Geometry and vibrational frequencies of the ground state of Si2O2 molecule are studied using density function theory （DFT） at the level of cc-pvtz and 6-311-k＋G^＊＊. It is found that the optimizing value by B31yp/...Geometry and vibrational frequencies of the ground state of Si2O2 molecule are studied using density function theory （DFT） at the level of cc-pvtz and 6-311-k＋G^＊＊. It is found that the optimizing value by B31yp/cc-pvtz is closer to the experimental data. The excited properties under different external electric fields are also investigated by the time-dependent-DFT method. Transitions from the ground state of Si2O2 molecule to the first singlet state under different external electric fields can take place more easily. The corresponding absorption spectral line is about 360 nm in wavelength and the excitation energy is about 3.4 eV.展开更多
SnSe is considered to be a promising thermoelectric material due to a high ZT value and abundant and non-toxic composition elements.However,the thermal stability is an important issue for commercial application.In par...SnSe is considered to be a promising thermoelectric material due to a high ZT value and abundant and non-toxic composition elements.However,the thermal stability is an important issue for commercial application.In particular,thermoelectric materials are in the high temperature for a long time due to the working condition.The present work investigates the thermal stability and oxidation resistance of single crystal SnSe thermoelectric materials.The scanning electron microscopy(SEM)and transmission electron microscopy(TEM)results show that the internal of SnSe crystal is not easily oxidized,while the x-ray photoelectron spectroscopy(XPS)results indicate that the surface of SnSe is slight oxidized to SnO_(2).Even if the surface is oxidized,the SnSe crystal still exhibits stable thermoelectric properties.Meanwhile,the crystallization quality of SnSe samples can be improved after the appropriate heat treatment in the air,which is in favor of the carrier mobility and can improve the electrical conduction properties of SnSe.Moreover,the decrease of defect density after heat treatment can further improve the Seebeck coefficient and electrical transport properties of SnSe.The density functional theory(DFT)calculation verifies the important role of defect on the electrical conductivity and electron configuration.In summary,appropriate temperature annealing is an effective way to improve the transmission properties of SnSe single crystal thermoelectric materials.展开更多
The 0.9Pb（Sc0.5Ta0.5）O3-0.1PbTiO3/0.55Pb（Sc0.5Ta0.5）O3-0.45 PbTiO3 multilayer thin films（（PSTT10/45）n, n = 1-6, 10） are deposited on SiO2/Si（100） substrates by radio frequency magnetron sputtering technique ...The 0.9Pb（Sc0.5Ta0.5）O3-0.1PbTiO3/0.55Pb（Sc0.5Ta0.5）O3-0.45 PbTiO3 multilayer thin films（（PSTT10/45）n, n = 1-6, 10） are deposited on SiO2/Si（100） substrates by radio frequency magnetron sputtering technique with La Ni O3 buffer and electrode layer, and the films are subsequently annealed by a two-step rapid thermal approach. It is found that the interfacial density of the film has an important influence on the electric property of the film. The electric property of the film increases and reaches its critical point with the increase of interface density, and then decreases with the further increase of the interface density. With an interfacial density of 16 μm-1, the film shows an optimized dielectric property（high dielectric constant, εr = 765, lowest dielectric loss, tan δ = 0.041, at 1 k Hz） and ferroelectric property（highest remnant polarization,2Pr = 36.9 μC/cm2, low coercive field, 2Ec = 71.9 k V/cm）. The possible reason for the electric behavior of the film is the competition of the interface stress with the interface defect.展开更多
