High-performance lead-free piezoelectric ceramic and preparation method thereof

Abstract

The invention discloses a high-performance lead-free piezoelectric ceramic and a preparation method thereof, belongs to the technical field of electronic ceramic materials, and provides a component system of (1-x) [(Ba0. 85Ca0. 15) (Zr0. 10Ti0. 90) O3] + x [Bi (Zn0. 5Ti0. 5) O3] + ywt% sintering aid (x is more than or equal to 0.01 and less than or equal to 0.04, and y is more than or equal to 0.2 and less than or equal to 0.6) aiming at the problems of low Curie temperature, high sintering temperature and unstable performance caused by Bi-based modification volatile property of the existing BCZT, and a Li2CO3-Bi2O3-CuO (1: 1: 3) composite aid is adopted for secondary ball milling coating, so that the high-performance lead-free piezoelectric ceramic is prepared. And sintering at 1280-1320 DEG C to obtain the ceramic. According to the scheme, Tc is increased through BZT, the sintering temperature is reduced through an auxiliary liquid phase, and a Bi-rich environment is provided to realize in-situ compensation and inhibition of Bi volatilization defects, so that the ceramic has high d33, low loss and better thermal stability.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic materials technology, specifically relating to a high-performance lead-free piezoelectric ceramic and its preparation method. Background Technology

[0002] Piezoelectric ceramics are fundamental materials in the modern electronics industry, widely used in sensors, actuators, and ultrasonic transducers. With increasingly stringent environmental regulations, lead-free piezoelectric materials to replace traditional lead-containing PZT ceramics have become a research hotspot. Among them, (Ba,Ca)(Zr,Ti)O3 (BCZT)-based lead-free piezoelectric ceramics are considered one of the most promising systems due to their excellent piezoelectric coefficient (d33>500pC / N) near the quasi-isomorphic phase boundary (MPB).

[0003] However, existing BCZT ceramics face severe technical bottlenecks in practical applications: (1) Low Curie temperature (Tc): The Tc of BCZT is usually below 100℃, resulting in a narrow operating temperature range. Its high voltage performance degrades sharply at slightly higher ambient temperatures, which cannot meet the needs of high-temperature environments such as automotive electronics.

[0004] (2) High sintering temperature: High-temperature sintering of 1450℃~1500℃ is usually required for densification, which not only consumes a lot of energy, but also easily leads to abnormal grain growth and reduces the mechanical strength of ceramics.

[0005] (3) The contradiction between component volatilization and performance stability: In order to improve Tc, existing technologies often try to introduce bismuth (Bi)-based components with high Curie points for doping. However, Bi is extremely volatile at high temperatures, resulting in A-site vacancies in the crystal lattice. This not only disrupts the stoichiometry but also generates a large number of defect dipoles, leading to increased dielectric loss and reduced piezoelectric activity.

[0006] Therefore, how to significantly increase the Curie temperature of BCZT ceramics while reducing the sintering temperature, and effectively solve the performance degradation problem caused by volatile components, so as to achieve synergistic improvement of multiple properties, is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] This invention aims to solve the technical problems of existing BCZT lead-free piezoelectric ceramics, such as low Curie temperature, high sintering temperature, and unstable performance due to the volatilization of modified components. It provides a high-performance lead-free piezoelectric ceramic and its preparation method. Specifically, this invention achieves synergistic effects between raw materials by specifically improving the modified components and sintering aids, utilizing specific components in the aids to "compensate" for the volatilization of the modified components during sintering through "in-situ compensation." More specifically, the technical solution adopted by this invention is as follows: A high-performance lead-free piezoelectric ceramic, the components of which include a matrix material, a modifying component and a sintering aid; The chemical formula of the matrix material is: (Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 O3; The chemical formula of the modified component is: Bi(Zn) 0.5 Ti 0.5 O3; The sintering aid is composed of lithium carbonate (Li2CO3), bismuth oxide (Bi2O3), and copper oxide (CuO).

[0008] The overall chemical composition expression of the high-performance lead-free piezoelectric ceramic is as follows: (1−x)[(Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 )O3]+x[Bi(Zn 0.5 Ti 0.5 [O3] + ywt% sintering aid; Where x is the mole fraction, and 0.01≤x≤0.04; y is the mass percentage relative to the total mass of the matrix material and the modified component, and 0.2≤y≤0.6.

[0009] Furthermore, in the sintering aid, the molar ratio of Li2CO3, Bi2O3 and CuO is 1:1:3.

