The effective activation energy of one HgBaCaCuO 1223 superconductor as a function of current density was extracted from the magnetic relaxation measurements below 30K,and found to obey a power law.We also obtained ef...The effective activation energy of one HgBaCaCuO 1223 superconductor as a function of current density was extracted from the magnetic relaxation measurements below 30K,and found to obey a power law.We also obtained effective activation energy as a function of current density from the magnetic hysteresis loops(M-H).The data sets for the M-H loops at different temperatures overlap each other,and all fall on the smooth U_(eff)(J,0)curve based solely on the magnetization relaxation measurements.This indicates that the field dependence of magnetic critical current density is determined by the flux creep via nonlinear effective activation energy at low temperatures.展开更多
Samples of Bi_(2.2)Sr_(1.8)Ca_(1.05)Cu_(2.15-x)Na_(x)O_(8+y)(x=0,0.7)were prepared by melt-processing technique.The maximum transition temperature increased up to 100 K,and T_(c)0 achieved 92.5K.In order to study the ...Samples of Bi_(2.2)Sr_(1.8)Ca_(1.05)Cu_(2.15-x)Na_(x)O_(8+y)(x=0,0.7)were prepared by melt-processing technique.The maximum transition temperature increased up to 100 K,and T_(c)0 achieved 92.5K.In order to study the mechanism of T_(c) increasing,samples were annealed in a flowing oxygen,atmosphere.The reversibility of T_(c) was observed in undoped sample,while the T_(c) of Na-doped sample had no significant changes.We believe that the T_(c) is correlated with a redistribution of holes between the BiO layers and the CuO planes.Doping sodium changes the hole density of CuO planes into an“optimium”value so as to increase T_(c).展开更多
The effect of slow neutron irradiation at a low Auence of about 10^(8)n/cm^(2) on the microstructures of Bi-2223 polycrystalline samples was observed by transmission electron microscopy.By comparative study of the def...The effect of slow neutron irradiation at a low Auence of about 10^(8)n/cm^(2) on the microstructures of Bi-2223 polycrystalline samples was observed by transmission electron microscopy.By comparative study of the defect structures in a given area in one sample,we get evidence for the flux pinning enhancement by low Auence slow neutron irradiation.展开更多
The low t emperature part of hysteresis curves of the freezing and melting processes of ^(4)He in vycor glass with the lowest temperature O.4K were measured,as the pressure ranged from 36.45 to 55.18(1O^(5)Pa).Some no...The low t emperature part of hysteresis curves of the freezing and melting processes of ^(4)He in vycor glass with the lowest temperature O.4K were measured,as the pressure ranged from 36.45 to 55.18(1O^(5)Pa).Some novel characteristics of these curves were observed in such high temperature and pressure range.They may result from the existence of superfluid ^(4)He.展开更多
基金Supported by the National Center for Research and Development on Superconductivity of ChinaNational Foundation for Doctoral Education.
文摘The effective activation energy of one HgBaCaCuO 1223 superconductor as a function of current density was extracted from the magnetic relaxation measurements below 30K,and found to obey a power law.We also obtained effective activation energy as a function of current density from the magnetic hysteresis loops(M-H).The data sets for the M-H loops at different temperatures overlap each other,and all fall on the smooth U_(eff)(J,0)curve based solely on the magnetization relaxation measurements.This indicates that the field dependence of magnetic critical current density is determined by the flux creep via nonlinear effective activation energy at low temperatures.
基金the National Center for Research and Development on Superconductivitythe National Doctoral Education and Center of Material Analysis of Nanjing University.
文摘Samples of Bi_(2.2)Sr_(1.8)Ca_(1.05)Cu_(2.15-x)Na_(x)O_(8+y)(x=0,0.7)were prepared by melt-processing technique.The maximum transition temperature increased up to 100 K,and T_(c)0 achieved 92.5K.In order to study the mechanism of T_(c) increasing,samples were annealed in a flowing oxygen,atmosphere.The reversibility of T_(c) was observed in undoped sample,while the T_(c) of Na-doped sample had no significant changes.We believe that the T_(c) is correlated with a redistribution of holes between the BiO layers and the CuO planes.Doping sodium changes the hole density of CuO planes into an“optimium”value so as to increase T_(c).
基金Supported by the National Center for Research and Development on Superconductivity of China,and the Foundation for Doctoral Education。
文摘The effect of slow neutron irradiation at a low Auence of about 10^(8)n/cm^(2) on the microstructures of Bi-2223 polycrystalline samples was observed by transmission electron microscopy.By comparative study of the defect structures in a given area in one sample,we get evidence for the flux pinning enhancement by low Auence slow neutron irradiation.
文摘The low t emperature part of hysteresis curves of the freezing and melting processes of ^(4)He in vycor glass with the lowest temperature O.4K were measured,as the pressure ranged from 36.45 to 55.18(1O^(5)Pa).Some novel characteristics of these curves were observed in such high temperature and pressure range.They may result from the existence of superfluid ^(4)He.
