Superconducting Properties of V<SUB>3</SUB>Ga Tapes Made by a Composite Process

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  • V<SUB>3</SUB>Ga複合加工テープの超電導特性
  • V3Ga複合加工テープの超電導特性
  • V3Ga フクゴウ カコウ テープ ノ チョウデンドウ トクセイ

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Effects of the Cu-Ga alloy matrix composition and the heat treatment condition on the superconducting properties of the V3Ga composite tapes have been investigated. The composite tapes were prepared by fabricating a composite of a vanadium core and Cu-Ga solid-solution alloy matrix and subsequently by heat treating at temperatures 625∼800°C for 1∼100 hr. Critical temperature, Tc of 15.1 K and critical current density, Jc of 1×105 A/cm2 at 4.2 K, 170 kOe, which are equivalent to those for the V3Ga tapes made by the so-called surface diffusion process, have been obtained. The highest upper critical field, Hc2 measured at 4.2 K is about 208 kOe. Jc of the tape is greatly affected by both the Cu-Ga alloy composition and the heat treatment condition. Higher Jc is obtained in the specimen with higher matrix gallium concentration and heat treated at lower temperatures. Specimens heat treated at higher temperatures and for longer times show pronounced “peak effect” at a magnetic field of about 170 kOe. At magnetic fields below 100 kOe, Jc seems to be strongly related to the V3Ga grain size. At the peak field, however, Jc is nearly independent of the heat treatment condition, i.e. the V3Ga grain size. The present study reveals that V3Ga superconductors with high Tc, Hc2 and Jc can easily be produced by the composite process, in which the most proper matrix gallium concentration is 18–20 at% and the heat treatment condition is at 625°C for 20∼100 hr.

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