Potassium-sodium niobate-based lead-free piezoelectric ceramic and preparation method thereof

Abstract

This invention relates to the field of piezoelectric ceramics technology, and more particularly to a lead-free potassium sodium niobate-based piezoelectric ceramic and its preparation method. The piezoelectric ceramic is composed of alternating layers of p-type and n-type components, and its general chemical composition is: 0.94(Na...) 1‑y K y ) 1‑z Nb 1‑h Ta h O3-0.06A i B k O3+8%N. This invention constructs a stable, strong built-in field for sodium potassium niobate-based ceramics, exciting the material's domain response. This enables the reduction-resistant sodium potassium niobate-based lead-free piezoelectric ceramics to exhibit an ultra-high voltage strain coefficient under a low driving electric field, with an electrostrain coefficient far exceeding that of current mainstream lead-based piezoelectric materials. The fabrication process meets the requirements for multilayer devices co-fired with nickel electrodes. After fabrication into multilayer devices, it can effectively reduce the electrode cost of lead-free piezoelectric multilayer devices by more than 90%.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ceramics technology, and in particular to a lead-free potassium sodium niobate-based piezoelectric ceramic and its preparation method. Background Technology

[0002] Piezoelectric materials, as key materials for bidirectional conversion of mechanical and electrical energy, are widely used in fields such as ultrasonic imaging and sonar detection. However, the global market for piezoelectric devices is dominated by lead-based materials, and due to the toxicity of lead, its use in electronic devices is strictly restricted. Breaking through the technological bottleneck of lead-free piezoelectric materials is imperative. Potassium sodium niobate (KNN)-based materials have become a research hotspot in lead-free piezoelectric ceramics due to their advantages such as high Curie temperature, large electromechanical coupling coefficient, and environmental friendliness. Driven by green and sustainable development, KNN-based ceramics have been established as an important research direction. Figure 1 As shown in (a), after years of research, its piezoelectric properties have been significantly improved, surpassing some traditional lead-based materials, and it has the commercial potential to replace lead-based materials.

[0003] Piezoelectric devices are trending towards miniaturization and are widely used in high-end equipment and consumer electronics. Miniature devices, such as piezoelectric actuators for microelectromechanical systems and loudspeakers for electronic devices, utilize strain coefficients (…). = or = displacement L / Voltage U The core performance indicator is the strain hysteresis of the material, and the operating voltage is typically low (1.8V~30V). Multilayer design of the device can reduce the application voltage and increase the displacement, but due to limitations in the fabrication process, optimizing performance by increasing the number of layers and reducing the thickness of the dielectric layer still faces technical bottlenecks. In addition, the strain hysteresis of the material (…) H The height directly determines the positioning accuracy and repeatability of micro-devices, which is a core requirement for the manufacture of high-precision instruments.

[0004] Existing research (Hong CH et al. Lead-free piezoceramics -Where to move on?. Journal of Materiomics 2, 1-24 (2016)) reports a comparison of strain (S) in some lead-free and lead-based piezoelectric ceramic systems, such as... Figure 1 (a). Analysis of the latest reported data on lead-based PZT-PMN materials shows that its... E D For 0.4kV / mm Values ​​can reach 1600 pm / V (Jiang YQ et al. Low-field-driven large strain in leadzirconate titanium-based piezoceramics incorporating relaxor lead magnesiumniobate for actuation, Nature Communications.). Currently, many research teams at home and abroad have not yet achieved a key breakthrough in the development of KNN-based materials, namely low... E D (≤0.4 kV / mm) induced high (>1600 pm / V). Patent CN118545996A discloses a KNN-based lead-free piezoelectric ceramic with ultra-high inverse piezoelectric performance, capable of exhibiting an ultra-high inverse piezoelectric coefficient under extremely low electric fields. E D Reaching 0.9kV / mm and With a value as high as 1730 pm / V, it has the potential to catch up with PZT-PMN materials, but there is still a certain gap compared with PZT-PMN materials.

