It is significant for low-cost preparation of YBa2Cu3O7-δ（YBCO） coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the ...It is significant for low-cost preparation of YBa2Cu3O7-δ（YBCO） coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the present work,a distinct nucleation mechanism was proposed based on a transient liquid phase induced by the size effect as well as near-equilibrium assumption. With this scheme the nucleation of YBCO prepared by metal–organic deposition（MOD） or the physical vapor deposition BaF2 process was semi-quantitatively analyzed, revealing that the direct driving force for nucleation is YBCO supersaturation in the liquid phase. The theoretical analysis on the nucleation orientation portion is evidenced by the experimental result.展开更多
Interfaces and surfaces of YBa_2Cu_3O_(7-x)(YBCO)-Ag have been studied by SEM-EDX and AES.No effect of Ag on 123 structure in X-ray diffraction pattern was observed for 0.4 mol Ag doped YBCO.AES analysis indicated tha...Interfaces and surfaces of YBa_2Cu_3O_(7-x)(YBCO)-Ag have been studied by SEM-EDX and AES.No effect of Ag on 123 structure in X-ray diffraction pattern was observed for 0.4 mol Ag doped YBCO.AES analysis indicated that Ag segregated on surface of YBCO and resulted in decrease of YBCO-metal lead resistance.In addition,solution and segregation of Ag as elemental state were often appeared on interfaces and surfaces of high temperature annealed YBCO,whether elemental Ag or compound Ag_2O and AgNO_3 adopted as doping material.展开更多
The patterning technologies and process order of high Tc(86K) super-conducting film bolometers have been studied. After the deposition, a conventional lithographic process was used to pattern the films with aqueous so...The patterning technologies and process order of high Tc(86K) super-conducting film bolometers have been studied. After the deposition, a conventional lithographic process was used to pattern the films with aqueous solution of HCl, and then the films were transferred into a tube furnace for annealing to form superconducting film. It eliminates the degradation of patterning process. The bolometric responsivity of approximately 34. 32 V/W is measured, and the detectivity is greater than 1. 62× 108cm · Hz1/2 · W-1, the noise equivalent powers NEP is 2. 1×10-9W.展开更多
By means of X-ray diffraction investigations and electric resistivity measurements the tempera- ture dependence of phase structure and supercon- ductivity in YBa_2Cu_3O_(7_x) over the temperature range of 20℃-950℃ h...By means of X-ray diffraction investigations and electric resistivity measurements the tempera- ture dependence of phase structure and supercon- ductivity in YBa_2Cu_3O_(7_x) over the temperature range of 20℃-950℃ have been studied.The lattice parameters a,b and c as well as conductivity as a function of annealing temperatures can be roughly divided into three zones which are superconductive orthorhombic structure 1(a<b(?)c/3) at 20℃-500℃,normal conductive orthorhombic structure 2(a<b<c/3)from 550℃ to about 750℃ and semiconductive-like tetragonal structure (a=b<c/3)from about 800℃ to 950℃.However, the boundaries of the three zones is not much distinctive because there is a continuous transi- tion from the orthorhombic to tetragonal struc- ture.Furthermore,the processes of orthorhom- bic-tetragonal transition in the range of 350℃-950℃ are not only continuous but also reversible.The isothermal transition of orthorhombic 2 to orthorhombic 1 occurs at 350℃-500℃,while the maximum rate of transition and high T_c superconductivity can be obtained at about 460℃.This process of isothermal transition depends on the ordering of oxygen atoms or vacancies and the thermodynamic equilibrium to allow the oxygen diffusion.展开更多
