Crystal structure and electronic properties of the new compounds U3Co12−xX4 with X=Si, Ge

The new compounds U3Co12−xX4 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 P63/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 EuMg5.2 structure type, and is closely related to the Sc3Ni11Si4 and Gd3Ru4−xAl12+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 U3Co12−xSi4 and U3Co12−xGe4, respectively. The electronic properties of both compounds were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The U3Co12−xX4 compounds are both Pauli paramagnets with their electrical resistivity best described as poor metallic or dirty metallic behavior.