A lead-free piezoelectric ceramic material, a method for manufacturing the same, and a piezoelectric device

Abstract

The application provides a lead-free piezoelectric ceramic material, a preparation method thereof and a piezoelectric device. The lead-free piezoelectric ceramic material is expressed by a chemical general formula as follows: (1-x-y)(K 1‑a Na a )(Nb 1‑b M b )O3-xAWO4-yBMoO4; wherein (K 1‑a Na a )(Nb 1‑b M b )O3 represents a potassium sodium niobate-based ceramic material, 0.4<=a<=0.6, 0<=b<=0.1, M is a doped metal element; x and y are molar fractions, and satisfy: 0

Description

Technical Field

[0001] This invention relates to the field of functional ceramic materials, and in particular to a lead-free piezoelectric ceramic material and its preparation method, as well as a piezoelectric device made from the lead-free piezoelectric ceramic material. Background Technology

[0002] Piezoelectric ceramics are functional materials capable of converting mechanical energy into electrical energy. They possess properties such as piezoelectricity (when a force is applied to a piezoelectric ceramic material, charge separation occurs, i.e., mechanical energy is converted into electrical energy; conversely, when an external electric field is applied to a piezoelectric ceramic material, the piezoelectric ceramic material will also deform), dielectricity, and elasticity. They are widely used in electronic components such as sensors, actuators, transducers, and piezoelectric motors.

[0003] Taking piezoelectric motors as an example, a piezoelectric motor is a drive device that works based on the piezoelectric effect, converting electrical energy into mechanical motion by utilizing the properties of piezoelectric materials. Piezoelectric motors have advantages such as high speed, high precision, and no magnetic field, and are widely used in many fields. A piezoelectric motor consists of two parts: a vibrating component and a moving component, without windings, magnets, or insulation structures. The power density of a piezoelectric motor is much higher than that of a conventional motor, and its output is mostly low-speed, high-thrust (or torque), enabling direct drive of loads. Piezoelectric materials are a key component of piezoelectric motors. Currently, the mainstream piezoelectric ceramic materials on the market are lead-based piezoelectric ceramics, such as lead zirconate titanate (PZT) and bismuth scandium titanate (BS-PT), which possess high piezoelectricity and Curie temperature. However, because the lead content of these lead-based piezoelectric ceramic materials is as high as 60%, they pose serious harm to human health and cause severe environmental pollution throughout their entire lifecycle (from production and use to disposal). Therefore, developing lead-free alternative materials has become an inevitable trend.

[0004] Potassium sodium niobate ((K,Na)NbO3, KNN) lead-free piezoelectric ceramics are considered one of the most promising alternative materials due to their high Curie temperature and good piezoelectric properties. However, the piezoelectric constant (d) of pure KNN ceramics... 33 Its low pC / N ratio results in poor overall performance, making it difficult to apply in piezoelectric devices such as piezoelectric motors.

[0005] Therefore, there is an urgent need to develop a high-performance lead-free piezoelectric ceramic material with excellent overall performance and stable preparation process.

[0006] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] To overcome the deficiencies of the prior art, the present invention provides a lead-free piezoelectric ceramic material, a preparation method thereof, and a piezoelectric device.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions.

[0009] In a first aspect, a lead-free piezoelectric ceramic material is provided, which is represented by the chemical formula: (1 - x - y)(K 1- a Na a )(Nb 1-b M b )O3 - xAWO4 - yBMoO4; wherein, (K 1-a Na a )(Nb 1-b M b )O3 represents a sodium potassium niobate-based ceramic material, 0.4 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.1, M is a doped metal element; x and y are mole fractions, satisfying: 0 < x ≤ 0.05, 0 < y ≤ 0.05, and 0 < x + y ≤ 0.1; AWO4 is a tungstate, and BMoO4 is a molybdate.

