阅读说明：本技术 一种铁电晶体单轴压下压电系数的测量装置及方法 (Device and method for measuring piezoelectric coefficient under uniaxial depression of ferroelectric crystal ) 是由 赵小东 徐卓 田昊 乔辽 李飞 杨静雅 于 2021-04-23 设计创作，主要内容包括：本发明提供的一种铁电晶体单轴压下压电系数的测量装置及方法,包括用于安装待测样品的夹具、用于获取设定电压下的待测样品位移量的数据采集单元、用于向待测样品提供直流电压的外电场单元,以及分别与数据采集单元和外电场单元连接的控制系统；本系统能够避免现有方法中涉及的单轴压力与低频交变力的叠加的问题,同时,能够无损失的传递位移,保证了测试精度。(The invention provides a device and a method for measuring piezoelectric coefficient under uniaxial depression of a ferroelectric crystal, which comprises a clamp for mounting a sample to be measured, a data acquisition unit for acquiring displacement of the sample to be measured under set voltage, an external electric field unit for providing direct current voltage for the sample to be measured, and a control system respectively connected with the data acquisition unit and the external electric field unit; the system can avoid the problem of superposition of uniaxial pressure and low-frequency alternating force related in the existing method, and meanwhile, the displacement can be transmitted without loss, so that the test precision is ensured.)

1. The device for measuring the piezoelectric coefficient under the uniaxial depression of the ferroelectric crystal is characterized by comprising a clamp (2) for mounting a sample to be measured, a data acquisition unit for acquiring the displacement of the sample to be measured under set voltage, an external electric field unit for providing direct-current voltage for the sample to be measured, and a control system respectively connected with the data acquisition unit and the external electric field unit.

2. The device for measuring the uniaxial pressing piezoelectric coefficient of the ferroelectric crystal as claimed in claim 1, wherein the data acquisition unit comprises a capacitance micrometer test probe (1), and the capacitance micrometer test probe (1) is connected with the displacement test point of the clamp (2).

3. The device for measuring the uniaxial pressing piezoelectric coefficient of the ferroelectric crystal according to claim 1, wherein the external electric field unit is a direct current high voltage source (6), and an output end of the direct current high voltage source (6) is connected with two ends of an electrode of a sample (4) to be measured.

4. The device for measuring the uniaxial pressing piezoelectric coefficient of the ferroelectric crystal according to claim 1, wherein the clamp (2) comprises a bottom plate (201), an alumina electrode plate (3), a displacement transmission plate (202), a force application spring (203), a stress panel (204) and a locking nut (205), wherein a support frame is arranged on the bottom plate (201), and the displacement transmission plate (202) and the stress panel (204) are arranged on the support frame in sequence from bottom to top;

the sample (4) to be detected is arranged between the bottom plate (201) and the displacement transfer plate (202), and the upper and lower polar surfaces of the sample (4) to be detected are respectively contacted with the electrode surfaces of the two aluminum oxide electrode plates (3);

a force application spring (203) is arranged between the displacement transfer plate (202) and the stress panel (204), and the force application spring (203) is sleeved on the support frame;

the supporting frame is also provided with a locking nut (205), wherein the locking nut (205) is arranged above the stressed panel (204);

a rigid metal rod (206) is arranged on the displacement transfer plate (202), and a displacement test point is arranged at the top of the rigid metal rod (206); the data acquisition unit is connected with the displacement test point.

5. The device for measuring uniaxial pressing piezoelectric coefficient of a ferroelectric crystal as claimed in claim 4, wherein said supporting frame comprises three metal rods (206), and said three metal rods (206) are arranged in a triangular structure.

6. A device for measuring uniaxial depression piezoelectric coefficient of a ferroelectric crystal as in claim 4, wherein said aluminum oxide electrode sheet (3) has a lead wire on its electrode surface, and said lead wire is connected to an external electric field unit.

7. A method for measuring piezoelectric coefficient under uniaxial pressure of a ferroelectric crystal is characterized in that the device for measuring piezoelectric coefficient under uniaxial pressure of a ferroelectric crystal is based on any one of claims 1 to 6, and comprises the following steps:

applying direct-current voltages with different uniaxial pressures and different voltages to the polarized ferroelectric single crystal (6) to be detected to enable the polarized sample (4) to be detected to generate mechanical deformation vibration;

measuring mechanical deformation under variable uniaxial pressure and variable direct current voltage, and further calculating to obtain piezoelectric constants under different uniaxial pressures and different voltages;

and performing linear fitting on the obtained piezoelectric constants under different uniaxial pressures and different voltages to obtain the piezoelectric coefficient of the sample (4) to be detected.