YBa2Cu3O7-x(YBCO) thin film has been epitaxially deposited on (1120) sapphire with Y2O3-stabilized ZrO2 (YSZ) buffer layer and shown a high critical current density Jc of 1. 6×106A/cm2 at 77 K in zero magnetic fi...YBa2Cu3O7-x(YBCO) thin film has been epitaxially deposited on (1120) sapphire with Y2O3-stabilized ZrO2 (YSZ) buffer layer and shown a high critical current density Jc of 1. 6×106A/cm2 at 77 K in zero magnetic field. The orientation relationship of the multilayer film superconductor has been determined. The(001) plane of the YBCO film is parallel to the(100) surface of the YSZ intermediate layer. YSZ buffer layer with(100) preferred orientation is about 20 nm thick and contains element Ba, due to out-diffusion of Ba from YBCO layer. The(100) preferred orientation of YSZ buffer permits the growth of high quality YBCO thin film. Y2BaCuO5 precipitates with small size distribute uniformly in the YBCO thin film and it is favourable to raise critical current density Jc.展开更多
Y_(1-x)Ho_xBa_2Cu_3O_(7-δ)(0<x<1) sinsle crystal thin films oriented with the caxis perpendicular to the sur-face were grown by DC magnetron sputtering technique. Target was pieced together with half of YBa_2Cu...Y_(1-x)Ho_xBa_2Cu_3O_(7-δ)(0<x<1) sinsle crystal thin films oriented with the caxis perpendicular to the sur-face were grown by DC magnetron sputtering technique. Target was pieced together with half of YBa_2Cu_3O_(7-δ)(YBCO) and half of HoBa_2Cu_3O_(7-δ)(HBCO) superconducting materials. As the distance between HBCO targetmaterial and substrate is varied , the Ho content in material is changed respectively. When the content of Ho is0. 7 (atom ratio) , the T_c>83K.展开更多
Thin films of superconductors HoBa_2Cu_3O_(7-δ)(HBCO) were prepared by DC-sputtering technique. The epi-taxial growth was controlled by the ratio of the oxygen pressure and Ar pressure (O_2/Ar) , the subetrate temper...Thin films of superconductors HoBa_2Cu_3O_(7-δ)(HBCO) were prepared by DC-sputtering technique. The epi-taxial growth was controlled by the ratio of the oxygen pressure and Ar pressure (O_2/Ar) , the subetrate temperature T_s and the distance of the target to subetrate. Thin films deposited under the optimum conditions (Po_2/P_(Ar)= 1:2 ; T_s=730℃) show a critical temlierature clase to 87K and a transition width less than 1K. X-raydiffraction analysis shows that the films are highiy c-axis oriented. Auger electron spectroscopy depth profilingdemonstrates Ho diffusion into the Zr(Y)O_2 subetrate owing to the Ho subetitution for Y.展开更多
In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of t...In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of the high Tc superconductors Gd1Ba2Cu3O7−δ phase with Sr substitution has been synthesized, i.e. Gd1(Ba2−xSrx)Cu3O7−δ compound. The sample was synthesized by using a solid-state reaction method with a wet mixing, sintered for 12 hours at temperature 900°C. The synthesis results are characterized by using XRD. The results of Match-3 software analysis showed high (higher 85%) Gd1Ba2Cu3O7−δ phase was formed. The Sr substitution causes changes to the structure, i.e. the lattice parameters a, b and c, where the orthorhombicity tends to decrease with increasing Sr content. Refinement results show that based on the oxygen occupancy, the total oxygen content tends to increase.展开更多
High-entropy REBa_(2)Cu_(3)O_(7-δ)(RE=Y_(0.7)+Dy_(0.2)+Gd_(0.2)+Sm_(0.2)+Eu_(0.2))(HE-REBCO) superconducting films doped with multiple rare earth elements were successfully fabricated with thickness up to 800 nm by a...High-entropy REBa_(2)Cu_(3)O_(7-δ)(RE=Y_(0.7)+Dy_(0.2)+Gd_(0.2)+Sm_(0.2)+Eu_(0.2))(HE-REBCO) superconducting films doped with multiple rare earth elements were successfully fabricated with thickness up to 800 nm by a trifluoroacetate-metal organic deposition(TFA-MOD).The enhanced entropy change ΔS of the HEREBCO system promotes the c-axis growth of REBCO thin film in the competition with a/b-axis growth.The microstructure and element distribution were investigated by the transmission electron microscopy(TEM) and energy dispersive spectroscopy(EDS).The results show that HE-REBCO films have a great amount of stacking defects,lattice distortions and various rare earth oxides.Furthermore,the microstrain of HE-REBCO films increases significantly compared to the undoped YBCO and(Y,Dy)BCO films.Finally,the superco nducting critical temperature(T_c^(onset)) of HE-REBCO films is about 93 K,and the in-field properties are significantly improved,especially at the temperature of about 77 K.The maximum pinning force density(F_(p,max)) of the HE-REBCO samples at 77 K is 1.7 times higher than that of the undoped YBCO films.展开更多
