By using transport and magnetic measurement,the upper critical field H_(c2)(T)and the irreversibility line Hirr(T)has been determined.A big separation between H_(c2)(0)and Hirr(0)has been found showing the existence o...By using transport and magnetic measurement,the upper critical field H_(c2)(T)and the irreversibility line Hirr(T)has been determined.A big separation between H_(c2)(0)and Hirr(0)has been found showing the existence of a quantum vortex liquid state induced by quantum fluctuation of vortices in the new superconductor MgB_(2).Further investigation on the magnetic relaxation shows that both the quantum tunneling and the thermally activated flux creep depends weakly on temperature.However,when the melting field Hirr is approached,a drastic rise of the relaxation rate is observed.This may indicate that the melting of the vortex matter at a finite temperature is also induced by the quantum fluctuation of vortices.展开更多
Mo_(1-x)Ge_(x),Mo_(1-x)Si_(x),films were prepared by getter sputtering onto liquid nitrogen cooled substrates.The amorphous phase formations were Ge>22 at.%,Si>18 at.%respectively.With the increase of Ge,Si cont...Mo_(1-x)Ge_(x),Mo_(1-x)Si_(x),films were prepared by getter sputtering onto liquid nitrogen cooled substrates.The amorphous phase formations were Ge>22 at.%,Si>18 at.%respectively.With the increase of Ge,Si content,Tc decreased from 6 to 3K in the amorphous state.The measured results of(dBc2/dT)T_(c),Jc andρ(300K)/ρ(8K)indicated that the four chosen Mo_(1-x)Si_(x)films exhibit fundamental characteristics of amorphous superconductors.展开更多
The specific heat of the recently discovered superconductor MgB_(2) has been measured at temperatures ranging from 4.5 to 80 K.Superconducting anomalyΔC at Tc is clearly observed.The total specific heat in normal sta...The specific heat of the recently discovered superconductor MgB_(2) has been measured at temperatures ranging from 4.5 to 80 K.Superconducting anomalyΔC at Tc is clearly observed.The total specific heat in normal state can be well fitted by electronic and phonon contributions.The Debye temperatureθD is obtained to be 737 K,much larger than other intermetallic superconductors.Normal state electronic specific heat coefficientγis found to be 2.48±0.5 mJ/mol.K^(2) andΔC/γTc is between 1.41 and 2.15.展开更多
Structural features of MgB2 superconductors prepared under different conditions have been analysed by means of transmission electron microscopy.The MgB_(2) crystal is identified to have a hexagonal structure with the ...Structural features of MgB2 superconductors prepared under different conditions have been analysed by means of transmission electron microscopy.The MgB_(2) crystal is identified to have a hexagonal structure with the space group of P6/mmm.Superconducting materials synthesized under a high pressure of 6 Gpa are made of regularly stacked grains as large as a few microns in sizes.Stacking faults and microstructure properties of grain boundaries either with or without impurities,appearing in a sample with the critical current density greater than 10^(5)A/cm^(2),have been systematically investigated.展开更多
Polycrystalline samples of the new superconductor MgB_(2) are prepared by solid state reaction using Mg and B powders.The resistance measurement shows that the onset transition temperature and zero resistance transiti...Polycrystalline samples of the new superconductor MgB_(2) are prepared by solid state reaction using Mg and B powders.The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are Tonsetc=43.8 K and Tc0=37 K,respectively.The Tc0 depends on measuring current strongly.The diamagnetic transition temperature of~38 K is obtained by the ac susceptibility measurement.X-ray powder diffraction spectra of MgB_(2) can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a=0.30864 and c=0.35212 nm.A second phase,probably MgO,is also found.展开更多
The new superconductor MgB_(2) has been prepared by two ways: high pressure and ambient pressure synthesis. Their superconducting properties were measured and compared. It is found that the sample prepared by high pre...The new superconductor MgB_(2) has been prepared by two ways: high pressure and ambient pressure synthesis. Their superconducting properties were measured and compared. It is found that the sample prepared by high pressure is much denser than that prepared under ambient pressure. Accordingly the high pressure sample has a very narrow transition width and a much higher bulk critical current density.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.19825111the Ministry of Science and Technology of China(NKBRSF-G1999064602).
文摘By using transport and magnetic measurement,the upper critical field H_(c2)(T)and the irreversibility line Hirr(T)has been determined.A big separation between H_(c2)(0)and Hirr(0)has been found showing the existence of a quantum vortex liquid state induced by quantum fluctuation of vortices in the new superconductor MgB_(2).Further investigation on the magnetic relaxation shows that both the quantum tunneling and the thermally activated flux creep depends weakly on temperature.However,when the melting field Hirr is approached,a drastic rise of the relaxation rate is observed.This may indicate that the melting of the vortex matter at a finite temperature is also induced by the quantum fluctuation of vortices.
文摘Mo_(1-x)Ge_(x),Mo_(1-x)Si_(x),films were prepared by getter sputtering onto liquid nitrogen cooled substrates.The amorphous phase formations were Ge>22 at.%,Si>18 at.%respectively.With the increase of Ge,Si content,Tc decreased from 6 to 3K in the amorphous state.The measured results of(dBc2/dT)T_(c),Jc andρ(300K)/ρ(8K)indicated that the four chosen Mo_(1-x)Si_(x)films exhibit fundamental characteristics of amorphous superconductors.
基金Supported by the National Natural Science Foundation of China under Grant No.19825111.
文摘The specific heat of the recently discovered superconductor MgB_(2) has been measured at temperatures ranging from 4.5 to 80 K.Superconducting anomalyΔC at Tc is clearly observed.The total specific heat in normal state can be well fitted by electronic and phonon contributions.The Debye temperatureθD is obtained to be 737 K,much larger than other intermetallic superconductors.Normal state electronic specific heat coefficientγis found to be 2.48±0.5 mJ/mol.K^(2) andΔC/γTc is between 1.41 and 2.15.
基金Supported by the“Hundreds of Talents”Program of Chinese Academy of Sciences.
文摘Structural features of MgB2 superconductors prepared under different conditions have been analysed by means of transmission electron microscopy.The MgB_(2) crystal is identified to have a hexagonal structure with the space group of P6/mmm.Superconducting materials synthesized under a high pressure of 6 Gpa are made of regularly stacked grains as large as a few microns in sizes.Stacking faults and microstructure properties of grain boundaries either with or without impurities,appearing in a sample with the critical current density greater than 10^(5)A/cm^(2),have been systematically investigated.
基金Supported by the Ministry of Science and Technology of China(NKBRSF-G1999064602)the National Natural Science Foundation of China under Grant No.59872043the Fundamental Research Bureau,Chinese Academy of Sciences.
文摘Polycrystalline samples of the new superconductor MgB_(2) are prepared by solid state reaction using Mg and B powders.The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are Tonsetc=43.8 K and Tc0=37 K,respectively.The Tc0 depends on measuring current strongly.The diamagnetic transition temperature of~38 K is obtained by the ac susceptibility measurement.X-ray powder diffraction spectra of MgB_(2) can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a=0.30864 and c=0.35212 nm.A second phase,probably MgO,is also found.
基金Supported by the Ministry of Science and Technology of China(NKBRSF-G19990646)the National Natural Science Foundation of China under Grant No.19825111。
文摘The new superconductor MgB_(2) has been prepared by two ways: high pressure and ambient pressure synthesis. Their superconducting properties were measured and compared. It is found that the sample prepared by high pressure is much denser than that prepared under ambient pressure. Accordingly the high pressure sample has a very narrow transition width and a much higher bulk critical current density.