8. The method for measuring the piezoelectric coefficient under the uniaxial pressure of the ferroelectric crystal according to the step 7 is characterized by comprising the following steps of:

step 1, applying a set uniaxial pressure to a polarized sample to be detected (4);

step 2, keeping the uniaxial pressure unchanged; then applying direct current voltages with different amplitudes to the sample (4) to be detected to obtain a displacement-voltage curve under the single axis;

step 3, changing uniaxial pressure applied to the polarized sample to be detected (4);

step 4, repeating the step 2 and the step 3 until the applied uniaxial pressure reaches the uniaxial pressure upper limit value required by the process, and obtaining displacement-voltage curves under different uniaxial pressures;

step 5, calculating piezoelectric constants under different uniaxial pressures and different voltages according to the obtained displacement-voltage curves under different uniaxial pressures;

and 6, fitting the obtained piezoelectric constants under different uniaxial pressures and different voltages to obtain the piezoelectric coefficient of the sample (4) to be detected.

Technical Field

The invention relates to the technical field of representing piezoelectric coefficients under uniaxial depression of ferroelectric crystals, in particular to a device and a method for measuring piezoelectric coefficients under uniaxial depression of ferroelectric crystals.

Background

Ferroelectric crystals, such as lead magnesium niobate-lead titanate (PMN-PT) and lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT), have been widely regarded by ferroelectric researchers all over the world due to their excellent piezoelectric and electromechanical, optical, acoustical and ferroelectric properties and the ability to achieve interconversion between various functional properties, and thus have been widely used in the fields of ultrasonic transducers, piezoelectric sensors, hydrophones, ferroelectric memories, electro-optical modulators, and the like.

Piezoelectric coefficient d under uniaxial pressure of ferroelectric material₃₃Is the piezoelectric strain constant, which is one of the most common important parameters for characterizing the piezoelectric performance of piezoelectric materials, i.e. the polarization intensity component generated on the crystal plane perpendicular to the z-axis when the ferroelectric single crystal is only stressed along the z-direction. The ferroelectric crystal is usually required to work under a uniaxial pressure state in engineering application, and the influence of the uniaxial pressure on the piezoelectric performance of the ferroelectric crystal is an important factor which must be considered in the engineering application of the ferroelectric crystal, so the piezoelectric coefficient under the uniaxial pressure is an important parameter of the ferroelectric.

At present, three methods, namely a quasi-static method, a dynamic method and a static method, are generally used for measuring the longitudinal piezoelectric coefficient. The quasi-static method and the static method have the same testing principle, but the force loading mode is changed from constant force to low-frequency alternating force. Because the longitudinal piezoelectric coefficient of the material under uniaxial pressure needs to be tested, for uniaxial pressure, low-frequency alternating force applied by a quasi-static method needs to be superposed under the uniaxial pressure to be a small mechanical signal actually, and due to the combined action of two forces, the low-frequency alternating force has small contribution to the piezoelectric effect and is difficult to distinguish, so that the method is not suitable for measuring the longitudinal piezoelectric coefficient under uniaxial pressure. The dynamic method is also called as a resonance-antiresonance method, and the impedance spectrum of a material needs to be tested, and the resonance frequency and the antiresonance frequency are found out so as to calculate and obtain the longitudinal piezoelectric coefficient. The method is only suitable for lossless conditions, when the material is under uniaxial pressure and is in a clamping state, the phase angle is far away from 90 degrees, impedance spectrum distortion is caused, and resonance and anti-resonance frequency are difficult to distinguish, so that the method is not suitable for measuring the longitudinal piezoelectric coefficient under the uniaxial pressure.

Disclosure of Invention

The invention aims to provide a device and a method for measuring a piezoelectric coefficient of a ferroelectric crystal under uniaxial pressure, which solve the problem that the conventional ferroelectric crystal has inaccurate piezoelectric coefficient under uniaxial pressure.

