Method for electric-field-induced strain enhancement of sodium bismuth titanate-based relaxor ferroelectrics

Abstract

The present application relates to the technical field of material, and discloses a method for enhancing the electrostriction of sodium bismuth titanate-based relaxor ferroelectric.The present application induces the original large-size non-percolating polar region in the percolating sodium bismuth titanate-based relaxor by pre-polarizing the sodium bismuth titanate-based relaxor ferroelectric ceramic near the critical position synthesized by the traditional solid-phase method, reduces the nucleation barrier in the field-induced strain process, and significantly enhances the electrostriction effect.The sodium bismuth titanate-based relaxor ferroelectric ceramic of the present application has obviously improved electrostriction under the excitation of 60 kV / cm electric field compared with the initial state, and has more excellent performance than the ordinary sodium bismuth titanate-based relaxor ferroelectric ceramic.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a method for enhancing electrostriction of sodium bismuth titanate-based relaxor ferroelectrics. BACKGROUND

[0002] The electromechanical conversion characteristics of piezoelectric materials have been widely used in various fields (such as aerospace, power engineering). Piezoelectric brake is an important branch of piezoelectric devices, which is related to the braking process in the mechanical driving process. Electrostriction is a very key performance of piezoelectric brake, including maximum strain, driving electric field, etc. At present, lead-based materials occupy the main market of piezoelectric brake, but considering the volatilization of toxic lead element in the preparation process of lead-based materials, it is urgent to develop lead-free high-performance piezoelectric materials to replace lead-based materials. According to the periodic table of elements, Bi 0.5 Na 0.5 TiO3(BNT) lead-free material is considered to be the best candidate material for brake devices, but the electrostriction performance of general BNT-based materials still has not small gap compared with traditional lead-based materials. It is relatively inefficient to select appropriate components to improve the electrostriction characteristics of BNT-based materials by using the traditional trial-and-error method, which hinders the industrialization process of lead-free piezoelectric brake.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] In order to solve the problems in the background art, the present application provides a method for enhancing electrostriction of sodium bismuth titanate-based relaxor ferroelectrics.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] The method for enhancing electrostriction of sodium bismuth titanate-based relaxor ferroelectrics comprises the following steps:

[0007] Surface metallization is performed on the synthesized sodium bismuth titanate-based relaxor ferroelectric;

[0008] Pre-polarization is performed on the sodium bismuth titanate-based relaxor ferroelectric after surface metallization by applying an alternating current field;

[0009] The voltage of the alternating current field is 1.4 times or more than the field-induced strain driving electric field value of the sodium bismuth titanate-based relaxor ferroelectric, and the frequency of the alternating current field is 3-5 Hz.

[0010] The sodium bismuth titanate-based relaxor ferroelectric is a sodium bismuth titanate-based solid solution material located at or near the critical state.

[0011] Preferably, the sodium bismuth titanate-based relaxor ferroelectric is synthesized by a conventional solid-phase method.

[0012] Preferably, the conventional solid-phase synthesis method comprises:

[0013] The raw materials of the sodium bismuth titanate-based relaxor ferroelectric are mixed and ball milled into a mixed slurry;

[0014] The mixed slurry is dried into a precursor powder;

[0015] Polyvinyl alcohol solution is added to the precursor powder for granulation and tabletting to obtain a ceramic green body;

[0016] After the polyvinyl alcohol solution in the ceramic green body is removed, the ceramic green body is sintered at a temperature increasing rate of 3-4 °C / min at 1130-1150 °C for 3-4 hours.

[0017] Preferably, the method for drying the mixed slurry into a precursor powder comprises: baking and compacting the mixed slurry, then increasing the temperature to 800-900 °C at a temperature increasing rate of 3-4 °C / min, and naturally cooling to room temperature after keeping the temperature for 4-6 hours.

[0018] Preferably, the ball milling time is 10-24 hours, and the rotation speed is 180 rpm.

[0019] Preferably, the mass percentage of the polyvinyl alcohol solution is 8-10%.

