Zhang Yifei, Brorsson Joakim, Kamiyama Takashi, Saito Takashi, Erhart Paul, Palmqvist Anders E C
Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden.
Institute of Materials Structure Science, KEK, Tokai, Ibaraki319-1106, Japan.
Inorg Chem. 2021 Nov 15;60(22):16977-16985. doi: 10.1021/acs.inorgchem.1c01932. Epub 2021 Nov 3.
Recently, there has been an increased interest in quaternary clathrate systems as promising thermoelectric materials. Because of their increased complexity, however, the chemical ordering in the host framework of quaternary clathrates has not yet been comprehensively analyzed. Here, we have synthesized a prototypical quaternary type-I clathrate BaAlGaGe by Czochralski and flux methods, and we employed a combination of X-ray and neutron diffraction along with atomic scale simulations to investigate chemical ordering in this material. We show that the site occupancy factors of trivalent elements at the 6 site differ, depending on the synthesis method, which can be attributed to the level of equilibration. The flux-grown samples are consistent with the simulated high-temperature disordered configuration, while the degree of ordering for the Czochralski sample lies between the ground state and the high-temperature state. Moreover, we demonstrate that the atomic displacement parameters of the Ba atoms in the larger tetrakaidecahedral cages are related to chemical ordering. Specifically, Ba atoms are either displaced toward the periphery or localized at the cage centers. Consequently, this study reveals key relationships between the chemical ordering in the quaternary clathrates BaAlGaGe and the structural properties, thereby offering new perspectives on designing these materials and optimizing their thermoelectric properties.
最近，作为有前景的热电材料，四元笼合物体系受到了越来越多的关注。然而，由于其复杂性增加，四元笼合物主体框架中的化学有序性尚未得到全面分析。在这里，我们通过提拉法和助熔剂法合成了典型的I型四元笼合物BaAlGaGe，并结合X射线和中子衍射以及原子尺度模拟来研究该材料中的化学有序性。我们表明，6位三价元素的占位因子因合成方法而异，这可归因于平衡水平。助熔剂生长的样品与模拟的高温无序构型一致，而提拉法样品的有序度介于基态和高温态之间。此外，我们证明了较大十四面体笼中Ba原子的原子位移参数与化学有序性有关。具体来说，Ba原子要么向周边位移，要么定位在笼中心。因此，本研究揭示了四元笼合物BaAlGaGe中的化学有序性与结构性质之间的关键关系，从而为设计这些材料和优化其热电性能提供了新的视角。
