The role of simultaneous substitution of Cr and Ru on the thermoelectric properties of defect manganese silicides MnSi_¦Ä (1.73 < ¦Ä < 1.75)

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• 作者：V. Ponnambalam ; Donald T. Morelli ; S. Bhattacharya ; Terry M. Tritt
• 关键词：Higher manganese silicides ; Thermoelectrics ; Seebeck coefficient ; Resistivity ; Hall coefficient
• 刊名：Journal of Alloys and Compounds
• 出版年：2013
• 出版时间：15 December, 2013
• 年：2013
• 卷：580
• 期：Complete
• 页码：598-603
• 全文大小：1916 K

文摘

Defect manganese silicides have been substituted with Cr and Ru, in order to study the role of these substitutions on the resulting resistivity (¦Ñ), Seebeck (¦Á) and Hall coefficients and thermal conductivity. The resistivity and Seebeck coefficient measurements suggest that these compounds are degenerate semiconductors. The Hall measurements indicate that the carrier concentration increases in Cr and Ru substituted compounds. The majority carriers are holes and the change of hole concentration is only marginal. While the hole concentration (p) of MnSi_1.74 is ¡«2.1 ¡Á 10²¹ cm^?3, in heavily substituted Mn_0.65Cr_0.2Ru_0.15Si_1.74, p increases only to ¡«4.5 ¡Á 10²¹ cm^?3. The increase in p is presumably due to Si precipitation. One interesting feature is the low lattice thermal conductivity (¦Ê_L) which is ¡«2-2.5 W/m K at 300 K depending upon the composition. In addition, ¦Ê_L shows a weak temperature dependence. Because of the combination of high power factor (¦Á²/¦Ñ) ¡« 2 mW/m K² and low thermal conductivity ¡«2.5-2.7 W/m K, Mn_0.95Cr_0.5Si_1.74 and Mn_0.97Cr_0.3Si_1.74 exhibit highest ZT of 0.6 at 850 K. For other compounds, a moderate ZT value of 0.3-0.5 is realized at 850 K. In Ru substituted compounds, the ZT is not improved beyond 0.5, due to the decrease of charge carrier mobility.