Bismuth layered high-temperature piezoelectric ceramic polarization method and application thereof

Abstract

The invention relates to polarization of a high-temperature piezoelectric ceramic material, in particular to a polarization method and application of bismuth layered high-temperature piezoelectric ceramic. The method comprises the following steps: putting bismuth layered high-temperature piezoelectric ceramic into silicone oil, and heating; applying a plurality of pulse voltages to the bismuth layered high-temperature piezoelectric ceramics, wherein the electric field intensity of the pulse voltages is iEc / N; after the pulse voltage is finished, increasing the electric field intensity of the polarization voltage to iEc / N, and keeping the polarization voltage for continuous polarization; maintaining the polarization voltage, reducing the temperature of the silicone oil to normal temperature, then reducing the polarization voltage to zero, taking out the bismuth-layered high-temperature piezoelectric ceramic from the silicone oil, and removing surface oil stains through ultrasonic cleaning; according to the invention, the pulse voltage is applied before continuous polarization to activate the ferroelectric domain in the ceramic, the energy barrier required by the overturning of the ferroelectric domain in the continuous polarization process is reduced, and the full polarization of the bismuth layered high-temperature piezoelectric ceramic is realized in combination with a multi-step polarization method, so that the piezoelectric property and the temperature stability of the ceramic are greatly improved.

Description

Technical Field

[0001] The present application relates to the polarization of high-temperature piezoelectric ceramic materials, and in particular to a polarization method of bismuth layered high-temperature piezoelectric ceramics and applications thereof. Background Art

[0002] Since bismuth layered high-temperature piezoelectric ceramics have the advantages of high Curie temperature and temperature stability, they are widely used in aerospace, nuclear energy and other fields, becoming the core material for high-temperature devices such as high-temperature piezoelectric vibration sensors and filters.

[0003] Bismuth layered high-temperature piezoelectric ceramics have a high coercive field (~10kV / mm), which makes it difficult to fully polarize them through conventional polarization methods, thus limiting the further improvement of their piezoelectric performance and temperature stability. Traditional polarization methods usually use a period of polarization high voltage, which may not be able to fully excite all the electric domains in the piezoelectric ceramics, resulting in less than ideal polarization effects; and different piezoelectric ceramic materials may require different polarization conditions, and a fixed period of polarization high voltage may not be able to meet the polarization requirements of all materials.

[0004] At present, patent CN111900246A has designed a method for multiple polarization of lead-free piezoelectric ceramics, and patent CN113956073A has designed a method for improving the piezoelectric stability of bismuth layered piezoelectric ceramics. Although the piezoelectric performance or piezoelectric stability of ceramics can be improved by multiple polarization of ceramics or by high-temperature aging treatment and repolarization after polarization, these methods have obvious defects. On the one hand, the high coercive field makes it difficult to flip the ferroelectric domain, and it is difficult to achieve full polarization even under high voltage; on the other hand, a period of polarization high voltage can easily cause a sharp increase in leakage current, resulting in an increased risk of ceramic breakdown, which seriously affects the success rate and reliability of the product. Summary of the invention

[0005] In order to solve the problems existing in the prior art, this patent provides a bismuth layered high-temperature piezoelectric ceramic polarization method and its application, so that the bismuth layered high-temperature piezoelectric ceramic can be fully polarized to meet the application requirements of high piezoelectric performance and high temperature stability of high-temperature piezoelectric ceramics.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] In the first aspect of the present application, the present application proposes a polarization method for bismuth layered high temperature piezoelectric ceramics, which is specifically as follows:

[0008] S1: Preparation before polarization: put the bismuth layered high-temperature piezoelectric ceramic into silicone oil and heat it up;

[0009] S2: During polarization: multiple pulse voltages are applied to the bismuth layered high temperature piezoelectric ceramics, and the electric field strength of the pulse voltage is iE c / N; After the pulse voltage ends, increase the electric field strength of the polarization voltage to iE c / N, maintain the polarization voltage for continuous polarization; E c It represents the electric field strength of the ceramic coercive field, i represents the current polarization times, and N represents the total number of polarizations;

[0010] S3: End after polarization: maintain the polarization voltage, reduce the silicone oil temperature to room temperature, then reduce the polarization voltage to zero, take out the bismuth layered high-temperature piezoelectric ceramics from the silicone oil, and remove the surface oil stains by ultrasonic cleaning.

