Fundamentals of niobium-based superconductors

Superconductivity, discovered by Onnes (1) in 1911, is the total disapapearance of resistance at a finite low temperature (transition temperatureTc).The phenomenon is not rare; 25 out of the elements shown in Fig. 1 (2) and over 1000 alloys and compounds are now known as superconductors (3). The appearance of such a large number is quite surprising and challenging. In a historical overview of the research and development of the superconductors, following the works (4, 5) in 1950's a significant breakthrough occurred in 1961 when Kunzler at Bell Labs (6) found Nb3Sn remained superconducting in magnetic fields in excess of 9 tesla, while carrying high current densitites. This truly opened the door to the so-called type II or "hard" superconductors which resulted in the compact, high field superconducting magnets commonly used today. Such an epoch can be seen in Fig. 2 which is a chronological plot (7) of T 's in superconductors discovered... (AU)