Large-grain REBa_(2)Cu_(3)O_(7-δ)(REBCO,RE=rare earth)bulk superconductors offer promising magnetic field trapping capabilities due to their high critical current density,making them ideal for many important applicat...Large-grain REBa_(2)Cu_(3)O_(7-δ)(REBCO,RE=rare earth)bulk superconductors offer promising magnetic field trapping capabilities due to their high critical current density,making them ideal for many important applications such as trapped field magnets.However,for such large-grain superconductor bulks,there are lots of voids and cracks forming during the process of melting preparation,and some of them can be up to hundreds of microns or even millimeters in size.Consequently,these larger size voids/cracks pose a great threat to the strength of the bulks due to the inherent brittleness of superconductor REBCO materials.In order to ensure the operational safety of related superconducting devices with bulk superconductors,it is firstly important to accurately detect these voids/cracks in them.In this paper,we proposed a method for quantitatively evaluating multiple voids/cracks in bulk superconductors through the magnetic field and displacement response signals at superconductor bulk surface.The proposed method utilizes a damage index constructed from the magnetic field signals and displacement responses to identify the number and preliminary location of multiple defects.By dividing the detection area into subdomains and combining the magnetic field signals with displacement responses within each subdomain,a particle swarm algorithm was employed to evaluate the location and size parameters of the defects.In contrast to other evaluation methods using only magnetic field or displacement response signals,the combined evaluation method using both signals can identify the number of cracks effectively.Numerical studies demonstrate that the morphology of voids and cracks reconstructed using the proposed algorithm ideally matches real defects and is applicable to cases where voids and cracks coexist.This study provides a theoretical basis for the quantitative detection of voids/cracks in bulk superconductors.展开更多
To study the influence of thickness on the magnetic properties of ReBCO(Re = Y, Gd, Sm, Nd, etc.) bulk superconductors, a single domain gadolinium barium copper oxide(GdBCO) bulk superconductor fabricated by the Re + ...To study the influence of thickness on the magnetic properties of ReBCO(Re = Y, Gd, Sm, Nd, etc.) bulk superconductors, a single domain gadolinium barium copper oxide(GdBCO) bulk superconductor fabricated by the Re + 011 top seeded infiltration growth(Re + 011 TSIG) method was continuously sliced along the bottom to obtain samples of different thickness. The levitation force and attractive force of these samples were tested at 77 K in the zero-field-cooled(ZFC)state. It is found that as the sample thickness decreases, the levitation force decreases gradually whereas the attractive force increases. This is related to the varied ability to resist the penetration of magnetic field occasioned by varying sample thickness, which are deeply revealed by combining with the characteristics of the non-ideal type-II superconductor. Further,the levitation force exhibits a trend of slow initial change followed by rapid change, which may be attributed to the growth of the sample. Measurement of the trapped field shows that a similar distribution of trapped field at the top and bottom surfaces can be achieved by removing some materials from the bottom of the bulk. These results provide a reference for meeting the actual requirements of ReBCO bulks of different thicknesses and greatly contribute to practical designs and applications.展开更多
The top-seeded infiltration and growth process (TSIG) is very effective method for the preparation of YBa2Cu3O7-x (YBCO) bulk superconductors. In order to improve the levitation force of the samples, a series of singl...The top-seeded infiltration and growth process (TSIG) is very effective method for the preparation of YBa2Cu3O7-x (YBCO) bulk superconductors. In order to improve the levitation force of the samples, a series of single domain YBCO bulk superconductors with different ratios of nanoscale Y2Ba4CuBiOy (YBi2411) inclusions in the solid phase pellet is successfully fabricated by the TSIG technique on the basis of previous research. In the present work, the results of YBCO bulk superconductors with YBi2411 and CeO2 (1 wt%) codoping system indicate that, the optimum doping of YBi2411 is 2 wt%, the size of Y211 particles is reduced compared with the samples without CeO2 doping;the largest levitation force is about 15 N obtained in the samples with optimum YBi2411, which is about two times higher than that of the sample without CeO2 doping. The results are very helpful for the fabrication of high quality single domain YBCO bulk superconductors.展开更多
In the applications of superconducting materials,the critical current density J_(c)(B)is a crucial performance parameter.The conventional method of measuring J_(c)(B)of bulk superconductor is magnetization method.Howe...In the applications of superconducting materials,the critical current density J_(c)(B)is a crucial performance parameter.The conventional method of measuring J_(c)(B)of bulk superconductor is magnetization method.However,there are errors in the estimation of J_(c)(B)in the lower field,and the estimation is not applicable in the region where the magnetic field reverses.In this paper,J_(c)(B)of the bulk superconductor is determined by the hysteresis and magnetostriction loops with artificial neural network(ANN),respectively.Compared with double‐output ANN,the critical current density obtained by single‐output ANN is more accurate.Finally,the prediction results given by the hysteresis and magnetostriction loops are discussed.展开更多
