Cu2Se is a promising"phonon liquid-electron crystal"thermoelectric material with excellent thermoelectric performance.In this work,Cd-doped Cu2-xSeCdx(x=0,0.0075,0.01,and 0.02)samples were prepared using NaC...Cu2Se is a promising"phonon liquid-electron crystal"thermoelectric material with excellent thermoelectric performance.In this work,Cd-doped Cu2-xSeCdx(x=0,0.0075,0.01,and 0.02)samples were prepared using NaCl flux method.The solubility of Cd in Cu2Se at room temperature was less than 6%,and a second phase of CdSe was found in the samples with large initial Cd content(x=0.01 and 0.02).Field-emission scanning electron microscopic image showed that the arranged lamellae formed a large-scale layered structure with an average thickness of approximately 100 nm.Transmission electron microscopy demonstrated that doping of Cd atoms did not destroy the crystal integrity of Cu2Se.A small amount of Cd in Cu2Se could reduce the electrical and thermal conductivities of the material,thus significantly enhancing its thermoelectric performance.With the increase in Cd content in the sample,the carrier concentration decreased and the mobility increased gradually.Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point.Excessive Cd doping led to the emergence of the second phase of CdSe in the sample,thus significantly increasing the thermal conductivity of the material.A maximum ZT value of 1.67 at 700 K was obtained in the Cu1.9925SeCd0.0075 sample.展开更多
We study the thermal and electronic transport properties as well as the thermoelectric(TE)performance of three two-dimensional(2 D)XI_(2)(X=Ge,Sn,Pb)bilayers using density functional theory and Boltzmann transport the...We study the thermal and electronic transport properties as well as the thermoelectric(TE)performance of three two-dimensional(2 D)XI_(2)(X=Ge,Sn,Pb)bilayers using density functional theory and Boltzmann transport theory.We compared the lattice thermal conductivity,electrical conductivity,Seebeck coefficient,and dimensionless figure of merit(ZT)for the XI_(2)monolayers and bilayers.Our results show that the lattice thermal conductivity at room temperature for the bilayers is as low as~1.1 W·m^(-1)·K^(-1)-1.7 W·m^(-1)·K^(-1),which is about 1.6 times as large as the monolayers for all the three materials.Electronic structure calculations show that all the XI_(2)bilayers are indirect-gap semiconductors with the band gap values between 1.84 eV and 1.96 eV at PBE level,which is similar as the corresponding monolayers.The calculated results of ZT show that the bilayer structures display much less direction-dependent TE efficiency and have much larger n-type ZT values compared with the monolayers.The dramatic difference between the monolayer and bilayer indicates that the inter-layer interaction plays an important role in the TE performance of XI_(2),which provides the tunability on their TE characteristics.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61864012 and 21701140)the Program for Innovative Research Team(in Science and Technology)in University of Yunnan Province,China.
文摘Cu2Se is a promising"phonon liquid-electron crystal"thermoelectric material with excellent thermoelectric performance.In this work,Cd-doped Cu2-xSeCdx(x=0,0.0075,0.01,and 0.02)samples were prepared using NaCl flux method.The solubility of Cd in Cu2Se at room temperature was less than 6%,and a second phase of CdSe was found in the samples with large initial Cd content(x=0.01 and 0.02).Field-emission scanning electron microscopic image showed that the arranged lamellae formed a large-scale layered structure with an average thickness of approximately 100 nm.Transmission electron microscopy demonstrated that doping of Cd atoms did not destroy the crystal integrity of Cu2Se.A small amount of Cd in Cu2Se could reduce the electrical and thermal conductivities of the material,thus significantly enhancing its thermoelectric performance.With the increase in Cd content in the sample,the carrier concentration decreased and the mobility increased gradually.Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point.Excessive Cd doping led to the emergence of the second phase of CdSe in the sample,thus significantly increasing the thermal conductivity of the material.A maximum ZT value of 1.67 at 700 K was obtained in the Cu1.9925SeCd0.0075 sample.
基金Project supported by the Fundamental Research Fund for the Central Universities and the Zhongying Young Scholar Program of Southeast University。
文摘We study the thermal and electronic transport properties as well as the thermoelectric(TE)performance of three two-dimensional(2 D)XI_(2)(X=Ge,Sn,Pb)bilayers using density functional theory and Boltzmann transport theory.We compared the lattice thermal conductivity,electrical conductivity,Seebeck coefficient,and dimensionless figure of merit(ZT)for the XI_(2)monolayers and bilayers.Our results show that the lattice thermal conductivity at room temperature for the bilayers is as low as~1.1 W·m^(-1)·K^(-1)-1.7 W·m^(-1)·K^(-1),which is about 1.6 times as large as the monolayers for all the three materials.Electronic structure calculations show that all the XI_(2)bilayers are indirect-gap semiconductors with the band gap values between 1.84 eV and 1.96 eV at PBE level,which is similar as the corresponding monolayers.The calculated results of ZT show that the bilayer structures display much less direction-dependent TE efficiency and have much larger n-type ZT values compared with the monolayers.The dramatic difference between the monolayer and bilayer indicates that the inter-layer interaction plays an important role in the TE performance of XI_(2),which provides the tunability on their TE characteristics.
