Ge Tape Research Articles

Strain effect in the critical current densities of superconducting Nb3Ge tapes

The dependence of the critical current density in chemical-vapor-deposited Nb3Ge tapes on tensile strain was investigated in magnetic fields up to 14 T perpendicular to the tape plane. The pinning force density Fp was found to be well represented by the strain scaling relation, Fp=c[Hc2(ε)]0.93h0.46(1−h)2.4, where Hc2(ε) is the upper critical field dependent on the applied strain ε and h is the reduced magnetic field H/Hc2(ε). For the Nb3Ge tapes studied, Hc2(ε) was found to be expressed by the form Hc2(ε)=Hc2(εm)[1−1550‖ε0‖1.92], where εm is the applied strain corresponding to zero intrinsic strain and ε0 is an intrinsic strain expressed by ε−εm. From the strain scaling relation, the values of the maximum upper critical field corresponding to the zero intrinsic strain, Hc2(εm), were calculated as 27.2 T for the Nb3Ge tape with 10.6-μm-thick Nb3Ge layers and a critical temperature Tc (midpoint) of 19.6 K, and 24.8 T for the Nb3Ge tape with 1.3-μm-thick Nb3Ge layers and Tc of 18.3 K. For these same tapes, the critical fields at the zero applied strain, Hc2(0), were 25.7 and 22.8 T, respectively.

Crystal structure of the ordered Nb 10Ge 7 phase

The structure of a new ordered phase, Nb 10Ge 7 (or Nb 5Ge 3Ge 0.5; trigonal), is described on the basis of electron microscopic and electron diffraction data. The new phase was found in a Nb Ge tape prepared by the coevaporation technique. The new structure can be derived from the hexagonal D8 8-structure of Nb 5Ge 3 by periodically inserting Ge-atoms at octahedral sites. The lattice parameters of this structure can be described as follows, using the lattice parameters of the D8 8-structure a= √3 ·a Nb 5Ge 3(D 88 and c=C Nb 5Ge 3(D 88) in hexagonal description. The grains of this phase are usually elongated along the c-direction. Structural data of the new phase: Nb 10Ge 7,trigonal, hP51, P 3¯2/ml,a= 1.337nm,c= 0.537nm,Z= 3,V Nb 10Ge 7 ≈ 3V Nb 5Ge 3(D 88) . The structure represents a new structure type with an ordered atom arrangement, intermediate between the Mn 5Si 3 type and the Ti 5Ga 4 type, in which the octahedral sites are only partly occupied.

Nb3Al AND Nb3(Al,Ge) SUPERCONDUCTING TAPES BY LASER BEAM ANNEALING

ABSTRACT Nb3Al AND Nb3(Al,Ge) tapes with excellent superconducting properties have been fabricated using high energy density laser beam irradiation, irradiations were carried out continuously on Nb-25at%AI and Nb-20at%Al -5at%Ge tapes prepared by powder metallurgical processing. With the high power density and short irradiation time, the tape could be heated and cooled much faster than a tape heat treated by conventional methods. The results were fine structure and large critical current density Jc values at high magnetic fields. Jc at 23 Tesla was over 104 A/cm2. This value was much greater than that obtained from a commercial Nb3Sn superconductor. New continuous irradiation systems have been developed for scale-up development. Nb3Al tapes 10 m in length were successfully fabricated. There was some scatter in Jc along the tape length. Small coil tests in magnetic fields indicated that the tape had excellent stability against a flux jump and mechanical strain.

Effects of H2/Cl2 ratio on CVD synthesis of superconducting Nb3Ge tapes

Abstract This Paper investigates the effects of H 2 /Cl 2 ratio, R g , [H 2 /Cl 2 (Nb,Ge)] in chemical vapour deposition processes on the synthesis and superconducting properties of Nb 3 Ge tapes. Critical temperature, T c , critical current density, J c , and grain size of A15 Nb 3 Ge vary considerably with the gas ratio, R g . The lattice parameter of A15 Nb 3 Ge and its volume ratio to Ge-rich Nb 5 Ge 3 phases are also dependent on R g . The volume ratio of A15 Nb 3 Ge to Nb 5 Ge 3 increases with increasing R g , while the grain size of Nb 3 Ge considerably decreases. The highest T c , 19 K, (mid-point) was obtained for Nb 3 Ge tape where the A15 Nb 3 Ge compound coexisted with a small amount of tetragonal or hexagonal Nb 5 Ge 3 compounds. The largest J c was ≈ 4.5 × 10 8 A m −2 at 16 T and 4.2 K.

