Ternary-system potassium-sodium niobate-based leadless piezoelectric ceramic and preparation method thereof

Abstract

The invention discloses a ternary system potassium sodium niobate-based leadless piezoelectric ceramic and a preparation method thereof, the chemical composition of the potassium sodium niobate-based leadless piezoelectric ceramic is (0.96-x) (K < 0.48 > Na < 0.52 >) (Nb < 0.96 > Sb < 0.04 >) O < 3 >-0.04 wt% Bi < 0.5 > Na < 0.5 > Zr < 0.85 > Hf < 0.15 > O < 3-x > Bi < Sc > O < 3-0.85 wt% Cu < O >-0.2 wt% Fe < 2 > O < 3 >, x is the molar percentage of Bi < Sc > O < 3 >, and x is more than or equal to 0.01 and less than or equal to 0.1. The invention relates to the technical field of lead-free piezoelectric ceramic preparation. According to the ternary system potassium-sodium niobate-based lead-free piezoelectric ceramic and the preparation method, the ternary system potassium-sodium niobate-based lead-free piezoelectric ceramic has a high piezoelectric constant and a high mechanical quality factor, keeps a high Curie temperature at the same time, is the lead-free piezoelectric ceramic with great potential, and can be applied to the fields of ultrasound, atomization and the like. The ceramic powder is prepared by adopting a two-step method, the ceramic block is prepared by adopting a two-step sintering method, the preparation method can be suitable for industrial production, and the prepared ceramic is stable in performance, high in practical value and wide in application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of lead-free piezoelectric ceramic preparation, in particular to a ternary potassium sodium niobate-based lead-free piezoelectric ceramic and a preparation method thereof. Background Art

[0002] As a kind of functional material that can realize the mutual conversion between electrical energy and mechanical energy, piezoelectric ceramics are widely used in sensors, transducers, actuators and other fields. Lead-containing piezoelectric ceramics such as lead zirconate titanate (PZT) dominate or even monopolize the commercial market due to their excellent piezoelectric properties and temperature stability. However, lead-containing materials have serious harm to the ecological environment and human body. Based on the concept of sustainable development and green development, various countries have issued a series of laws to restrict their use. At the same time, lead-free piezoelectric ceramics such as barium titanate, potassium sodium niobate and sodium bismuth titanate have attracted widespread attention and have developed rapidly.

[0003] Potassium sodium niobate {(Ka,Na)NbO3,KNN} has a high Curie temperature (TC≈410℃) and moderate piezoelectric properties (piezoelectric constant d 33 =80-150pC / N), is a class of lead-free piezoelectric ceramics with great potential. In order to further improve the piezoelectric properties of KNN-based ceramics, researchers have proposed strategies such as element doping modification, construction of polymorphic phase boundaries, and optimization of preparation processes to regulate the composition, structure and morphology of ceramics. Studies have shown that by replacing the A-position (K, Na) + with elements such as Li+ and Ag+, replacing the B-position Nb5+ with elements such as Sb5+ and Ta5+, and selecting ABO3-type compounds such as (Bi0.5M0.5)NO3 (where M is Na / Ag / K and N is Zr / Hf) and XNO3-type compounds (where X is Ca / Ba / Sr and N is Zr / Hf) as additives, the polymorphic phase transition can be regulated, and a multiphase coexistence structure can be formed at room temperature, thereby greatly improving the piezoelectric properties of potassium sodium niobate-based ceramics.

[0004] The alkali metal elements K and Na in potassium sodium niobate ceramics are easily volatilized during high-temperature sintering, which causes the ceramic chemical composition to deviate from the stoichiometric ratio and reduces the density of the ceramic. Studies have shown that element doping and the introduction of low-melting-point sintering aids can help inhibit the volatilization of alkali metals and improve the density. In addition, the two-step sintering method, the spark plasma sintering method or the use of nanopowders can also reduce the sintering temperature to a certain extent, reduce the volatilization of alkali metals, and thus improve the performance of ceramics. Although the piezoelectric properties of potassium sodium niobate-based ceramics can be improved to a certain extent by doping modification and process optimization, it is still difficult to achieve the synergistic optimization of multiple properties such as piezoelectric constant, mechanical quality factor, and Curie temperature. Therefore, it is urgent to find new ways to improve the comprehensive performance of potassium sodium niobate-based lead-free piezoelectric ceramics. Summary of the invention

[0005] In order to solve the problem that the piezoelectric constant, mechanical quality factor and Curie temperature of lead-free potassium sodium niobate-based piezoelectric ceramics in the prior art cannot be optimized in a coordinated manner, the present invention proposes a ternary potassium sodium niobate-based lead-free piezoelectric ceramic and a preparation method thereof. The ternary potassium sodium niobate-based lead-free piezoelectric ceramic has a high piezoelectric constant and mechanical quality factor, and can maintain a high Curie temperature.