[0010] The present invention also provides a method for preparing the above-mentioned high-performance lead-free piezoelectric ceramic, comprising the following steps: Step 1: Matrix and modified components are mixed (one-time batching): According to the chemical formula (1−x)[(Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 )O3]+x[Bi(Zn 0.5 Ti 0.5 )O3] Calculate the amount of each raw material, weigh high-purity BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, and ZnO. All raw materials are analytical grade (AR grade, ≥99.0%) and are standard chemical raw materials that are available on the market. Step 2: Mixing and Pre-firing: Mix the raw materials weighed in step 1, add anhydrous ethanol at a solid-liquid ratio of 1g:1.5mL, and then add zirconium oxide balls at a ball-to-material ratio of 3:1. Ball mill in a planetary ball mill for 24 hours to obtain a slurry. After drying the slurry, sieve it and place it in an alumina crucible. Pre-calcine (calcine) it at 900℃~950℃ for 4 hours to synthesize the main crystalline phase powder. Step 3: Preparation and addition of additives (secondary batching): Li2CO3, Bi2O3 and CuO were weighed separately and mixed evenly in a molar ratio of 1:1:3 to prepare a composite additive powder. The composite additive powder was weighed according to the mass percentage y wt% and added to the main crystalline phase powder after pre-calcination in step 2. Anhydrous ethanol was added to it according to a solid-liquid ratio of 1g:1.5mL, and zirconia balls were added to it according to a ball-to-material ratio of 3:1. The mixture was ball-milled for 24 hours to make the composite additive powder uniformly coat the particle surface of the main crystalline phase powder, and the slurry after the second ball milling was obtained. Step 4: Granulation and molding: The slurry after secondary ball milling is dried, passed through an 80-mesh sieve, and 2% to 3% of polyvinyl alcohol (PVA) aqueous solution (5wt%) is added as a binder. The mixture is then manually ground and granulated. The granulated powder is pressed into round green discs with a diameter of 12 mm and a thickness of 1.2 mm under a pressure of 150 MPa. Step 5: Debinding and Sintering The circular green blank is placed on an alumina plate and heated to 600-650℃ at 1℃ / min and held for 2 hours to remove the binder. Then, the temperature is increased to 1280-1320℃ at 3℃ / min and held for 3 hours for sintering. The blank is then naturally cooled to room temperature in the furnace to obtain the sintered ceramic sheet. Step 6: Silvering and Polarization: The sintered ceramic sheet is coated with silver paste on both sides and calcined at 650-670℃ for 15-20 minutes to form an electrode. In a silicone oil bath, a DC electric field of 3.5 kV / mm is applied at 40-50℃ for 30 minutes to polarize the ceramic. After polarization, the ceramic is left to stand for 24 hours to obtain a high-performance lead-free piezoelectric ceramic.

[0011] The beneficial effects of this invention are: (1) Modified component Bi(Zn) 0.5 Ti 0.5 Enhanced polarization effect of BZT (BZT): This invention introduces BZT as a modifier. 3 + Exhibiting lone pair electron effects, Zn can generate strong lattice distortion and polarization, significantly increasing the Curie temperature (Tc) of the material. Meanwhile, Zn... 2+ and Ti 4+The resulting composite ions can stabilize the perovskite structure, allowing the ceramic to maintain its high voltage electrical activity while increasing the temperature (Tc) to over 130°C.

[0012] (2) Liquid phase sintering effect of Li2CO3-Bi2O3-CuO additive: This ternary composite additive forms a low eutectic liquid phase, which can wet the grains, promote grain rearrangement and mass transfer, and significantly reduce the sintering temperature of ceramics from the conventional 1480℃ to 1280℃~1320℃, significantly reducing energy consumption and inhibiting abnormal grain growth.

[0013] (3) Synergistic Effect of Raw Materials - "In-situ Self-Compensation" Mechanism: This is the core innovation of this invention. In conventional doping, Bi in BZT is highly volatile during sintering, leaving vacancies at A sites and leading to performance degradation. The additives specially formulated in this invention contain Bi2O3. During sintering, the liquid phase formed by the additives surrounds the grains, creating a local "Bi-rich environment". According to the principle of chemical equilibrium, this effectively suppresses the volatilization of Bi in the BZT composition inside the crystal lattice; at the same time, if Bi is lost from the crystal lattice surface, Bi in the liquid phase can quickly diffuse to fill the vacancies, achieving "in-situ compensation". This synergistic effect solves the contradiction between "increasing Tc (requiring Bi addition)" and "maintaining high performance (requiring suppression of Bi volatilization)", enabling the material to achieve high Tc while still maintaining extremely low dielectric loss and high voltage constant.

