Systematics of Superconductivity in Ternary Compounds

Abstract

The discoveries of superconductivity in two particular classes of ternary compounds by MATTHIAS et al. [2.1, 2] catalyzed the recent intense research on ternary superconductors [2.3], These classes are: (i) rhombohedral or triclinic Chevrel phases Mx Mo6X8, where X is a chalcogen and M can be any of a large number of metal atoms [2.4–6], including the rare earths (RE) [2.7, 8], and (ii) primitive tetragonal borides MRh4B4, where M can be Y, Th or one of nine RE atoms [2.2, 9]. The former class of compounds exhibits the highest upper critical magnetic fields ever observed (e. g., Hc2 ≈ 600 kG for PbMo6S8 [2.10–12]), whereas those of the latter class are quite low. In addition, when M is a magnetic RE element, superconductivity occurs in both classes of compounds even though the RE concentrations are high (7 at.% and 11 at.%, respectively) [2.2, 7, 8]. Since the RE atoms form a spatially ordered array in each of the two structures, these materials have provided the first opportunities to explore the interaction between superconductivity and long-range magnetic order [2.13–16], The unique superconducting behavior of these materials also provided the impetus for work in the synthesis of other and diverse ternary systems; this in turn led to the discovery of a large number of new ternary superconductors, many of which also contain spatially ordered arrays of RE atoms. Our primary purpose in this chapter is to survey the systematics of superconductivity in ternary compounds with an emphasis on those recently discovered.