Superconducting Bulk Samples Research Articles

Vortex instability and time effects in I–V curves of superconducting Y1Ba2Cu3O7−δ

We have investigated the effect of the current sweep rate (CSR) on the vortex dynamics in a superconducting bulk sample of Y1Ba2Cu3O7−δ. It has been found that the CSR has several effects on vortex motion in that it gives rise to enhancement of dissipation as the CSR decreases, significant time effects and instabilities in current–voltage (I–V) curves. Those anomalies are discussed in terms of depinning/pinning together with disorder in the coupling strength between the superconducting grains. In addition, for a given field and temperature domain, it is shown that the CSR together and a relevant current scale is of importance in the evolution of I–V curves.

Vortex instability and hysteresis effects in I– V curves of superconducting Y 1Ba 2Cu 3O 7− δ

We have investigated the effect of the current sweep rate (CSR) on the vortex dynamics in superconducting bulk sample of Y 1Ba 2Cu 3O 7− δ . It has been found that the CSR has several dramatic effects on the vortex motion by giving rise enhancement in dissipation as decreasing the CSR, significant time effects, and instabilities in current–voltage ( I– V) curves. The hysteresis loops concerning the I– V curves in both the current-increase and -decrease branches of the forward current region, and also the branches of the reversed current region have been observed together with a gradual diminutive of the hysteresis effects with decreasing the CSR. Due to the field and temperature domain considered, it is also observed that the moving state becomes unstable giving rise some instabilities such as small jumps and steps for both low and moderate current values as a function of CSR. Those anomalies have been discussed in terms of the depinning–pinning correlated to the plastic flow regime together with the disorder in the coupling strength between the superconducting grains, and compared qualitatively to the numerical computer simulations. In addition, for a given field and temperature domain, it has been shown that the CSR together with a relevant current scale is of importance in evolution of the I– V curves and is a useful tool in investigating the details of the vortex dynamics.

Influence of the current sweep rate on vortex dynamics in superconducting YBa 2Cu 3O 7− x

The effect of the current sweep rate (CSR) on the vortex dynamics in superconducting bulk sample of YBa 2Cu 3O 7− δ has been investigated at the temperatures near the critical temperature. It has been found that the CSR has several effects on the vortex motion by giving rise enhancement in dissipation as decreasing the CSR, significant time effects and instabilities in current–voltage ( I– V) curves. Those anomalies have been discussed in terms of the depinning/pinning together with the disorder in the coupling strength between the superconducting grains.

Spectrophotometric determination of oxygen stoichiometry in YBCO superconducting bulk samples

The spectrophotometric method [Anal. Chim. Acta 336 (1996) 223] for the determination of the non-stoichiometric oxygen in YBa 2Cu 3O 6.5+ δ superconductors is discussed. Considerable improvements in the experimental conditions of the procedure for the bulk sample analyses are made. The potassium iodide is placed in the dry beaker instead of in the funnel, and its quantity is increased to 7.5 g. Nitrilothrieacetic acid or glycine is used as a ligand for the copper(II) ions instead of ethylendiaminetetraacetic acid. A differential mode only of the absorbance measurement is used. The blank sample solution is prepared simultaneously with the sample solution, passing through all the stages of the procedure. The δ-results for the oxygen coefficient of a monophase superconducting bulk sample obtained by the improved method are accurate and more precise than these of the previous method. Their accuracy is confirmed by coulometry.

Hard materials and tool steels

We present results of a comprehensive study, both theoretical and experimental, of an ‘electromaglev’ system, in which a high-temperature superconducting bulk sample, e.g. YBa2Cu3O7 − δ (YBCO), is levitated stably in a DC magnetic field generated by electromagnets placed underneath the floating object. Results of the zeroth-order theory agree quite well with experimental results on lift-to-weight ratio and suspension stiffness for three bulk samples: (1) a solid YBCO disc; (2) a YBCO annulus; and (3) a YBCO annulus with a neodymium-iron-boron (Nd-Fe-B) permanent magnet disc (PMD) filling the centre. The experiment has also verified the need to satisfy two requirements to achieve stable levitation with a DC magnetic field only: (1) the spatial flow of the supercurrent in the sample must have at least two degrees of freedom; and (2) the electromagnets must generate a magnetic field profile that satisfies spatial requirements for lateral and pitch stability. A permanent magnet disc has only one degree of freedom for its Amperian current, thus it cannot be levitated stably in this system; the experiment has also demonstrated that an HTS solenoid (wound with silver-sheathed BSCCO-2223 tape) cannot be levitated stably, because the solenoid supercurrent flow is also restricted to the azimuthal direction only. The zeroth-order theory together with the Bean model shows that the supercurrent induced in a YBCO sample is independent of the critical current density, Jc, of the material but is directly proportional to the axial component of the field and that the lift of the sample is directly proportional to the product of the axial and radial components of the magnetic field generated by the electromagnets.