[0010] In a second aspect, a preparation method of the lead-free piezoelectric ceramic material described in the first aspect is provided, including the following steps: (1)配料与一次球磨:以K2CO3、Na2CO3、Nb2O5、掺杂金属元素的氧化物为原料,按所述化学通式中(1-x-y) (K 1-a Na a )(Nb 1-b M b )O3的化学计量比进行配料,经球磨混合、烘干、过筛后得到一次混合粉体; (1)配料与一次球磨:以K2CO3、Na2CO3、Nb2O5、掺杂金属元素的氧化物为原料,按所述化学通式中(1-x-y) (K (2)预烧:将步骤(1)得到的所述一次混合粉体压制成型,在预定温度下进行预烧,得到预烧粉体; (2) Pre-sintering: The primary mixed powder obtained in step (1) is pressed into a shape and pre-sintered at a predetermined temperature to obtain a pre-sintered powder; (3)二次球磨与掺杂:向步骤(2)得到的所述预烧粉体中,按所述化学通式中xAWO4和yBMoO4的化学计量比加入为钨酸盐AWO4和钼酸盐BMoO4,进行二次球磨混合、烘干、过筛,得到二次混合粉体; (3) Secondary ball milling and doping: To the pre-sintered powder obtained in step (2), tungstate AWO4 and molybdate BMoO4 are added according to the stoichiometric ratios of xAWO4 and yBMoO4 in the chemical formula, followed by secondary ball milling, drying, and sieving to obtain a secondary mixed powder; (4)成型与烧结:向步骤(3)得到的所述二次混合粉体中加入粘结剂,进行造粒、过筛、压制成型得到生坯;将所述生坯进行排胶处理后,在1070-1140℃下保温进行烧结,得到烧结体; (4) Forming and sintering: A binder is added to the secondary mixed powder obtained in step (3), followed by granulation, sieving, and pressing into a green body; after degumming the green body, it is sintered at 1070 - 1140 °C for heat preservation to obtain a sintered body; (5)将步骤(3)得到的所述烧结体进行极化处理,得到所述无铅压电陶瓷材料。 (5) The sintered body obtained in step (3) is subjected to poling treatment to obtain the lead-free piezoelectric ceramic material.

[0011] Thirdly, a piezoelectric device is provided, wherein the piezoelectric component of the piezoelectric device is made of the lead-free piezoelectric ceramic material.

[0012] The beneficial effects of this invention include: This invention provides a lead-free piezoelectric ceramic material with high voltage constant, low dielectric loss, and easy sintering and densification, overcoming the shortcomings of traditional KNN-based ceramics and the environmental pollution problems of lead-based materials, thus improving the piezoelectric performance of KNN-based piezoelectric ceramics. Specifically, this invention synergistically introduces tungstate and molybdate into KNN-based ceramic materials, utilizing W... 6 ⁺and Mo 6 ⁺ Ion pair with B-site Nb 5 The composite substitution of ⁺ ions introduces a non-uniform stress field and gradient-varying lattice distortion into the perovskite lattice, widening the quasi-isomorphic phase boundary region, promoting the formation of polar nanoregions, and reducing domain wall pinning effects, thereby significantly enhancing the material's polarization reversal capability. Simultaneously, the low-melting-point tungstates and molybdates generate a liquid phase during sintering, promoting uniform grain growth and material densification, and compensating for the volatilization of alkali metal elements at high temperatures. The synergistic effect of these factors ultimately enables the lead-free piezoelectric ceramic material of this invention to achieve high voltage constant, low dielectric loss, and excellent overall electrical performance at a relatively low sintering temperature. Piezoelectric devices made from the high-voltage lead-free piezoelectric ceramic material of this invention possess advantages such as high precision, high reliability, and environmental friendliness. Attached Figure Description

[0013] Figure 1 This is a scanning electron microscope (SEM) image of the lead-free piezoelectric ceramic material prepared in Example 1 of the present invention. Detailed Implementation

[0014] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be emphasized that these embodiments are for illustrative purposes only and are not intended to limit the scope or application of the invention. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. Modifications and substitutions made by those skilled in the art without departing from the spirit of the invention fall within the protection scope of the present invention.

