Electronic conductivity superconductors

The two-phase nature of all ceramic samples of the electron-doped superconductors probably accounts for their less desirable properties, including low Meissner fractions in many samples, low and nonmetallic conductivity in the normal state, and... 

Hiickel MO theory with the AO overlap integral Sab included generates an instability for the (homonuclear) three-electron bond when Sab exceeds 0.3 [33], and heteronuclear three-electron bonds are also overlap destabilized under compression. The following speculation, which utilizes the overlap instability of three-electron bonds, may have relevance for the provision of a VB formulation for aspects of the mechanism for electron conduction in the high Tc superconductor YBa2Cu3C>7. 

Funahashi M, Shimura H, Yoshio M, Kato T (2008) Functional Liquid-Crystalline Polymers for Ionic and Electronic Conduction. 128 151-179 Furrer A (2005) Neutron Scattering Investigations of Charge Inhomogeneities and the Pseudogap State in High-Temperature Superconductors 114 171-204... 

Lao.8Sr0.2Y02.9 was more active than the LaY03 perovskite (table 8). The partial substitution of La by Sr increased the concentration of the oxygen vacancies and the valency of Y, without making it an electronic conductor. In other strontium-substituted perovskites, like the superconductor La2. cSrtCu03 <5, the Sr addition increased not only the vacancies of oxygen and Cu valency but also their electronic conductivities. Therefore,... 

At first sight, metals, ceramics and polymers have little in common. This is because of two main factors - the chemical bonding holding the atoms together and the microstructure of the solids themselves - that are quite different in representative examples of each material. However, the difference is illusory. Many ceramics can be considered as metals, for example the ceramic superconductors. Many polymers show electronic conductivity greater than metals and have use in lightweight batteries and electronic devices. The material in this and later chapters will allow these apparent anomalies to be understood. 

The lack of free electrons endows basic ceramics with poor thermal and electronic conductivity. The chemical flexibihty of ceramics, however, allows them to be selectively doped with other ions. In particular, doping with transition metal or lanthanide ions generates a wide variety of colours and can radically alter electronic and magnetic properties. Thus, insulators can be transformed into superconductors. How this comes about is described in Part 4, Chapters 10-15. 

Electroceramics with ac-tive functions Electric conductors Electron conductivity, temperature- and stress-dependent electrical resistance Electrodes, heating rods, varistors, igniters, thermistors, high-temperatuie superconductors... 

In Fig. 25-4, electron conduction mechanisms are displayed for p and n type semiconductors, which involve silicon doped with gallium and arsenic, respectively. Figure 25-5 gives the following speculative mechanism for electron conduction in the high temperature superconductor YBa2Cu307. It makes use of the instability of Pauling 3-electron bonds under compression (cf. Section 3-10). 

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