PHOSPHIDES AND ARSENIDES WITH THE ZRFE4SI2-TYPE STRUCTURE

The compounds UMn4P2, ScFe4P2, ZrFe4P2, ScNi4As2, ZrNi4As2 and RNi4As2 (R ≡ Y, Gd-Lu) crystallize with the tetragonal ZrFe4Si2-type structure. The structure was refined from single-crystal X-ray data for ScFe4P2 (a = 696.2 pm, c = 362.2 pm, R = 0.014 for 267 F values) and DyNi4As2 (a = 723.9 pm, c = 376.0 pm, R = 0.019 for 278 F values). The magnetic susceptibilities of UMn4P2 were determined between 5 and 400 K with a SQUID magnetometer at magnetic flux densities between 1 and 5 T. UMn4P2 shows two antiferromagnetic transitions which are ascribed to the ordering of the uranium and manganese magnetic moments with Néel temperatures of TN(U) = 22 ± 1 K and TN(Mn) = 123 ± 1 K. Chemical bonding in the ZrFe4Si2-type and related compounds with high metal content is briefly discussed. In phosphides and arsenides where the cell volumes suggest intermediate valence for cerium, europium and ytterbium the valence of the lanthanoid atoms (estimated from the cell volumes) is higher in the phosphides than in the arsenides. This correlates with the greater electronegativity of phosphorus. © 1990.