[0020] Preferably, the general formula of the sodium bismuth titanate-based relaxor ferroelectric is: (Bi 0.5 Na 0.4-x K 0.1 Li x ) 1-y Sr y Ti 1-z- m Ta z Zr m O3, wherein the value ranges of x, y, z and m are respectively 0 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.02, 0 ≤ z ≤ 0.015 and 0 ≤ m ≤ 0.02.

[0021] Preferably, the surface metallization is to coat the synthesized sodium bismuth titanate-based relaxor ferroelectric with a conductive electrode by means of screen printing or electroplating.

[0022] The application further discloses a sodium bismuth titanate-based relaxor ferroelectric obtained by using the electric strain enhancement method.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] The application induces the original large-size non-wandering polar region in the BiNaTiO3-based relaxor by the pre-polarization operation of the alternating electric field on the BiNaTiO3-based relaxor ferroelectric body in the critical state or near the critical state, reduces the nucleation barrier in the field-induced strain process, and significantly enhances the electrostrictive effect. The BiNaTiO3-based relaxor ferroelectric ceramic has obvious improvement in the electrostrictive effect under the electric field excitation of 60 kV / cm after simple treatment compared with the initial state, and has more excellent performance than the ordinary BiNaTiO3-based relaxor ferroelectric ceramic.

[0025] The BiNaTiO3-based relaxor ferroelectric body obtained by the application can maintain excellent electrostrictive characteristics even after aging, has the advantages of simplicity, stability and low cost, and can be popularized to large-scale industrial applications.

[0026] The process of the pre-polarization induced electrostrictive enhancement does not have other reaction steps, which helps researchers to comprehensively and deeply study the strain regulation mechanism of the BiNaTiO3-based relaxor ferroelectric body, so as to further design and optimize the BiNaTiO3-based relaxor ferroelectric body. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Bi 0.495 Na 0.396 K 0.099 Sr 0.01 Ti 0.99 Ta 0.01 Comparison of electrostrictive curves before and after pre-polarization;

[0028] Figure 2 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 Comparison of electrostrictive curves before and after pre-polarization;

[0029] Figure 3 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 Comparison of electrostrictive curves before and after pre-polarization;

[0030] Figure 4 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03X-ray diffraction (XRD) pattern comparison before and after pre-polarization;

[0031] Figure 5 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 X-ray diffraction (XRD) pattern comparison before and after pre-polarization when the applied pre-polarization voltage is substandard;

[0032] Figure 6 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 Change in electro-strain curve after aging;

[0033] Figure 7 Bi 0.5 Na 0.36 K 0.1 Li 0.04 Ti 0.94 Ta 0.06 X-ray diffraction (XRD) pattern comparison before and after pre-polarization;

[0034] Figure 8 Bi 0.4975 Na 0.3582 K 0.0995 Li 0.0398 Sr 0.005 Ti 0.95 Ta 0.05 X-ray diffraction (XRD) pattern comparison before and after pre-polarization;

[0035] Figure 9 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.995 Zr 0.005 X-ray diffraction (XRD) pattern comparison before and after pre-polarization;

[0036] Figure 10 Bi 0.4975 Na 0.36815 K 0.0995 Li 0.02985 Sr 0.005 Ti 0.995 Zr 0.005 X-ray diffraction (XRD) pattern comparison before and after pre-polarization. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be described in further detail below with reference to the specific embodiments. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present application. Moreover, in the following description, the description of well-known structures and techniques is omitted to avoid unnecessary confusion of the concept of the present application. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained by commercial purchase.

[0038] As a potential lead-free piezoelectric brake raw material, the research in the prior art is focused on improving the electric strain performance of sodium bismuth titanate-based relaxor ferroelectric ceramics. For sodium bismuth titanate-based materials, piezoelectric performance and electric strain performance cannot be obtained at the same time. The piezoelectric performance is directly related to the residual ferroelectricity after polarization, and for sodium bismuth titanate-based ferroelectric materials, the electric strain performance is mainly derived from a phase transition process, the size of the polar region is small, the residual ferroelectricity is weak, and the piezoelectricity can be almost ignored. In addition, for sodium bismuth titanate materials, the piezoelectricity is lower than other materials, and it is not meaningful to study the piezoelectricity, and more importantly, the electric strain characteristics are studied.

