Electronic Structure and Phase Stability of Yb-Filled CoSb3 Skutterudite Thermoelectrics from First-Principles
Electronic Structure and Phase Stability of Yb-Filled CoSb3 Skutterudite Thermoelectrics from First-Principles
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DOI：
10.1021/acs.chemmater.9b01630
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发表时间：
2019-08-27
影响因子：
8.6
通讯作者：
Wolverton, Christopher
中科院分区：
文献类型：
--
作者：
Isaacs, Eric B.;Wolverton, Christopher
用Rattler原子R填充方钴矿CoSb 3的晶体结构中的大空隙提供了增加载流子浓度和破坏晶格热传输的途径，从而产生令人印象深刻的热电性能。虽然R对方钴矿材料的晶格动力学的影响已经得到了很好的研究，但R填充的方钴矿材料的相稳定性以及R的存在和有序性对电子结构的影响仍然不清楚。在这里，重点是Yb填充的方钴矿YbxCo 4Sb 12，我们采用第一性原理方法来计算相稳定性和电子结构。Yb填充的CoSb 3表现出（1）相分离成富Yb和贫Yb区域的温和趋势和（2）化学分解成Co-Sb和Yb-Sb二元化合物的强烈趋势（即，CoSb 3、CoSb 2和YbSb 2）。我们发现，在合理的合成温度下，构型熵稳定单相固溶体与有限的Yb溶解度，与实验一致。用Yb填充CoSb 3增加了带隙，增强了载流子有效质量，并产生新的低能量“涌现”导带最低点，这不同于传统的带会聚图，即对齐现有的带极值的能量。明确存在的R是必要的，以实现紧急的导带最低点，虽然rattler排序并没有强烈影响的电子结构。出射导带在空间上定位在富Yb区域中，不同于形成未填充的方钴矿带边缘的布里渊区中心处的离域电子态。
Filling the large voids in the crystal structure of the skutterudite CoSb3 with rattler atoms R provides an avenue for both increasing carrier concentration and disrupting lattice heat transport, leading to impressive thermoelectric performance. While the influence of R on the lattice dynamics of skutterudite materials has been well studied, the phase stability of R-filled skutterudite materials and the influence of the presence and ordering of R on the electronic structure remain unclear. Here, focusing on the Ybfilled skutterudite YbxCo4Sb12, we employ first-principles methods to compute the phase stability and electronic structure. Yb-filled CoSb3 exhibits (1) a mild tendency for phase separation into Yb-rich and Yb-poor regions and (2) a strong tendency for chemical decomposition into Co-Sb and Yb-Sb binaries (i.e.,CoSb3, CoSb2, and YbSb2). We find that, at reasonable synthesis temperatures, configurational entropy stabilizes single-phase solid solutions with limited Yb solubility, in agreement with experiments. Filling CoSb 3 with Yb increases the band gap, enhances the carrier effective masses, and generates new low-energy "emergent" conduction band minima, which is distinct from the traditional band convergence picture of aligning the energies of existing band extrema. The explicit presence of R is necessary to achieve the emergent conduction band minima, though the rattler ordering does not strongly influence the electronic structure. The emergent conduction bands are spatially localized in the Yb-rich regions, unlike the delocalized electronic states at the Brillouin zone center that form the unfilled skutterudite band edges.