A multilayer lead-free piezoelectric ceramic electrode and its preparation method

Abstract

This invention discloses a multilayered lead-free piezoelectric ceramic electrode and its fabrication method, relating to the field of piezoelectric ceramic technology. The multilayered lead-free piezoelectric ceramic electrode comprises alternating piezoelectric ceramic layers and an inner electrode layer. The inner electrode layer adopts an Ag-Pd alloy / nickel gradient composite structure, and a transition layer is provided between the piezoelectric ceramic layers and the inner electrode layer; the transition layer is made of BaCo. 0.4 Fe 0.4 Zr 0.2 O 3‑δ With BaZr 0.7 Ce 0.2 Y 0.1 O 3‑δ The electrodes are composited at a mass ratio of 7:3, with the thickness ratio of Ag-Pd alloy to nickel in the inner electrode layer being 1:2 to 1:3. This invention solves the technical problems of high cost, low bonding strength, and poor high-temperature stability of existing multilayer piezoelectric ceramic electrodes. It has the advantages of excellent piezoelectric performance, low cost, and long service life, and can be widely used in precision manufacturing, medical equipment, and other fields.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ceramics technology, specifically to a multilayer lead-free piezoelectric ceramic electrode and its preparation method. Background Technology

[0002] Multilayer piezoelectric ceramics play a crucial role in high-tech fields such as precision machining, medical equipment, aerospace, and laser communication due to their advantages of small size, high displacement resolution, fast response speed, and large output force. The core structure of multilayer piezoelectric ceramics consists of alternating layers of piezoelectric ceramics and an inner electrode layer. The performance of the inner electrode and the bonding quality with the ceramic layers directly determine the overall performance and lifespan of the device.

[0003] Currently, the internal electrodes of multilayer piezoelectric ceramics widely used in industry are mainly Ag-Pd alloy electrodes. Although Ag-Pd alloys possess good conductivity and high-temperature stability, and can be co-fired with the ceramic layer, Pd, as a precious metal, is expensive, resulting in high device manufacturing costs and severely limiting its large-scale application. To reduce costs, researchers have attempted to use base metals such as nickel and copper as alternatives to Ag-Pd alloys as internal electrodes. However, base metal electrodes face numerous technical challenges during high-temperature co-firing: on the one hand, base metals need to be sintered in a reducing atmosphere to avoid oxidation, but a reducing atmosphere leads to a significant increase in the oxygen vacancy concentration in the piezoelectric ceramic material, damaging the ceramic's crystal structure and causing increased leakage conductivity and decreased piezoelectric performance; on the other hand, the significant difference in thermal expansion coefficients between the base metal and the piezoelectric ceramic layer easily generates interfacial thermal stress after co-firing, resulting in low interfacial bonding strength and failure phenomena such as delamination and detachment, severely affecting the device's lifespan.

[0004] Furthermore, the electrode-ceramic layer interface in existing multilayer piezoelectric ceramics is mostly in direct contact, lacking an effective transition structure, which further exacerbates the interface bonding problem. Related studies show that the bonding strength of traditional multilayer piezoelectric ceramic electrodes is typically only 25-30 MPa. Under long-term dynamic operating conditions, interface failure easily occurs. 4 Performance degradation can exceed 10% after a single electrical cycle. Meanwhile, the performance of existing lead-free piezoelectric ceramics still cannot match that of commercially available lead-based ceramics. How to reduce costs by using base metal electrodes while ensuring excellent piezoelectric performance and high-temperature stability has become a pressing technical bottleneck in the field of multilayer piezoelectric ceramics. Summary of the Invention

[0005] To address the technical problems of existing multilayer lead-free piezoelectric ceramic electrodes, such as high cost, low bonding strength, poor high-temperature stability, and insufficient piezoelectric performance, the present invention aims to provide a multilayer lead-free piezoelectric ceramic electrode and its preparation method. By designing a gradient composite internal electrode structure, introducing a functional transition layer, and optimizing the co-firing process parameters, the invention achieves high-efficiency compatibility between base metal electrodes and lead-free piezoelectric ceramics, effectively improving electrode bonding strength and overall device performance, thereby reducing costs, improving electrode bonding strength and piezoelectric performance, and extending service life.