[0015] In the process of preparing sodium potassium niobate-based lead-free piezoelectric ceramics (perovskite structure) by the existing solid-phase sintering method, alkali metals sodium and potassium are prone to volatilization during high-temperature sintering. Specifically, in sodium potassium niobate-based ceramic materials, metallic potassium and metallic sodium exist in the form of potassium oxide and sodium oxide respectively. Usually, at 900 °C to 950 °C, potassium element begins to volatilize, and at 1000 °C to 1050 °C, sodium element begins to volatilize. During the process of sintering densification, both will volatilize together and cannot exist in solid form above 1140 °C, resulting in a large number of vacancies in the perovskite structure, making it difficult to sinter densely, and thus deteriorating the ceramic properties. For example, the piezoelectric constant of pure KNN-based piezoelectric ceramics is about 80 pC / N. However, the piezoelectric constant (d 33 ) of piezoelectric motors usually requires to be greater than 480 pC / N or more. The above pure KNN-based piezoelectric ceramics are difficult to be applied in piezoelectric motors.

[0016] Therefore, the concept of the present invention is to provide a high-performance lead-free piezoelectric ceramic material, which co-dopes specific proportions of tungstate (AWO4) and molybdate (BMoO4) in KNN-based ceramic materials (including KNN, KNNS, etc.), and utilizes the synergistic effect of W 6 ⁺ and Mo 6 ⁺ ions to compensate for the volatilization of alkali metal ions during sintering, reduce the sintering temperature, induce lattice distortion and enhance the polarization ability, thereby significantly improving the piezoelectric performance and densification of lead-free piezoelectric ceramic materials. The following examples will show the specific implementation methods of different compositions and processes.

[0017] The specific implementation manner of the present invention provides a lead-free piezoelectric ceramic material, which is represented by the chemical general formula: (1 - x - y)(K 1-a Na a )(Nb 1-b M b )O3 - xAWO4 - yBMoO4; wherein, (K 1-a Na a )(Nb 1-b M b )O3 represents sodium potassium niobate (KNN)-based ceramic material, 0.4 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.1, M is a doped metal element; x and y are mole fractions, satisfying: 0 < x ≤ 0.05, 0 < y ≤ 0.05, and 0 < x + y ≤ 0.1; AWO4 is tungstate, and BMoO4 is molybdate.

[0018] The above lead-free piezoelectric ceramic material synergistically introduces tungstate and molybdate in the sodium potassium niobate-based ceramic material. Due to W 6+ and Mo 6+ ions to Nb 5+The recombination of ions introduces a non-uniform stress field and gradient-varying lattice distortion into the perovskite lattice, widening the quasi-isomorphic phase boundary region, promoting the formation of polar nanoregions, and reducing domain wall pinning effects, thereby significantly enhancing the polarization reversal capability of the material. Simultaneously, the low-melting-point tungstates and molybdates generate a liquid phase during sintering, promoting uniform grain growth and material densification, and compensating for the volatilization of alkali metal elements at high temperatures, reducing perovskite structural vacancies caused by element volatilization. The combined effect of tungstates and molybdates ultimately enables this lead-free piezoelectric ceramic material to achieve a high piezoelectric constant and excellent comprehensive electrical properties far exceeding those of pure KNN ceramics at a relatively low sintering temperature, meeting the application requirements of piezoelectric devices. Specifically, the microscopic mechanism by which the synergistic effect of tungstates and molybdates enables the lead-free piezoelectric ceramic material to possess the aforementioned superior properties is mainly as follows: (1) Asymmetric stress field and polarization gradient: W 6 ⁺and Mo 6 The subtle differences in the ionic radii of ⁺ ions, when coexisting at the B site, introduce a non-uniform, gradient-varying stress field into the lattice. This complex internal stress distribution results in a rich energy state for the polarization vector at the nanoscale. The energy barrier is significantly reduced in certain regions, and polarization reversal no longer requires overcoming a uniform, high energy barrier. Instead, different regions have different "shortcuts," thus significantly enhancing the overall polarization reversal capability.

[0019] (2) Widening phase boundaries and constructing polar nanoregions: Co-doping with W and Mo can more effectively regulate the phase transition behavior of KNN-based ceramic materials, making the transition between orthorhombic and tetragonal phases less sharp, thereby widening the quasi-isomorphic phase boundary region. Within this widened phase boundary region, different phases with similar energies (such as orthorhombic and tetragonal phases) can coexist at the nanoscale. Polar nanoregions are formed between these different phase regions. They are themselves extremely unstable, and their orientation is easily changed by the external electric field, providing a large number of easily activated "switches" for polarization reversal.

