A lead-free piezoelectric ceramic material, a method for preparing the same, and an application thereof

Abstract

The application relates to a lead-free piezoelectric ceramic material and a preparation method and application thereof, and belongs to the technical field of piezoelectric ceramics. The lead-free piezoelectric ceramic material comprises a matrix powder represented by a chemical general formula (K 0.5‑a Na 0.5‑b Li a Bi b )(Nb 1‑c‑ d Hf c Sc d )O3, satisfies 0.01<=a<=0.04, 0.01<=b<=0.04, 0.02<=c<=0.08 and 0.01<=d<=0.04, and 0.1-0.4wt% of SiO2 is further introduced into the matrix powder. The scheme can maintain charge balance while regulating a crystal lattice structure, so that the material can take into account piezoelectric performance and temperature stability, in addition, can improve crystal boundary wettability and promote densification in a sintering process, and can hinder defect migration, thereby reducing the adverse influence of internal defects of the material on electrical performance and improving long-term stability of the material.

Description

Technical Field

[0001] This application relates to a lead-free piezoelectric ceramic material, its preparation method, and its application, belonging to the field of piezoelectric ceramic technology. Background Technology

[0002] Piezoelectric ceramic materials are widely used in sensors, actuators, transducers, and microelectromechanical systems (MEMS) because they can convert mechanical energy into electrical energy. Currently, the most commercially mature piezoelectric materials are lead-based piezoelectric ceramics, such as PZT piezoelectric ceramics, which have excellent piezoelectric properties and stable electrical characteristics.

[0003] However, the aforementioned lead-containing piezoelectric materials contain a large amount of lead, which may have adverse effects on the environment and human health during production, use, and disposal. With increasingly stringent environmental regulations, the research and application of lead-free piezoelectric materials has gradually become an important development direction in this field. Among numerous lead-free piezoelectric systems, materials based on KNN piezoelectric ceramics are considered one of the most promising candidates to replace traditional lead-containing piezoelectric ceramics due to their high Curie temperature, good piezoelectric properties, and relatively excellent environmental friendliness.

[0004] However, KNN-based piezoelectric ceramics still face several unresolved issues in practical applications. On one hand, alkali metal elements are prone to volatilization during sintering, causing the composition to deviate from the design values, thus affecting the material's density and electrical properties. On the other hand, current technologies often employ single or conventional doping methods to modify KNN materials. While this improves material performance to some extent, the overall control effect is limited, making it difficult to simultaneously achieve multiple performance indicators such as piezoelectric properties, density, and temperature stability. Furthermore, the performance stability of the material during long-term use still needs further improvement.

[0005] Therefore, there is an urgent need to provide a technical solution that can improve the density, temperature stability and long-term reliability of KNN-based piezoelectric ceramics while ensuring their environmentally friendly and lead-free characteristics, so as to meet their application requirements in high-performance piezoelectric devices. Summary of the Invention

[0006] To address the aforementioned issues, a lead-free piezoelectric ceramic material, its preparation method, and its application are provided, utilizing Li... + / Bi 3+ With Hf 4+ / Sc 3+Synergistic doping enables lattice structure regulation and charge compensation. Simultaneously, the SiO2 system can promote grain boundary wetting and diffusion during sintering, thereby improving grain boundary compactness. Combined with a staged atmosphere sintering process, alkali metal volatilization and defect generation are suppressed, thus obtaining KNN-based lead-free piezoelectric ceramic materials with high density, excellent piezoelectric properties and good temperature stability.

[0007] This application provides a lead-free piezoelectric ceramic material, wherein the lead-free piezoelectric ceramic material comprises materials with the general chemical formula (K... 0.5-a Na 0.5-b Li a Bi b (Nb) 1-c-d Hf c Sc d The matrix powder of O3 satisfies 0.01≤a≤0.04, 0.01≤b≤0.04, 0.02≤c≤0.08, 0.01≤d≤0.04, and 0.1~0.4wt% of SiO2 is also introduced into the matrix powder.

[0008] Where a, b, c, and d satisfy (0.5-a) + (0.5-b) + a + 3b + (1-cd) * 5 + 4c + 3d = 6. It should be noted that in actual product preparation, this value can be close to 6. For example, if necessary, this value can be made slightly lower than 6, thereby introducing a controllable number of oxygen vacancies.

