Piezoelectric ceramic high-temperature polarization device
Piezoelectric ceramics as an important functional materials has been more widely used. Piezoelectric ceramics by polarized ferroelectric ceramics obtained. The ferroelectric ceramics potential applications of piezoelectric polarization process by improving the ability to obtain adequate mining, has become a topic of great interest to people.
Under normal circumstances, the polarization of the perfect program often subject to strong polarization field, polarization and polarization time temperature and other process factors. Under the premise of material properties allow to improve the polarization field strength and temperature, polarization will contribute to the extension of time tends to completely polarized, but the polarization of the polarization field strength improved facilities will make demanding, but also so the failure rate increased polarization of the sample; impact polarization time of polarization exponential relationship, after polarization rate of about 90 percent to extend the time for the polarization is no longer effective in improving the rate of production and the anti-efficiency is significantly reduced; polarized ferroelectric domain of temperature will increase mobility, polarization is easy, but it also increases the leak guide, the breakdown field strength decreased significantly.
2 high temperature polarization mechanism and process
Polarization refers to the usual high temperature polarization process compared to the polarization temperature is higher, the degree of polarization of a piezoelectric ceramic more complete polarization process. And also the mechanism of polarization different from the conventional process; using conventional techniques at a certain temperature, the applied electric poling field is turned domain; the temperature of the ferroelectric polarization of the ceramic paraelectric - ferroelectric phase transition with conducted under the conditions of the external electric field. Therefore, the essence of the high temperature phase change process of polarization is occurring in the external electric field oriented along the electrical domain, complete the "field ordering paraelectric - ferroelectric phase transition."
Since the field-induced ordering of the paraelectric - ferroelectric phase transition ferroelectric domain ordering is conducive to complete, and even if a small portion of the formation 180 degrees, 90 degree domain, but also because at the higher temperature domain wall mobility and easy large steering, easy-polarization trend completely. If this is almost entirely orderly arrangement of ferroelectric domain structure of the cooling effect of external electric field under the conditions of maintaining such an orderly structure was completely "frozen", the polarization effect will become completely fixed.
We conducted a large number of test results show that the poling temperature can be appropriately increased greatly facilitate the stage of the polarization, the polarization field strength is also reduced so that a number of (e.g. at a high temperature lower than the polarization field strength 0.2V / um can be obtained conventional polarization process 3V / um polarization field strength of polarization effects), which is sufficient to remedy the insulation resistance of the sample due to temperature drop caused by the shortcomings that may arise, which shows the feasibility of high-temperature polarization. In particular, the line of the direction of polarization of the sample size, from the perspective of safety and efficiency of the process to see. More practical significance.
In the course of our study, using a variety of programs on several samples polarization process test, the test results from the processing of data analysis: Polarization temperature should be slightly higher than the Curie temperature of the ferroelectric polarization sample; polarization field strength should electromechanical coupling coefficient ratio - the polarization field strength corresponding to a turning point in the curve to flatten slightly higher field strength; boost cooling rate in the sample breakdown field strength characteristics permitting try to get higher, the temperature should be lower termination polarization in a sample of the ferroelectric Curie temperature of 100 degrees. Such measures can increase the polarization effect, and help solve problems with the conventional process for a large degree of polarization direction of the line size of the sample is difficult to polarization.
In order to meet the needs of different types of polarization condition ferroelectric ceramics sample selection, we designed and developed a high-temperature polarization test device and evaluate the effects of polarization test analysis program. We developed the test using polarization can be measured sequentially ferroelectric Curie temperature of the sample by adjusting the selector switch and adjust the potentiometer and select polarization temperature, the sample was measured breakdown field intensity, polarization voltage selection of the sample and polarization time, the test to determine the boost cooling (maintaining the voltage on the sample) rate of the polarized, thereby selecting the polarization of the sample at high temperature process parameters.
The test device is a prototype of the high-temperature polarization polarization devices, as long as the removal of the Curie temperature of the test part on the basis of the test apparatus, the increasing polarization voltage controllable range and power, can become a useful high temperature of equipment.
Design Concept 3 polarization test device
Compared with conventional polarization conditions provide polarization equipment, test equipment for high-temperature polarization polarization should have the following characteristics:
Temperature is higher than the polarization of the ferroelectric Curie temperature of the sample temperature and the drying conditions, and clean the porcelain surface of the guide may be a negligible leakage, so that the whole polarization process may be performed in air, insulating oil sump can save design.
To adapt to different temperature ferroelectric Habitat types of ferroelectric ceramics, device temperature controlled heating chamber should range from room temperature to 500 degrees. Taking into account the influence of the heater structure, size, material thermal conductivity and thermal resistance and other factors, such as the heating rate in order to meet the requirements of the heating power of the heater should be selected in 200-1500W and continuously adjustable.
Given the temperature increases, the volume of the ferroelectric ceramic material conductivity is increased leakage, high breakdown field of the sample was significantly reduced, and the completion of the polarization field reduction at high temperature strength than the conventional polarization down more, the line of the direction of polarization in order to meet polarization of different sample sizes needed and taking into account temperature and polarization polarization field strength of the connection between the polarization voltage range should be in the tens of kilovolts and continuously adjustable supremacy.
The polarization direction of the line is sandwiched between samples of different sizes, the spacing holding fixture should be adjusted.
Heaters should have some insulation properties, but reduce the thermal inertia parties to obtain the desired cooling rate, the heater should be a smaller amount equivalent heat easily (ie, the material is smaller than the heat, use less) and take appropriate forced cooling (air) system.
To stably maintain the effect of the high temperature polarization, with the decrease of temperature, with sample volume of the polarization voltage drop and increase the drain conductance. Depending on its characteristics should follow the temperature characteristics of the ferroelectric ceramic material volume resistivity varies, should be equipped with adjustable polarization voltage coefficient follow - follow the polarization temperature systems.
As a fumble polarization condition of the sample, individual breakdown damage may occur, should be set with the sample number corresponding breakdown alarm indication on the device control panel.
