On the structural and magnetic properties of the ternary silicides Ce6M1.67Si3 (M=Co, Ni) and Ce5Ni1.85Si3

Contrary to that reported previously, the ternary silicide “Ce6Ni2Si3” does not exist. The melting of this alloy, followed or not by annealing, leads to the existence of the two new ternary compounds, Ce6Ni1.67Si3 and Ce5Ni1.85Si3. The investigation of these ternary silicides based on nickel and Ce6Co1.67Si3 by X-ray diffraction on single crystal reveals an ordered distribution between Ni (or Co) and Si atoms. The nickel or cobalt positions in the chains of face-shared octahedra of cerium are not fully occupied with a strong delocalisation of their electron density. The structural investigations of these compounds confirm that the “Ce6Ni2Si3” and “Ce5Ni2Si3” structural type have to be rewritten as Ce6Ni2−xSi3 and Ce5Ni2−xSi3. Magnetisation and specific heat measurements evidence a magnetic ordering at 3.8(2) K for Ce6Ni1.67Si3 and a heavy fermion behaviour for Ce6Co1.67Si3.