[0011] Furthermore, in step S1, the temperature of the silicone oil is raised to 120-180°C at a rate of 3-10°C / min.

[0012] Furthermore, in step S2, the number of pulse voltages is at least 3, the time interval between the pulse voltages is less than 10 seconds, and the duration of the pulse voltages is 1-10 seconds.

[0013] Furthermore, in step S2, the electric field strength of the pulse voltage is gradually increased to iE c / N, the electric field strength of each pulse voltage gradually increases.

[0014] Furthermore, in step S2, the polarization voltage is maintained for 5-60 minutes.

[0015] Further, in step S2, the electric field strength of the polarization voltage is gradually increased to iE c / N.

[0016] In the second aspect of the present application, the present application provides an application of a bismuth layered high-temperature piezoelectric ceramic, and the application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic as described in the first aspect of the present invention in a high-temperature acceleration sensor.

[0017] In the third aspect of the present application, the present application provides an application of a bismuth layered high-temperature piezoelectric ceramic, and the application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic as described in the first aspect of the present invention in a high-temperature piezoelectric transducer.

[0018] In the fourth aspect of the present application, the present application provides an application of a bismuth layered high-temperature piezoelectric ceramic, and the application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic as described in the first aspect of the present invention in a high-temperature piezoelectric driver.

[0019] Beneficial effects of the present invention:

[0020] 1. The present invention aims to solve the problem that bismuth layered high-temperature piezoelectric ceramics have a high coercive field (~10kV / mm) and are difficult to fully polarize. The present invention activates the ferroelectric domains inside the ceramics by applying a pulse voltage before continuous polarization, thereby reducing the energy barrier required for the ferroelectric domain flipping during the continuous polarization process. Combined with a multi-step polarization method, the present invention achieves full polarization of the bismuth layered high-temperature piezoelectric ceramics, thereby greatly improving the piezoelectric properties and temperature stability of the ceramics.

[0021] 2. In order to solve the ceramic breakdown problem caused by the instantaneous excessive leakage current caused by the one-stage polarization high-voltage method used in the prior art, the present invention proposes a multi-stage polarization method, which decomposes the polarization process into multiple stages to achieve multi-level sustained release of the leakage current of piezoelectric ceramics during the polarization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart of a polarization method of a bismuth layered high-temperature piezoelectric ceramic according to an embodiment of the present application;

[0023] Figure 2 A flow chart of a polarization method of a bismuth layered high-temperature piezoelectric ceramic according to another embodiment of the present application;

[0024] Figure 3 This is a schematic diagram of non-increasing pulse multi-segment polarization of Example 1 of the present application;

[0025] Figure 4 This is a schematic diagram of the incremental pulse multi-segment polarization of Example 2 of the present application;

[0026] Figure 5 This is a schematic diagram of pulse-free multi-segment polarization according to Example 3 of the present application;

[0027] Figure 6 A schematic diagram of a single-segment polarization for a comparative example of the present application;

[0028] Figure 7 This is a comparison chart of the high-temperature stability of piezoelectric constants of piezoelectric ceramics polarized in different polarization methods. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Polarization electric field, polarization temperature and polarization time are three key elements in the polarization process. They are interrelated and influence each other, and together determine the quality of the polarization effect. In the polarization process, the parameters of these three elements need to be strictly controlled to obtain the best polarization effect and piezoelectric performance.

[0031] Polarization electric field: Polarization electric field is one of the most important factors in the polarization process, which determines the direction and arrangement of electric domains. Under the action of the polarization electric field, the electric domains will be oriented and arranged, forming a macroscopic polarization effect. The intensity, direction and application method of the polarization electric field will affect the polarization effect. Generally speaking, the stronger the polarization electric field, the greater the effect of oriented arrangement of electric domains, the better the polarization effect of the material, and the better the piezoelectric performance obtained. However, too high an electric field strength may cause breakdown or damage to piezoelectric ceramics, so it is necessary to select the polarization electric field strength within an appropriate range.

