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	High-Temperature Structural and Thermoelectric Study,of Argyrodite Ag8GeSe6
	Shen, Xingchen1,2,3,4; Yang, Chun-Chuen5; Liu, Yamei2; Wang, Guiwen6; Tan, Huan1; Tung, Yung-Hsiang5; Wang, Guoyu3,4; Lu, Xu1; He, Jian2; Zhou, Xiaoyuan1,6
	2019-01-16
摘要	Argyrodites with a general chemical formula of A(8)BX(6) (A = Cu, Ag; B = Si, Ge, Sn; and X = S, Se, and Te) are known for the intimate interplay among mobile ions, electrons, and phonons, which yields rich material physics and materials chemistry phenomena. In particular, the coexistence of fast ionic conduction and promising thermoelectric performance in Ag8GeTe6, Ag8SnSe6, Ag8SiTe6, Ag8SiSe6, and Cu8GeSe6 at high temperatures ushered us to their chemical neighbor Ag8GeSe6, whose high-temperature crystal structure and thermoelectric properties are not yet reported. In this work, we have employed a growth-from-the-melt technique followed by hot pressing to prepare polycrystalline Ag8GeSe6 samples, on which the crystal structure, micro-morphology, compositional analysis, UV vis absorption, specific heat, speed of sound, and thermoelectric properties were characterized as a function of the Se-deficiency ratio and temperature. We found that (i) the crystal structure of Ag8GeSe6 evolved from orthorhombic at room temperature to face center cubic above 410 K, with a region of phase separations in between; (ii) like other argyrodite 816 phases, Ag8GeSe6 exhibited ultralow thermal conductivities over a wide temperature range as the phonon mean free path was down to the order of interatomic spacing; and (iii) varying Se deficiency effectively optimized the carrier concentration and power factor, a figure of merit zT value similar to 0.55 was achieved at 923 K in Ag8GeSe5.88. These results not only fill a knowledge gap of Ag8GeSe6 but also contribute to a comprehensive understanding of 816 phase argyrodites at large.
关键词	Ag8GeSe6 argyrodites crystal structure lattice dynamics elastic properties thermoelectric properties
DOI	10.1021/acsami.8b19819
发表期刊	ACS APPLIED MATERIALS & INTERFACES
ISSN	1944-8244
卷号	11期号:2页码:2168-2176
收录类别	SCI
WOS记录号	WOS:000456351100047
语种	英语