The homogeneity of the microstructure and composition are critical in determining the properties of rare earthbarium‐cuprate,single grain bulk superconductors[(RE)BCO].The magnitude of the trapped magnetic field achi...The homogeneity of the microstructure and composition are critical in determining the properties of rare earthbarium‐cuprate,single grain bulk superconductors[(RE)BCO].The magnitude of the trapped magnetic field achieveable in these technologically important materials,in particular,is influenced heavily by the size and distribution of(RE)_(2)BaCuO_(x)(RE‐211)flux pinning inclusions in the bulk microstructure,whereas the size and distribution of silver agglomerates present within the bulk superconducting matrix correlate directly with improved mechanical properties.With careful engineering,these materials have significant potential for application in range of devices related to energy storage,medicine,electro‐magnetic machinery and microelectronic technology.Fabrication of(RE)BCO bulk superconductors typically involves heating a powder compact above its peritectic decomposition temperature followed by slow cooling to facilitate the growth of a single grain.Each(RE)BCO composition has a different peritectic temperature and growth rate,which,therefore,necessitates different requirements in the heating profile.The fabrication temperature and growth rate,for example,may have an effect on the RE‐211 and silver distribution,which may,in turn,affect the superconducting properties of the resulting single grain.In this work we compare the distributions of silver and RE‐211 in the single grain microstructures of YBCOAg,GdBCO‐Ag,EuBCO‐Ag and SmBCO‐Ag bulk superconductors using optical microscopy,scanning electron microscopy and energy dispersive X‐ray spectroscopy.We observe that the distributions are very similar along both the a/b‐axis and c‐axis of these materials.This suggests that factors other than the maximum temperature used to achieve peritectic decomposition and the rate of single grain growth are particularly influential in determining the properties of the as‐processed samples in the top seeded melt growth process.This observation demonstrates there is freedom to use(RE)materials interchangeably between different applications as required,for example,for functional or economic reasons.展开更多
A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface supercond...A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface superconducting gaps and topological surface states have been observed.However,the simultaneous presence of bulk and surface superconductivity has remained unresolved.In this study,we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi_(2) using ultra-low-temperature scanning tunneling microscopy/spectroscopy.The bulk gap,Δ,is∼0.053 meV,with a critical temperature(T_(c))of∼0.5K and a critical field below 0.01 T,accompanied by a vortex lattice and vortex bound states and yielding a coherence length of∼200 nm.Remarkably,certain surface regions exhibit a much larger gap(Δ)of∼0.42 meV,persisting up to a T_(c)value of∼3K and surviving magnetic fields of up to 2 T,yet lacking a static vortex lattice.This coexistence of robust surface and bulk superconductivity establishes γ-PtBi_(2)as a unique platform for exploring the interplay between bulk and surface Cooper pairings in topological superconductors.展开更多
Pure MgB2 bulk samples are successfully synthesized by self-propagatlng hlgh-temperature synthesis （SHS） method. The experiments show that the best preheating temperature is 250℃, the highest Jc values of the prepa...Pure MgB2 bulk samples are successfully synthesized by self-propagatlng hlgh-temperature synthesis （SHS） method. The experiments show that the best preheating temperature is 250℃, the highest Jc values of the prepared MgB2 reach 1.5×10^6A/cm^2 （10K, 0.5T） and 1.7×10^6A/cm^2 （20K, 0T）, and the MgB2 particle sizes range from 2 to 5μm. The advantages of this method are that it is simple, economical and suitable for the manufacture of bulk MgB2 materials on industrial scale.展开更多
Bulk YBa2Cu3O7 samples were prepared by PMP method. Through adjusting ingredients and preparation procedures, a pellet with 3. 5 cm in diameter and 0. 9 cm in thickness was synthesized. A mass of 1. 3 kg on a magnet c...Bulk YBa2Cu3O7 samples were prepared by PMP method. Through adjusting ingredients and preparation procedures, a pellet with 3. 5 cm in diameter and 0. 9 cm in thickness was synthesized. A mass of 1. 3 kg on a magnet can be levitated at about 1 mm height at 77 K. The XRD and SEM indicated that magnetic lifting property can be enhanced by addition of Ag2O and Y2BaCuO5.展开更多
We fabricated YBa2Cu3O7–d bulk ceramics with a domestic microwave oven and investigated the effect of pressure at the press procedure. If the pressure was not high enough, the ratio of BaCuO2 phase became large, esti...We fabricated YBa2Cu3O7–d bulk ceramics with a domestic microwave oven and investigated the effect of pressure at the press procedure. If the pressure was not high enough, the ratio of BaCuO2 phase became large, estimated from x-ray diffraction (XRD) measurements. We found that the pressure should be 700 kgf/cm2 at least in order to suppress the BaCuO2 phase.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12232005 and 12072101).
