YBCO／CeO2／Si多层膜超导材料的分析电镜研究

在具有ＣｅＯ２隔离层的Ｓｉ基片上获得了较高质量的ＹＢａ２Ｃｕ３Ｏ７－ｘ（ＹＢＣＯ）高温超导薄膜。在零磁场下，７７Ｋ时其临界电流密度达到１×１０６Ａ／ｃｍ２。研究发现，ＹＢＣＯ的（００１）面平行于Ｓｉ基片的（１００）面，而ＣｅＯ２过渡层由许多约４０ｎｍ×１００ｎｍ的细小ＣｅＯ２晶粒组成，其取向呈散乱分布。尽管ＣｅＯ２和Ｓｉ之间的晶格错配很小（约０．４％），ＣｅＯ２却不能在Ｓｉ上外延生长，而ＹＢＣＯ却能在取向凌乱的ＣｅＯ２上形成［００１］择优取向。ＣｅＯ２和Ｓｉ的界面处有一层极薄的过度层。ＹＢＣＯ和ＣｅＯ２界面存在Ｙ２ＢａＣｕＯ５（２１１相）。在ＹＢＣＯ薄膜中观察到有与１２３相混生的２４８相。     

电泳沉积法制备YBaCuO厚膜工艺的研究

在极间距为 2 .5 cm的电泳容器中 ,以丙酮为分散介质 ,沉积速度随着粉末浓度和碘加入量的增加先增加后减小 ,最佳参数值 YBa Cu O粉末浓度 3g/ l,碘 0 .3/ l。在本实验设备条件下 ,外加直流电压应为 110 V。在 930℃下恒温 4小时就能达到固化效果 ,没有裂纹出现。固化膜对基带的附着力用划格法测量 ,按 ASTM( American Standards of Testing Mate-rial)标准可达 1级。     

Enhancement of pinning and the peak effect in Y1–xFexBa2Cu3Oy high-temperature superconductors

Complex structural and magnetic studies of polycrystalline samples of the Y_{1 – x}Fe_xBa₂Cu₃O_y high-T_c superconductor (x = 0, 0.02, 0.05) have been carried out in order to determine the effect of weak doping with a magnetic 3d ion on structural changes and the critical current density J_c. An increase in the Fe content results in a significant change in J_c and its field dependence. The dependences J_c(H) become nonmonotonic and demonstrate a pronounced peak (peak effect); as a result, the J_c increases strongly in wide temperature and magnetic field regions. The analysis of the field dependences of the pinning force reveals a scaling behavior. The parameters of the scaling function correspond to the point magnetic defects under strong effects of a thermally activated flux flow. Thus, the weak Fe doping (several molar percent) is a promising way to significant improvement of transport properties of high-T_c superconducting materials based on 123-type compounds.     

Cracking and oxygenation of YBaCuO bulk superconductors: application to c-axis elements for current limitation

A process to elaborate crack free, oxygenated c-axis samples in YBa₂Cu₃O_x bulk superconductors is reported. This includes texturing of crack free pellets and development of an adequate oxygen annealing treatment to avoid cracking during oxygen uptake. For current limitation in c-direction such a process is needed as c-axis elements are particularly susceptible to ab-plane cracking during oxygenation. Mechanical properties have been compared for different annealing treatments by flexural strength measurements. With the load applied in ab-direction the mean flexural strength is 58 MPa in as-textured c-axis bars and 48 MPa in c-axis bars which were oxygenated using a customized annealing treatment. The conventional oxygen annealing treatments lead to macroscopic oxygenation cracks which reduced flexural strength to 10–20 MPa. Bars cut in ab-direction do not show significant variation in flexural strength (load applied in c-direction) as a function of the annealing condition with an average value of 145 MPa.     

Crack reduction in a large bulk Y–Ba–Cu–O superconductor through liquid binder addition

We have studied the effects of the incorporation of polyvinyl acetate (PVA) aqueous solution on the formability of the precursor Y–Ba–Cu–O samples with the aim of improving the mechanical properties of large bulk RE–Ba–Cu–O superconductors that are susceptible to cracking. We found that the green compacts of YBa₂Cu₃O_y and Y₂BaCuO₅ powders added with PVA liquid binder exhibited good mechanical properties and could be mechanically machined without defects. We could successfully drill 17 holes of 1 mm diameter into the green compact. The drilled samples were subjected to melt-processing and oxygen annealing, and further characterized with microstructural observations and magnetization measurements. The results showed that liquid binder addition was very effective in reducing cracks for large melt-processed Y–Ba–Cu–O superconductors.     

Damage in Y-Ba-Cu-O films produced by4He ions

The question of destructibility of an ion beam technique applied to the analysis of high temperature superconductors is discussed, namely the influence of the often used analyzing⁴He ion beam on a monocrystalline YBa₂Cu₃O₇ film. The rate of irradiation defect production is measured for 1 and 3.07 MeV⁴He⁺ irradiation and compared with a Monte Carlo simulation. It is shown that the usual depth profiling by⁴He ion beams does not change the measured element profiles, but is destructive from the view point of the superconducting properties of a sample, due to the great number of defects produced. Using a large solid angle detector one can minimize the analyzing dose to avoid the destruction of superconducting properties.     

An experimental study of Josephson effect in bulk YBaCUO

We have observed Josephson effect in bulk YBaCuO. The size of bulk is 7.5×2.2×0.3 mm and the microwave frequency is 9.82 GHz in our experiment. Several microwave induced steps can easily be observed. When an external magnetic field is applied to the bulk, the critical supercurrent at zero voltage is suppressed significantly. It has been demonstrated that YBaCuO bulk can be seen as a network of Josephson junctions. An experimental study of Josephson effect in bulk YBaCuO at millimeter wave frquency is in progress.     

车载高温超导磁悬浮系统的设计

介绍车载高温超导磁悬浮系统的设计问题。为了完成系统的设计 ,首先进行了单块和多块YBCO高温超导体块材的悬浮力的研究 ,同时考虑了 YBCO高温超导体块材的选取问题。设计的目标是稳定悬浮 350 kg,采用 8个车载液氮低温容器 ,这种容器是底壁仅 3mm厚的长方体形的。     

Superconducting mechanism of YBaCuO superconductors

Electromagnetic properties of YBaCuO superconductor were measured on applying an external magnetic field to study non-volatile magnetic effect. The voltage increases with increase in applied magnetic flux, but it becomes constant at about 10⁻² T. The appearance of the voltage is ascribed to the trapping of magnetic flux. By changing the density of external magnetic flux, changes in inductance of a coil in which a superconducting bar inserted were also measured. The results showed that the filament model was valid to explain the mechanism of the occurrence of a voltage in superconducting sample. It was concluded that the electromagnetic properties arose from the interaction between the trapped magnetic flux and weak link of the filament formed in the superconducting bulk.     

Oscillation of Y2BaCuO5 particle concentration in the melt-grown YBaCuO bulk superconductors

The oscillation of Y₂BaCuO₅ (2 1 1) particle concentration in form of bands parallel to the growth front was observed in top-seeded melt-grown (TSMG) single-grain YBa₂Cu₃O₇/Y₂BaCuO₅ bulk superconductors. The formations of these bands have been associated with temperature fluctuations at the growth front, which induce the fluctuation of the growth rate of the YBa₂Cu₃O₇ (123) crystal and consequently also the fluctuation of the amount of trapped 211 particles. We have shown that the oscillation of 211-particle concentration does not occur when the growth front is horizontal and the crystal solidifies from below upwards. In the a-growth sector (a-GS) the oscillation was observed only in the nests with very small 211 particles.