[0032] Polarization temperature: Polarization temperature is another important factor that affects the polarization effect. During the polarization process, appropriate temperature can shorten the polarization time and improve the polarization efficiency. As the temperature increases, the anisotropy of the crystal structure decreases, the resistance to the electric domain turning becomes smaller, and it is conducive to the orientation and arrangement of the electric domain along the direction of the electric field. At the same time, the volume resistivity of the material decreases at high temperatures, making the space charge polarization easy to disappear under the action of the electric field, further promoting the turning and arrangement of the electric domain. However, too high a temperature may cause the Curie temperature of the piezoelectric ceramic to decrease or generate thermal stress, thereby affecting its performance. Therefore, polarization needs to be carried out within a suitable temperature range.

[0033] Polarization time: Polarization time refers to the heat preservation and pressure holding time required for ceramic products to change from one equilibrium state to another. The length of polarization time will affect whether the electric domain is fully arranged. Generally speaking, the longer the polarization time, the higher the degree of directional arrangement of the electric domain, and the better the polarization effect. However, the polarization time is different for different materials. At the same time, the stronger the electric field and the higher the temperature, the shorter the polarization time. If the material has better density and high breakdown strength, it can be carried out under a high polarization electric field, and the polarization time can be shortened; if the insulation resistance of the material is low, high-temperature polarization is easy to break down, the polarization temperature can be appropriately reduced, and the polarization time can be appropriately extended. Therefore, it is necessary to determine the appropriate polarization time according to the specific material and polarization conditions.

[0034] On the basis of the above three elements, this embodiment further defines the number of polarization segments, which refers to the number of stages in which the applied electric field strength changes with time during the polarization process. The polarization process includes three stages: boost, hold, and buck. The combination and sequence of these stages constitute the so-called "polarization segment".

[0035] The present application proposes a polarization method for bismuth layered high-temperature piezoelectric ceramics, which optimizes the polarization electric field, polarization temperature, polarization time and polarization segment number, so that the bismuth layered high-temperature piezoelectric ceramics can be fully polarized to meet the application requirements of high-voltage electrical performance and high temperature stability of high-temperature piezoelectric ceramics.

[0036] Bismuth layered high temperature piezoelectric ceramics are a type of ceramic material with ferroelectric properties, which have important applications in the manufacture of piezoelectric components under high temperature and high frequency working conditions. It is a type of ferroelectric ceramic material with a special layered structure. This type of material usually has a low dielectric constant, a high spontaneous polarization intensity, a high Curie temperature, a high mechanical quality factor, and good piezoelectric and dielectric properties. The following is an exemplary description of the process of the polarization method of bismuth layered high temperature piezoelectric ceramics.

[0037] Figure 1 Flow chart of the polarization method of the bismuth layered high temperature piezoelectric ceramic of the embodiment of the present application; Figure 1 As shown, the method includes:

[0038] S11: Preparation before polarization: put the bismuth layered high-temperature piezoelectric ceramic into silicone oil and heat it up;

[0039] S12: During polarization: multiple pulse voltages are applied to the bismuth layered high temperature piezoelectric ceramics, and the electric field strength of the pulse voltage is iE c / N; After the pulse voltage ends, increase the electric field strength of the polarization voltage to iE c / N, maintain the polarization voltage for continuous polarization; E c It represents the electric field strength of the ceramic coercive field, i represents the current polarization times, and N represents the total number of polarizations;

[0040] S13: End after polarization: maintain the polarization voltage, reduce the silicone oil temperature to room temperature, then reduce the polarization voltage to zero, take out the bismuth layered high-temperature piezoelectric ceramics from the silicone oil, and remove the surface oil stains by ultrasonic cleaning.

