A Theory of Superconductivity based on Bose-Einstein Statistics and Its Application

A theory of superconductivity based on Bose-Einstein statistics was proposed,which can lead to a formula for T(critical temperature)similar to that of BCS theory,and provide a possible explanation for the complexity of isotope effect and the normal state energy gap in copper-oxides.We proceeded from a 3-dimensional harmonic oscillator model to equivalent the superconducting state to a two-dimensional Bose-Einstein condensate bound longitudinally,and pointed out the application conditions of the theory.Under this scheme,we analyzed some typical structural features in copper oxides that favor the production of high-temperature superconductivity.We also discovered that combining this theory with an alternative mechanism-strong coupling to local spin configurations-provided some useful hints for exploring new superconducting materials.In addition,we pointed out a possible link between the phenomenon of superconductivity and magnetostriction,then we proposed some combinations of elements as possible candidates for high temperature superconducting materials based on those analysis.

Morphological evolution of CdS films prepared by chemical bath deposition

In this article, the growth process of chemical bath deposited CdS films was systematically investigated. The structural, optical, and morphological properties were investigated by X-ray diffraction （XRD）, transmission electron microscope （TEM）, UV-Vis spectrophotometer, scanning electron microscope （SEM）, respectively. CdS nanocubes with size of less than 500 nm and nanocrystal-lites with diameter of less than 5 nm forming in reaction solution are observed. According to the TEM results and the SEM morphological evolution of CdS films, a crystal-lite-by-crystallite growth mechanism is proposed to eluci-date the growth process of chemical bath deposited CdS films based on the present growth mechanism.

Microstructure evolution of Nb_3Sn superconductors during diffusion treatment by bronze route

The element diffusion process of Nb_3Sn superconductors by bronze route was studied using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The critical current of superconductors was measured by four-point method. The results show that a diffusion layer has formed around the boundaries between the filaments and bronze matrix after 15 h heat treatment. The diffusion layer thickness keeps stable after heat treatment duration of 50~75 h. The stable and solid Nb 3 Sn layer is obtained in the sample after 100 h heat treatment. Excessive heat treatment would induce superconductivity degeneration because of superconductor grain coarsening. The characteristics of the element diffusion process were discussed. The diffusion of tin atom is the governing factor in diffusion. In this study, Nb_3_Sn superconductors with good superconducting property were fabricated successfully at 670 °C after 100h heat treatment.

Synthesis, characterization, and thermostability of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)barium(Ⅱ)

The metal-organic chemical vapor deposition （MOCVD） technique is a promising process for high-tem- perature superconductor YBa2Cu307_6（YBCO） preparation. In this technique, it is a challenge to obtain barium precursors with high volatility. In addition, the purity, evaporation characteristics, and thermostability of adopted precursors in whole process will decide the quality and reproducible results of YBCO film. In the present report, bis（2,2,6,6-tetramethyl- 3,5-heptanedionato）barium（II） （Ba（TMHD）2） was synthe- sized, and its structure was identified by PTIR, 1H NMR, 13C NMR, and ESI-MS spectroscopy. Subsequently, the thermal properties and the kinetics of decomposition were systemati- cally investigated by nonisothermal thermogravimetric anal- ysis methods. Based on the average apparent activation energy evaluated by the Ozawa, Kissinger, and Friedman methods, the volatilization process was discussed, and all results show that Ba（TMHD）2 is unstable and highly sensitive to the change of temperature during the whole evaporation process. There- fore, it is very important to choose suitable volatilization technology and conditions for avoiding Ba（TMHD）2 break- down （or thermal aging） during MOCVD process. Subse- quently, the possible conversion function is estimated through the Coats-Redfern method to characterize the evaporation patterns and follows a phase boundary reaction mechanism by the contracting surface equation with average activation energy of 118.7 kJ.mo1-1.

Effects of thickness on superconducting properties and structures of Y_2O_3/BZO-doped MOD-YBCO films

We report the thickness dependence of critical current density （Jc） in YBa2Cu3O7-x （YBCO） films with BaZrO3 （BZO） and Y2O3 additions grown on single crystal LaAlO3 substrates by metalorganic deposition using trifluoroacetates （TFA-MOD）. Comparing with pttre YBCO films, the Jc of BZO/Y2O3-doped YBCO films was significantly enhanced. It was also found that with the increase of the thickness of YBCO film from 0.25 μm to 1.5 μm, the Ic of BZO/Y2O3-doped YBCO film increased from 130 A/cm to 250 A/cm and yet Jc of YBCO film decreased from 6.5 MA/cm2 to 2.5 M A/cm2. The thick BZO/Y2O3-doped MOD-YBCO film showed lower Jc, which is mainly attributed to the formation of a-axis grains and pores.

