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Articles 31 - 47 of 47
Full-Text Articles in Engineering
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
Shi Xue Dou
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 Sucrose (C12h22o11) Doping On The Critical Current Density Of Mgb2, Y. Zhang, S. Zhou, Alexey Pan, S. X. Dou
Effect Of Sucrose (C12h22o11) Doping On The Critical Current Density Of Mgb2, Y. Zhang, S. Zhou, Alexey Pan, S. X. Dou
Shi Xue Dou
MgB2 bulk samples doped with sucrose were fabricated with the formula MgB2-x Cx ( x= 0, 0.08, 0.12, 0.2, 0.3, 0.5). Appropriate amounts of sucrose corresponding to the desired carbon content were added. The doping effect of sucrose was observed. It was found that samples doped with x = 02 sucrose have optimized current density at high magnetic field. The optimized sintering temperature for high current density was found to be 850 C. H 2 and H irr were both found to be improved due to the sucrose doping.
Dependence Of The Flux-Creep Activation Energy On Current Density And Magnetic Field For The Mgb2 Superconductor, M. J. Qin, Xiaolin Wang, Saeid Soltanian, Aihua Li, Hua-Kun Liu, S. X. Dou
Dependence Of The Flux-Creep Activation Energy On Current Density And Magnetic Field For The Mgb2 Superconductor, M. J. Qin, Xiaolin Wang, Saeid Soltanian, Aihua Li, Hua-Kun Liu, S. X. Dou
Shi Xue Dou
Systematic ac susceptibility measurements have been performed on a MgB2 bulk sample. We demonstrate that the flux creep activation energy is a nonlinear function of the current density U(j)∝j-0.2, indicating a nonlogarithmic relaxation of the current density in this material. The dependence of the activation energy on the magnetic field is determined to be a power law U(B)∝B-1.33, showing a steep decline in the activation energy with the magnetic field, which accounts for the steep drop in the critical current density with magnetic field that is observed in MgB2. The irreversibility field is also found to be rather low, therefore, …
On The Limiting Mechanism Of Irradiation Enhancement Of I/Sub C/, A. Gandini, R. Weinstein, D. Parks, R. Sawh, S. X. Dou
On The Limiting Mechanism Of Irradiation Enhancement Of I/Sub C/, A. Gandini, R. Weinstein, D. Parks, R. Sawh, S. X. Dou
Shi Xue Dou
Irradiation may significantly increase I/sub c/ in HTS. A systematic pattern occurs: R=I/sub c/(afterirr.)/I/sub c/(beforeirr.) increases at low defect density, d. It reaches a peak, and then it falls below 1 at high d. The pinning center mechanism, which causes R to increase, has been extensively studied. The falloff in R has not. It has been considered a secondary effect. Here, we will show that the fall-off plays an important role in determining the maximum I/sub c/ enhancement achievable. A phenomenological model to describe the R-vs.-d curve, over the entire d range, is proposed. The idea is that R is …
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
Shi Xue Dou
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.
Magneto-Optical Images Of Ag/Bi-2223 Tapes Processed By Flat Rolling, “Sandwich” Rolling And Pressing, Hua-Kun Liu, A. Polyanskii, W. M. Chen, Y. C. Guo, S. X. Dou, M. Apperley
Magneto-Optical Images Of Ag/Bi-2223 Tapes Processed By Flat Rolling, “Sandwich” Rolling And Pressing, Hua-Kun Liu, A. Polyanskii, W. M. Chen, Y. C. Guo, S. X. Dou, M. Apperley
Shi Xue Dou
Magneto-optical imaging (MOI) has been used for study Ag/Bi-2223 tapes processed using flat rolling, “sandwich” rolling, and pressing methods for the intermediate mechanical deformation in powder-in-tube process. The results show that not only the density of the microcracks but also their distribution affect Jc. Rolled tapes have a higher density of microcracks than pressed tapes. Although the flat rolled tape and “sandwich” rolled tape have the same level density of microcracks at the same reduction, the cracks in the former are more in the transverse direction than in the latter. In all three cases, Jc reaches a maximum value at …
Transport Properties Of Multilayered Mgb2/Mg2si Superconducting Thin Film, Y. Zhao, M. J. Qin, S X. Dou, M. Ionescu, P. Munroe
Transport Properties Of Multilayered Mgb2/Mg2si Superconducting Thin Film, Y. Zhao, M. J. Qin, S X. Dou, M. Ionescu, P. Munroe
Shi Xue Dou
Electronic transport measurements have been carried out on superconducting MgB2/Mg2Si multilayer film, using a standard four-probe method in perpendicular and parallel applied fields. The film, which was prepared by pulsed-laser deposition, has a layered structure with each MgB2 layer being 40–50 nm thick and the Mg2Si interlayers about 5 nm thick. The flux flow activation energy is deduced from the resistivity-temperature curves using an Arrhenius fit. The results show a clearly enhanced anisotropy of the vortex activation energy in the multilayered film. The irreversibility field and the vortex activation energy are significantly increased in parallel fields.