In order to achieve the purpose, the invention adopts the technical scheme that:

the invention provides a device for measuring piezoelectric coefficient under uniaxial pressure of a ferroelectric crystal, which comprises a clamp for mounting a sample to be measured, a data acquisition unit for acquiring displacement of the sample to be measured under set voltage, an external electric field unit for providing direct current voltage for the sample to be measured, and a control system respectively connected with the data acquisition unit and the external electric field unit.

Preferably, the data acquisition unit comprises a capacitance micrometer test probe, and the capacitance micrometer test probe is connected with the displacement test point of the clamp.

Preferably, the external electric field unit is a direct current high voltage source, and an output end of the direct current high voltage source is connected to two ends of an electrode of the sample to be measured.

Preferably, the clamp comprises a bottom plate, an aluminum oxide electrode plate, a displacement transfer plate, a force application spring, a stress panel and a locking nut, wherein a support frame is arranged on the bottom plate, and the displacement transfer plate and the stress panel are sequentially arranged on the support frame from bottom to top;

the sample to be detected is arranged between the bottom plate and the displacement transfer plate, and the upper and lower pole faces of the sample to be detected are respectively contacted with the electrode faces of the two aluminum oxide electrode plates;

a force application spring is arranged between the displacement transfer plate and the stress panel and sleeved on the support frame;

the supporting frame is also provided with a locking nut, wherein the locking nut is arranged above the stressed panel;

a rigid metal rod is arranged on the displacement transfer plate, and a displacement test point is arranged at the top of the rigid metal rod; the data acquisition unit is connected with the displacement test point.

Preferably, the support frame comprises three metal rods, and the three metal rods are arranged in a triangular structure.

Preferably, the electrode surface of the aluminum oxide electrode plate is provided with a lead, and the lead is connected with an external electric field unit.

A method for measuring piezoelectric coefficient under uniaxial pressure of a ferroelectric crystal is based on a device for measuring piezoelectric coefficient under uniaxial pressure of a ferroelectric crystal, and comprises the following steps:

applying direct-current voltages with different uniaxial pressures and different voltages to the polarized sample to be detected so as to enable the polarized sample to be detected to generate mechanical deformation vibration;

by measuring mechanical deformation under the variable uniaxial pressure and the variable direct current voltage, piezoelectric constants under different uniaxial pressures and different voltages are calculated;

and performing linear fitting on the obtained piezoelectric constants under different uniaxial pressures and different voltages to obtain the piezoelectric coefficient of the sample to be measured.

Preferably, the method comprises the following steps:

step 1, applying a set uniaxial pressure to a polarized sample to be detected;

step 2, keeping the uniaxial pressure unchanged; then applying direct current voltages with different amplitudes to the sample to be tested to obtain a displacement-voltage curve under the single axis;

step 3, changing uniaxial pressure applied to the polarized sample to be tested;

step 4, repeating the step 2 and the step 3 until the applied uniaxial pressure reaches the uniaxial pressure upper limit value required by the process, and obtaining displacement-voltage curves under different uniaxial pressures;

step 5, calculating piezoelectric constants under different uniaxial pressures and different voltages according to the obtained displacement-voltage curves under different uniaxial pressures;

and 6, fitting the obtained piezoelectric constants under different uniaxial pressures and different voltages to obtain the piezoelectric coefficient of the sample to be measured.

Compared with the prior art, the invention has the beneficial effects that:

the existing quasi-static method test actually utilizes the positive piezoelectric effect of the piezoelectric material, takes low-frequency alternating force as excitation, and takes the release of charges as response. The piezoelectric coefficient is calculated by applying low-frequency alternating force and collecting released charges, but under uniaxial pressure, the low-frequency alternating force is actually a small dynamic signal, and because the two forces act together, the low-frequency alternating force has small contribution to the piezoelectric effect and is difficult to distinguish, so that the method is not suitable for measuring the longitudinal piezoelectric coefficient under uniaxial pressure. The invention actually utilizes the inverse piezoelectric effect of the piezoelectric material, takes an electric field as excitation and strain as response, induces the crystal to deform by applying the electric field to the ferroelectric crystal under the state of applying uniaxial pressure, and calculates the piezoelectric coefficient of the crystal by measuring the deformation. This avoids the superposition of uniaxial pressure and low frequency alternating forces involved in the quasi-static method. In addition, compared with the collection and quantification of charges, the deformation test is easier to test under the existing conditions, and the test is more accurate.

