Extraordinary Responsive Intermetallic Compounds: the R5T4 Family (R = Rare Earth, T = Group 13-15 Element)

The R5T4 intermetallic compounds of rare earth elements (R) with the group 14 elements(T) adopt a number of layered crystal structures that reversibly transform into each other. The transformations proceed through massive shear displacements of their main structural units, i.e. slabs, which are pseudo two dimensional blocks of atoms stacked along a certain crystallographic direction. These transformations can be triggered by change in chemical composition of the compounds( including partial substitutions of the group 14 elements by the group 13 or 15 elements), temperature, applied pressure, or applied magnetic field. The physical properties of these compounds are usually intimately related to their crystallography, and especially the concomitant magnetic and crystallographic transitions. As a result, strong magnetocaloric, magnetostrictive, magnetoresistance, and other effects are commonly observed. Consequently, a large change of the materials' properties can be achieved by a relatively weak change of external thermodynamic conditions.