[0014] (4) Significant progress: Li in the additives + Small ionic radius, some Li + It diffuses into the A-site of the crystal lattice, further filling vacancies and acting as a flux; Cu 2+ As an acceptor dopant, it can improve the mechanical quality factor (Qm) of the material. The superposition of multiple mechanisms gives the product of this invention both high d33, high Tc and excellent fatigue resistance. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Meanwhile, the specifications of the raw materials and reagents used in the following embodiments are described as follows: Barium carbonate (BaCO3), calcium carbonate (CaCO3), lithium carbonate (Li2CO3): Sinopharm Chemical Reagent Co., Ltd., purity ≥99.0%.

[0016] Zirconium dioxide (ZrO2), titanium dioxide (TiO2), bismuth oxide (Bi2O3), zinc oxide (ZnO), copper oxide (CuO): Shanghai Aladdin Biochemical Technology Co., Ltd., purity ≥99.9%.

[0017] Example 1

[0018] A high-performance lead-free piezoelectric ceramic and its preparation method: (1) Chemical composition and formulation: Target chemical composition: (1-x)[(Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 )O3]+x[Bi(Zn 0.5 Ti 0.5 [O3] + ywt% sintering aid; Values: x = 0.01, y = 0.2.

[0019] Additive ratio: Li2CO3:Bi2O3:CuO=1:1:3 (molar ratio).

[0020] (2) Raw materials: Weigh the analytical grade / high purity raw materials according to the above stoichiometric ratio: BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, ZnO; 1. Molar basis of main crystalline phase (matrix + modifying component): Based on the principle that "total amount of main crystalline phase = 1 mol": BCZT molar number: (1-x) mol; chemical formula (Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 O3; BZT molar number: x mol; chemical formula Bi(Zn) 0.5 Ti 0.5 O3; 2. Raw material selection and stoichiometry: The raw materials used for primary batching are: BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, and ZnO. Their stoichiometric relationships (based on 1 mol of the main crystalline phase) are as follows: BaCO3: 0.85(1-x) mol; CaCO3: 0.15(1-x) mol; ZrO2: 0.10(1-x) mol; TiO2: 0.90(1-x)+0.5x mol; ZnO: 0.5x mol Bi₂O₃: 0.5x mol (because Bi in BZT is 1 mol, the corresponding Bi₂O₃ is 0.5 mol).

[0021] Table 1: Weighing mass table based on 1 mol of main crystalline phase:

[0022] The auxiliary raw materials are Li2CO3, Bi2O3, and CuO.

[0023] Based on the theoretical molar mass of the principal crystalline phase: M BCZT ≈228.26 g / mol; M BZT ≈312.15 g / mol; m 主晶相 =(1-x)M BCZT +xM BZT ≈229.10 g; The total mass of the additives is: m 助剂 =0.2%×229.10≈0.458 g; Internal distribution of additives (molar ratio 1:1:3; by mass fraction: Li2CO3≈12.91%, Bi2O3≈61.39%, CuO≈25.70%).

[0024] Table 2: Weighing and Mass Table of Additives

[0025] (3) Preparation method: Step 1: Primary ingredient preparation (matrix + modified components): Calculate the amount of each powder substance according to x=0.01 and convert it to weighing mass. Weigh BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, and ZnO.

[0026] Step 2: Mixing, ball milling, and pre-firing: Add anhydrous ethanol, solid-liquid ratio: 1g:1.5mL; Zirconia balls were added at a ball-to-material ratio of 3:1. Planetary ball milling: 24 hours; slurry obtained.

[0027] After the slurry is dried and sieved, it is placed into an alumina crucible. Pre-calcination: Hold at 900℃ for 4 hours (the temperature can be selected within the range of 900 to 950℃, and 900℃ is used in this example); After cooling, the powder is lightly crushed and sieved to obtain the main crystalline phase powder.

[0028] Step 3: Secondary batching (additive preparation and coating-type secondary ball milling): Weigh out Li2CO3, Bi2O3 and CuO in a molar ratio of 1:1:3, mix them evenly to prepare a composite additive powder; Weigh out 0.2 wt% of the composite additive powder and add it to the main crystalline phase powder; Add anhydrous ethanol (solid-liquid ratio 1g:1.5mL) and zirconium oxide balls (ball-to-material ratio 3:1); The mixture is ball-milled a second time for 24 hours to ensure that the additives are evenly dispersed and to achieve uniform coating on the surface of the main powder particles; thus, a secondary slurry is obtained.

