V3Si Multifilamentary Superconductor with High Overall Jc
V3Si is one of the A15-type superconducting compounds from which single crystals can be quite easily obtained due to the nature of the equilibrium phase diagram. Thus, the fundamental characteristics of A15 compounds (such as electronic structure1 and cubic-totetragonal structural transformation2) have been studied with this compound. V3Si is, however, also promising in practical use as an alternative to Nb3Sn for high field magnets, since the upper critical field Hc2 (4.2 K) is more than 20 T.3 Although the “bronze process”, the established commercial process to produce Nb3Sn conductors, is also available for V3Si,4,5 the ternary section of the Cu-V-Si phase diagram indicates two diffusion paths are possible: one from the bronze with low Si content (Si < lat.%) directly to V3Si, and the other from the bronze with higher Si content to V3Si via V5Si3.6 The high Si bronze is likely to be advantageous in reducing the bronze volume fraction and hence achieving high overall critical current density J. This is because the initially formed V5Si3 is eventually converted to V3Si as long as the total proportion of V to Si in the composite (overall V/Si molar ratio) is kept around 3. However, long times at high temperatures are necessary for appreciable V3Si layer growth, thereby yielding grain growth of V3Si and lowering the Jc of the V3Si compound and the overall Jc accordingly.
KeywordsCritical Current Density Heat Treatment Time Optimum Reaction Time Composite Wire Versus Core
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