New Trick for an Old Dog: From Prediction to Properties of “Hidden Clathrates” Ba2Zn5As6 and Ba2Zn5Sb6,Journal of the American Chemical Society

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New Trick for an Old Dog: From Prediction to Properties of “Hidden Clathrates” Ba2Zn5As6 and Ba2Zn5Sb6
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-02-14 , DOI: 10.1021/jacs.2c12435
Philip Yox _{1,

2} , Frank Cerasoli ₃ , Arka Sarkar _{1,

2} , Victoria Kyveryga ₁ , Gayatri Viswanathan _{1,

2} , Davide Donadio ₃ , Kirill Kovnir _{1,

2}

Affiliation

The zinc–antimony phase space has been heavily investigated due to the structural complexity and abundance of high-performing thermoelectric materials. Consequentially, the desire to use zinc and antimony as framework elements to encage rattling cations and achieve phonon-glass-electron-crystal-type properties has remained an enticing goal with only two alkali metal clathrates to date, Cs₈Zn₁₈Sb₂₈ and K₅₈Zn₁₂₂Sb₂₀₇. Guided by Zintl electron-counting predictions, we explored the Ba–Zn–Pn (Pn = As, Sb) phase space proximal to the expected composition of the type-I clathrate. In situ powder X-ray diffraction studies revealed two “hidden” compounds which can only be synthesized in a narrow temperature range. The ex situ synthesis and crystal growth unveiled that instead of type-I clathrates, compositionally close but structurally different new clathrate-like compounds formed, Ba₂Zn₅As₆ and Ba₂Zn₅Sb₆. These materials crystallize in a unique structure, in the orthorhombic space group Pmna with the Wyckoff sequence i²h⁶gfe. Single-phase synthesis enabled the exploration of their transport properties. Rattling of the Ba cations in oversized cages manifested low thermal conductivity, which, coupled with the high Seebeck coefficients observed, are prerequisites for a promising thermoelectric material. Potential for further optimization of the thermoelectric performance by aliovalent doping was computationally analyzed.

中文翻译：

老狗的新把戏：从预测到“隐藏包合物”Ba2Zn5As6 和 Ba2Zn5Sb6 的性质

由于高性能热电材料的结构复杂性和丰富性，人们对锌-锑相空间进行了大量研究。因此，使用锌和锑作为框架元素来捕获不稳定的阳离子并实现声子-玻璃-电子-晶体类型特性的愿望仍然是一个诱人的目标，迄今为止只有两种碱金属包合物 Cs 8 _Zn 18 _Sb 28_和K ₅₈锌₁₂₂锑₂₀₇。在 Zintl 电子计数预测的指导下，我们探索了 Ba-Zn- Pn ( Pn= As, Sb) 相空间接近于 I 型包合物的预期组成。原位粉末 X 射线衍射研究揭示了两种只能在狭窄温度范围内合成的“隐藏”化合物。非原位合成和晶体生长表明，形成的不是 I 型包合物，而是组成上接近但结构不同的新型包合物状化合物 Ba ₂ Zn ₅ As ₆和 Ba ₂ Zn ₅ Sb ₆。这些材料以独特的结构结晶，在具有威科夫序列i ² h ⁶ gfe的正交空间群Pmna中. 单相合成使探索它们的传输特性成为可能。超大笼中 Ba 阳离子的嘎嘎声表明热导率低，再加上观察到的高塞贝克系数，是有前途的热电材料的先决条件。通过计算分析了通过异价掺杂进一步优化热电性能的潜力。

更新日期：2023-02-14

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