[0029] Step 4: Granulation and molding: The slurry is dried twice and then passed through an 80-mesh sieve. Add binder: Add 5wt% PVA aqueous solution at 2% of the powder mass; Grinding and granulation; Compression molding: Pressed at 150MPa into a round blank with a diameter of 12 mm and a thickness of about 1.2 mm.

[0030] Step 5: Debinding and Sintering Glue removal: Heat to 600℃ at a rate of 1℃ / min and hold for 2 hours; Sintering: Heat to 1280℃ at 3℃ / min and hold for 3 hours; cool to room temperature in the furnace; obtain dense ceramic sheets.

[0031] Step 6: Electrodes and Polarization: Double-sided silver paste coating; electrode formation by firing at 650℃ for 15 minutes; Silicone oil bath polarization: 40℃, DC field strength 3.5kV / mm, 30min; After polarization, the product is left to stand for 24 hours to obtain a lead-free piezoelectric ceramic product.

[0032] Example 2

[0033] A high-performance lead-free piezoelectric ceramic and its preparation method: (1) Chemical composition and formulation: Target chemical composition: (1-x)[(Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 )O3]+x[Bi(Zn 0.5 Ti 0.5 [O3] + ywt% sintering aid; Values: x = 0.025, y = 0.4.

[0034] Additive ratio: Li2CO3:Bi2O3:CuO=1:1:3 (molar ratio).

[0035] (2) Raw materials: Weigh the following analytical grade / high purity raw materials according to the above stoichiometric ratios: BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, ZnO; 1. Molar basis of main crystalline phase (matrix + modifying component): Based on the principle that "total amount of main crystalline phase = 1 mol": BCZT molar number: (1-x) mol; chemical formula (Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 O3; BZT molar number: x mol; chemical formula Bi(Zn) 0.5 Ti 0.5 O3; 2. Raw material selection and stoichiometry: The raw materials used for primary batching are: BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, and ZnO. Their stoichiometric relationships (based on 1 mol of the main crystalline phase) are as follows: BaCO3: 0.85(1-x) mol; CaCO3: 0.15(1-x) mol; ZrO2: 0.10(1-x) mol; TiO2: 0.90(1-x)+0.5x mol; ZnO: 0.5x mol Bi₂O₃: 0.5x mol (because Bi in BZT is 1 mol, the corresponding Bi₂O₃ is 0.5 mol).

[0036] Table 3: Weighing mass table based on 1 mol of main crystalline phase:

[0037] The auxiliary raw materials are Li2CO3, Bi2O3, and CuO.

[0038] Based on the theoretical molar mass of the principal crystalline phase: M BCZT ≈228.26 g / mol; M BZT ≈312.15 g / mol; m 主晶相 =(1-x)M BCZT +xM BZT ≈230.35 g; The total mass of the additives is: m 助剂 =0.4%×230.35≈0.921 g; Internal distribution of additives (molar ratio 1:1:3; by mass fraction: Li2CO3≈12.91%, Bi2O3≈61.39%, CuO≈25.70%).

[0039] Table 4: Weighing and Mass Table of Additives

[0040] (3) Preparation method: Step 1: Primary ingredient preparation (matrix + modified components): Calculate the amount of each powder substance according to x=0.025 and convert it to weighing mass. Weigh BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, and ZnO.

[0041] Step 2: Mixing, ball milling, and pre-firing: Add anhydrous ethanol, solid-liquid ratio: 1g:1.5mL; Zirconia balls were added at a ball-to-material ratio of 3:1. Planetary ball milling: 24 hours; slurry obtained.

[0042] After the slurry is dried and sieved, it is placed into an alumina crucible. Pre-calcination: Hold at 940℃ for 4 hours (the temperature can be selected within the range of 900-950℃, and 940℃ is used in this example); After cooling, the powder is lightly crushed and sieved to obtain the main crystalline phase powder.

[0043] Step 3: Secondary batching (additive preparation and coating-type secondary ball milling): Weigh out Li2CO3, Bi2O3 and CuO in a molar ratio of 1:1:3, mix them evenly to prepare a composite additive powder; Weigh out 0.4wt% of the composite additive powder and add it to the main crystalline phase powder; Add anhydrous ethanol (solid-liquid ratio 1g:1.5mL) and zirconium oxide balls (ball-to-material ratio 3:1); The mixture is ball-milled a second time for 24 hours to ensure that the additives are evenly dispersed and to achieve uniform coating on the surface of the main powder particles; thus, a secondary slurry is obtained.

[0044] Step 4: Granulation and molding: The slurry is dried twice and then passed through an 80-mesh sieve. Add binder: Add 3% of the powder mass of 5wt% PVA aqueous solution; Grinding and granulation; Compression molding: Pressed at 150MPa into a round blank with a diameter of 12 mm and a thickness of about 1.2 mm.

