Valence-band structure of the skutterudite compounds CoAs 3 , CoSb 3 , and RhSb 3 studied by x-ray photoelectron spectroscopy
Valence-band structure of the skutterudite compounds CoAs 3 , CoSb 3 , and RhSb 3 studied by x-ray photoelectron spectroscopy
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DOI：
10.1103/physrevb.62.10737
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发表时间：
2000-10
影响因子：
3.7
通讯作者：
H. Anno;K. Matsubara;T. Caillat;J. Fleurial
中科院分区：
文献类型：
--
作者：
H. Anno;K. Matsubara;T. Caillat;J. Fleurial
通过X射线光电子能谱研究了具有方钴矿型晶体结构的CoAs 3 、CoSb 3 和RhSb 3 的价带结构。将光电发射光谱与最近的态密度计算进行比较。我们的光电发射光谱结果和理论结果对于金属d态和pnicogen p态的能量位置非常吻合，但是对于pnicogen s态的位置发现了相对较大的差异。根据我们的光发射光谱，电子键合状态和化学趋势可以通过简单的紧束缚模型进行定性解释。还讨论了金属 d 态的双定域和流动性质与方钴矿性质的关系。 CoSb 3 、CoAs 3 和RhSb 3 的金属d衍生态密度特征分别在约1.2-、1.4-和2.4-eV结合能处清晰地观察到。从晶体场效应的角度来看，可以认为该d特征带主要源自具有T 2 g对称性的d轨道，而具有E g对称性的d轨道与形成导带的p轨道强烈杂化。由于t 2 g 态被认为几乎完全充满，对应于零自旋S= 0 态（1 A 1，t 2 g 6），因此大多数方钴矿表现出抗磁性。另一方面，与纯元素相比，核心能级的轻微化学位移表明方钴矿中从金属到磷元素原子的少量电荷转移，导致金属 d 态和磷元素 p 态之间的杂化。 pd 杂化不仅导致金属位点原子库仑相互作用的大量屏蔽，而且在这些材料中产生强共价键合。关于方钴矿中能带结构的特定点，我们在价带边缘附近的光电子发射光谱显示了由于单个能带穿过赝能隙而导致费米能级周围的小态密度的明显实验证据。
The valence-band structure of CoAs 3, CoSb 3, and RhSb 3 with a skutterudite-type crystal structure has been investigated by x-ray photoelectron spectroscopy. The photoemission spectra are compared with recent density-of-states calculations. Our photoemission spectra results and theoretical results are in good agreement for the energy positions in the metal d states and the pnicogen p states, but relatively large differences are found for the positions in the pnicogen s states. Based on our photoemission spectra, the electronic bonding states and the chemical trends are explained qualitatively in terms of a simple tight-binding model. The double localized and itinerant nature of the metal d states is also discussed in relation to the properties of the skutterudites. The metal d-derived density of states feature is clearly observed at about 1.2-, 1.4-, and 2.4-eV binding energies for CoSb 3, CoAs 3, and RhSb 3, respectively. From the point of view of the crystal-field effects, it can be considered that this d-character band originates predominantly from the d orbitals with T 2 g symmetry, while d orbitals with E g symmetry hybridize strongly with the p orbitals forming the conduction band. Since the t 2 g states are considered to be almost completely filled, corresponding to the zero spin S= 0 state (1 A 1, t 2 g 6), most of skutterudites exhibit diamagnetic properties. On the other hand, the slight chemical shifts of the core levels as compared with the pure elements indicate a small charge transfer from metal to pnicogen atoms in the skutterudites, leading to hybridization between metal d states and pnicogen p states. pd hybridization causes not only a substantial screening of atomic Coulomb interactions at metal sites, but also a strong covalent bonding in these materials. Concerning a particular point of the band structure in skutterudites, our photoemission spectra near the valence-band edge show clear experimental evidence of a small density of states around the Fermi level due to a single band crossing the pseudogap.