A new method to determine jc in bulk superconductor from saturated diamagnetic field by magneto-optic imaging

The diamagnetic field created by supercurrent will be saturated after superconducting bulk sample is fully penetrated by the external magnetic field. The critical current density of a sample could be determined from the saturated diamagnetic field, which is easily and precisely observed by magneto-optic imaging.

Effect of sintering conditions and addition of molybdenum on sintering of coarse iron powder : S.Unami, K.Hayashi. (University of Tokyo, Tokyo, Japan.) J. Jpn Soc. Powder Powder Metall., vol 44, no 8, 1997, 765–769. (In Japanese.)

We present results of a comprehensive study, both theoretical and experimental, of an ‘electromaglev’ system, in which a high-temperature superconducting bulk sample, e.g. YBa2Cu3O7 − δ (YBCO), is levitated stably in a DC magnetic field generated by electromagnets placed underneath the floating object. Results of the zeroth-order theory agree quite well with experimental results on lift-to-weight ratio and suspension stiffness for three bulk samples: (1) a solid YBCO disc; (2) a YBCO annulus; and (3) a YBCO annulus with a neodymium-iron-boron (Nd-Fe-B) permanent magnet disc (PMD) filling the centre. The experiment has also verified the need to satisfy two requirements to achieve stable levitation with a DC magnetic field only: (1) the spatial flow of the supercurrent in the sample must have at least two degrees of freedom; and (2) the electromagnets must generate a magnetic field profile that satisfies spatial requirements for lateral and pitch stability. A permanent magnet disc has only one degree of freedom for its Amperian current, thus it cannot be levitated stably in this system; the experiment has also demonstrated that an HTS solenoid (wound with silver-sheathed BSCCO-2223 tape) cannot be levitated stably, because the solenoid supercurrent flow is also restricted to the azimuthal direction only. The zeroth-order theory together with the Bean model shows that the supercurrent induced in a YBCO sample is independent of the critical current density, Jc, of the material but is directly proportional to the axial component of the field and that the lift of the sample is directly proportional to the product of the axial and radial components of the magnetic field generated by the electromagnets.

Carbon nitride : J.Hofmann. (PRAMET AS, Sumperk, Czech Republic.) Pokroky Praskove Metal., vol 35, no 4, 1997, 5–20. (In Czech.)

We present results of a comprehensive study, both theoretical and experimental, of an ‘electromaglev’ system, in which a high-temperature superconducting bulk sample, e.g. YBa2Cu3O7 − δ (YBCO), is levitated stably in a DC magnetic field generated by electromagnets placed underneath the floating object. Results of the zeroth-order theory agree quite well with experimental results on lift-to-weight ratio and suspension stiffness for three bulk samples: (1) a solid YBCO disc; (2) a YBCO annulus; and (3) a YBCO annulus with a neodymium-iron-boron (Nd-Fe-B) permanent magnet disc (PMD) filling the centre. The experiment has also verified the need to satisfy two requirements to achieve stable levitation with a DC magnetic field only: (1) the spatial flow of the supercurrent in the sample must have at least two degrees of freedom; and (2) the electromagnets must generate a magnetic field profile that satisfies spatial requirements for lateral and pitch stability. A permanent magnet disc has only one degree of freedom for its Amperian current, thus it cannot be levitated stably in this system; the experiment has also demonstrated that an HTS solenoid (wound with silver-sheathed BSCCO-2223 tape) cannot be levitated stably, because the solenoid supercurrent flow is also restricted to the azimuthal direction only. The zeroth-order theory together with the Bean model shows that the supercurrent induced in a YBCO sample is independent of the critical current density, Jc, of the material but is directly proportional to the axial component of the field and that the lift of the sample is directly proportional to the product of the axial and radial components of the magnetic field generated by the electromagnets.