[0006] In a first aspect, the present invention provides a multilayered lead-free piezoelectric ceramic electrode, comprising alternating piezoelectric ceramic layers and an inner electrode layer, wherein a transition layer is provided between the piezoelectric ceramic layers and the inner electrode layer; the inner electrode layer is an Ag-Pd alloy / nickel gradient composite structure, wherein from the side near the transition layer to the side away from the transition layer, there are sequentially Ag-Pd alloy sublayers and nickel sublayers, and the thickness ratio of the Ag-Pd alloy sublayer to the nickel sublayer is 1:2-1:3; the transition layer is made of BaCo. 0.4 Fe 0.4 Zr 0.2 O 3-δ With BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ The composite material is formed at a mass ratio of 7:3, with a transition layer thickness of 1-3 μm; the piezoelectric ceramic layer is a strontium-doped potassium sodium niobate (KNSN)-based lead-free piezoelectric ceramic (K... 0.5 Na 0.5 ) 1−x Sr x NbO3 (where x = 0.01~0.10), with a single layer thickness of 20-60 μm.

[0007] Furthermore, the mass fraction of Pd in ​​the Ag-Pd alloy sublayer is 5-12%, with the remainder being Ag; the nickel sublayer is a Zr-doped nickel electrode with a Zr doping amount of 0.5-1.0 wt%, and the Zr doping can improve the reduction resistance and mechanical stability of the nickel electrode.

[0008] Secondly, the present invention also provides a method for preparing the above-mentioned multilayer lead-free piezoelectric ceramic electrode, comprising the following steps: S1: Preparation of piezoelectric ceramic slurry: KNSN-based lead-free piezoelectric ceramic powder, dispersant, binder, plasticizer and solvent are mixed and ball-milled for 24-36 hours to obtain a uniform piezoelectric ceramic slurry; S2: Casting: Piezoelectric ceramic slurry is cast and dried to obtain a piezoelectric ceramic green film. The thickness of the green film is controlled to be 20-60μm. S3: Preparation of transition layer slurry and internal electrode slurry: The transition layer slurry is made of BaCo... 0.4 Fe0.4 Zr 0.2 O 3-δ Powder, BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ It is made by mixing powder, binder and solvent; the internal electrode paste includes Ag-Pd alloy paste and nickel paste. The Ag-Pd alloy paste is made of Ag powder, Pd powder, binder and solvent, and the nickel paste is made of nickel powder, Zr powder, binder and solvent. S4: Coating and Lamination: Transition layer paste and inner electrode paste are screen-printed sequentially on one side of the piezoelectric ceramic green film. After drying, a ceramic film with a transition layer and an inner electrode layer is obtained. The ceramic films with transition layers and inner electrode layers are alternately stacked so that the polarity of the inner electrode layers of adjacent ceramic films is opposite, thus obtaining a laminated green body. S5: Pressing and Debinding: The laminated preform is subjected to isostatic pressing at a pressure of 80-100 MPa. The temperature is 60-70℃, and the holding time is 5-10 min. Then, debinding is performed, with a heating rate of 1-2℃ / min, heating to 500℃, and holding for 2-3 h. S6: Sintering: Place the debinding green body in a reducing atmosphere furnace for sintering. The reducing atmosphere is a N2-H2 mixed gas with an H2 volume fraction of 5-8%. The heating rate is 3-5℃ / min. The temperature is raised to 980-1050℃ and held for 2-4 hours. Then, the green body is cooled to room temperature in the furnace. S7: Preparation of end electrodes: Apply silver paste to both ends of the sintered laminated preform, and fire it at 600-650℃ for 30-60 minutes to obtain the finished laminated lead-free piezoelectric ceramic electrode.

[0009] Further, in step S1, the dispersant is polyvinylpyrrolidone, the binder is ethyl cellulose, the plasticizer is dibutyl phthalate, and the solvent is ethanol; the mass ratio of piezoelectric ceramic powder, dispersant, binder, plasticizer, and solvent is 100:2-3:5-8:3-5:40-60.

