Electronic Band Structures and Physical Properties of Intercalation Compounds of Transition-Metal Dichalcogenides

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Electronic and structures and bonding natures of intercalation compounds of M_xTiS_2 (M=transition metal) are studied on the basis of tne APW band calcuation. RKKY interaction in M_xNbS_2 is also studied by using the realistic band structures of 2H-NbS_2. The main results are summarized as follows.1. Electronic bands and bonding natures of non-magnetic M_xTis_2.(1) On intercalation the M-3d states form a new bands between the Ti-d<gamma> and S-p bonding band and the Ti-d non-bonding band. The Fermi level lies in this new band. The Ti-d<gamma> and S-p components are mixed significantly in this new band and its band width is fairly large.(2) The M-d<gamma> and S-p orbitals make also covalent-like bonds. The d orbitals of Ti and M ions hybridise significantly and form also bonding and anti-bonding states. These results suggest clearly that the so-called rigid-band-model cannot be applied for MxTiS_2 and that the M-od electrons should be treated as itinerant electrons.2. Electronic bonds of ferromagnetic Fe_<1/3>TiS_2 and FeTiS_2.Up- and down-spin bands of Fe 3d components show a large splitting, shich cannot be described as a rigid splitting of the non-magnetic bands. The spin moment is evaluated as 2.55<mu>_B/unit cell in Fe_<1/3>TiS_2 and 3.22<mu>_B/unit cell in FeTiS_2. This result indicate also itinerant character of the M 3d electrons.3. RKKY interaction in M_xNbS_2.Exchange couplings due to RKKY interaction in M_xNbS_2 are calculated on the basis of the rigid-band-model by using the realistic band structures of 2H-NbS_2. When x=1/4, Fourier transform of the exchange couplings takes the almost same extremum at the T and K points, which indicate either ferromagnetic or triangular spin arrangement is likely to be realsized. When x=1/3, the most stable spin arrangement is the antiferromagnetic structure corresponding to the M point which is realized in Co^</3>NbS_2.