Synthesis, Crystal Structure, and Thermoelectric Properties of Na2+xAl2+xSn4–x (x = −0.38, –0.24)

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• 作者：Masahiro Kanno ; Takahiro Yamada ; Hisanori Yamane ; Hideaki Nagai
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：January 26, 2016
• 年：2016
• 卷：28
• 期：2
• 页码：601-607
• 全文大小：349K
• ISSN：1520-5002

文摘

Single crystals of novel compounds, Na_2+xAl_2+xSn_4–x with x = ?0.38 and ?0.24, were prepared by slow cooling from the melts of the constituent element metals from 1023 and 1123 K, respectively. Single-crystal X-ray diffraction analysis revealed that the compounds crystallize in hexagonal cells (space group P6₁22) (x = ?0.38, a = 6.4050(6) and c = 6.1427(6) ?; x = ?0.24, a = 6.3984(3) and c = 6.1529(3) ?). In the crystal structures, four-bonded Al and Sn atoms form frameworks in which helical tunnels are contained. Na atoms are statistically arranged at positions of a 6b site in the tunnels with occupancies of approximately 0.3. Polycrystalline bulk samples with a nominal composition X = ?0.24 were prepared by heating compacts of a NaSn, Al, and Sn powder mixture at 623 K. The electrical conductivity and Seebeck coefficient of the polycrystalline samples changed from 3.09 × 10³ to 1.03 × 10⁴ S m^–1 and from ?222 to ?185 μV K^–1, respectively, with increasing temperature from 295 to 472 K. The thermal conductivity was 0.29–0.36 W m^–1 K^–1 at 295–371 K. The dimensionless figures of merit ZT were 0.15–0.21 at 295–371 K.