[0010] Furthermore, in step S3, the solid content of the transition layer slurry is 50-60 wt%, the solid content of the Ag-Pd alloy slurry is 50-80 wt%, and the solid content of the nickel slurry is 55-65 wt%; the binder in all three slurries is ethyl cellulose, and the amount used is 3-5 wt% of the powder mass. Beneficial effects

[0011] This invention employs an Ag-Pd alloy / nickel gradient composite internal electrode structure, which significantly reduces the amount of precious metal Pd used, resulting in lower costs compared to traditional pure Ag-Pd electrodes. At the same time, the Ag-Pd alloy sublayer exhibits good compatibility with the transition layer and nickel sublayer, and the Zr-doped nickel sublayer possesses excellent anti-reduction properties, thus solving the compatibility problem of base metal electrodes co-fired with lead-free ceramics.

[0012] The transition layer uses BaCo 0.4 Fe 0.4 Zr 0.2 O 3-δ With BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ The composite system has a thermal expansion coefficient that matches well with both the piezoelectric ceramic layer and the inner electrode layer, effectively alleviating interfacial thermal stress during co-firing. At the same time, the transition layer has good ionic conductivity, which can promote interfacial charge transport, improve the piezoelectric performance of the device, and increase the electrode bonding strength to over 45 MPa.

[0013] The optimized sintering process parameters, combined with the gradient electrode and transition layer structure, fully utilize the piezoelectric properties of KNSN-based lead-free ceramics, achieving a piezoelectric coefficient d33 of over 850 pm / V, far exceeding the 590 pm / V of commercial PZT-5H ceramics. The devices exhibit excellent temperature and cycle stability, with an output displacement change rate ≤8% from room temperature to 100℃. 6 Performance degradation ≤5% after each electrical cycle.

[0014] The preparation method of this invention adopts mature processes such as casting and screen printing. The process is simple, highly controllable, suitable for large-scale industrial production, and has broad application prospects. 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. The described embodiments are only some preferred embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Unless otherwise specified, the experimental methods used in the embodiments are conventional or common methods in the art, and the materials and reagents used are commercially available unless otherwise specified.

[0017] Example 1 A method for preparing a multilayer lead-free piezoelectric ceramic electrode includes the following steps: S1: Preparation of piezoelectric ceramic slurry: KNSN-based lead-free piezoelectric ceramic powder (K 0.5 Na 0.5 ) 99.9 Sr 0.1 100g of NbO3, 2g of polyvinylpyrrolidone, 5g of ethyl cellulose, 3g of dibutyl phthalate and 40g of ethanol were mixed and ball-milled for 24h to obtain a uniform piezoelectric ceramic slurry.

[0018] S2: Casting: The piezoelectric ceramic slurry is cast and dried to obtain a piezoelectric ceramic green film with a thickness of 20μm.

[0019] S3: Preparation of transition layer slurry and internal electrode slurry: The transition layer slurry is made of BaCo... 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder 7g, BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ The solid content of the powder is 50wt% when 3g of powder, 0.5g of ethyl cellulose and 10.5g of ethanol are mixed together; the Ag-Pd alloy slurry is made of 95g of Ag powder, 5g of Pd powder, 5g of ethyl cellulose and 70g of ethanol, with a solid content of 60wt%; the nickel slurry is made of 99.5g of nickel powder, 0.5g of Zr powder, 5g of ethyl cellulose and 86g of ethanol, with a solid content of 55wt%.

[0020] S4: Coating and Lamination: Transition layer paste (1 μm thick) and internal electrode paste (Ag-Pd alloy sublayer thickness 1 μm, nickel sublayer thickness 2 μm) are sequentially screen-printed on one side of the piezoelectric ceramic green film. After drying at 120℃ for 30 min, a ceramic film with transition layer and internal electrode layer is obtained. Twenty ceramic films with transition layer and internal electrode layer are alternately stacked so that the polarity of the internal electrode layer of adjacent ceramic films is opposite, to obtain a laminated green body.

[0021] S5: Pressing and Debinding: The laminated preform is subjected to warm isostatic pressing at a pressure of 80 MPa and a temperature of 60°C for 5 min; then debinding is performed at a heating rate of 1°C / min, heating to 500°C and holding for 2 h.

[0022] S6: Sintering: Place the debinding blank in a reducing atmosphere furnace for sintering. The reducing atmosphere is a N2-H2 mixed gas (H2 volume fraction 5%). The heating rate is 3℃ / min. The temperature is raised to 980℃ and held for 2 hours. Then, the blank is cooled to room temperature in the furnace.