文摘Large-grain REBa_(2)Cu_(3)O_(7-δ)(REBCO,RE=rare earth)bulk superconductors offer promising magnetic field trapping capabilities due to their high critical current density,making them ideal for many important applications such as trapped field magnets.However,for such large-grain superconductor bulks,there are lots of voids and cracks forming during the process of melting preparation,and some of them can be up to hundreds of microns or even millimeters in size.Consequently,these larger size voids/cracks pose a great threat to the strength of the bulks due to the inherent brittleness of superconductor REBCO materials.In order to ensure the operational safety of related superconducting devices with bulk superconductors,it is firstly important to accurately detect these voids/cracks in them.In this paper,we proposed a method for quantitatively evaluating multiple voids/cracks in bulk superconductors through the magnetic field and displacement response signals at superconductor bulk surface.The proposed method utilizes a damage index constructed from the magnetic field signals and displacement responses to identify the number and preliminary location of multiple defects.By dividing the detection area into subdomains and combining the magnetic field signals with displacement responses within each subdomain,a particle swarm algorithm was employed to evaluate the location and size parameters of the defects.In contrast to other evaluation methods using only magnetic field or displacement response signals,the combined evaluation method using both signals can identify the number of cracks effectively.Numerical studies demonstrate that the morphology of voids and cracks reconstructed using the proposed algorithm ideally matches real defects and is applicable to cases where voids and cracks coexist.This study provides a theoretical basis for the quantitative detection of voids/cracks in bulk superconductors.
基金supported by the National Natural Science Foundation of China (Grant No. 52072229)the Key-grant Project of the Ministry of Education of China (Grant No. 311033)+1 种基金the Fundamental Research Funds for the Central Universities (Grant No. GK201706001)the Teaching Reform and Innovation Project of Higher Education in Shanxi Province, China (Grant No. J2021719)。
文摘To study the influence of thickness on the magnetic properties of ReBCO(Re = Y, Gd, Sm, Nd, etc.) bulk superconductors, a single domain gadolinium barium copper oxide(GdBCO) bulk superconductor fabricated by the Re + 011 top seeded infiltration growth(Re + 011 TSIG) method was continuously sliced along the bottom to obtain samples of different thickness. The levitation force and attractive force of these samples were tested at 77 K in the zero-field-cooled(ZFC)state. It is found that as the sample thickness decreases, the levitation force decreases gradually whereas the attractive force increases. This is related to the varied ability to resist the penetration of magnetic field occasioned by varying sample thickness, which are deeply revealed by combining with the characteristics of the non-ideal type-II superconductor. Further,the levitation force exhibits a trend of slow initial change followed by rapid change, which may be attributed to the growth of the sample. Measurement of the trapped field shows that a similar distribution of trapped field at the top and bottom surfaces can be achieved by removing some materials from the bottom of the bulk. These results provide a reference for meeting the actual requirements of ReBCO bulks of different thicknesses and greatly contribute to practical designs and applications.
文摘The top-seeded infiltration and growth process (TSIG) is very effective method for the preparation of YBa2Cu3O7-x (YBCO) bulk superconductors. In order to improve the levitation force of the samples, a series of single domain YBCO bulk superconductors with different ratios of nanoscale Y2Ba4CuBiOy (YBi2411) inclusions in the solid phase pellet is successfully fabricated by the TSIG technique on the basis of previous research. In the present work, the results of YBCO bulk superconductors with YBi2411 and CeO2 (1 wt%) codoping system indicate that, the optimum doping of YBi2411 is 2 wt%, the size of Y211 particles is reduced compared with the samples without CeO2 doping;the largest levitation force is about 15 N obtained in the samples with optimum YBi2411, which is about two times higher than that of the sample without CeO2 doping. The results are very helpful for the fabrication of high quality single domain YBCO bulk superconductors.
基金support from the National Natural Science Foundation of China(Grant Nos.U2241267,12172155 and 11872195).
文摘In the applications of superconducting materials,the critical current density J_(c)(B)is a crucial performance parameter.The conventional method of measuring J_(c)(B)of bulk superconductor is magnetization method.However,there are errors in the estimation of J_(c)(B)in the lower field,and the estimation is not applicable in the region where the magnetic field reverses.In this paper,J_(c)(B)of the bulk superconductor is determined by the hysteresis and magnetostriction loops with artificial neural network(ANN),respectively.Compared with double‐output ANN,the critical current density obtained by single‐output ANN is more accurate.Finally,the prediction results given by the hysteresis and magnetostriction loops are discussed.
