the impacts of polarization conditions on the piezoelectric ceramics

Polarization conditions have a greater impact on the performance of piezoelectric ceramics, the polarization electric field is the main factor in the polarization conditions. Theoretically, when the conical piezoelectric transducers applied electric field exceeds the coercive field strength, most of the domains should be redirected and polarized rearranged to complete polarization, but under such an electric field, even if polarized for a long time, piezoelectric ceramic transducers can not be obtained better piezoelectric performance. In order to give full play to the piezoelectric properties of materials, the electric field of ultrasound piezoelectric sensormust be added to the saturation field strength, the value of the coercive field strength is 3 to 4 times, so the coercive field is the polarization of the lower limit of the selected electric field, the saturation field strength. You can think of the upper limit of the field of polarization, more than the saturation field strength of thickness mode vibration is easy to find breakdown. After comprehensive consideration, Determining the best polarization process parameters of 6. 5MHz is piezoelectric ceramic filter: polarization electric field intensity is 2. 2kV / mm, the polarization temperature is 130 ℃, on this basis to determine the best pole ,The time is 15 min.Experimental results show that when the polarization time of working piezoelectric sensor exceeds 15 min to improve the piezoelectric properties of the role is not obvious. Experiments also found that in the process of silver burning silver paste with low temperature conductive paste instead of commonly used high-temperature silver paste, to a certain extent, to improve the mechanical properties of piezo knock sensor piezoelectric ceramic , but the bonding strength is lower, and the cost is more high,which is not suitable for industrial production. During the sintering process, it was found that the ceramic sheets fired at temperatures above 1,250 ° C and holding time is longer than 2 h were prone to breakdown during polarization, resulting in the increase of the number of lobes. This is because the higher the firing temperature, the longer the holding time generally results in severe recrystallization, so that smaller grains become large grains, which often results in increased porosities of the ceramic and a decrease in the density of the ceramic , So that its mechanical strength and dielectric constant decreased, while reducing the mechanical quality factor ceramic.