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Process of piezoelectric ceramics transducer transformer

Views:2     Author:Site Editor     Publish Time: 2019-09-04      Origin:Site

The production and research of piezoelectric ceramic materials for high-power piezoelectric transformers In the research of piezoelectric ceramic materials, China's research is relatively backward. According to statistics, in the six years of 1997-2002, among the more than 60 patents published in China for piezoelectric ceramics and their applications, there were about 50 applications , of which only accounted for nearly 80 of them.there are 2 items in Korea, and there are only 4 items in China, of which only one is expected to be applied to piezoelectric transformers. In recent years, although no other foreign companies have submitted patents on the research and application of piezoelectric ceramic materials in China, they can be used to manufacture PZT-based piezoelectric ceramics for high power piezoelectric ceramic transformers. It can be used to manufacture piezoelectric transformers with output power above 30W. It has been successfully applied to fluorescent lamps for daily usage. Ferroperm's PZT-based Pz24 has also been successfully applied to high-power transducers. Although in our country, some research institutes have used piezoelectric materials based on NEC materials to prepare piezoelectric transformers with output power below low (but the situation of piezoelectric ceramics research and application is still not optimistic.

Since multi-layer piezoelectric ceramic transformers are easy to achieve miniaturization and high power output, some researchers at home and abroad often adopt the multi-layer structure in the research of piezoelectric transformers. The simplest Rosen-type multilayer piezoelectric ceramic transformer structure can be considered as the composite and simplified process in a thickness direction by a plurality of single-piece rosen-type piezoelectric ceramic transformers. The input end is alternately laminated and fired by a piezoelectric ceramic disc and an electrode material, which inevitably involves a co-firing problem between the piezo ceramic material and the electrode material. At present, many PZT piezo ceramic materials for piezoelectric transformers have a problem of excessively high temperature ( > 11000C) in the production of multilayer piezoelectric ceramic transformers, it is necessary to use a higher proportion of electrode materials containing precious metals. In the production of piezoelectric transformers, the cost of electrode materials for about 2/3 of the total cost. Therefore, in order to reduce the production cost, the piezoelectric material of the piezoelectric transformer  is imperative, but the anti-oxidation performance of the base metal under high temperature is extremely poor. Due to the simplicity and economy of the process, most piezoelectric device manufacturers in China currently use oxidizing atmosphere sintering during production. When the sintering temperature is above 1100° C, the base metal such as Ni is easily oxidized, which increases the contact resistance between the electrode and the ceramic material and has a great negative influence on the device. In the current situation , there are two ways to "ruthenium metallization" of piezoelectric device electrodes: First, under the condition that the performance of the device is not affected, the sintering temperature of the piezo ceramic material used is appropriately reduced, thereby reducing the current domestic .The amount of precious metal piezo ceramic is used in the widely silver electrode material; the second is the thorough "ruthenium metallization" adopted, which is sintered in a reducing atmosphere. The realization of the second way for China's current electronic piezo ceramics production, the difficulty is very large. Because most of China's current electronic ceramics production plant, the use of step-type kiln oxidizing atmosphere. Achieving a reductive sintering means a substantial replacement of the original equipment, which is obviously unbearable for the electronic piezo ceramics production in China, which has a late start. Therefore, achieving low-grade burning is one of the research directions of high-power piezoelectric transformer materials. Such a performance of the existing lead-free materials is not satisfactory. Although in the field of piezoelectric research, the use of lead-free materials to replace existing PT or PZT materials is the future trend, and it is difficult to achieve in the short term due to the existing scientific and technological conditions. At the same time, Qm and Kp of pure PZT materials are a pair of mutually restrictive factors, one high and the other one must be low. Therefore, in the research field of high-power piezoelectric materials, researchers' eyes are mostly concentrated on lead lanthanum manate (PMS), lead nimanate (PMN), lead zinc niobate (PZN) and other components and PZT. Research on ternary, quaternary or multivariate systems. From the above examples, it can be seen that the high-power piezoelectric ceramics have the following characteristics in terms of composition: the main components of high-power piezoelectric ceramics are mainly PZT, and the Zr/Ti ratio is near the quasi-homophase boundary. This is mainly due to the existence of a quasi-homophase boundary between the relaxed ferroelectric complex and PZT piezo. Due to the existence of the quasi-homogeneous phase boundary, there is a large adjustment space for the selection and design of the material composition and performance. The new research results on the quasi-homophase boundary also show that C20-221: there exists a monoclinic ferroelectric phase at the quasi-homophase boundary, and the polar axis of the monoclinic ferroelectric phase can be between them. In any direction, so that in the material of the composition near the quasi-homophase boundary, the deflection of the domain during polarization is easier, and the piezoelectric properties of the material near the quasi-homophase boundary are optimal. Since the curie temperature of the relaxed ferroelectrics is relatively low, such as: Pb (Z n, /3Nb2/3), its Tc = 1400C, so in order to ensure that the material has a higher Tc temperature, the PZT content in these systems is higher.