基金support from the Engineering and Physical Sciences Research Council(EPSRC)grant EP/T014679/1.
文摘The homogeneity of the microstructure and composition are critical in determining the properties of rare earthbarium‐cuprate,single grain bulk superconductors[(RE)BCO].The magnitude of the trapped magnetic field achieveable in these technologically important materials,in particular,is influenced heavily by the size and distribution of(RE)_(2)BaCuO_(x)(RE‐211)flux pinning inclusions in the bulk microstructure,whereas the size and distribution of silver agglomerates present within the bulk superconducting matrix correlate directly with improved mechanical properties.With careful engineering,these materials have significant potential for application in range of devices related to energy storage,medicine,electro‐magnetic machinery and microelectronic technology.Fabrication of(RE)BCO bulk superconductors typically involves heating a powder compact above its peritectic decomposition temperature followed by slow cooling to facilitate the growth of a single grain.Each(RE)BCO composition has a different peritectic temperature and growth rate,which,therefore,necessitates different requirements in the heating profile.The fabrication temperature and growth rate,for example,may have an effect on the RE‐211 and silver distribution,which may,in turn,affect the superconducting properties of the resulting single grain.In this work we compare the distributions of silver and RE‐211 in the single grain microstructures of YBCOAg,GdBCO‐Ag,EuBCO‐Ag and SmBCO‐Ag bulk superconductors using optical microscopy,scanning electron microscopy and energy dispersive X‐ray spectroscopy.We observe that the distributions are very similar along both the a/b‐axis and c‐axis of these materials.This suggests that factors other than the maximum temperature used to achieve peritectic decomposition and the rate of single grain growth are particularly influential in determining the properties of the as‐processed samples in the top seeded melt growth process.This observation demonstrates there is freedom to use(RE)materials interchangeably between different applications as required,for example,for functional or economic reasons.
基金supported by the National Natural Science Foundation of China(Grant No.62488201)the National Key Research and Development Projects of China(Grant Nos.2022YFA1204100 and 2023YFA1607400)+1 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-003)the Innovation Program of Quantum Science and Technology(Grant No.2021ZD0302700)。
文摘A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface superconducting gaps and topological surface states have been observed.However,the simultaneous presence of bulk and surface superconductivity has remained unresolved.In this study,we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi_(2) using ultra-low-temperature scanning tunneling microscopy/spectroscopy.The bulk gap,Δ,is∼0.053 meV,with a critical temperature(T_(c))of∼0.5K and a critical field below 0.01 T,accompanied by a vortex lattice and vortex bound states and yielding a coherence length of∼200 nm.Remarkably,certain surface regions exhibit a much larger gap(Δ)of∼0.42 meV,persisting up to a T_(c)value of∼3K and surviving magnetic fields of up to 2 T,yet lacking a static vortex lattice.This coexistence of robust surface and bulk superconductivity establishes γ-PtBi_(2)as a unique platform for exploring the interplay between bulk and surface Cooper pairings in topological superconductors.
基金Project supported by the Natural Science Foundation of Gansu province of China （Grant No ZS032-B25-019）.
文摘Pure MgB2 bulk samples are successfully synthesized by self-propagatlng hlgh-temperature synthesis （SHS） method. The experiments show that the best preheating temperature is 250℃, the highest Jc values of the prepared MgB2 reach 1.5×10^6A/cm^2 （10K, 0.5T） and 1.7×10^6A/cm^2 （20K, 0T）, and the MgB2 particle sizes range from 2 to 5μm. The advantages of this method are that it is simple, economical and suitable for the manufacture of bulk MgB2 materials on industrial scale.
文摘Bulk YBa2Cu3O7 samples were prepared by PMP method. Through adjusting ingredients and preparation procedures, a pellet with 3. 5 cm in diameter and 0. 9 cm in thickness was synthesized. A mass of 1. 3 kg on a magnet can be levitated at about 1 mm height at 77 K. The XRD and SEM indicated that magnetic lifting property can be enhanced by addition of Ag2O and Y2BaCuO5.
文摘We fabricated YBa2Cu3O7–d bulk ceramics with a domestic microwave oven and investigated the effect of pressure at the press procedure. If the pressure was not high enough, the ratio of BaCuO2 phase became large, estimated from x-ray diffraction (XRD) measurements. We found that the pressure should be 700 kgf/cm2 at least in order to suppress the BaCuO2 phase.