[0045] Step 5: Debinding and Sintering Glue removal: Heat to 650℃ at a rate of 1℃ / min and hold for 2 hours; Sintering: Heat to 1320℃ at 3℃ / min and hold for 3 hours; cool to room temperature in the furnace; obtain dense ceramic sheets.

[0046] Step 6: Electrodes and Polarization: Double-sided silver paste coating; electrode formation by firing at 670℃ for 18 minutes; Silicone oil bath polarization: 45℃, DC field strength 3.5kV / mm, 30min; After polarization, the product is left to stand for 24 hours to obtain a lead-free piezoelectric ceramic product.

[0047] Example 3

[0048] A high-performance lead-free piezoelectric ceramic and its preparation method: (1) Chemical composition and formulation: Target chemical composition: (1-x)[(Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 )O3]+x[Bi(Zn 0.5 Ti 0.5 [O3] + ywt% sintering aid; Values: x=0.04, y=0.6.

[0049] Additive ratio: Li2CO3:Bi2O3:CuO=1:1:3 (molar ratio).

[0050] (2) Raw materials: Weigh the analytical grade / high purity raw materials according to the above stoichiometric ratio: BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, ZnO; 1. Molar basis of main crystalline phase (matrix + modifying component): Based on the principle that "total amount of main crystalline phase = 1 mol": BCZT molar number: (1-x) mol; chemical formula (Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 O3; BZT molar number: x mol; chemical formula Bi(Zn) 0.5 Ti 0.5 O3; 2. Raw material selection and stoichiometry: The raw materials used for primary batching are: BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, and ZnO. Their stoichiometric relationships (based on 1 mol of the main crystalline phase) are as follows: BaCO3: 0.85(1-x) mol; CaCO3: 0.15(1-x) mol; ZrO2: 0.10(1-x) mol; TiO2: 0.90(1-x)+0.5x mol; ZnO: 0.5x mol Bi₂O₃: 0.5x mol (because Bi in BZT is 1 mol, the corresponding Bi₂O₃ is 0.5 mol).

[0051] Table 5: Weighing mass table based on 1 mol of main crystalline phase:

[0052] The auxiliary raw materials are Li2CO3, Bi2O3, and CuO.

[0053] Based on the theoretical molar mass of the principal crystalline phase: M BCZT ≈228.26 g / mol; M BZT ≈312.15 g / mol; m 主晶相 =(1-x)M BCZT +xM BZT ≈231.62 g; The total mass of the additives is: m 助剂 =0.6%×231.62≈1.390 g; Internal distribution of additives (molar ratio 1:1:3; by mass fraction: Li2CO3≈12.91%, Bi2O3≈61.39%, CuO≈25.70%).

[0054] Table 6: Weighing and Mass Table of Additives

[0055] (3) Preparation method: Step 1: Primary ingredient preparation (matrix + modified components): Calculate the amount of each powder substance according to x=0.04 and convert it to weighing mass. Weigh BaCO3, CaCO3, ZrO2, TiO2, Bi2O3, and ZnO.

[0056] Step 2: Mixing, ball milling, and pre-firing: Add anhydrous ethanol, solid-liquid ratio: 1g:1.5mL; Zirconia balls were added at a ball-to-material ratio of 3:1. Planetary ball milling: 24 hours; slurry obtained.

[0057] After the slurry is dried and sieved, it is placed into an alumina crucible. Pre-calcination: Hold at 950℃ for 4 hours (the temperature can be selected within the range of 900 to 950℃, and 950℃ is used in this example); After cooling, the powder is lightly crushed and sieved to obtain the main crystalline phase powder.

[0058] Step 3: Secondary batching (additive preparation and coating-type secondary ball milling): Weigh out Li2CO3, Bi2O3 and CuO in a molar ratio of 1:1:3, mix them evenly to prepare a composite additive powder; Weigh out 0.6 wt% of the composite additive powder and add it to the main crystalline phase powder; Add anhydrous ethanol (solid-liquid ratio 1g:1.5mL) and zirconium oxide balls (ball-to-material ratio 3:1); The mixture is ball-milled a second time for 24 hours to ensure that the additives are evenly dispersed and to achieve uniform coating on the surface of the main powder particles; thus, a secondary slurry is obtained.

[0059] Step 4: Granulation and molding: The slurry is dried twice and then passed through an 80-mesh sieve. Add binder: Add 3% of the powder mass of 5wt% PVA aqueous solution; Grinding and granulation; Compression molding: Pressed at 150MPa into a round blank with a diameter of 12 mm and a thickness of about 1.2 mm.