High power components are added on top of the principal component, such as PMS, PMN, PZ N, etc. Moreover, the piezo elements contained in these modified addition components tend to have both "donor" and "acceptor" functions. It is known from the knowledge of piezoelectricity that the doping element is added to the PZT in the donor state, which promotes the generation of cation vacancies, which is beneficial to the rotation of the domain during polarization, and the material becomes "soft"; otherwise, if the doping piezo element is entering into the PZT in the state promotes the generation of oxygen vacancies and is not conducive to the rotation of the domains, and the PZT material is relatively hard. Eventually, due to the different doping, the properties of the material occur in two distinct variations. In addition, proper "soft" or "hard" doping of PZT-based materials will also contribute to the overall anti-aging properties of the material . It is a comparison of the properties of “soft”ceramics and “hard”ceramic. From the comparison, we can see that when it is preparing high power piezoelectric ceramics, PZT ceramic is simply doped with “donor” or “acceptor” elements. Miscellaneous, it is difficult to meet the requirements of "double high" and "double low" for high-power piezoelectric materials. Therefore, it is necessary to "two-pronged", that is, doping modification of PZT (including "main addition element" - a doping piezo element added in the form of a relaxing ferroelectric, and "additional element" added in an oxidized form. When the piezo element is doped, a certain amount of piezo elements having donor and acceptor doping effects are incorporated in a certain ratio, so that the material achieves the best performance in the interaction of the two doping effects. As in the examples listed above, the "auxiliary addition" element or the combination of Ni manganese, Nie Zinc and Bismuth Manganese. In addition, when it is necessary to make a separate adjustment to the "soft" or "hard" properties of the material during the research process, it is also possible to select some elements such as Ming. Such a trace can sometimes also prevent the growth of crystal grains during sintering, and the performance can be optimized when a plurality of doping piezo ceramic sensor is properly matched. Moreover, the proper selection of the "main plus" and "auxiliary" elements can also form a transition liquid phase in combination with lead during the sintering process of the porcelain, so that the material can be sintered into porcelain at a lower temperature to lower the sintering temperature.

Through the above analysis, the following principles are available for the selection and design of materials for high-power piezoelectric ceramic transformers:

(1) The main component material is selected by PZT to ensure that the material has a high . The temperature can finally be guaranteed to have a wide operating temperature range for the piezoelectric transformer;
(2) The main component Zr/Ti ratio should be selected near the quasi-homophase boundary to ensure good piezoelectric activity of the material;
(3) Forming a multi-component material to adjust and enhance the material by using a relaxed ferroelectric material or piezo element having both a "donor" and an "acceptor" doping function as an "auxiliary" element or a third or fourth component. It is comprehensive performance
(4) Appropriately selected“auxiliary elements”, such as silver and antimony, can prevent the growth of crystal grains during sintering, which is beneficial to obtain fine-grained ceramics and improve the overall performance of the materials.

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