喷雾冷冻干燥制备复合氧化物超细粉的研究

喷雾冷冻干燥(FD 法)制备的超细粉对于功能无机材料的合成具有重要意义。本文以制备陶瓷超导复合氧化物 BaPb_(1-x)Bi_xO_(?)超细粉为例,讨论了各种不同工艺条件对 FD 法制备过程的影响,所制备的超细粉在500℃时就形成单相复合氧化物,粒径<500(?),比表面可达55m~2/g。用同样条件制备的 YBa_2Cu_3O_(7-δ)复合氧化物陶瓷超导材料,具有 T_c(ρ=0)=90.6K 的高温超导电性。     

二硼化镁多带超导电性研究进展

在金属材料中,多带以及多费米面是个普遍特征。当材料进入超导态以后,一般在费米面上要打开超导能隙,因此多能带会导致多能隙的出现。在很多超导材料中,由于极强的带间散射,多带效应会被大大削弱。但是,在一些具有准二维特性的超导材料中,由于不同能带上面电子运动波函数的正交性,多带和多能隙效应就会表现出来。     

Ba-Y-Cu-O系陶瓷厚膜材料

本文报导采用典型的微电子学厚膜工艺即丝网印刷法,制备Ba-Y-Cu-O系的陶瓷厚膜超导材料,研究了不同热处理温度及时间对厚膜材料性能的影响。实验证明,陶瓷超导材料的厚膜工艺设备简单,适合于大规模生产。用这种方法制备的厚膜超导材料已具有较高的临界超导转变温度:T_c(mid)=80K,T_c(ρ=0)=72.1K,而且工艺稳定,重复性好。     

Bi系高T_c超导材料的类多型结构及其超导电性

用 X 射线旋进照相、电子衍射和 TEM 方法观察到 Bi 系超导材料中某些类多型结构特征,显示了一维无序结构及衍射的弧化效应、带状结构均与它存在交生现象有关;用类多型结构特征阐明 BiO 层结构中 Bi~(+++)的位移将导致 BiO 层中多余的氧正是其超导电性改变的一种标志。     

Bi-Sr-Ca-Cu-O系高温超导体结构的电子显微镜研究

本文用透射电子显微术和 EDAX 对 Bi 系超导体的成份和晶体结构进行了分析研究。结果表明该 Bi 系超导体中存在 a=b=5.41(?)c=24.21(?)四方结构超导相,为改进成份、热处理工艺提供了依据。     

稀土纳米氧化物的应用及生产技术

稀土元素本身具有丰富的电子结构,表现出许多光、电、磁的特性。稀土纳米化后,表现出许多特性,如小尺寸效应、高比表面效应、量子效应、极强的光电磁声性质、超导性、高化学活性等,能大大提高材料的性能和功能,又开发出许多新功能材料。在光学材料、发光材料、晶体材料、磁性材料、电池材料、电子陶瓷、工程陶瓷、催化剂等高新科技领域,将发挥重要的作用。     

Doping of Bi-Sr-Ca-Cu-O superconductors with Pb,Sn and Ag

Basic and substituted superconductors in the homologous series Bi₂Sr₂Ca _n−1Cu _n O_2n+4+y , Bi_2−x/2Sr_2−x/2L _x Ca _n−1Cu _n O_2n+4+y and Bi₂Sr_2−x L _x Ca _n−1Cu _n O_2n+4+y (L=Sn, Pb or Ag,x=0−0.4,n=2, 3 or 4) have been synthesized. All the prepared ceramic samples show superconducting behaviour with zero resistance atT _c=70 to 85 K. The compounds withn=3 or 4 showed onset temperature around 115K indicating involvement of a disproportionate solid-state reaction and formation of a two-phase system. The phase involving tin or lead oxides showed similar superconducting properties. Final rapid quenching of samples contributed to preservation of the high temperature equilibria with higher solubility of tin oxide in the quaternary system Bi-Sr-Ca-Cu-O. Silver was not soluble but precipitated in a colloidal form at interfaces between the crystalline grains.     

AC susceptibility studies on Bi-Sr-Ca-Cu-O system

We report the low field a.c. susceptibility data χ′(T, H _rms), χ″(T, H _rms) for the newly prepared superconducting system Bi _x Sr₄Ca₂Cu₄O _y (x=0·5, 1·0 and 1·5) containing Bi at concentrations lower than that in the conventional Bi-based system. Our experimental results are discussed in the light of existing theories.     

Role of dopants in Bi-Sr-Ca-Cu-O system

The role of Al and Ag dopants in the nominal composition, 4336 of Bi-Sr-Ca-Cu oxide has been studied, using a new chemical phase analysis method known as differential dissolution besides XRD and resistivity and magnetic susceptibility measurements. Our investigation reveals that (a) it is relatively easy to realize high-T _c phase (2223) in both Al- and Ag-doped samples with the same nominal composition and heat treatment history (b) both samples consist of superconducting phases with more or less the same basic composition and equal amounts, (c) 2112 phase may be a superconductor and (d) superconducting properties with Al and Ag dopants are different.     

