Kumari Nirma, Pai Namit, Chavan Vikram, Sarkar Arnab, Sarkar Debattam, Biswas Kanishka, Samajdar Indradev, Dasgupta Titas
Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400 076, India.
New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560064, India.
ACS Appl Mater Interfaces. 2023 Oct 11;15(40):46995-47003. doi: 10.1021/acsami.3c09988. Epub 2023 Sep 29.
MgSbBi solid-solutions represent an important class of thermoelectric (TE) materials due to their high efficiency and variable operating temperature range. Of particular significance for midtemperature applications is the MgSbBi composition whose superior thermoelectric (TE) performance is attributed to the complex conduction band edge in conjunction with alloy dominated phonon scattering. In this work, we show that microstructure also plays a significant role in lowering the lattice thermal conductivity which in turn affects the overall TE performance (change in peak zT values between 1.1 and 1.4 have been observed). Temperature dependent TE properties of MgSbBi compositions with varying nominal Mg content ( = 0.2, 0.3, 0.4) have been studied. A marked reduction of the lattice thermal conductivity (κ) is observed in compositions with low nominal Mg content ( = 0.2), which is due to the presence of lamellar structures within the grains. These lamellar regions are isostructural to the matrix with a low misfit angle and represent compositional fluctuations in the Bi to Sb ratio. Both the size (200 nm-500 nm) and the interfacial strain contribute to the enhanced phonon scattering. A quantitative estimate of κ reduction due to these structures have been carried out using a mean free path (MFP) spectrum analysis which reveal a good match with experiments at room temperature. Further, the electrical properties are not influenced by these lamellar structures as observed from the similar power-factor (σ) and weighted mobilities in all of the compositions. This is due to their similar orientation to the adjacent matrix region. Thus, the zT parameter in the various compositions with similar carrier concentration can be significantly altered (∼25%) by adjusting the nominal Mg content. The results demonstrate that preferential phonon scattering by microstructure modification can be a new route for property improvement in MgSbBi solid-solutions.
MgSbBi固溶体因其高效率和可变的工作温度范围而成为一类重要的热电（TE）材料。对于中温应用而言，特别重要的是MgSbBi成分，其优异的热电（TE）性能归因于复杂的导带边缘以及合金主导的声子散射。在这项工作中，我们表明微观结构在降低晶格热导率方面也起着重要作用，这反过来又影响了整体TE性能（观察到峰值zT值在1.1和1.4之间变化）。研究了具有不同名义Mg含量（= 0.2、0.3、0.4）的MgSbBi成分的温度依赖性TE特性。在名义Mg含量低（= 0.2）的成分中观察到晶格热导率（κ）显著降低，这是由于晶粒内存在层状结构。这些层状区域与基体同构，错配角低，代表了Bi与Sb比例的成分波动。尺寸（200 nm - 500 nm）和界面应变都有助于增强声子散射。使用平均自由程（MFP）谱分析对由于这些结构导致的κ降低进行了定量估计，结果表明在室温下与实验结果吻合良好。此外，从所有成分中相似的功率因子（σ）和加权迁移率可以看出，这些层状结构不会影响电学性能。这是由于它们与相邻基体区域的取向相似。因此，通过调整名义Mg含量，在具有相似载流子浓度的各种成分中，zT参数可以显著改变（约25%）。结果表明，通过微观结构改性实现的优先声子散射可以成为改善MgSbBi固溶体性能的新途径。
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