Superconductors electron microscopy

Chemical Characterization of Oxide Superconductors by Analytical Electron Microscopy... 

Phase distributions in electron beams can be measured to within 2n /100, which has opened the way to measuring microscopic objects and fields with ultra-high precision. These developments allow the direct observation of individual vortices in a superconductor. Electron phase microscopy can be used to clarify the fundamental and practical applications of superconductivity, especially in the field of high superconductors. 

This chapter is intended as a convenience to those readers actively engaged in the investigation of high Tc superconductors by transmission electron microscopy (TEM). A future possible application of the newly discovered high Tc superconductors is their use in electronic devices. The electrical properties of a device strongly depend on their microstructure, since grain boundaries in these materials can behave as weak links as reported by Dimos et al. [4.1], Therefore, TEM is an important tool in the study of the relationship between the microstructure and the electrical properties. 

It is clear that electron microscopy is not the most favourable technique for structure determination of new (superconducting) phases X-ray diffraction and particularly neutron diffraction do a far better job in the ab initio structure determination. Electron microscopy and electron diffraction are extremely powerful however to determine the local structure i.e. to detect deviations from the average structure, as determined by X-rays or neutrons. In this way several new phases have been first identified by electron microscopy some of them have been later made into bulk superconductors. In other cases the identification of isolated defects in an existing material have inspired chemists to produce new superconducting materials this was, for example, the case for the occurrence of double HgO layers in a one-layer Hg-1223 superconductor. 

In the first part of this contribution we will focus on the well known YBa2Cu307 superconductor this material allows a large number of substitutions without drastically altering its structural aspects, but with sometimes completely different physical properties. In the second part, we will concentrate on the more recent Hg-based superconductors and illustrate the extreme importance of the different electron microscopy techniques in the development of new superconducting compounds. 

Electron microscopy techniques are essential tools needed for the investigation of the local structure and composition of grain boundaries in high-temperature superconductors. While we have emphasized structural aspects here, analytical characterizations (see Chapters 8 and 11) are extremely important and must be part of establishing direct connections to transport properties. 

The examples also indicate that device production on the basis of cuprate superconductors demands an essentially atomically resolving technique for structure investigation and for proper inspection and control of the results of the individual fabrication processes. This can be provided by modem transmission electron microscopy combined with cross-sectional specimen preparation. 

High-Ti Superconductors. High-resolution electron microscopy and electron diffraction have recently been applied extensively in structural studies of high-Tt, oxide superconductors. In particular, YBa2Cu307, 5 and the related 1-2-3... 

Vortices in superconductors can be observed quantitatively by interference microscopy [2.18, 2.19] and Lorentz microscopy [2.20] with our 350 kV holography electron microscope [2.21]. In the experiments we conducted, a superconductive thin film was tilted with respect to both the electron beam and the magnetic field. 

This is is a clear and up-to-date account of the application of electron-based microscopies to the study of high superconductors. 

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