The structural characteristics of different alkoxides of Y. Ba and Cu are studied with quantum chemi-cal CNDO /2 calculations. The relative hydrolysis rate coefficients k_M of them are obtained according tothe relati...The structural characteristics of different alkoxides of Y. Ba and Cu are studied with quantum chemi-cal CNDO /2 calculations. The relative hydrolysis rate coefficients k_M of them are obtained according tothe relationship between frontier orbitals and organic chemical reactions. Based on the above results. properexperimental conditions for the preparation of homogeneous ultra-purity. submicro high-T_cYBa_2Cu_3O_(7-δ) superconducting powders are proposed.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
The quantum chemical calculations of cluster YBa_2Cu_3O_7 considering all electrons have been per- formed by using the ab initio HF method with self-consistence crystal field.A Hartree-Fork surface potential is propos...The quantum chemical calculations of cluster YBa_2Cu_3O_7 considering all electrons have been per- formed by using the ab initio HF method with self-consistence crystal field.A Hartree-Fork surface potential is proposed to make an asymmetric duster model possess a relatively symmetric potential field and to obtain a relatively symmetric electronic structure,electronic distributions,frontier orbitals,and bond order,etc.The suggestions that there exists a covalent bonding complex,[CuO_2-O-CuO-O-Cu_2]^(6,8-),in the cell unit of the crystal,and the cell units are connected with each other by ionic bonds along the c direction of the crys- tal lattice are offered based on the chemical bonding characteristics from the calculated results.The important contribution of the apical oxygen to superconductivities is emphasized as well.展开更多
Microstructure of high-quality YBa2Cu3O7-x superlattices has been investigated using high-resolution transmission electron microscope (HRTEM). The observations revealed that the superlattioes had atomic sharp interfac...Microstructure of high-quality YBa2Cu3O7-x superlattices has been investigated using high-resolution transmission electron microscope (HRTEM). The observations revealed that the superlattioes had atomic sharp interfaces between YBCO and PrBCO layers without interdiffusion. But undulations and. steps of the layer thickness existed in the specimen. An intermediate layer about 1 nm in thickness with many defects, which was caused by the surface steps and dislocations at SrTiO3 substrate surface, was observed at the film-substrate interfaces. However, the films did not have large extended defects beyond several unit cells. The results suggested that when studying the two-dimensional transport properties and superconducting mechanism of YACO using YBCO/PrBCO superlattioes or ultra-thin YBCO films, the influence of the micro-structural elements must be taken into account.展开更多
基金Project supported by the Science and Technology Commission of Shanghai Municipality,China(Grant Nos.13111102300 and 11dz1100302)the National Natural Science Foundation of China(Grant Nos.11174193 and 51202141)+1 种基金the National Basic Research Program of China(Grant Nos.2011CBA00105)the Science and Technology Commission of Shanghai Municipality,China(Grant No.14DZ2260700)
文摘It is significant for low-cost preparation of YBa2Cu3O7-δ（YBCO） coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the present work,a distinct nucleation mechanism was proposed based on a transient liquid phase induced by the size effect as well as near-equilibrium assumption. With this scheme the nucleation of YBCO prepared by metal–organic deposition（MOD） or the physical vapor deposition BaF2 process was semi-quantitatively analyzed, revealing that the direct driving force for nucleation is YBCO supersaturation in the liquid phase. The theoretical analysis on the nucleation orientation portion is evidenced by the experimental result.
