Crystal structure and electronic properties of the new compounds U 3Co 12−xX 4 with X=Si, Ge

Abstract

The new compounds U 3Co 12− xX 4 with X=Si, Ge were prepared by direct solidification of the corresponding liquid phase, followed by subsequent annealing at 1173 K. Single crystal X-ray diffraction carried out at room temperature showed that they crystallize with the hexagonal space group P6 3 /mmc (no.194) and the unit-cell parameters a=8.130(5), c=8.537(5) Å and a=8.256(1), c=8.608(1) Å for the silicide and germanide, respectively. Their crystal structure derives from the EuMg 5.2 structure type, and is closely related to the Sc 3Ni 11Si 4 and Gd 3Ru 4− x Al 12+ x types. For the present compounds, no substitution mechanisms have been observed, the partial occupancy of one Co site results from the presence of vacancies, only. The homogeneity ranges, evaluated by energy dispersive spectroscopy analysis, extend from x=0.0(2) to 0.3(2) and from x=0.0(2) to 1.0(2) for U 3Co 12− x Si 4 and U 3Co 12− x Ge 4, respectively. The electronic properties of both compounds were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The U 3Co 12− xX 4 compounds are both Pauli paramagnets with their electrical resistivity best described as poor metallic or dirty metallic behavior.