[0020] (3) Synergistic regulation of defect dipoles: In the process of high-valence ion doping, compensatory defects are generated inside the material in order to maintain electroneutrality. Co-doping of W and Mo may induce more complex defect combinations. These defects may form defect dipoles, which interact with the polarization field of the material itself, which can further reduce the domain wall pinning effect and make the electric domains move more freely.

[0021] In some embodiments, A in AWO4 is one of K and Na; BMoO4 is one of K and Na. By selecting different A and B elements, the dielectric, piezoelectric, and mechanical properties of the piezoelectric ceramic material can be specifically adjusted to adapt to different application scenarios. At the same time, by selecting alkali metal salts of tungstate and molybdate, an excess atmosphere of alkali metal elements sodium and potassium is introduced, which can further compensate for the volatilization of alkali metal ions during the sintering process.

[0022] In some implementations, AWO4 is K2WO4 and BMoO4 is Na2MoO4.

[0023] By selecting specific K2WO4 and Na2MoO4 as additives, K2WO4 and Na2MoO4 have lower melting points (921℃ and 687℃, respectively), making it easier to generate a large amount of liquid phase during sintering, thus lowering the overall sintering temperature, making the surface grains of the piezoelectric ceramic material more uniform, promoting the density of the ceramic, and thereby improving the overall performance of the material.

[0024] In some embodiments, among the lead-free piezoelectric ceramic materials, potassium sodium niobate-based ceramic materials (K... 1-a Na a (Nb) 1-b M b O3 has a perovskite structure, and Nb in this perovskite structure 5+ The lattice sites of the ions are partially affected by W generated by xAWO4. 6+ And Mo produced by yBMoO4 6+ Ion substitution; the doping metal element M is one of Sb, Ta, Ge, Fe, Mn, La, and Eu (these doping elements are respectively represented by Sb in this potassium sodium niobate-based ceramic material). 5+ Ta 5+ 、Ge 4+ Fe 3+ Mn 4+ La 3+ Eu 3+ (Ions are present).

[0025] In some embodiments, the potassium sodium niobate-based ceramic material is KNNS (i.e., the doped metal element is Sb), and more preferably, the potassium sodium niobate-based ceramic material is (K 0.48 Na 0.52 (Nb) 0.96 Sb 0.04 )O3.

[0026] Potassium sodium niobate-based ceramic materials possess a perovskite ABO3 structure. The A-sites are jointly occupied by potassium and sodium ions. Due to the random distribution and size differences of potassium and sodium ions, the surrounding lattice of potassium and sodium ions undergoes expansion or contraction of different lengths, resulting in lattice distortion. The B-sites are occupied by Nb and doped metal elements (if present). Under specific heat treatment or the influence of certain compositions, the originally disordered niobium ions will exhibit ordered arrangement at the nanoscale. In addition, the volatilization of alkali metal ions and the doping of other elements will affect the structure of KNN-based ceramic materials, causing changes in the local electric field and stress field, thereby altering the material's properties. Therefore, the above-described implementation method, through the co-doping of W and Mo, not only lowers the sintering temperature of lead-free piezoelectric ceramic materials but also increases their piezoelectric constant and reduces their dielectric loss, resulting in a significant improvement in their overall performance.

[0027] In some implementations, x and y satisfy: x=0.05, y=0.05; or, x and y satisfy: x=0.025, y=0.025; or, x and y satisfy: x=0.01, y=0.01.

[0028] In some embodiments, the total mass content of W and Mo in the lead-free piezoelectric ceramic material is 1wt% to 16wt%. By optimizing the molar ratio of x and y, the optimal composition point for piezoelectric performance can be found, thereby controlling the total mass content of W and Mo in the lead-free piezoelectric ceramic material. This ensures that these two metal ions can effectively enter the crystal lattice and play their role, avoiding the formation of impurity phases due to excess.