[0039] It should be noted that in the present application, "in or near the critical state" specifically refers to the mixed state of the sodium bismuth titanate-based material being traversed and non-traversed.

[0040] The present application is mainly to solve the bottleneck of scientific research and industry faced by the existing sodium bismuth titanate-based relaxor ferroelectric, and proposes a method for improving the electric strain of sodium bismuth titanate-based relaxor ferroelectric, that is, by pre-polarizing the sodium bismuth titanate-based relaxor ferroelectric ceramic in or near the critical state, there will be a certain large-size polar region in the sodium bismuth titanate-based ceramic material after pre-polarization. The large-size polar region reduces the nucleation barrier of the traversed relaxor micro-region in the field-induced strain process, promotes the phase transition process of relaxor-ferroelectric, and thus significantly enhances the electric strain effect. The sodium bismuth titanate-based relaxor ferroelectric prepared by the method can maintain excellent electric strain characteristics even after aging, which is very beneficial to the actual brake application. At the same time, there is no other reaction in the pre-polarization process, which helps researchers to comprehensively and deeply study the physical mechanism of strain regulation of sodium bismuth titanate-based relaxor ferroelectric, so as to further design and optimize the sodium bismuth titanate-based relaxor ferroelectric. The present application provides a simple, effective and low-cost electric strain enhancement method, which provides a new idea for the design and performance improvement of sodium bismuth titanate-based relaxor ferroelectric.

[0041] The embodiment of the present application provides an electric strain enhancement method for a sodium bismuth titanate-based relaxor ferroelectric, comprising the following steps: surface metallization of a synthesized sodium bismuth titanate-based relaxor ferroelectric; pre-polarization of the sodium bismuth titanate-based relaxor ferroelectric after surface metallization by applying an alternating current electric field; wherein the voltage of the alternating current electric field is 1.4 times or more than the field-induced strain driving electric field value of the sodium bismuth titanate-based relaxor ferroelectric, and the frequency of the alternating current electric field is 3-5 Hz; and the sodium bismuth titanate-based relaxor ferroelectric is a sodium bismuth titanate-based solid solution material at or near a critical state.

[0042] The sodium bismuth titanate-based relaxor ferroelectric at or near the critical state can ensure the reversibility of the electric strain and enhance the electric strain effect after inducing a large polar region. The present application forms a relatively large polar region in the relaxor sodium bismuth titanate-based material by controlling the intensity and frequency of the pre-polarization alternating current electric field, so as to reduce the nucleation barrier and enhance the field-induced strain effect.

[0043] It should be noted that the large-size polar region induced by the alternating current electric field is non-oriented and original. This is more conducive to the nucleation step in the subsequent field-induced phase change process and improves the electric strain effect.

[0044] For the field-induced strain driving electric field of the sodium bismuth titanate-based relaxor ferroelectric, the driving electric field of most sodium bismuth titanate-based ferroelectric ceramics at or near the critical state is between 30-50 kV / cm.

[0045] In some preferred modes, the surface metallization is to ensure the bonding strength and integrity of the electrode, and a conductive electrode is coated on the sintered ceramic material by screen printing or electroplating.

[0046] As some preferred modes, the general formula of the sodium bismuth titanate-based relaxor ferroelectric can be: (Bi 0.5 Na 0.4- x K 0.1 Li x ) 1-y Sr y Ti 1-z-m Ta z Zr m O3; wherein the value ranges of x, y, z and m are respectively 0 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.02, 0 ≤ z ≤ 0.015 and 0 ≤ m ≤ 0.02.

[0047] The preparation method of the sodium bismuth titanate-based relaxor ferroelectric is not particularly limited, as long as the prepared sodium bismuth titanate-based relaxor ferroelectric ceramic is in a critical state or near the critical state. As some preferred embodiments, the sodium bismuth titanate-based relaxor ferroelectric can be synthesized by a traditional solid-phase method, which specifically comprises the following steps:

[0048] The raw materials of the sodium bismuth titanate-based relaxor ferroelectric are mixed and ball milled into a mixed slurry; the mixed slurry is dried into a precursor powder; polyvinyl alcohol solution is added to the precursor powder for granulation and tabletting to obtain a ceramic green body; after removing the polyvinyl alcohol solution in the ceramic green body, the ceramic green body is sintered at a temperature of 1130-1150°C for 3-4 hours at a temperature increasing rate of 3-4°C / min.