[0009] Optional, a=0.02, b=0.02, c=0.02, d=0.01.

[0010] Optionally, 0.2 wt% SiO2 may be introduced into the matrix powder.

[0011] This application provides a method for preparing the above-mentioned lead-free piezoelectric ceramic material, comprising the following steps: S1. The ingredients are prepared according to the composition of the matrix powder, and after ball milling and drying, a mixed powder is obtained. The mixed powder is then pre-calcined to obtain a pre-calcined powder. S2. After ball milling the pre-calcined powder again, add SiO2 and continue ball milling to ensure that the additive is evenly dispersed in the matrix powder. S3. After adding the binder, the mixture is granulated, sieved, and pressed into shape to obtain a green body. S4. The green body is sintered to obtain a sintered body; S5. After preparing electrodes from the obtained sintered body, perform polarization treatment to obtain the lead-free piezoelectric ceramic material.

[0012] Optionally, step S4 includes: 1) Increase the temperature to 600±20℃ at a rate of 2~4℃ / min and hold for 100~150min; 2) Continue heating to 1000±20℃ and hold for 100~150 minutes; 3) Continue to heat to 1120±20℃ and keep warm for 100~150 minutes.

[0013] Optionally, step 1) is performed in an air atmosphere; step 2) is performed in a sealed crucible environment; and step 3) is performed at an oxygen partial pressure of 1*10. -2 ~3*10 -2 Sintering is carried out under the low oxygen partial pressure environment of atm.

[0014] Optionally, step 2) during sintering may also include the step of adding pre-fired powder to cover the green blank.

[0015] Optional, the coverage thickness is not less than 5mm.

[0016] Optionally, after the green compact is sintered, it is cooled to room temperature at a rate of 2~4℃ / min.

[0017] This application provides the application of the aforementioned lead-free piezoelectric ceramic material in the fabrication of piezoelectric actuators.

[0018] The beneficial effects of this application include, but are not limited to: 1. Based on the lead-free piezoelectric ceramic material, its preparation method, and its application, this application describes a method for introducing Li into the A-site. + with Bi 3 + Introduce Hf at position B 4+ With Sc 3+ By forming a heterovalent synergistic doping system, the lattice structure can be controlled while maintaining charge balance, enabling the material to take into account both piezoelectric properties and temperature stability, thus overcoming the problem that traditional single doping methods cannot optimize multiple performance indicators at the same time.

[0019] 2. According to the lead-free piezoelectric ceramic material, its preparation method and application, by introducing SiO2 precursor, the wettability of grain boundaries can be improved and densification can be promoted during sintering. At the same time, it can hinder the migration of defects, thereby reducing the adverse effects of internal defects on electrical properties and improving the long-term stability of the material.

[0020] 3. According to the lead-free piezoelectric ceramic material, its preparation method and application, a staged sintering process is adopted. In the intermediate temperature stage, the volatilization of K and Na is suppressed by constructing an alkali metal compensation environment. In the high temperature stage, the oxygen partial pressure is controlled to regulate the oxygen vacancy concentration, thereby effectively maintaining the stability of the material composition and reducing the defect content, and improving the consistency and reliability of the material.

[0021] 4. Based on the lead-free piezoelectric ceramic material, its preparation method, and its application, the combination of synergistic doping, grain boundary regulation, and sintering process optimization, and the synergistic effect from three levels—lattice structure, grain boundary state, and sintering process—enables an overall improvement in the material's density, piezoelectric properties, and temperature stability, significantly addressing the problem of existing KNN-based piezoelectric ceramics having difficulty in achieving a balance between performance. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a scanning electron microscope (SEM) characterization image of the KNN matrix powder involved in the embodiments of this application. Detailed Implementation

[0023] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents in the embodiments of the present application are all purchased through commercial channels.

[0024] The present application solution will be described below through specific embodiments.

[0025] Example 1 This embodiment provides a lead-free piezoelectric ceramic material based on KNN piezoelectric ceramics and its preparation method. The chemical composition of the piezoelectric ceramic is (KNN piezoelectric ceramics). 0.48 Na 0.48 Li 0.02 Bi 0.02 (Nb) 0.97 Hf 0.02 Sc 0.01 O3, and 0.2wt% SiO2 was introduced into the matrix powder as a grain boundary regulation precursor.

