I. INTRODUCTIONT<sub>c</sub> of the oxide Bi-Sr-Cu-O system without lanthanide is 20 K. Doping Ca in proper amount will make it show 85 K superconductivity accompanied by 110 K superconducting trace. Y. Ko...I. INTRODUCTIONT<sub>c</sub> of the oxide Bi-Sr-Cu-O system without lanthanide is 20 K. Doping Ca in proper amount will make it show 85 K superconductivity accompanied by 110 K superconducting trace. Y. Koike et al. have obtained Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>y</sub> single crystal and measured its fundamental superconductivity parameters. Endo et al. have prepared single-phase 110 K Bi-展开更多
Based on environmental considerations, global economic pressures, enacted by legislations in several countries, have warranted the elimination of lead from solders used in electronic applications. Sn3.5Ag, SnAgCu, and...Based on environmental considerations, global economic pressures, enacted by legislations in several countries, have warranted the elimination of lead from solders used in electronic applications. Sn3.5Ag, SnAgCu, and Sn0.7Cu have emerged among various lead-free candidates as the most promising solder alloys to be utilized in microelectronic industries. However, with the vast development and miniaturization of modern electronic packaging, new requirements such as superior service capabilities have been posed on lead-free solders. In order to improve the comprehensive property of the solder alloys, two possible approaches were adopted in the current research and new materials developed were patented. One approach was involved with the addition of alloying elements to make new ternary or quaternary solder alloys. Proper addition of rare earth element such as La and Ce have rendered solder alloys with improved mechanical properties, especially creep rupture lives of their joints. Another approach, the composite approach, was developed mainly to improve the service temperature capability of the solder alloys. Composite solders fabricated by mechanically incorporating various reinforcement particles to the solder paste have again exhibited enhanced properties without altering the existing processing characteristics. The recent progress and research efforts carried out on lead-free solder materials in Beijing University of Technology were reported. The effects of rare earth addition on the microstructure, processing properties, and mechanical properties were presented. The behaviors of various Sn-3.5Ag based composite solders were also explicated in terms of the roles of reinforcement particles on intermetallic growth, steady-state creep rate, the onset of tertiary creep, as well as the overall creep deformation in the solder joints. Thermomechanical fatigue (TMF) behavior of the solder alloys and composite solders were investigated with different parameters such as ramp rate, dwell time, etc. The damage accumulation features and residual mechanical properties of the thermomechanically-fatigued composite solder joints were compared with non-composite solder joints. To match the lead-free alloys, various types of water soluble no-clean soldering flux have also been developed and their properties were presented.展开更多
In the magnetization curve of Tl_4Ba_3Ca_3Cu_4O_y, bulk superconductor, there exists an anomaly of magnetization in the magnetic field lower than H_(Cl). The time dependence of DC magnetization in zero-field-cooled sa...In the magnetization curve of Tl_4Ba_3Ca_3Cu_4O_y, bulk superconductor, there exists an anomaly of magnetization in the magnetic field lower than H_(Cl). The time dependence of DC magnetization in zero-field-cooled sample has been investigated. The experimental result shows that there are giant flux creeps and flux jumps during the flux creep. The magnetization decay rate depends upon both the field and the temperature. The thermal activation of flux lines for U_0≈0.14 eV at 77.3 K is discussed.展开更多
本文对零场冷却充磁(ZFC)后放置于随时间变化的外磁场中的含中心夹杂长圆柱超导体模型磁弹性问题进行解析计算和数值计算分析.为了更加真实地反映模型的力学行为,首先将模型定义为磁性能各向异性材料,其次对模型的磁通分布状态分别考虑...本文对零场冷却充磁(ZFC)后放置于随时间变化的外磁场中的含中心夹杂长圆柱超导体模型磁弹性问题进行解析计算和数值计算分析.为了更加真实地反映模型的力学行为,首先将模型定义为磁性能各向异性材料,其次对模型的磁通分布状态分别考虑了外场黏性磁通流动效应和内场磁通蠕变效应.通过控制复合材料的弹性模量Er/E i r m、体积分数f等弹性系数以及影响磁通分布的黏性磁通流动速度v1、磁通蠕变作用系数K、蠕变发生几率n等参变量的取值,对模型的径向应力分布状态和磁致伸缩特性进行深入分析.将本文的解析计算结果与数值模拟结果进行了比较,结果反映两者绘制的参变量曲线分布规律几乎完全吻合,不同的是数值大小存在明显差异,其原因为数值模拟过程中假定超导体电导率满足强非线性E-J关系,并施加了脉冲形式的外磁场;而解析计算过程中采用了场相关的临界态模型,将感应电流假定为临界电流,所以导致计算结果数值存在一定差异.展开更多
Ⅰ. INTRODUCTION HTSC films are very important to the fundamental research and application of high T_c superconductors. The critical current density J_c is the key parameter for its application. However, the mechanism...Ⅰ. INTRODUCTION HTSC films are very important to the fundamental research and application of high T_c superconductors. The critical current density J_c is the key parameter for its application. However, the mechanism of the flux pinning that influences the critical current density is not clear. So the preparation of high quality films and the study of the characteristics of their critical current densities are very necessary for understanding the mechanism of flux pinning.展开更多
We show that the second magnetization peak(SMP),i.e.,an increase in the magnetization hysteresis loop width in type-11 superconductors,vanishes for samples smaller than a critical size,We argue that the SMP is not rel...We show that the second magnetization peak(SMP),i.e.,an increase in the magnetization hysteresis loop width in type-11 superconductors,vanishes for samples smaller than a critical size,We argue that the SMP is not related to the critical current enhancement but can be well explainde within a frameword of the thermomagenetic flux-jump in stability theory,where flux jumps reduce the absolute irreversible magnetization relative to the isothermal critical state value at low enough magnetic fields.The recovering of the isothermal critical sate with increasing field leads to the SMP.The low-field SMP takes place in both low-T.conventional and high*t.unconventional superconductors.Our results show that the rsstoration of the isothermal critical state is rsponsible for the SMP occurrence in both cases.展开更多
基金Project supported by the National Centre for Research and Development on Superconductivity and the Office for Research on Superconductivity, Academia Sinica.
