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

本文在APW能带计算的基础上，研究了M_xTiS_2（M=过渡金属）层间化合物的电子结构和成键性质。利用2 H-NbS_2的实际能带结构研究了M_xNbS_2中的RKKY相互作用。主要研究结果如下：1.非磁性M_xTis_2的电子能带和成键性质(1)在嵌入过程中，M-3d态在Ti-d<gamma>和S-p成键带与Ti-d非成键带之间形成一个新的带。费米能级位于这个新的能带中。新<gamma>谱带中Ti-d和S-p成分明显混合，且带宽较大。(2)M-d<gamma>和S-p轨道也形成类共价键。Ti和M离子的d轨道显著杂化，并且形成成键和反键状态。这些结果表明，MxTiS_2不能采用刚性带模型，M-od电子应视为巡游电子.铁磁Fe_（1/3）TiS_2和FeTiS_2的电子键。Fe 3d组元的上、下自旋带出现较大的劈裂，不能用非磁性带的刚性劈裂来描述。计算出<mu>Fe_（1/3）TiS_2的自旋磁矩为2.55 _B/晶胞，<mu>FeTiS_2的自旋磁矩为3.22 _B/晶胞。这一结果也表明了M3 d电子的巡游性质.利用2 H-NbS_2的实际能带结构，在刚性能带模型的基础上计算了M_xNbS_2中RKKY相互作用引起的交换耦合。当x=1/4时，交换耦合的傅里叶变换在T点和K点取几乎相同的极值，这表明铁磁或三角自旋排列都可能是真实的。当x=1/3时，最稳定的自旋排列是对应于M点的反铁磁结构，这在Co^ NbS_2中实现</3>。

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.