[0029] The present invention also provides a method for preparing the lead-free piezoelectric ceramic material, comprising the following steps: (1) Batching and primary ball milling: Using K2CO3, Na2CO3, Nb2O5, and oxides doped with metal elements as raw materials, according to the general chemical formula (1-xy) (K 1-a Na a (Nb) 1-b M b The ingredients are prepared according to the stoichiometric ratio of O3, and after ball milling, drying and sieving, a primary mixed powder is obtained. (2) Pre-calcination: The first-mixed powder obtained in step (1) is pressed into shape and pre-calcined at a predetermined temperature to obtain pre-calcined powder; (3) Secondary ball milling and doping: tungstate AWO4 and molybdate BMoO4 are added to the pre-calcined powder obtained in step (2) according to the stoichiometric ratio of xAWO4 and yBMoO4 in the general chemical formula, and the mixture is ball-milled, dried and sieved to obtain a secondary mixed powder. (4) Molding and sintering: Add binder to the secondary mixed powder obtained in step (3), granulate, sieve and press to form green body; after debinding the green body, sinter it at 1070-1140℃ to obtain sintered body; (5) The sintered body obtained in step (3) is subjected to polarization treatment to obtain the lead-free piezoelectric ceramic material.

[0030] In the above embodiments, by ball milling twice and adding tungstate and molybdate after pre-calcination, the premature introduction of tungstate and molybdate during the high-temperature pre-calcination stage is avoided, which would cause component deviation and impurity phase formation, thus ensuring the accuracy of the stoichiometry of the final product and the purity of the phase structure.

[0031] In some embodiments, step (2), the preheating at a predetermined temperature includes: heating to 800-900°C at a heating rate of 1-5°C / minute and holding at that temperature for 4-8 hours.

[0032] In some embodiments, in step (4), the mass of the added binder accounts for 10% to 20% of the mass of the secondary mixed powder.

[0033] In some embodiments, step (4) includes: heating to 450-650°C at a heating rate of 1-3°C / minute and holding at that temperature for 4-10 hours.

[0034] In some embodiments, step (4), the sintering at 1070-1140°C includes: heating to 1070-1140°C at a heating rate of 1-3°C / min and holding at that temperature for 1-4 hours to perform densification sintering, and then cooling to 500-700°C at a cooling rate of 1-3°C / min and then cooling to room temperature with the furnace.

[0035] By controlling the heating rate, holding temperature, and time during pre-firing, debinding, and sintering, the grain size, densification process, and final properties can be precisely controlled.

[0036] In some embodiments, step (5) includes polarization in an electric field after silver is printed and burned onto the sintered body.

[0037] In some embodiments, step (5) of the polarization treatment includes: uniformly applying silver paste to both sides of the sintered body, drying it, heating it to 800-900°C at a heating rate of 1-5°C / min and holding it at that temperature for 0.5-1 hour to perform silver firing, then cooling it to room temperature in the furnace, and then placing it in high-temperature silicone oil at 60-110°C, applying an electric field of 20-40 kV / cm, and holding it at that temperature for 10-30 minutes to perform polarization. By optimizing the process parameters of the polarization treatment, it is possible to ensure that the electric domains are fully oriented, thereby obtaining the best piezoelectric performance.

[0038] The present invention also provides a piezoelectric device (an electronic component made using the piezoelectric effect of materials), wherein the piezoelectric component of the piezoelectric device is made of the lead-free piezoelectric ceramic material.

[0039] The invention is further described below with specific examples.

[0040] Example 1 Step 1: Using analytical grade K₂CO₃, Na₂CO₃, Nb₂O₅, Sb₂O₃, K₂WO₄, and Na₂MoO₄ as raw materials, according to the chemical formula 0.9 (K 0.48 Na 0.52 (Nb) 0.96 Sb 0.04 The ingredients are prepared as follows: O3-0.05K2WO4-0.05Na2MoO4, wherein K2CO3, Na2CO3, Nb2O5, and Sb2O3 are prepared in proportions of 14.6wt%, 12.06wt%, 55.63wt%, and 2.56wt%, respectively.

[0041] Step 2: Pour the prepared raw materials into a fluorinated bottle, add 2 to 4 times the weight of zirconium balls and 0.5 to 1 times the weight of anhydrous ethanol, and mix on a roller mill for 12 to 24 hours.

[0042] Step 3: Pour the slurry obtained in Step 2 into a glass petri dish and dry it in an oven at 70~100℃. Grind it through an 80~120 mesh sieve for later use.