According to the device for measuring the piezoelectric coefficient under the uniaxial pressure of the ferroelectric crystal, provided by the invention, stable uniaxial pressure is applied to a sample to be measured through the clamp, so that the sample is prevented from cracking or being damaged due to the sudden increase of the uniaxial pressure; meanwhile, the electrical system can be ensured to be insulated from the rigid metal clamp, and finally, the clamp is completely rigid, so that the displacement can be transmitted without loss, and the testing precision is ensured.

Further, this anchor clamps have used the structure that spring and screw combined together, through screw locking power, stable axial pressure is applyed to the sample to the mode of spring transmission, because the both ends elasticity of spring can not suddenly change, can avoid because of the sample fracture or the damage that the unipolar pressure suddenly increases and lead to.

Furthermore, the clamp applies voltage to a sample to be tested by using an aluminum oxide electrode plate, and the structure of single-side gold plating can apply voltage to the sample, and simultaneously ensures that an electrical system and a rigid metal clamp are insulated, so that lossless transfer displacement can be realized, and the test precision is ensured.

Drawings

FIG. 1 is a schematic view of a measuring device according to the present invention;

FIG. 2 is a schematic view of a digital display press according to the present invention

FIG. 3 is a front view of a special fixture for uniaxial pressing test according to the present invention;

FIG. 4 is a top view of the special fixture for uniaxial pressing test according to the present invention;

FIG. 5 is a schematic view of an alumina electrode plate according to the present invention;

FIG. 6 is a flow chart of the test of the present invention

FIG. 7 is a graph of piezoelectric coefficient-electric field curves of a PIN-PMN-PT relaxed ferroelectric single crystal polarized in the [001] direction under different uniaxial pressures;

FIG. 8 is a linear fitting graph of longitudinal piezoelectric coefficients (20 MPa for example) at different voltages;

FIG. 9 is a graph showing piezoelectric coefficients of a PIN-PMN-PT relaxed ferroelectric single crystal polarized in the [001] direction under different uniaxial pressures.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

As shown in fig. 1, the device for measuring the uniaxial depression piezoelectric coefficient of a ferroelectric crystal provided by the present invention comprises a capacitance micrometer test probe 1, a clamp, a sample 4 to be tested, a capacitance micrometer display panel 5 and a direct current high voltage source 6, wherein an output end of the direct current high voltage source 6 is connected to two ends of an electrode of the sample 4 to be tested and provides a direct current voltage for the sample; the capacitance micrometer test probe 1 is connected with the displacement test point on the clamp 2, and the output is connected with the capacitance micrometer display panel 5 to obtain the ferroelectric crystal displacement under a certain voltage.

As shown in fig. 2, the uniaxial pressing press 7 according to the present invention.

As shown in fig. 3 and 4, the uniaxial pressure test fixture 2 according to the present invention includes a bottom plate 201, a displacement transmission plate 202, an application spring 203, a force-receiving panel 204, and a locking nut 205, wherein the bottom plate 201 is provided with a support frame, and the displacement transmission plate 202 and the force-receiving panel 204 are sequentially provided on the support frame from bottom to top.

The sample 4 to be detected is arranged between the bottom plate 201 and the displacement transfer plate 202, and the upper and lower polar surfaces of the sample 4 to be detected are respectively connected with the alumina electrode slice 3.

A force application spring 203 is arranged between the displacement transmission plate 202 and the force bearing panel 204, and the force application spring 203 is sleeved on the support frame.

The support frame is further provided with a locking nut 205, wherein the locking nut 205 is arranged above the stressed panel 204.

The support frame comprises three metal rods 207, and the three metal rods 207 are arranged in a triangular structure; the upper portion of each metal rod 207 is provided with external threads which function to support the entire clamp and to lock pressure in cooperation with a locking nut.

The displacement transmission plate 202 is provided with a rigid metal rod 206, and the rigid metal rod 206 is disposed at the center of the displacement transmission plate 202.

The top of the rigid metal rod 206 is provided with a displacement test point.

The free end of the rigid metal rod 206 is placed over the force-bearing face plate through the force-bearing face plate 204.