[0023] S7: Preparation of end electrodes: Silver paste is coated on both ends of the sintered laminated blank, and silver is fired at 600℃ for 30 minutes to obtain the finished laminated lead-free piezoelectric ceramic electrode.

[0024] Example 2 A method for preparing a multilayer lead-free piezoelectric ceramic electrode includes the following steps: S1: Preparation of piezoelectric ceramic slurry: KNSN-based lead-free piezoelectric ceramic powder (K 0.5 Na 0.5 ) 99.9 Sr 0.1 100g of NbO3, 2.5g of polyvinylpyrrolidone, 6.5g of ethyl cellulose, 4g of dibutyl phthalate, and 50g of ethanol were mixed and ball-milled for 30h to obtain a uniform piezoelectric ceramic slurry.

[0025] S2: Casting: The piezoelectric ceramic slurry is cast and dried to obtain a piezoelectric ceramic green film with a thickness of 40μm.

[0026] S3: Preparation of transition layer slurry and internal electrode slurry: The transition layer slurry is made of BaCo... 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder 7g, BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ The solid content of the mixture is 55wt% (3g powder, 0.5g ethyl cellulose, and 8.7g ethanol). The Ag-Pd alloy slurry is made from 88g Ag powder, 12g Pd powder, 5g ethyl cellulose, and 57g ethanol, with a solid content of 65wt%. The nickel slurry is made from 99g nickel powder, 1g Zr powder, 5g ethyl cellulose, and 71g ethanol, with a solid content of 60wt%.

[0027] S4: Coating and Lamination: Transition layer paste (2 μm thick) and internal electrode paste (Ag-Pd alloy sublayer thickness 1 μm, nickel sublayer thickness 2.5 μm) are sequentially screen-printed on one side of the piezoelectric ceramic green film. After drying at 120℃ for 40 min, a ceramic film with transition layer and internal electrode layer is obtained. Twenty ceramic films with transition layer and internal electrode layer are alternately stacked so that the polarity of the internal electrode layer of adjacent ceramic films is opposite to obtain a laminated green body.

[0028] S5: Pressing and Debinding: The laminated preform is subjected to warm isostatic pressing at a pressure of 90 MPa and a temperature of 65°C for 8 min; then debinding is performed at a heating rate of 1.5°C / min, heating to 500°C and holding for 2.5 h.

[0029] S6: Sintering: Place the debinding blank in a reducing atmosphere furnace for sintering. The reducing atmosphere is a N2-H2 mixed gas (H2 volume fraction 6.5%). The heating rate is 4℃ / min. The temperature is raised to 1020℃ and held for 3 hours. Then, the blank is cooled to room temperature in the furnace.

[0030] S7: Preparation of end electrodes: Silver paste is coated on both ends of the sintered laminated preform, and silver is fired at 620℃ for 45 minutes to obtain the finished laminated lead-free piezoelectric ceramic electrode.

[0031] Example 3 A method for preparing a multilayer lead-free piezoelectric ceramic electrode includes the following steps: S1: Preparation of piezoelectric ceramic slurry: KNSN-based lead-free piezoelectric ceramic powder (K 0.5 Na 0.5 ) 99.9 Sr 0.1 100g of NbO3, 3g of polyvinylpyrrolidone, 8g of ethyl cellulose, 5g of dibutyl phthalate and 60g of ethanol were mixed and ball-milled for 36 hours to obtain a uniform piezoelectric ceramic slurry.

[0032] S2: Casting: The piezoelectric ceramic slurry is cast and dried to obtain a piezoelectric ceramic green film with a thickness of 60μm.

[0033] S3: Preparation of transition layer slurry and internal electrode slurry: The transition layer slurry is made of BaCo... 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder 7g, BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ The solid content of the mixture is 60wt% (3g powder, 0.5g ethyl cellulose, and 7g ethanol). The Ag-Pd alloy slurry is made from 92g Ag powder, 8g Pd powder, 5g ethyl cellulose, and 45g ethanol, with a solid content of 70wt%. The nickel slurry is made from 99.2g nickel powder, 0.8g Zr powder, 5g ethyl cellulose, and 56.5g ethanol, with a solid content of 65wt%.