Strongly enhanced flux pinning in the YBa_2Cu_3O_(7-X) films with the co-doping of Ba TiO_3 nanorod and Y_2O_3 nanoparticles at 65 K

YBa2Cu3O7-x（YBCO） films with co-doping BaTiO3（BTO） and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates（TFA-MOD）. The properties of the BTO/Y2O3co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction（XRD）, Raman spectra, and scanning electron microscope（SEM）. The optimized content of yttrium excess in the BTO/Y2O3co-doped YBCO films is 10 mol.%, and the critical current density is as high as - 17 mA/cm^2（self-field, 65 K） by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density（JC） not only at the self-magnetic field, but also in the applied magnetic field.

Enhancement of Critical Current Density and Flux Pinning in Acetone and La2O3 Codoped MgB2 Tapes

MgB2 tape samples with simultaneous additions of acetone and La2O3 were prepared by an in？situ processed powder-in-tube method. Compared to the pure and single doped tapes, both transport Jc and fluxing pinning are greatly improved by acetone and La2O3 codoping. Acetone supplies carbon into the MgB2 crystal lattice and increases the upper critical field, while the La2O3 reacts with B to form LaB6 nanoparticles as effective flux pining centers. The improvement of the superconducting properties in codoped tapes can be attributed to the combined effects of improvement in Hc2 and flux pinning.

Influence of oxygen pressure on critical current density and magnetic flux pinning structures in YBa_2 Cu_3 O_(7-x) fabricated by chemical solution deposition

This paper studies the effect of oxygen partial pressure on the fabrication of YBa2Cu307-x films on （00/） LaAIO3 substrates by metalorganic deposition using trifluoroacetates （TFA-MOD）. As the oxygen partial pressure increases to 1500 Pa, a great increase in the superconducting properties is observed at high magnetic fields parallel to the YBCO c axis. The cross-sectional transmission electron microscope images show that a high density of stacking faults in the size range of 10-15 nm may act as flux pinning centres to enhance the critical current density of the YBCO films

Precursor evolution and growth mechanism of BTO/YBCO films by TFA–MOD process

In this study, BaTiO3 （BTO）-doped YBCO films are prepared on LaA103 （100） single-crystal substrates by metal- organic decomposition （MOD） using trifluoroacetate （TFA） precursor solutions. The critical current density （Jc） of BTO/YBCO film is as high as 10 MA/cm2 （77 K, 0 T）. The BTO peak is found in the X-ray diffraction （XRD） pattern of a final YBCO superconductivity film. Moreover, a comprehensive study of the precursor evolution is conducted mainly by X-ray analysis and μ-Raman spectroscopy. It is found that the TFA begins to decompose at the beginning of the thermal process, and then further decomposes as temperature increases, and at 700 ℃ BTO nanoparticles begin to appear. It sug- gests that the YBCO film embedded with BTO nanoparticles, whose critical current density （Jc） is enhanced, is successfully prepared by an easily scalable chemical solution deposition technique.

Fabrication and Properties of Aligned Sr_(0.6)K_(0.4)Fe_(2)As_(2) Superconductors by High Magnetic Field Processing

We fabricated a c−axis aligned Sr_(0.6)K_(0.4)Fe_(2)As_(2)superconductor using a two−step magnetic field procedure.The effect of the magnetic fields on the structure and superconducting properties of Sr_(0.6)K_(0.4)Fe_(2)As_(2) is investigated using x−ray diffraction and magnetic measurements.The degree of orientation of the samples is about 0.39 for the c axis and 0.51 for ab-plane orientation,as evaluated from the Lotgering factor of x-ray diffraction.This technology may be useful in a variety of potential applications,including preparing iron-based superconducting bulks and wires with high critical currents.

