1.4 Structure and Properties of A₃C₆₀

Very soon after bulk quantities of crystalline C₆₀ were available, attempts were made to intercalate them with electron donors (and other atoms) in order to vary their electronic properties. Haddon et al. [29] reported the first observation of metallic behaviour in intercalated C₆₀, and shortly afterwards Hebard et al. [30] observed superconductivity in K₃C₆₀. The properties of superconducting A₃ are summarized below without detailed references, but we begin with a list of relevant review articles to which the reader is referred for more detail and specific references. Some general reviews of experimentally determined properties of A₃ superconductors are those of Ramirez[31], Holczer and Whetten[32], Tanigaki and Zhou[33], and Haddon[5]. There are two recent reviews of the NMR in A₃: that of Pennington and Stenger[34] and that of Zimmer[35]. A recent review that focuses on the magnetic properties of the superconducting state of A₃ is that of Buntar and Weber[36]. Theoretical aspects of these systems have been reviewed by Gelfand[6], Schlüter et al. [37], and recently by Gunnarsson[7].

There are two classes of A₃ superconductors, those containing only alkali ions larger than Na⁺ and those containing Na⁺. First we discuss the former.