Thermoelectric effects in metals

[Moreno]

It seems that some thermoelectric effects (such as Seebeck and Peltier effects) can be associated with carriers (electrons and holes) generation and recombination. But thermoelectric effects can be observed in many metals as well, not only in semiconductors. Can there be such effects as carrier generation and recombination in metals? It doesn't seem to be possible as all electrons in metals are typically free electrons even at 0 K, at elevated temperatures all the more so. How then could there be an electron-hole recombination in metals? For example in Bismuth, Antimony, etc.?

[Bender]

No band gap = no holes = no recombination. 

To get recombination in metals you need to turn them into a semi-conductor.

[Sensei]

Only 1, 2, rarely more, are free electrons in the single metal atom.

Copper for instance has 1 free electron per atom. So you have at most the same number of free electrons as quantity of Copper atoms.

 

[Moreno]

21 hours ago, Sensei said:

Only 1, 2, rarely more, are free electrons in the single metal atom.

Copper for instance has 1 free electron per atom. So you have at most the same number of free electrons as quantity of Copper atoms.

 

Well, obviously I meant: "all the valence electrons are free". Though this is a rude approximation.

[Moreno]

How can it be explained that Platinum has the smallest Seebeck coefficient among pure metals which is conditionally taken for zero?

https://en.wikipedia.org/wiki/Seebeck_coefficient#Definition

[Toffo]

On 6/11/2018 at 3:11 PM, Moreno said:

How can it be explained that Platinum has the smallest Seebeck coefficient among pure metals which is conditionally taken for zero?

https://en.wikipedia.org/wiki/Seebeck_coefficient#Definition

 

 

When two blocks of platinum are brought together electrons do not tend to move from block to another block, because the blocks are identical.  Zero motion means zero Seebeck effect.

When a block of platinum and a block of iron are brought together electrons do tend to move from one block to another block. Then some works must be done to separate the blocks. The blocks form a charged capacitor. 

If there was a way to connect wires to that capacitor so that there is no Seebeck effect between the blocks and the wires, then we would have a perpetual motion machine. 

Actually there is a way to adjust the contact voltage between the wires and the blocks: Temperature. 

Heat in the contact decreases the contact voltage, I guess. The effect is called contact voltage if I remember correctly. I mean the effect of contact becoming a charged capacitor.

 

What happens when a cool platinum block and a hot platinum block are brought together?

Interesting question there ... some electrons move from the hot block to the cool block. Electrons have less potential energy in the cool block, so electrons tend to fall from hot block to the cool block.  This effect is probably same in all metals, so this effect's effect on the Seebeck effect is zero, probably.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Moreno]

14 hours ago, Toffo said:

 

 

When two blocks of platinum are brought together electrons do not tend to move from block to another block, because the blocks are identical.  Zero motion means zero Seebeck effect.

When a block of platinum and a block of iron are brought together electrons do tend to move from one block to another block. Then some works must be done to separate the blocks. The blocks form a charged capacitor. 

If there was a way to connect wires to that capacitor so that there is no Seebeck effect between the blocks and the wires, then we would have a perpetual motion machine. 

Actually there is a way to adjust the contact voltage between the wires and the blocks: Temperature. 

Heat in the contact decreases the contact voltage, I guess. The effect is called contact voltage if I remember correctly. I mean the effect of contact becoming a charged capacitor.

 

What happens when a cool platinum block and a hot platinum block are brought together?

Interesting question there ... some electrons move from the hot block to the cool block. Electrons have less potential energy in the cool block, so electrons tend to fall from hot block to the cool block.  This effect is probably same in all metals, so this effect's effect on the Seebeck effect is zero, probably.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

No, it is not.