[0005] In addition, such as Figure 1 (b) While KNN-based piezoelectric multilayer devices have commercial potential, their internal electrodes utilize expensive silver-palladium materials, resulting in high costs. Replacing them with base metal nickel electrodes can reduce electrode costs by over 90% and device costs by up to 20%. However, nickel electrodes have poor oxidation resistance, requiring a strong reducing atmosphere during co-firing. This leads to the generation of more oxygen vacancies and free electrons in the ceramic, narrowing the bandgap and deteriorating room-temperature and high-temperature insulation properties. Decreased insulation hinders polarization and impairs piezoelectric performance. Regulating the reduction resistance of KNN-based materials is a prerequisite for designing low-cost, high-performance multilayer devices that can be co-fired with nickel electrodes. Therefore, developing KNN-based materials that combine reduction resistance, high strain, and low driving electric field is crucial for promoting their application in consumer electronics and high-end manufacturing. Summary of the Invention

[0006] To address the above shortcomings, this invention provides a lead-free piezoelectric ceramic based on potassium sodium niobate, capable of inducing an ultra-high voltage strain coefficient under extremely low driving electric field, meeting the requirements of multilayer devices co-fired with nickel electrodes, and effectively reducing electrode costs by more than 90% for lead-free piezoelectric multilayer devices. The specific technical solution is as follows: A lead-free piezoelectric ceramic based on potassium sodium niobate with resistance to reduction, wherein the piezoelectric ceramic is composed of alternating layers of p-type and n-type components, and the general chemical formula of the p-type component layer is: 0.94(Na 1-y Ky ) 1-z Nb 1-h Ta h O3 - 0.06A i B k O3 + 8%N, where y, z, h, i, and k represent mole fractions, 0.47 < y < 0.54, -0.1 ≤ z ≤ 0, 0 ≤ h ≤ 0.1, 0.90 ≤ i ≤ 1, 2 < k ≤ 5, A refers to Ca, Sr, Ba, B refers to Zr, Ti, Hf, Sn, Sb, N refers to manganese compounds, and the manganese compounds are MnO, Mn2O3, MnCO3, or MnO2; The component chemical composition general formula of the n-type layer is: 0.94(Na 1-y K y ) 1-z Nb 1-h Ta h O3 - 0.06A i B k O3 + 8%N, where y, z, h, i, and k represent mole fractions, 0.47 < y < 0.54, 0 < z ≤ 0.1, 0 ≤ h ≤ 0.1, 1 ≤ i ≤ 1.5, 0.8 ≤ k ≤ 2, A refers to Ca, Sr, Ba, B refers to Zr, Ti, Hf, Sn, Sb, N refers to manganese compounds, and the manganese compounds are MnO, Mn2O3, MnCO3, or MnO2. The p-type layer is composed of p-type conductive mechanism components, and the n-type layer is composed of n-type conductive mechanism components.

[0007] Preferably, in the above-reducing-resistant sodium potassium niobate-based lead-free piezoelectric ceramics, classified according to the stacking mode of the p-type layer and the n-type layer, the piezoelectric ceramic structure is a p-n type, p-n-p type, or n-p-n type structure. At present, when researchers design high-performance KNN-based piezoelectric materials, a necessary prerequisite is that the KNN-based materials must first have high insulation performance. The present invention designs with reverse thinking, such as Figure 2As shown, p-n type, p-n-p type, and n-p-n type structures are designed. The p-n type structure is composed of a p-type group layer and an n-type group layer from top to bottom. The p-n-p type structure is composed of a p-type group layer, an n-type group layer, and a p-type group layer from top to bottom. The n-p-n type structure is composed of an n-type group layer, a p-type group layer, and an n-type group layer from top to bottom. By controlling the carrier migration through the p-n junction effect, the withstand voltage characteristic is maintained, and the Maxwell-Wagner effect is strengthened at the interface to excite the piezoelectric properties of the KNN-based composite material. In the figure, the depletion layer of the p-n junction refers to a high-resistance region near the interface between the p-type and n-type semiconductors, which almost contains no mobile carriers, and is also called the space charge region or the barrier region. The p-type group layer has a p-type conduction mechanism and conducts electricity with holes as the majority carriers. The n-type group layer has an n-type conduction mechanism and conducts electricity with free electrons as the majority carriers.

[0008] Preferably, in the above-mentioned anti-reducing sodium potassium niobate-based lead-free piezoelectric ceramics, the component chemical composition general formula of the p-type group layer is: 0.94(Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i, and k represent mole fractions, 0.47 < y < 0.54, -0.05 ≤ z ≤ 0, 0 ≤ h ≤ 0.07, 0.90 ≤ i ≤ 1, 2 < k ≤ 3, A refers to Ca, Sr, Ba, B refers to Zr, Ti, Hf, Sn, Sb, and N refers to manganese compounds. The manganese compounds are MnO, Mn2O3, MnCO3, or MnO2; The component chemical composition general formula of the n-type group layer is: 0.94(Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i, and k represent mole fractions, 0.47 < y < 0.54, 0 < z ≤ 0.05, 0 ≤ h ≤ 0.07, 1 ≤ i ≤ 1.5, 1.5 ≤ k ≤ 2, A refers to Ca, Sr, Ba, B refers to Zr, Ti, Hf, Sn, Sb, and N refers to manganese compounds. The manganese compounds are MnO, Mn2O3, MnCO3, or MnO2. The p-type group layer is composed of p-type conduction mechanism components, and the n-type group layer is composed of n-type conduction mechanism components.

