A unidirectional reaction for synthesis of the high T_c superconductor YBa_2Cu_3O_x has been proposed, Its T_c is 90-94.5 K and △T is 1 K. The phase relationships in the system Y_2BaCuO_5-Y_2Cu_2O_5-CuO-YBa_2Cu_3O_x ...A unidirectional reaction for synthesis of the high T_c superconductor YBa_2Cu_3O_x has been proposed, Its T_c is 90-94.5 K and △T is 1 K. The phase relationships in the system Y_2BaCuO_5-Y_2Cu_2O_5-CuO-YBa_2Cu_3O_x were studied and discussed.展开更多
By means of X-ray diffraction and adiabatic scanning calorimeter,the specific heats of five compounds in the Sm_2O_3-BaO--CuO system,such as Sm_2BaO_4,Sm_2CuO_4,BaCuO_4, Sm_2BaCuO_5,SmBa_2Cu_3O_(7-x),from -150℃ to 80...By means of X-ray diffraction and adiabatic scanning calorimeter,the specific heats of five compounds in the Sm_2O_3-BaO--CuO system,such as Sm_2BaO_4,Sm_2CuO_4,BaCuO_4, Sm_2BaCuO_5,SmBa_2Cu_3O_(7-x),from -150℃ to 800℃ have been measured.It is found that the specific heats of these compounds increase smoothly with the increase of temperature.展开更多
Raman spectroscopy can provide much information on the superconductivity mechanism and is also an important part in the physical study of high temperature superconductors. At present, many papers on the Raman spectra ...Raman spectroscopy can provide much information on the superconductivity mechanism and is also an important part in the physical study of high temperature superconductors. At present, many papers on the Raman spectra of the Bi-series high T_c superconductors have been published. However, there are still great differences among the ex-展开更多
Discovery of the superconductivity in Ba-Y-Cu-O system above liquid nitrogen transition temperature has stimulated the extensive studies. The properties of superconducting material depend on the temperature and atmosp...Discovery of the superconductivity in Ba-Y-Cu-O system above liquid nitrogen transition temperature has stimulated the extensive studies. The properties of superconducting material depend on the temperature and atmosphere during its sinter. In fact, the oxygen content in sample can be affected seriously by sintering and annealing procedure. The results of X-ray and neutron diffraction analysis indicate that the oxygen vacancy plays an important role in superconductor Ba-Y-Cu-O展开更多
This paper reports the experimental results of the investigation on elemental substitution effects in YBa_2Cu_3O_(7-δ) and the new physical ideas deduced comprehensively. It is shown that all the orthorhombic crystal...This paper reports the experimental results of the investigation on elemental substitution effects in YBa_2Cu_3O_(7-δ) and the new physical ideas deduced comprehensively. It is shown that all the orthorhombic crystalline structure, oxygen content, oxidation valence of Cu atoms, and metal-semiconductor (insulator) transition are only the extrinsic factors deter mining the T_c of the systems, and there are two mechanisms of substitution effects, namely the mechanism of the substitution effects outside the CuO_2 planes and that within the CuO_2 planes. We suggest that the mobile carrier concentration and the dynamic, short-range antiferromagnetic correlation between Cu(2) atoms on the CuO_2 planes are the two intrinsic factors determining the high T_c superconductivity.展开更多
A very strong nonresonant low-field signal can be detected near and below zero resistance phase transition temperature T_c by either electron spin resonance (ESR) or nuclear magnetic resonance (NMR)in almost all syste...A very strong nonresonant low-field signal can be detected near and below zero resistance phase transition temperature T_c by either electron spin resonance (ESR) or nuclear magnetic resonance (NMR)in almost all systems of high T_c superconductive oxides. The essence of this phenomenon is that there is some loss absorption of electromagnetic radiant in the sample when it is in the normal state; and the absorption decreases obviously when it is in the superconducting state, but the absorption increases when the sample is in magnetic field, especially when the applied field H is greater than the superconducting展开更多
