The nonstoichiometric ternary cerium iron sulfide Ce 2Fe 1.82S 5

Abstract

The nonstoichiometric ternary cerium iron sulfide Ce 2Fe 1.82(6)S 5 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. Ce 2Fe 1.82S 5 crystallizes in the polar orthorhombic space group P m n 2 1 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 La 2Fe 2S 5 structure type. The parent structure contains both octahedral and tetrahedral iron sites, within one-dimensional chains of edge-sharing [FeS x ]-polyhedra that run along the [100] direction. In Ce 2Fe 1.82S 5, 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 M IV,V edge of Ce 2Fe 1.82S 5 showed no evidence of the occurrence of tetravalent cerium. The presence of Fe 3+ 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 Ce 2Fe 1.82S 5 is nearly linear at higher temperatures. A rapid decrease in χ −1 below approximately 90 K suggests a ferrimagnetic transition.