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Fast ion conductor



Fast ion conductors, also known as solid electrolytes and superionic conductors, are solid state electrical conductors which conduct due to the movement of ions through voids (or empty crystallographic positions)in their crystal lattice. One component of the structure, cationic or anionic, is essentially free to move throughout the structure, acting as charge carrier.

Additional recommended knowledge

The important case of fast ionic conduction is one in a surface space-charge layer of ionic crystals. Such conduction was first predicted by Kurt Lehovec (www.kurtlehovec.com) in the paper “Space-charge layer and distribution of lattice defects at the surface of ionic crystals” ( J. Chem. Phys. 1953. V.21. P.1123 -1128). As a space-charge layer has nanometer thickness, the effect is directly related to nanoionics (nanoionics-I). The Lehovec’s effect had given a basis for creation of multitude nanostructured fast ion conductors for portable lithium batteries and fuel cells.

Fast ion conductors are intermediate in nature between crystalline solids (see crystal) which possess a regular structure with immobile ions, and liquid electrolytes which have no regular structure and entirely mobile ions.

Solid electrolytes find use in all solid state supercapacitors, batteries and fuel cells, and in various kinds of chemical sensors.

Proton conductors are a special class of solid electrolytes, where hydrogen ions act as charge carriers.

There is difference between solid electrolytes and superionic conductors. In solid electrolytes (glasses or crystals), the ionic conductivity Ωi is arbitrary value but it should be greatly large than electronic one. Usually, the solids, where electronic conductivity Ωe is arbitrary value but Ωi is an order of 0.0001-0.1 Ohm-1 cm-1 (300 K), are called by superionic conductors.  . Superionic conductors, where Ωi is more than 0.1 Ohm-1 cm-1 (300 K) and activation energy for ion transport Ei is small (about 0.1 eV), are called by advanced superionic conductors. The famous example of advanced superionic conductor-solid electrolyte is RbAg4I5 where Ωi > 0.25 Ohm-1 cm-1 and Ωe ~10-9 Ohm-1 cm-1 at 300 K.


The Ωe – Ωi systematic diagram distinguishing the different types of solid state ionic conductors is given on the figure[1]

Fig. Classification of solid state ionic conductors by the lg Ωe - lg Ωi diagram (Ohm-1 cm-1).

2, 4 and 6 – known solid electrolytes (SEs), materials with Ωi >> Ωe;

1, 3, and 5 – known mixed ion-electron conductors;

3 and 4 – superionic conductors (SICs), i.e. materials with Ωi > 0.001 Ohm-1cm-1, Ωe – arbitrary value;

4 – SIC and simultaneously SE, Ωi > 0.001 Ohm-1cm-1, Ωi >>Ωe;

5 and 6 – advanced superionic conductors (AdSICs), where Ωi > 10-1 Ohm-1cm-1 (300 K), energy activation Ei about 0.1 eV, Ωe – arbitrary value;

6 – AdSIC and simultaneously SE, Ωi > 10-1 Ohm-1cm-1, Ei about 0.1 eV, Ωi >>Ωe;

7 and 8 – hypothetical AdSIC with Ei ≈ kBT ≈0.03 eV (300 К);

8 – hypothetical AdSIC and simultaneously SE.

Examples

Examples of fast ion conductors include sodium chloride, beta-alumina solid electrolyte, zirconium dioxide and silver iodide.

References

  1. ^ (2007) "Высокоёмкие конденсаторы для 0,5 вольтовой наноэлектроники будущего" (in Russian) (Portable Document Format). СОВРЕМЕННАЯ ЭЛЕКТРОНИКА (7): 24 -29. Retrieved on November 2 2007. (2007) "High-capacity capacitors for 0.5 voltage nanoelectronics of the future" (Portable Document Format). Modern Electronics (7): 24 -29. Retrieved on November 2 2007.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fast_ion_conductor". A list of authors is available in Wikipedia.
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