Materials science challenges for high-temperature superconducting wire

Abstract

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.

Significant tunability of thin film functionalities enabled by manipulating magnetic and structural nano-domains

“…4,34,68,74 , films deposited at low repetition rates had smoother surfaces, which is in opposite to our results provided in Table I. However in those works, the roughness was studied on thicker films (> 200 nm) with highly developed surface structures containing outgrowths, holes, pinholes and other defects formed due to incomplete island coalescence of relatively thick films 4,34 or stress-guided surface roughening after complete coalescence 5,33,35 . Upon deposition on highly developed surface with low deposition rates adatoms have more time to diffuse to sites with high coordination number, reducing roughness as observed in Refs.…”

“…The films where annealed in oxygen atmosphere at 400 • C for one hour after deposition for oxygenation. The thin films measured in this work are of optimal thickness d p 300 nm thick 5,6,33 , measured by Dektak profiler. The critical temperature was T c 90.0 ± 0.5 K for films deposited with 5 Hz and 8 Hz frequencies and T c 91.5 ± 0.5 K for 1 Hz deposited film, measured by DC magnetic measurements in PPMS at B a = 2.5 mT.…”

“…For physical vapour deposition (PVD) technologies, this control is conventionally achieved by manipulating interdependent parameters, such as temperature, atmosphere, flux of material, resultant film thickness [1][2][3][4][5][6] and laser frequency [6][7][8][9][10] . In particular, the laser frequency for pulsed-based deposition (PLD) influences the film structure in many different ways, whose mechanisms can be contentious and not easily understood [7][8][9][10][11] .…”

“…Furthermore, a critical thickness for the optimal YBCO performance exists 5,6,33,34 . In thicker films, the surface becomes rough and their properties degrade, unless a multilayered structure is introduced 35 .…”

“…In thinner films, the integral capabilities of the films are reduced. The optimal thickness, defined at the maximum of the critical current density (J c ) as the function of the film thickness 5,33 , is usually obtained at the deposition stage with all YBCO islands coalesced 5,6,34 . In this work, it is shown that the island density and the island growth kinetics can be effectively varied by changing deposition conditions (in particular, laser frequency), thus the optimal thickness can be adjusted at will.…”