Preparation of metal-oxide composite particles under vacuum: H.Kaga et al. (Hokkaido Industrial Technology Centre, Hokkaido, Japan.) Powder Technol., vol 91, no 2, 1997, 147–155

We present results of a comprehensive study, both theoretical and experimental, of an ‘electromaglev’ system, in which a high-temperature superconducting bulk sample, e.g. YBa2Cu3O7 − δ (YBCO), is levitated stably in a DC magnetic field generated by electromagnets placed underneath the floating object. Results of the zeroth-order theory agree quite well with experimental results on lift-to-weight ratio and suspension stiffness for three bulk samples: (1) a solid YBCO disc; (2) a YBCO annulus; and (3) a YBCO annulus with a neodymium-iron-boron (Nd-Fe-B) permanent magnet disc (PMD) filling the centre. The experiment has also verified the need to satisfy two requirements to achieve stable levitation with a DC magnetic field only: (1) the spatial flow of the supercurrent in the sample must have at least two degrees of freedom; and (2) the electromagnets must generate a magnetic field profile that satisfies spatial requirements for lateral and pitch stability. A permanent magnet disc has only one degree of freedom for its Amperian current, thus it cannot be levitated stably in this system; the experiment has also demonstrated that an HTS solenoid (wound with silver-sheathed BSCCO-2223 tape) cannot be levitated stably, because the solenoid supercurrent flow is also restricted to the azimuthal direction only. The zeroth-order theory together with the Bean model shows that the supercurrent induced in a YBCO sample is independent of the critical current density, Jc, of the material but is directly proportional to the axial component of the field and that the lift of the sample is directly proportional to the product of the axial and radial components of the magnetic field generated by the electromagnets.

Magnetic properties of sintered iron-chromium alloy in alternating field: T.Kato et al. (Daido Inst. of Technology, Nagoya, Japan.) J. Jpn Soc. Powder Powder Metall., vol 43, no 2, 1996, 226–229. (In Japanese.)

We present results of a comprehensive study, both theoretical and experimental, of an ‘electromaglev’ system, in which a high-temperature superconducting bulk sample, e.g. YBa2Cu3O7 − δ (YBCO), is levitated stably in a DC magnetic field generated by electromagnets placed underneath the floating object. Results of the zeroth-order theory agree quite well with experimental results on lift-to-weight ratio and suspension stiffness for three bulk samples: (1) a solid YBCO disc; (2) a YBCO annulus; and (3) a YBCO annulus with a neodymium-iron-boron (Nd-Fe-B) permanent magnet disc (PMD) filling the centre. The experiment has also verified the need to satisfy two requirements to achieve stable levitation with a DC magnetic field only: (1) the spatial flow of the supercurrent in the sample must have at least two degrees of freedom; and (2) the electromagnets must generate a magnetic field profile that satisfies spatial requirements for lateral and pitch stability. A permanent magnet disc has only one degree of freedom for its Amperian current, thus it cannot be levitated stably in this system; the experiment has also demonstrated that an HTS solenoid (wound with silver-sheathed BSCCO-2223 tape) cannot be levitated stably, because the solenoid supercurrent flow is also restricted to the azimuthal direction only. The zeroth-order theory together with the Bean model shows that the supercurrent induced in a YBCO sample is independent of the critical current density, Jc, of the material but is directly proportional to the axial component of the field and that the lift of the sample is directly proportional to the product of the axial and radial components of the magnetic field generated by the electromagnets.

Magnetic properties of neodymium-iron-boron sintered from granulated powders: O.Yamashita, Y.Kishimoto. (Sumitomo Special Metals Co Ltd. Osaka, Japan.) J. Jpn Soc. Powder Powder Metall., vol 43, no 2, 1996, 249–255. (In Japanese.)

