challenges for high-temperature superconducting wire -

Since the 1986 discovery of high-temperature superconducting (HTS) materials1, the promise of zero-resistance devices operating at liquid-nitrogen temperature has fuelled a worldwide research investment that is now around one billion US dollars. Most research has been in the electric power area for applications such as magnets, motors and power-transmission lines; all power applications share a common requirement that the superconducting material be formed into a long, strong and flexible conductor so that it can be used like the copper wire it is intended to replace. And this is where the problems began, because the HTS materials are ceramics that are more like a piece of chalk than the ductile metal copper.

Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and — the downside of high transition temperature — performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.
Introduction

Source :
Materials science challenges for high-temperature superconducting wire - pp631 - 642
In Nature materials
S. R. Foltyn, L. Civale, J. L. MacManus-Driscoll, Q. X. Jia, B. Maiorov, H. Wang & M. Maley
doi:10.1038/nmat1989