Organization structure and function principle of thermistor

Ceramic materials are usually used as excellent insulators with high resistance. Ceramic PTC thermistor is based on barium titanate and doped with other polycrystalline ceramic materials. It has low resistance and semiconductivity.

By purposefully doping a material with higher chemical value as the lattice element of the crystal, a part of barium ion or titanate ion in the lattice is replaced by a higher price ion, thus a certain number of conductive electrons are generated. For the PTC thermistor effect, that is to say, the reason for the step increase of the resistance value is that the material structure is composed of many small microcrystals. A potential barrier is formed on the grain boundary, that is, the so-called grain boundary (grain boundary), which prevents the electrons from crossing the boundary into the adjacent area, resulting in high resistance.

This effect is counteracted at low temperatures: high dielectric constant and spontaneous polarization at the grain boundary hinder the formation of the barrier and allow electrons to flow at low temperatures. However, at high temperature, the dielectric constant and polarization intensity decrease greatly, which leads to the increase of potential barrier and resistance, showing a strong PTC effect.