In the inorganic thermoelectric generator studys, there is some evidence to prove the connection between porosity and seebeck coefficient. In the case of organic thermoelectric generator, I can`t sure about that thing.
please tell me about that things.
thank you.
Dear Jaeun,
The Seebeck coefficient does not depend on the porosity of material, while the figure of merit do it because it is a mean of decreasing the thermal conductivity. It is well established that the porosity decrease the thermal conductivity in the usual thermolectric materials.
Dear Jaeun,
the first question from me would be: Do you mean the relationship between porosity and Seebeck coefficient or between porosity and thermoelectric efficiency?
- The thermoelectric efficiency is a function of the figure of merit Z*T = S2*sigma/lambda.(S - Seebeck coefficient, sigma - electrical conductivity, lambda - thermal conductivity.) The porosity of the material would influence especially the thermal conductivity. To get a higher efficiency, the porosity most be enhanced. Nevertheless, the conductivity would be influenced too. Therefore, this structural change would have a small effect only.
- A change of the Seebeck coefficient could be essential for nano structures. (We observed a decrease of S in nanowires with indentations). In nanostructures we have 2 effects: The density of states changes with size and the surface to volume ratio changes:
The Mott equation describes S proportional to d sigma/d E (E energy). If the density of states changes (due to size changes as a consequence of porosity), S changes. The surface is not considered by Mott. But we found, that interaction with the surface reduce S.
Generally, it is a complex physics and has to be investigated in detail.
With Regard
R. Mitdank
Dear Rüdinger,
In any case the Mott formula for the Seebeck coefficient cannot depend on the porosity of the material. Even if we consider that the Mott formula is not the most general form to obtain the Seebeck coefficient. Another thing is if we think in the phononic part of the thermal conductivity which seems quite logic that this holes in the crystal decrease the velocity of propagation for the phonons. Another issue very different is the Seebeck coefficient on nanostructures or low dimensional materials where I agree the complexity and difficulty for distinguishing all these things: the electron-electron can be higher than allow Mott formula or phonon-phonon, besides electron-phonon.
First of all thank you for your kind reply.
Now I have another question. Porosity can reduce the phonon propagation, and seebeck coefficient has a deep relationship with phonon drag. With this idea, I think that reducing the phonon propagation with controlling porosity can affect to seebeck coefficient increasing.
With Regard
J. Ha
Dear Jaeun,
One thing is to transform phonons in electricity (Seebeck) changing importantly the entropy and another to change the transport of the phonons( phononic conductivity). Both things are independent (or almost), you can play with the phonons all that you want without getting any important change on the Seebeck coefficient.
- Badges
- Science topic
- Similar topics
- Chemistry, Organic
- Organic