Platinum Metals Rev., 1992, 36, (2), 97
Platinum in High-Temperature Superconductors
High temperature superconductors have been known about since 1987 when YBaCuO superconductors with critical temperatures above 77 K, the temperature at which nitrogen liquefies, were first synthesised. If such superconductors are to become widely used, however, they will have to be able to achieve high current densities without the superconductivity of the material being destroyed. Thus flux pinning is essential in order to prevent magnetic flux interactions between superconducting regions, otherwise the critical magnetic flux density could be exceeded, destroying the superconductivity and causing Joule heating.
Platinum already finds a variety of applications in high temperature superconductor technology; now researchers at the International Superconductivity Technology Center, Nagoya, Japan have found that additions of platinum or rhodium in certain YBaCuO superconductors can produce a much increased critical current density (“Effects of the Platinum Group Element Addition on Preparation of YBCO Superconductor by Melt Growth Method”, M. Yoshida, N. Ogawa, I. Hirabayashi and S. Tanaka, Physica C, 1991, 185–189, (IV), 2409–2410).
It has been reported previously that high critical current densities can be attained in large (123) crystals of YBa2Cu3Oy which have fine (211) Y2BaCuO5 particles uniformly dispersed throughout them. This dispersion of (211) particles is reported to suppress crack formation, allow the oxygen diffusion rate to increase and also serve as flux pinning centres.
In the current work the microstructure of superconductors containing 0.5 weight per cent platinum group metals, and prepared by a partial melting and slow cooling process, were studied by optical microscopy, while the high critical current density was estimated from magnetisation hysteresis curves. It was found that the addition of platinum or rhodium facilitates the heterogeneous nucleation of the (211) phase; the mechanism for this is discussed. Other platinum group metals had no significant effect, however. For typical platinum-doped melt grown samples, at 77 K and 1 T, critical current densities exceed 18,000 A/cm2; corresponding values for other samples are less than 10,000 A/cm2.