Potassium-sodium niobate-based leadless piezoelectric ceramic material and piezoelectric ceramic layer, ceramic slurry and nickel inner electrode piezoelectric ceramic actuator prepared from potassium-sodium niobate-based leadless piezoelectric ceramic material

Abstract

The general formula of the potassium-sodium niobate-based leadless piezoelectric ceramic material is x (K < 0.495 > Na < 0.505 >) Sr < 0.02 > Nb < 0.99 > Sn < 0.01 > O < 3-y > mol% ZrO2, x is greater than or equal to 0.92 and less than or equal to 0.94, and y is greater than or equal to 0.8 and less than or equal to 1.5. The invention also discloses ceramic slurry containing the potassium sodium niobate-based lead-free piezoelectric ceramic material, and a prepared piezoelectric ceramic layer and nickel inner electrode co-fired type lead-free ceramic laminated actuator. According to the invention, Zr ions are introduced to enhance the anti-reduction characteristic of a KNN-based lead-free ceramic matrix, the high strain response activity of a perovskite A-site vacancy defect dipole is fully utilized, the nickel inner electrode co-fired type lead-free piezoelectric ceramic laminated actuator with high electrostrictive displacement output characteristic is obtained in a reduction sintering atmosphere, and the piezoelectric ceramic laminated actuator has excellent driving performance and can be applied to the field of piezoelectric ceramics. Good linear correlation exists between displacement output and driving voltage amplitude.

Description

Technical Field

[0001] The invention relates to the field of functional inorganic non-metallic materials, in particular to a potassium sodium niobate-based lead-free piezoelectric ceramic material and a piezoelectric ceramic layer, ceramic slurry and nickel inner electrode piezoelectric ceramic actuator prepared therefrom. Background Art

[0002] Piezoelectric ceramic actuators use the inverse piezoelectric effect to convert electrical energy into mechanical energy. They are one of the important cornerstones of the booming development of cutting-edge science and technology. They have an important strategic position and practical application value in the fields of nanoimprinting, lithography, micro-electromechanical systems, and optical control platforms. Piezoelectric ceramic actuators with alternating stacked layer configurations are usually composited with metal conductive materials using tape casting technology. Precious metals such as silver / palladium or platinum have become the first choice for electrodes in traditional stacked actuators due to their excellent high-temperature oxidation resistance.

[0003] The high production costs of these precious metal materials significantly increase the economic burden of piezoelectric actuators. In addition, the lead element used in the ceramic matrix not only poses a serious threat to the ecological environment, but also poses a potential hazard to human health.

[0004] As an environmentally friendly alternative, potassium sodium niobate (KNN)-based lead-free piezoelectric ceramics stand out for their good matching characteristics with base metal nickel electrodes during co-firing, and are considered to be the material system with the greatest potential to replace traditional lead zirconate titanate (PZT)-based ceramics. However, there are still many challenges in the transformation process of stacked actuators that realize the co-firing matching of KNN-based lead-free piezoelectric ceramics and nickel electrodes: First, the electro-strain performance of KNN-based ceramics is low, and only less than 0.2% strain output can be obtained under an electric field of 40 kV / cm, which is significantly different from the commercial standards. Second, nickel electrodes are easily oxidized during the high-temperature sintering stage and need to be sintered in a reducing atmosphere to protect the electrodes, but the reducing atmosphere is extremely unfavorable for the sintering of ceramics, which will lead to a significant decrease in the ceramic forming property of the ceramics and a significant increase in the leakage conductivity. Even if it can be sintered into ceramics in the end, its strain performance is extremely limited, and the inverse piezoelectric coefficient usually does not exceed 500 pm / V. In view of this, it is particularly necessary to further develop new ceramic material systems and improve the anti-reduction properties of KNN-based ceramic matrix.

