QUATERNARY SILICIDE CARBIDES AT2SiC (A=RARE EARTH ELEMENTS AND ACTINOIDS, T=Mn, Re, Ru, Os) WITH DyFe2SiC-TYPE STRUCTURE

摘要

The 49 compounds AMn2SiC (A=Y, Sm, Gd-Tm, Lu, Th, U), ARe2SiC (A=Y, Ce-Nd, Sm, Gd-Tm, Th), ARu2SiC (A=Y, Ce-Nd, Sm, Gd-Tm, Th), and AOs2SiC (A=Y, La-Nd, Sm, Gd-Tm, Th, U) have been prepared for the first time. They crystallize with DyFe2SiC-type structure, which was refined for PrOs2SiC from single-crystal X-ray data: Cmcm, a=396.02(5) pm, b=1105.8(1) pm, c=717.2(1) pm, Z=4, R=0.030 for 320 structure factors F and 18 variable parameters V. The refinement of the occupancy parameters revealed that the silicon site contains 2.0(3)% osmium. Mixed occupancy for this site resulted also from two structure refinements of the corresponding thorium compound, yielding the compositions ThOs2.040(2)Si0.960(2)C (a=396.41(7) pm, b=1115.5(1) pm, c=717.0(1) pm, R=0.013, 245 F, 18 V) and ThOs2.284(2) Si0.716(2)C (a=397.1(1) pm, b=1113.9(2) pm, c=724.5(1) pm, R=0.025, 483 F, 18 V). No such deviations from the ideal compositions were detected by the (less accurate) Rietveld refinements of the structures of TbRe2SiC, DyRu2SiC, and HoRu2SiC. Magnetic susceptibility measurements with a SQUID magnetometer indicate Pauli paramagnetism for YRu2SiC and YOs2SiC. Chemical bonding in the DyFe2SiC-type compounds is discussed. It is shown that an electron count of 18 can be achieved for most of the transition metal atoms. 31 refs.