Rare earth-rich cadmium compounds RE10TCd3 (RE=Y, Tb, Dy, Ho, Er, Tm, Lu; T=Rh, Pd, Ir, Pt) with an ordered Co2Al5-type structure

摘要

Eighteen new rare earth-rich intermetallic phases RE10TCd3 (RE=Y, Tb, Dy, Ho, Er, Tm, Lu; T=Rh, Pd, Ir, Pt) were obtained by induction melting of the elements in sealed niobium ampoules followed by annealing in muffle furnaces. All samples were characterized by X-ray powder diffraction. The structures of four representatives were refined from single-crystal X-ray diffractometer data: ordered Co2Al5 type, P63/mmc, a=951.2(1), c=962.9(2) pm, wR=0.0460, 595 F2 values, 20 parameters for Er10RhCd3; a=945.17(4), c=943.33(4), wR=0.0395, 582 F2 values, 21 parameters for Lu9.89PdCd3.11; a=964.16(6), c=974.93(6) pm, wR=0.0463, 614 F2 values, 21 parameters for Y10Ir1.09Cd2.91; a=955.33(3), c=974.56(3) pm, wR=0.0508, 607 F2 values, 22 refined parameters for Dy9.92IrCd3.08. Refinements of the occupancy parameters revealed small homogeneity ranges resulting from RE/Cd, respectively T/Cd mixing. The basic building units of the RE10TCd3 phases are transition metal-centered RE6 trigonal prisms (TP) that are condensed with double-pairs of empty RE6 octahedra via common triangular faces. A second type of rods is formed by slightly distorted RE3@Cd6RE6 icosahedra which are condensed via Cd3 triangular faces. The shortest interatomic distances occur for RE–T, compatible with strong covalent bonding interactions. Temperature dependent magnetic susceptibility measurements were performed for RE10RhCd3 (RE=Dy–Tm, Lu), RE10IrCd3 (RE=Er, Tm, Lu) and RE10PtCd3 (RE=Y, Lu). While Y10PtCd3 and Lu10TCd3 (T=Rh, Ir, Pt) show Pauli paramagnetic behavior, the compounds containing paramagnetic rare earth elements show Curie-Weiss behavior (the experimental magnetic moments indicate stable trivalent RE3+) and magnetic ordering at low temperatures: TC=80.5 K for Dy10RhCd3 and Neél temperatures of 42.1, 23.3, 12.6, 5.9, 10.0 K for Ho10RhCd3, Er10RhCd3, Er10IrCd3, Tm10RhCd3, Tm10IrCd3, respectively.