[0005] Although current research reports have pointed out that defect structure control strategies can help obtain comprehensive electrostrain properties comparable to commercial lead-containing ceramic materials, it is still difficult to achieve coordinated optimization of the impedance characteristics and electrostrain properties of KNN-based lead-free ceramics through defect reconstruction under low oxygen partial pressure. Therefore, it is of great research significance and economic value to develop defect structure optimization strategies under reducing atmosphere and develop low-cost, high-driving performance, green and environmentally friendly piezoelectric ceramic actuators. Summary of the invention

[0006] To achieve the above objectives, the present invention provides a lead-free piezoelectric ceramic system with good dielectric insulation properties and excellent electrostrain properties, and prepares a low-cost and high-performance nickel inner electrode co-fired lead-free piezoelectric ceramic stack actuator based on this system.

[0007] The technical solution adopted by the present invention is: A potassium sodium niobate-based lead-free piezoelectric ceramic material, the general formula of which is x (K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3- y mol% ZrO2, of which 0.92≤ x ≤0.94,0.8≤ y ≤1.5.

[0008] Preferably, x=0.93, y=1. That is, the general formula of the preferred potassium sodium niobate-based lead-free piezoelectric ceramic material is 0.93 (K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3-1mol%ZrO2.

[0009] The potassium sodium niobate-based lead-free piezoelectric ceramic material can be prepared by the following method: The raw materials are weighed according to the chemical formula of potassium sodium niobate-based lead-free piezoelectric ceramic materials, mixed with anhydrous ethanol, ball-milled and dried, and the dried powder is ground and refined, and then pre-fired at 800-900° C. in a muffle furnace for 3-10 hours. After the pre-fired powder is cooled, it is added to anhydrous ethanol again, ball-milled and dried for the second time, and then passed through a 40-mesh sieve after grinding to obtain potassium sodium niobate-based lead-free piezoelectric ceramic powder particles.

[0010] The raw materials include carbonates of K, Na, and Sr, and oxides of Nb, Sn, and Zr.

[0011] The preferred pre-firing temperature is 850°C and the preferred pre-firing time is 6 h.

[0012] The present invention also provides a piezoelectric ceramic layer, wherein the piezoelectric ceramic layer is made of the potassium sodium niobate-based lead-free piezoelectric ceramic material.

[0013] Furthermore, the piezoelectric ceramic layer is prepared by tape-casting a ceramic slurry including a potassium sodium niobate-based lead-free piezoelectric ceramic material and then drying it.

[0014] Furthermore, the ceramic slurry includes the following components: potassium sodium niobate-based lead-free piezoelectric ceramic material, solvent, plasticizer, dispersant, defoamer and binder.

[0015] The solvent is n-butyl acetate and anhydrous ethanol; preferably, the volume ratio of n-butyl acetate to anhydrous ethanol is 1.3-1.6:1; The plasticizer is dioctyl phthalate; The dispersant includes dispersant AKM-0531; The defoaming agent is n-butanol; The binder is polyvinyl butyral.

[0016] Furthermore, in the ceramic slurry, based on the total mass of the solvent, plasticizer, dispersant, defoamer and binder, the mass fractions of each component are: 60-85 parts by mass of solvent, 5-10 parts by mass of plasticizer, 5-10 parts by mass of dispersant, 0.5-1.5 parts by mass of defoamer, and 10-25 parts by mass of binder.

[0017] Furthermore, preferably, in the ceramic slurry, based on the total mass of the solvent, plasticizer, dispersant, defoamer and binder, the mass fractions of each component are: 40-55 parts by mass of n-butyl acetate, 20-30 parts by mass of anhydrous ethanol, 5-10 parts by mass of dioctyl phthalate, 0.5-1.5 parts by mass of n-butanol, 5-10 parts by mass of AKM-0531, and 10-25 parts by mass of polyvinyl butyral.

[0018] Furthermore, in the ceramic slurry, the solid content of the potassium sodium niobate-based lead-free piezoelectric ceramic material powder is 40-60wt%.

