Materials ionic resistance

With the conductivity of an aqueous electrolyte (e.g., IN KCl) serving as a reference, comparable conductivities can be achieved in solid electrolytes under certain conditions. Some of the best solid ionic conductors, commonly referred to as superionic conductors , have resistivities comparable to those of aqueous electrolytes at room temperature (e.g., RbAg4l5 and single crystal MgO-stabilized 6"-alumina). However, they are either in the form of single crystals, which is impractical for most applications, or composed of very expensive and relatively unstable materials. Resistivities comparable to those of aqueous electrolytes can be achieved in solid electrolytes at higher temperatures in both superionic conductors like 6"-alumina (i.e., 300°C) and normal ionic conductors such as stabilized zirconia (800-1000°C), stabilized cerium oxide (>800 C), and stabilized bismuth oxide (>600°C). Sodium ion conducting glasses are much less conductive than polycrystalline 8 -alumina. 

The Resistance of Ionic Materials with Multiply Charged Ions to Dissolve ... 

Zone II (10 mHz to 10 Hz) provides quantitative assessment of the series electronic resistance of the conductors and the ionic electrolyte resistance Rj(T). In this range, the equivalent series resistance is composed of = R + Ri(T) resistances and varies according to the dependence of R, on cell temperature. The ionic resistance is more prevalent at low frequencies as a result of better ion penetration into the pores of the electrode material. 

Contact Resistance Contact resistance is a result of imperfectly matched material interfaces in the fuel cells. At every location where there is a noncontinuous contact between dissimilar materials, there is an electronic or ionic contact resistance, as illustrated in Figure 4.29. The contact resistance is a function of the material surface state and roughness and the contact pressure between the materials (values of area contact resistance are given in units of m or cm ) ... 

Specific resistance (ASR). The high-frequency intercept on the real impedance axis rqtresents the value of ohmic ASR in the cell, which is generated from the ionic resistance in the electrolyte layer, both ionic electronic resistances in the electrodes, and the contact resistance from the interfaces and current collectors [58], From this figure, it is seen that ohmic ASR of the cells were reduced with the decrease in the electrolyte thickness of the cells. Assuming each cell had the same ohmic resistances in their electrodes, interfaces, and current collectors because of their similar material compositions, structures, and fabrication techniques, the ionic resistance in the electrolyte layer was decreased significantly by the reduction in the electrolyte thiek-ness. This is also one of the major reasons for the higher power output of thinner electrolyte layer that is shown in Figure 11.24a. 

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. 

---