Preparation of A15 Nb<inf>3</inf>Ge tape by a single-roller rapid quenching technique

We have Prepared a high Tc Nb 3 Ge tape by using a single-roller rapid quenching apparatus specially made for high melting point alloy applications. The rapid quenching of Nb 3 Ge produced amorphous ribbons for compositions at Ge = 21 ∼ 27at %. Heat-treatment at 700° c for 100 hours converted these amorphous ribbons into nearly single phase A15 (Ge = 21 ∼ 24at.%) and A15+Nb 5 Ge 3 (Ge = 25 ∼ 27at.%). The superconducting transition temperature Tc was about 4K for the amorphous phase, While the heat-treatment improved Tc values considerably; the highest Tc value, 18.3K(onset) with ΔTc=0.6K, was obtained from Ge=23at.%.

A small Nb<inf>3</inf>Ge test solenoid

Behaviour and properties of a small test solenoid made from a long piece of stabilized Nb 3 Ge superconductor prepared by the CVD method are described. The used CVD apparatus allows to prepare continuously pieces of more than 200 m in length. A total length of 43.5 m of the 61 m long Nb 3 Ge tape has been used for a construction of a test solenoid. The solenoid properties were measured in an outside magnetic field produced by 40 mm bore superconducting magnet. The contribution of the test solenoid was 0.84 T in the total magnetic field of 4.35 T and 0.42 T in the total field of 9.25 T.

Nb<inf>3</inf>Al and Nb<inf>3</inf>(Al,Ge) composite tapes fabricated by CO<inf>2</inf>laser beam irradiation

Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Al and Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Al,Ge) tapes with excellent superconducting properties were fabricated by the laser beam irradiation method. Nb-25 at %Al and Nb-20 at % Al-5 at % Ge tapes were prepared by the powder metallurgy process. Continuous CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser beam irradiation was carried out on the tape surface in an argon gas atmosphere at 1-13m/min, velocities. Beam power was 0.3-4kW and beam diameter at the tape surface was 0.5-3mm. As the power density was high and irradiation time was short, the tape could be heated and cooled much faster than a tape that was heat treated by the conventional method. The results were fine grain structure and large J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values at high magnetic fields. T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> for an as-irradiated tape was 16-18K. This T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> increased by ∼2K by the subsequent annealings at 700°C for 100 hours. The maximum T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (onset) values obtained were 18.6K for the Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Al tape and 20.1K for the Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Al,Ge) tape, which indicated that stoichiometric compounds could be formed by laser beam irradiation. Annealed tapes, after the irradiation, showed excellent J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values, especially at high magnetic fields. J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values over 2×10 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 23 Tesla were obtained for both Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Al and Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Al,Ge) tapes. These values are much larger than those obtained by conventional heat treatment. J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values of as-irradiated tapes at high fields were smaller than those for annealed tapes, due to the lower T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> and, hence, lower H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</inf> . The large J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values, as well as easy scale-up procedure, indicate that the laser irradiation method is promising for the fabrication of advanced superconductors, e.g. Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Al and Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Al,Ge) capable of generating fields over 20 Tesla.

Preparation of high field Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Al and Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;(Al,Ge) superconducting tapes by an electron beam annealing

Nb 3 Al and Nb 3 (Al,Ge) tape superconductors with excellent high-field properties have been successfully prepared by an electron beam annealing. The electron beam irradiation was performed on Nb-25at.%Al and Nb- 20at.%Al-5at.%Ge composite tapes moved at a velocity of 6m/min.. The accelerate voltage, current and diameter of the electron beam were 20kv, 5-20mA and 0.5-3mm, respectively. During the irradiation, the Al fibers reacted at a high temperature with surrounding Nb matrix to form A15 phase with stoichiometric composition. T c 's above 17K have been easily obtained after the electron beam irradiation, which can be increased by 1-2K by the following low temperature annealing at 700-800°C. Maximum T c 's attained for Nb-Al and Nb-Al-Ge tapes are 18.4K and 19.8K(midpoint), respectively. The J c -H curves show no degradation in high magnetic fields up to 23T, exceeding 104A/cm2. The highest overall J c (for irradiated area) at 23T and 4.2K is 3×10 4 A/cm2obtained for the Nb-Al-Ge tape. A new continuous irradiation system has been developed to fabricate longer tape of 10-100m.

電子ビーム照射により作製したNb&lt;SUB&gt;3&lt;/SUB&gt;AlおよびNb&lt;SUB&gt;3&lt;/SUB&gt;(Al, Ge) 複合テープの組織と超電導特性