[0034] S4: Coating and Lamination: Transition layer paste (thickness 3μm) and internal electrode paste (Ag-Pd alloy sublayer thickness 1μm, nickel sublayer thickness 3μm) are sequentially screen-printed on one side of the piezoelectric ceramic green film. After drying at 120℃ for 60min, a ceramic film with transition layer and internal electrode layer is obtained. Twenty ceramic films with transition layer and internal electrode layer are alternately stacked so that the polarity of the internal electrode layer of adjacent ceramic films is opposite, to obtain a laminated green body.

[0035] S5: Pressing and Debinding: The laminated preform is subjected to warm isostatic pressing at a pressure of 100 MPa and a temperature of 70°C for 10 min; then debinding is performed at a heating rate of 2°C / min, heating to 500°C and holding for 3 h.

[0036] S6: Sintering: Place the debinding blank in a reducing atmosphere furnace for sintering. The reducing atmosphere is a N2-H2 mixed gas (H2 volume fraction 8%). The heating rate is 5℃ / min. The temperature is raised to 1050℃ and held for 4 hours. Then, the blank is cooled to room temperature in the furnace.

[0037] S7: Preparation of end electrodes: Silver paste is coated on both ends of the sintered laminated preform, and silver is fired at 650℃ for 60 minutes to obtain the finished laminated lead-free piezoelectric ceramic electrode.

[0038] Comparative Example 1 The preparation method is the same as in Example 2, except that there is no transition layer, the inner electrode is a pure Ag-Pd alloy, and there is no nickel sublayer.

[0039] Comparative Example 2 The preparation method is the same as in Example 2, except that there is no transition layer, the inner electrode is a pure nickel electrode (without Zr doping), and there is no Ag-Pd alloy sublayer.

[0040] Comparative Example 3 The preparation method is the same as in Example 2, except that the inner electrode is a single nickel electrode (Zr doping amount 0.8wt%) without an Ag-Pd alloy sublayer.

[0041] Comparative Example 4 The preparation method is the same as in Example 2, except that the transition layer slurry is made of BaCo. 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder 6g, BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ It is prepared by mixing 4g of powder, 0.5g of ethyl cellulose and 8.7g of ethanol, with a solid content of 55wt%.

[0042] Comparative Example 5 The preparation method is the same as in Example 2, except that the transition layer slurry is made of BaCo. 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder 8g, BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ It is prepared by mixing 2g of powder, 0.5g of ethyl cellulose and 8.7g of ethanol, with a solid content of 55wt%.

[0043] Performance verification test The multilayer lead-free piezoelectric ceramic electrodes prepared in Examples 1-3 and Comparative Examples 1-5 were used as test samples, and five parallel samples were prepared for each sample.

[0044] Electrode bonding strength test: According to "CB / T3794-2014 Test Method for Performance of Piezoelectric Ceramic Materials - Test of Electrode Bond Strength", the welding tensile test is conducted, the tensile force value at the moment of electrode detachment is recorded, and the bonding strength is calculated.

[0045] Piezoelectric performance testing: The piezoelectric coefficient d33 was tested using a quasi-static d33 tester; the planar electromechanical coupling coefficient kp and dielectric loss tanδ (1kHz) were tested using an impedance analyzer.

[0046] Temperature stability test: The piezoelectric coefficient d33 of the sample is tested every 20°C within the range of room temperature to 100°C, and the output displacement change rate is calculated.

[0047] Cyclic stability test: The sample was subjected to a unipolar electric field of 20 kV / cm for 10 cycles. 6 The piezoelectric coefficient d33 was recorded before and after the second electric cycle test, and the performance degradation rate was calculated.

