Crystal structure and physical properties of the carbides UAl 3C 3 and YbAl 3C 3

Abstract

UAl 3C 3 — previously described with the tentative composition UAl 5C 4 — was prepared from the elemental components by arc melting. The new compound YbAl 3C 3 was obtained best in a lithium flux, which subsequently was dissolved in ethanol. Both carbides are isotypic with ScAl 3C 3. Their hexagonal lattice constants are a = 339.88(5) pm, c = 1711.3(2) pm and a = 338.9(1) pm, c = 1739.4(3) pm for the ytterbium and uranium compound respectively. The crystal structure of UAl 3C 3 was refined from single-crystal X-ray data to a residual of R = 0.039 for 231 structure factors and 12 variable parameters. Mass spectroscopy analyses of the hydrolyses products of YbAl 3C 3 and UAl 3C 3 with 2N hydrochloric acid essentially show only methane. Magnetic susceptibility measurements with a SQUID magnetometer indicate antiferromagnetism with Néel temperatures T N = 8 ± 1 K (YbAl 3C 3) and T N = 13 ± 1 K (UAl 3C 3). At lower temperatures the uranium compound shows metamagnetic behaviour. Electrical conductivity measurements of a single crystal of YbAl 3C 3 indicate semiconductivity.