Conductivity behavior

Physical Properties Electrical. Electrical properties have been the main focus of study of organic semiconductors, and conductivity studies on organic materials have led to the development of materials with extremely low resistivities and large anisotropies. A discussion of conductivity behaviors for various classes of compounds follows. 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

The temperature dependence of the thermal conductivity of CBCF has been examined by several workers [10,13,14]. Typically, models for the thermal conductivity behavior include a density term and two temperaUrre (7) terms, i.e., a T term representing conduction within the fibers, and a term to account for the radiation contribution due to conduction. The thermal conductivity of CBCF (measured perpendicular to the fibers) over the temperature range 600 to 2200 K for four samples is shown in Fig. 6 [14]. The specimen to specimen variability in the insulation, and typical experimental scatter observed in the thermal conductivity data is evident in Fig. 6. The thermal conductivity of CBCF increases with temperature due to the contribution from radiation and thermally induced improvements in fiber structure and conductivity above 1873 K. 

At salt concentration below those shown in Fig. 5, molar conductivity behavior has been identified with the formation of electrically neutral ion pairs [8]. Between concentration of 0.01 and 0.1 mol L 1 (up to an 0 M ratio of -50 1) the molar conductivity rises and this can be explained by the formation of mobile... 

Recent investigations into the charge-transport properties of M-DNA have indicated highly conducting behavior (2 77). Fluorescence lifetime... 

Another factor which appears to be of importance in the conductivity behavior of zero-valent poly-I is the absence of nonelectroactive ions in the polymer. The difference in potential between the 2+/1+ and 1+/0 couples in solution is significantly smal ler than the difference in potential between the 1+/0 and 0/1-... 

Studies of the conductivity behavior of [Pt(dppm)2]X2 (X = Cl, Br, I, PF6, BF4) in solution have been reported.274 Both conductivity and NMR studies of the halide complexes are consistent with the five-coordinate adduct [Pt(dppm)2X]+ being present in chlorinated hydrocarbon and ethane-... 

Anariba F, McCreery RL (2002) Electronic conductance behavior of carbon-based molecular junctions with conjugated structures. J Phys Chem B 106 10355-10362... 

Billups, B., Rossi, D and Attwell, D. (1996) Anion conductance behavior of the glutamate uptake carrier in salamander retinal glial cells../. Neurosci. 16, 6722-6731. 

Codoped Single Doped Effect on Conduction Behaviors... 

Reading the literature on mammalian semiochemistry over the past decade, a chemist is impressed by the enormous volume of biological information that has been gathered in well planned and meticulously executed studies of the modulation of the behavior of mammals by the chemicals released by con-specifics. One cannot, however, escape the impression that the chemical basis of many of these studies is lacking. Some of the problem areas were pointed out in the foregoing sections. To a certain extent there seems to be lack of appreciation of the diffusion rates of compounds with different volatilities and of the extent to which these differences can influence the outcome of behavioral tests. It is difficult to make an estimate of the persistence of semiochemicals that are released into the laboratory atmosphere or that are left on objects or surfaces in arenas in which tests are conducted. From what is known about the evaporation rate of some heavy compounds that are considered to be semiochemicals, it could take several weeks or even months for these compounds to be depleted to levels that cannot be detected by currently available instrumentation levels at which meaningful information could still be available to experimental animals. This then leaves the question unanswered as to when it would be safe to conduct behavioral experiments in a laboratory or arena that had been occupied by conspecifics. 

Further evidence for microphase separahon has been seen by AFM. As expected, BPSH 00, with no ionic regions, displays no significant features in its AFM image. For BPSH 20, isolated ionic clusters have dimensions of 10-25 nm. These clusters are even more readily discerned from the non-ionic matrix in BPSH 40, but the domains appear to remain relatively segregated from each other. In the case of BPSH 50 and 60, connections between domains are clearly visible, especially in the case of the latter sample. It also should be noted, however, that these samples were in a dehydrated state. Therefore, it might be expected that even in the case of the lower acid content samples, it is likely that some channel formation between ionic domains will still occur upon the uptake of water. This can be clearly seen in its linear conductivity behavior as a function of disulfonated monomer (i.e., the percolation threshold has been reached by at least 20-30% content of disulfonated monomer). 

Cation—sulfonate interactions, as well as proton mobility, are also expressed in the electrical conductance behavior of these membranes. Many studies of this property have been reported, and there is no attempt in this review to cite and describe them all. Rather, a few notable examples are chosen. Most testing is done using alternating current of low voltage to avoid complications in the form of chemical... 

Conductance behavior is dependent on the material and what is conducted. For instance, polymeric materials are considered poor conductors of sound, heat, electricity, and applied forces in comparison with metals. Typical polymers have the ability to transfer and mute these factors. For instance, as a force is applied, a polymer network transfers the forces between neighboring parts of the polymer chain and between neighboring chains. Because the polymer matrix is seldom as closely packed as a metal, the various polymer units are able to absorb (mute absorption through simple translation or movement of polymer atoms, vibrational, and rotational changes) as well as transfer (share) this energy. Similar explanations can be given for the relatively poor conductance of other physical forces. 

As the temperature of the semiconductor is increased electrons are thermally removed from interatomic bonds to the conduction band, simultaneously creating a positive hole and a free electron. Under the influence of an applied potential, the hole and electron move away from each other in opposite directions giving rise to an electric current. Occasionally an electron and a hole will meet in a recombination process and the electron will fall back into the interatomic bond. Upon heating to a sufficiently high temperature any insulator is expected to show this intrinsic conduction behavior. 

It is interesting to compare conductance behavior with that of the shear viscosity, because conventional hydrodynamic conductance theories relate A to the frictional resistance of the surrounding medium. At first glance, one would expect from the Stokes-Einstein equation a critical anomaly of the... 

The general shape of the equivalent conductance vs. concentration plot for metal-ammonia solutions is shown by the behavior of sodium in NHs at —33° C. in Figure 2. The conductance behavior of metal-ammonia solutions is quite analogous to the behavior of electrolytes in solvents of low dielectric constant. The dilute region equivalent conductance decreases with increasing concentration, eventually goes... 

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