Nb3Al and Nb3(Al, Ge) composite tapes with excellent superconducting properties were fabricated by the continuous electron beam irradiation method. Nb-25 at%Al and Nb-20 at%Al-5 at%Ge tapes were prepared by the powder metallurgy process using Nb-sheath. Electron beam irradiation was applied to the tape surface in a vacuum at a tape velocity of 6 m/min. The acceleration voltage, current and diameter of the electron beam were 20 kV, 5-30 mA and 0.5-3 mm, respectively. As the power density was high and the irradiation time was short, the tapes were heated and cooled much faster than a tape heat-treated by a conventional method. As a result stoichiometric A-15Nb3Al and Nb3(Al, Ge) compounds were formed without any excess grain coarsening. Tc of the as-irradiated tape was 16-18 K, which was increased by ∼2 K by a subsequent annealing at 973 K for 360 ks (100 h). The maximum Tc(onset) values obtained were 18.5 K for the Nb-Al tape and 20.2 K for the Nb-Al-Ge tape. Jc increases with increasing power density until the melting occurs and then rapidly decreases at higher power densities, due to the decrease of A-15 volume fraction. The Nb-Al and Nb-Al-Ge tapes processed under proper conditions show excellent Jc-H properties. Jc exceeds 108 A/m2 in the fields up to 25 Tesla for Nb-Al and up to 30 Tesla for Nb-Al-Ge. Jc of Nb-Al-Ge is the largest one so far obtained in the superconducting materials at ∼30 T. The large Jc values in the fields, as well as the easy scale-up procedure, indicate that the continuous electron beam irradiation method is promising for the fabrication of advanced superconductors, e.g. Nb3Al and Nb3(Al, Ge) capable of generating fields over 20 Tesla.

Development of long Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Ge tape with T&amp;lt;inf&amp;gt;c&amp;lt;/inf&amp;gt;above 20 K

Superconducting Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge tapes were prepared continuously by chemical vapor deposition. The chlorides NbCl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> and GeCl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> prepared "in situ" were used. Films were deposited on the stainless steel substrate heated by passing the direct current through it. The content of the Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge phase in the deposited layer films at constant molar ratio of NbCl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> and GeCl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> depends mainly on the heating current of the substrate as well as on the flow of the reaction gas mixture. The tapes with critical temperatures above 20 K in undoped atmosphere have been produced. The addition of oxygen into the reaction gas mixture in amount up to 0.027 mole did not lower generally the T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> 's under the 20 K value. The critical current densities of the Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge layers are from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> to 5.10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in magnetic field of 3 T.

Development of long continuous Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Ge tape conductors with high current density at elevated temperature and field

Superconductors based on Nb 3 Ge have been fabricated by the chemical vapor deposition (CVD) process in continuous lengths up to 20 m. This material exhibits a transition temperature T_{c} > 21.0 K and a self field critical current density J_{c} \geq 2.5 \times 10^{6} A/cm2@ 14 K and offers the possibility of high current operation at temperatures > 14.0 K. Values of J c measured in high magnetic fields exceed 8 \times 10^{4} A/cm2at 18T @ 4 K. The material development program that resulted in reproducing the excellent short sample superconducting properties on long continuous lengths of tape is described. The tapes consist of 3-6 μm of Nb 3 Ge coated completely around 0.64-cm-wide, 25-μm-thick substrates of Cu, Ni, or Cu-clad stainless steel. More than 150 m of this tape has been fabricated for use in winding a 1-m prototype transmission cable. AC-loss measurements on short samples of the long tapes show complete shielding of the substrate and losses which are acceptably low for power transmission applications.

High magnetic field properties of CVD-prepared Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Ge and Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;(Ge,X&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt;)

Measurements of the field dependent critical current density, J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (H), and the upper critical field, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</inf> , have been performed on a number of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge samples prepared by the chemical vapor deposition (CVD) process. These samples, obtained from up to 20 m lengths of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge tape, were deposited on various substrates at temperatures between 835 and 950°C. Flux pinning, provided by the introduction of controlled amounts of second phase precipitate, Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> Ge <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , produced good high field properties with 4.2 K critical current densities on the order of 8.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 18 T. Measurements of J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (H) performed on these samples in both liquid helium and hydrogen in fields up to 18.5T have been analyzed in terms of Kramer's model of flux pinning. Qualitative agreement has been found with the scaling laws predicted by this theory. The effect of ternary additions of Si and Ga on both H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</inf> and J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (H) have been investigated as well. Contrary to expectation, the addition of ternaries into the A-15 lattice results in somewhat depressed critical characteristics. The effect of deposition parameters on the high field properties of both Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge and Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Ge,X) will be discussed.

Superconducting Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Ge for high-field magnets

Superconducting Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge tape conductors 5 to 10 m long were fabricated by chemical vapor deposition. Such tapes could be used in high-field magnet applications. Average tape properties set the upper performance limit of a magnet at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H_{\max} = 17</tex> tesla (4.2 K). Highest critical-current densities obtained in thin and layered films set <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H_{\max} = 20</tex> tesla (4.2 K).

Teaching Oral-Aural Communication Skills in a Rehabilitation Center for the Blind

Oral-aural communication skills include listening, conversation, use of playback-recording devices, techniques of aural reading, and knowledge of the sources of recorded reading materials. The class activities involve instruction and practice with the Sony 105A tape recorder, Sony (TC70 and TC40) and GE tape cassette machines, talking book machines, and telephone. Exercises include listening and speaking skills and the many uses to which the equipment can be put.