[0009] Preferably, in the above-mentioned potassium sodium niobate-based lead-free piezoelectric ceramic with anti-reduction properties, the p-type component layer and the n-type component layer are each composed of 1 to 30 thin sheets stacked together.

[0010] Preferably, in the above-mentioned potassium sodium niobate-based lead-free piezoelectric ceramic with resistance to reduction, the thickness of each thin sheet is 0.01 to 0.5 mm.

[0011] Preferably, in the above-mentioned potassium sodium niobate-based lead-free piezoelectric ceramic with resistance to reduction, the number of thin film layers in the p-type component layer is less than the number of thin film layers in the n-type component layer.

[0012] On the other hand, the present invention also provides a method for preparing the above-mentioned potassium sodium niobate-based lead-free piezoelectric ceramic, comprising the following steps: (1) Weigh the raw materials according to the molar percentage of the general formula of the chemical composition, and then ball mill, dry and calcine them in sequence to obtain the ceramic material; (2) The ceramic material is ball-milled for 10-14 hours with anhydrous ethanol as the medium, and then a dispersant and solvent 2-butanone are added. After ball milling, a binder and a plasticizer are added, and the mixture is ball-milled for another 10-14 hours to obtain p-type wet powder slurry and n-type wet powder slurry respectively. Vacuum degassing is performed to obtain p-type casting slurry and n-type casting slurry. (3) Apply p-type casting slurry and n-type casting slurry to a glass plate using a casting machine to obtain wet films, and dry them to obtain p-type dry films and n-type dry films; (4) Cut the p-type dry sheet and the n-type dry sheet into small sheets, and stack the small sheets to form p-type component layers and n-type component layers respectively; (5) The component layers are stacked together and clamped according to the structural type, and dried to obtain a composite stack; the composite stack structure is pre-pressed, vacuumed, sealed, and then pressurized to obtain a tablet preform. (6) The tablet blank is debinded and then sintered and re-oxidized in a reducing atmosphere to obtain a lead-free piezoelectric ceramic based on potassium sodium niobate that resists reduction.

[0013] Preferably, in the above-mentioned method for preparing potassium sodium niobate-based lead-free piezoelectric ceramics, in step (1), the ball milling process parameters are: the ball milling medium is anhydrous ethanol, the ball milling speed is 300-400 r / min, and the time is 20-30 h; the calcination process parameters are: the temperature is 800-950℃, and the time is 2-6 h.

[0014] Preferably, in the above-mentioned method for preparing potassium sodium niobate-based lead-free piezoelectric ceramics, the dispersant in step (2) is triethyl phosphate, the binder is polyvinyl butyral, and the plasticizer is dibutyl phthalate; the ratio of ceramic material to anhydrous ethanol is 18~20g:10~15mL, the amount of dispersant added is 3-5wt.% of the ceramic material, the amount of binder added is 8-10wt.% of the ceramic material, and the amount of plasticizer added is 8-10wt.% of the ceramic material.

[0015] Preferably, in the above-mentioned method for preparing potassium sodium niobate-based lead-free piezoelectric ceramics, the raw materials are selected from the following: analytical grade Na2CO3, K2CO3, Nb2O5, Ta2O5, ZrO2, MnO, Mn2O3, MnCO3, MnO2, BaCO3, SnO2, CaCO3, SrCO3, HfO2, Sb2O5, and TiO2.

[0016] Preferably, in the above-mentioned method for preparing potassium sodium niobate-based lead-free piezoelectric ceramics, the vacuum degassing process in step (2) is as follows: the rotation speed in the first stage is 100-200 r / min for 15-30 min, the rotation speed in the second stage is 300-400 r / min for 15-30 min, and the rotation speed in the third stage is 100-200 r / min for 15-30 min.

[0017] Preferably, in the above-mentioned method for preparing potassium sodium niobate-based lead-free piezoelectric ceramics, in step (5), the pre-pressing condition is 12-15 MPa for 5-10 min; the static pressure condition is to pressurize to 25-35 MPa for 5-15 min.

