Space Charge Conductance

Before we do so, let us mention a particular difference between solid and liquid systems which is very important in this context, namely the occurrence of a network of internal boundaries in multiphase or polycrystalline materials. The proportion of boundary regions can be so high that the overall conductivity can be interfacially dominated. 

Possible space charge situations and the respective conductance effects parallel ( ) or perpendicular (J.) to the interface.105 (Reprinted from S. Kim, J. Fleig and J. Maier, Space charge conduction Simple analytical solutions for ionic and mixed conductors and application to nanocrystalline ceria. , Phys. Chem. Chem. Phys. 2268-2273, 5, Copyright 2003 with permission 

One consequence of the modified defect chemistry being restricted to the boundary is readily seen in Fig. 27. Unlike in the case of homogeneous doping, in heterogeneous doping the transition from interstitial to vacancy type does not show up as a knee in the conductivity curves, since, as soon as the boundary zone becomes less conductive, the bulk which is in parallel, dominates.113 

Oxide admixtures also proved beneficial (see, e.g. reference116) in the case of ion conducting polymers. Even though mobility effects occur, too, the separation of an ion pair in the rather covalent matrix by adsorbing one partner is possible, an effect that can be subsumed under the phenomenon of heterogeneous doping.37 

The second contact problem of significance is the contact of two ionic (or more generally two mixed) conductors (see Fig. 22, case b) 94,io, ii7,ii8 jjere a re(jjstrj5uti0I1 affects two boundary layers (charge 

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Serious problems with respect to a quantitative analysis can occur if the assumption of identical grain boundaries is violated. In sintering processes, inhomogeneities are the rule rather than the exception and grain boundary cores in one and the same polycrystal can easily differ in terms of structure and chemistry [109, 120, 242-246], Hence, core as well as space charge conductivities might also vary from boundary to... 

The second major assumption made in calculating the space-charge conductance from Eq. (14) is that the conductivity piefactors [Pg.322]

For calculating the space-charge conductance (j(F,) we need to know the density of states g E) and the surface potential F,. Under favorable conditions, F, of a free surface can be obtained by the Kelvin probe method or from the saturation value of the surface photovoltage. These methods will be illustrated with some preliminary results obtained on a-Si H. We then shall discuss metastable light-induced changes of the surface potential and conductance. 

Tredgold, R. H., (1966), Space Charge Conduction in Solids, Elsevier Publishing Co., New York. 

S. W. Kim, J. Fleig, and J. Maier [2003] Space Charge Conduction Simple Analytical Solntions for Ionic and Mixed Conductors and Application to Nanocrystalline Ceria, Phys. Chem. 

If a strong depletion of oxide ion vacancies occms in the space charge layer, electrons should form the majority carriers there. Maier formd rmder these conditions and under the assumptions that no frozen-in profiles exist and a low mobility for the acceptor impurities, for the Po. dependence of the space charge conductivity theoretically the exponent -J, which is concordant with the experimental value. 

The dielectric loss factor is made up of two components one due to relaxation or space-charge conduction processes and the other due to the dc conduction of the material. We may write... 

Fig. 5.105 a) Area related conductance per film thickness representing the measured excess space charge conductivity, as a function of inverse spacing, b) Area related conductance per boundary thickness representing the mean specific excess space charge conductivity, as a function of inverse spacing. The boundary concentration is assumed to be invariant. Prom Ref. [289]. 

The effective space charge conductivities are obtained as calculated in Section 5.8. If tl Too, Eq. (7.127) approximately results in at least two semicircles in the impedance plot. For the high frequency semicircle = oo + fv L L i the boundary... 

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