[0049] As some preferred embodiments, the solid-phase method for the sodium bismuth titanate-based relaxor ferroelectric comprises the following steps:

[0050] (1) The required mass of each raw material is calculated according to the chemical formula of the ceramic material;

[0051] (2) The weighed raw materials are ball milled for 10-24 hours at a speed of 180 rpm;

[0052] (3) The slurry after ball milling in step (2) is baked and dried, and then placed in a muffle furnace and heated to a temperature of 800-900°C at a temperature increasing rate of 3-4°C / min, and then naturally cooled to room temperature after being kept at the temperature for 4-6 hours;

[0053] (4) The precursor powder obtained in step (3) is granulated by adding a polyvinyl alcohol solution with a mass fraction of 8%-10% and then pressed into a round sheet to obtain a ceramic green body;

[0054] (5) The ceramic green body obtained in step (4) is placed in a muffle furnace to remove the PVA in the ceramic green body, and then sintered at a temperature of 1130-1150°C for 3-4 hours at a temperature increasing rate of 3-4°C / min to obtain the ceramic material.

[0055] In order to make the technical scheme of the present application clearer, the electric strain enhancement method and performance test of the present application are described in detail below by means of specific examples.

[0056] In the following specific examples, the driving electric field of each sample is determined by the current curve before pre-polarization.

[0057] Example 1: Improvement of the electric strain effect of Bi 0.495 Na 0.396 K 0.099 Sr 0.01 Ti 0.99 Ta 0.01 O3

[0058] (1) Preparation of sodium bismuth titanate-based relaxor ferroelectric ceramic powder by solid phase method

[0059] The raw materials are calculated according to the general formula Bi 0.495 Na 0.396 K 0.099 Sr 0.01 Ti 0.99 Ta 0.01 O3, and the stoichiometric raw materials are weighed and batched, placed in a ball mill tank, and ball milled for 12 h at a speed of 180 rpm with anhydrous ethanol as the dispersion medium. Then, the material is discharged, baked to dryness in an oven, and then continuously heated to 850°C in a program-controlled temperature box furnace for 6 h to obtain the sodium bismuth titanate-based relaxor ferroelectric ceramic powder.

[0060] (2) Granulation and tabletting

[0061] After adding 10wt% polyvinyl alcohol solution to the above-mentioned powder and thoroughly mixing, granulation is performed, and then the sodium bismuth titanate-based ceramic green body with a diameter of 10 mm and a thickness of 0.6 mm is pressed at a pressure of 15 MPa.

[0062] (3) Debinding and sintering

[0063] The above-mentioned ceramic green body is debound at a temperature of 850°C, and then sintered at 1130-1150°C for 3-4 hours to obtain the desired ceramic material.

[0064] (4) Surface metallization

[0065] The sodium bismuth titanate-based relaxor ferroelectric ceramic sheet obtained by sintering is appropriately polished to about 0.4 mm, then conductive silver paste is coated thereon by screen printing, and the electrode is heated at 600°C for 10 min to have a certain bonding strength.

[0066] (5) Pre-polarization

[0067] The AC polarization operation is performed by using a TF-2000 ferroelectric analysis test system, and the selected AC field strength is 85 kV / cm and the field frequency is 5 Hz.

[0068] Figure 1 Comparison of the electrostrictive strain curves of Bi 0.495 Na 0.396 K 0.099 Sr 0.01 Ti 0.99 Ta 0.01 O3 relaxor ferroelectric ceramic before and after pre-polarization. Compared with the initial sample, the electrostrictive strain of the sample after pre-polarization is greatly improved under the same electric field. The maximum electrostrictive strain of the sample after pre-polarization isS max Dynamic piezoelectric coefficient can reach 0.394% d 33 * Up to 656 pm / V, which is 150 pm / V higher than before pre-polarization.