[0018] Preferably, in the above-mentioned method for preparing potassium sodium niobate-based lead-free piezoelectric ceramics resistant to reduction, the sintering process parameters in step (6) are as follows: heating rate of 4-6℃ / min, sintering temperature of 1050-1120℃, holding time of 0.5-1.5h, reducing atmosphere consisting of 0.6-1.5% H2 and 99.4-98.5% N2 by volume, and oxygen partial pressure of 1×10⁻⁶. -10 -1×10 - 13 atm.

[0019] Preferably, in the above-mentioned method for preparing potassium sodium niobate-based lead-free piezoelectric ceramics with resistance to reduction, in step (6), the re-oxidation is performed as follows: after sintering and holding at a certain temperature, the temperature is reduced to 800-900℃ at a cooling rate of 4-7℃ / min, and the oxygen partial pressure of the reducing atmosphere is controlled to be 10 by adjusting the ratio of N2 and H2. -6 -10 -9The process involves holding the material at 0.8-2.0 h at a specific temperature, followed by cooling to room temperature while maintaining the same atmosphere. This invention shortens the sintering and re-oxidation times. Firstly, the reducing atmosphere and variable-valence Mn and Sn ions increase the ionic radius during sintering, inducing large lattice distortion. Simultaneously, the large number of oxygen vacancies induced by the reducing atmosphere significantly enhances the ion diffusion path, promoting material densification and reducing sintering holding time. Secondly, the purpose of material re-oxidation is primarily to reduce oxygen vacancies and the concentration of freely moving charge carriers, thereby improving the material's insulation performance. This invention, through the component-controlled design of n-type and p-type materials, forms a pN junction after composite formation, controlling charge carrier migration and eliminating the need for prolonged re-oxidation.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. The potassium sodium niobate-based lead-free piezoelectric ceramic of the present invention significantly reduces the driving electric field to as low as 3kV / cm by constructing a stable strong built-in field in the potassium sodium niobate-based ceramic, thereby exciting the electric domain response of the material. This is 3 / 10 of the current market PZT material (10kV / cm), and it is expected to be applied to precision micro actuators with extremely high requirements for power consumption and miniaturization.

[0021] 2. The potassium sodium niobate-based lead-free piezoelectric ceramic of the present invention can generate an ultra-high voltage strain coefficient (2300 pm / V) at 3 kV / cm, which is much higher than that of the current mainstream lead-based piezoelectric materials.

[0022] 3. The potassium sodium niobate-based lead-free piezoelectric ceramic of the present invention has anti-reduction properties, and the preparation process meets the requirements of multilayer devices co-fired with base metal inner electrodes (such as nickel). After being prepared into multilayer devices, it can effectively reduce the electrode cost of lead-free piezoelectric multilayer devices by more than 90%.

[0023] 4. The preparation method of the potassium sodium niobate-based lead-free piezoelectric ceramic of the present invention greatly shortens the sintering and re-oxidation time. The sintering holding time is reduced from the traditional 2 hours to less than 1.5 hours. At the same time, the re-oxidation time is reduced from 4 to 10 hours to less than 2 hours. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1The performance comparison of some existing piezoelectric materials is as follows: (a) is a comparison of strain (S) of some lead-free and lead-based piezoelectric ceramic systems; (b) is a comparison of the market unit price of existing electrodes with different silver-palladium ratios and nickel electrodes; where (a) is from reference [1]; Figure 2 This is a schematic diagram of the design concept of the potassium sodium niobate-based lead-free piezoelectric ceramic structure of the present invention; the depletion layer of the pN junction in the figure refers to the high-resistivity region formed near the interface between p-type and n-type semiconductors, which contains almost no mobile charge carriers, also known as the space charge region or barrier region; Figure 3 This is a bipolar strain diagram of the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic prepared in Example 1 of the present invention, showing the change of electric field at room temperature.

[0026] Figure 4 This is a unipolar strain diagram of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in Example 1 of the present invention as a function of the driving electric field; Figure 5 This is a unipolar strain diagram of the lead-free potassium sodium niobate-based piezoelectric ceramic prepared in Example 2 of the present invention as a function of the driving electric field; Figure 6 This is a unipolar strain diagram of the lead-free potassium sodium niobate-based piezoelectric ceramic prepared in Example 3 of the present invention as a function of the driving electric field; Figure 7 This is a unipolar strain diagram of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in Example 4 of the present invention as a function of the driving electric field. Figure 8 This is a unipolar strain diagram of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in Example 5 of the present invention as a function of the driving electric field; Figure 9 This is a unipolar strain diagram of the lead-free potassium sodium niobate-based piezoelectric ceramic prepared in Comparative Example 1 of the present invention as a function of the driving electric field.