Joining the bulk high T_c superconducting ceramics is an unavoidable problem people will face in the application of the new material. The primary requirement is that the joints have to have the superconductivities sim...Joining the bulk high T_c superconducting ceramics is an unavoidable problem people will face in the application of the new material. The primary requirement is that the joints have to have the superconductivities similar to those of the bulk materials. That means the joints must have the same composition with the bulk materials. Fusion welding of the ceramies is thought to be the most reliable and efficient joining process for oxide ceramics.展开更多
1 Introduction S. Wu reported the brittle-ductile transition master curve for the relation between the notched izod impact strength of Nylon-6/EPDM blends and rubber fractions. It was interpreted by the strong interac...1 Introduction S. Wu reported the brittle-ductile transition master curve for the relation between the notched izod impact strength of Nylon-6/EPDM blends and rubber fractions. It was interpreted by the strong interaction between polar Nylon-6 matrix and modified EPDM dispersed phase. However, similar brittle-ductile transition master curve in non-polar PP/EPDM blends was also observed in this laboratory (Fig. 1).展开更多
With the Becchi-Rouet-Stora-Tyutin(BRST) quantization of gauge theory,we solve the long-standing difficult problem of the local constraint conditions,i.e.the single occupation of a slave particle per site,in the slave...With the Becchi-Rouet-Stora-Tyutin(BRST) quantization of gauge theory,we solve the long-standing difficult problem of the local constraint conditions,i.e.the single occupation of a slave particle per site,in the slave particle theory.This difficulty is actually caused by inconsistently dealing with the local Lagrange multiplier λ_(i) which ensures the constraint:in the Hamiltonian formalism of the theory,λ_(i) is time-independent and commutes with the Hamiltonian while in the Lagrangian formalism,λ_(i)(t) becomes time-dependent and plays a role of gauge field.This implies that the redundant degrees of freedom of λ_(i)(t) are introduced and must be removed by the additional constraint,the gauge fixing condition(GFC) ?_tλ_(i)(t)= 0.In literature,this GFC was missed.We add this GFC and use the BRST quantization of gauge theory for Dirac's first-class constraints in the slave particle theory.This GFC endows λ_(i)(t) with dynamics and leads to important physical results.As an example,we study the Hubbard model at half-filling and find that the spinon is gapped in the weak U and the system is indeed a conventional metal,which resolves the paradox that the weak coupling state is a superconductor in the previous slave boson mean field(MF) theory.For the t-J model,we find that the dynamic effect of λ_(i)(t) substantially suppresses the d-wave pairing gap and then the superconducting critical temperature may be lowered at least a factor of one-fifth of the MF value which is of the order of 1000 K.The renormalized T_c is then close to that in cuprates.展开更多
By the r. f. magnetron sputtering method, the CeO_2 buffer layers were prepared on (100) LaAlO_3 sub-strates. The results of X-ray diffraction and Ф-scan indicated that the CeO_2 films were unique ( 100)-orientedand ...By the r. f. magnetron sputtering method, the CeO_2 buffer layers were prepared on (100) LaAlO_3 sub-strates. The results of X-ray diffraction and Ф-scan indicated that the CeO_2 films were unique ( 100)-orientedand epitaxial. The YBa_2Cu_3O_(7-6)(YBCO) films, which were deposited on the CeO_2/LaAlO_3 by d. c. magnetronsputtering, exhibited transition temperatures of 89～91 K,and had critical current densities exceeding 10￣6 A/cm￣2 at 77 K in zero magnetic field.展开更多
Ag-sheathed(Bi,Pb)_2Sr_2Ca_2Cu_3O_x tapes were fabricated by a powder-in-tube method.A high critical current density of 2.8×10~4 A/cm^2 at 77K,0T and 4×10~4 A/cm^2 at 4.2K,5T(H⊥ab),6.3× 10~4 A/cm^2 at ...Ag-sheathed(Bi,Pb)_2Sr_2Ca_2Cu_3O_x tapes were fabricated by a powder-in-tube method.A high critical current density of 2.8×10~4 A/cm^2 at 77K,0T and 4×10~4 A/cm^2 at 4.2K,5T(H⊥ab),6.3× 10~4 A/cm^2 at 4.2K,7T(H∥ab)is obtained.The microstructure of the tapes with high J_c values was in- vestigated by transmission electron microscope(TEM)and X-ray energy dispersive spectrum system(EDS). For comparison,a tape fabricated by a different procedure with a low J_c of about 1×10~4 A/cm^2 at 77K,0T was also studied.The relationship between J_c and microstructure of the tapes and the effect of the processing on the microstructure and J_c were elucidated.展开更多