[0026] 1) Raw materials and ingredients The following raw materials were selected: potassium carbonate (K₂CO₃), sodium carbonate (Na₂CO₃), lithium oxide (Li₂O), bismuth oxide (Bi₂O₃), niobium pentoxide (Nb₂O₅), hafnium dioxide (HfO₂), scandium oxide (Sc₂O₃), and nano-silica (SiO₂, particle size ≤ 50 nm). Each raw material was weighed according to the above stoichiometric ratio, and the batching was based on 100 g of powder. The K₂CO₃ and Na₂CO₃ amounts were increased by 5 mol% from the theoretical amounts to compensate for the loss of alkali metals through volatilization during high-temperature sintering.

[0027] 2) Powder preparation The weighed raw materials were added to a planetary ball mill, using zirconia balls as the grinding medium (ball-to-material ratio 5:1) and anhydrous ethanol as the dispersion medium. The ball milling conditions were 300 rpm for 12 hours to achieve thorough mixing and refinement of the raw materials.

[0028] After ball milling, the slurry was dried in an 80℃ forced-air drying oven for 12 hours to obtain a uniformly mixed powder. The dried powder was then placed in a covered alumina crucible and pre-fired in a box-type resistance furnace at a heating rate of 5℃ / min, reaching 850℃ and holding for 4 hours to obtain a preliminary KNN-based solid solution powder, such as... Figure 1 As shown.

[0029] 3) Grain boundary control treatment The pre-calcined powder was ball-milled again, and 0.2 wt% SiO2 was added to the original powder. The same ball milling media and dispersion method as above were used, and the powder was ball-milled at 250 rpm for 6 hours to ensure that the additive was uniformly dispersed in the powder.

[0030] 4) Molding A 5 wt% polyvinyl alcohol (PVA) solution was added to the powder after secondary ball milling as a binder. After mixing evenly, the mixture was granulated by passing it through a 100-mesh sieve. Subsequently, it was shaped by unidirectional pressing using a 12 mm diameter mold and held under 5 MPa pressure for 2 minutes to obtain a circular blank with a thickness of approximately 1.5 mm.

[0031] 5) Staged atmosphere sintering The resulting green body was placed in a covered alumina crucible for further processing and then sintered in a controlled atmosphere resistance furnace in three stages. 5.1) Degreasing stage: Heat to 600℃ at 3℃ / min, hold for 2 hours in an air atmosphere to remove organic binders; 5.2) Medium-temperature sintering and alkali-locking stage: Continue heating to 1000℃ and hold for 2 hours. A relative seal is achieved by placing the crucible lid on the crucible opening. With the help of protective powder, an alkali metal compensation environment can be constructed to inhibit the volatilization of K and Na elements. Specifically, the green body is covered with the previously prepared pre-calcined powder, with a covering thickness of 5mm. 5.3) High-temperature densification stage: Further heat to 1120℃ and hold for 2 hours, with an oxygen partial pressure of approximately 1*10. -2 Sintering is carried out under the low oxygen partial pressure environment of atm to promote material densification and control oxygen vacancy concentration; After sintering, the sample was cooled to room temperature at a rate of 3°C / min.

[0032] 6) Electrode preparation and polarization treatment The sintered ceramic sample was coated with silver paste on both sides, and electrodes were prepared by screen printing. The electrodes were then sintered at 600℃ for 10 minutes to form conductive electrodes. Subsequently, the sample was placed in silicone oil and polarized for 20 minutes at 120℃ with a DC electric field of 3kV / mm to complete the polarization treatment, thus obtaining the final product.

[0033] Example 2 This embodiment is basically the same as Embodiment 1, except that the oxygen partial pressure in step 5.3) is 8*10. -2 atm.

[0034] Example 3 This embodiment is basically the same as Embodiment 1, except that step 5.2) does not include the step of adding the previously prepared pre-fired powder to cover the green body.

[0035] Example 4 This embodiment is basically the same as embodiment 1, except that step 5) sintering process adopts the traditional one-step sintering process, directly heating to 1120℃ and holding at that temperature in air atmosphere for 4 hours.

[0036] Example 5 This embodiment is basically the same as embodiment 1, except that after the green blank is sintered in step 5), it is cooled to room temperature at a rate of 5°C / min.