[0006] On the one hand, the present invention provides a ternary potassium sodium niobate-based lead-free piezoelectric ceramic, the chemical composition of which is: (0.96-x)(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 O3-xBiScO3-0.85wt%CuO-0.2wt%Fe2O3, wherein x is the molar percentage of BiScO3, 0.01≤x≤0.1.

[0007] The lead-free ternary piezoelectric ceramics of potassium sodium antimony niobate-sodium hafnium zirconate-bismuth scandate doped with trace amounts of copper oxide and iron oxide in the present invention have a perovskite ferroelectric phase structure at room temperature. 5+ KNN is modified by doping, and sodium hafnium zirconate bismuth and scandate are used to regulate the polymorphic phase transition. At room temperature, it is a coexistence structure of rhombohedral phase-orthorhombic phase-tetragonal phase. The low energy barrier between the phases makes it easier to flip the polarization direction, thereby showing a higher piezoelectric response. Trace amounts of CuO and Fe2O3 doping can help sintering and promote the hardening of piezoelectric ceramics, which is beneficial to improving the mechanical quality factor of ceramics.

[0008] In various embodiments of the present invention, the piezoelectric constant d of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic is 33 375-505pC / N, mechanical quality factor Q m The Curie temperature is 125-201 and 338-344℃.

[0009] In a preferred embodiment of the present invention, the molar ratio of BiScO3 in the ternary potassium sodium niobate-based lead-free piezoelectric ceramic satisfies 0.03≤x≤0.05.

[0010] In a preferred embodiment of the present invention, when 0.03≤x≤0.05, the piezoelectric constant d of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic is 33 505pC / N, mechanical quality factor Q m The Curie temperature is 201 and 338℃.

[0011] In various embodiments of the present invention, the plane electromechanical coupling coefficient K of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic is p It is 0.41-0.52.

[0012] On the other hand, the present invention provides a method for preparing a ternary potassium sodium niobate-based lead-free piezoelectric ceramic, comprising: Step 1: Mix ingredients and ball mill, select analytically pure reagents K2CO3, Na2CO3, Nb2O5, Li2CO3, Sb2O5, Bi2O3, ZrO2, HfO2, Sc2O3, CuO and Fe2O3 as raw materials, weigh and ball mill them according to the stoichiometric ratio, and place the wet powder in an oven to dry to obtain a mixed powder; Step 2: pre-calcining, placing the mixed powder of step 1 in a muffle furnace for high-temperature calcination to synthesize clinker powder; Step 3: Secondary ball milling, ball milling, drying and sieving the clinker powder from step 2; Step 4: Granulation, adding a binder to the powder sieved in step 3, grinding it fully, granulating it and pressing it into a shape to obtain a green body; Step 5: debinding and sintering, placing the green body prepared in step 4 in a muffle furnace at 600-800°C for 12 hours for debinding treatment, followed by two-step high-temperature sintering to obtain a ceramic block; Step 6: Silver polarization: the ceramic block prepared in step 5 is polished on both sides and then silver polarized in a silicone oil bath to obtain a ternary potassium sodium niobate-based lead-free piezoelectric ceramic polarization sample.

[0013] In a preferred embodiment of the present invention, the ball milling media used in step 1 are anhydrous ethanol and zirconium dioxide balls, wherein the mass ratio of powder: anhydrous ethanol: zirconium dioxide balls is 1:2:3, the ball milling speed is 300-400rpm, and the ball milling time is 10-24h.

[0014] In a preferred embodiment of the present invention, the synthesis temperature in step 2 is 800-900° C. and the time is 2-4 hours.