We present results of a comprehensive study, both theoretical and experimental, of an ‘electromaglev’ system, in which a high-temperature superconducting bulk sample, e.g. YBa2Cu3O7 − δ (YBCO), is levitated stably in a DC magnetic field generated by electromagnets placed underneath the floating object. Results of the zeroth-order theory agree quite well with experimental results on lift-to-weight ratio and suspension stiffness for three bulk samples: (1) a solid YBCO disc; (2) a YBCO annulus; and (3) a YBCO annulus with a neodymium-iron-boron (Nd-Fe-B) permanent magnet disc (PMD) filling the centre. The experiment has also verified the need to satisfy two requirements to achieve stable levitation with a DC magnetic field only: (1) the spatial flow of the supercurrent in the sample must have at least two degrees of freedom; and (2) the electromagnets must generate a magnetic field profile that satisfies spatial requirements for lateral and pitch stability. A permanent magnet disc has only one degree of freedom for its Amperian current, thus it cannot be levitated stably in this system; the experiment has also demonstrated that an HTS solenoid (wound with silver-sheathed BSCCO-2223 tape) cannot be levitated stably, because the solenoid supercurrent flow is also restricted to the azimuthal direction only. The zeroth-order theory together with the Bean model shows that the supercurrent induced in a YBCO sample is independent of the critical current density, Jc, of the material but is directly proportional to the axial component of the field and that the lift of the sample is directly proportional to the product of the axial and radial components of the magnetic field generated by the electromagnets.

‘Electromaglev’—magnetic levitation of a superconducting disc with a DC field generated by electromagnets: Part 1. Theoretical and experimental results on operating modes, lift-to-weight ratio, and suspension stiffness

We present results of a comprehensive study, both theoretical and experimental, of an ‘electromaglev’ system, in which a high-temperature superconducting bulk sample, e.g. YBa 2Cu 3O 7 − δ (YBCO), is levitated stably in a DC magnetic field generated by electromagnets placed underneath the floating object. Results of the zeroth-order theory agree quite well with experimental results on lift-to-weight ratio and suspension stiffness for three bulk samples: (1) a solid YBCO disc; (2) a YBCO annulus; and (3) a YBCO annulus with a neodymium-iron-boron (Nd-Fe-B) permanent magnet disc (PMD) filling the centre. The experiment has also verified the need to satisfy two requirements to achieve stable levitation with a DC magnetic field only: (1) the spatial flow of the supercurrent in the sample must have at least two degrees of freedom; and (2) the electromagnets must generate a magnetic field profile that satisfies spatial requirements for lateral and pitch stability. A permanent magnet disc has only one degree of freedom for its Amperian current, thus it cannot be levitated stably in this system; the experiment has also demonstrated that an HTS solenoid (wound with silver-sheathed BSCCO-2223 tape) cannot be levitated stably, because the solenoid supercurrent flow is also restricted to the azimuthal direction only. The zeroth-order theory together with the Bean model shows that the supercurrent induced in a YBCO sample is independent of the critical current density, J c , of the material but is directly proportional to the axial component of the field and that the lift of the sample is directly proportional to the product of the axial and radial components of the magnetic field generated by the electromagnets.

Electrical motor with bulk Y-Ba-Cu-O pellets

The interaction between a magnetic field and a superconducting (SC) bulk sample produces not only levitation forces but also transverse ones. They may be used in an electromagnetic coupling device to transmit a torque or in an electrical motor to produce a torque. The authors have designed and built a disk type motor (vertical axial gap) with a static three-phase armature resistive winding and a rotating part composed of eight YBaCuO pellets immersed in a liquid nitrogen vessel. The SC samples are melt textured using the top seed melt texturing method. The armature winding is fed by a power converter. Then the supplied frequency and the speed of rotation are variable. The motor was tested in different conditions and operated without magnetizing the SC samples. It works in a way as a variable reluctance motor even if the hysteresis behaviour of the SC pellets complicates the operation. Other experiments were carried out magnetizing the SC samples before their use as an inductor. The operation is close then to a permanent magnet motor. The experimental set up and the different tests are reported.

高温超電導バルク材の実効的磁束フロー抵抗率測定手法 パルス励振法

We propose a new method for measuring flux flow resistivity, and name it the “pulse-excited vibration method, ” This method is capable of evaluating effective flux flow resistivity, which is important to analyze the properties of superconducting bulk materials in a transient mode. In this paper, we describe the pulse-excited vibration method in detail, and estimate the flux flow resistivity of a superconducting bulk sample based on our model. Furthermore, the validity of this method was verified successfully by applying the measurement process to a superconducting tape.