[0037] Comparative Example 1 This comparative example is basically the same as Example 1, except that the type of dopant element at the B site is different, and the chemical composition of the piezoelectric ceramic is (K 0.485 Na 0.485 Li 0.02 Bi 0.01 (Nb) 0.98 Hf 0.02 )O3.

[0038] Comparative Example 2 This comparative example is basically the same as Example 1, except that the type of dopant element at site A is different, and the chemical composition of the piezoelectric ceramic is (K 0.49 Na 0.49 Bi 0.02 (Nb) 0.97 Hf 0.02 Sc 0.01 )O3.

[0039] Comparative Example 3 This comparative example is basically the same as Example 1, except that SiO2 is not added in step 3).

[0040] Comparative Example 4 This comparative example is basically the same as Example 1, except that in step 1), the matrix powder is prepared according to (K0.48 Na 0.48 Li 0.04 (Nb) 0.96 Ta 0.04 O3 was used for preparation.

[0041] Test Example 1 The performance of the lead-free piezoelectric ceramic materials obtained in the examples and comparative examples was tested. The average value of three samples was taken for each group of data. The results are shown in Table 1 below.

[0042] Density was determined using the Archimedes method. After drying the sample at 120°C for 2 hours, the dry weight m1 was measured. The sample was then immersed in deionized water under vacuum for 1 hour to remove air from the open pores. Subsequently, the saturated mass m2 and the suspended mass m3 in water were measured. The bulk density of the sample was calculated based on Archimedes' principle.

[0043] d 33 d is the piezoelectric constant; a larger d value indicates better piezoelectric properties of the piezoelectric ceramic material. 33 Using quasi-static d 33 The tester performs measurements by placing the sample between the test probes and reading d under small signal excitation conditions. 33 value.

[0044] The dielectric properties of the samples were tested using a precision LCR meter. During testing, silver electrodes were sintered onto both sides of the sample, which was then placed in a temperature-controlled furnace. The dielectric constant and dielectric loss were measured as a function of temperature at a frequency of 1 kHz. The test temperature range was from room temperature to 400 °C, with a heating rate of 2 °C / min. The Curie temperature of the material was obtained by plotting the dielectric constant-temperature curve.

[0045] The electrical performance of the samples was tested using a source meter (Keithley testing system), and the leakage current density was calculated by measuring the current-voltage curve. During the test, the voltage (0-500V) was gradually applied at room temperature, and the current changes were recorded. Combined with the dielectric loss (tanδ) test results, the influence of internal defects (oxygen vacancies) on the electrical performance of the material was analyzed.

[0046] To evaluate the long-term performance of the material, aging tests were conducted on the polarized samples, specifically temperature cycling stability tests. The samples were subjected to multiple heating and cooling cycles within the range of 25℃ to 150℃, and the temperature before and after each cycle was measured. 33 And changes in dielectric properties.

[0047] Table 1 Performance test results of lead-free piezoelectric ceramic materials in the examples and comparative examples

[0048] Table 1 (continued)

[0049] As shown in Table 1, Example 1 has the highest bulk density (4.52 g / cm³). 3 The relative density is greater than 95%, indicating that the material has good compactness and the leakage current density is the lowest (1.2*10). -6 A / cm 2 Compared with other solutions, this application has significant performance advantages. It can be seen that the solution of this application, through the synergistic effect of synergistic doping, grain boundary regulation and staged sintering process, is significantly better than the existing technology and comparative examples in terms of density, piezoelectric performance and temperature stability, which verifies the effectiveness and superiority of the technical solution of this application.

[0050] In Example 2, due to the change in oxygen partial pressure, the defect balance and grain boundary diffusion behavior during the sintering process are altered, resulting in a decrease in the densification of the material, which in turn increases the leakage current density and reduces the piezoelectric properties.

[0051] In Example 3, the lack of pre-calcined powder covering led to alkali metal volatilization, causing the density to decrease to 4.45 g / cm³. 3 Furthermore, the leakage current increased significantly.

[0052] Example 4 uses a one-step sintering process, which significantly degrades both density and electrical properties, indicating that staged sintering plays a crucial role in densification and defect control.

[0053] In Example 5, the cooling rate was too fast, which led to uneven distribution of defects during the rapid cooling process. The local enrichment of defects resulted in a decrease in its piezoelectric properties and stability compared to Example 1.

