Platinum Metals Rev., 1995, 39, (1), 32
A Copper-Free Ruthenium Perovskite Superconductor
In recent years layered perovskite structures exhibiting superconductivity at low temperatures have been synthesised. Work on these compositions, with various substitutions, has resulted in materials which display significantly higher transition temperatures, and hence are superconducting at relatively higher temperatures. These increases in transition temperature are sufficiently large to suggest that a market for such materials is likely to develop during the last few years of this century.
Materials developed to-date are based upon systems, such as La2-xBaxCuO4, where the copper is present in layers, together with oxygen. This layering is necessary to induce superconductivity, as are the barium substitutions into the basic perovskite structure. However, work is now reported on the evaluation of a perovskite compound based on Srn +1Run O3n +1 (Y. Maeno, H. Hashimoto, K. Yoshida, S. Nishizaki, T. Fujita, J. G. Bednorz and F. Lichtenberg, Nature, 1994, 372, (6506), 532–534). When n =1 Sr2RuO4 is formed, having crystal structure isostructural with La2 xBaxCuO4.
Single crystals of Sr2RuO4 were cleaved, and measurements made which revealed superconductivity below about 1 K. The transition temperature, Tc, was 0.93 ± 0.03 K. Critical current density measurements were made at 0.32 K.
While Sr2RuO4 does not possess the higher transition temperatures likely to be the basis for future opportunities, the system may be important for a basic understanding of such materials, since comparison with other superconductors with significantly different Tc values will help to explain the role of the various electronic components of the superconducting effect.
In conclusion it should be noted that this work demonstrates that the presence of copper is not a prerequisite for the existence of superconductivity in layered perovskites, but that the high transition temperatures possible when it is present would appear to indicate that it has a special role. On this basis the existence of superconductivity in Sr2RuO4 may be a valuable discovery, particularly to clarify the mechanisms permitting superconductivity. A.S.P.