FLUX CREEP, FLUX PINNING AND CRITICAL CURRENT DENSITY OF Y-, Gd-, AND Tl-BASED SUPERCONDUCTIVE THIN FILMS

Magnetic hysteresis loops have been measured for YBa₂Cu₃O_6+x, GdBa₂Cu₃O_6+x and Tl₂Ba₂Ca₂Cu₃O_10-y films at different temperatures with a vibrating sample magnetometer. Based on Bean model, magnetic critical current density J_cm has been derived approximately. The field and temperature dependence of J_cm for all samples can be written as: J_cm= J_c0(T)×f(B,T), Where f(B,T) = 1 - Aln(B/B₀(T)), which is similar to the transport critical density strongly affected by flux creep: J_ct = J_c0(B,t)(1 - (k_BT/U₀)ln(BΩd/E_c)). The extraordinary similarity suggests that J_cm is determined not only by flux pinning but also by flux creep. In the first formula, f(B,T) may be correlated with the effect of flux creep on J_cm, and J_c0(T) is determined by flux pinning. J_c0(T) is independent of magnetic field and is proportional to (T_c - T). Similar results have also been found for other samples. It may be the common characteristic of high-T_c superconductors. Magnetic relaxation of YBa₂Cu₃O_6+x and GdBa₂Cu₃O_6+x films has been measured at LN₂ temperature. Using the equation of Hagen et al., effective activation energy U₀ has been deduced, which is about 0.3eV, one order bigger than the value obtained by A = k_BT/U₀. U₀ is almost independent of the field in the field range selected.     

INVESTIGATION OF THE EFFECT OF SLOW NEUTRON IRRADIATION ON HALOGEN-DOPED HIGH-Tc SUPERCONDUCTORS AND ITS MECHANISM

Irradiation effect of low-fluence (-10⁸ n/cm² ) slow neutrons on halogen-doped superconductors is presented in this paper. And the mechanism of the effect is also described from the viewpoint of nuclear physics for both fast and slow neutrons on high-temperature superconductors (HTSC). It is shown ex-perimentally and theoretically that slow neutrons of low fluence has a similar irradiation effect to that of fast neutron beams with an energy E_n>0.1 MeV and fluence 10¹⁶-10¹⁸ n/cm²-However,quite differ-ent mechanisms are involved in them: Fast neutrons transfer their energies through elastic scattering in HTSC, whereas slow neutrons give off their energies during the slow neutron capture (n,γ) reaction.     

区域熔炼法制备YBa_2Cu_3O_(6 x)的非对数磁弛豫

考虑到有效钉扎势U(J)与临界电流密度的非线性关系,将U(J)展开为三级泰勒级数,最后推导出一个普遍适用于描述高温超导体磁弛豫的等温衰减方程,并用这一方程研究了具有高J_c,强钉扎的区域熔炼法制备YBa_2Cu_3O_(6 x)的磁弛豫,而且对目前被普遍采用的几个钉扎模型进行了讨论.     

Bi_（2．2）Sr_（1．8）Ca_（1．05）Cu（2．15－x）NaxO_

本文介绍了用熔融法制备Ｂｉ２．２Ｓｒ１．８Ｃａ１．０５Ｃｕ２．１５－ｘＮａｘＯ８＋ｙ（ｘ＝０，０．４～０．８）样品，发现诸样品零电阻温度都在９０Ｋ左右，其小ｘ＝０．７．Ｔｃ０达到９２，５Ｋ．在８１Ｋ较高温区，该类样品仍然表现出良好的超导电性，其临界电流密度还达到１０３Ａ／ｃｍ２量级．     

STUDY OF HALOGEN DOPING IN POLYCRYSTALLINE YBa2Cu3O7-δ

This paper presents systematically the doping effects of halogens in YBa₂Cu₃O_7-δ polycrystalline samples, with a series of concentrations of fluorine, chlorine, bromine or iodine. All samples were prepared by chemical method of citrate pyrolysis, which makes the halogen concentration in the samples more uniform. Samples doped with F have T_c as high as 94.5K, Cl, Br and I dopings also raise T_c to a certain extent. In addition, the influence of halogen doping on critical current density, morphology, constitution and so forth is discussed.     

熔融织构YBa_2Cu_3O_x中碰通钉扎的各向异性及211相对钉力的影响

通过测量不同温度的磁滞回线和不同温度、不同磁场下的磁弛豫，对熔融织构ＹＢａ２ＣＵ３Ｏｘ样品的钉扎各向异性及２１１含量对钉扎力的影响进行了研究（外加磁场分别平行和垂直于Ｃ轴），发现熔融织构样品的钉扎力具有强各向异性，这是由钉扎中心形状的各向异性导致的．临界电流随２１１含量的增加反而降低，表明在这些样品中２１１相颗粒及其周围的缺陷对磁通钉扎起负作用．仅当外场平行于ｃ轴时，才能观察到鱼尾效应，表明这些样品中至少存在两种钉扎中心．     

添加Ag_2O对YBa_2Cu_3O_(7-δ)体材料显微结构与超导电性的影响 (Ⅰ)制备工艺与超导电性

本文比较系统地研究了添加 Ag_2O 对 YBa_2Cu_3O_(7-δ)体材料超导电性的影响.结果表明:在制备过程中添加适量 Ag_2O 可以显著增强 YBa_2Cu_3O_(7-δ)晶粒间的耦合,并改善 YBa_2Cu_3·O_(7-δ)体材料的超导性能.对于在930—1000℃范围内烧成,名义组成为(YBa_2Cu_3O_(7-δ))_(1-x)Ag_x(x=0.2～0.55)的复合超导试样来说,烧成温度对试样的超导性能起关键的作用,而 Ag_2O的添加量(x)和预烧温度的作用相对要小得多,当烧成温度高于970℃时 Ag_2O 的添加效果极为明显.例如1000℃烧成的 x=0.3的试样在77K 下的磁化临界电流密度 J_c 比相同工艺条件制备的未加 Ag_2O 试样提高五倍多.     

~3He恒温器减压池抽气管路的解析特征

本文提出设计~3He恒温器减压池抽气管路的解析方法,并且发现管路具有截止直径等物理特征。以及论证了0.2K是~3He恒温器的极限温度。     

关于Fe~(3+)/CNS~-平衡

FeCl_3与NH_4CNS的溶液反应是一个常用的验证浓度对化学平衡影响的反应。对于这个反应,Fowles给出如下化学方程式: FeCl_3+3NH_4CNS=Fe(CNS)_3+3NH_4Cl 溶液的颜色可以作为平衡位置的量度。混和等体积的10~(-3)M FeCl_3与NH_4CNS溶液,分为五份。第一份作为参考基础。第二、三两份内分别加入少量固体FeCl_3和NH_4CNS,震荡后颜色都加深,这容易解释。第四份内加进一满匙固体NH_4Cl搅拌,溶液颜色显著减弱。这现象通常用“增加生成物,促使平衡向减少生成物方向移动”解释。一般学     

理想Ⅱ类超导体在相变点的体积效应

本文以超导热力的唯象理论为基础,应用Abrikosov的高场磁通点阵周期场结果,对理想Ⅱ类超导体在Hc2相变点的体积效应进行讨论,经过典型的热力学唯象理论讨论。揭示了理想Ⅱ类超导体在Hc2相变点的相变体积效应的二级相变特征。