The common feature of the semiconductor ceramic production process is that it must go through a semiconducting process. The semiconducting process can replace some of the main crystal phase ions by doping unequal ions (for example, Ba2+ in BaTiO3 is replaced by La3+) to cause defects in the crystal lattice and form donor or acceptor energy levels to obtain n-type or p-type Type semiconductor ceramics. Another method is to control the firing atmosphere, sintering temperature and cooling process. For example, an oxidizing atmosphere can cause excess oxygen, and a reducing atmosphere can cause insufficient oxygen, which can make the composition of the compound deviate from the stoichiometry and achieve semiconductivity. The production process of semiconductor ceramic sensitive materials is simple, low in cost, small in size, and widely used. Pressure sensitive ceramics refer to ceramics with non-linear volt-ampere characteristics. Such as silicon carbide, zinc oxide ceramics. Their resistivity is variable with respect to voltage, and the resistance value is very high at a certain critical voltage, and the resistance drops sharply when this critical voltage is exceeded. Typical products are zinc oxide varistor ceramics, which are mainly used for surge absorption, high voltage stabilization, voltage and current limitation, and overvoltage protection.
Thermal ceramic
Also known as thermistor ceramics, it refers to ceramics whose conductivity changes significantly with temperature. There are three types: ①Negative temperature coefficient thermistor (abbreviated as NTC), such as oxide semiconductor ceramics of some transition metals such as manganese, iron, cobalt, nickel, etc. The characteristic is that as the temperature increases, the resistance decreases exponentially. ②Positive temperature coefficient thermistor (referred to as PTC), such as doped barium titanate semiconductor ceramics, is characterized by an increase in resistance as the temperature increases and a sharp change at the Curie point. ③Abruptly changing thermistors (CTR for short), such as vanadium oxide and its doped semiconductor ceramics, have a negative temperature coefficient, and at a certain temperature, the resistance changes drastically, and the change value can reach 3 to 4 orders of magnitude. Thermal ceramics are mainly used for temperature compensation, temperature measurement, temperature control, fire detection, overheat protection and color TV demagnetization.
Photosensitive ceramics
Refers to ceramics with photoconductor or photovoltaic effect. Such as cadmium sulfide, cadmium telluride, gallium arsenide, indium phosphide, bismuth germanate and other ceramics or single crystals. When light hits its surface, the conductivity increases. Mainly used as an automatically controlled optical switch and solar battery. Semiconductor ceramics.
Gas-sensitive ceramics
Refers to the ceramic whose conductivity changes with the type of gas molecules it contacts. Ceramics such as zinc oxide, tin oxide, iron oxide, vanadium pentoxide, zirconium oxide, nickel oxide and cobalt oxide. Mainly used for leak detection, disaster prevention alarm and measurement of different gases.
Moisture-sensitive ceramics
Refers to ceramics whose conductivity changes significantly with humidity. Such as triiron tetraoxide, titanium oxide, potassium oxide-iron oxide, magnesium chromate-titanium oxide and zinc oxide-lithium oxide-vanadium oxide and other systems of ceramics. Their conductivity is particularly sensitive to water and is suitable for humidity measurement and control.
The control system has become more and more systematic. It needs to be able to detect two or more physical and chemical parameters and provide multi-functional sensitive elements that do not interfere with each other's electrical signals. Humidity-gas-sensitive ceramics and temperature-humidity-sensitive ceramics and other multifunctional sensitive ceramics are being developed to meet this need.