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
Shi Xue Dou
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 …
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
Shi Xue Dou
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 …
Synthesis Of Layered-Structure Limn1–Xcrxo2 By The Pechini Method, Z. P. Guo, S. Zhong, G. X. Wang, G. W. Walter, Hua-Kun Liu, S. X. Dou
Synthesis Of Layered-Structure Limn1–Xcrxo2 By The Pechini Method, Z. P. Guo, S. Zhong, G. X. Wang, G. W. Walter, Hua-Kun Liu, S. X. Dou
Shi Xue Dou
LiMn1-xCrxO2 compounds with an α-NaFeO2 layer-type crystal structure have been prepared by the Pechini method. The effects of ethylene glycol (EG) content and calcination temperature on powder characteristics and electrochemical performance are evaluated. It is found that the homogeneity of the powder is increased by increasing the molar ratio of EG to citric acid, and a trace of MnO can be detected in the powder calcined below 800°C for 4 h. Compared with the ss-LiMn1-xCrxO2 powder (made by the solid-state reaction), the p-LiMn1-xCrxO2 compound (made by the Pechini method) yielded higher specific capacity for both charge and discharge, and the …
Dip Effect In Ac Susceptibility Due To Surface Barrier With Flux Creep, X. Leng, Shichao Ding, Y. Liu, Z. H. Wang, Hua-Kun Liu, S. X. Dou
Dip Effect In Ac Susceptibility Due To Surface Barrier With Flux Creep, X. Leng, Shichao Ding, Y. Liu, Z. H. Wang, Hua-Kun Liu, S. X. Dou
Shi Xue Dou
A model is proposed to describe the effect of surface barrier (SB) on ac susceptibility (ACS) and a different kind of dip effect ~DE! in ACS is observed. Simulation based on this model with flux creep reveals two dips in ACS curve, one at temperature Td8 in real part x8 and the other at temperature Td9 in imaginary part x9. These two dips are different from the ones resulting from the peak effect in critical current density jc , where the dips in x8 and x9 occur at the same temperature Tp . The DE is also characterized by a …
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
Shi Xue Dou
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 …
Influence Of Ball-Milled Low Purity Boron Powder On The Superconductivity Of Mgb2, X. Xu, J. H. Kim, W. K. Yeoh, M. Rindfleisch, M. Tomsic, D. I. Dos Santos, S. X. Dou
Influence Of Ball-Milled Low Purity Boron Powder On The Superconductivity Of Mgb2, X. Xu, J. H. Kim, W. K. Yeoh, M. Rindfleisch, M. Tomsic, D. I. Dos Santos, S. X. Dou
Shi Xue Dou
MgB2 samples were prepared using as-supplied commercial 96% boron with strong crystalline phase and the same 96% boron (B) after ball milling. The effects of the properties of the starting B powder on the superconductivity were evaluated. We observed that samples using ball-milled 96% B, in comparison with the one made from the as-supplied 96% B, were characterized by small grain size, broadened full width at half maximum (FWHM), and enhanced magnetic critical current density ( ). reached 2 103 Acm 2 at 5 K and 8 T. The improved pinning of these samples seems to be caused by enhanced …
Calculation Of The Hysteretic Force Between A Superconductor And A Magnet, M. J. Qin, G. Li, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Calculation Of The Hysteretic Force Between A Superconductor And A Magnet, M. J. Qin, G. Li, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Shi Xue Dou