[0015] In a preferred embodiment of the present invention, the binder in step 4 is a polyvinyl alcohol (PVA) aqueous solution with a mass fraction of 5-10wt%, and the added amount is 5-10% of the mass of the ceramic powder.

[0016] In a preferred embodiment of the present invention, the sintering temperature of the first step in step 5 is 1100-1175° C., and the time is 15-30 min. The sintering temperature of the second step is 1000-1150° C., and the time is 2-4 h.

[0017] In a preferred embodiment of the present invention, in step 6, the oil bath polarization temperature is 100-150° C., the polarization field strength is 3-5 kV / mm, and the polarization time is 10-30 min.

[0018] Beneficial Effects

[0019] The present invention provides a ternary potassium sodium niobate-based lead-free piezoelectric ceramic and a preparation method thereof. Compared with the prior art, it has the following beneficial effects: (1) The ternary potassium sodium niobate-based lead-free piezoelectric ceramic and preparation method thereof have high piezoelectric constant and mechanical quality factor, while maintaining a high Curie temperature. They are highly potential lead-free piezoelectric ceramics that can be applied to the fields of ultrasound, atomization, etc. The present invention adopts a two-step method to prepare ceramic powder and a two-step sintering method to prepare ceramic blocks. The preparation method is applicable to industrial production. The prepared ceramic has stable performance, high practical value, and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD spectra of the lead-free piezoelectric ceramics prepared in Examples 1-4 of the present invention; Figure 2 is a SEM image of the lead-free piezoelectric ceramics prepared in Examples 1-4 of the present invention; Figure 3 is a curve diagram showing the change of dielectric constant of the lead-free piezoelectric ceramics prepared in Examples 1-4 of the present invention with temperature; Figure 4 is the piezoelectric constant d of the lead-free piezoelectric ceramics prepared in Comparative Examples 1-3 of the present invention. 33 , mechanical quality factor Qm; Figure 5 is the piezoelectric constant d of the lead-free piezoelectric ceramics prepared in Examples 1-4 of the present invention 33 , mechanical quality factor Qm; Figure 6 is the planar electromechanical coupling coefficient kp of the lead-free piezoelectric ceramics prepared in Examples 1-4 of the present invention and Comparative Examples 1-3. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] See also Figures 1 to 6 The present invention provides four embodiments: a ternary potassium sodium niobate-based lead-free piezoelectric ceramic and a preparation method, specifically including the following embodiments: If the specific experimental conditions are not specified in the examples, they are usually based on conventional conditions or the conditions recommended by the reagent company; the reagents, consumables, etc. used in the following examples, unless otherwise specified, can be obtained through commercial channels, and the processes used, unless otherwise specified, are all conventional process methods in the art.

[0023] The preparation method adopted in the embodiment can be summarized as follows: Step 1: Raw material powders K2CO3, Na2CO3, Nb2O5, Li2CO3, Sb2O5, Bi2O3, ZrO2, HfO2, HfO2, Sc2O3, CuO and Fe2O3 are prepared according to the designed ternary potassium sodium niobate-based lead-free piezoelectric ceramics (0.96-x) (K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 The stoichiometric ratio of O3-xBiScO3-0.85wt%CuO-0.2wt%Fe2O3 was weighed and the purity was analytically pure. The ball milling media used in the ball milling process were anhydrous ethanol and zirconium dioxide balls, wherein the mass ratio of powder: anhydrous ethanol: zirconium dioxide balls was 1:2:3. During the ball milling process, the ball milling speed was 300-400rpm and the ball milling time was 10-24h.

[0024] Step 2: Place the ball-milled mixed powder in an oven for drying for 24 hours, and place the obtained mixed powder in a muffle furnace for high-temperature calcination to obtain a clinker powder, wherein the synthesis temperature is 800-900° C. and the time is 2-4 hours.

[0025] Step 3: ball-milling, drying and sieving the pre-burned clinker powder for the second time; Step 4: Add a binder to the sieved clinker powder, grind it fully, granulate it, and press it into a round green piece with a diameter of 10-15 mm at a pressure of 2-10 MPa; Step 5: Place the green body in a muffle furnace at 600-800°C for 12 hours for debinding treatment, and then perform two-step high-temperature sintering to obtain a ceramic block, wherein the sintering temperature of the first step is 1100-1175°C for 15-30 minutes, and the sintering temperature of the second step is 1000-1150°C for 2-4 hours.

