High quality Sr14-xCaxCu24O41 single-crystals are successfully grown by floating-zone technique, and the trans- port properties are studied. The temperature dependence of resistivity along the c-axis direction is semi...High quality Sr14-xCaxCu24O41 single-crystals are successfully grown by floating-zone technique, and the trans- port properties are studied. The temperature dependence of resistivity along the c-axis direction is semiconductor- like for x ≤ 10 and it can be fitted by the thermal activation equation p = po exp（ △ /kBT） with kB being the Boltzmann constant and A the activation energy. A break in the slope of thermopower （S） versus the inverse temperature （1 IT） corresponding to the formation of charge-density waves （CD W） is first observed for x ≤ 6. The temperature dependence of thermopower becomes metallic for x ≥ 8 while the resistivity is still semiconductorlike. We propose that the insulation behaviour of the resistivity in the Ca doping range 8 ≤ x ≤ 11 could result from the localization of the charge carriers due to the disorder induced by Ca doping and a revised electronic phase diagram is derived based on our observations.展开更多
The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-con...The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-concentration x were obtained by using Rietveld method. The dc resistivity investigated in the temperature range of 80～300 K indicates that the electric properties exhibit a metallic-insulator (semiconducting) (M-I) transition for 0.2<x<0.3. The samples with x=0.2 is close to the M-I transition boundary. The influence of sintering conditions on the lattice parameters, resistivity and the ferromagnetic phase transition temperature T_C of La_ 1-xSr_xCoO_3 for the cases x=0.2 and 0.5 was discussed. The change of the electric properties of semiconductor-like sample (x=0.2) with sintering temperature and sintering period is just opposite to that of metallic sample (x=0.5). Annealing in flowing oxygen can decrease the resistivity of semiconductor-like sample.展开更多
This paper reports that high quality CuGeO3 single crystals were successfully grown by floating-zone technique and the magnetic property was studied. The temperature dependence of magnetic susceptibility below the spi...This paper reports that high quality CuGeO3 single crystals were successfully grown by floating-zone technique and the magnetic property was studied. The temperature dependence of magnetic susceptibility below the spin-Peierls （SP） transition temperature （Tsp） under magnetic fields applying along both the a- and c-axis direction can be fitted well by a model of noninteracting dimmers. The spin gap derived from the fitting is consistent with other reports. There is a very weak anisotropy in the fitting parameters for different directions, which should be expected from a SP system. A small upturn in susceptibility at low temperature due to paramagnetic impurities and/or defects can be observed. A suppression of the upturn by magnetic field is first discovered in this system and the possible origins for this suppression are discussed.展开更多
The measurements of temperature dependence of the magnetic susceptibility of La1-xSrxCoO3 perovskite oxides at different Sr doping （0 ≤x ≤0.5） and annealing temperature were presented. For the sample with x = 0.1,...The measurements of temperature dependence of the magnetic susceptibility of La1-xSrxCoO3 perovskite oxides at different Sr doping （0 ≤x ≤0.5） and annealing temperature were presented. For the sample with x = 0.1, a shoulder was observed around 150 K, and a peak which is one feature of spin glass appeared around 50 K in the curve of susceptibility versus temperature. The high-temperature （250 - 420 K）susceptibility fits well with Curie-Weiss law for all samples. Weiss constant and effective magnetic moment were determined and their variations with Sr doping and oxygen annealing condition were obtained. The Weiss constant increases monotonously with Sr content for x 〉 0.2. The values of effective moments were interpreted with the spin state of cobalt ions. Studies on the susceptibilities of the samples with x = 0.2 under different preparation temperatures and annealing temperatures show that the rising of sintering temperature and annealing temperature will increase the para-ferromagnetic transition temperature, and reduce the effective moment to normal value. Our result shows that both Co^3＋ and Co^4＋ ions should be in IS state after annealing and the oxygen annealing causes the transition of Co^3＋ spin state from HS to IS.展开更多
We investigate the electrical conductivity and thermal conductivity of polycrystalline gold nanofilms,with thicknesses ranging from 40.5nm to 115.8 nm,and identify a thickness-dependent electrical conductivity,which c...We investigate the electrical conductivity and thermal conductivity of polycrystalline gold nanofilms,with thicknesses ranging from 40.5nm to 115.8 nm,and identify a thickness-dependent electrical conductivity,which can be explained via the Mayadas and Shatzkes(MS)theory.At the same time,a suppressed thermal conductivity is observed,as compared to that found in the bulk material,together with a weak thickness effect.We compare the thermal conductivity of suspended and supported gold films,finding that the supporting substrate can effectively suppress the in-plane thermal conductivity of the polycrystalline gold nanofilms.Our results indicate that grain boundary scattering and substrate scattering can affect electron and phonon transport in polycrystalline metallic systems.展开更多
In the Acknowledgement, the following sentence "JH and JL are supported by the National Science Foundation (Award number CBET-1943813) and the Faulty Research and Professional Development Fund at North Carolina S...In the Acknowledgement, the following sentence "JH and JL are supported by the National Science Foundation (Award number CBET-1943813) and the Faulty Research and Professional Development Fund at North Carolina State University" should be changed to "JH and JL are supported by the Faulty Research and Professional Development Fund at North Carolina State University".展开更多
The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time.There have been several approaches to explain the thermal conductivities in these systems,...The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time.There have been several approaches to explain the thermal conductivities in these systems,for example,Bridgman's formula for simple liquids,the concept of the minimum thermal conductivity for amorphous solids,and the thermal resistance network model for amorphous polymers.Here,we present a ubiquitous formula to calculate the thermal conductivities of liquids and amorphous solids in a unified way,and compare it with previous ones.The calculated thermal conductivities using this formula without fitting parameters are in excellent agreement with the experimental data.Our formula not only provides a detailed microscopic mechanism of heat transfer in these systems,but also resolves the discrepancies between existing formulae and experimental data.展开更多
基金Supported by the National Basic Research Programme of China under Grant No 2007CB925001, and the Natural Science Foundation of Zhejiang Province under Grant No Y605106.
