Thermoelectric stability of Eu- and Na-substituted PbTe

As one family of the most investigated thermoelectrics (TE), PbTe-based materials have been developed into state-of-the-art p-type and n-type TE materials. However, there are quite a few studies focusing on the reproducibility of TE properties and microstructure evolution during different heat treat...

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Published in:Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2018, Vol.6 (35), p.9482-9493
Main Authors: Wang, Xinke, Veremchuk, Igor, Burkhardt, Ulrich, Bobnar, Matej, Böttner, Harald, Kuo, Chang-Yang, Chen, Chien-Te, Chang, Chun-Fu, Zhao, Jing-Tai, Grin, Yuri
Format: Article
Language:English
Subjects:
Annealing
Carrier density
Europium
Heat treating
Heat treatment
Intermetallic compounds
Laser sintering
Lattice parameters
Microstructure
Reproducibility
Sodium
Spark plasma sintering
Surface stability
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Summary:As one family of the most investigated thermoelectrics (TE), PbTe-based materials have been developed into state-of-the-art p-type and n-type TE materials. However, there are quite a few studies focusing on the reproducibility of TE properties and microstructure evolution during different heat treatments. In this work, Pb 0.98− x Na 0.02 Eu x Te ( x = 0-0.030) samples were systematically examined after three different kinds of heat treatments: spark plasma sintering (SPS), laser flash measurement (LFA), and long-term annealing. The maximal solubility of Eu ( ca. 1.0 atom%) in Pb 0.98− x Na 0.02 Eu x Te was established at 873 K. The most inhomogeneous samples (samples after SPS) show highest values of figure-of-merit, ZT max , of up to 2.1 at 760 K, due to a large number of micrometer-scale sodium- and europium-rich aggregations in them. After additional heat treatment (LFA measurement or long-term annealing), the ZT max value reduces to 1.6. The distribution of Eu and Na in the samples becomes much more homogeneous, accompanied by increased lattice parameters and decreased carrier concentrations. The long-term annealed samples have the best stable TE properties and good mechanical stability in the cyclic measurements. Surface protection needs to be considered for the temperatures above 773 K in order to avoid material decomposition. The out-of-equilibrium samples show highest values of figure-of-merit, ZT max , up to 2.1.
ISSN:2050-7526
2050-7534
DOI:10.1039/c8tc03142h