The synthesis kinetics of YBa_2Cu_30_x supercon- ductor was studied through comparing the calcina- tion (sintering) processes of different kinds of powders. It was shown that the temperature of synthesis of YBa_2Cu_30...The synthesis kinetics of YBa_2Cu_30_x supercon- ductor was studied through comparing the calcina- tion (sintering) processes of different kinds of powders. It was shown that the temperature of synthesis of YBa_2Cu_30_x phase can be lowered from 950℃ to 800℃ through direct calcination of multiphase powder with uniform chemical com- position. The stress which is caused by the volume change during synthetic reaction breaks the particles. It facilitates the formation of highly active superfines of superconductor.展开更多
We have developed an experimental setup that has been proven suitable for the study of photoresponse of high Tc superconductors. The distinguish feature of this experimental setup lies mainly in the data acquisition s...We have developed an experimental setup that has been proven suitable for the study of photoresponse of high Tc superconductors. The distinguish feature of this experimental setup lies mainly in the data acquisition system which is equipped with computer as well as the IEEE-488 interface bus. which ensures the accuracy to experimental results. Using the experimental setup, the optical response to laser radiation in high-Tc superconductors has been examined, both of bolometric effect and nonequilibrium optical response are revealed.展开更多
After the discovery of high T<sub>c</sub> superconductivity in RE-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems, at the beginning of the year 1988, the superconductor with zero resistance transition temperature T<s...After the discovery of high T<sub>c</sub> superconductivity in RE-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems, at the beginning of the year 1988, the superconductor with zero resistance transition temperature T<sub>c</sub>（0） 120 K was discovered in Tl-Ba-Ca-Cu-O system. In this note, the crystal structure of the superconductor with T<sub>c</sub>（0） 120. 3 K and bulk critical current density of 1630 A/cm<sup>2</sup> at LN<sub>2</sub> temperature have been studied.展开更多
Ⅰ. INTRODUCTIONSoon after J. G. Bednorz and K. A. Müller discovered the high T_C superconductor, they reported a zero magnetic field microwave absorption in Ba-La-Cu-O. Thereafter, this phenomenon has been obser...Ⅰ. INTRODUCTIONSoon after J. G. Bednorz and K. A. Müller discovered the high T_C superconductor, they reported a zero magnetic field microwave absorption in Ba-La-Cu-O. Thereafter, this phenomenon has been observed by ESR spectrometer in almost all kinds of high T_C展开更多
The superconducting phases with T<sub>C</sub> （0）=120-125 K and 110 K were found in the Tl-Ba-Ca-Cu-O （TBCCO） system and the Bi-Sr-Ca-Cu-O（BSCCO）system. The preparation and the prospective applicatio...The superconducting phases with T<sub>C</sub> （0）=120-125 K and 110 K were found in the Tl-Ba-Ca-Cu-O （TBCCO） system and the Bi-Sr-Ca-Cu-O（BSCCO）system. The preparation and the prospective application of TBCCO are restricted because Tl<sub>2</sub>O<sub>3</sub> is toxic, expensive and volatile. For these reasons, the BSCCO system draws more attention to some extent.展开更多
Mass transport of Y(dpm)2 Ba(dpm)5· OH· 2Ho and Cu (dpm)2 by a carrier gas(argon) was theoretically considered and experimentally studied as a function of the system with operating parameters including tempe...Mass transport of Y(dpm)2 Ba(dpm)5· OH· 2Ho and Cu (dpm)2 by a carrier gas(argon) was theoretically considered and experimentally studied as a function of the system with operating parameters including temperature, carrier gas flow rate and system pressure. The experimental results are in a good agreement with the theoretical prediction. The mechanism of mass transport of these organometallic precursors and their use for YBCO film stoichiometry control and reproducibility are discussed.展开更多
文摘A unidirectional reaction for synthesis of the high T_c superconductor YBa_2Cu_3O_x has been proposed, Its T_c is 90-94.5 K and △T is 1 K. The phase relationships in the system Y_2BaCuO_5-Y_2Cu_2O_5-CuO-YBa_2Cu_3O_x were studied and discussed.