Simple One-Step Synthesis and Superconducting Properties of SmFeAsO1-xFx

The recent discovery of superconductivity in REFeAsO （RE, rare-earth metal） has generated enormous interest because these materials axe the first non-copper oxide superconductors with critical temperatures Tc exceeding 50 K as well as upper critical fields well above 100 T. However, for these new superconductors, very complicated synthesis routes, such as the complex two-step synthesis or high-pressure sintering, are required. Furthermore, there is the toxicity and volatility of arsenic to consider, sometimes a sealed quartz tube of arsenic exploded during annealing. We present a new method for producing high-temperature SmFeAsO1-xFx superconductors by using a one-step sintering process. Superconducting transition with the onset temperature of 54.6 K and high critical fields Hc2（0）≥200 T were confirmed in SmFeAsO0.7F0.3. At 5 K and at self field, critical current densities Jc estimated from the magnetization hysteresis using the whole sample size and the average particle size have reached 8.5×10^3 and 1.2×10^6 A/cm^2, respectively. Moreover, Jc exhibited a very weak dependence on magnetic field. This simple and safe one-step synthesis technique should be effective in other rare earth derivatives of iron-based superconductors.

Co-doped BaFe_(2)As_(2) Josephson junction fabricated with a focused helium ion beam

Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices,therefore the preparation of high-quality iron pnictide Josephson junctions is of great importance.In this work,we have successfully fabricated Josephson junctions from Co-doped BaFe_(2)As_(2)thin films using a direct junction fabrication technique which utilizes high energy focused helium ion beam(FHIB).The electrical transport properties were investigated for junctions fabricated with various He^(+)irradiation doses.The junctions show sharp superconducting transition around 24 K with a narrow transition width of 2.5 K,and a dose correlated foot-structure resistance which corresponds to the effective tuning of junction properties by He^(+)irradiation.Significant J_c suppression by more than two orders of magnitude can be achieved by increasing the He^(+)irradiation dose,which is advantageous for the realization of low noise ion pnictide thin film devices.Clear Shapiro steps are observed under 10 GHz microwave irradiation.The above results demonstrate the successful fabrication of high quality and controllable Co-doped BaFe_(2)As_(2)Josephson junction with high reproducibility using the FHIB technique,laying the foundation for future investigating the mechanism of iron-based superconductors,and also the further implementation in various superconducting electronic devices.

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes

We report the temperature, magnetic field and time dependences of magnetization in advanced Ba122 superconducting tapes. The sample exhibits peculiar vortex creep behavior. Below 10 K, the normalized magnetization relaxation rate S = d ln(-M)/d ln(t) shows a temperature-insensitive plateau with a value comparable to that of low-temperature superconductors, which can be explained within the framework of collective creep theory. It then enters into a second collective creep regime when the temperature increases. Interestingly, the relaxation rate below 20 K tends to reach saturation with increasing the field. However, it changes to a power law dependence on the field at a higher temperature. A vortex phase diagram composed of the collective and the plastic creep regions is shown. Benefiting from the strong grain boundary pinning, the advanced Bal22 superconducting tape has potential to be applied not only in liquid helium but also in liquid hydrogen or at temperatures accessible with cryocoolers.

Strong flux pinning enhancement in YBa_2Cu_3O_(7-x) films by embedded BaZrO_3 and BaTiO_3 nanoparticles

YBa2Cu3O7-x （YBCO） films with embedded BaZrO3 and BaTiO3 nanoparticles were fabricated by metalorganic deposition using trifluoroacetates （TFA-MOD）. Both X-ray diffraction and transmission electron microscopy revealed that these BaZrO3 and BaTiO3 nanoparticles had random orientations and were distributed stochastically in the YBCO matrix. The unique combined microstructure enhances the critical current density （Jc） of the BaZrO3/BaTiO3 doped-YBCO films, while keeping the critical transition temperature （Tc） close to that in the pure YBCO films. These results indicate that BaZrO3 and BaTiO3 nanoparticles provide strong flux pinning in YBCO films.

Enhancing in-field performance of GdBCO coated conductors by cooperative irradiation with Ti ions and protons

Irradiation can accurately manipulate defects and adjust pinning landscapes within REBa_(2)Cu_(3)O_(7-δ) (REBCO, RE: rare earths) coated conductors (CCs). This study reports a productive method to dramatically boost the in-field critical current density (J_(c) ) for GdBCO CCs using cooperative irradiation with Ti ions and protons. Remarkably, the in-field J_(c) of commercial CCs can be almost doubled at a wide range of temperatures and magnetic fields. Defects of various sizes induced by cooperative irradiation are more uniform distribution through the entire GdBCO film to improve the vortex pinning characteristics, thereby enhancing the in-field performance of the GdBCO CC. This method highlights how combining different particle irradiation types can tailor defect size and distribution, optimizing pinning landscapes for commercial REBCO CCs.