[0048] Table 1 Performance Verification Test Results Record Sheet

[0049] According to the data in Table 1, 1) the electrode bonding strength of Examples 1-3 is above 45 MPa, with an average of 46.8 MPa, significantly higher than that of Comparative Examples 1-3 (22.6-30.5 MPa). This is because the thermal expansion coefficients of the transition layer, piezoelectric ceramic layer, and inner electrode layer in Examples 1-3 are well matched, effectively alleviating the interfacial thermal stress during co-firing. Simultaneously, the composite oxide of the transition layer can form a strong chemical bond with the electrode and ceramic layer, improving the interfacial bonding strength. Comparative Example 1, however, lacks a transition layer, resulting in a weak interfacial bonding between the pure Ag-Pd electrode and the ceramic layer. Comparative Example 2, lacking a transition layer and using a pure nickel electrode, suffers from poor interfacial thermal stress and chemical compatibility, leading to the lowest bonding strength. Although Comparative Example 3 has a transition layer, the inner electrode lacks an Ag-Pd alloy sublayer, resulting in a lower interfacial bonding strength than the examples. In Comparative Examples 4-5, the transition layer contains BaCo... 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder and BaZr 0.7 Ce 0.2 Y 0.1 O 3-δThe mass ratios of the powders were 6:4 and 8:2, which resulted in differences in the coefficients of thermal expansion between the transition layer and the piezoelectric ceramic layer and the inner electrode layer. The interfacial thermal stress during the co-firing process was greater than that in Examples 1-3, which led to a weakening of the interfacial bonding strength.

[0050] The piezoelectric coefficients d33 of Examples 1-3 are all above 850 pm / V, significantly higher than the piezoelectric coefficients 523-650 pm / V of Comparative Examples 1-3. This is because the transition layer has good ionic conductivity, which promotes interfacial charge transport and reduces charge loss; at the same time, the gradient electrode structure reduces the interfacial barrier, allowing the piezoelectric performance of KNSN-based ceramics to be fully utilized. Although the pure Ag-Pd electrode of Comparative Example 1 has good conductivity, the lack of a transition layer hinders interfacial charge transport, and the intrinsic piezoelectric performance of commercial PZT ceramics is lower than that of the optimized KNSN-based ceramics; Comparative Examples 2 and 3 have poor interfacial bonding and large charge loss, resulting in piezoelectric performance inferior to the Examples. The kp values ​​of the Examples are all above 0.62 and tanδ is below 0.028, indicating that the devices have good electromechanical coupling performance and low energy loss characteristics. The transition layer compositions of Comparative Examples 4-5 are similar to those of Examples 1-3, therefore their kp and tanδ values ​​are close to those of Examples 1-3.

[0051] Temperature stability analysis: The output displacement change rate of Examples 1-3 in the range of room temperature to 100℃ is all below 8%, which is better than 9.5% of Comparative Example 1, 12.3% of Comparative Example 2, and 10.1% of Comparative Example 3. This is because the synergistic effect of the transition layer and gradient electrode reduces the influence of interfacial thermal stress on the ceramic crystal structure, making the device more stable in performance when the temperature changes; while Comparative Examples 2 and 3 have poor interface matching, and the interface is prone to microcracks when the temperature changes, resulting in larger performance fluctuations. Comparing Example 2 with Comparative Examples 4-5, it can be seen that BaCo in the transition layer 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder and BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ The mass ratio of powder can affect the temperature stability of the device.

[0052] Cyclic stability analysis: Examples 1-3 were analyzed after 10 cycles. 6The performance degradation rate after each cycle was below 5%, with an average of 4.4%, which is better than that of Comparative Example 1 (5.8%), Comparative Example 2 (12.5%), and Comparative Example 3 (9.8%). This is because the Zr-doped nickel sublayer has excellent fatigue resistance, and the transition layer can effectively suppress the initiation and propagation of interface cracks, thus extending the device's lifespan. In contrast, the pure nickel electrode of Comparative Example 2 is prone to oxidation and fatigue failure during cycling, and Comparative Example 3 lacks an Ag-Pd alloy sublayer, resulting in poor interface stability. Comparative Examples 4 and 5 can extend the device's lifespan because the transition layer can suppress interface cracks; however, the proportion of the transition layer was not optimized, so their cycle stability is worse than that of Examples 1-3, but better than that of Comparative Examples 1-3.

[0053] In summary, the multilayered lead-free piezoelectric ceramic electrode and its preparation method of the present invention solve the problems of high cost, low bonding strength and unstable performance of the prior art through the synergistic design of gradient composite electrode, functional transition layer and optimized co-firing process, and have excellent comprehensive performance and industrialization prospects.

