Ceramic materials are usually good for high-insulation resistance, ceramic PTC thermistor is barium titanate-based and doped with other polycrystalline ceramic materials in manufacturing.

It has lower resistance and semi-conducting properties.

It is realized by doping a material of higher chemical valence (acting as Dot Matrix Element):

In the crystal lattice, Barium or Titanate ion were taken place by the ions of higher valence, it create some free electrons with electro-conductivity. For the PTC thermistor, it is the reason of resistance’s increasing.

The effect is counteracted when the temperature is low.

If the temperature rise higher, the resistance increase greatly accordingly, too.

This is just called “PTC effect”.