Electronic Structure and Phase Stability of Yb-Filled CoSb3 Skutterudite Thermoelectrics from First-Principles,Chemistry of Materials

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Electronic Structure and Phase Stability of Yb-Filled CoSb3 Skutterudite Thermoelectrics from First-Principles
Chemistry of Materials ( IF 7.2 ) Pub Date : 2019-08-05 00:00:00 , DOI: 10.1021/acs.chemmater.9b01630
Eric B. Isaacs ₁ , Christopher Wolverton ₁

Affiliation

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 Yb-filled skutterudite Yb_xCo₄Sb₁₂, 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 CoSb₃ 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.

中文翻译：

第一性原理的Yb填充CoSb _3方钴矿热电材料的电子结构和相稳定性

用rat杂原子R填充方钴矿CoSb ₃晶体结构中的大空隙，为增加载流子浓度和破坏晶格传热提供了一条途径，从而带来了令人印象深刻的热电性能。尽管已经很好地研究了R对方钴矿材料晶格动力学的影响，但仍不清楚R填充方钴矿材料的相稳定性以及R的存在和有序对电子结构的影响。在这里，我们着眼于Yb填充方钴矿Yb _x Co ₄ Sb ₁₂，采用第一原理方法来计算相稳定性和电子结构。掺Yb的CoSb ₃表现出（1）相分离进入富Yb和贫Yb的区域的温和趋势，以及（2）化学分解成Co-Sb和Yb-Sb二元（即CoSb ₃，CoSb ₂和YbSb ₂）的强烈趋势）。我们发现，在合理的合成温度下，与实验一致，构型熵稳定了Yb溶解度有限的单相固溶体。填充CoSb ₃Yb增大了带隙，增强了载流子的有效质量，并产生了新的低能量“紧急”导带最小值，这与传统的将现有带极能量对准的带收敛图不同。R的显式存在对于实现出现的导带极小值是必不可少的，尽管响尾蛇的排序不会强烈影响电子结构。出现的导带在空间上位于富Yb区域，这与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不同。

更新日期：2019-08-05

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