The effect of calcination conditions on the superconducting properties of Y−Ba−Cu−O powders

Calcination conditions of the precursor powders, i.e. temperature, type of atmosphere and duration, were determined with a view to obtain superconducting powders with the most advantageous physico-chemical properties. Investigated were powders in the Y−Ba−Cu−O system prepared by the sol-gel method. Thermogravimetric examinations of the powders have revealed that the decomposition kinetics of BaCO3 determines the formation rate of the superconducting YBa2Cu3O7−x (‘123’) phase. It follows from the decomposition kinetics of BaCO3 that the process is the most intensive in argon, whereas in static air and oxygen it is the slowest. The phase composition analysis (XRD) and low-temperature magnetic susceptibility measurements of the calcinated powders, confirm the above mentioned changes in the decomposition kinetics. The reaction of barium carbonate can be completed if the calcination process is conducted at the temperature of 850°C for 25 h, yielding easily sinterable powders for obtaining single-phase superconducting bulk samples with advantageous functional parameters.

Rapid consolidation of BiPbSrCaCuO powders by a plasma activated sintering process

A new rapid powder consolidation technique—plasma activated sintering (PAS)—was used to obtain high density disk-shaped bulk superconductor samples in the BiPbSrCaCuO system. Different powder precursors prepared by the glass-ceramic route, sol-gel processing, and solid state reactions were investigated. Results of density, hardness, and critical superconducting transition temperature were compared after PAS processing of powder precursors. Microstructures showing oriented grains of the 2223 phase were obtained as a result of PAS densification in very short time frames ( <10 min).

The temperature energy gap evolution of Ba 0.6K 0.4BiO 3 by electron tunneling

We report tunneling experiments using sandwich type junctions, with superconducting bulk samples of Ba 0.6K 0.4BiO 3 and evaporated thin film Sn counterelectrodes. The tunneling characteristics show the energy gap feature, and structure in the d 2I/dV 2 curves. The results demonstrate that the temperature energy gap variation follows a BCS behavior. The ratio 2Δ/k BT c is 3.75 suggesting an intermediate coupling.

Electron tunneling in superconducting Ba0.6K0.4BiO3

Abstract We report tunneling measurements using superconducting bulk samples of Ba 0.6 K 0.4 BiO 3 and evaporated counterelectrodes of Sn. With our procedure, we find reproducible tunneling characteristics that show the gap feature and high frequency structure in the d I /d V versus V curves. This structure may be related to the phonon spectrum or to the excitations that give rise to superconductivity in these ceramic materials. The energy gap evolution with temperature follows BCS-like behavior, with ratio 2Δ/ K B T c at T =0 K in the range of intermediate coupling.

The role of specimen morphology in the preparation of High-TC superconductors for Transmission Electron Microscopy

It is vital in TEM investigations, especially for high resolution studies, that specimen quality be optimized and the information desired in a particular TEM analysis often prescribes the method of specimen preparation required. We have found that the morphology of a bulk superconductor sample can significantly influence the ultimate success of the preparation technique utilized.Methods employed for the production of electron transparent foils of ceramic oxide superconductors include mechanical grinding, cleavage, jet polishing, ultramicrotomy and ion milling. Grinding and cleavage are both low cost, quick and easy specimen preparation techniques. However, because of the layered crystal structures of these materials, they display a marked tendency to cleave along (001) planes, and hence the range of crystallographic orientations available with these methods is restricted. With grinding in particular, mechanical deformation can be a problem while with cleavage, transparent areas are confined to the vicinity of particle edges.

Superconductivity in Bi-Sr-Ca-Cu-O bulk samples made by thermal decomposition of metal oxalates

The preparation and characteristic properties of superconducting powders and ceramics in the system Bi-Sr-Ca-Cu-O were investigated. Powders of 3 different nominal compositions were prepared along the wet-chemical oxalate route. Bulk samples with high amounts of Bi 2 Sr 2 Ca 2 Cu 3 O 10-δ (high- T c phase) and zero resistance up to 105 K could be prepared between 870°C and 880°C. The influence of sintering conditions on the fabrication of superconducting bulk samples and on the formation of the high- T c compound Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ was evaluated.