[0019] The polyvinyl butyral binder is one or both of PVB-60H and PVB-30H, preferably a mixture of PVB-60H and PVB-30H in a mass ratio of 5-8:3-4.

[0020] The viscosity of the ceramic slurry is in the range of 500-5000 mpa·s.

[0021] The present invention also provides the use of the potassium sodium niobate-based lead-free piezoelectric ceramic material or the piezoelectric ceramic layer in the preparation of a nickel inner electrode co-fired lead-free ceramic laminate actuator.

[0022] Furthermore, the present invention also provides a nickel internal electrode co-fired lead-free ceramic laminate actuator, comprising a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers; the piezoelectric ceramic layers and the internal electrode layers are alternately stacked, and at least one layer of the piezoelectric ceramic layer is made of a ceramic slurry comprising a potassium sodium niobate-based lead-free piezoelectric ceramic material.

[0023] The inner electrode layer is a nickel electrode.

[0024] The shape of the inner electrode can be rectangular, circular or a combination of multiple patterns. The inner electrode material is based on nickel powder, and other organic components that make up the electrode slurry are optional. The effective electrode area, the thickness of the piezoelectric ceramic layer and the electrode layer, and the number of effective ceramic layers can be designed and determined according to actual application requirements.

[0025] The present invention also provides a method for preparing a nickel inner electrode co-fired lead-free ceramic laminate actuator, the method comprising the following steps: (1) Preparation of ceramic slurry from potassium sodium niobate-based lead-free piezoelectric ceramic materials, solvents, plasticizers, dispersants and binders; (2) The ceramic slurry is tape-cast into a film and dried to obtain a ceramic green strip, which is the piezoelectric ceramic layer; (3) Printing the nickel electrode slurry onto the surface of the ceramic green strip by screen printing, and drying to obtain a ceramic green strip with a printed electrode pattern; (4) The ceramic green body strips with printed electrode patterns are laminated layer by layer to obtain a multilayer ceramic actuator green body block; (5) The multilayer ceramic actuator green body is subjected to a binder removal treatment, sintering, and annealing heat treatment to obtain a co-fired stacked ceramic actuator. External electrodes are provided on both sides of the co-fired stacked ceramic actuator and solidified to obtain the nickel inner electrode co-fired lead-free ceramic stacked actuator.

[0026] Furthermore, in the step (2), a PET film strip coated with silicone oil on one side is generally used as a substrate, and the ceramic slurry is cast into a film on a casting machine and then dried.

[0027] The scraper height of the casting machine is 200-250 microns, the transmission speed of the PET film belt is 150-200 mm / min, and the heating temperature is 50~60 ℃.

[0028] Preferably, in step (3), the nickel electrode slurry may be a commercially available product.

[0029] In the step (3), a matching printing screen plate can be designed and manufactured according to the specific size requirements of the target electrode pattern. The ceramic green strip is punched and positioned at a predetermined position to ensure accurate alignment of subsequent processes. A high-precision screen printer is used to evenly print the nickel electrode slurry onto the surface of the dried ceramic green strip.

[0030] After screen printing is completed, the drying temperature is 50 ~ 55 ° C and the time is 2-5 min to ensure the initial curing and stability of the electrode slurry.

[0031] In the step (4), the lamination is performed by bidirectional hot pressing, the temperature of the bidirectional hot pressing is set to 60-65°C, the pressing pressure is 50-55 MPa, and the hot pressing time is 20-25 s.

[0032] In the step (4), the number of layers of the multilayer ceramic actuator green body block varies according to specific application requirements and design goals, and can range from a few layers to hundreds of layers.

[0033] Preferably, in step (5), the heating rate of the debinding treatment is 0.5-0.6°C / min, the target temperature is 500-550°C, and the holding time is 10-12 h.