[0041] Figure 2 This is a flow chart of a polarization method of a bismuth layered high temperature piezoelectric ceramic according to another embodiment of the present application; Figure 2 As shown, the method includes:

[0042] S21: Preparation before polarization: put the bismuth layered high-temperature piezoelectric ceramic into silicone oil and heat it up;

[0043] S22: During the first polarization, multiple pulse voltages are applied to the bismuth layered high temperature piezoelectric ceramics, and the electric field strength of the pulse voltage is E c / 3; After the pulse voltage ends, increase the electric field strength of the polarization voltage to E c / 3, maintain the polarization voltage for continuous polarization; E c Indicates the electric field strength of the ceramic coercive field;

[0044] S23: During the second polarization, multiple pulse voltages are applied to the bismuth layered high temperature piezoelectric ceramics, and the electric field strength of the pulse voltage is 2E c / 3; After the pulse voltage ends, increase the electric field strength of the polarization voltage to E c / 3, maintain the polarization voltage for continuous polarization;

[0045] S24: During the third polarization, multiple pulse voltages are applied to the bismuth layered high temperature piezoelectric ceramics, and the electric field strength of the pulse voltage is E c ; After the pulse voltage ends, increase the electric field strength of the polarization voltage to E c , maintain the polarization voltage for continuous polarization;

[0046] S25: End after polarization: maintain the polarization voltage, reduce the temperature of the silicone oil to room temperature, then reduce the polarization voltage to zero, take out the bismuth layered high-temperature piezoelectric ceramics from the silicone oil, and remove the surface oil stains by ultrasonic cleaning.

[0047] In an optional embodiment, in step S11 or S21, the temperature of the silicone oil is raised to 120-180° C. at a rate of 3-10° C. / min. It may also be preferably raised to 150° C. at a rate of 5° C. / min.

[0048] It should be noted that the total number of polarizations N≥3. The above embodiment shows three polarizations. In actual application, multiple polarizations greater than three can also be used. Accordingly, the electric field strength of the pulse voltage and the electric field strength of the polarization voltage will be adjusted accordingly according to the ceramic coercive field and the number of polarization segments (polarization times).

[0049] In an optional embodiment, in step S12 or S22, the number of pulse voltages is at least 3, the time interval of the pulse voltages is less than 10 seconds, the duration of the pulse voltages is 1-10 seconds, and the polarization voltage holding time is 5-60 minutes.

[0050] In an optional embodiment, in step S12 or S22, the electric field strength of the pulse voltage is directly increased to iE c / N. For example, suppose E c =12kV / mm, a total of three polarizations N=3 are set, in the first polarization i=1, the first pulse is 4kV / mm, and the next pulse after an interval of 1S is still 4kV / mm. By applying a pulse voltage before continuous polarization to activate the ferroelectric domain inside the ceramic, the energy barrier required for the ferroelectric domain flipping during the continuous polarization process is reduced, thereby reducing the leakage current caused by the ferroelectric domain flipping during the continuous polarization process and improving the polarization success rate.

[0051] In an optional embodiment, in step S12 or S22, the electric field strength of the pulse voltage is gradually increased to iE c / N, the electric field strength of each pulse voltage gradually increases. For example, assuming E c=12kV / mm, a total of three polarizations N=3 are set, in the first polarization i=1, the first pulse is 2kV / mm, the next pulse after an interval of 1S may be 3kV / mm, and the next pulse after an interval of 1S may be 4kV / mm; this method of asymptotically increasing the electric field strength can further reduce the energy barrier required for the ferroelectric domain reversal during the polarization process, realize the gradual reversal of the ferroelectric domain before continuous polarization, reduce the leakage current caused by the ferroelectric domain reversal during continuous polarization, and improve the polarization success rate.

