Study on High Temperature Superconductors -Properties and Formation Techniques of Bulk and Thin Film-

高温超导体中电耗散的Kosterlitz-Thouless理论预言，电流-电压特性在相变温度(T_C)以上而不是在T_c以下。我们给出了一个普适标度曲线的表达式，它很好地拟合了在零磁场下外延YBa2Cu3O7薄膜的数据。在含有相当比例的绝缘211相的YBCO复合烧结体样品中观察到了异常的低磁场行为。这些复合材料的电学特性在低于平均场超导转变温度T_c的温度T_p处发生相变。当外加磁场在低于Tc的温度下从零开始增加时，电耗散在大约5Gauss时表现出最小值，然后以超导陶瓷中常见的方式增加。在低于相移…的温度下研究了YBa2Cu3O7：Y2BaCuO5复合烧结体的电流电压(I-V)特性，表明存在二级相变。对于每一种烧结矿成分，在广泛的磁场范围内都有相似的特性家族。V和I之间的关系可以看作是V=f(i，xi(B，T))的形式，其中简单参数xi包含所有的场和温度依赖关系。研究了B，T平面上Xi(B，T)为常数的点的轨迹，确定了一个低场和一个高场区域。不同组成的样品表现出一系列的I-V特性，它们以一种简单的方式相互缩放，因此我们假设V=f(i，xi(B，T，p))，其中p是稀释分数。在低于转变温度时采集的数据，其指数与磁场和成分无关。研究了高温超导晶须在BSCCO(2212)体系中的生长条件。晶须的生长速度强烈地依赖于玻璃熔体中的铋含量和热处理温度。在硝酸溶剂中加入过氧化氢可以抑制粉末中杂质的形成。获得了较高丰度(90%)的低T_c相。较少

The Kosterlitz-Thouless theory for the electrical dissipation in the high temperature superconductors predicts scaling of the current voltage characteristics above th phase transition temperature (Tc) but not below. We give an expression for universal scaling curve which provides an excellent fit to the data for epitaxial YBa_2Cu_3O_7 thin films taken in zero applied magnetic field.Unusual low magnetic field behaviours have been observed in samples of the YBCO composite sinters which contain an appreciable proportion of the insulating 211 phase. These composite materials exhibit a phase-transition in their electrical characteristics at a temperature Tp which is less than Tc the mean field superconducting transition temperature. As an applied magnetic field is increased from zero at temperatures below Tc, the electrical dissipation exhibits a minimum at about 5 Gauss, before it increases in the manner usually found in the superconducting ceramics. At temperatures below the phase transit … More ion temperature Tp, a further sharp minimum in the dissipation develops at zero field.We have investigated features in the current voltage (I-V) characteristics of YBa_2Cu_3O_7:Y_2BaCuO_5 composite sinters which indicate the occurrence of a second-order phase transition. For each sinter composition similar families of characteristics are found for a wide range of magnetic fields. the relation between V and I is seen to be of the form V=f(I, xi (B,T)) where simple parameter xi contains all of the field and temperature dependence. The locus of points in the B,T plane for which xi (B,T) is a constant have been examined, and a low field and a high field regime have been identified. Samples of different composition show families of I-V characteristics which scale onto one another in a simple way, hence we are let to suppose the V = f(I, xi (B,T,p)) where p is the dilution fraction. Data taken at temperatures below transition, with exponents which are independent of magnetic field and composition. Above the transition, however, the behavior is more complex.Growth condition of the high temperature superconducting whiskers has been investigated in the BSCCO(2212) system. Growth rate of the whisker depends strongly on Bi content in the melt-quenched glass substance and an annealing temperature.Superconducting fine powder has been prepared by spray pyrolysis. Hydrogen peroxide which is added in the nitrid acid solvent is found to suppress the impurity formation in the powder. A higher abundance (90%) of Low-Tc phase was achieved. Less