[0034] During the debinding treatment, the gas atmosphere is a nitrogen and hydrogen mixed gas, and the air in the furnace is first evacuated by a vacuum pump before the gas is introduced. In the nitrogen and hydrogen mixed gas, the volume ratio of hydrogen is preferably 0.5-4%.

[0035] The nitrogen and hydrogen mixed gas is a reducing atmosphere, which can prevent the nickel electrode from being oxidized during the high-temperature sintering stage.

[0036] During the debinding process, the organic residues in the ceramic green body are slowly decomposed by precisely controlling the heating rate and atmosphere conditions to avoid cracking or defective holes caused by violent decomposition.

[0037] After the debinding is completed, the temperature is gradually increased to the sintering temperature range and maintained for a certain period of time to achieve the densification of the ceramic matrix and the co-firing bonding of the electrode material.

[0038] During the sintering process, the gas atmosphere is the same as that during the debinding process, which is a nitrogen and hydrogen mixed gas, and the volume ratio of hydrogen is preferably 0.5-4%.

[0039] The heating rate of the sintering treatment is 2~3℃ / min, the target temperature is 1130-1150℃, and the holding time is 3-6h.

[0040] The heating rate of the annealing heat treatment is 2-2.5°C / min, the target temperature is 780-790°C, and the holding time is 8-10 h.

[0041] The annealing heat treatment uses nitrogen as the annealing heat treatment atmosphere. After heating to a specified temperature at a constant heating rate, a heat preservation operation is performed, and then the furnace is cooled, and finally a co-fired stacked ceramic actuator block with good dielectric insulation is obtained.

[0042] The present invention finds that after sintering, the leakage conductance of the ceramic matrix is ​​still relatively high, so an annealing heat treatment is performed to oxidize the ceramic matrix to reduce the concentration of oxygen vacancy defects and improve dielectric insulation performance.

[0043] In step (5), the external electrode is generally a silver electrode. Silver electrode slurry is applied on both sides of the co-fired stacked ceramic actuator, and the positive and negative electrodes are respectively led out using copper wires, and after curing treatment, effective connection with the electrodes in each layer is achieved.

[0044] The curing process is generally: curing temperature 50~70℃, curing time 2~3h.

[0045] Compared with the prior art, the present invention introduces Zr ions to enhance the anti-reduction properties of the KNN-based lead-free ceramic matrix, designs and fully utilizes the high strain response activity of the vacancy defect dipole at the A site of the perovskite, and successfully obtains a nickel inner electrode co-fired lead-free piezoelectric ceramic stack actuator with high electro-induced displacement output characteristics under a reducing sintering atmosphere. The present invention solves the problem that the sintering of nickel electrodes in a reducing atmosphere will affect the porcelain-forming properties, and greatly improves the strain performance, meeting the use standards of commercial products. Compared with existing lead-containing piezoelectric ceramic stack actuator products, the lead-free ceramic actuator not only has the advantages of low cost and green environmental protection, but also exhibits excellent driving performance, and its displacement output has a good linear correlation with the driving voltage amplitude. This feature enables it to achieve a higher degree of integration in precision control systems, and effectively reduce the negative impact of lead and its compounds on the environment and human health during production and recycling, and has significant social and environmental benefits, so it has great market potential and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 For 5 different chemical compositions in the embodiment x (K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3- y X-ray diffraction pattern of mol% ZrO2 piezoelectric ceramic material.

[0047] Figure 2 Four different chemical compositions x (K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3- y Complex impedance spectrum of mol% ZrO2 piezoelectric ceramic material.

[0048] Figure 3 For 5 different chemical compositions in the embodiment x (K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3- yThe electrostrain curve of mol% ZrO2 piezoelectric ceramic material and the schematic diagram of the defect dipole structure in the perovskite lattice; the upper figure is the electrostrain curve, and the lower figure is the schematic diagram of the defect dipole structure in the perovskite lattice, (i) is a complete and defect-free perovskite lattice, (ii) is a perovskite lattice with an A-site vacancy defect dipole, and (iii) is a lattice containing an A-site vacancy defect dipole and a defect dipole formed by Zr substitution defects and oxygen vacancies.

