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

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, P6(3)/mmc, a = 951.2(1), c = 962.9(2) pm, wR = 0.0460, 595 F-2 values, 20 parameters for Er10RhCd3; a = 945.17(4), c = 943.33(4), wR = 0.0395, 582 F-2 values, 21 parameters for Lu9.89PdCd3.11; a = 964.16(6), c = 974.93(6) pm, wR = 0.0463, 614 F-2 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 Cd-3 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 = DyTm, 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: T-C = 80.5 K for Dy10RhCd3 and Neel temperatures of 42.1, 23.3, 12.6, 5.9, 10.0 K for Ho10RhCd3, Er10RhCd3, Er10IrCd3, Tm10RhCd3, Tm10IrCd3, respectively.