文摘Interfaces and surfaces of YBa_2Cu_3O_(7-x)(YBCO)-Ag have been studied by SEM-EDX and AES.No effect of Ag on 123 structure in X-ray diffraction pattern was observed for 0.4 mol Ag doped YBCO.AES analysis indicated that Ag segregated on surface of YBCO and resulted in decrease of YBCO-metal lead resistance.In addition,solution and segregation of Ag as elemental state were often appeared on interfaces and surfaces of high temperature annealed YBCO,whether elemental Ag or compound Ag_2O and AgNO_3 adopted as doping material.
文摘The patterning technologies and process order of high Tc(86K) super-conducting film bolometers have been studied. After the deposition, a conventional lithographic process was used to pattern the films with aqueous solution of HCl, and then the films were transferred into a tube furnace for annealing to form superconducting film. It eliminates the degradation of patterning process. The bolometric responsivity of approximately 34. 32 V/W is measured, and the detectivity is greater than 1. 62× 108cm · Hz1/2 · W-1, the noise equivalent powers NEP is 2. 1×10-9W.
文摘By means of X-ray diffraction investigations and electric resistivity measurements the tempera- ture dependence of phase structure and supercon- ductivity in YBa_2Cu_3O_(7_x) over the temperature range of 20℃-950℃ have been studied.The lattice parameters a,b and c as well as conductivity as a function of annealing temperatures can be roughly divided into three zones which are superconductive orthorhombic structure 1(a<b(?)c/3) at 20℃-500℃,normal conductive orthorhombic structure 2(a<b<c/3)from 550℃ to about 750℃ and semiconductive-like tetragonal structure (a=b<c/3)from about 800℃ to 950℃.However, the boundaries of the three zones is not much distinctive because there is a continuous transi- tion from the orthorhombic to tetragonal struc- ture.Furthermore,the processes of orthorhom- bic-tetragonal transition in the range of 350℃-950℃ are not only continuous but also reversible.The isothermal transition of orthorhombic 2 to orthorhombic 1 occurs at 350℃-500℃,while the maximum rate of transition and high T_c superconductivity can be obtained at about 460℃.This process of isothermal transition depends on the ordering of oxygen atoms or vacancies and the thermodynamic equilibrium to allow the oxygen diffusion.
文摘YBa2Cu3O7-x(YBCO) thin film has been epitaxially deposited on (1120) sapphire with Y2O3-stabilized ZrO2 (YSZ) buffer layer and shown a high critical current density Jc of 1. 6×106A/cm2 at 77 K in zero magnetic field. The orientation relationship of the multilayer film superconductor has been determined. The(001) plane of the YBCO film is parallel to the(100) surface of the YSZ intermediate layer. YSZ buffer layer with(100) preferred orientation is about 20 nm thick and contains element Ba, due to out-diffusion of Ba from YBCO layer. The(100) preferred orientation of YSZ buffer permits the growth of high quality YBCO thin film. Y2BaCuO5 precipitates with small size distribute uniformly in the YBCO thin film and it is favourable to raise critical current density Jc.
文摘Y_(1-x)Ho_xBa_2Cu_3O_(7-δ)(0<x<1) sinsle crystal thin films oriented with the caxis perpendicular to the sur-face were grown by DC magnetron sputtering technique. Target was pieced together with half of YBa_2Cu_3O_(7-δ)(YBCO) and half of HoBa_2Cu_3O_(7-δ)(HBCO) superconducting materials. As the distance between HBCO targetmaterial and substrate is varied , the Ho content in material is changed respectively. When the content of Ho is0. 7 (atom ratio) , the T_c>83K.
文摘Thin films of superconductors HoBa_2Cu_3O_(7-δ)(HBCO) were prepared by DC-sputtering technique. The epi-taxial growth was controlled by the ratio of the oxygen pressure and Ar pressure (O_2/Ar) , the subetrate temperature T_s and the distance of the target to subetrate. Thin films deposited under the optimum conditions (Po_2/P_(Ar)= 1:2 ; T_s=730℃) show a critical temlierature clase to 87K and a transition width less than 1K. X-raydiffraction analysis shows that the films are highiy c-axis oriented. Auger electron spectroscopy depth profilingdemonstrates Ho diffusion into the Zr(Y)O_2 subetrate owing to the Ho subetitution for Y.
