At present, all kinds of electronic instruments, household audio and video equipment and micro-electronic computers are protected by ZnO varistor in order to prevent noise and surge voltage caused by external power lines, signal lines or airborne transmission, as well as human static electricity and other factors that lead to misoperation or breakdown damage of semiconductor devices.

However, ZnO varistor is a pure resistive element. Although it has good varistor sensitivity, its development and application are limited by its small dielectric constant, large dielectric loss, high frequency noise absorption and slow response speed to steep pulse surge, which affects the improvement of the reliability of instruments and instruments.

YalIllaoka after 1983, completed in reducing atmosphere _7 】 【 donor doping nanometer strontium titanate is after the semiconducting ceramics, on its surface coated with Na and Na: o pulp and secondary processing in oxidizing atmosphere, obtained the pressure sensitive characteristics of nanometer strontium titanate ceramic grain boundary layer capacitor, it not only has excellent dielectric property and significant nonlinear volt-ampere characteristics, but also absorbs 1000 ~ ~ 3000 cm2 such high surge capability, so the material with large capacity and the function of the pressure sensitive resistor capacitor.

In the field of low voltage work, it can completely replace ZnO varistor, and has a variety of electrical functions that can overcome the deficiency of ZnO varistor. That is why the varistor is called srTi03 multifunctional ceramics (MFC). This new type of element has the function of capacitor with large capacitance under low voltage (the capacitance is larger than 0. Ol core), and has the function of voltage sensitive resistor (the voltage nonlinear coefficient is greater than 15, and the inrush current can reach L 800 ~ cm2) after the voltage exceeds a certain critical value.

2.5 The most commonly used positive temperature coefficient (PTC) thermistor is (srBa) Ti03 series thermistor, whose PTC effect is directly related to ferroelectric property, and the sudden change of resistivity corresponds to Curie temperature. To satisfy different USES, PTC materials and components are required to have different Curie temperatures: for example, the Curie temperature is about 50 when the color TV degausser is used. C. PTC of physiotherapy equipment requires Curie temperature to be between 35 and 60. C High temperature heaters require Curie temperatures between 300 and 400. C.



Research status of strontium titanate

As a peak shifting agent, nanometer strontium titanate can reduce the temperature of PTC ceramics [8]. In addition. (S R's Pb) Ti03 thermal sensitive material has both negative temperature coefficient (NTc) and positive temperature coefficient (PTC) characteristics, and has a wide application prospect in the aspects of preventing inrush current element, overvoltage automatic protection, temperature detection and control, etc. 2.6 State SrTi0 is an oxygen-sensitive material. Oxygen vacancy exists in the crystal lattice of the material. When the atmosphere concentration changes, the oxygen vacancy also changes accordingly, thus causing the change of material resistance. Semiconductor oxygen sensors have been widely used in combustion management, environmental protection, safety and explosion protection, metallurgy, food industry and gas separation.

Oxide semiconductor oxygen sensor spirit for a short oxygen sensitive response when asked, high sensitivity, small volume, simple structure, does not need to reference the advantages of oxygen electrode, yukon hope instead of oxygen concentration cell type semiconductor and 2.7 sites humidity-sensitive material 1 doping elements (such as Sr, K, etc.) after nanometer strontium titanate, will absorb the water in the surrounding atmosphere, make the electronic conductivity and dielectric constant to improve, so that the conductivity increased. Therefore, nano-titanate saw material can be used as humidity sensitive material to control the humidity around electronic equipment. In the above application fields, strontium titanate powder is firstly prepared, and then directly used as a material, or the powder is used as raw material to further process into devices. Therefore, the preparation of strontium titanate ultrafine powder is the premise of the application of strontium titanate functional materials, and also directly affects the properties of the materials.



The traditional preparation method of strontium titanate ultrafine powder is the high temperature solid reaction method. With the development of various related industries, the requirements on powder properties are getting higher and higher, and the uniformity, purity, particle size and stoichiometric ratio of particles need to be strictly controlled. The strontium titanate powder prepared by the traditional solid reaction method cannot meet the above requirements, so many chemical liquid phase powder preparation methods have been developed.



The data process engineering journal 3.1 high temperature solid instead of ten thousand method [J high temperature solid instead should method is the traditional method of preparation of strontium titanate powder, usually within the S (or SrC03) and Ti02 powder in a ball mill machine mixing, pelleting, high temperature (1000. C above) calcined in a few hours to a few hours, and then through the ground at the end of the line to the strontium titanate powder. The law generally need to be done at high temperatures, can appear, which wastes energy and particle growth, is not conducive to forming superfine powders.



In addition, there are also the following problems :(a) the solid reaction should be carried out at the particle interface, and the reaction is often incomplete and the composition is not uniform; (b) Solid phase doping is difficult to be uniformly mixed, especially when trace doping (O. 1%-1%), it is impossible to achieve complete uniform mixing. 3.2 a Sol Gel method (Sol - Gel) 【 l deputy Sol Gel method refers to metal organic or inorganic compounds by a Sol Gel solution is dry, then through calcination methods of oxide (or heat treatment). A Sol Gel method materials including metal alkoxide, acetate, acetyl acetone, nitrate, chloride salt, etc.; the metal alkoxide, easy to use with distilling and recrystallization technology, soluble in ordinary organic solvents, easy hydrolysis characteristics, it is widely used in of powder prepared by Sol - Gel;

The disadvantages are that metallic alcohols are expensive and the common solvents used for alcohols are poisonous. At present, this method is used for the preparation of powders such as alumina and cobalt oxide. The sol-gel method of strontium titanate electronic ceramics is still in the research and exploration stage. The basic process is that firstly, the strontium titanate and strontium salt (including the organic compounds of strontium) are used as raw materials, and the organic complex is used as chelate and alcohol as solvent to prepare homogeneous sol and gel. After drying, strontium titanate ultrafine powder can be obtained by calcining at 9000C for several hours. The key to this method is to produce homogeneous gels, the formation of which is due to the formation of polymers in the system. Strontium ions are uniformly adsorbed in the gel body due to electrostatic action.