[0052] In an optional embodiment, in step S12 or S22, the electric field strength of the polarization voltage is gradually increased to iE c / N. For example, let's assume that E c =12kV / mm, a total of three polarizations N=3 are set, in the first polarization, i=1, after the pulse voltage ends, the electric field strength of the pulse voltage recovers to 0, at this time the electric field strength of the polarization voltage needs to be gradually increased from 0 to 4kV / mm; similarly, in the second polarization, i=2, after the pulse voltage ends, the electric field strength of the pulse voltage recovers to 4kV / mm, at this time the electric field strength of the polarization voltage needs to be gradually increased from 4kV / mm to 8kV / mm; in the third polarization, i=3, after the pulse voltage ends, the electric field strength of the pulse voltage recovers to 8kV / mm, at this time the electric field strength of the polarization voltage needs to be gradually increased from 8kV / mm to 12kV / mm.

[0053] In some embodiments of the present application, the present application provides an application of a bismuth layered high-temperature piezoelectric ceramic, and an application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic in a high-temperature acceleration sensor.

[0054] In some embodiments of the present application, the present application provides an application of a bismuth layered high-temperature piezoelectric ceramic, and the application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic in a high-temperature piezoelectric transducer.

[0055] In some embodiments of the present application, the present application provides an application of a bismuth layered high-temperature piezoelectric ceramic, and an application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic in a high-temperature piezoelectric driver.

[0056] The following further exemplifies the present application in detail. It should also be understood that the following examples are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Some non-essential improvements and adjustments made by technicians in this field based on the above content of the present application belong to the scope of protection of the present application. The specific process parameters and the like in the following examples are only an example within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description of this article, and are not limited to the specific values ​​​​exemplified below. In the following embodiments, unless otherwise specified, normal temperature / room temperature generally refers to 25°C.

[0057] Embodiment 1:

[0058] like Figure 3 As shown, the polarization of the bismuth layered high temperature piezoelectric ceramics of this embodiment is carried out according to the following steps:

[0059] S101: placing a bismuth layered high-temperature piezoelectric ceramic sample into silicone oil, heating the silicone oil to 140°C at a rate of 5°C / min, and maintaining the temperature;

[0060] S102: applying three pulse voltages with an electric field strength of 4 kV / mm and an interval of 1 s to the piezoelectric ceramic, and setting the polarization electric field strength to 4 kV / mm for 10 min;

[0061] S103: applying three pulse voltages with an electric field strength of 8 kV / mm and an interval of 1 s to the piezoelectric ceramic, and setting the polarization electric field strength to 8 kV / mm for 10 min;

[0062] S104: applying three pulse voltages with an electric field strength of 12 kV / mm and an interval time of 1 s to the piezoelectric ceramic, and setting the polarization electric field strength to 12 kV / mm for 10 min;

[0063] S105: Keeping the polarization electric field strength unchanged, cooling the silicone oil to room temperature (25° C.), removing the electric field, taking the ceramic sample out of the silicone oil, and removing the silicone oil on the surface;

[0064] S106: After being placed in the air for 24 hours, the piezoelectric properties are measured using a quasi-static piezoelectric constant tester, and the piezoelectric constant at room temperature is found to be 20 pC / N;

[0065] S107: The ceramics are annealed at 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C for 2h, and their piezoelectric properties are measured after cooling to room temperature. The piezoelectric constants after annealing are 20pC / N, 20pC / N, 20pC / N, 20pC / N, 20pC / N, and 19pC / N, respectively.

[0066] Embodiment 2:

[0067] like Figure 4 As shown, the polarization of the bismuth layered high temperature piezoelectric ceramics of this embodiment is carried out according to the following steps:

[0068] S201: placing a bismuth layered high temperature piezoelectric ceramic sample into silicone oil, heating the silicone oil to 140°C at a rate of 5°C / min, and maintaining the temperature;

[0069] S202: applying three pulse voltages with electric field strengths of 2 kV / mm, 3 kV / mm, and 4 kV / mm, respectively, with an interval time of 1 s to the piezoelectric ceramic, and setting the polarization electric field strength to 4 kV / mm for 10 min;

[0070] S203: applying three pulse voltages with electric field strengths of 4 kV / mm, 6 kV / mm, and 8 kV / mm, respectively, with an interval of 1 s to the piezoelectric ceramic, and setting the polarization electric field strength to 8 kV / mm for 10 min;

