High temperature resistivity Thermionic Emission
Abstract
Thermionic emission, also known as thermal electron emission, is the process by which charge carriers, such as electrons or ions, move over a surface or some sort of energy barrier by the induction of heat. Charge carriers naturally restrain activity; however, in thermionic emission, thermal energy is introduced to the carriers, causing them to overcome these forces. The reason behind the charge carriers’ ability to perform this action is because electrons and ions are mobile and unbound to the normal chains of atomic structure that affect other particles. Traditionally, these charge carriers were referred to as “thermions.”
One property of the thermionic emission theory is that the emitting region is sustained with a charge opposite to the original but equal in magnitude. This means that the location of the charge carrier prior to emission will generate a positive charge in the case of electrons. However, this can be altered using a battery. The emission is neutralized when the carriers are farther away from the region, resulting in no change to the original state.
Introduction
Thermionic emission must not be confused with thermic emission (of black body for example) where photons are emitted from heated body. In the case of thermionic emission we observe emitted electrons from a metal due to its high temperature.

Mobile electrons in metals, also called valence electrons, are responsible for electric current conduction. If we increase the temperature of the metal, electrons start to move faster and some may have enough energy to escape (evaporate) from the metal. The higher the temperature, the higher will be the current of escaping electrons. This temperature induced electron flow is called thermionic emission.

If we use the hot metal from which electrons evaporate as a cathode on a high potential difference to the anode, then we get electric field between cathode and anode and emission of…