The microstructure and superconducting properties of Bi-2223 superconductor fabricated in high magnetic fields were investigated. The results shows that the Bi-2212 grains with their c-axis parallel to the magnetic fi...The microstructure and superconducting properties of Bi-2223 superconductor fabricated in high magnetic fields were investigated. The results shows that the Bi-2212 grains with their c-axis parallel to the magnetic field were formed after the partial-melting and solidification in 8 T magnetic field, and transformed into the Bi-2223 grains with c-axis alignment during the further sintering process at 840 ℃ without magnetic field. The conversion of Bi-2212 grains to Bi-2223 grains has the heredity in grain alignment. The mixed structures of the Bi-2223 and the Bi-2212 grains with their c-axis parallel to the magnetic field are formed in samples sintered at 850?855 ℃ in 10 T magnetic field. When sintered in 10 T below 845 ℃, a high proportion of Bi-2223 phase is obtained, however no preferred orientation is observed. The Bi-2223 grains with their c-axis parallel to the axial direction of the vertical tube furnace are formed not only on the surface, but also in the center of the sample sintered at 850 ℃ for 120 h in a 15 ℃/cm temperature gradient without magnetic field. Moreover, the samples sintered in the temperature gradient and in a 10 T magnetic field have a stronger c-axis alignment of Bi-2223 phase.展开更多
The Bi_2(Sr,Ca)_3Cu_2O_x system superconductor was prepared by different melting procedures and after treatment.The effects of cooling rate,annealing temperature and time,as well as melting procedures on phase transfo...The Bi_2(Sr,Ca)_3Cu_2O_x system superconductor was prepared by different melting procedures and after treatment.The effects of cooling rate,annealing temperature and time,as well as melting procedures on phase transformation were investigated.The structure and properties were examined by X-ray diffraction,optical microscopy,EPMA,DTA,TGA and measurements of electric and magnetic properties.When the melt of nominal composition Bi_2(Sr,Ca)_3Cu_2O_x solidified in air,the Bi_2(Sr,Ca)_3Cu_2O_(8+δ)(2212)superconducting phase is stable,the easily solidified product including Bi_2(Sr,Ca)_2CuO_(6+δ)(2201)phase is metastable, and another may be amorphous if rapidly quenched.The last two may transform into 2212 phase by after treatment at an optimal annealing temperature ranging 780—870℃.While 2201 phase,prepared by the laser floating zone melting method,may easily transform into 2212 phase at layer or filament in shape which is favourable to improve the links among superconducting grains and critical current density.展开更多
Cux Bi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser- based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 supercondu...Cux Bi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser- based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirae cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ～4000 Oe for the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.g K. The relation between the upper critical field He2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cuo.3Bi2Se3 superconductors up to room temperature. These observations provide useful information for further study of this possible candidate for topological superconductors.展开更多
In this paper, samples of antimony doped Bi-based superconductor with stoichiometric composition Bi1.7Pb0.2Sb0.1Sr2Ca2Ca3O10 were prepared by a solid state reaction method. The effect of sintering time on the supercon...In this paper, samples of antimony doped Bi-based superconductor with stoichiometric composition Bi1.7Pb0.2Sb0.1Sr2Ca2Ca3O10 were prepared by a solid state reaction method. The effect of sintering time on the superconducting properties was studied;all samples were sintered in air at 850°C for different sintering time (80, 100, 120, 140, and 160) h. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements were performed for determination of the crystal structure and surface morphology of samples, respectively. All samples showed an orthorhombic structure with two phases, high-Tc phase (2223) and low-Tc phase (2212) in addition to an impure phase. It has been observed that the critical temperature and the high-Tc phase increases and appears to be the dominant phase when the sintering time is increased to 140 h, while with increasing sintering time to 160 h, both Tc and the high phase started to decrease. (SEM) results show that increasing sintering time enhances the growing of superconducting phase unidirectional and suppresses the high phase intrusion which leads to the production of nearly single Bi-2223 phase with higher Tc.展开更多
A modified spark plasma sintering（SPS） technique was developed for the fabrication of Bi2Sr2CaCu2Ox（Bi-2212）superconducting bulks with better intergrain connections. The influences of the modified SPS process on t...A modified spark plasma sintering（SPS） technique was developed for the fabrication of Bi2Sr2CaCu2Ox（Bi-2212）superconducting bulks with better intergrain connections. The influences of the modified SPS process on the microstructures, intergrain connections, and related superconducting properties were systematically analyzed. The modified SPS process can not only increase the final density of the bulk samples but also enhance the texture structures. Clean grain boundaries were obtained instead of the intergrain amorphous layers. Therefore the intergranular properties were obviously improved. Due to the better intergrain connections and the stronger flux pinning properties, the critical current densities of the Bi-2212 bulks obtained via the modified SPS process were greatly increased. The obtained improvements imply the possibility for the modified SPS technique to be used for enhancing the superconducting properties of the Bi-2212 tapes.展开更多
Dislocation structures in a bulk Pb-doped Bi Sr- Ca- Cu- O high temperature superconductor wereimaged. Dislocation morphologies shown by transmission electron microscopy were discussed.