[0060] Step 5: Debinding and Sintering Glue removal: Heat to 650℃ at a rate of 1℃ / min and hold for 2 hours; Sintering: Heat to 1320℃ at 3℃ / min and hold for 3 hours; cool to room temperature in the furnace; obtain dense ceramic sheets.

[0061] Step 6: Electrodes and Polarization: Double-sided silver paste coating; electrode formation by firing at 670℃ for 20 minutes; Silicone oil bath polarization: 50℃, DC field strength 3.5kV / mm, 30min; After polarization, the product is left to stand for 24 hours to obtain a lead-free piezoelectric ceramic product.

[0062] Comparative Examples 1-6 Comparative Examples 1 through 6 served as control groups for Example 2, as detailed below: Comparative Example 1 Composition: x=0; additives remain y=0.4 (Li2CO3:Bi2O3:CuO=1:1:3); the rest of the process is the same as in Example 2, and finally lead-free piezoelectric ceramic products are obtained.

[0063] Comparative Example 2 Composition: x=0.025; y=0, sintering is still performed at 1320℃ / 3h; the rest of the process is the same as in Example 2, and finally lead-free piezoelectric ceramic product is obtained.

[0064] Comparative Example 3 The additives were changed to a binary mixture: Li2CO3:CuO=1:3 (keeping the total amount y=0.4 unchanged; Bi2O3 was directly omitted); the rest of the process was the same as in Example 2, and finally lead-free piezoelectric ceramic products were obtained.

[0065] Comparative Example 4 Additives: Li2CO3:Bi2O3=1:1 (y=0.4); the rest of the process is the same as in Example 2, and finally lead-free piezoelectric ceramic products are obtained.

[0066] Comparative Example 5 Additives: Bi2O3:CuO=1:3 (y=0.4); the rest of the process is the same as in Example 2, and finally lead-free piezoelectric ceramic products are obtained.

[0067] Comparative Example 6 The molar ratio of additives Li2CO3:Bi2O3:CuO was changed to 1:1:1 (y=0.4); the rest of the process was the same as in Example 2, and finally lead-free piezoelectric ceramic products were obtained.

[0068] The lead-free piezoelectric ceramic products prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests. The performance test process is as follows, and the test results are shown in Table 7. (1) Piezoelectric constant (d33): The piezoelectric constant (d33) was measured at room temperature (25℃) using a ZJ-3A quasi-static d33 measuring instrument.

[0069] (2) Curie temperature (Tc): Using an Agilent 4294A precision impedance analyzer connected to a temperature control chamber, the change of dielectric constant with temperature (25~200℃) at a frequency of 1kHz was tested. The temperature corresponding to the maximum value of dielectric constant is Tc.

[0070] (3) Dielectric loss (tanδ): Measured using an impedance analyzer at 1 kHz and room temperature. The lower the loss, the fewer the defects and the better the insulation.

[0071] (4) Bulk density: tested using Archimedes' displacement method.

[0072] (5) Temperature stability test: The polarized sample was placed in a high-temperature environment of 100℃ for 1 hour, then removed and cooled to room temperature. The d33 was measured again, and the depolarization rate at 100℃ was calculated as: (initial d33 - d33 after high temperature) / initial d33 × 100%. The smaller the depolarization rate at 100℃, the better the thermal stability.

[0073] Table 7 Test Results

[0074] The core technical problem to be solved by this invention is: in BCZT-based lead-free piezoelectric ceramics, simultaneously achieving (i) a significant increase in Curie temperature Tc to broaden the operating temperature range, (ii) a decrease in sintering temperature to reduce energy consumption and facilitate densification / controllable microstructure, and (iii) while introducing volatile Bi-based modified components to increase Tc, suppressing performance instability problems such as increased dielectric loss, decreased piezoelectric activity, and severe high-temperature depolarization caused by volatilization-related defects.

[0075] Based on the analysis of Examples 1-3, Comparative Examples 1-6, and Table 7, the beneficial effects of the present invention compared to the prior art can be summarized as "synergistic improvement of multiple indicators and better stability", and this effect is achieved by the synergistic effect of "BZT modification + Li2CO3-Bi2O3-CuO ternary additive".

