Electrical conduction mechanism superconductors

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

The search for new organic metals and superconductors has attracted a great deal of attention in synthetic chemistry and material science since the discovery of high electrical conductivity in conjugated polymers such as polyacetylene [1], Lots of theoretical studies have been carried out in order to understand the mechanism of conductivity and superconductivity in the conjugated polymers and related... 

Polythiazyl. This polymer, (SN), known since 1910, can now be obtained in a pure state. It is golden bronze in color and displays metallic type electrical conductance more remarkable still is the fact that at 0.26 K it becomes a superconductor. In the crystal the kinked, nearly planar, chains (12-IX) lie parallel and conductance takes place along the chains, in which n electrons are extensively delocalized according to molecular quantum mechanical calculations. A partially brominated substance, (SNBr04) , is an even better conductor. 

On the other hand, aluminum-stabilized superconductors are desirable because aluminum has excellent low-temperature electrical conductivity, low magnetoresistance, low heat capacity during cooldown, and low density. The great differences in mechanical properties between high-purity aluminum and NbTi alloys, however, make it very difficult to fabricate an aluminum-stabilized multifilamentary superconductor. 

Superconducting ceramics of Y,Ba2Cu30jj g have been used as substrates for the electrochemical deposition of either poly pyrrole or poly thiophene [87]. Ceramics are typically obtained by firing pressed powders of the oxide compounds. Thus, electrical and mechanical contacts made between the ceramics and wires produced mechanically or by vacuum deposition of metal are often found to be inadequate. Superconductors modified by conducting polymers may help improve the contact area. 

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