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Development of piezoelectric ceramic materials

Views:1     Author:Site Editor     Publish Time: 2019-09-27      Origin:Site

Piezoelectric ceramics are a kind of polycrystals with piezoelectric properties and an important part of information functional piezoelectric ceramics. With the advantages of high electromechanical coupling coefficient, low price and easy mass production, piezoelectric ceramics have been widely used in various fields of social production. Especially in the fields of ultrasound and electronic science and technology, piezoelectric ceramics have gradually been in an absolute dominant position, such as medical and industrial ultrasonic testing, underwater acoustic detection, etc. Piezoelectric transducer, ultrasonic motor, display device, electronically controlled polychromatic filter, etc. However, in practical components, different applications require different PZT material parameter of piezoelectric ceramics, which forces people to improve the performance of piezoelectric ceramics. At present, there are two main methods at home and abroad: one is doping modification, that is, doping some impurity ions; the other is improving the preparation process,the latest progress, research and application of piezoelectric ceramics and its development trend are briefly reviewed.        

 

Basic Properties of Piezoelectric Ceramics 
        
 The most important characteristics of piezoelectric ceramics plates transducers are positive piezoelectricity and inverse piezoelectricity. Positive piezoelectricity refers to the polarization caused by the relative displacement of the positive and negative charge centers in some dielectrics under the action of external mechanical forces, which results in the appearance of symbolic opposite bound charges on the surface of both ends of dielectrics. When the external force is not too large, the charge density is proportional to the external force, following the formula and the surface charge density is the piezoelectric constant, is the expansion stress. On the contrary, when an external electric field is applied to a piezoelectric dielectrics, the positive and negative charge centers in the dielectrics not only displace and polarize, but also deform the dielectrics due to the displacement. This effect is called inverse piezoelectricity. When the electric field is not very strong, the deformation is in line with the external electric field. The sexual relationship is piezoelectric strain constant, $ is external electric field and strain. The strength of piezoelectric effect reflects the coupling degree between the elastic and dielectric properties of crystals, that is, the coupling degree between mechanical and electrical effects, which is expressed by the electromechanical coupling coefficient.      


 Performance Improvement of Piezoelectric Ceramics   

   

Lead-containing piezoelectric cylinder transducer is superior to other ceramics in piezoelectric properties, temperature stability and curie temperature due to lead zirconate-titanate. Their electrophysical properties can be adjusted in a wide range by changing components or changing external conditions, such as ternary system and quaternary system, to meet different needs. The sintering temperature of piezo ceramics is generally higher, while the volatilization temperature of lead oxide is about 1. In addition, with the development of surface assembly technology, multi-layer chip capacitors, inductors, resistors and other chip devices are popular in the market for their high efficiency, miniaturization and functional integration. However, the high sintering temperature of piezoelectric ceramics makes it difficult for piezo ceramic materials and electrode materials to achieve one-time co-firing. Because of low temperature co-firing, base metals such as nickel, copper, silver and so on can be used as internal electrodes. If the sintering process can be improved in terms of reducing sintering temperature, it will not only have important technical and economic value in restraining, volatilizing, ensuring material performance, reducing environmental pollution and prolonging equipment life, but also be widely used in the primary sintering of multilayer piezoelectric ceramic components using pure silver level. At the same time, it saves energy. Therefore, the development of low temperature sintered piezoelectric ceramics has become an important research direction for the development of high performance, high reliability and low cost multilayer piezoelectric ceramic composites. At present, low temperature sintering methods include adding cosolvent method, superfine powder method, hot pressing sintering method, etc. The results show that the sintering temperature of ceramic powders synthesized by hydrothermal method is lower than that of powders without sintering aids by adding trace plasma into the powders. The sintering temperature of powders synthesized by hydrothermal method is lower than that of powders prepared by conventional solid-state method. The original piezoelectric ceramics based on piezoelectric ceramics are the sintering temperature of the ceramics can be greatly reduced by adding glass to the ceramics, and the piezoelectric and dielectric properties of the ceramics can be improved. In addition, they also think that the ceramics prepared by the method have good piezoelectric properties when they sintering ceramics in the following way. It is found that ceramics have the best dielectric and piezoelectric properties at medium temperature.
          
Relative permittivity,        
Piezoelectric strain constant,       
The electromechanical coupling coefficient,         
The mechanical quality factor,         
Dielectric loss.      

   

  These characteristics are especially suitable for high-power devices, such as ultrasonic motors, piezoelectric converters, motor transducers and other electronic devices. Because piezoelectric ceramics have high hardness, high brittleness and are difficult to process. Therefore, the fabrication of piezoelectric ceramics with complex structures has always been a difficult problem. The gel casting process of piezoelectric ceramics is used to solve the problems that need to be solved in the preparation of piezoelectric ceramics. Through comparison, it is concluded that different dispersants have great influence on the electrical properties of ceramics, and the density of gel casting is higher and more uniform than that of ordinary dry pressing. Low temperature sintered piezoelectric ceramics also inhibit the diffusion of silver ions into the ceramics during sintering and silver infiltration. Ceramics belong to insulating medium. Only polarized ceramics have piezoelectric properties. But ceramics can't be polarized directly like metals, they must be metallized first and the upper electrode. The polarization of piezoelectric ceramics directly affects the properties of ceramics. The polarization problem of ceramics is solved by low temperature sintering and silver infiltration method and chemical silver precipitation method. It is found that silver ions are seldom directed in the sintering process.


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