The positron annihilation lifetime and Doppler broadened line-shapeparameter have been measured between 77 and 300 K for Bi<sub>1.8</sub>Pb<sub>0.1</sub>Sb<sub>0.1</sub>Sr<sub>...The positron annihilation lifetime and Doppler broadened line-shapeparameter have been measured between 77 and 300 K for Bi<sub>1.8</sub>Pb<sub>0.1</sub>Sb<sub>0.1</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub>,Bi<sub>1.8</sub>Sb<sub>0.2</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub> and Bi<sub>1.7</sub>Pb<sub>0.2</sub>Sb<sub>0.1</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>2</sub>O<sub>x</sub>. The charge transfer from Cu-Olayers to Bi-O layers has been observed across T<sub>c</sub>s for all samples.Three samples allshow two normal state anomalies around 160 K and 240 K,respectively.The anomalyaround 160 K is attributed to the structural instability and that around 240 Kpresumably to the displacement phase transition.展开更多
High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clea...High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels:the bonding sheet corresponds to a doping level of 0.14,which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped,giving an overall doping level of 0.20 for the sample.Different superconducting gap sizes on the two Fermi surface sheets are revealed.The superconducting gap on the antibonding Fermi surface sheet follows a standard d-wave form while it deviates from the standard d-wave form for the bonding Fermi surface sheet.The maximum gap difference between the two Fermi surface sheets near the antinodal region is～2 meV.These observations provide important information for studying the relationship between the Fermi surface topology and superconductivity,and the layer-dependent superconductivity in high temperature cuprate superconductors.展开更多
文摘The microstructure and superconducting properties of Bi-2223 superconductor fabricated in high magnetic fields were investigated. The results shows that the Bi-2212 grains with their c-axis parallel to the magnetic field were formed after the partial-melting and solidification in 8 T magnetic field, and transformed into the Bi-2223 grains with c-axis alignment during the further sintering process at 840 ℃ without magnetic field. The conversion of Bi-2212 grains to Bi-2223 grains has the heredity in grain alignment. The mixed structures of the Bi-2223 and the Bi-2212 grains with their c-axis parallel to the magnetic field are formed in samples sintered at 850?855 ℃ in 10 T magnetic field. When sintered in 10 T below 845 ℃, a high proportion of Bi-2223 phase is obtained, however no preferred orientation is observed. The Bi-2223 grains with their c-axis parallel to the axial direction of the vertical tube furnace are formed not only on the surface, but also in the center of the sample sintered at 850 ℃ for 120 h in a 15 ℃/cm temperature gradient without magnetic field. Moreover, the samples sintered in the temperature gradient and in a 10 T magnetic field have a stronger c-axis alignment of Bi-2223 phase.
文摘The Bi_2(Sr,Ca)_3Cu_2O_x system superconductor was prepared by different melting procedures and after treatment.The effects of cooling rate,annealing temperature and time,as well as melting procedures on phase transformation were investigated.The structure and properties were examined by X-ray diffraction,optical microscopy,EPMA,DTA,TGA and measurements of electric and magnetic properties.When the melt of nominal composition Bi_2(Sr,Ca)_3Cu_2O_x solidified in air,the Bi_2(Sr,Ca)_3Cu_2O_(8+δ)(2212)superconducting phase is stable,the easily solidified product including Bi_2(Sr,Ca)_2CuO_(6+δ)(2201)phase is metastable, and another may be amorphous if rapidly quenched.The last two may transform into 2212 phase by after treatment at an optimal annealing temperature ranging 780—870℃.While 2201 phase,prepared by the laser floating zone melting method,may easily transform into 2212 phase at layer or filament in shape which is favourable to improve the links among superconducting grains and critical current density.
