Structure and physical features of the rare-earth borides

Abstract
During the last three decades a large interest has developed in the field of rare-earth borides. Six different families have been discovered: REB2, REB4, RE2B5, REB6, REB12 and REB∼66. Their extension is discussed, and it is shown on the base of both geometrical and electronic considerations how the RE atoms contribute to the stabilization of the electron-deficient boron framework. Attention has been devoted to the ability of metal or non-metal impurities either to stabilize a particular structure or to modify drastically the electrical and magnetic properties of the borides. A wide range of the fascinating physical properties of the rare-earth borides is considered, including insulator–metal transitions, superconductivity, mixed-valence behaviour, magnetic phase transitions and thermoelectronic properties.