[0049] Figure 4 It is a schematic structural diagram of the nickel inner electrode co-fired lead-free ceramic laminate actuator of the present invention.

[0050] Figure 5 The figure below shows the unipolar electrodisplacement output curve and the relationship between the electrodisplacement output and the amplitude of the applied voltage of a nickel inner electrode co-fired multilayer ceramic actuator with 20 effective layers and a single layer thickness of about 50 microns. The left figure is the electrodisplacement output loop of the actuator under a DC drive voltage, and the right figure is a curve showing the change of the displacement output performance with the amplitude of the applied drive voltage. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0052] Embodiment 1: In this embodiment, five piezoelectric ceramic materials are prepared according to the following chemical compositions: 0.93(K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3-1mol%ZrO2 (denoted as 93KNSNS-1mol%Zr); 0.93(K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3-2mol%ZrO2 (denoted as 93KNSNS-2mol%Zr); 0.93(K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3-3mol%ZrO2 (denoted as 93KNSNS-3mol%Zr); 0.95(K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01O3-1mol%ZrO2 (denoted as 95KNSNS-1mol%Zr); and 0.95(K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3-3mol%ZrO2 (denoted as 95KNSNS-3mol%Zr).

[0053] The preparation method is as follows: according to the chemical formula of the potassium sodium niobate-based lead-free piezoelectric ceramic material, raw materials of potassium carbonate, sodium carbonate, niobium oxide, strontium carbonate, tin oxide and zirconium oxide powder are weighed.

[0054] After the raw materials are mixed with anhydrous ethanol, they are fully mixed by ball milling, and then the mixed slurry is dried. After the dried powder is ground and refined, it is placed in a muffle furnace for pre-sintering at 850 ° C for 6 h to promote the formation of the initial crystal phase. After the pre-sintered powder is cooled, anhydrous ethanol is added again as a wet grinding medium for secondary ball milling. The wet-milled slurry is then dried, ground and passed through a 40-mesh sieve to finally obtain lead-free piezoelectric ceramic powder particles, providing basic ceramic powder for subsequent device preparation.

[0055] The five piezoelectric ceramic materials were tested for XRD patterns and piezoelectric properties, and the results are as follows: Figure 1 The X-ray diffraction patterns of the piezoelectric ceramics with five different chemical compositions in the embodiment are shown in the figure. It is found from the pattern that the piezoelectric ceramics with different compositions prepared in the embodiment all exhibit a perovskite phase crystal structure at room temperature, proving that Zr ions are doped into the lattice and the introduced A-site vacancy defect does not cause the formation of a second phase.

[0056] Figure 2 The complex impedance spectra of piezoelectric ceramics with four different chemical compositions show three characteristics: First, ZrO2 doping and the introduction of A-site vacancy defects will cause convergence between the activation energies of grains and grain boundaries. For example, the activation energies of the grain boundary and grains of 95KNSNS-1mol%ZrO2 are 0.92 eV and 0.85 eV, respectively, while in the 93KNSNS-1mol%ZrO2 sample, the corresponding activation energy values ​​are 1.44 eV and 1.42 eV, respectively, and the activation energy difference of the latter is significantly smaller than that of the former. The difference between Ea (grain boundary) and Ea (grain) of KNSNS-based ceramics doped with 3mol%ZrO2 is negligible, so that it can be fitted and analyzed by a single RC equivalent circuit. This shows that the introduction of the above two types of defects helps to reduce the concentration of charged defects at the grain boundary, such as oxygen vacancies, thereby increasing the short-range jump transition barrier of oxygen vacancies, thereby improving the dielectric insulation properties of the material.