[0069] Example 2: Pre-polarization to achieve Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 Improvement of electro-strain effect

[0070] (1) Preparation of sodium bismuth titanate-based relaxor ferroelectric ceramic powder by solid phase method

[0071] The raw materials are calculated according to the general formula Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 The stoichiometric raw materials are weighed and prepared, placed in a ball mill tank, and ball milled for 16 h at a speed of 180 rpm with anhydrous ethanol as the dispersion medium. Then, the material is discharged, dried in an oven, and then continuously heated to 850°C in a program-controlled temperature box furnace for 6 h to obtain sodium bismuth titanate-based relaxor ferroelectric ceramic powder.

[0072] (2) Granulation and tabletting

[0073] After adding 10wt% polyvinyl alcohol solution to the above powder and mixing thoroughly, granulation is performed, and then sodium bismuth titanate-based ceramic green bodies with a diameter of 10 mm and a thickness of 0.6 mm are pressed at a pressure of 15 MPa.

[0074] (3) Debinding and sintering

[0075] The ceramic green body is debound at a temperature of 850°C, and then sintered at 1130-1150°C for 3 hours to obtain the desired ceramic material.

[0076] (4) Surface metallization

[0077] The sodium bismuth titanate-based relaxor ferroelectric ceramic sheet obtained by sintering is appropriately polished to about 0.4 mm, then conductive silver paste is applied by screen printing, and the electrode is heated at 600°C for 10 min to have a certain bonding strength.

[0078] (5) Pre-polarization

[0079] The TF-2000 ferroelectric analysis test system was used for the AC polarization operation, and the selected AC electric field strength was 80 kV / cm, and the electric field frequency was 3 Hz.

[0080] Figure 2 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 The change of the electric strain curve of the ceramic before and after pre-polarization. Compared with the initial sample, the electric strain of the sample after pre-polarization was significantly improved. The maximum electric strain of the sample after pre-polarization under the electric field of 60 kV / cm S max can reach 0.432%, and the dynamic piezoelectric coefficient d 33 * can reach 720 pm / V, which is improved by 235 pm / V compared with the state before pre-polarization.

[0081] Figure 3 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 The change of the electric hysteresis loop of the ceramic before and after pre-polarization. After pre-polarization, the residual polarization of the sample is significantly increased, indicating that large-size polar regions are induced, which is directly related to the improvement of the electric strain effect. Figure 4 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 The X-ray diffraction image of the ceramic before and after pre-polarization. After pre-polarization, the characteristic diffraction peak of the sodium bismuth titanate-based ceramic shows a splitting trend, indicating that the ferroelectricity of the sample after pre-polarization is enhanced, which corresponds to the appearance of large-size polar regions, indicating that the large-size polar regions have a significant enhancement effect on the electric strain of the sodium bismuth titanate-based relaxor ferroelectric ceramic.

[0082] Figure 5 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 The change of the electric strain curve before and after the pre-polarization voltage is not up to standard. The pre-polarization voltage is about 50 kV / cm, which is 1.1 times the driving electric field, and the frequency is 3 Hz. It is found that the electric strain curve does not change significantly, and the field-induced phase transition is not enhanced. Figure 6 Bi0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.97 Ta 0.03 The strain curve of the sample after aging changes. After one week of placement, the electro-strain characteristics of the sample can still be maintained at a very high level, indicating that the improvement of the electro-strain performance caused by the method is effective, stable, and conducive to promoting the industrial application of sodium bismuth titanate-based materials.

[0083] Example 3: Pre-polarization to achieve Bi 0.5 Na 0.36 K 0.1 Li 0.04 Ti 0.94 Ta 0.06 Improvement of electro-strain effect

[0084] (1) Preparation of sodium bismuth titanate-based relaxor ferroelectric ceramic powder by solid phase method

[0085] The raw materials are calculated according to the general formula Bi 0.5 Na 0.36 K 0.1 Li 0.04 Ti 0.94 Ta 0.06 The stoichiometric ratio of the raw materials is weighed and prepared, placed in a ball mill tank, and ball milled for 12 h with anhydrous ethanol as the dispersion medium at a speed of 180 rpm. Subsequently, the material is discharged, dried in an oven, and then continuously heated to 850°C in a program-controlled temperature box furnace for 6 h to obtain sodium bismuth titanate-based relaxor ferroelectric ceramic powder.