[0076] (1) Regarding the piezoelectric constant d33, Examples 1-3 of this invention achieved 520, 560, and 545 pC / N respectively, which are significantly better than the multiple control groups. In particular, Example 2 (x=0.025, y=0.4) achieved the highest d33 of 560 pC / N in this group of data. Comparative Example 2 (also x=0.025 but without additives, y=0) only had 395 pC / N, indicating that BZT modification alone without additive synergy would lead to a significant deterioration in piezoelectric performance; while the addition of ternary additives in Example 2 increased d33 to 560 pC / N, indicating that additives play a decisive role in the recovery / enhancement of piezoelectric activity. Comparative Example 1 (x=0, only additives) had 490 pC / N, which is lower than the 560 pC / N of Example 2, further proving that "BZT modification provides high piezoelectric potential" and "ternary additives ensure sintering and defect control" must be present simultaneously to obtain the highest level of d33.

[0077] (2) Regarding the Curie temperature Tc, Examples 1-3 were 118, 138, and 156 °C, respectively, which increased with the increase of the BZT mole fraction x from 0.01→0.025→0.04, demonstrating the direct contribution of BZT introduction to the increase of Tc. In contrast, Comparative Example 1 (x=0) had a Tc of only 96 °C, proving that the Tc was low without the introduction of BZT; while Comparative Example 2 (x=0.025) had a Tc of 140 °C, which was comparable to 138 °C in Example 2, indicating that "the main reason for the increase in Tc comes from BZT modification", and the introduction of the additive did not come at the expense of Tc (at least in Table 7, the Tc of Example 2 and Comparative Example 2 are on the same order of magnitude), thus achieving a balance between "increasing Tc" and "maintaining high voltage".

[0078] (3) In terms of dielectric loss tanδ and high-temperature stability (depolarization rate at 100℃), the synergistic advantage of ternary additives is the most obvious. Example 2 has tanδ=0.78% and depolarization rate of 4.8%, both of which are the best or near-optimal levels in Table 7; while Comparative Example 2 (without additives) has a tanδ as high as 1.60% and a depolarization rate of 18.0%, indicating that when BZT (containing Bi) is present but ternary additives are lacking, defects / insulation degradation is significant and high-temperature depolarization is severe. Further comparison of the additive composition: Comparative Example 3 (no Bi2O3, only Li2CO3:CuO=1:3) tanδ=1.45%, depolarization rate 14.5%; Comparative Example 4 (no CuO, only Li2CO3:Bi2O3=1:1) tanδ=1.05%, depolarization rate 8.5%; Comparative Example 5 (no Li2CO3, only Bi2O3:CuO=1:3) tanδ=1.10%, depolarization rate 9.0%; Comparative Example 6 (ternary but ratio 1:1:1) tanδ=1.20%, depolarization rate 10.5%. These data all point to the fact that only when the additive simultaneously contains Li2CO3, Bi2O3, and CuO in a molar ratio of 1:1:3 (Example 2) can the loss be reduced to 0.78% and the depolarization rate reduced to 4.8%; the absence of any component or an improper ratio will cause an increase in loss, a larger depolarization rate, and a worse thermal stability. This result is consistent with the "in-situ self-compensation" approach proposed in the invention: BZT introduces high Tc but also introduces the risk of Bi volatilization, while Bi2O3 in the ternary additive provides a locally Bi-rich environment during sintering, which is beneficial for suppressing / compensating Bi-related defects, thus directly reflected in a significant reduction in tanδ and a significant decrease in depolarization rate at 100℃. In Table 7, the results of "with BZT but without Bi2O3 additive" (Comparative Example 3) and "with BZT and Bi2O3 but lacking other components or with inappropriate proportions" (Comparative Examples 4-6) did not achieve the low loss and low depolarization rate of Example 2, which also proves the necessity of the synergistic system of the present invention from the opposite perspective.

[0079] (4) Regarding densification (density) and sintering feasibility, the densities of Examples 2 and 3 were 5.83 and 5.85 g / cm³, respectively. 3 The concentration was significantly higher than that of control example 2 (5.55 g / cm³) without the additive. 3 This indicates that the additives have a substantial promoting effect on sintering densification; and densification is usually consistent with the improvement of piezoelectric properties, which is also consistent with the fact that d33 in Example 2 is significantly higher than that in Comparative Example 2. The simultaneous achievement of "high density + low tanδ + low depolarization" shows that the present invention does not simply pursue a single indicator, but achieves overall balanced optimization of performance within the same component / process framework.

