首页|Thermoelectric properties of heavily Co-doped β-FeSi2
Thermoelectric properties of heavily Co-doped β-FeSi2
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Element doping is a widely employed strategy to enhance the thermoelectric(TE)properties of various materials.β-FeSi2 is a promising low-cost high-temperature TE material with exceptional thermal stabil-ity;however,the doping limit of β-FeSi2 is usually very low,which limits the tunability of electrical and thermal properties.Recently,a high doping content of 0.16 in β-FeSi2 has been achieved by the introduc-tion of iridium(Ir),leading to the highest reported figure of merit(zT)of 0.6 in β-FeSi2.Motivated by the successful heavy doping with Ir,this work aims to explore element heavy doping in β-FeSi2 with cobalt(Co),a cheaper,more readily available dopant with a smaller atomic radius and closer electronegativity to iron(Fe).In this study,we successfully obtained a record-high doping content of 0.24 in Co-dopedβ-FeSi2 through a prolonged annealing process.Despite the absence of a substantial enhancement in the zT of Co-doped β-FeSi2 at high doping levels,with a maximum zT of 0.3 at 900 K in Fe0.92Co0.08Si2,we observed a transition in the carrier transport mechanism as a function of Co doping content,attributed to changes in the band structure.At a low Co doping content(x ≤ 0.12),Fe1-xCoxSi2 demonstrates dominant carrier transport via impurity levels within the band gap,exhibiting hopping conduction.As the Co dop-ing content increases(x＞0.16),the impurity levels overlap and form an impurity band,and the carrier transport turns into the impurity band conduction.The observed band conduction behavior of Fe1-xCoxSi2(x＞0.16)mirrors that of Ir-doped β-FeSi2,but Fe1-xCoxSi2 shows much lower mobility,which can be at-tributed to the localized feature of the impurity band introduced by the Co doping.Overall,this study provides insights into the heavy Co doping and its influence on the TE properties and carrier conduction mechanisms in β-FeSi2,helpful for the further development of this TE system.
State Key Laboratory of High Performance Ceramics and Superfine Microstructure,Shanghai Institute of Ceramics,Chinese Academy of Sciences,Shanghai 200050,China
Center of Materials Science and Optoelectronics Engineering,University of Chinese Academy of Sciences,Beijing 100049,China
School of Chemistry and Materials Science,Hangzhou Institute for Advanced Study,University of Chinese Academy of Sciences,Hangzhou 310024,China
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National Natural Science Foundation of ChinaNational Natural Science Foundation of ChinaNational Natural Science Foundation of ChinaShanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai BranchShanghai Governmentsynchrotron beamline RIKEN BL44B2
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