Wang Jian, Lebedev Oleg I, Lee Kathleen, Dolyniuk Juli-Anna, Klavins Peter, Bux Sabah, Kovnir Kirill
Department of Chemistry , Iowa State University , Ames , Iowa 50011 , USA.
Department of Chemistry , University of California , Davis , CA 95616 , USA . Email:
Chem Sci. 2017 Dec 1;8(12):8030-8038. doi: 10.1039/c7sc03482b. Epub 2017 Sep 29.
A new type-I clathrate, BaCuGeP, was synthesized by solid-state methods as a polycrystalline powder and grown as a cm-sized single crystal the vertical Bridgman method. Single-crystal and powder X-ray diffraction show that BaCuGeP crystallizes in the cubic space group 3 (no. 223). BaCuGeP is the first representative of anionic clathrates whose framework is composed of three atom types of very different chemical natures: a transition metal, tetrel element, and pnicogen. Uniform distribution of the Cu, Ge, and P atoms over the framework sites and the absence of any superstructural or local ordering in BaCuGeP were confirmed by synchrotron X-ray diffraction, electron diffraction and high-angle annular dark field scanning transmission electron microscopy, and neutron and X-ray pair distribution function analyses. Characterization of the transport properties demonstrate that BaCuGeP is a p-type semiconductor with an intrinsically low thermal conductivity of 0.72 W m K at 812 K. The thermoelectric figure of merit, , for a slice of the Bridgman-grown crystal of BaCuGeP approaches 0.63 at 812 K due to a high power factor of 5.62 μW cm K. The thermoelectric efficiency of BaCuGeP is on par with the best optimized p-type Ge-based clathrates and outperforms the majority of clathrates in the 700-850 K temperature region, including all tetrel-free clathrates. BaCuGeP expands clathrate chemistry by bridging conventional tetrel-based and tetrel-free clathrates. Advanced transport properties, in combination with earth-abundant framework elements and congruent melting make BaCuGeP a strong candidate as a novel and efficient thermoelectric material.
通过固态方法合成了一种新型的I型包合物BaCuGeP，得到了多晶粉末，并采用垂直布里奇曼法生长出厘米尺寸的单晶。单晶和粉末X射线衍射表明，BaCuGeP结晶于立方空间群Pm3n（编号223）。BaCuGeP是阴离子包合物的首个代表物，其骨架由三种化学性质差异很大的原子类型组成：过渡金属、四价元素和氮族元素。同步辐射X射线衍射、电子衍射、高角度环形暗场扫描透射电子显微镜以及中子和X射线对分布函数分析证实，Cu、Ge和P原子在骨架位点上均匀分布，且BaCuGeP中不存在任何超结构或局部有序。对其输运性质的表征表明，BaCuGeP是一种p型半导体，在812 K时本征热导率低至0.72 W m-1 K-1。由于功率因子高达5.62 μW cm-1 K-2，在812 K时，一片用布里奇曼法生长的BaCuGeP晶体的热电优值zT接近0.63。BaCuGeP的热电效率与最佳优化的p型锗基包合物相当，并且在700 - 850 K温度范围内优于大多数包合物，包括所有无四价元素的包合物。BaCuGeP通过连接传统的含四价元素和无四价元素的包合物，扩展了包合物化学。先进的输运性质，再加上地壳中丰富的骨架元素和一致熔化特性，使BaCuGeP成为一种新型高效热电材料的有力候选者。
