Rare earth-ruthenium-magnesium intermetallics

Abstract

Abstract Eight new intermetallic rare earth-ruthenium-magnesium compounds have been synthesized from the elements in sealed niobium ampoules using different annealing sequences in muffle furnaces. The compounds have been characterized by powder and single crystal X-ray diffraction. Sm9.2Ru6Mg17.8 (a=939.6(2), c=1779(1) pm), Gd11Ru6Mg16 (a=951.9(2), c=1756.8(8) pm), and Tb10.5Ru6Mg16.5 (a=942.5(1), c=1758.3(4) pm) crystallize with the tetragonal Nd9.34Ru6Mg17.66 type structure, space group I4/mmm. This structure exhibits a complex condensation pattern of square-prisms and square-antiprisms around the magnesium and ruthenium atoms, respectively. Y2RuMg2 (a=344.0(1), c=2019(1) pm) and Tb2RuMg2 (a=341.43(6), c=2054.2(7) pm) adopt the Er2RuMg2 structure and Tm3Ru2Mg (a=337.72(9), c=1129.8(4) pm) is isotypic with Sc3Ru2Mg. Tm3Ru2Mg2 (a=337.35(9), c=2671(1) pm) and Lu3Ru2Mg2 (a=335.83(5), c=2652.2(5) pm) are the first ternary ordered variants of the Ti3Cu4 type, space group I4/mmm. These five compounds belong to a large family of intermetallics which are completely ordered superstructures of the bcc subcell. The group-subgroup scheme for Lu3Ru2Mg2 is presented. The common structural motif of all three structure types are ruthenium-centered rare earth cubes reminicent of the CsCl type. Magnetic susceptibility measurements of Y2RuMg2 and Lu3Ru2Mg2 samples revealed Pauli paramagnetism of the conduction electrons.