Effect of Polarization Temperature on Piezoelectric Properties(一)
Piezoelectric properties of piezo ceramic crystal
E = 2.0 kV / mm, t = 15 min under the conditions of changing the piezoelectric T polarization, with the increase of T, d33 began to increase faster When the polarization temperature reaches 130 ℃, the value of d33 remains basically unchanged. Because piezoelectric ceramics is at lower temperatures, as the temperature increases, the crystallographic axial ratio c / a becomes smaller and the activity of the domains increases. As a result, the internal stress due to the electric field inversion at 90°decreases, that is, the electric steering of piezo discs and cylinders
is affected ,The resistance piezo ceramic for ultrasonic welding
becomes smaller, domains are easy to align, so polarization is easier. When T reaches 130℃, most of the piezo disc with P4 material
is completed turning to saturation, so the value of d33 no longer changes. 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 applied electric field exceeds the coercive field strength, most should be redirected rearranged to complete polarization, but under such an electric field, even if polarized for a long time, they can not be obtained better piezoelectric performance. In order to give full to the 1Mhz piezo disc piezoelectric properties of materials, the electric field must be added to the saturation field strength, the value of the coercive field strength is 3 to 4 times, therefore, the coercive field of cylinder piezoelectric sensor is the lower limit of the polarization in the selected electric field, the saturation of field strength is field of polarization, if more than the saturation field strength ,it is easy to find breakdown. After comprehensive consideration, determining the best polarization process parameters is 6. 5MHz .For piezoelectric ceramic filter, Intensity of polarization electric field 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 to improve the piezoelectric properties when the polarization time exceeds 15 min, the role is not obvious. high temperature piezoceramic is also found that in the process of silver burning silver silver paste with low temperature conductive paste instead of commonly high-temperature silver paste, to a certain extent, to improve the piezoelectric ceramic and mechanical properties, but the bonding strength is lower, and the cost is more high, it is not suitable for industrial production.