[0027] [1] Hong, CH et al. Lead-free piezoceramics - Where to move on? .Journal of Materiomics 2, 1-24 (2016). Detailed Implementation

[0028] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0029] Example 1 A lead-free piezoelectric ceramic based on potassium sodium niobate with a reduction resistant structure is pn-type, consisting of p-type component layers and n-type component layers stacked from top to bottom.

[0030] The composition of the p-type component layer is 0.94 (Na). 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i, and k represent mole fractions, y=0.48, z=0, h=0.045, i=0.99, and k=2.1; A is Ba, B is Zr, and N is MnO. Specifically, it consists of 8 thin sheets (with a thickness of ~20 micrometers).

[0031] The general chemical formula for the components of the n-type component layer is: 0.94 (Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i and k represent mole fractions, y=0.48, z=0.04, h=0.04, i=1, k=2; A is Ba, B is Zr, N is MnO, specifically composed of 20 thin sheets (thickness ~20 micrometers).

[0032] This embodiment also provides a method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic resistant to reduction, comprising the following steps: (1) Using analytical grade Na2CO3, K2CO3, Nb2O5, Ta2O5, ZrO2, MnO and BaCO3 as raw materials, weigh the raw materials according to the molar percentage of the general formula of the chemical composition, put the weighed raw materials into a ball mill jar, add anhydrous ethanol, the amount of anhydrous ethanol is 15 times the weight of the raw materials, ball mill at 350 r / min for 24 h, dry the powder by rotary evaporation (temperature is 60℃, time is 1 h), and then calcine at 850℃ for 5 h to obtain ceramic material; (2) Using anhydrous ethanol as the medium, the ratio of ceramic material to anhydrous ethanol is 19g:12mL. Triethyl phosphate and 2-butanone are added. The amount of triethyl phosphate added is 4wt.% of the ceramic material. After ball milling for 10h, polyvinyl butyral and dibutyl phthalate are added. The amount of polyvinyl butyral added is 8.5wt.% of the ceramic material, and the amount of dibutyl phthalate added is 8.5wt.% of the ceramic material. Ball milling continues for 10h to obtain p-type wet powder slurry and n-type wet powder slurry respectively. The p-type wet powder slurry and n-type wet powder slurry are vacuum defoamed. Specifically, the rotation speed of the first stage is 150r / min for 30min, the rotation speed of the second stage is 350r / min for 30min, and the rotation speed of the third stage is 150r / min for 30min to obtain p-type casting slurry and n-type casting slurry. (3) The p-type casting slurry and the n-type casting slurry are respectively coated onto a glass plate using a casting machine to obtain wet films, which are then dried at 80°C to obtain p-type dry films and n-type dry films. (4) Cut the prepared p-type dry sheet and n-type dry sheet into small sheets respectively. According to the layer requirements of p-type component layer and n-type component layer, stack the cut sheets to form p-type component layer and n-type component layer respectively. (5) Stack the p-type component layer and the n-type component according to the pn structure. The number of structural layers is designed as follows: 8 layers of p-type component and 20 layers of n-type component to obtain a composite stack. Pre-compress the composite stack under the following conditions: temperature 70℃, pressure 14MPa for 5min; evacuate, seal, and continue to pressurize to 30MPa for 10min to obtain a tablet preform. (6) Remove the glue from the tablet preform. The glue removal process parameters are: heating rate of 2℃ / min, temperature of 550℃, and holding time of 2h. (7) Sintering is then carried out in a reducing atmosphere. The sintering process parameters are as follows: heating rate of 5℃ / min, sintering temperature of 1080-1090℃, holding time of 0.5h, reducing atmosphere consisting of ~0.6% H2 and ~99.4% N2 by volume, and oxygen partial pressure of 1×10⁻⁶. -11 -1×10 -13 atm; After sintering and holding at that temperature, the temperature is reduced to 850°C at a rate of 5°C / min, and the oxygen partial pressure of the reducing atmosphere is controlled to be 10 by adjusting the ratio of N2 and H2. -6 -10 -8 The atmosphere was heated to atm for 1 hour, and then kept at this atmosphere until the temperature dropped to room temperature, thus obtaining a lead-free piezoelectric ceramic based on potassium sodium niobate that resists reduction.