The center of the stress panel 204 is provided with a connecting pipe, and the free end of the connecting pipe is connected with a single-shaft pressure machine. The free end of the rigid metal rod 206 fits within the connecting tube.

As shown in fig. 5, the aluminum oxide electrode plate 3 is an aluminum oxide sheet with a very smooth surface, a silver electrode is plated on one side, and a lead is led out from the silver electrode; the structure firstly provides an electrical test electrode for a sample 4 to be tested, secondly ensures the insulation of an electrical system and the outside by single-side silver plating, and thirdly, because the aluminum oxide has very high rigidity, the aluminum oxide also serves as a medium for displacement transmission.

The force application spring applies uniaxial pressure to the displacement transmission plate and then to the sample due to the interaction principle of force. The force-bearing panel is used for receiving pressure applied by the digital display press. The locking nut locks the pressure at a preset value while the digital display press applies the pressure.

The invention provides a method for measuring piezoelectric coefficient of a ferroelectric crystal under uniaxial pressure, which comprises the following steps:

applying direct-current voltages with different uniaxial pressures and different voltages to the polarized sample to be detected so as to enable the polarized sample to be detected to generate mechanical deformation vibration;

by measuring mechanical deformation under the variable uniaxial pressure and the variable direct current voltage, piezoelectric constants under different uniaxial pressures and different voltages are calculated;

and performing linear fitting on the obtained piezoelectric constants under different uniaxial pressures and different voltages to obtain the piezoelectric coefficient of the sample to be measured.

Preferably, in step 2, a digital display manual press is used for applying a certain uniaxial pressure to the ferroelectric crystal, and the pressure is tested by using a screw on a uniaxial pressure test fixture;

preferably, in step 3, a direct current electric field is applied to the ferroelectric crystal by using a direct current high-voltage source;

preferably, in step 4, the displacement of the ferroelectric crystal under different electric fields is obtained by using a contact capacitance micrometer;

preferably, in step 5, the piezoelectric coefficient under uniaxial pressure of the ferroelectric crystal is calculated according to the electric field applied in step 4 and the displacement obtained in step 4 by:

and calculating the ratio of the displacement to the voltage to obtain the piezoelectric coefficients of the ferroelectric crystal under different uniaxial pressures.

As shown in FIG. 6, the method for using the device for measuring the piezoelectric coefficient under the uniaxial pressure of the ferroelectric crystal comprises the following steps:

step 1, preparing a sample to be measured, and measuring the thickness h and the area s;

step 2, testing the clamp according to the graph of FIG. 4, putting a sample in the clamp and ensuring that the contact between the sample electrode and the alumina electrode is good;

and 3, calculating to obtain the relation between the required pressure and kilograms according to the definition of the pressure and the unit relation of the press: for an area of 1cm²For the sample of (1), 1MPa corresponds to 10 kg of the press machine, and according to this relationship, uniaxial pressure is applied. The specific operation steps are as follows: placing the clamp on an operation table of a press machine, pressing a force application rod downwards, observing a display meter, keeping when the pressure reaches a set numerical value, and screwing a locking nut until the uniaxial pressure application process is finished;

step 4, placing the sample and the clamp after force application on a vibration reduction table, adjusting the positions of the vibration reduction table and a capacitance micrometer test probe to enable the probe to be suspended above the displacement test point, connecting an electrode lead with a high-voltage source, and finally adjusting a zero setting button on the capacitance micrometer test probe and a display panel to enable the panel to display zero;

and 5, turning on the direct-current high-voltage source, gradually increasing the voltage in a certain range, and reading the displacement value on the display panel of the capacitance micrometer after the voltage is increased every time. So far, a displacement-voltage curve under the uniaxial pressure can be obtained;

step 6, repeating the steps 3 to 5 until the applied pressure reaches the required upper pressure limit, and obtaining displacement-voltage curves under different uniaxial pressures;

step 7, from d₃₃The piezoelectric constants under different voltages under different uniaxial voltages are calculated as displacement/voltage, and the crystal is in a polarization state due to a pressurization test, so that the piezoelectric coefficient of the material (without the voltage) is finally obtained by fitting the piezoelectric coefficients under different voltages. The specific fitting method is linear fitting, a test result under a certain uniaxial pressure is selected, a piezoelectric coefficient-voltage curve is fitted by taking voltage as a horizontal coordinate and piezoelectric coefficient as a vertical coordinate, and the intercept of the line on a vertical axis is the piezoelectric coefficient of the material per se under different uniaxial pressures.

