The resistivity of ceramics with semiconductor properties is about 10-5~ 107ω.cm, and the semiconductor properties of ceramic materials can be obtained by doping or causing lattice defects caused by stoichiometric deviation. Ceramics using this method include TiO2,
ZnO, CdS, BaTiO3, Fe2O3, Cr2O3 and SiC. The different characteristics of semiconductor ceramics are that their electrical conductivity changes with the environment, which can be used to make various types of ceramic sensitive devices.
Such as heat sensitive, gas sensitive, humidity sensitive, pressure sensitive, light sensitive and other sensors. Semiconductor spinel materials, such as Fe3O4, are mixed with non-conductor spinel materials, such as MgAl2O4, in controlled solid solutions.
MgCr2O4, and Zr2TiO4, can be used as thermistors, which are carefully controlled resistance devices that vary with temperature. ZnO can be modified by adding oxides such as Bi, Mn, Co and Cr.
Most of these oxides are not solidly dissolved in ZnO, but deflection on the grain boundary to form a barrier layer, so as to obtain ZnO varistor ceramic materials, and is a kind of material with the best performance in varistor ceramics.
SiC doping (such as human carbon black, graphite powder) can prepare semiconductor materials with high temperature stability, used as various resistance heating elements, that is, silicon carbon rods in high temperature electric furnaces. Control the resistivity and cross section of SiC to achieve almost anything desired
Operating conditions (up to 1500 ° C), increasing its resistivity and reducing the cross section of the heating element will increase the heat generated. Silicon carbon rod in the air will occur oxidation reaction, the use of temperature is generally limited to 1600°C below, the ordinary type of silicon carbon rod
The safe operating temperature is 1350°C. In SiC, a Si atom is replaced by an N atom, because N has more electrons, there are excess electrons, and its energy level is close to the lower conduction band and it is easy to raise to the conduction band, so this energy state is also called the donor level, this half
The conductors are N-type semiconductors or electronically conducting semiconductors. If an Al atom is used in SiC to replace an Si atom, due to the lack of an electron, the formed material energy state is close to the valence electron band above, it is easy to accept electrons, and is therefore called acceptant
The main energy level, which leaves a vacant position in the valence band that may conduct electrons because the vacant position acts the same as the positive charge carrier, is called a P-type semiconductor or hole semiconductor (H. Sarman,1989).
Post time: Sep-02-2023