Electron transport random motion

In gases and liquids, conduction is due to the collisions and diffusion of the molecules during their random motion. In solids, it is due to the combination of vibrations of the molecules in a lattice and the energy transport by free electrons. A cold canned drink in a svarm room, for example, eventually warms up to the room temperature as a result of heat transfer from the room to the drink through the aluminum can by conduction. 

Two diffusion coefficients are of interest in MIECs the component diffusion coefficient, Dk, and the chemical diffusion coefficient, D. The component diffusion coefficient reflects the random walk of a chemical component. It is therefore equal to the tracer diffusion coefficient, except for a correlation factor which is of the order of unity. It is also proportional to the component mobility as given by the Nemst-Einstein relations. The chemical diffusion coefficient, I), reflects the transport of neutral mass under chemical potential gradients. In MIECs mass is carried by ions, and transport of neutral mass occurs via ambipolar motion of ions and electrons or holes so that the total electric current vanishes. b can be determined from steady-state permeation measurements, as mentioned in Section IV.H. However, D is usually determined from the time dependence of a response to a step change in a parameter, e.g., the applied current. Alternatively, D is determined from the response to an ac signal applied to the MIEC. 

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