TWO EXOTIC AND UNIQUE FAMILIES OF RARE EARTH INTERMETALLIC COMPOUNDS

The rare earth metals form two unique, one of a kind, families of intermetallic compounds. One family crystallizes in the simple cubic CsCl, B2-type structure with 2 atoms in the unit cell; while the second family has the complex orthorhombic Nd11Pd4In9-type structure with 48 atoms in the unit cell. The first family, the RM compounds with the B2-type structure, where R is a rare earth metal and M = Cu, Ag, and Au, are ductile phases. Some non-rare earths containing B2 phases have also been studied and most were found to follow the criteria for ductility/brittleness established by the RM phases. The second family, the R11M4In9 phases where M = Ni, Pd and Pt, form a fibrous microstructure. The microstructure is self-assembled directly from the melt (whether rapidly or slow cooled) and is probably due to the large aspect ratio of 6.0 for the b/c lattice parameter ratio and the very short In-In bonds in the a-b plane which give rise to kinetic hindrance during solidifying and prevent the crystal from growing in the a and b directions.