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What is PTC thermistor?

2013-01-21
PTC thermistor (Positive Temperature Coefficient of resistance) is a kind of positive temperature coefficient thermistor, mainly made up of BaTiO3 ceramics.BaTiO3 ceramics is a kind of typical ferroelectric material with the resistively of greater than 10 Ω.cm under normal temperature, through semi-conductor doping it has a strong PTC efficacy-----it has extremely low resistance under normal temperature rises. This is because a barrier layer induced by the surface state exists on the crystal particle border of the multicrystal BaTiO3 semiconductor material. Under curie temperature, the high-resistance crystal boundary has ferroelectric characteristics with great dielectric constant and low potential barrier, electrons can easily penetrate the potential barrier and corresponding materials have low resistivity. When above curie temperature, crystal lattice occurs at the high resistance layer and the ferroelectric constant decreases quickly. The potential barrier increases because the dielectric constant drops in accordance with the Curie-Weiss Law. With the dramatic increase of the barrier height, it becomes difficult for electrons to pass potential barrier and the resistivity of the corresponding materials rises dramatically. This behaves as the PTC efficacy of the material in a macro manner. Due to this property, the PTC thermistor is widely used both on industrial electronic equipment and household appliances. The field of its application is classified in light of the three basic electric performances of the PTC thermistor.