通过对多壁碳纳米管(MWNTS)／高密度聚乙烯(High density polyethylene,HDPE)复合材料的电阻- 温度特性进行了研究。发现MWNTs填充质量分数为1％-2％时,复合体系呈现渗流行为,表现出优异的导电性。同时体系存在特殊的V形温度系数特性(V-...通过对多壁碳纳米管(MWNTS)／高密度聚乙烯(High density polyethylene,HDPE)复合材料的电阻- 温度特性进行了研究。发现MWNTs填充质量分数为1％-2％时,复合体系呈现渗流行为,表现出优异的导电性。同时体系存在特殊的V形温度系数特性(V-PTC特性),即当MWNTs质量分数超过渗流阈值后,体系的电阻率随温度的升高先下降,出现负温度系数特性(NTC转变),然后才出现通常的正温度系数特性(PTC 转变),且具有很好的循环稳定性。V-PTC这种特性源于基体体积膨胀、MWNTs缠结链松弛以及基体的“退火”效应的协同作用。马来酸酐接枝苯乙烯-(乙烯-丁烯)-苯乙烯共聚物(MA-g-SEBS)的加入,可改善MWNTs 和HDPE之间的相互作用,并可基本上消除V-PTC特性,改善导电性。展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 10774039)the Natural Science Foundation of Henan Province,China (Grant No. 092300410249)+1 种基金the Natural Science Foundation of the Education Bureau of Henan Province,China (Grant No. 2010A140008)the Foundation for University Young Core Instructors of Henan Province,China (Grant No. 2009GGJS-044)
文摘Geometry and vibrational frequencies of the ground state of Si2O2 molecule are studied using density function theory （DFT） at the level of cc-pvtz and 6-311-k＋G^＊＊. It is found that the optimizing value by B31yp/cc-pvtz is closer to the experimental data. The excited properties under different external electric fields are also investigated by the time-dependent-DFT method. Transitions from the ground state of Si2O2 molecule to the first singlet state under different external electric fields can take place more easily. The corresponding absorption spectral line is about 360 nm in wavelength and the excitation energy is about 3.4 eV.
基金Project supported by the National Natural Science Foundation of China(Grant No.61864012)
文摘SnSe is considered to be a promising thermoelectric material due to a high ZT value and abundant and non-toxic composition elements.However,the thermal stability is an important issue for commercial application.In particular,thermoelectric materials are in the high temperature for a long time due to the working condition.The present work investigates the thermal stability and oxidation resistance of single crystal SnSe thermoelectric materials.The scanning electron microscopy(SEM)and transmission electron microscopy(TEM)results show that the internal of SnSe crystal is not easily oxidized,while the x-ray photoelectron spectroscopy(XPS)results indicate that the surface of SnSe is slight oxidized to SnO_(2).Even if the surface is oxidized,the SnSe crystal still exhibits stable thermoelectric properties.Meanwhile,the crystallization quality of SnSe samples can be improved after the appropriate heat treatment in the air,which is in favor of the carrier mobility and can improve the electrical conduction properties of SnSe.Moreover,the decrease of defect density after heat treatment can further improve the Seebeck coefficient and electrical transport properties of SnSe.The density functional theory(DFT)calculation verifies the important role of defect on the electrical conductivity and electron configuration.In summary,appropriate temperature annealing is an effective way to improve the transmission properties of SnSe single crystal thermoelectric materials.
基金Project supported by the National Natural Science Foundation of China(Grant No.60771016)the Scientific Research Foundation of Mianyang Normal University,China(Grant No.QD2013A07)
文摘The 0.9Pb（Sc0.5Ta0.5）O3-0.1PbTiO3/0.55Pb（Sc0.5Ta0.5）O3-0.45 PbTiO3 multilayer thin films（（PSTT10/45）n, n = 1-6, 10） are deposited on SiO2/Si（100） substrates by radio frequency magnetron sputtering technique with La Ni O3 buffer and electrode layer, and the films are subsequently annealed by a two-step rapid thermal approach. It is found that the interfacial density of the film has an important influence on the electric property of the film. The electric property of the film increases and reaches its critical point with the increase of interface density, and then decreases with the further increase of the interface density. With an interfacial density of 16 μm-1, the film shows an optimized dielectric property（high dielectric constant, εr = 765, lowest dielectric loss, tan δ = 0.041, at 1 k Hz） and ferroelectric property（highest remnant polarization,2Pr = 36.9 μC/cm2, low coercive field, 2Ec = 71.9 k V/cm）. The possible reason for the electric behavior of the film is the competition of the interface stress with the interface defect.
