Nature 367, 252 - 253 (20 January 1994); doi:10.1038/367252a0

Superconductivity in the quaternary intermetallic compounds LnNi₂B₂C

R. J. Cava, H. Takagi^*, H. W. Zandbergen^†, J. J. Krajewski, W. F. Peck Jr, T. Siegrist, B. Batlogg, R. B. van Dover, R. J. Felder, K. Mizuhashi^*, J. O. Lee^*, H. Eisaki^* & S. Uchida^*

AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974, USA
^*Department of Applied Physics, University of Tokyo, Tokyo 113, Japan
^†National Centre for High Resolution Electron Microscopy, Delft University of Technology, Rottersdamsweg 137, 2628 AL Delft, The Netherlands

THE attainment of unprecedentedly high transition temperatures (T _cs) in the copper oxide superconductors illustrates how working with more complex chemical systems allows greater opportunity to balance opposing forces within a single chemical compound, leading to a better optimization of physical properties. For many desired properties, materials with optimal chemical complexity have undoubtedly not yet been found. This appears to be the case for the intermetallic superconductors, whose study has languished in recent years, and which almost never show T _cs above 15 K. These are almost all binary compounds with substitution-type additives, or, rarely, true ternary compounds such as LuRh₄B₄ (T _c = 11.7 K; refs 1, 2). If, as some argue (refs 3, 4), materials such as A_XC₆₀ (ref. 5) and Ba_0.6K_0.4BiO₃ (refs 6, 7) are conventional electron–phonon superconductors with Jcs of ˜30 K, then the absence of higher T _cs in intermetallic compounds may mean only that more complex materials have not been sufficiently explored. We have recently found superconductivity at 23 K (a T _c equal to that of the previous intermetallic record holder, Nb₃Ge; ref. 9) in the quaternary intermetallic system yttrium–palladium–boron–carbon⁸, but we were unable to identify the superconducting phase. Here we report superconductivity at temperatures up to 16.6 K for the single-phase quaternary intermetallic compounds LnNi₂B₂C (where Ln stands for Y, Tm, Er, Ho or Lu). The presence of the 3d transition metal nickel, and the layered crystal structure¹⁰ raise intriguing questions about the origin of the superconductivity, and the relatively high T _cs of these and the Y–Pd–B–C superconductor suggest that there may yet be more surprises in store.

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