[0057] Secondly, ZrO2 doping will reduce the average activation energy of oxygen vacancies, while the appropriate introduction of A-site vacancy defects will increase the activation energy. The reason is that excessive introduction of Zr doping will lead to an increase in the concentration of oxygen vacancies, reducing the average activation energy, while the introduction of A-site vacancies will not significantly affect the concentration of oxygen vacancies, and thus the restriction on oxygen vacancy jump transitions will dominate, and the corresponding average activation energy will increase.

[0058] Third, the A-site vacancy defect will lead to an increase in the electrical conductivity of the ceramic sample. The reason is that the A-site vacancy defect itself induces the deterioration of the dielectric insulation properties of the piezoelectric ceramic. Therefore, an excessive concentration of A-site vacancy defects will make it difficult for the ceramic material to obtain excellent dielectric insulation properties.

[0059] Figure 3 It is the electrostrain curve diagram of 5 piezoelectric ceramic materials with different chemical compositions in the embodiment and the schematic diagram of the defect dipole structure in the perovskite lattice. It can be seen that the defect dipole structure formed by the A-site vacancy defect dipole and the Zr substitution oxygen vacancy regulates the electrostrain performance of the ceramic: the introduction of the A-site vacancy defect helps to improve the asymmetry of the bipolar electrostrain response of the piezoelectric ceramic, while the defect structure caused by Zr doping tends to form a symmetrical electrostrain output. The asymmetric strain response characteristics can significantly improve the unipolar electrostrain performance of one side. For example, 93KNSNS-1mol%ZrO2 ceramics obtained a strain value of 0.24% under a 20 kV / cm unipolar electric field, and the corresponding inverse piezoelectric coefficient reached 1200pm / V. The conventional commercially available PZT-5H lead-based ceramic material has a strain value of 0.17% at 20kv / cm, and the corresponding inverse piezoelectric coefficient is 850 pm / V. The driving performance of the piezoelectric ceramic material of this embodiment far exceeds that of commercial ceramic materials and is suitable for the preparation of co-fired multilayer ceramic actuators.

[0060] Example 2 (1) 15 g of potassium sodium niobate-based lead-free piezoelectric ceramic material (93KNSNS-1mol% ZrO2 ceramic), 9 g of n-butyl acetate, 6 g of anhydrous ethanol, 2 g of dioctyl phthalate, 0.2 g of n-butanol, 1.5 g of AKM-0531, 2.0 g of PVB-60H, and 1.5 g of PVB-30H were fully mixed by horizontal ball milling, and a ceramic slurry with good fluidity was obtained after a vacuum degassing process; the viscosity of the obtained ceramic slurry was 4000 mpa·s.

[0061] (2) Using a PET film strip coated with silicone oil on one side as a substrate, casting the ceramic slurry on a casting machine to form a film and drying it to obtain a ceramic green strip with good demoulding properties, strength and toughness and uniform texture, which is the piezoelectric ceramic layer; The scraper height of the casting machine is 200-250 microns, the transmission speed of the PET film belt is 150-200 mm / min, and the heating table temperature is 55 °C.

[0062] When the ceramic slurry is slowly and evenly poured into the material tank, the pouring rate should be properly controlled to maintain a constant liquid level of the slurry in the scraper tank. A stable liquid level helps reduce the strip thickness deviation caused by uneven slurry during the casting process. A reasonable slurry replenishment method not only ensures the uniformity of slurry distribution in the front and rear sections of the scraper tank, but also effectively avoids inconsistent strip thickness caused by liquid level fluctuations.

[0063] (3) Design and manufacture a matching printing screen plate according to the specific size requirements of the target electrode pattern. Punch holes in the ceramic green strip at predetermined positions to ensure precise alignment of subsequent processes. Use a high-precision screen printer to evenly print the nickel electrode slurry onto the surface of the dried ceramic green strip. After printing, place the strip on a temperature-controlled heating table and dry it at 50 °C for 2-5 minutes to ensure the initial curing and stability of the electrode slurry.