文摘I. INTRODUCTIONT<sub>c</sub> of the oxide Bi-Sr-Cu-O system without lanthanide is 20 K. Doping Ca in proper amount will make it show 85 K superconductivity accompanied by 110 K superconducting trace. Y. Koike et al. have obtained Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>y</sub> single crystal and measured its fundamental superconductivity parameters. Endo et al. have prepared single-phase 110 K Bi-
基金This work was financially supported by the National863High-Tech.Project,Ministry of Science andTechnology,Ministry of Education,Beijing Science&Technology Commission(No.2004B03)and Beijing Educational Commission.
文摘Based on environmental considerations, global economic pressures, enacted by legislations in several countries, have warranted the elimination of lead from solders used in electronic applications. Sn3.5Ag, SnAgCu, and Sn0.7Cu have emerged among various lead-free candidates as the most promising solder alloys to be utilized in microelectronic industries. However, with the vast development and miniaturization of modern electronic packaging, new requirements such as superior service capabilities have been posed on lead-free solders. In order to improve the comprehensive property of the solder alloys, two possible approaches were adopted in the current research and new materials developed were patented. One approach was involved with the addition of alloying elements to make new ternary or quaternary solder alloys. Proper addition of rare earth element such as La and Ce have rendered solder alloys with improved mechanical properties, especially creep rupture lives of their joints. Another approach, the composite approach, was developed mainly to improve the service temperature capability of the solder alloys. Composite solders fabricated by mechanically incorporating various reinforcement particles to the solder paste have again exhibited enhanced properties without altering the existing processing characteristics. The recent progress and research efforts carried out on lead-free solder materials in Beijing University of Technology were reported. The effects of rare earth addition on the microstructure, processing properties, and mechanical properties were presented. The behaviors of various Sn-3.5Ag based composite solders were also explicated in terms of the roles of reinforcement particles on intermetallic growth, steady-state creep rate, the onset of tertiary creep, as well as the overall creep deformation in the solder joints. Thermomechanical fatigue (TMF) behavior of the solder alloys and composite solders were investigated with different parameters such as ramp rate, dwell time, etc. The damage accumulation features and residual mechanical properties of the thermomechanically-fatigued composite solder joints were compared with non-composite solder joints. To match the lead-free alloys, various types of water soluble no-clean soldering flux have also been developed and their properties were presented.
基金Project supported by the National Center for Research and Development of Superconductivity.
文摘In the magnetization curve of Tl_4Ba_3Ca_3Cu_4O_y, bulk superconductor, there exists an anomaly of magnetization in the magnetic field lower than H_(Cl). The time dependence of DC magnetization in zero-field-cooled sample has been investigated. The experimental result shows that there are giant flux creeps and flux jumps during the flux creep. The magnetization decay rate depends upon both the field and the temperature. The thermal activation of flux lines for U_0≈0.14 eV at 77.3 K is discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.51904138 and 51076061)the Natural Science Foundation of Gansu Province(Grant No.B061709).
文摘本文对零场冷却充磁(ZFC)后放置于随时间变化的外磁场中的含中心夹杂长圆柱超导体模型磁弹性问题进行解析计算和数值计算分析.为了更加真实地反映模型的力学行为,首先将模型定义为磁性能各向异性材料,其次对模型的磁通分布状态分别考虑了外场黏性磁通流动效应和内场磁通蠕变效应.通过控制复合材料的弹性模量Er/E i r m、体积分数f等弹性系数以及影响磁通分布的黏性磁通流动速度v1、磁通蠕变作用系数K、蠕变发生几率n等参变量的取值,对模型的径向应力分布状态和磁致伸缩特性进行深入分析.将本文的解析计算结果与数值模拟结果进行了比较,结果反映两者绘制的参变量曲线分布规律几乎完全吻合,不同的是数值大小存在明显差异,其原因为数值模拟过程中假定超导体电导率满足强非线性E-J关系,并施加了脉冲形式的外磁场;而解析计算过程中采用了场相关的临界态模型,将感应电流假定为临界电流,所以导致计算结果数值存在一定差异.
基金Project supported by the National Center for R & D on Superconductivity of China and by the Third World Academy of Science under contract of Research Grant No. Mp90-036
文摘Ⅰ. INTRODUCTION HTSC films are very important to the fundamental research and application of high T_c superconductors. The critical current density J_c is the key parameter for its application. However, the mechanism of the flux pinning that influences the critical current density is not clear. So the preparation of high quality films and the study of the characteristics of their critical current densities are very necessary for understanding the mechanism of flux pinning.
文摘We show that the second magnetization peak(SMP),i.e.,an increase in the magnetization hysteresis loop width in type-11 superconductors,vanishes for samples smaller than a critical size,We argue that the SMP is not related to the critical current enhancement but can be well explainde within a frameword of the thermomagenetic flux-jump in stability theory,where flux jumps reduce the absolute irreversible magnetization relative to the isothermal critical state value at low enough magnetic fields.The recovering of the isothermal critical sate with increasing field leads to the SMP.The low-field SMP takes place in both low-T.conventional and high*t.unconventional superconductors.Our results show that the rsstoration of the isothermal critical state is rsponsible for the SMP occurrence in both cases.