基金the National Natural Science Foundation of China under Grant Nos 11190022,91021006 and 11374338the National Basic Research Program of China under Grant Nos 2011CB921703,2011CBA00110 and 2013CB921700the Strategic Priority Research Program(B) of the Chinese Academy of Sciences under Grant No XDB07020300
文摘Cux Bi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser- based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirae cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ～4000 Oe for the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.g K. The relation between the upper critical field He2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cuo.3Bi2Se3 superconductors up to room temperature. These observations provide useful information for further study of this possible candidate for topological superconductors.
文摘In this paper, samples of antimony doped Bi-based superconductor with stoichiometric composition Bi1.7Pb0.2Sb0.1Sr2Ca2Ca3O10 were prepared by a solid state reaction method. The effect of sintering time on the superconducting properties was studied;all samples were sintered in air at 850°C for different sintering time (80, 100, 120, 140, and 160) h. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements were performed for determination of the crystal structure and surface morphology of samples, respectively. All samples showed an orthorhombic structure with two phases, high-Tc phase (2223) and low-Tc phase (2212) in addition to an impure phase. It has been observed that the critical temperature and the high-Tc phase increases and appears to be the dominant phase when the sintering time is increased to 140 h, while with increasing sintering time to 160 h, both Tc and the high phase started to decrease. (SEM) results show that increasing sintering time enhances the growing of superconducting phase unidirectional and suppresses the high phase intrusion which leads to the production of nearly single Bi-2223 phase with higher Tc.
基金Project supported by the National Basic Research Program of China(Grant No.2011CBA00104)the National Natural Science Foundation of China(Grant No.51472206)+1 种基金the ITER Project of China(Grant No.2013GB110001)the Program for Innovative Research Team in Shaanxi Province,China(Grant No.2013KCT-07)
文摘A modified spark plasma sintering（SPS） technique was developed for the fabrication of Bi2Sr2CaCu2Ox（Bi-2212）superconducting bulks with better intergrain connections. The influences of the modified SPS process on the microstructures, intergrain connections, and related superconducting properties were systematically analyzed. The modified SPS process can not only increase the final density of the bulk samples but also enhance the texture structures. Clean grain boundaries were obtained instead of the intergrain amorphous layers. Therefore the intergranular properties were obviously improved. Due to the better intergrain connections and the stronger flux pinning properties, the critical current densities of the Bi-2212 bulks obtained via the modified SPS process were greatly increased. The obtained improvements imply the possibility for the modified SPS technique to be used for enhancing the superconducting properties of the Bi-2212 tapes.
文摘Dislocation structures in a bulk Pb-doped Bi Sr- Ca- Cu- O high temperature superconductor wereimaged. Dislocation morphologies shown by transmission electron microscopy were discussed.
基金The project supported by IAEA under the Contract No.5295/RBby China National Nuclear Corporation.
文摘The positron annihilation lifetime and Doppler broadened line-shapeparameter have been measured between 77 and 300 K for Bi<sub>1.8</sub>Pb<sub>0.1</sub>Sb<sub>0.1</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub>,Bi<sub>1.8</sub>Sb<sub>0.2</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub> and Bi<sub>1.7</sub>Pb<sub>0.2</sub>Sb<sub>0.1</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>2</sub>O<sub>x</sub>. The charge transfer from Cu-Olayers to Bi-O layers has been observed across T<sub>c</sub>s for all samples.Three samples allshow two normal state anomalies around 160 K and 240 K,respectively.The anomalyaround 160 K is attributed to the structural instability and that around 240 Kpresumably to the displacement phase transition.
基金Supported by the National Natural Science Foundation of China under Grant No 11888101the National Key Research and Development Program of China under Grant Nos 2016YFA0300300 and 2017YFA0302900+3 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB25000000)the Youth Innovation Promotion Association of CAS under Grant No2017013the Research Program of Beijing Academy of Quantum Information Sciences under Grant No Y18G06supported by the Office of Basic Energy Sciences,U.S.Department of Energy(DOE)under Contract No de-sc0012704
文摘High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels:the bonding sheet corresponds to a doping level of 0.14,which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped,giving an overall doping level of 0.20 for the sample.Different superconducting gap sizes on the two Fermi surface sheets are revealed.The superconducting gap on the antibonding Fermi surface sheet follows a standard d-wave form while it deviates from the standard d-wave form for the bonding Fermi surface sheet.The maximum gap difference between the two Fermi surface sheets near the antinodal region is～2 meV.These observations provide important information for studying the relationship between the Fermi surface topology and superconductivity,and the layer-dependent superconductivity in high temperature cuprate superconductors.
