Mgb2 Superconductor, J. Horvat, Saeid Soltanian, Xiaolin Wang, S. X. Dou
Effect Of Sample Size On Magnetic Jc For Mgb2 Superconductor, J. Horvat, Saeid Soltanian, Xiaolin Wang, S. X. Dou
Josip Horvat
A strong effect of sample size on magnetic Jc(H) was observed for bulk MgB2 when Jc is obtained directly from the critical state model. Thus obtained zero-field Jc (Jc0) decreases strongly with the sample size, attaining a constant value for the samples larger than a few millimetres. On the other hand, the irreversibility field (Hirr) defined at Jc = 100 A/cm2 increases with the sample size. The decrease of Jc0 is described in terms of voids in the bulk MgB2 samples and superconducting screening around the cells of superconducting material between these voids (35 micro-m), because of concentration of the …
Magnetic Hysteresis And Relaxation In Bi2212 Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, G. D. Gu, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Magnetic Hysteresis And Relaxation In Bi2212 Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, G. D. Gu, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Josip Horvat
Magnetic hysteresis and magnetic relaxation measurements have been performed to study vortex pinning behaviors for pure, Fe doped and heavily Pb doped Bi2212 single crystals. Unlike pure and Fe doped Bi2212 crystals, heavily Pb doped crystal showed strong vortex pinning behavior. We interpret the strong pinning in heavily Pb doped Bi2212 single crystals as arising from the improved Josephson coupling in Bi2212 single crystal after heavy Pb doping. In heavily Pb doped single Bi2212 crystals, H/sub dis/(T) was observed to decrease with increasing T. Here, H/sub dis/(T) is an order-disorder field that separates a weakly elastically disordered vortex lattice from …