Overview of High Field LTS Materials (Without Nb3Sn)

Abstract

Up to the discovery of HTS compounds in 1987, the highest known superconducting transition temperature was Tc = 23 K, as reported by Gavaler (1973) for the A15 type compound Nb3Ge. Most known superconductors were either metallic or intermetallic compounds, but some oxides were also found to be superconducting, with a highest transition temperature Tc = 13 K, as reported by Johnston et al. (1973) for LiTi2O4. After the discovery of the new class of Cu-based perovskites with much higher Tc values by (Bednorz and Müller 1986), the latter are generally called HTS (for High Tc superconductors), in contrast to LTS (Low Tc superconductors), listed in Table E3.6.1. After 1986, several other classes of superconductors were discovered, with Tc values lying between LTS and HTS: the fullerenes Rb3C60 and RbCs2C60, with Tc = 28.6 and 33 K, respectively (Tanigaki et al., 1991, Wang et al., 1991), the compounds Ba1–xKxBiO3 with Tc = 32 K (Cava et al., 1988), MgB2 with Tc = 39 K (Nagamatsu et al., 2001). The AsFe-based pnictides, discovered by Kamihara et al. (2006), reached a highest Tc value of 53 K, as reported by Hosono et al. (2015). Among these “intermediate” superconductors, two of them present a particular interest: MgB2, for current leads in CERN accelerators, see Chapters B2 and H1.2 and the Fe-based pnictides – see Chapter C5 – as possible candidates for future high field magnets.