The sample measurement method is convenient and easy to control, high in safety and capable of completing the piezoelectric coefficient test work of the ferroelectric crystal under the uniaxial pressure.

The test was carried out using a [001] polarized PIN-PMN-PT relaxed ferroelectric single crystal as a sample.

Example one

A method for measuring piezoelectric coefficient under uniaxial pressure of a ferroelectric crystal comprises the following steps:

step one, performing crystallographic orientation on the PIN-PMN-PT relaxation ferroelectric single crystal by using X-ray diffraction, then cutting according to the crystallographic direction to obtain [001] oriented crystal, wherein the crystal size is 7.5mm by 8mm by 3mm, the thickness direction of 3mm is the direction of applying a direct current electric field to the ferroelectric crystal, after the crystal is processed by an electrode, polarizing the crystal along the thickness direction by adopting a 1kV/mm direct current electric field to obtain the ferroelectric crystal 8

Step two, preparing a sample to be tested, and testingThe thickness is 3mm and the area is 0.6cm²；

Step three, according to the test fixture shown in the figure 4, a sample is placed into the test fixture, and a universal meter is used for testing whether the lead is conducted with the silver electrode on the aluminum oxide electrode plate or not, so that the conduction is ensured, the contact is good, and the resistance of two ends is not more than 3 ohms;

and step three, calculating to obtain the relation between the required pressure and kilograms according to the definition of the pressure and the unit relation of the press: 1MPa corresponds to a pressure of 6 Kg. The gradient is 5MPa, the highest pressure is 30MPa, and the applied pressure is 0, 30, 60, 90, 120, 150 and 180Kg, which corresponds to the uniaxial pressure of 0, 5, 10, 15, 20, 25 and 30 MPa. According to this relationship, uniaxial pressure is applied. The specific operation steps are as follows: placing the clamp on an operation table of a press machine, pressing a force application rod downwards, observing a display meter, keeping when the pressure reaches a set numerical value, and screwing a locking nut until the uniaxial pressure application process is finished;

and step four, placing the sample and the clamp after force application on a vibration reduction table, and adjusting the vibration reduction table by taking the level gauge as a reference to ensure the level of the vibration reduction table surface. Adjusting the positions of the clamp and the capacitance micrometer test probe to enable the probe to be just suspended above the displacement test point;

connecting the electrode lead with a high-voltage source, and finally adjusting a probe of the capacitance micrometer and a zero setting button on the display panel to enable the panel to display zero;

and step six, turning on the direct-current high-voltage source, gradually increasing the voltage by taking 300V as a gradient, and reading the displacement value on the display panel of the capacitance micrometer after increasing the voltage every time. So far, a displacement-voltage curve under the uniaxial pressure can be obtained;

step six, repeating the step three to the step five until the applied pressure reaches the required upper pressure limit, and obtaining displacement-voltage curves under different uniaxial pressures;

step seven, by₃₃And (3) calculating piezoelectric constants under different uniaxial pressures and different voltages as displacement/voltage, and fitting to obtain the piezoelectric constant of the material.

The test results of this example are given in fig. 7-9. FIG. 7 shows piezoelectricity of a relaxor ferroelectric single crystal at different voltagesCoefficient-uniaxial pressure curve. It can be seen that the d of the relaxor ferroelectric single crystal increases with the uniaxial pressure₃₃Decrease rapidly and with the same uniaxial reduction d₃₃As the test voltage increases, the increase tends to be approximately linear. FIG. 8 shows d at 20MPa for example₃₃A fitted curve of voltage, the linear fitting of which results in good linearity and reliable results, giving the d of the material itself at zero voltage₃₃Is 59 pC/N. Using the same fitting method, the d of the relaxor ferroelectric single crystal under 0-30MPa uniaxial pressure is obtained₃₃As shown in FIG. 9, d is increased with increase in uniaxial pressure₃₃The reduction rate is continuously reduced, the reduction rate is first large and then small, and the reduction rate is reduced along with the increase of the uniaxial pressure.