[0043] Step 4: Place the powder obtained in Step 3 into a 40mm diameter mold and press it into a cylindrical block. Place it into a box furnace with programmable temperature control and heat it to 850℃ at a heating rate of 5℃ / min. Hold it at that temperature for 6 hours. Then cool it to room temperature with the furnace to complete the pre-firing. Grind it and pass it through an 80-mesh sieve for later use to obtain powder. Pure phase KNNS ceramics were synthesized through Step 4.

[0044] Step 5: Add 7.97wt% K2WO4 and 7.18wt% Na2MoO4 to the powder obtained in Step 4, put it into a ball mill, and ball mill it a second time at 800 rpm for 24 h.

[0045] Step 6: Pour the slurry obtained in Step 5 into a glass petri dish and dry it in an 80 ℃ oven. Grind it through an 80 mesh sieve for later use.

[0046] Step 7: Add an appropriate amount (10% to 20% of the powder mass) of 10wt% polyvinyl butyral (PVB) ethanol solution to the powder obtained in Step 6, grind and granulate it, and then pass it through an 80-mesh sieve for later use.

[0047] Step 8: Place the powder obtained in Step 7 into a mold with a diameter of 10mm and press it into a green body under a pressure of 127MPa.

[0048] Step 9: Place the green blank obtained in Step 8 into a programmable temperature controlled box furnace, raise the temperature to 600 ℃ at a heating rate of 2 ℃ / min and hold for 2 h for debinding. Then raise the temperature to the sintering temperature (see table) at a heating rate of 2 ℃ / min and hold for 2 h for densification sintering. Finally, lower the temperature to 600 ℃ at a cooling rate of 2 ℃ / min and cool to room temperature with the furnace.

[0049] Step 10: The material obtained in Step 9 is processed to impart piezoelectric properties. Specifically, this involves: smoothing the ceramic sheet obtained in Step 9 with sandpaper; evenly applying silver paste to both sides of the ceramic sheet with a brush; drying it in an 80°C oven; then firing it in a muffle furnace at a heating rate of 5°C / min to 850°C, holding it at that temperature for 30 min, and then cooling it to room temperature with the furnace. The resulting ceramic sheet is then placed in high-temperature silicone oil at 100°C, and an electric field of 30 kV / cm is applied and held for 20 min to polarize it, thus preparing the material with the chemical formula 0.9 (K... 0.48 Na 0.52 (Nb) 0.96 Sb 0.04 Lead-free piezoelectric ceramic material of O3-0.05K2WO4-0.05Na2MoO4.

[0050] The lead-free piezoelectric ceramic material obtained in step ten was subjected to electrical performance testing. The sintering temperature and electrical performance test results of Example 1 are shown in Table 1 below: In the table, d 33 d represents the piezoelectric constant; 31 Kp represents the transverse piezoelectric constant; Qm represents the planar electromechanical coupling coefficient; Tc represents the Curie temperature; ε represents the mechanical quality factor; and Tc represents the Curie temperature. r denoted by δ(%), which represents the relative permittivity; tan δ(%) represents the loss factor.

[0051] like Figure 1 The image shown is a scanning electron microscope (SEM) image of the lead-free piezoelectric ceramic material prepared in Example 1, which is used to show its microstructure, grain size and compactness. As can be seen from the image, the large grain size of the ceramic is 10~20 micrometers, and the surface is dense without large pores, which is beneficial to the improvement of the dielectric properties of the ceramic.

[0052] Example 2 Using analytically pure K₂CO₃, Na₂CO₃, Nb₂O₅, Sb₂O₃, K₂WO₄, and Na₂MoO₄ as raw materials, according to the chemical formula 0.95 (K 0.48 Na0.52 (Nb) 0.96 Sb 0.04 The ingredients are prepared as follows: O3-0.025K2WO4-0.025Na2MoO4, wherein K2CO3, Na2CO3, Nb2O5, and Sb2O3 are prepared in proportions of 15.86wt%, 13.11wt%, 60.46wt%, and 2.77wt%, respectively; K2WO4 and Na2MoO4 are prepared in proportions of 4.10wt% and 3.70wt%, respectively. The specific preparation steps are the same as in Example 1.

