• Bräunling, Daniel
• Schnelle, Walter
• Pöttgen, Rainer
• Sebastian, C. Peter
• Ruck, Michael
• Rosner, Helge
• Mills, Allison M.

Abstract

<p>La₃Fe_2-δS₇ (δ=0.042(6)) was synthesized through a reaction of the elements in a LiCl/KCl flux at 970 K, and its structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the polar hexagonal space group P6₃ with a=10.1906(6), c=5.9543(4) Å and Z=2, and adopts the Ce₆Al_10/3S₁₄ structure type. The structure contains both octahedral and tetrahedral iron sites: one-dimensional rods of face-sharing FeS₆ octahedra run along the 6₃ screw axis of the cell; FeS₄ tetrahedra, all pointing in the same direction, are stacked along the threefold rotation axes. The iron-centered polyhedra are linked by lanthanum atoms, which are coordinated by [7+1] sulfur atoms in a bicapped trigonal prismatic arrangement. ⁵⁷Fe Mößbauer spectroscopy confirms that Fe^III and Fe^II cations occupy the tetrahedral and octahedral iron sites, respectively. Magnetic susceptibility data indicate an antiferromagnetic transition at T_N≈155 K. Density functional band structure calculations within the local density approximation reveal two covalent Fe-S subsystems within the compound that mix only weakly. A large anisotropy is indicated by bands that disperse predominantly along the hexagonal axis. The electronic band structure suggests pseudo-one-dimensional metallic conductivity along the rods of face-sharing FeS₆ octahedra. However, due to the defects on the Fe^II positions, La₃Fe_2-δS₇ shows an activated conducting behavior.</p>

Topics

• density
• impedance spectroscopy
• compound
• x-ray diffraction
• defect
• Lanthanum
• iron
• susceptibility
• one-dimensional
• band structure
• space group