High temperature superconductors electronic structure

Non-stoichiometric compounds are of potential use to industry because their electronic, optical, magnetic, and mechanical properties can be modified by changing the proportions of the atomic constituents. This is widely exploited and researched by the electronics and other industries. Currently, the best known example of non-stoichiometry is probably that of oxygen vacancies in the high temperature superconductors such as YBCO (1-2-3) (YBa2Cu307 J. The structure of these is discussed in detail in Chapter 10. 

SOME STRUCTURAL-ELECTRONIC ASPECTS OF HIGH TEMPERATURE SUPERCONDUCTORS... 

Some Structural-Electronic Aspects of High Temperature Superconductors 207... 

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. 

An abundance of electron spectroscopic data has been reported for the high temperature superconductors. These include the valence band (VB), Cu 2p, and O Is photoelectron (UPS and XPS) data, the LuW and LasMiiV Auger (AES) data, the O K and Cu Lu x-ray emission (XES) data, and the O K and Cu Lta electron energy loss (EELS) and x-ray absorption near edge structure (XANES) data. These data reflect 1-, 2-, and 3-vaIence hole and core-hole density of states (DOS) and thertfore can provide direct measures of the Hubbard U and transfer parameters. Unfortunately, this data has proved to be difficult to interpret not surprisingly since the data for CuO is not even well understood. 

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