Views: 4 Author: Site Editor Publish Time: 2020-03-16 Origin: Site
Comparison of density, dielectric constant and piezoelectric coefficient of PZN-PZ-PT ceramic film obtained by casting method and dry pressing method:
The figure shows the static voltage-displacement characteristic curve of the PZT multilayer chip piezoelectric ceramic micro-actuator in the longitudinal displacement mode. From this curve, it can be seen that when the applied voltage gradually increases and then returns to zero, the device starts As shown in equation (1), the displacement is generated in a linear and quasi-linear manner, and then shifted in a non-linear manner; when the voltage decreases from the maximum voltage, its displacement no longer returns as the original displacement, but a displacement lag occurs. This hysteresis relationship between voltage and displacement is an important feature of PZT-based flexible stock piezoceramic ring displacement devices. The reason for this voltage-displacement hysteresis is related to the crystal structure and electric domain structure of PZT-based piezoelectric ceramics. Because PZT piezo crystal structure of the piezoelectric ceramics is a perovskite structure, and its lattice constants of a and c axes are different; when the piezoelectric ceramics are polarized, there are still many 90 electric domains in the crystals. In a low electric field (The corresponding voltage is also relatively low), the displacement of piezoelectric ceramics is mainly due to the polarization of the electric dipole under the action of the electric field, so that the change in its polarization intensity is combined with the electrostrictive effect, or inverse electrical effect causes its linear mechanical displacement; however, when the piezoelectric ceramic is subjected to a high electric field, the 90 domains in the crystal begin to turn, so that the a and c axes of the unequal lattice constants cause the The displacement of piezoelectric ceramics increases non-linearly in the direction parallel to or perpendicular to the electric field. When the voltage decreases from the maximum value, there are two reversible and irreversible domains in the 90 domains. These irreversible domains exist. This makes the piezoelectric ceramics appear hysteresis loop phenomenon of voltage-displacement.
The piezoelectric performance of each piezoelectric ceramic layer in the chip piezoelectric ceramic micro-actuator is intuitively evaluated. When the multilayer chip piezoelectric ceramic micro-actuator is applied with a voltage of 2.3 V (the electric field is 50 V / mm, it is close to the electric domain turning and threshold electric field), the device generates a total displacement of about 0.04 μm. When the electric domain steering is considered to have a small effect on piezoelectric strain, the average piezoelectric strain of each piezoelectric ceramic layer can be calculated from equation (2) The coefficient d33≈500pC / N. This value is basically close to the value of d33 listed . Therefore, it can be considered that the piezoelectric performance of the monolithic piezoceramic cylinder transducer developed in this work has reached the monolithic cast ceramic film and bulk.
The results of the figure also show that the multilayer chip piezoelectric ceramic microactuator can produce a large displacement of about 1 μm under the relatively low operating voltage of 38V, but the device size is very small. Therefore, this device can be applied to some high-tech fields with low operating voltage, large displacement, and small device size, hard disk drives require small device size and operating voltage <12V. When is using PZT piezo series flexible piezoelectric ceramics, When the reverse voltage or electric field in the opposite direction is changed, it is easy to cause the depolarization of the piezoelectric ceramics,which is reducing the piezoelectric performance and reducing the displacement. Therefore, multi-layer chip devices are usually operated with a unidirectional positive voltage. Multi-layer chip device of unidirectional sinusoidal AC voltage waveform and its dynamic displacement response spectrum. From the displacement response curve shown in the figure, it can be seen that the multi-layer chip device has a unidirectional sinusoidal AC current at a peak-peak 12V and a frequency of 1kHz. Under the action, the maximum displacement is 0.28μm, which is basically the same as the static displacement at 12V DC, it is indicating that under 250V / mm electric field, there is no obvious dependence between its displacement and frequency. in addition, the dynamic displacement of the device is basically in the form of a sine wave, and the phase difference from the voltage is also very small (difficult to calculate the phase difference in the figure), indicating that the displacement of the multilayer device can follow the change of the electric field to produce displacement. Fact In the above, the performance of the above dynamic displacement is basically unchanged in the frequency range measuring from 100Hz to 5kHz, which can be seen from the displacement and phase difference spectrum curves of the multilayer chip device shown. The voltage waveform V = 6 (1 + sinωt), the dynamic displacement generated under the effect of different voltage frequencies hardly change with frequency, and its phase difference only changes around 5kHz.
2. The voltage-displacement characteristics of multilayer chip devices are related to the crystal structure and electric domain behavior of PZT piezoelectric ceramic materials under the action of electric fields. The electric domains can still turn well under the action of low-frequency electric fields, which is making the frequency range of 100Hz to 5kHz .The size of the internal dynamic displacement of piezoelectric ceramic cylinder remains basically unchanged.
3.Using the inverse piezoelectric effect to study the change law of the displacement caused by electric dipoles and domains under the action of an electric field is a good method to study the microscopic properties of a piezoelectric body and piezoelectric coefficient.
