Conductive materials, charge carrier

Classical theories of electrical and thermal conductance assume a huge number of atoms and free electrons. Let s assume a silicon cube with one side dimension of a and with common doping of lO cm. In an n-doped silicon cube with the size of (100 nm) there are 5><10 atoms and 10 free electrons at 300 K, but in the Si cube with the size of (10 nm) there are 5x10 atoms and 1% chance only to find one free electron. Free electrons are necessary for electrical conductance as charge carriers. In order to keep the conductive properties of the semiconductor material one should apply more intensive doping, 10 ° cm. However, such intensive doping decreases resistivity of the material dramatically (from 2x10" Qm to 10 Qm, respectively, for n-type Si, at 300 K). Low number of free electrons should be scattered evenly in whole volume of a material. 

The electrical conductivity of SMMO was found to be 1-4 S/cm in H-JAi and 10 S/cm in H2, at 800°C [83,84], The slight differences in the values possibly result from differences in synthesis methods. The conductivity decreases with increasing PO2, indicative of -type conductivity. The charge carriers are electrons generated by the reduction of Mo(VI) to Mo(V) to compensate for the charge imbalance created by the formation of oxygen vacancies in the material [84]. No studies have yet been conducted to optimize the electrical conductivity. 

In an extrinsic semiconductor, tlie conductivity is dominated by tlie e (or h ) in tlie CB (or VB) provided by shallow donors (or acceptors). If tlie dominant charge carriers are negative (electrons), tlie material is called n type. If tlie conduction is dominated by holes (positive charge carriers), tlie material is called p type. 

For insulators, Z is very small because p is very high, ie, there is Htde electrical conduction for metals, Z is very small because S is very low. Z peaks for semiconductors at - 10 cm charge carrier concentration, which is about three orders of magnitude less than for free electrons in metals. Thus for electrical power production or heat pump operation the optimum materials are heavily doped semiconductors. 

Ions in ceramic crystalline materials constitute potential charge carriers that can contribute to electrical conductivity, but analysis requires a... 

In simplistic terms, the conductivity of a material is controlled by both the density, and mobility, p, of the charge carriers, having a charge of e. 

Microwave measurements are typically performed at frequencies between 8 and 40 Gc/s. The sensitivity with which photogenerated charge carriers can be detected in materials by microwave conductivity measurements depends on the conductivity of the materials, but it can be very high. It has been estimated that 109-1010 electronic charge carriers per cubic centimeter can be detected. Infrared radiation can, of course, also be used to detect and measure free electronic charge carriers. The sensitivity for such measurements, however, is several orders of magnitude less and has been estimated to be around 1015 electronic charge carriers per cubic centimeter.1 Microwave techniques, therefore, promise much more sensitive access to electrochemical mechanisms. 

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