基金This report is part of the fundamental research report with contract No.486 127/UN14.2/PNL.01.03.00/2016.
文摘In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of the high Tc superconductors Gd1Ba2Cu3O7−δ phase with Sr substitution has been synthesized, i.e. Gd1(Ba2−xSrx)Cu3O7−δ compound. The sample was synthesized by using a solid-state reaction method with a wet mixing, sintered for 12 hours at temperature 900°C. The synthesis results are characterized by using XRD. The results of Match-3 software analysis showed high (higher 85%) Gd1Ba2Cu3O7−δ phase was formed. The Sr substitution causes changes to the structure, i.e. the lattice parameters a, b and c, where the orthorhombicity tends to decrease with increasing Sr content. Refinement results show that based on the oxygen occupancy, the total oxygen content tends to increase.
基金Project supported in part by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB25000000)National Natural Science Foundation of China (52172271)。
文摘High-entropy REBa_(2)Cu_(3)O_(7-δ)(RE=Y_(0.7)+Dy_(0.2)+Gd_(0.2)+Sm_(0.2)+Eu_(0.2))(HE-REBCO) superconducting films doped with multiple rare earth elements were successfully fabricated with thickness up to 800 nm by a trifluoroacetate-metal organic deposition(TFA-MOD).The enhanced entropy change ΔS of the HEREBCO system promotes the c-axis growth of REBCO thin film in the competition with a/b-axis growth.The microstructure and element distribution were investigated by the transmission electron microscopy(TEM) and energy dispersive spectroscopy(EDS).The results show that HE-REBCO films have a great amount of stacking defects,lattice distortions and various rare earth oxides.Furthermore,the microstrain of HE-REBCO films increases significantly compared to the undoped YBCO and(Y,Dy)BCO films.Finally,the superco nducting critical temperature(T_c^(onset)) of HE-REBCO films is about 93 K,and the in-field properties are significantly improved,especially at the temperature of about 77 K.The maximum pinning force density(F_(p,max)) of the HE-REBCO samples at 77 K is 1.7 times higher than that of the undoped YBCO films.
文摘The structural characteristics of different alkoxides of Y. Ba and Cu are studied with quantum chemi-cal CNDO /2 calculations. The relative hydrolysis rate coefficients k_M of them are obtained according tothe relationship between frontier orbitals and organic chemical reactions. Based on the above results. properexperimental conditions for the preparation of homogeneous ultra-purity. submicro high-T_cYBa_2Cu_3O_(7-δ) superconducting powders are proposed.
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.
文摘The quantum chemical calculations of cluster YBa_2Cu_3O_7 considering all electrons have been per- formed by using the ab initio HF method with self-consistence crystal field.A Hartree-Fork surface potential is proposed to make an asymmetric duster model possess a relatively symmetric potential field and to obtain a relatively symmetric electronic structure,electronic distributions,frontier orbitals,and bond order,etc.The suggestions that there exists a covalent bonding complex,[CuO_2-O-CuO-O-Cu_2]^(6,8-),in the cell unit of the crystal,and the cell units are connected with each other by ionic bonds along the c direction of the crys- tal lattice are offered based on the chemical bonding characteristics from the calculated results.The important contribution of the apical oxygen to superconductivities is emphasized as well.
文摘Microstructure of high-quality YBa2Cu3O7-x superlattices has been investigated using high-resolution transmission electron microscope (HRTEM). The observations revealed that the superlattioes had atomic sharp interfaces between YBCO and PrBCO layers without interdiffusion. But undulations and. steps of the layer thickness existed in the specimen. An intermediate layer about 1 nm in thickness with many defects, which was caused by the surface steps and dislocations at SrTiO3 substrate surface, was observed at the film-substrate interfaces. However, the films did not have large extended defects beyond several unit cells. The results suggested that when studying the two-dimensional transport properties and superconducting mechanism of YACO using YBCO/PrBCO superlattioes or ultra-thin YBCO films, the influence of the micro-structural elements must be taken into account.