Molecular beam epitaxial growth of high-Tc Bi-Sr-Ca-Cu-O Films

Molecular beam epitaxy (MBE) has been used to grow high-temperature superconducting Bi-Sr-Ca-Cu-O films with adequate control over growth of number of unit layers. Oxide sources of Sr and Ca used for electron beam evaporation have been found to be useful for epitaxial growth of films. Deposited films show superconducting properties comparable to films deposited by using pure metals with a complicatedin situ oxidation technique. Optimum deposition and annealing conditions have been obtained to growc-axis-oriented 2212 phase BSCCO film.In situ reflection high-energy electron diffraction (RHEED) study of the films has revealed the growth of epitaxial films with atomically smooth surfaces.     

超导电力应用的进展

综述国外低温超导材料和高温超导材料及其在同步发电机、电力变压器、电力电缆、电力贮能装置、限流器等电力设备中应用的进展情况。     

Study of Josephson effects in microbridges of Bi-Sr-Ca-Cu-O films made by spray pyrolysis

Superconducting Bi-Sr-Ca-Cu-O (2212) films were prepared by spraying stoichiometric aqueous solutions of nitrates of bismuth, strontium, calcium and copper on heated MgO (100) substrates and subsequent annealing in air. TheR-T curves of the films show metallic behaviour above the superconducting transition temperature.T _c (R=0) is observed between 80 and 85 K. Annealing temperature has a profound effect onT _c (R=0) and on the orientation of the film. Annealing in air in near-melting region yields highly oriented films withc-axis perpendicular to the substrate. These films show a sharp superconducting transition with zero resistance at 85 K. Microbridges of the dimensions of 50 μm × 50 μm have been patterned photolithographically followed with chemical etching. The 1 V characteristics of the microbridges show Josephson effects due to the presence of grain boundary weaklinks. The temperature dependence of the critical current for these microbridges suggest formation of superconductor-normal-superconductor type weaklinks.     

Study of galvanomagnetic effects in Bi-Sr-Ca-Cu-O films

Galvanomagnetic effect has been studied at 77 K on Bi-Sr-Ca-Cu-O films as a function of d.c. bias current. These films were prepared by spray pyrolysis and screen-printing techniques, withT _c (R=0) 80 K and 100 K respectively. Magnetic field dependence ofI _c of sprayed-film showed very small hysteresis whereas screen-printed film showed greater hysteresis. Application of small magnetic field on these films destroyed the zero-resistance state and a finite resistance was developed. The slope of the resistance vs magnetic field curveΔR/ΔH depended on the current flowing through the sample. To increaseΔR/ΔH, meander-shape pattern was prepared on the sprayed film. In generalΔR/ΔH increased by a factor of 10³ after sample patterning. The possibility of using these films as a sensitive magnetic field sensor is discussed.     

Superconducting Bi-Sr-Ca-Cu-O films formed diffusion of metallic bismuth on Sr2Ca2Cu4O y substrates

Superconducting Bi-Sr-Ca-Cu-O films have been prepared on Sr₂Ca₂Cu₄O _y substrates by thermal evaporation of metallic Bi layer and heat-treatment at 830°C for a few minutes in air. The zero resistance temperature of Bi₂Sr₂Ca₁Cu₂O _y film of 1–μm in thickness is about 70 K. The surface diffusion process of Bi on the granular structure of Sr₂Ca₂Cu₄O _y was observed by scanning electron microscope and thermogravimetry analysis. The stripe pattern of superconducting film, typically 2μm thick and 0·3 mm wide, is formed by using a mask.     

The Effect of Electron Beam Irradiation on Electron Diffraction Patterns of Bi-Sr-Ca-Cu-O High- Tc Superconductors

The effect of electron irradiation having the energy of 75, 100, and 200 keV on structural modifications of Bi-2212 superconducting samples has been studied. For the last energy, the irradiation time from zero to 150 min was used. At a constant energy of the electrons, the observed phenomena consist in the disappearance of the incommensurate unidimensional modulation, in the decreasing of spots' intensity and their elongation along the equivalent crystallographic axis a, and even spot splitting with the occurrence of double extra spots, with the increase of the irradiation time.After electron irradiation with energy of 75 and 100 keV, the structural modifications lead to some spot patterns consisting of some planar lattices (in some cases a pseudo-tetragonal one) that are twisted on each other at different angles (8°, 13.6°, 19°, etc.) around the axis of the incident electron beam. For the irradiation at increased doses of thin microcrystals having reduced lateral dimensions, the electron diffraction spots were arranged in discrete or partial continuous Debye rings or continuous concentric Debye rings characteristic for the polycrystalline state.After electron irradiation with energy of 200 keV, the effects of electron irradiation on Bi-2212 samples depend strongly on irradiation fluence rate and time and consisted in the following: disordering defects in the diffraction patterns (disappearance of some spots, spot intensity modification, streaks occurrence, spot elongation); alteration and disappearance of incommensurate structural modification; conversion of single crystal particle areas into polycrystalline material; and quasi-amorphization.A simple approach based on the evaluation of the displacement yield of in-plane oxygen atoms vs. irradiation time for the different incident energy and electron fluence rates could explain the general trend of irradiation damage in HTS materials.