[0033] Figure 1 A comparison of the properties of some publicly available piezoelectric materials, through Figure 1 (a) It is evident that the strain properties of the KNN-based material system are comparable to those of the lead-based system, demonstrating significant potential to replace lead-based materials in various applications. The material of this invention possesses the ability to be sintered in a reducing atmosphere, enabling the fabrication of multilayer devices co-fired with nickel electrodes. Figure 1 (b) It can be seen that the cost of electrodes can be reduced by more than 90%, and the device has a great cost advantage.

[0034] Table 1 shows the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramics prepared in this embodiment under different driving electric fields. E D Inverse piezoelectric coefficient under) (Inverse piezoelectric coefficient = maximum strain / electric field). As shown in the table, the piezoelectric ceramic driving electric field in this embodiment is as low as 3kV / cm, and its piezoelectric strain coefficient can reach more than 2300pm / V, which is much higher than the current mainstream lead-based piezoelectric materials.

[0035] Table 1 Different driving electric fields ( E D Inverse piezoelectric coefficient under)

[0036]

[0037] The bipolar strain curve of the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic in this embodiment is as follows: Figure 3 As shown, the lead-free potassium sodium niobate-based piezoelectric ceramic of this embodiment exhibits good symmetry in bipolar strain testing, indicating that the material will not reduce the accuracy of the device due to large cumulative displacement errors in future device applications.

[0038] Figure 4 The image shows the unipolar strain curve of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in this embodiment as a function of the driving electric field.

[0039] Example 2 A lead-free piezoelectric ceramic based on potassium sodium niobate with reduction resistance is disclosed. The p-type and n-type components are the same as in Example 1, maintaining a pn-type structure composed of layers of p-type and n-type components stacked sequentially from top to bottom. The structure is designed with 6 p-type layers and 22 n-type layers. The preparation method is the same as in Example 1.

[0040] Table 2 shows the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramics prepared in Example 2 under different driving electric fields. E D Inverse piezoelectric coefficient under) As shown in the table, the piezoelectric ceramic driving electric field in this embodiment is as low as 4kV / cm, and its piezoelectric strain coefficient can reach more than 1790pm / V, which is generally higher than that of currently commercially available lead-based piezoelectric materials.

[0041] Table 2 Different driving electric fields ( E D Inverse piezoelectric coefficient under)

[0042]

[0043] Figure 5 The image shows the unipolar strain curve of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in Example 2 as a function of the driving electric field.

[0044] Example 3 A lead-free piezoelectric ceramic based on potassium sodium niobate with reduction resistance is disclosed. It retains a pn-type structure, composed of stacked p-type and n-type component layers from top to bottom. The structure is designed with 8 p-type component layers and 20 n-type component layers. The preparation method is the same as in Example 1.

[0045] The composition of the p-type component layer is 0.94 (Na). 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i and k represent mole fractions, y=0.48, z=0, h=0.04, i=0.99, k=2.1; A is Ba, B is Zr, and N is Mn2O3, specifically composed of 8 thin sheets (thickness ~20 micrometers).

[0046] The general chemical formula for the components of the n-type component layer is: 0.94 (Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i and k represent mole fractions, y=0.48, z=0.03, h=0.04, i=1, k=1.9; A is Ba, B is Zr, N is Mn2O3, specifically composed of 20 thin sheets (thickness ~20 micrometers).

[0047] Table 3 shows the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramics prepared in this embodiment under different driving electric fields. E D Inverse piezoelectric coefficient under) As shown in the table, the piezoelectric ceramic driving electric field in this embodiment is as low as 3kV / cm, and its piezoelectric strain coefficient can reach more than 2226pm / V, which is much higher than that of the current mainstream lead-based piezoelectric materials.

[0048] Table 3 Different driving electric fields ( E D Inverse piezoelectric coefficient under)

[0049]

[0050] Figure 6 The image shows the unipolar strain curve of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in this embodiment as a function of the driving electric field.

[0051] Example 4 A lead-free piezoelectric ceramic based on potassium sodium niobate with reduction resistance is disclosed. It retains a pn-type structure, composed of stacked p-type and n-type component layers from top to bottom. The structure is designed with 8 p-type component layers and 20 n-type component layers. The preparation method is the same as in Example 1.

[0052] The composition of the p-type component layer is 0.94 (Na). 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i and k represent mole fractions, y=0.48, z=-0.06, h=0, i=1, k=2.2; A is Sr, B is Zr, and N is MnO2, specifically composed of 8 thin sheets (thickness ~20 micrometers).