[0054] Based on the results of Comparative Example 1 and Comparative Example 2, d in Example 1 33 Achieving 312 pC / N, significantly superior to Comparative Example 1 (220 pC / N) and Comparative Example 2 (235 pC / N), demonstrates that using only partial A-site or B-site doping makes it difficult to simultaneously achieve piezoelectric performance and temperature stability. In contrast, the proposed solution simultaneously performs specific doping on both the A-site and B-site, using Li... + / Bi 3+ With Hf 4+ / Sc 3+ Co-doping plays a key role in charge compensation and lattice modulation, thus exhibiting superior performance.

[0055] Based on the results of Comparative Example 3, after removing SiO2, the density and d of Comparative Example 3 were... 33 While leakage current decreased significantly, leakage current increased significantly. In this application, the addition of specific additives during sintering can promote grain boundary wetting and diffusion, which plays a very important role in improving compactness and inhibiting defect migration.

[0056] It is important to note that Example 1 maintained a high d even after aging. 33 At the Curie temperature, the performance degradation was minimal, while the comparative samples generally showed a significant performance decline, especially comparative sample 3, whose d 33 It dropped to 195 pC / N.

[0057] Compared with Comparative Example 4 in the prior art, Comparative Example 4 has a slightly higher d 33 (252pC / N), but its Curie temperature is relatively low (310℃), indicating that although the traditional Li-Ta isovalent doping system can improve piezoelectric performance to a certain extent, it still has certain limitations in terms of Curie temperature and overall performance optimization.

[0058] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a lead-free piezoelectric ceramic material, characterized in that, The lead-free piezoelectric ceramic material includes materials with the general chemical formula (K). 0.5-a Na 0.5-b Li a Bi b (Nb) 1-c-d Hf c Sc d The matrix powder of O3 satisfies 0.01≤a≤0.04, 0.01≤b≤0.04, 0.02≤c≤0.08, 0.01≤d≤0.04, and 0.1~0.4wt% of SiO2 is introduced into the matrix powder; The preparation method of the lead-free piezoelectric ceramic material includes the following steps: S1. The ingredients are prepared according to the composition of the matrix powder, and after ball milling and drying, a mixed powder is obtained. The mixed powder is then pre-calcined to obtain a pre-calcined powder. S2. After ball milling the pre-calcined powder again, add SiO2 and continue ball milling to ensure that the additive is evenly dispersed in the matrix powder. S3. After adding the binder, the mixture is granulated, sieved, and pressed into shape to obtain a green body. S4. Sintering the green body to obtain a sintered body: 1) Heating to 600±20℃ at 2~4℃ / min and holding for 100~150min; 2) Heating further to 1000±20℃ and holding for 100~150min; 3) Heating further to 1120±20℃ and holding for 100~150min; Step 1) is performed in an air atmosphere; Step 2) is performed in a sealed crucible environment; Step 3) is performed in an oxygen partial pressure of 1 10 -2 ~3 10 -2 Sintering is carried out under the low oxygen partial pressure environment of atm; S5. After preparing electrodes from the obtained sintered body, perform polarization treatment to obtain the lead-free piezoelectric ceramic material.

2. The method for preparing lead-free piezoelectric ceramic material according to claim 1, characterized in that, Step 2) in S4, when sintering in a sealed crucible environment, also includes the step of adding pre-fired powder to cover the green blank.

3. The method for preparing lead-free piezoelectric ceramic material according to claim 2, characterized in that, The coverage thickness is not less than 5mm.

4. The method for preparing lead-free piezoelectric ceramic material according to claim 1, characterized in that, After the green blank is sintered, it is cooled to room temperature at a rate of 2~4℃ / min.

5. The lead-free piezoelectric ceramic material obtained by the preparation method according to any one of claims 1 to 4.

6. The lead-free piezoelectric ceramic material according to claim 5, characterized in that, a=0.02, b=0.02, c=0.02, d=0.

01.

7. The lead-free piezoelectric ceramic material according to claim 5, characterized in that, 0.2 wt% SiO2 was introduced into the matrix powder.

8. The use of the lead-free piezoelectric ceramic material as described in any one of claims 5 to 7 in the preparation of piezoelectric actuators.

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