Electrical conductivity intrinsic

Material Band Gap (eV) Electron Mobility (m /F-s) Hole Mobility (m /F-s) Electrical Conductivity (Intrinsic)(ilm)... 

This polymer may be prepared by stirring the molten w-aminoundecanoic acid at about 220°C. The reaction may be followed by measurements of the electrical conductivity of the melt and the intrinsic viscosity of solutions in w-cresol. During condensation 0.4-0.6% of a 12-membered ring lactam may be formed by intramolecular condensation but this is not normally removed since its presence has little effect on the properties of the polymer. 

During the past 30 years considerable research has been undertaken that has led to electrically conducting polymers that do not rely on the use of fillers, the so-called intrinsically conductive polymers. Such polymers depend on the presence of particles which can transport or carry an electric charge. Two types may be distinguished ... 

The mechanical activity of the heart (contraction of the atria and ventricles) occurs as a result of the electrical activity of the heart. The heart possesses an intrinsic electrical conduction system (Fig. 6-1). Normal myocardial contraction cannot occur without proper and normal function of the heart s electrical conduction system. Electrical depolarization of the atria results in atrial contraction, and ventricular depolarization is... 

The above mechanistic aspect of electron transport in electroactive polymer films has been an active and chemically rich research topic (13-18) in polymer coated electrodes. We have called (19) the process "redox conduction", since it is a non-ohmic form of electrical conductivity that is intrinsically different from that in metals or semiconductors. Some of the special characteristics of redox conductivity are non-linear current-voltage relations and a narrow band of conductivity centered around electrode potentials that yield the necessary mixture of oxidized and reduced states of the redox sites in the polymer (mixed valent form). Electron hopping in redox conductivity is obviously also peculiar to polymers whose sites comprise spatially localized electronic states. 

For any electrode, there is an intrinsic maximum current density it can pass - this follows simply because of the electrical conductivity of the metal from which the electrode is made and the maximum flux of analyte that can impinge on the electrode surface per unit time, itself a function of the rotation speed and solution viscosity and density. We see that it is quite possible for a small counter electrode to reach its maximum current density, ami thus limit the overall current flowing through the working electrode, all because the counter electrode is smaller than the working electrode. In summary, we must always remember that Iiv cannot exceed Ic ." they cannot be different in magnitude, only in terms of sign. 

Mechanistic Ideas. The ordinary-extraordinary transition has also been observed in solutions of dinucleosomal DNA fragments (350 bp) by Schmitz and Lu (12.). Fast and slow relaxation times have been observed as functions of polymer concentration in solutions of single-stranded poly(adenylic acid) (13 14), but these experiments were conducted at relatively high salt and are interpreted as a transition between dilute and semidilute regimes. The ordinary-extraordinary transition has also been observed in low-salt solutions of poly(L-lysine) (15). and poly(styrene sulfonate) (16,17). In poly(L-lysine), which is the best-studied case, the transition is detected only by QLS, which measures the mutual diffusion coefficient. The tracer diffusion coefficient (12), electrical conductivity (12.) / electrophoretic mobility (18.20.21) and intrinsic viscosity (22) do not show the same profound change. It appears that the transition is a manifestation of collective particle dynamics mediated by long-range forces but the mechanistic details of the phenomenon are quite obscure. 

Note 1 The bulk electrical conductivity of an intrinsically conducting polymer is comparable to that of some metals and results from its macromolecules acquiring positive or negative charges through oxidation or reduction by an electron acceptor or donor (charge-transfer agent), termed a dopant. 

Electrical conductivity is due to the motion of free charge carriers in the solid. These may be either electrons (in the empty conduction band) or holes (vacancies) in the normally full valence band. In a p type semiconductor, conductivity is mainly via holes, whereas in an n type semiconductor it involves electrons. Mobile electrons are the result of either intrinsic non-stoichiometry or the presence of a dopant in the structure. To promote electrons across the band gap into the conduction band, an energy greater than that of the band gap is needed. Where the band gap is small, thermal excitation is sufficient to achieve this. In the case of most iron oxides with semiconductor properties, electron excitation is achieved by irradiation with visible light of the appropriate wavelength (photoconductivity). 

Megnamisi-Belombe M (1977) Evidence for intrinsic electrical conduction in the linear metal-chain semiconductor bis(l,2-benzoquinonedioximato)platinum(II), Pt(bqd)2. J Solid State Chem 22 151-156... 

In intrinsic semiconductors, the number of holes equals the number of mobile electrons. The resulting electrical conductivity is the sum of the conductivities of the valence band and conduction band charge carriers, which are holes and electrons, respectively. In this case, the conductivity can be expressed by modifying Eq. (6.9) to account for both charge carriers ... 

The following electrical conductivity characteristics for both the intrinsic and extrinsic forms of a semiconductor have been determined at room temperature. Recall that qe = qu = 1.602 X 10 coulombs. 

Here and N are the effective densities of states in the conduction and valence bands respectively, and ws are the mobilities. The final expression for the electrical conductivity of an intrinsic semiconductor is given by... 

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