Ternary oxides Ce3NbO7 and Ce3TaO7 were successfully synthesized by the solid state reaction under flowing hydrogen atmosphere. The structures were determined by the powder X-ray diffraction. Both the compounds were crystallized in the orthorhombic space groups Pnma (for Ce3NbO7) and Cmcm (for Ce3TaO7).
Both the structures have similar features: two kinds of infinite chains formed by corner-sharing NbO6 (TaO6) octahedra and edge-sharing Ce(1)O-8 cubes, the slabs consisting of alternate chains, and 7-coordinated Ce(2) ions existing between the slabs. In the structure of Ce3NbO7, the NbO6 octahedra running along the alpha-axis are titled towards the 001 direction, while in the Ce3TaO7 structure, the TaO6 octahedra running along the c-axis are titled towards the 010 direction.
Magnetic susceptibility measurements for Ce3NbO7 and Ce3TaO7 show that both compounds are paramagnetic down to 1.8 K, and confirm that the Ce ion is in the trivalent state. From specific heat (C-p) measurements, a rapid increase of C-p/T has been observed below 3 K for both the compounds, indicating the onset of magnetic ordering between Ce3+ ions at further lower temperatures.