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Sorry for the stupid question, but actually there's something that seems unclear to me.
It is said that the electrons of the insulator are bound to their atoms. Fine.
So, these electrons can't access the conduction band to participate to the electric flow. Alright.
Still, the conduction band does exist. So, if the electric source injects some electrons on the conduction band of the material, what prevents these electrons from progressing on said conduction band? In other words : why should the charge transfer be due exclusively to the electrons that belong to the material?
I miss omething....
87.86.104.115 thanks for the insightful question. I agree the article could be clearer. A substance must have intrinsic charge carriers to conduct electricity, in order to maintain electrical neutrality; it can't get them from the source. When an electron in a metal leaves its atom to become a conduction electron, it leaves behind a positive ion so the metal is still neutral. If you attached metal electrodes to a good insulator like ceramic and applied a voltage across them, at the negative electrode electrons would diffuse a short distance from the metal into the ceramic under the influence of the electric field. But because there are no balancing positive charged ions in the ceramic, the electrons would be attracted back to the positive ions they left in the metal, and would form a negative surface charge layer, creating an opposing electric field which would prevent more electrons from entering. --
ChetvornoTALK 15:15, 29 June 2021 (UTC)reply
thanks both for your prompt replies :)
I had read the article about breakdown, but it didn't really clarify things, because it explains how electrons of the material go from bound to unbound state.
My concern was more about : why don't we just have electrons from the source that circulate on the conduction band?
If I understand
Chetvorno's reply, it's related to the fact that an electron leaving the negative electrode would leave an positive charge on said electrode, attracting back the electron (and the ceramic sample getting a negative charge, would repell electrons back anyway).
But I'm sill confused (sorry :D ).
If my electrodes are actually connected to, say, a condensator. The negative electrode is due to an excess of electrons in the electrode (and we have positive ions on the positive electrode side) : the voltage results from this charge imbalance.
So, electrons will reach the ceramic sample.
If they can't move, then I agree that again the electrons "concentration" will equilibrate between the electrode and the sample (locally), and no current occurs. And on the positive side, no electron reaches the positive elctrode, bc there's no mobile electron amyway.
But (that's precisely my concern), if electrons are on the conduction band, they actually can move from the negative to the positive electrode, even if it implies that the ceramic ends-up with a slight negative charge eccess (the condensator wouldn't be able to empty totally, as it would with a metal sample ; but a circulation of part of the electrons would nevertheless be possible).
This is obviously not what we observe, but I don't get what my reasonning is missing.
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