Structure, electrical transport, and optical properties of a new ordered iron intercalated dichalcogenide, Fe_0.34TiSe₂

The compound Fe_0.34TiSe₂ crystallizes in space group D³_3d-P3&#x0304;ml of the trigonal system with 8 formula units in a cell of dimensions a = 7.148(4), c = 11.880(7) Å at 117 K. The structure of Fe_0.34TiSe₂ can be derived from that of TiSe₂ by insertion of Fe atoms into some of the octahedral holes between the layers. No two adjacent octahedral holes along c contain Fe atoms, that is no two Fe atoms are related by a translation of c 2. The compound Fe_xTiSe₂, x = 0.34, exhibits physical properties remarkably different from those found in either the host material, TiSe₂, or in low iron concentration (x < 0.2) intercalated materials. The electrical resistivity of this compound exhibits a sharp decrease below 120 K which is coincident with a well defined peak in the Hall coefficient. These data have been interpreted as the onset of antiferromagnetic ordering as suggested by results of magnetic susceptibility measurements. Optical reflectance measurements indicate a simple Drude-like free carrier behavior and are consistent with the interpretation of iron as an electron donor in this material.