基金The project supported by the National Natural Science Foundation of China
文摘By means of X-ray diffraction and adiabatic scanning calorimeter,the specific heats of five compounds in the Sm_2O_3-BaO--CuO system,such as Sm_2BaO_4,Sm_2CuO_4,BaCuO_4, Sm_2BaCuO_5,SmBa_2Cu_3O_(7-x),from -150℃ to 800℃ have been measured.It is found that the specific heats of these compounds increase smoothly with the increase of temperature.
文摘Raman spectroscopy can provide much information on the superconductivity mechanism and is also an important part in the physical study of high temperature superconductors. At present, many papers on the Raman spectra of the Bi-series high T_c superconductors have been published. However, there are still great differences among the ex-
基金Project supported by the National Natural Science Foundation of China & Academia Sinics.
文摘Discovery of the superconductivity in Ba-Y-Cu-O system above liquid nitrogen transition temperature has stimulated the extensive studies. The properties of superconducting material depend on the temperature and atmosphere during its sinter. In fact, the oxygen content in sample can be affected seriously by sintering and annealing procedure. The results of X-ray and neutron diffraction analysis indicate that the oxygen vacancy plays an important role in superconductor Ba-Y-Cu-O
基金Project supported by the Combined Centre of Research and Development of Superconduction Technology and the National Natural Science Foundation of China.
文摘This paper reports the experimental results of the investigation on elemental substitution effects in YBa_2Cu_3O_(7-δ) and the new physical ideas deduced comprehensively. It is shown that all the orthorhombic crystalline structure, oxygen content, oxidation valence of Cu atoms, and metal-semiconductor (insulator) transition are only the extrinsic factors deter mining the T_c of the systems, and there are two mechanisms of substitution effects, namely the mechanism of the substitution effects outside the CuO_2 planes and that within the CuO_2 planes. We suggest that the mobile carrier concentration and the dynamic, short-range antiferromagnetic correlation between Cu(2) atoms on the CuO_2 planes are the two intrinsic factors determining the high T_c superconductivity.
基金Project supported by the National Center for Research and Development on Superconductivity.
文摘A very strong nonresonant low-field signal can be detected near and below zero resistance phase transition temperature T_c by either electron spin resonance (ESR) or nuclear magnetic resonance (NMR)in almost all systems of high T_c superconductive oxides. The essence of this phenomenon is that there is some loss absorption of electromagnetic radiant in the sample when it is in the normal state; and the absorption decreases obviously when it is in the superconducting state, but the absorption increases when the sample is in magnetic field, especially when the applied field H is greater than the superconducting
文摘Joining the bulk high T_c superconducting ceramics is an unavoidable problem people will face in the application of the new material. The primary requirement is that the joints have to have the superconductivities similar to those of the bulk materials. That means the joints must have the same composition with the bulk materials. Fusion welding of the ceramies is thought to be the most reliable and efficient joining process for oxide ceramics.
基金Project supported by the National Natural Science Foundation of China.
文摘1 Introduction S. Wu reported the brittle-ductile transition master curve for the relation between the notched izod impact strength of Nylon-6/EPDM blends and rubber fractions. It was interpreted by the strong interaction between polar Nylon-6 matrix and modified EPDM dispersed phase. However, similar brittle-ductile transition master curve in non-polar PP/EPDM blends was also observed in this laboratory (Fig. 1).
文摘With the Becchi-Rouet-Stora-Tyutin(BRST) quantization of gauge theory,we solve the long-standing difficult problem of the local constraint conditions,i.e.the single occupation of a slave particle per site,in the slave particle theory.This difficulty is actually caused by inconsistently dealing with the local Lagrange multiplier λ_(i) which ensures the constraint:in the Hamiltonian formalism of the theory,λ_(i) is time-independent and commutes with the Hamiltonian while in the Lagrangian formalism,λ_(i)(t) becomes time-dependent and plays a role of gauge field.This implies that the redundant degrees of freedom of λ_(i)(t) are introduced and must be removed by the additional constraint,the gauge fixing condition(GFC) ?_tλ_(i)(t)= 0.In literature,this GFC was missed.We add this GFC and use the BRST quantization of gauge theory for Dirac's first-class constraints in the slave particle theory.This GFC endows λ_(i)(t) with dynamics and leads to important physical results.As an example,we study the Hubbard model at half-filling and find that the spinon is gapped in the weak U and the system is indeed a conventional metal,which resolves the paradox that the weak coupling state is a superconductor in the previous slave boson mean field(MF) theory.For the t-J model,we find that the dynamic effect of λ_(i)(t) substantially suppresses the d-wave pairing gap and then the superconducting critical temperature may be lowered at least a factor of one-fifth of the MF value which is of the order of 1000 K.The renormalized T_c is then close to that in cuprates.