[0053] The general chemical formula for the components of the n-type component layer is: 0.94 (Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i and k represent mole fractions, y=0.5, z=0.005, h=0, i=1, k=1.9; A is Sr, B is Zr, N is MnO2, specifically composed of 20 thin sheets (thickness ~20 micrometers).

[0054] Figure 7 Table 4 shows the unipolar strain curves of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in this embodiment as a function of the driving electric field. E D Inverse piezoelectric coefficient under) .

[0055] Table 4 Different driving electric fields ( E D Inverse piezoelectric coefficient under)

[0056]

[0057] As shown in Table 4, the piezoelectric ceramic driving electric field in this embodiment is as low as 5kV / cm, and its piezoelectric strain coefficient can reach more than 1490pm / V.

[0058] Example 5 A reduction-resistant potassium sodium niobate-based lead-free piezoelectric ceramic has a pnp-type structure, consisting of a series of p-type component layers, n-type component layers, and p-type component layers stacked from top to bottom. The structure is designed with 8 p-type component layers, 20 n-type component layers, and 8 p-type component layers. The preparation method is the same as in Example 1.

[0059] The composition of the p-type component layer is 0.94 (Na). 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i and k represent mole fractions, y=0.48, z=0, h=0, i=1, k=2.3; A is Sr, B is Zr, and N is MnO, specifically composed of 8 thin sheets (sheets ~20 micrometers thick).

[0060] The general chemical formula for the components of the n-type component layer is: 0.94 (Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i and k represent mole fractions, y=0.5, z=0.005, h=0, i=1, k=1.8; A is Sr, B is Zr, N is MnO, specifically composed of 20 thin sheets (thickness ~20 micrometers).

[0061] Figure 8Table 5 shows the unipolar strain curves of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in this embodiment as a function of the driving electric field. E D Inverse piezoelectric coefficient under) .

[0062] Table 5 Different driving electric fields ( E D Inverse piezoelectric coefficient under)

[0063]

[0064] As shown in Table 5, the piezoelectric ceramic driving electric field in this embodiment is as low as 5kV / cm, and its piezoelectric strain coefficient can reach 1510pm / V.

[0065] Comparative Example 1 The material with pure p-type components is 0.94 (Na). 1-y K y ) 1- Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i, and k represent mole fractions, y=0.48, z=0, h=0.045, i=0.99, k=2.1, A is Ba, B is Zr, and N is MnO. Specifically, it consists of 28 thin sheets (sheets ~20 micrometers thick). Other aspects are the same as in Example 1.

[0066] Figure 9 Table 6 shows the unipolar strain curves of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in this embodiment as a function of the driving electric field. Table 6 shows the unipolar strain curves of the potassium sodium niobate-based lead-free piezoelectric ceramic prepared in Comparative Example 1 under different driving electric fields (…). E D Inverse piezoelectric coefficient under) .

[0067] Table 6 Different driving electric fields ( E D Inverse piezoelectric coefficient under)

[0068]

[0069] As shown in the table, the piezoelectric ceramic driving electric field in this embodiment is as high as 20 kV / cm, and its piezoelectric strain coefficient is 582 pm / V. Comparative Example 2 The general chemical formula for the components of a pure n-type component layer is: 0.94 (Na 1-y K y )1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i, and k represent mole fractions, y=0.48, z=0.04, h=0.04, i=1, and k=2; A is Ba, B is Zr, and N is MnO, specifically composed of 28 thin sheets (sheets ~20 micrometers thick). Other aspects are the same as in Example 1.

[0070] Table 7 shows the comparison results of lead-free potassium sodium niobate-based piezoelectric ceramics prepared under different driving electric fields. E D Inverse piezoelectric coefficient under) As shown in the table, the piezoelectric ceramic driving electric field in this embodiment is as high as 20 kV / cm, and its piezoelectric strain coefficient is 502 pm / V. However, the sample resistivity is too low, only 6.5 × 10⁻⁶. 8 The Ω·cm test is prone to breakdown, resulting in incomplete data.

