Element doping is a widely employed strategy to enhance the thermoelectric(TE)properties of various materials.β-FeSi_(2)is a promising low-cost high-temperature TE material with exceptional thermal stabil-ity;however...Element doping is a widely employed strategy to enhance the thermoelectric(TE)properties of various materials.β-FeSi_(2)is a promising low-cost high-temperature TE material with exceptional thermal stabil-ity;however,the doping limit ofβ-FeSi_(2)is usually very low,which limits the tunability of electrical and thermal properties.Recently,a high doping content of 0.16 inβ-FeSi_(2)has been achieved by the introduc-tion of iridium(Ir),leading to the highest reported figure of merit(zT)of 0.6 inβ-FeSi_(2).Motivated by the successful heavy doping with Ir,this work aims to explore element heavy doping inβ-FeSi_(2)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-FeSi_(2)through a prolonged annealing process.Despite the absence of a substantial enhancement in the zT of Co-dopedβ-FeSi_(2)at high doping levels,with a maximum zT of 0.3 at 900 K in Fe_(0.92)Co_(0.08)Si_(2),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-x Cox Si_(2)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-x Cox Si_(2)(x>0.16)mirrors that of Ir-dopedβ-FeSi_(2),but Fe1-x Cox Si_(2)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 inβ-FeSi_(2),helpful for the further development of this TE system.展开更多
We successfully synthesize a series of polycrystalline CeRuxFe1-xCe3（0≤x≤0.5）samples,which are characterized using powder x-ray diffraction,resistivity and specific heat measurements.The expansion of the lattice c...We successfully synthesize a series of polycrystalline CeRuxFe1-xCe3（0≤x≤0.5）samples,which are characterized using powder x-ray diffraction,resistivity and specific heat measurements.The expansion of the lattice constants with increasing x demonstrates the successful doping of Ru into the CeFeGe3 lattice.Upon doping,it is found that the temperature up to which Landau-Fermi liquid behavior is observed in the resistivity is reduced.Meanwhile,there is also a pronounced increase in the resistivity coefficient and residual resistivity,as well as a clear upturn in C/T at low temperatures,suggesting that Ru doping may tune the system towards a quantum critical point.展开更多
The P‐type 4H‐SiC epitaxy has gained increased interest due to the pressure of power devices demand.The objective of this study was to understand the behaviors of aluminum(Al)dopant influenced by different chemical ...The P‐type 4H‐SiC epitaxy has gained increased interest due to the pressure of power devices demand.The objective of this study was to understand the behaviors of aluminum(Al)dopant influenced by different chemical potentials(i.e.,growth monomers)on the different atomic step surfaces and therefore,design an optimized growth method to achieve a heavily‐doped,high‐quality,and large‐size epitaxy.The theoretical simulations showed that a C‐rich growth condition(i.e.,high C/Si ratio)was beneficial to the adsorption of Al atom on the 4H‐SiC step surfaces,but the potentially negative impact on the step heights required attention.Subsequently,6‐inch epitaxial experiments with four C/Si ratios were designed and tested,and a compromise between the doping efficiency and material quality was found.A growth optimization was further conducted,and a 1.0×10^(19)cm^(−3)Al‐doping concentration was ach-ieved in the epitaxial growth but without sacrificing material quality.This study demonstrated a growth method of monomers selection to control the Al‐doping concentration from the theoretical to experimental aspects and could contribute to the field of power device fabrication.展开更多
基金This work was supported by the National Natural Science Foun-dation of China(Nos.91963208,52232010,and 52122213)the Shanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai Branch(No.JCYJ-SHFY-2022–002)+3 种基金Shang-hai Government(No.20JC1415100)The authors would like to thank the synchrotron beamline RIKEN BL44B2(No.2023A1294)at SPring-8 for the beamtime allocationKenichi Kato is acknowl-edged for support during synchrotron experiments at BL44B2This work also acknowledged the Shanghai Technical Service Center of Science and Engineering Computing,Shanghai University.
文摘Element doping is a widely employed strategy to enhance the thermoelectric(TE)properties of various materials.β-FeSi_(2)is a promising low-cost high-temperature TE material with exceptional thermal stabil-ity;however,the doping limit ofβ-FeSi_(2)is usually very low,which limits the tunability of electrical and thermal properties.Recently,a high doping content of 0.16 inβ-FeSi_(2)has been achieved by the introduc-tion of iridium(Ir),leading to the highest reported figure of merit(zT)of 0.6 inβ-FeSi_(2).Motivated by the successful heavy doping with Ir,this work aims to explore element heavy doping inβ-FeSi_(2)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-FeSi_(2)through a prolonged annealing process.Despite the absence of a substantial enhancement in the zT of Co-dopedβ-FeSi_(2)at high doping levels,with a maximum zT of 0.3 at 900 K in Fe_(0.92)Co_(0.08)Si_(2),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-x Cox Si_(2)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-x Cox Si_(2)(x>0.16)mirrors that of Ir-dopedβ-FeSi_(2),but Fe1-x Cox Si_(2)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 inβ-FeSi_(2),helpful for the further development of this TE system.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474251,11604291 and U1632275the National Key Research and Development Program of China under Grant Nos 2017YFA0303100 and 2016YFA0300202the Science Challenge Project of China under Grant No TZ2016004
文摘We successfully synthesize a series of polycrystalline CeRuxFe1-xCe3（0≤x≤0.5）samples,which are characterized using powder x-ray diffraction,resistivity and specific heat measurements.The expansion of the lattice constants with increasing x demonstrates the successful doping of Ru into the CeFeGe3 lattice.Upon doping,it is found that the temperature up to which Landau-Fermi liquid behavior is observed in the resistivity is reduced.Meanwhile,there is also a pronounced increase in the resistivity coefficient and residual resistivity,as well as a clear upturn in C/T at low temperatures,suggesting that Ru doping may tune the system towards a quantum critical point.
基金Key Scientific and Technological Program of Xiamen,Grant/Award Number:3502Z20231045Innovation Program for Quantum Science and Technology,Grant/Award Number:2021ZD0303400。
文摘The P‐type 4H‐SiC epitaxy has gained increased interest due to the pressure of power devices demand.The objective of this study was to understand the behaviors of aluminum(Al)dopant influenced by different chemical potentials(i.e.,growth monomers)on the different atomic step surfaces and therefore,design an optimized growth method to achieve a heavily‐doped,high‐quality,and large‐size epitaxy.The theoretical simulations showed that a C‐rich growth condition(i.e.,high C/Si ratio)was beneficial to the adsorption of Al atom on the 4H‐SiC step surfaces,but the potentially negative impact on the step heights required attention.Subsequently,6‐inch epitaxial experiments with four C/Si ratios were designed and tested,and a compromise between the doping efficiency and material quality was found.A growth optimization was further conducted,and a 1.0×10^(19)cm^(−3)Al‐doping concentration was ach-ieved in the epitaxial growth but without sacrificing material quality.This study demonstrated a growth method of monomers selection to control the Al‐doping concentration from the theoretical to experimental aspects and could contribute to the field of power device fabrication.
