• Harms, Wiebke
• Hossain, Zakir
• Laubschat, Clemens
• Geibel, Christoph
• Ruck, Michael
• Wagner, Friedrich E.
• Mills, Allison M.
• Söhnel, Tilo

Abstract

<p>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 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 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.</p>

Topics

• impedance spectroscopy
• x-ray diffraction
• defect
• iron
• susceptibility
• one-dimensional
• space group
• Cerium