PTC refers to a thermistor phenomenon or material with a sharp increase in resistance and a positive temperature coefficient at a certain temperature, which can be specially used as a constant temperature sensor. The material is a sintered body with BaTiO3, SrTiO3 or PbTiO3 as the main component, in which a small amount of oxides such as Nb, Ta, Bi, Sb, y, La and other oxides are added to control the atomic valence to make it semiconducting. This semiconducting barium titanate and other materials are often referred to as semiconducting (bulk) porcelain; at the same time, oxides of manganese, iron, copper, chromium and other additives are added to increase the temperature coefficient of positive resistance.
PTC refers to a thermistor phenomenon or material with a sharp increase in resistance and a positive temperature coefficient at a certain temperature, which can be specially used as a constant temperature sensor. The material is a sintered body with BaTiO3, SrTiO3 or PbTiO3 as the main component, in which a small amount of oxides such as Nb, Ta, Bi, Sb, y, La and other oxides are added to control the atomic valence to make it semiconducting. This semiconducting barium titanate and other materials are often referred to as semiconducting (bulk) porcelain; at the same time, oxides of manganese, iron, copper, chromium and other additives are added to increase the temperature coefficient of positive resistance. Platinum titanate and its solid solution are semiconductorized by ordinary ceramic molding and high-temperature sintering to obtain thermistor materials with positive characteristics. Its temperature coefficient and Curie point temperature vary with composition and sintering conditions (especially cooling temperature).
Barium titanate crystals belong to the perovskite structure. It is a ferroelectric material, and pure barium titanate is an insulating material. After the addition of trace rare earth elements to barium titanate and proper heat treatment, the resistivity increases sharply by several orders of magnitude around the Curie temperature, resulting in a PTC effect, which is consistent with the ferroelectricity of barium titanate crystals and the material at the Curie temperature. nearby phase transitions. Barium titanate semiconductor ceramics are polycrystalline materials with interfaces between grains. When the semiconductor ceramic reaches a certain temperature or voltage, the grain boundary changes, resulting in a sharp change in resistance
The PTC effect of barium titanate semiconductor ceramics comes from grain boundaries (grain boundaries). For conducting electrons, the interface between particles acts as a potential barrier. When the temperature is low, due to the action of the electric field in the barium titanate, the electrons can easily pass through the potential barrier, so the resistance value is small. When the temperature is raised near the Curie point temperature (i.e. critical temperature), the internal electric field is destroyed, which cannot help conducting electrons to cross the potential barrier. This is equivalent to an increase in the potential barrier and a sudden increase in resistance, resulting in the PTC effect. The physical models of the PTC effect of barium titanate semiconductor ceramics include the Haiwang surface barrier model, the barium vacancy model and the superposition barrier model of Daniels et al. They have made a reasonable explanation for the PTC effect from different aspects.
Post time: Mar-09-2022