[0064] Nickel electrode slurry was purchased from Fenghua High-Tech, specification model NN0050.

[0065] (4) Use a bidirectional hot press to laminate the ceramic green body strips with printed electrode patterns layer by layer, and align each layer of strips precisely in the designed order and position to ensure the consistency of the conductive path and mechanical properties between the internal electrodes and the ceramic layers. During the hot pressing process, by reasonably adjusting the pressure and temperature parameters, the interface between the strips is tightly bonded, thus forming a dense multilayer ceramic actuator green body block; The bidirectional hot pressing temperature was set to 60-65 °C, the pressing pressure was set to 50-55 MPa, and the holding time was set to 20 s.

[0066] (5) The multilayer ceramic actuator green body is neatly placed in a crucible and placed in a tube furnace for debinding and sintering. The organic residues in the ceramic green body are slowly decomposed by precisely controlling the heating rate and atmosphere conditions to avoid cracking or defect holes caused by violent decomposition. The heating rate of the debinding stage is 0.5 °C / min, the target temperature is 500 °C, and the holding time is 10 h. The heating rate and target temperature of the sintering stage are 2 °C / min and 1130-1150 °C, respectively, and the holding time is 5 h.

[0067] The gas composition uses a N2 / H2 mixed gas with a H2 ratio of 2-3%, and the air in the tube furnace is first pumped out with a vacuum pump before the gas is introduced. After the binder is removed, the atmosphere is maintained as a N2 / H2 mixed gas, and the temperature is gradually increased to the sintering temperature range and maintained for a certain period of time to achieve densification of the ceramic matrix and co-firing of the electrode material.

[0068] After sintering, the temperature is lowered to room temperature with the furnace, and then nitrogen atmosphere is used to increase the temperature to 780 °C annealing target temperature at 2 °C / min for annealing heat treatment. The holding time is 9 h, and the furnace is cooled to obtain a co-fired stacked ceramic actuator with good dielectric insulation. Silver electrode slurry is coated on both sides of the co-fired stacked ceramic actuator, and copper wires are used to lead out the positive and negative electrodes respectively. After curing treatment, effective connection with the electrodes in each layer is achieved to obtain the nickel internal electrode co-fired lead-free ceramic stacked actuator.

[0069] The curing process is generally as follows: curing temperature 50~70℃, curing time 2~3h.

[0070] After sintering, if annealing heat treatment is not performed, the leakage conductance of the obtained ceramic is very large and it will break down at only 20~30V, making it impossible to perform performance testing.

[0071] An annealing step is necessary to obtain ceramic actuator samples.

[0072] Figure 4 It is a structural schematic diagram of the co-fired piezoelectric ceramic actuator described in the embodiment, wherein adjacent electrode layers are characterized by a cross arrangement, and each electrode layer is electrically connected through a side electrode, and each layer of ceramic is connected in parallel and has the same driving voltage amplitude under the electrical signal released by the same driving power supply, and each layer of piezoelectric ceramic responds simultaneously and contributes to the macroscopic displacement response output of the stacked actuator.

[0073] The unipolar electro-displacement output curve of the nickel inner electrode co-fired multilayer ceramic actuator with an effective number of 20 layers and a single piezoelectric ceramic layer thickness of about 50 microns and the relationship between the electro-displacement output and the applied voltage amplitude are shown in the figure. Figure 5 As shown. Using a voltage amplifier to output a driving electrical signal with an amplitude of 100 V (corresponding to a single-layer ceramic subjected to an electric field strength of 20 kV / cm) to stimulate the actuator to produce electro-induced displacement, it can be seen that the 93KNSNS-1mol%ZrO2 piezoelectric ceramic stack actuator can produce a high displacement output of 1.78 μm at a driving voltage of 100 V, and the average inverse piezoelectric coefficient of the corresponding single-layer ceramic is 890 pm / V, which is much better than commercial lead-based ceramic actuator products (590 pm / V).

