Thermoelectric and magnetic properties of rare earth borides: Boron cluster and layered compounds

Several interesting physical properties which are closely related to the interesting crystal structures of rare earth borides will be reviewed. Experimentally it has been indicated that the B-12 icosahedral cluster enhances magnetic interaction and mediates it in dilute magnetic systems. There is interest in the potential of borides as hightemperature thermoelectric materials for use in topping cycles for power plants and other applications. Boron icosahedral compounds generally exhibit large Seebeck coefficients. They also tend to possess relatively small thermal conductivities despite the typically strong covalent bonding and high sound velocities of the materials. The paper reviews possible mechanisms proposed to lower the lattice thermal conductivity in borides, p-n controllable compounds, and several borides recently found with enhanced thermoelectric properties.