[0053] The sintering temperature and electrical performance test results of Example 2 are shown in Table 2 below.

[0054] Table 2 Example 3 Using analytically pure K₂CO₃, Na₂CO₃, Nb₂O₅, Sb₂O₃, K₂WO₄, and Na₂MoO₄ as raw materials, according to the chemical formula 0.98 (K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 The ingredients are prepared as follows: O3-0.01K2WO4-0.01Na2MoO4, wherein K2CO3, Na2CO3, Nb2O5, and Sb2O3 are prepared in proportions of 16.66wt%, 13.77wt%, 63.49wt%, and 2.91wt%, respectively; K2WO4 and Na2MoO4 are prepared in proportions of 1.67wt% and 1.5wt%, respectively. The specific preparation steps are the same as in Example 1.

[0055] The sintering temperature and electrical performance test results of Example 3 are shown in Table 3 below.

[0056] Table 3 Comparative Example 1 Using analytical grade K₂CO₃, Na₂CO₃, Nb₂O₅, Sb₂O₃, and Na₂MoO₄ as raw materials, according to the chemical formula 0.95 (K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 The ingredients are prepared as follows: K2CO3-0.05Na2MoO4, wherein K2CO3, Na2CO3, Nb2O5 and Sb2O3 are 15.90wt%, 13.14wt%, 60.60wt% and 2.78wt% respectively; in addition, 7.58wt% Na2MoO4 is added before the second ball milling. The specific preparation steps are the same as in Example 1.

[0057] The sintering temperature and electrical performance test results of Comparative Example 1 are shown in Table 4 below.

[0058] Table 4 Comparative Example 2 Using analytical grade K₂CO₃, Na₂CO₃, Nb₂O₅, Sb₂O₃, and K₂WO₄ as raw materials, according to the chemical formula 0.95 (K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 The ingredients are O3-0.05K2WO4, wherein K2CO3, Na2CO3, Nb2O5 and Sb2O3 are taken as 15.82wt%, 13.08wt%, 60.30wt% and 2.77wt% respectively. In addition, 8.03wt% K2WO4 is added before the second ball milling. The specific preparation steps are the same as in Example 1.

[0059] The sintering temperature and electrical performance test results of Comparative Example 2 are shown in Table 5 below.

[0060] Table 5 To address the poor overall performance of pure KNN ceramics, the inventors explored various methods, such as adding tungstate (e.g., Comparative Example 2) or molybdate (e.g., Comparative Example 1) as sintering aids. However, these improvements were either limited in effectiveness or introduced new problems, such as the potential decrease in certain performance parameters due to single doping, or the inability to effectively balance high piezoelectric constant with low sintering temperature. The embodiments of this invention, through the synergistic effect of tungstate and molybdate, not only reduce the sintering temperature of lead-free piezoelectric ceramic materials (from the prior art's 1150℃~1200℃ to the present application's 1070℃~1140℃), but also improve the piezoelectric constant (d) of lead-free piezoelectric ceramic materials. 33 This reduces the dielectric loss of lead-free piezoelectric ceramic materials, greatly improving their overall performance. They can be applied to piezoelectric devices with high requirements for piezoelectric performance, such as piezoelectric motors.

[0061] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A lead-free piezoelectric ceramic material, characterized in that: The lead-free piezoelectric ceramic material is represented by the chemical general formula: (1-x-y)(K 1-a Na a )(Nb 1-b M b )O3-xAWO4-yBMoO4; where, (K 1-a Na a )(Nb 1-b M b )O3 represents a sodium potassium niobate-based ceramic material, 0.4 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.1, M is a doping metal element; x and y are mole fractions, satisfying: 0 < x ≤ 0.025, 0 < y ≤ 0.025, and 0 < x + y ≤ 0.05; AWO4 is tungstate, and BMoO4 is molybdate.

2. The lead-free piezoelectric ceramic material as described in claim 1, characterized in that, In AWO4, A is either K or Na; in BMoO4, it is either K or Na.

3. The lead-free piezoelectric ceramic material as described in claim 1, characterized in that, AWO4 is K2WO4, and BMoO4 is Na2MoO4.

