Question

Depending on the composition, some metals show positive potential at the hot end, while others show negative potential at the hot end. Explain what causes these different behaviour. This is regards to the concept of Seebeck effect.

Answer 1

If Seebeck coefficient is positive than the hotter end is at lower potential else the cooler end is at lower potential.

What we need to understand is how this sign changes for different materials depending upon their composition ?

In metal charge carriers are electrons in conduction band. Therefore if the Fermi level is higher in the conduction band it will act like an N-type semiconductor which means that electron will flow from hotter side which will accumulate electrons on other side creating a low potential there. So hotter side is at higher potential. But if Fermi level is low and resides more towards valence band exactly reverse thing happen.