EuTa2Al20, Ca6W4Al43 and other compounds with CeCr2Al20 and Ho6Mo4Al43 type structures and some magnetic properties of these compounds

摘要

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, Y6Nb4Al43, 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, respectively, which were refined from single-crystal X-ray data of EuTa2Al20 (Fd (3) over bar m, a=1478.3(1) pm, R=0.025 for 312 structure factors and 15 variable parameters) and Ca6W4Al43 (P6(3)/mcm, a=1108.4(4) pm, c=1778.8(6) pm, R=0.010 for 849 F values and 53 variables). All atomic positions are fully occupied, with the exception of one aluminium site of EuTa2Al20, which has an occupancy of only 81(2)%. The compounds 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 compounds 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 elements. Magnetic susceptibility data, measured with a SQUID magnetometer, show Pauli paramagnetism for LaTi2Al20, LaMo2Al20, CeTi2Al20, CeV2Al20, and CeMo2Al20, thus indicating cerium to be tetravalent in agreement with the cell volumes of these compounds. The magnetic susceptibilities of EuTi(2)Al(20)and EuMo2Al20 follow the Curie-Weiss law; their magnetic moments correspond to divalent europium. (C) 1998 Elsevier Science S.A. [References: 21]