Ghosh Sanyukta, Shankar Gyan, Karati Anirudha, Rogl Gerda, Rogl Peter, Bauer Ernst, Murty B S, Suwas Satyam, Mallik Ramesh Chandra
Thermoelectric Materials and Devices Laboratory, Department of Physics, Indian Institute of Science, Bangalore 560012, India.
Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India.
Dalton Trans. 2020 Nov 17;49(44):15883-15894. doi: 10.1039/d0dt03429k.
Filling the voids of cage forming compounds with loosely bound electropositive elements and by incorporating nano-sized secondary phases are promising approaches to enhance the thermoelectric figure of merit of these materials. Hence, in this work, by combining these two approaches-inserting In into the voids of skutterudite Co4Sb12 as well as dispersing nanoparticles (GaSb)-we have synthesized various samples via ball-milling and spark plasma sintering. InSb as the secondary phase of the matrix, mixed with GaSb, forms the solid solution Ga1-xInxSb. Nanocrystalline grains together with a few larger grains (10-30 μm) are found to be spread in In0.2Co4Sb12. The former is comprised of either InSb, GaSb or Ga1-xInxSb. Because of their identical space group and similar lattice parameters, InSb, GaSb and Ga1-xInxSb could not be detected separately in EBSD. High resolution transmission electron microscopy (HRTEM) was used to resolve different phases, which showed GaSb grains of size ∼10-30 nm and InSb grains of size ∼30-100 nm. Scattering of charge carriers at the interfaces of InSb, GaSb and Ga1-xInxSb as well as the matrix phases increased both the electrical resistivity and Seebeck coefficient. The multi-scale size distribution of grains, of both the matrix phase and the secondary phases, scattered phonons within a broad wavelength range, resulting in very low lattice thermal conductivities. As a result, an enhanced figure of merit of 1.4 was achieved for the (GaSb)0.1 + In0.2Co4Sb12 nanocomposite at 773 K.
用松散结合的正电元素填充笼状形成化合物的空隙，并引入纳米尺寸的第二相，是提高这些材料热电优值的有前景的方法。因此，在本工作中，通过结合这两种方法——将铟插入方钴矿Co4Sb12的空隙以及分散纳米颗粒（锑化镓）——我们通过球磨和放电等离子体烧结合成了各种样品。作为基体第二相的锑化铟与锑化镓混合，形成固溶体Ga1-xInxSb。发现纳米晶粒与一些较大的晶粒（10 - 30微米）散布在In0.2Co4Sb12中。前者由锑化铟、锑化镓或Ga1-xInxSb组成。由于它们相同的空间群和相似的晶格参数，在电子背散射衍射（EBSD）中无法分别检测到锑化铟、锑化镓和Ga1-xInxSb。使用高分辨率透射电子显微镜（HRTEM）来分辨不同的相，结果显示锑化镓晶粒尺寸约为10 - 30纳米，锑化铟晶粒尺寸约为30 - 100纳米。电荷载流子在锑化铟、锑化镓和Ga1-xInxSb以及基体相的界面处的散射增加了电阻率和塞贝克系数。基体相和第二相的晶粒的多尺度尺寸分布在很宽的波长范围内散射声子，导致非常低的晶格热导率。结果，在773 K时，（GaSb）0.1 + In0.2Co4Sb12纳米复合材料的优值提高到了1.4。
