L. Eyring & K.A. Gschneidner 
Handbook on the Physics and Chemistry of Rare Earths [PDF ebook] 
High Temperature Rare Earths Superconductors — I

This volume of the Handbook is the first of a two-volume set of reviews devoted to the rare-earth-based high-temperature oxide superconductors (commonly known as hi TC superconductors). The history of hi TC superconductors is a few months short of being 14 years old when Bednorz and Muller published their results which showed that (La, BA)2Cu O4 had a superconducting transition of ~30 K, which was about 7K higher than any other known superconducting material. Within a year the upper temperature limit was raised to nearly 100K with the discovery of an ~90K superconducting transition in YBa2Cu3O7-&dgr;. The announcement of a superconductor with a transition temperature higher than the boiling point of liquid nitrogen set-off a frenzy of research on trying to find other oxide hi TC superconductors. Within a few months the maximum superconducting transition reached 110 K (Bi2Sr2Ca2Cu3010, and then 122K (Tl Ba2Ca3Cu4O11. It took several years to push TC up another 11 K to 133 K with the discovery of superconductivity in Hg Ba2Ca2Cu3O8, which is still the record holder today.