[0086] (2) Granulation and tabletting

[0087] After adding 8wt% of polyvinyl alcohol solution to the above-mentioned powder and mixing thoroughly, granulation is performed, and then sodium bismuth titanate-based ceramic green bodies with a diameter of 10 mm and a thickness of 0.6 mm are pressed at a pressure of 15 MPa.

[0088] (3) Debinding and sintering

[0089] The above-mentioned ceramic green bodies are debound at a temperature of 850°C, and then sintered at 1130°C for 4 hours to obtain the desired ceramic material.

[0090] (4) Surface metallization

[0091] The sodium bismuth titanate-based relaxor ferroelectric ceramic sheet obtained by sintering is appropriately polished to about 0.4 mm, and then conductive silver paste is coated on it by screen printing, and the electrode is heated at 600°C for 10 min to have a certain bonding strength.

[0092] (5) Pre-polarization

[0093] The AC polarization operation was performed by using a TF-2000 ferroelectric analysis test system, and the selected AC electric field strength was 90 kV / cm, and the electric field frequency was 3 Hz.

[0094] Figure 7 Bi 0.5 Na 0.36 K 0.1 Li 0.04 Ti 0.94 Ta 0.06 The change of the electric strain curve of the ceramic before and after pre-polarization. Compared with the initial sample, the electric strain of the sample after pre-polarization was significantly improved. The maximum electric strain of the sample after pre-polarization under the electric field of 60 kV / cm S max can reach 0.380%, and the dynamic piezoelectric coefficient d 33 * can be 633 pm / V, which is improved by 155 pm / V compared with the state before pre-polarization.

[0095] Example 4: Pre-polarization realizes Bi 0.4975 Na 0.3582 K 0.0995 Li 0.0398 Sr 0.005 Ti 0.95 Ta 0.05 Improvement of the electric strain effect

[0096] (1) Preparation of sodium bismuth titanate-based relaxor ferroelectric ceramic powder by solid phase method

[0097] The raw materials were calculated according to the general formula Bi 0.4975 Na 0.3582 K 0.0995 Li 0.0398 Sr 0.005 Ti 0.95 Ta 0.05 The stoichiometric raw materials were weighed and batched, placed in a ball mill tank, and ball milled for 12 h with anhydrous ethanol as a dispersion medium, a planetary ball mill at a speed of 180 rpm, then discharged, baked in an oven to dry, and then continuously heated to 850°C in a program-controlled temperature box furnace for 6 h to obtain sodium bismuth titanate-based relaxor ferroelectric ceramic powder.

[0098] (2) Granulation and tabletting

[0099] An appropriate amount of 8wt% polyvinyl alcohol solution was added to the above powder and mixed thoroughly before granulation. Then, the mixture was pressed into a sodium bismuth titanate-based ceramic green body with a diameter of 10 mm and a thickness of 0.6 mm under a pressure of 15 MPa.

[0100] (3) Debinding and sintering

[0101] The above-mentioned ceramic green body was debonded at 850°C and then sintered at 1130°C for 4 hours to obtain the desired ceramic material.

[0102] (4) Surface metallization

[0103] The sodium bismuth titanate-based relaxor ferroelectric ceramic sheet obtained by the above sintering was appropriately polished to about 0.4 mm, and then conductive silver paste was applied by screen printing. The sheet was then kept at 600 °C for 10 min to give the electrode a certain bonding strength.

[0104] (5) Prepolarization

[0105] AC polarization operation was performed using the TF-2000 ferroelectric analysis and testing system, with an AC electric field strength of 80 kV / cm and an electric field frequency of 3 Hz.