文摘High quality Sr14-xCaxCu24O41 single-crystals are successfully grown by floating-zone technique, and the trans- port properties are studied. The temperature dependence of resistivity along the c-axis direction is semiconductor- like for x ≤ 10 and it can be fitted by the thermal activation equation p = po exp（ △ /kBT） with kB being the Boltzmann constant and A the activation energy. A break in the slope of thermopower （S） versus the inverse temperature （1 IT） corresponding to the formation of charge-density waves （CD W） is first observed for x ≤ 6. The temperature dependence of thermopower becomes metallic for x ≥ 8 while the resistivity is still semiconductorlike. We propose that the insulation behaviour of the resistivity in the Ca doping range 8 ≤ x ≤ 11 could result from the localization of the charge carriers due to the disorder induced by Ca doping and a revised electronic phase diagram is derived based on our observations.
文摘The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-concentration x were obtained by using Rietveld method. The dc resistivity investigated in the temperature range of 80～300 K indicates that the electric properties exhibit a metallic-insulator (semiconducting) (M-I) transition for 0.2<x<0.3. The samples with x=0.2 is close to the M-I transition boundary. The influence of sintering conditions on the lattice parameters, resistivity and the ferromagnetic phase transition temperature T_C of La_ 1-xSr_xCoO_3 for the cases x=0.2 and 0.5 was discussed. The change of the electric properties of semiconductor-like sample (x=0.2) with sintering temperature and sintering period is just opposite to that of metallic sample (x=0.5). Annealing in flowing oxygen can decrease the resistivity of semiconductor-like sample.
基金supported by the National Natural Science Foundation of China (Grant No 10634030)the Zhejiang Province Natural Science Foundation of China (Grant No Y605106)
文摘This paper reports that high quality CuGeO3 single crystals were successfully grown by floating-zone technique and the magnetic property was studied. The temperature dependence of magnetic susceptibility below the spin-Peierls （SP） transition temperature （Tsp） under magnetic fields applying along both the a- and c-axis direction can be fitted well by a model of noninteracting dimmers. The spin gap derived from the fitting is consistent with other reports. There is a very weak anisotropy in the fitting parameters for different directions, which should be expected from a SP system. A small upturn in susceptibility at low temperature due to paramagnetic impurities and/or defects can be observed. A suppression of the upturn by magnetic field is first discovered in this system and the possible origins for this suppression are discussed.
文摘The measurements of temperature dependence of the magnetic susceptibility of La1-xSrxCoO3 perovskite oxides at different Sr doping （0 ≤x ≤0.5） and annealing temperature were presented. For the sample with x = 0.1, a shoulder was observed around 150 K, and a peak which is one feature of spin glass appeared around 50 K in the curve of susceptibility versus temperature. The high-temperature （250 - 420 K）susceptibility fits well with Curie-Weiss law for all samples. Weiss constant and effective magnetic moment were determined and their variations with Sr doping and oxygen annealing condition were obtained. The Weiss constant increases monotonously with Sr content for x 〉 0.2. The values of effective moments were interpreted with the spin state of cobalt ions. Studies on the susceptibilities of the samples with x = 0.2 under different preparation temperatures and annealing temperatures show that the rising of sintering temperature and annealing temperature will increase the para-ferromagnetic transition temperature, and reduce the effective moment to normal value. Our result shows that both Co^3＋ and Co^4＋ ions should be in IS state after annealing and the oxygen annealing causes the transition of Co^3＋ spin state from HS to IS.
基金Supported by the National Natural Science Foundation of China(Grant Nos.51676121 and 12004242).
文摘We investigate the electrical conductivity and thermal conductivity of polycrystalline gold nanofilms,with thicknesses ranging from 40.5nm to 115.8 nm,and identify a thickness-dependent electrical conductivity,which can be explained via the Mayadas and Shatzkes(MS)theory.At the same time,a suppressed thermal conductivity is observed,as compared to that found in the bulk material,together with a weak thickness effect.We compare the thermal conductivity of suspended and supported gold films,finding that the supporting substrate can effectively suppress the in-plane thermal conductivity of the polycrystalline gold nanofilms.Our results indicate that grain boundary scattering and substrate scattering can affect electron and phonon transport in polycrystalline metallic systems.
文摘In the Acknowledgement, the following sentence "JH and JL are supported by the National Science Foundation (Award number CBET-1943813) and the Faulty Research and Professional Development Fund at North Carolina State University" should be changed to "JH and JL are supported by the Faulty Research and Professional Development Fund at North Carolina State University".
基金This work is supported by the National Key R&D Program of China(Grant No.2017YFB0406004)the National Natural Science Foundation of China(Grant No.11890703)+1 种基金JH and JL are supported by the National Science Foundation of USA(Award No.CBET-1943813)the Faculty Research and Professional Development Fund at North Carolina State University.
文摘The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time.There have been several approaches to explain the thermal conductivities in these systems,for example,Bridgman's formula for simple liquids,the concept of the minimum thermal conductivity for amorphous solids,and the thermal resistance network model for amorphous polymers.Here,we present a ubiquitous formula to calculate the thermal conductivities of liquids and amorphous solids in a unified way,and compare it with previous ones.The calculated thermal conductivities using this formula without fitting parameters are in excellent agreement with the experimental data.Our formula not only provides a detailed microscopic mechanism of heat transfer in these systems,but also resolves the discrepancies between existing formulae and experimental data.