The magnetic levitation forces exerted on a high-temperature superconducting (HTS) disk by a cylindrical permanent magnet (PM) are calculated from first principles for superconductors with finite thickness. The current j(p,z) and field B(p,z) profiles in the HTS in the nonuniform magnetic field generated by the PM are derived. The levitation force depends nonlinearly on the critical current density jc and on the thickness of the HTS. The flux creep is described by a current-voltage law E( j)=Ec( j/ jc)n, from which we show that the levitation force depends on the speed at which the PM approaches or recedes from the …
Co Valence By K-Edge X-Ray Absorption Spectroscopy, Magnetic Properties, And Structure Of Polycrystalline Bulk Zn/Sub 1-X/Co/Sub X/O, Germanas Peleckis, Xiaolin Wang, R. S. Liu, S. X. Dou
Co Valence By K-Edge X-Ray Absorption Spectroscopy, Magnetic Properties, And Structure Of Polycrystalline Bulk Zn/Sub 1-X/Co/Sub X/O, Germanas Peleckis, Xiaolin Wang, R. S. Liu, S. X. Dou
Shi Xue Dou
We report on magnetic properties and a Co K-edge X-ray absorption spectroscopy (XAS) study of polycrystalline bulk Zn1-xCoxO (x=0.10,0.15,0.17) samples. All samples show paramagnetic behavior and no ferromagnetism was observed. XAS results showed that for all samples the valence of Co is 2+. Spin state assessment derived from Currie-Weiss fitting indicated a possible spin state transition from Co2+ high spin to Co2+ low spin. Calculated μeff values for samples with x=0.10 and 0.15 indicated an orbital contribution to the effective magnetic moment of the Co ion.
Intergranular And Intragranular Critical Currents In Silver-Sheathed Pb-Bi-Sr-Ca-Cu-O Tapes, K. Muller, C. Andrikidis, Hua-Kun Liu, S. X. Dou
Intergranular And Intragranular Critical Currents In Silver-Sheathed Pb-Bi-Sr-Ca-Cu-O Tapes, K. Muller, C. Andrikidis, Hua-Kun Liu, S. X. Dou
Shi Xue Dou
The role of the intergranular and intragranular critical current densities in silver-sheathed Pb-Bi-Sr-Ca-Cu-O tapes is investigated by means of magnetic-moment measurements in perpendicular field at different temperatures using a superconducting quantum interference device magnetometer. We find that low-field magnetic-moment loops are mainly caused by the intergranular (transport) critical current density JcJ but that in high fields the contribution from the intragranular critical current density JcG becomes significant. The low-field data can be described well in terms of a critical-state model for a thin strip of a homogeneous type-II superconductor in a perpendicular field where JcJ flows over the entire tape. …
Infrared-Active Phonons Of Homn/Sub 1-X/Co/Sub X/O/Sub 3/ (X = 0-0.8), Feng Gao, Xiaolin Wang, M Mehdi Farhoudi, R. A. Lewis, S. X. Dou
Infrared-Active Phonons Of Homn/Sub 1-X/Co/Sub X/O/Sub 3/ (X = 0-0.8), Feng Gao, Xiaolin Wang, M Mehdi Farhoudi, R. A. Lewis, S. X. Dou
Shi Xue Dou
Polycrystalline HoMn/sub 1-x/Co/sub x/O/sub 3/ was synthesized by solid-state reaction. The infrared active phonons of the samples were investigated. The infrared transmission spectra of the sample at x = 0-0.8 doping level was also measured at room temperature. Also, X-ray diffraction (XRD) was used to analyze the crystal structure of the samples.