[0071] S204: applying three pulse voltages with electric field strengths of 6 kV / mm, 9 kV / mm, and 12 kV / mm, respectively, with an interval time of 1 s to the piezoelectric ceramic, and setting the polarization electric field strength to 12 kV / mm for 10 min;

[0072] S205: Keeping the electric field strength unchanged, cooling the silicone oil to room temperature (25° C.), removing the electric field, taking the ceramic sample out of the silicone oil, and removing the silicone oil on the surface;

[0073] S206: After being placed in the air for 24 hours, the piezoelectric properties are measured using a quasi-static piezoelectric constant tester, and the piezoelectric constant at room temperature is found to be 19 pC / N;

[0074] S207: Anneal the ceramics at 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C for 2h, and measure their piezoelectric properties after cooling to room temperature. The piezoelectric constants after annealing are 20pC / N, 20pC / N, 20pC / N, 20pC / N, 20pC / N, and 20pC / N, respectively.

[0075] Embodiment 3:

[0076] like Figure 5 As shown, the polarization of the bismuth layered high temperature piezoelectric ceramics of this embodiment is carried out according to the following steps:

[0077] S301: placing a bismuth layered high temperature piezoelectric ceramic sample into silicone oil, heating the silicone oil to 140°C at a rate of 5°C / min, and maintaining the temperature;

[0078] S302: setting the polarization electric field strength to 4 kV / mm and maintaining it for 10 min;

[0079] S303: setting the polarization electric field strength to 8 kV / mm and maintaining it for 10 min;

[0080] S304: setting the polarization electric field strength to 12 kV / mm and maintaining it for 10 min;

[0081] S305: Keeping the electric field strength unchanged, cooling the silicone oil to room temperature (25° C.), removing the electric field, taking the ceramic sample out of the silicone oil, and removing the silicone oil on the surface;

[0082] S306: After being placed in the air for 24 hours, the piezoelectric properties are measured using a quasi-static piezoelectric constant tester, and the piezoelectric constant at room temperature is found to be 19 pC / N;

[0083] S307: The ceramics are annealed at 100°C, 200°C, 300°C, 400°C, 500°C and 600°C for 2h, and their piezoelectric properties are measured after cooling to room temperature. The piezoelectric constants after annealing are 19pC / N, 19pC / N, 19pC / N, 19pC / N, 18pC / N and 17pC / N, respectively.

[0084] Comparative Example:

[0085] like Figure 6 As shown, compared with Examples 1, 2 and 3, the polarization of the bismuth layered high temperature piezoelectric ceramics in this comparative example is carried out according to the following steps:

[0086] S401: placing a bismuth layered high temperature piezoelectric ceramic sample into silicone oil, heating the silicone oil to 140°C at a rate of 5°C / min, and maintaining the temperature;

[0087] S402: setting the polarization electric field strength to 12 kV / mm and maintaining it for 30 min;

[0088] S403: Keeping the electric field strength unchanged, cooling the silicone oil to room temperature (25° C.), removing the electric field, taking the ceramic sample out of the silicone oil, and removing the silicone oil on the surface;

[0089] S404: After being placed in the air for 24 hours, the piezoelectric properties are measured using a quasi-static piezoelectric constant tester, and the piezoelectric constant at room temperature is found to be 17 pC / N;

[0090] S405: The ceramics are annealed at 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C for 2h, and their piezoelectric properties are measured after cooling to room temperature. The piezoelectric constants after annealing are 17pC / N, 17pC / N, 17pC / N, 17pC / N, 16pC / N, and 14pC / N, respectively.

[0091] like Figure 7As shown, the piezoelectric performance and temperature stability of Example 2 are the best, the piezoelectric performance and temperature stability of Example 1 are the second, the piezoelectric performance and temperature stability of Example 3 are the third, and the piezoelectric performance of the comparative example is the worst; this shows that the present invention decomposes the polarization process into multiple stages to achieve multi-stage sustained release of leakage current of piezoelectric ceramics during polarization. By applying a pulse voltage before continuous polarization to activate the ferroelectric domain inside the ceramic, the energy barrier required for the ferroelectric domain flipping during continuous polarization is reduced, and the method of multi-step polarization is combined to achieve full polarization of bismuth layered high-temperature piezoelectric ceramics, so that the piezoelectric performance and temperature stability of the ceramics are greatly improved.