A review of vortex pinning in REBa_(2)Cu_(3)O_(7-x) coated conductors

REBa_(2)Cu_(3)O_(7-x)exhibits outstanding qualities such as a high irreversible field(7 T)and strong current-carrying capacity(77 K,10^(6) A cm^(-2)),making it ideal for high magnetic field applications such as fusion,accelerators,and nuclear magnetic resonance.However,the degradation of in-field critical current density(Jc)due to vortex motion is a significant hurdle.Research indicates that improving vortex pinning can notably enhance Jc in REBCO,showing promise for its future high-field applications.This review explores vortex pinning mecha-nisms,artificial pinning centers(APCs),and how environmental conditions affect pinning characteristics,highlighting advancements in vortex pinning for REBCO in magnetic fields.Different methods for introducing APCs are discussed and compared for evaluating their efficacy in achieving optimal nanoparticle distri-butions and consequent superconducting performance improvements,under-scoring the importance of nano-defect features(type,size,and distribution)in optimizing the superconducting properties of the REBCO.Additionally,the re-view tackles current challenges,shares recent research breakthroughs,and out-lines future research directions for designing pinning landscapes to further improve REBCO performance.

Investigation on the spatiotemporal complementarity of wind energy resources in China

Wind power resources are abundant in China,especially in northern China and eastern coastal areas of China.Nevertheless,wind energy has intermittent and unstable characteristics,which leads to random power output and limits the large-scale utilization of wind energy resources.It has been shown that geographically dispersed wind plants have obvious spatiotemporal offsetting effect.Power output from each individual site exhibits the power ups and downs.However,when we simulate power lines connecting sites over a certain region,the output from them changes slowly and rarely reaches either very low or full power.Hence using the spatiotemporal complementarity of wind resources effectively is highly beneficial to the smoothing of power supply.This paper investigates the spatiotemporal complementarity of wind resources in China based on the relevant data of wind energy resources,which are offered by China Meteorological Administration(CMA).

Microstructure and superconducting properties of (BaTiO3,Y2O3)-doped YBCO films under different firing temperatures

YBaCuO(YBCO) films with co-doping of Ba Ti O(BTO) and YOnanostructures were successfully fabricated on La Al O(LAO) substrate by metal organic deposition using trifluoroacetates(TFA-MOD). The focus of this study was to optimize the process conditions during the firing heat treatment of high critical current density(J C)-co-doped YBCO films. The effect of the firing temperatures on both the surface morphology and the superconducting properties for the doped YBCO films was systematically studied. According to the X-ray diffraction(XRD) and scanning electron microscopy(SEM) results,the films prepared at 820 and 850 °C show poor electrical performance due to impurity phases and large pores. In contrast, the dense YBCO films prepared at 830 and840 °C with the critical current densities of 10 MA-cm(77 K, 0 T) are obtained.

Growth mechanism of CdS film prepared by chemical bath deposition

In this paper, sodium citrate was adopted as a complexing agent and ammonia merely served as pH adjustor to investigate the growth mechanism of CdS film The growth rate, structural properties, surface morphology microstructure, and optical properties of CdS films were studied by profilometer, X-ray diffractometer（XRD）scanning electron microscopy（SEM）, transmission elec tron microscopy（TEM）, and spectrophotometer, respec tively. The SEM images show that CdS films prepared with higher ammonia concentration have lower nucleation density on substrate. SEM and EDS results show that the formation of Cd（OH）2is not required in the growth of CdS film. As the ammonia concentration increases, the sites tha previously adsorbed S2-are taken by OH-which leads to lower S2-density on substrate. CdS film forms through direct reaction of Cd2？with the S2-which are adsorbed on the substrate. Lower S2-density on the substrate results in the decrease of particle density on the substrate. The as deposited CdS films have relatively high-average trans mittance（＊80 %） in the wavelength range from 500 to1,000 nm which makes them suitable to be used in sola cell.