Structure and physical features of the rare-earth borides

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 REBsub(approx.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, super conductivity, mixed-valence behaviour, magnetic phase transitions and thermoelectronic properties. (author)