[0106] Figure 8 for Bi 0.4975 Na 0.3582 K 0.0995 Li 0.0398 Sr 0.005 Ti 0.95 Ta 0.05 Changes in electrostrain curves before and after ceramic pre-polarization. Compared to the initial sample, the electrostrain of the pre-polarized sample was significantly increased. Maximum electrostrain of the pre-polarized sample under a 60 kV / cm electric field. S max The dynamic piezoelectric coefficient can reach 0.410%. d 33 * It can reach 683 pm / V, which is an improvement of 200 pm / V compared to the pre-polarized state.

[0107] Example 5: Prepolarization to achieve Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.995 Zr 0.005 Enhancement of electro-strain effect

[0108] (1) Preparation of sodium bismuth titanate-based relaxor ferroelectric ceramic powder by solid-state method

[0109] The raw materials are classified according to the general formula Bi. 0.5 Na0.37 K 0.1 Li 0.03 Ti 0.995 Zr 0.005 The formula is calculated, the raw materials in stoichiometric ratio are weighed and batched, placed in a ball mill tank, and ball milled with a planetary ball mill for 16 h at a speed of 180 rpm with anhydrous ethanol as a dispersion medium. Then, the material is discharged, baked to dryness in an oven, and then continuously heated to 850°C in a program-controlled temperature box furnace for 6 h to obtain sodium bismuth titanate-based relaxor ferroelectric ceramic powder.

[0110] (2) Granulation and tabletting

[0111] After adding 8 wt% of polyvinyl alcohol solution to the above powder and thoroughly mixing, granulation is performed, and then the sodium bismuth titanate-based ceramic green body with a diameter of 10 mm and a thickness of 0.6 mm is pressed at a pressure of 15 MPa.

[0112] (3) Debinding and sintering

[0113] The above ceramic green body is debound at a temperature of 850°C, and then sintered at 1150°C for 3 hours to obtain the desired ceramic material.

[0114] (4) Surface metallization

[0115] The sodium bismuth titanate-based relaxor ferroelectric ceramic sheet obtained by sintering is appropriately polished to about 0.4 mm, then conductive silver paste is applied by screen printing, and the electrode is heated at 600°C for 10 min to have a certain bonding strength.

[0116] (5) Pre-polarization

[0117] The AC polarization operation is performed using a TF-2000 ferroelectric analysis test system, and the selected AC electric field strength is 90 kV / cm, and the electric field frequency is 3 Hz.

[0118] Figure 9 Bi 0.5 Na 0.37 K 0.1 Li 0.03 Ti 0.995 Zr 0.005 The change of the electrostrictive strain curve before and after pre-polarization of the ceramic. Compared with the initial sample, the electrostrictive strain of the sample after pre-polarization is significantly improved. The maximum electrostrictive strain of the sample after pre-polarization under an electric field of 60 kV / cm S max can reach 0.365%, and the dynamic piezoelectric coefficient d 33 *Up to 610 pm / V, which is 75 pm / V higher than the state before pre-polarization.

[0119] Example 6: Pre-polarization realizes Bi 0.4975 Na 0.36815 K 0.0995 Li 0.02985 Sr 0.005 Ti 0.995 Zr 0.005 Improvement of electro-strain effect

[0120] (1) Preparation of sodium bismuth titanate-based relaxor ferroelectric ceramic powder by solid phase method

[0121] The raw materials are calculated according to the general formula Bi 0.4975 Na 0.36815 K 0.0995 Li 0.02985 Sr 0.005 Ti 0.995 Zr 0.005 The stoichiometric raw materials are weighed and batched, placed in a ball mill tank, and ball milled for 12 h with anhydrous ethanol as the dispersion medium at a speed of 180 rpm. Subsequently, the material is discharged, baked in an oven until dry, and then continuously heated to 850°C in a program-controlled temperature box furnace for 6 h to obtain sodium bismuth titanate-based relaxor ferroelectric ceramic powder.

[0122] (2) Granulation and tabletting

[0123] After adding 8wt% polyvinyl alcohol solution to the above-mentioned powder and mixing thoroughly, granulation is performed, and then sodium bismuth titanate-based ceramic green bodies with a diameter of 10 mm and a thickness of 0.6 mm are pressed at a pressure of 15 MPa.