[0080] In summary, based entirely on Table 7, it can be concluded that the present invention improves Tc by introducing BZT into BCZT (compared to Comparative Example 1), and achieves synergistic control of sintering densification and defects (characterized by tanδ and depolarization rate) through a specific molar ratio of 1:1:3 Li2CO3-Bi2O3-CuO ternary additive. This results in a significant increase in d33, a reduction in dielectric loss, and a significant improvement in depolarization resistance at 100℃ while maintaining / enhancing Tc. Among these, Example 2 (x=0.025, y=0.4) exhibits the best overall performance combination (highest d33, lowest tanδ, lowest depolarization rate, and high density) in this set of data, demonstrating the substantial technical effect of the "component + additive" synergistic design of the present invention.

[0081] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0082] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-performance lead-free piezoelectric ceramic, characterized in that, It includes matrix materials, modifying components, and sintering aids; The chemical formula of the matrix material is: (Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 O3; The chemical formula of the modified component is: Bi(Zn) 0.5 Ti 0.5 O3; The sintering aid is composed of lithium carbonate, bismuth oxide and copper oxide; The overall chemical composition expression of the high-performance lead-free piezoelectric ceramic is as follows: (1-x)[(Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 )O3]+x[Bi(Zn 0.5 Ti 0.5 [O3] + ywt% sintering aid; Where x is the mole fraction, and 0.01≤x≤0.04; y is the mass percentage relative to the total mass of the matrix material and the modified component, and 0.2≤y≤0.

6.

2. The high-performance lead-free piezoelectric ceramic according to claim 1, characterized in that, The molar ratio of Li2CO3, Bi2O3 and CuO in the sintering aid is 1:1:

3.

3. The high-performance lead-free piezoelectric ceramic according to claim 1, characterized in that, x = 0.025 and y = 0.

4.

4. A method for preparing a high-performance lead-free piezoelectric ceramic according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step (1): One batch of ingredients: according to (1-x)[(Ba 0.85 Ca 0.15 (Zr) 0.10 Ti 0.90 )O3]+x[Bi(Zn 0.5 Ti 0.5 Weigh out and mix BaCO3, CaCO3, ZrO2, TiO2, Bi2O3 and ZnO raw materials; Step (2): First ball milling and pre-calcination: Add anhydrous ethanol and ball mill, then dry and sieve, and pre-calcine at 900-950℃ for 4 hours to obtain the main crystalline phase powder; Step (3): Secondary batching: Mix Li2CO3, Bi2O3 and CuO in a set molar ratio to obtain composite additive powder, add it to the main crystalline phase powder at ywt% and ball mill it a second time to make the composite additive powder uniformly dispersed in the main crystalline phase powder; Step (4): Molding: Add binder, granulate, and press into green body; Step (5): Debinding and sintering: After debinding the green body, sinter at 1280-1320℃ to obtain ceramic sheets; Step (6): Electrode and polarization: An electrode is formed on the surface of the ceramic sheet and polarized to obtain a lead-free piezoelectric ceramic product.

5. The method for preparing a high-performance lead-free piezoelectric ceramic according to claim 4, characterized in that, In both the first ball milling in step (2) and the second ball milling in step (3), anhydrous ethanol was used as the medium, the solid-liquid ratio was 1g:1.5mL, the ball-to-material ratio was 3:1, and the ball milling time was 24 hours.

6. The method for preparing a high-performance lead-free piezoelectric ceramic according to claim 4, characterized in that, Step (5) The debinding process involves heating to 600-650℃ at 1℃ / min and holding for 2 hours; the sintering process involves heating to 1280-1320℃ at 3℃ / min and holding for 3 hours, followed by cooling to room temperature with the furnace.

7. The method for preparing a high-performance lead-free piezoelectric ceramic according to claim 4, characterized in that, In step (4), the binder is a polyvinyl alcohol (PVA) aqueous solution, and the amount added is 2% to 3% of the powder mass. The mass fraction of the PVA aqueous solution is 5 wt%.

8. The method for preparing a high-performance lead-free piezoelectric ceramic according to claim 4, characterized in that, In step (4), the granulated powder is pressed into a round green sheet with a diameter of 12 mm and a thickness of 1.2 mm under a pressure of 150 MPa.

9. The method for preparing a high-performance lead-free piezoelectric ceramic according to claim 4, characterized in that, In step (6), the electrode is coated with silver paste on both sides and formed by burning at 650-670℃ for 15-20 minutes; polarization is carried out in a silicone oil bath, the polarization temperature is 40-50℃, the DC electric field strength is 3.5 kV / mm, the polarization time is 30 minutes, and the electrode is left to stand for 24 hours after polarization.

10. The method for preparing a high-performance lead-free piezoelectric ceramic according to claim 4, characterized in that, In step (3), the composite additive powder is uniformly coated on the surface of the main crystalline phase powder particles by secondary ball milling.

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