[0054] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A multilayer lead-free piezoelectric ceramic electrode, characterized in that, The structure comprises alternating piezoelectric ceramic layers and an inner electrode layer, with a transition layer between the piezoelectric ceramic layers and the inner electrode layer. The inner electrode layer has an Ag-Pd alloy / nickel gradient composite structure, consisting of an Ag-Pd alloy sublayer and a nickel sublayer, arranged sequentially from the side closest to the transition layer to the side furthest away from it, with a thickness ratio of 1:2 to 1:3 between the Ag-Pd alloy sublayer and the nickel sublayer. The transition layer is made of BaCo. 0.4 Fe 0.4 Zr 0.2 O 3-δ With BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ The composite material is made in a mass ratio of 7:3, with a transition layer thickness of 1-3 μm; the piezoelectric ceramic layer is a strontium-doped potassium sodium niobate-based lead-free piezoelectric ceramic with a single layer thickness of 20-60 μm.

2. The multilayer lead-free piezoelectric ceramic electrode according to claim 1, characterized in that, The Pd mass fraction in the Ag-Pd alloy sublayer is 5-12%, with the remainder being Ag; the nickel sublayer is a Zr-doped nickel electrode with a Zr doping amount of 0.5-1.0 wt%.

3. A method for preparing a multilayer lead-free piezoelectric ceramic electrode as described in any one of claims 1-2, characterized in that, Includes the following steps: S1: Preparation of piezoelectric ceramic slurry: KNSN-based lead-free piezoelectric ceramic powder, dispersant, binder, plasticizer and solvent are mixed and ball-milled for 24-36 hours to obtain a uniform piezoelectric ceramic slurry; S2: Casting: Piezoelectric ceramic slurry is cast and dried to obtain a piezoelectric ceramic green film. The thickness of the green film is controlled to be 20-60μm. S3: Preparation of transition layer slurry and internal electrode slurry: The transition layer slurry is made of BaCo... 0.4 Fe 0.4 Zr 0.2 O 3-δ Powder, BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ It is made by mixing powder, binder and solvent; the internal electrode paste includes Ag-Pd alloy paste and nickel paste. The Ag-Pd alloy paste is made of Ag powder, Pd powder, binder and solvent, and the nickel paste is made of nickel powder, Zr powder, binder and solvent. S4: Coating and Lamination: Transition layer paste and inner electrode paste are screen-printed sequentially on one side of the piezoelectric ceramic green film. After drying, a ceramic film with a transition layer and an inner electrode layer is obtained. The ceramic films with transition layers and inner electrode layers are alternately stacked so that the polarity of the inner electrode layers of adjacent ceramic films is opposite, thus obtaining a laminated green body. S5: Pressing and debinding: The laminated preform is subjected to isostatic pressing at a pressure of 80-100MPa and a temperature of 60-70℃, with a holding time of 5-10min; then debinding is performed, with a heating rate of 1-2℃ / min, heating to 500℃ and holding for 2-3h. S6: Sintering: Place the debinding green body in a reducing atmosphere furnace for sintering. The reducing atmosphere is a N2-H2 mixed gas with an H2 volume fraction of 5-8%. The heating rate is 3-5℃ / min. The temperature is raised to 980-1050℃ and held for 2-4 hours. Then, the green body is cooled to room temperature in the furnace. S7: Preparation of end electrodes: Apply silver paste to both ends of the sintered laminated preform, and fire it at 600-650℃ for 30-60 minutes to obtain the finished laminated lead-free piezoelectric ceramic electrode.

4. The preparation method according to claim 3, characterized in that, In step S1, the dispersant is polyvinylpyrrolidone, the binder is ethyl cellulose, the plasticizer is dibutyl phthalate, and the solvent is ethanol; the mass ratio of piezoelectric ceramic powder, dispersant, binder, plasticizer, and solvent is 100:2-3:5-8:3-5:40-60.

5. The preparation method according to claim 3, characterized in that, In step S3, the solid content of the transition layer slurry is 50-60 wt%, the solid content of the Ag-Pd alloy slurry is 50-80 wt%, and the solid content of the nickel slurry is 55-65 wt%; the binder in all three slurries is ethyl cellulose, and the amount used is 3-5 wt% of the powder mass.

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