4. The lead-free piezoelectric ceramic material as described in claim 1, characterized in that, In the aforementioned lead-free piezoelectric ceramic materials, potassium sodium niobate-based ceramic materials (K 1-a Na a (Nb) 1-b M b O3 has a perovskite structure, and Nb in this perovskite structure 5+ The lattice sites of the ions are partially affected by W generated by xAWO4. 6+ And Mo produced by yBMoO4 6+ Ion substitution; the doped metal element M is one of Sb, Ta, Ge, Fe, Mn, La, and Eu.

5. The lead-free piezoelectric ceramic material as described in claim 1, characterized in that, x and y satisfy: x=0.025, y=0.025; or x and y satisfy: x=0.01, y=0.

01.

6. The lead-free piezoelectric ceramic material as described in claim 1, characterized in that, In the lead-free piezoelectric ceramic material, the total mass content of W and Mo is 1wt%~7.8wt%.

7. The lead-free piezoelectric ceramic material as described in claim 4, characterized in that, Potassium sodium niobate-based ceramic materials are (K 0.48 Na 0.52 (Nb) 0.96 Sb 0.04 )O3.

8. A method for preparing a lead-free piezoelectric ceramic material according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Batching and primary ball milling: Using K2CO3, Na2CO3, Nb2O5, and oxides doped with metal elements as raw materials, according to the general chemical formula (1-xy) (K 1-a Na a (Nb) 1-b M b The ingredients are prepared according to the stoichiometric ratio of O3, and after ball milling, drying and sieving, a primary mixed powder is obtained. (2) Pre-calcination: The first-mixed powder obtained in step (1) is pressed into shape and pre-calcined at a predetermined temperature to obtain pre-calcined powder; (3) Secondary ball milling and doping: tungstate AWO4 and molybdate BMoO4 are added to the pre-calcined powder obtained in step (2) according to the stoichiometric ratio of xAWO4 and yBMoO4 in the general chemical formula, and the mixture is ball-milled, dried and sieved to obtain a secondary mixed powder. (4) Molding and sintering: Add binder to the secondary mixed powder obtained in step (3), granulate, sieve and press to form green body; after debinding the green body, sinter it at 1070-1140℃ to obtain sintered body; (5) The sintered body obtained in step (3) is subjected to polarization treatment to obtain the lead-free piezoelectric ceramic material.

9. The method for preparing lead-free piezoelectric ceramic material according to claim 8, characterized in that, In step (2), the pre-firing at the predetermined temperature includes: heating to 800-900℃ at a heating rate of 1-5℃ / minute and holding at that temperature for 4-8 hours.

10. The method for preparing lead-free piezoelectric ceramic material according to claim 8, characterized in that, In step (4), the mass of the added binder accounts for 10% to 20% of the mass of the secondary mixed powder.

11. The method for preparing lead-free piezoelectric ceramic material according to claim 8, characterized in that, In step (4), the adhesive removal process includes: heating to 450-650℃ at a heating rate of 1-3℃ / minute and holding at that temperature for 4-10 hours.

12. The method for preparing lead-free piezoelectric ceramic material according to claim 8, characterized in that, In step (4), the sintering at 1070-1140℃ includes: heating to 1070-1140℃ at a heating rate of 1-3℃ / min and holding for 1-4 hours to perform densification sintering, and then cooling to 500-700℃ at a cooling rate of 1-3℃ / min and then cooling to room temperature with the furnace.

13. The method for preparing lead-free piezoelectric ceramic material according to claim 8, characterized in that, In step (5), the polarization process includes: after printing silver and burning silver on the sintered body, polarization is performed in an electric field.

14. The method for preparing lead-free piezoelectric ceramic material according to claim 13, characterized in that, In step (5), the polarization treatment includes: uniformly applying silver paste to both sides of the sintered body, drying it, heating it to 800-900℃ at a heating rate of 1-5℃ / min and holding it at that temperature for 0.5-1 hour to burn silver, then cooling it to room temperature with the furnace, and then placing it in high-temperature silicone oil at 60-110℃, applying an electric field of 20-40 kV / cm, and holding it at that temperature for 10-30 min to polarize it.

15. A piezoelectric device, characterized in that, The piezoelectric component of the piezoelectric device is made of the lead-free piezoelectric ceramic material as described in any one of claims 1 to 7.

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