The organization and function of thermistor

Ceramic materials are usually used as excellent insulators with high resistance. Ceramic PTC thermistor is based on barium titanate (IV) and is doped with other polycrystalline ceramic materials. It has lower resistance and semiconducting properties.

It is achieved by purposely doping a material with a higher chemical value as a lattice element of the crystal: part of the barium ion or titanate ion is replaced by a higher valence ion in the crystal lattice, so a certain amount of Conductive electron. The reason for the PTC thermistor effect, that is, the increase in resistance value, is that the material structure is composed of many small crystallites, and a potential barrier is formed at the interface of the grains, that is, the so-called grain boundaries (grain boundaries). Prevents electrons from crossing the border into adjacent areas, which results in high resistance.

This effect is canceled at low temperatures: high dielectric constants and spontaneous polarization strength at the grain boundaries hinder the formation of barriers and allow electrons to flow at low temperatures. However, at high temperatures, the dielectric constant and polarization strength are greatly reduced, which causes the potential barrier and resistance to be greatly increased, showing a strong PTC effect.