Superconductors: Structures and Applications

Abstract

Conventional Intermetallic Superconductors Superconductivity is by no means a new scientific entity. This phenomenon was discovered some 90 years ago, as described in a recent review (Chu, 1996). Over the past nine decades, the study of superconductivity has continued to capture attention. The maximum known Tc advanced at a rather slow pace before 1986, increasing from 4 K (Hg) to 23 K (Nb3Ge) over 75 years from 1911 to 1986. The 23 K value was a pre-1986 record temperature established in 1973 (Gavaler et aI., 1974), and theorists predicted a 40 K ceiling (Ginzburg and Kirznitz, 1982). In general, conventional superconductors are intermetallic compounds with Tc less than 23 K. Elemental superconductors are all metals. Alloys can be prepared with higher transition temperatures than elemental metals. For example, in 1959, the binary alloy Nb3Sn was found to have a Tc of 18 K. Subsequently, ternary alloys were found to have higher Tc, such as Nb12AhGe with a Tc of 20.8 K, !o higher than the boiling temperature of H2. A large number of low-temperature superconductors are documented in the Handbook of Physics and Chemistry (Lide, 1995). Some notable examples are Nb, NbC, NbN,V3Si, Nb3Sn, and Nb3Ge. In this chapter, we do not discuss further the conventional superconductors.