The nonstoichiometric ternary cerium iron sulfide Ce2Fe1.82S5

The nonstoichiometric ternary cerium iron sulfide Ce2Fe1.82(6)S5 was synthesized through reaction of the elements in a LiCl/KCl flux at 1120 K, and its structure was determined by single-crystal X-ray diffraction. Ce2Fe1.82S5 crystallizes in the polar orthorhombic space group Pmn21 with a=3.9590(2)Å, b=16.413(1)Å, c=11.2362(9)Å and Z=4. The structure is a defect variant of the La2Fe2S5 structure type. The parent structure contains both octahedral and tetrahedral iron sites, within one-dimensional chains of edge-sharing [FeSx]-polyhedra that run along the [100] direction. In Ce2Fe1.82S5, vacancies occur exclusively in the octahedral iron sites. The “tetrahedral” iron sites are split into three closely spaced partially occupied positions with coordination numbers of [4+1]. The presence of vacancies entails the partial oxidation of one of the cations to compensate the charge. The X-ray absorption near-edge structure (XANES) of the Ce MIV,V edge of Ce2Fe1.82S5 showed no evidence of the occurrence of tetravalent cerium. The presence of Fe3+ was unambiguously established on the basis of hyperfine fields observed in a 57Fe-Mößbauer spectrum at 4.2 K. The temperature dependence of the reciprocal magnetic susceptibility (χ−1) of Ce2Fe1.82S5 is nearly linear at higher temperatures. A rapid decrease in χ−1 below approximately 90 K suggests a ferrimagnetic transition.