文摘By the r. f. magnetron sputtering method, the CeO_2 buffer layers were prepared on (100) LaAlO_3 sub-strates. The results of X-ray diffraction and Ф-scan indicated that the CeO_2 films were unique ( 100)-orientedand epitaxial. The YBa_2Cu_3O_(7-6)(YBCO) films, which were deposited on the CeO_2/LaAlO_3 by d. c. magnetronsputtering, exhibited transition temperatures of 89～91 K,and had critical current densities exceeding 10￣6 A/cm￣2 at 77 K in zero magnetic field.
文摘Ag-sheathed(Bi,Pb)_2Sr_2Ca_2Cu_3O_x tapes were fabricated by a powder-in-tube method.A high critical current density of 2.8×10~4 A/cm^2 at 77K,0T and 4×10~4 A/cm^2 at 4.2K,5T(H⊥ab),6.3× 10~4 A/cm^2 at 4.2K,7T(H∥ab)is obtained.The microstructure of the tapes with high J_c values was in- vestigated by transmission electron microscope(TEM)and X-ray energy dispersive spectrum system(EDS). For comparison,a tape fabricated by a different procedure with a low J_c of about 1×10~4 A/cm^2 at 77K,0T was also studied.The relationship between J_c and microstructure of the tapes and the effect of the processing on the microstructure and J_c were elucidated.
文摘The synthesis kinetics of YBa_2Cu_30_x supercon- ductor was studied through comparing the calcina- tion (sintering) processes of different kinds of powders. It was shown that the temperature of synthesis of YBa_2Cu_30_x phase can be lowered from 950℃ to 800℃ through direct calcination of multiphase powder with uniform chemical com- position. The stress which is caused by the volume change during synthetic reaction breaks the particles. It facilitates the formation of highly active superfines of superconductor.
文摘We have developed an experimental setup that has been proven suitable for the study of photoresponse of high Tc superconductors. The distinguish feature of this experimental setup lies mainly in the data acquisition system which is equipped with computer as well as the IEEE-488 interface bus. which ensures the accuracy to experimental results. Using the experimental setup, the optical response to laser radiation in high-Tc superconductors has been examined, both of bolometric effect and nonequilibrium optical response are revealed.
文摘After the discovery of high T<sub>c</sub> superconductivity in RE-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems, at the beginning of the year 1988, the superconductor with zero resistance transition temperature T<sub>c</sub>（0） 120 K was discovered in Tl-Ba-Ca-Cu-O system. In this note, the crystal structure of the superconductor with T<sub>c</sub>（0） 120. 3 K and bulk critical current density of 1630 A/cm<sup>2</sup> at LN<sub>2</sub> temperature have been studied.
基金Project supported by the National Center for Research and Development on Superconductivity.
文摘Ⅰ. INTRODUCTIONSoon after J. G. Bednorz and K. A. Müller discovered the high T_C superconductor, they reported a zero magnetic field microwave absorption in Ba-La-Cu-O. Thereafter, this phenomenon has been observed by ESR spectrometer in almost all kinds of high T_C
文摘The superconducting phases with T<sub>C</sub> （0）=120-125 K and 110 K were found in the Tl-Ba-Ca-Cu-O （TBCCO） system and the Bi-Sr-Ca-Cu-O（BSCCO）system. The preparation and the prospective application of TBCCO are restricted because Tl<sub>2</sub>O<sub>3</sub> is toxic, expensive and volatile. For these reasons, the BSCCO system draws more attention to some extent.
文摘Mass transport of Y(dpm)2 Ba(dpm)5· OH· 2Ho and Cu (dpm)2 by a carrier gas(argon) was theoretically considered and experimentally studied as a function of the system with operating parameters including temperature, carrier gas flow rate and system pressure. The experimental results are in a good agreement with the theoretical prediction. The mechanism of mass transport of these organometallic precursors and their use for YBCO film stoichiometry control and reproducibility are discussed.