[0071] Table 7 Different driving electric fields ( E D Inverse piezoelectric coefficient under)

[0072]

[0073] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A lead-free piezoelectric ceramic based on potassium sodium niobate with resistance to reduction, characterized in that, The piezoelectric ceramic is composed of alternating layers of p-type and n-type components. The general chemical formula of the p-type component layer is: 0.94 (Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i, and k represent the mole fraction, 0.47 <y<0.54,-0.1≤z≤0,0≤h≤0.1,0.90≤i≤1,2< k ≤5, A refers to Ca, Sr, Ba, B refers to Zr, Ti, Hf, Sn, Sb, N refers to manganese compound, wherein the manganese compound is MnO, Mn2O3, MnCO3 or MnO2; The component chemical composition general formula of the n-type component layer is: 0.94(Na 1-y K y ) 1-z Nb 1-h Ta h O3-0.06A i B k O3+8%N, where y, z, h, i, and k represent mole fractions, 0.47 < y < 0.54, 0 < z ≤ 0.1, 0 ≤ h ≤ 0.1, 1 ≤ i ≤ 1.5, 0.8 ≤ k ≤ 2, A refers to Ca, Sr, Ba, B refers to Zr, Ti, Hf, Sn, Sb, N refers to a manganese compound, and the manganese compound is MnO, Mn2O3, MnCO3, or MnO2.

2. The potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 1, characterized in that, According to the combination of p-type component layers and n-type component layers, the piezoelectric ceramic structure is classified as pn-type, pnp-type, or npn-type structure.

3. The lead-free piezoelectric ceramic based on potassium sodium niobate with resistance to reduction according to claim 1, characterized in that, The p-type component layer and n-type component layer are each composed of 1 to 30 layers of thin sheets stacked together.

4. The lead-free piezoelectric ceramic based on potassium sodium niobate with resistance to reduction according to claim 3, characterized in that, The thickness of each sheet is 0.01 to 0.5 mm.

5. A method for preparing a lead-free piezoelectric ceramic based on potassium sodium niobate as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Weigh the raw materials according to the molar percentage of the general formula of the chemical composition, and then ball mill, dry and calcine them in sequence to obtain the ceramic material; (2) The ceramic material is ball-milled for 10-14 hours with anhydrous ethanol as the medium, dispersant and 2-butanone are added, and then binder and plasticizer are added and ball-milled for another 10-14 hours to obtain p-type wet powder slurry and n-type wet powder slurry respectively. Vacuum degassing is performed to obtain p-type casting slurry and n-type casting slurry. (3) Apply p-type casting slurry and n-type casting slurry to a glass plate using a casting machine to obtain wet films, and dry them to obtain p-type dry films and n-type dry films; (4) Cut the p-type dry sheet and the n-type dry sheet into small sheets, and stack the small sheets to form p-type component layers and n-type component layers respectively; (5) The component layers are stacked together and clamped according to the structural type, and dried to obtain a composite stack; the composite stack structure is pre-pressed, vacuumed, sealed, and then pressurized to obtain a tablet preform. (6) The tablet blank is debinded and then sintered and re-oxidized in a reducing atmosphere to obtain a lead-free piezoelectric ceramic based on potassium sodium niobate that resists reduction.

6. The method for preparing the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 5, characterized in that, The dispersant in step (2) is triethyl phosphate, the binder is polyvinyl butyral, and the plasticizer is dibutyl phthalate; the ratio of ceramic material to anhydrous ethanol is 18~20g:10~15mL, the amount of dispersant added is 3-5wt.% of ceramic material, the amount of binder added is 8-10wt.% of ceramic material, and the amount of plasticizer added is 8-10wt.% of ceramic material.

7. The method for preparing the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 5, characterized in that, In step (2), the vacuum degassing process is as follows: the rotation speed in the first stage is 100-200 r / min for 15-30 min, the rotation speed in the second stage is 300-400 r / min for 15-30 min, and the rotation speed in the third stage is 100-200 r / min for 15-30 min.

8. The method for preparing the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 5, characterized in that, In step (5), the pre-compression condition is 12-15MPa for 5-10 minutes; the static pressure condition is to pressurize to 25-35MPa for 5-15 minutes.

9. The method for preparing the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 5, characterized in that, In step (6), the sintering process parameters are as follows: heating rate is 4-6℃ / min, sintering temperature is 1050-1120℃, holding time is 0.5-1.5h, the reducing atmosphere consists of 0.6-1.5% H2 and 99.4-98.5% N2 by volume, and the oxygen partial pressure is 1×10⁻⁶. -10 -1×10 -13 atm.

10. The method for preparing the anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 5, characterized in that, In step (6), the re-oxidation is performed as follows: after sintering and holding at a certain temperature, the temperature is reduced to 800-900℃ at a cooling rate of 4-7℃ / min, and the oxygen partial pressure of the reducing atmosphere is controlled to be 10 by adjusting the ratio of N2 and H2. -6 -10 -9 Atm, maintain the temperature for 0.8-2.0 hours, and then keep the atmosphere at that temperature until it cools to room temperature.

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