EUTA2AL20, CA6W4AL43 AND OTHER COMPOUNDS WITH CECR2AL20 AND HO6MO4AL43 TYPE STRUCTURES AND SOME MAGNETIC-PROPERTIES OF THESE COMPOUNDS

The 25 new compounds CaT2Al20 (T=Ti, Nb, Ta, Mo), LnT(2)Al(20) (Ln=La, Ce, Pr, Nd, Sm, Eu; T=Nb, Ta), SmCr2Al20, TbCr2Al20, Ca6W4Al43, Y6Nb4 Al43, Y6Ta4Al43, and Ln(6)Mn(4)Al(43) (Ln=Ho-Yb) have been prepared by reaction of the elemental components in alumina crucibles under argon . They crystallize with CeCr2Al20 and Ho6Mo4Al43 type structures, resp ectively, which were refined from single-crystal X-ray data of EuTa2Al 20 (Fd (3) over bar m, a=1478.3(1) pm, R=0.025 for 312 structure facto rs and 15 variable parameters) and Ca6W4Al43 (P6(3)/mcm, a=1108.4(4) p m, c=1778.8(6) pm, R=0.010 for 849 F values and 53 variables). All ato mic positions are fully occupied, with the exception of one aluminium site of EuTa2Al20, which has an occupancy of only 81(2)%. The compound s LnCr(2)Al(20) (Ln=La-Nd, Eu) and LnV(2)Al(20) (Ln=La-Pr, Eu-Tb) are confirmed. The cell volumes of the cerium, europium and ytterbium comp ounds LnT(2)Al(20) (Ln=Ce, Eu; T=Ti, V, Nb, Ta, Cr, Mo, W), YbTi2Al20 and Yb6Mn4Al43 deviate from the smooth functions observed for the cell volumes of the compounds with the typically trivalent rare earth elem ents. Magnetic susceptibility data, measured with a SQUID magnetometer , show Pauli paramagnetism for LaTi2Al20, LaMo2Al20, CeTi2Al20, CeV2Al 20, and CeMo2Al20, thus indicating cerium to be tetravalent in agreeme nt with the cell volumes of these compounds. The magnetic susceptibili ties of EuTi(2)Al(20)and EuMo2Al20 follow the Curie-Weiss law; their m agnetic moments correspond to divalent europium. (C) 1998 Elsevier Sci ence S.A.