[0124] (3) Debinding and sintering

[0125] The ceramic green body is debound at a temperature of 850°C, and then sintered at 1130°C for 3 hours to obtain the desired ceramic material.

[0126] (4) Surface metallization

[0127] The sodium bismuth titanate-based relaxor ferroelectric ceramic sheet obtained by sintering is appropriately polished to about 0.4 mm, then conductive silver paste is applied by screen printing, and the electrode is heated at 600°C for 10 min to have a certain bonding strength.

[0128] (5) Pre-polarization

[0129] The TF-2000 ferroelectric analysis test system is used for AC polarization operation, and the selected AC field strength is 80 kV / cm, and the field frequency is 3 Hz.

[0130] Figure 10 Bi 0.4975 Na 0.36815 K 0.0995 Li 0.02985 Sr 0.005 Ti 0.995 Zr 0.005 The change of the electric-field induced strain curve before and after the ceramic pre-polarization. Compared with the initial sample, the electric-field induced strain of the pre-polarized sample is significantly improved. The maximum electric-field induced strain of the pre-polarized sample under the electric field of 60 kV / cm S max up to 0.414%, the dynamic piezoelectric coefficient d 33 * up to 690 pm / V, which is improved by 210 pm / V compared with the state before pre-polarization.

[0131] The above merely describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for enhancing the electrostriction of a sodium bismuth titanate-based relaxor ferroelectric, characterized by, Comprising the following steps: Surface metallization is performed on the synthesized sodium bismuth titanate-based relaxor ferroelectric; The surface-metallized sodium bismuth titanate-based relaxor ferroelectric is pre-polarized by applying an alternating current electric field; The voltage of the alternating current electric field is 1.4 times or more of the field-induced strain driving electric field value of the sodium bismuth titanate-based relaxor ferroelectric, and the frequency of the alternating current electric field is 3-5 Hz; The surface metallization is to cover the synthesized sodium bismuth titanate-based relaxor ferroelectric with a conductive electrode by screen printing or electroplating; The sodium bismuth titanate-based relaxor ferroelectric is a sodium bismuth titanate-based solid solution material in a critical state or near the critical state; The critical state or near the critical state means that the sodium bismuth titanate-based material is in a mixed state of traversal and non-traversal.

2. The electro-strain enhancement method of claim 1, wherein, The sodium bismuth titanate-based relaxor ferroelectric is synthesized by a solid phase method.

3. The electro-strain enhancement method of claim 2, wherein, The solid phase synthesis method comprises: Mixing the raw materials of the sodium bismuth titanate-based relaxor ferroelectric and ball milling into a mixed slurry; Drying the mixed slurry into a precursor powder; Adding a polyvinyl alcohol solution to the precursor powder to granulate and press into a tablet to obtain a ceramic green body; After removing the polyvinyl alcohol solution from the ceramic green body, sintering at a temperature of 1130-1150 °C for 3-4 hours at a temperature increasing rate of 3-4 °C / min.

4. The electro-strain enhancement method of claim 3, wherein, The method for drying the mixed slurry into a precursor powder is: After baking and compacting the mixed slurry, increase the temperature to 800-900 °C at a temperature increasing rate of 3-4 °C / min, and then naturally cool to room temperature after holding for 4-6 hours.

5. The electro-strain enhanced method of claim 3, wherein, The ball milling time is 10-24 hours, and the rotation speed is 180 rpm.

6. The electro-strain enhanced method of claim 3, wherein, The mass percentage of the polyvinyl alcohol solution is 8%-10%.

7. The electro-strain enhancement method of claim 1, wherein, The general formula of the sodium bismuth titanate-based relaxor ferroelectric is (Bi 0.5 Na 0.4-x K 0.1 Li x ) 1-y Sr y Ti 1-z-m Ta z Zr m O3, wherein the value ranges of x, y, z and m are respectively 0 ≤ x≤ 0.4, 0 ≤ y ≤ 0.02, 0 ≤ z ≤ 0.015 and 0 ≤ m ≤ 0.

02.

8. The sodium bismuth titanate-based relaxor ferroelectric obtained by the electro-strain enhancement method according to any one of claims 1-7.

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