[0074] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A potassium sodium niobate-based lead-free piezoelectric ceramic material, characterized in that Its general formula is x (K 0.495 Na 0.505 )Sr 0.02 Nb 0.99 Sn 0.01 O3- y mol% ZrO2, of which 0.92≤ x ≤0.94,0.8≤ y ≤1.

5.

2. The potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 1, characterized in that The potassium sodium niobate-based lead-free piezoelectric ceramic material is prepared by the following method: The raw materials were weighed according to the chemical formula of potassium sodium niobate-based lead-free piezoelectric ceramic materials, mixed with anhydrous ethanol, ball-milled and dried, and the dried powder was ground and refined, and then pre-fired at 800-900°C in a muffle furnace for 3-10 h. After the pre-fired powder was cooled, it was added to anhydrous ethanol again, ball-milled and dried for the second time, and passed through a 40-mesh sieve after grinding to obtain potassium sodium niobate-based lead-free piezoelectric ceramic powder particles.

3. A piezoelectric ceramic layer, wherein the piezoelectric ceramic layer is made of the potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 1.

4. The piezoelectric ceramic layer according to claim 3, characterized in that The piezoelectric ceramic layer is prepared by casting a ceramic slurry including a potassium sodium niobate-based lead-free piezoelectric ceramic material into a film and then drying it.

5. A ceramic slurry, characterized in that The ceramic slurry comprises the following components: The potassium sodium niobate-based lead-free piezoelectric ceramic material as claimed in claim 1, a solvent, a plasticizer, a dispersant, a defoaming agent and a binder.

6. Use of the potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 1 or the piezoelectric ceramic layer according to claim 3 in the preparation of a nickel inner electrode co-fired lead-free ceramic laminate actuator.

7. A nickel inner electrode co-fired lead-free ceramic laminate actuator, comprising a plurality of piezoelectric ceramic layers and a plurality of inner electrode layers; the piezoelectric ceramic layers and the inner electrode layers are alternately stacked, and at least one piezoelectric ceramic layer is made of a ceramic slurry comprising the potassium sodium niobate-based lead-free piezoelectric ceramic material as claimed in claim 1; The inner electrode layer is a nickel electrode.

8. The method for preparing a nickel inner electrode co-fired lead-free ceramic laminate actuator according to claim 7, characterized in that The method comprises the following steps: (1) Preparation of ceramic slurry from potassium sodium niobate-based lead-free piezoelectric ceramic materials, solvents, plasticizers, dispersants and binders; (2) The ceramic slurry is tape-cast into a film and dried to obtain a ceramic green strip, which is the piezoelectric ceramic layer; (3) Printing the nickel electrode slurry onto the surface of the ceramic green strip by screen printing, and drying to obtain a ceramic green strip with a printed electrode pattern; (4) The ceramic green body strips with printed electrode patterns are laminated layer by layer to obtain a multilayer ceramic actuator green body block; (5) The multilayer ceramic actuator green body is subjected to a binder removal treatment, sintering, and annealing heat treatment to obtain a co-fired stacked ceramic actuator. External electrodes are provided on both sides of the co-fired stacked ceramic actuator and solidified to obtain the nickel inner electrode co-fired lead-free ceramic stacked actuator.

9. The method according to claim 8, characterized in that In the step (5), the heating rate of the debinding treatment is 0.5-0.6°C / min, the target temperature is 500-550°C, and the holding time is 10-12 h; the heating rate of the sintering treatment is 2-3°C / min, the target temperature is 1130-1150°C, and the holding time is 3-6 h; During the debinding and sintering processes, the gas atmosphere is a mixture of nitrogen and hydrogen.

10. The method according to claim 8, characterized in that In the step (5), the heating rate of the annealing heat treatment is 2-2.5°C / min, the target temperature is 780-790°C, the holding time is 8-10 h, and the gas atmosphere is nitrogen.

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