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Handbook of High Temperature Superconductor Electronics Part 2

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Tham khảo tài liệu 'handbook of high temperature superconductor electronics part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 1 Introduction to High-Temperature Superconductors Neeraj Khare National Physical Laboratory New Delhi India 1.1 INTRODUCTION The discovery of superconductivity in copper oxide perovskite 1 has opened a new era of research in superconducting materials. This class of materials not only show high-temperature superconductivity but also show properties that are different from classical superconductors. This offers a great challenge to understanding the basic phenomenon that causes superconductivity in these materials and to developing the appropriate preparation methods so that these can be exploited for a wide range of applications. During the last one and half decades after the discovery of high-Tc materials several high-Tc superconductors have been discovered which show superconductivity at temperatures higher than liquid-nitrogen temperature 77 K . There has also been great progress in understanding the properties of these materials developing different methods of preparation and realizing superconducting devices which use these superconductors. This chapter will give a brief description of the historical developments in raising the transition temperature Tc of the superconductors preparation and structure of the material. Different properties of the high- Tc materials such as critical magnetic field penetration depth coherence length critical current density weak link and so forth are also discussed. Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. 1.2 RAISING THE TRANSITION TEMPERATURE Superconductivity is the phenomenon in which a material loses its resistance on cooling below the transition temperature Tc . Superconductivity was first discovered in mercury by Onnes 2 in 1911. The temperature at which mercury becomes superconducting was found to be close to the boiling point of liquid helium 4.2 K . Subsequently many metals alloys and intermetallic compounds were found to exhibit superconductivity. The highest Tc known was limited to 23.2 K 3 in the .