1. Structure and physical properties

1.1 History: from transparent semiconductors to superconductivity

The first studies of compounds similar to iron-based superconductors (IBS) date back to the mid-1980s. The discovery of high-temperature superconductors (cuprates) in 1986 led many groups at the time to investigate the electrical properties of compounds with a similar crystal structure for copper atoms, including RCuChO-type compounds (R a trivalent cation and Ch a chalcogen), without success. In the early 2000s, these compounds were again studied by a Japanese group, led by H. Hosono, for applications in transparent semiconductors. In the second half of the decade, the same group turned its attention to compounds in which copper is replaced by iron and chalcogen by pnictogen, discovered by a German group led by W. Jeitschko...