[0092] In the embodiment of the present invention, after testing, the piezoelectric constant of the ceramic is increased from 17pC / N of ordinary polarization to 20pC / N, the piezoelectric performance is improved by 18%, and the temperature stability of the piezoelectric constant in the temperature range of 25-600°C is increased from 17% to 5%. The product success rate of the bismuth layered high-temperature piezoelectric ceramic after multi-stage polarization is greatly improved. After testing, 200 pieces of ceramics were selected for polarization respectively, and the product polarization success rate was increased from 60% of ordinary polarization to 95%.

[0093] In summary, the polarization method of the present invention reasonably plans the polarization conditions, that is, controls the polarization temperature, electric field strength, duration and number of segments, controls the number, interval and electric field strength of the pulse voltage, and adopts a multi-step polarization method, so that the final bismuth layered high-temperature piezoelectric ceramic has excellent piezoelectric properties and temperature stability.

[0094] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polarization method for bismuth layered high temperature piezoelectric ceramics, characterized in that: The specific steps are as follows: S1: Preparation before polarization: put the bismuth layered high-temperature piezoelectric ceramic into silicone oil and heat it up; S2: During polarization: multiple pulse voltages are applied to the bismuth layered high temperature piezoelectric ceramics, and the electric field strength of the pulse voltage is iE c / N; After the pulse voltage ends, increase the electric field strength of the polarization voltage to iE c / N, maintain the polarization voltage for continuous polarization; E c It represents the electric field strength of the ceramic coercive field, i represents the current polarization times, and N represents the total number of polarizations; S3: End after polarization: maintain the polarization voltage, reduce the silicone oil temperature to room temperature, then reduce the polarization voltage to zero, take out the bismuth layered high-temperature piezoelectric ceramics from the silicone oil, and remove the surface oil stains by ultrasonic cleaning.

2. The polarization method of bismuth layered high temperature piezoelectric ceramics according to claim 1, characterized in that: In step S1, the temperature of the silicone oil is raised to 120-180°C at a rate of 3-10°C / min.

3. The polarization method of bismuth layered high temperature piezoelectric ceramics according to claim 1, characterized in that: In step S2, the total number of polarizations N≥3.

4. The polarization method of bismuth layered high temperature piezoelectric ceramics according to claim 1, characterized in that: In step S2, the number of pulse voltages is at least 3, the time interval between the pulse voltages is less than 10 seconds, and the duration of the pulse voltages is 1-10 seconds.

5. The polarization method of bismuth layered high temperature piezoelectric ceramics according to claim 1 or 4, characterized in that: In step S2, the electric field strength of the pulse voltage is gradually increased to iE c / N, the electric field strength of each pulse voltage gradually increases.

6. The polarization method of bismuth layered high temperature piezoelectric ceramics according to claim 1, characterized in that: In step S2, the polarization voltage is maintained for 5-60 minutes.

7. The polarization method of bismuth layered high temperature piezoelectric ceramics according to claim 1 or 6, characterized in that: In step S2, the electric field strength of the polarization voltage is gradually increased to iE c / N.

8. An application of a bismuth layered high temperature piezoelectric ceramic, characterized in that: Application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic as described in any one of claims 1 to 7 in a high-temperature acceleration sensor.

9. An application of a bismuth layered high temperature piezoelectric ceramic, characterized in that: Application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic as described in any one of claims 1 to 7 in a high-temperature piezoelectric transducer.

10. An application of a bismuth layered high temperature piezoelectric ceramic, characterized in that: Application of the bismuth layered high-temperature piezoelectric ceramic obtained by the polarization method of the bismuth layered high-temperature piezoelectric ceramic as described in any one of claim 17 in a high-temperature piezoelectric driver.

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