[0026] Step 6: The prepared ceramic block is polished on both sides and then silvered, and placed in a silicone oil bath device at 100-150°C for oil bath polarization, with a polarization field strength of 3-5 kV / mm and a polarization time of 10-30 min.

[0027] Example 1

[0028] Preparation of 0.95 (K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 O3-0.01BiScO3-0.85wt%CuO-0.2wt%Fe2O3 ceramic sheet: Step 1: Weigh the original powders of K2CO3, Na2CO3, Nb2O5, Li2CO3, Sb2O5, Bi2O3, ZrO2, HfO2, Sc2O3, CuO and Fe2O3 according to the ceramic stoichiometric ratio, and use anhydrous ethanol and zirconium dioxide balls as ball milling media for ball milling at a speed of 350 rpm for 12 hours. Place the mixed wet powder in an oven at 85°C and dry for 24 hours, and pass through a 100-mesh sieve to obtain a mixed powder.

[0029] Step 2: Place the mixed dry powder in a muffle furnace and calcine at 850° C. for 3 h to obtain clinker powder.

[0030] Step 3: The clinker powder was subjected to secondary ball milling at a ball milling speed of 350 rpm for 12 h. The secondary ball milled powder was then placed in an oven at 85°C for 24 h and passed through a 100-mesh sieve. The sieved powder was added with a polyvinyl alcohol binder for granulation and pressed under a pressure of 2 MPa to obtain a disc green body with a thickness of about 1 mm.

[0031] Step 4: Place the green body in a muffle furnace at 750°C for 12 hours for debinding treatment, and then perform two-step sintering, first heating to 1150°C for 30 minutes, then cooling to 1080°C for 3 hours, and obtain a ceramic block as the furnace cools.

[0032] Step 5: The ceramic block is polished on both sides and then silvered, and then placed in a silicone oil bath and heated to 100°C for polarization treatment. The polarization field strength is 3-5 kV / mm and the polarization time is 10-30 min to obtain a ternary potassium sodium niobate-based lead-free piezoelectric ceramic polarized sample.

[0033] Example 2

[0034] The preparation process of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic in Example 2 is similar to that in Example 1, except that: 0.92(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi0.5 Na 0.5 Zr 0.85 Hf 0.15 O3-0.04BiScO3-0.85wt%CuO-0.2wt%Fe2O3.

[0035] Example 3

[0036] The preparation process of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic in Example 3 is similar to that in Example 1, except that: 0.89(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 O3-0.07BiScO3-0.85wt%CuO-0.2wt%Fe2O3.

[0037] Example 4

[0038] The preparation process of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic in Example 4 is similar to that in Example 1, except that: 0.86(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 O3-0.1BiScO3-0.85wt%CuO-0.2wt%Fe2O3.

[0039] Comparative Example 1 The preparation process of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic in Comparative Example 1 is similar to that in Example 2, except that: The 0.92(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 When preparing O3-0.04BiScO3-0.85wt%CuO-0.2wt%Fe2O3 ceramics, the temperature is first raised to 1100°C and kept for 30 minutes, then cooled to 1080°C and kept for 3 hours, and then the ceramic block is obtained by cooling in the furnace.

[0040] Comparative Example 2 The preparation process of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic in Comparative Example 2 is similar to that in Example 2, except that: The 0.92(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 When preparing O3-0.04BiScO3-0.85wt%CuO-0.2wt%Fe2O3 ceramics, the temperature is first raised to 1125°C and kept for 30 minutes, then cooled to 1080°C and kept for 3 hours, and then the ceramic block is obtained by cooling in the furnace.

[0041] Comparative Example 3 The preparation process of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic in Comparative Example 3 is similar to that in Example 2, except that: The 0.92(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 When preparing O3-0.04BiScO3-0.85wt%CuO-0.2wt%Fe2O3 ceramics, the temperature is first raised to 1175°C and kept for 30 minutes, then cooled to 1080°C and kept for 3 hours, and then the ceramic block is obtained by cooling in the furnace.

[0042] Structural characterization and performance testing The ternary potassium sodium niobate-based lead-free piezoelectric ceramics prepared in Examples 1-4 were characterized and tested for performance as follows: (1) Figure 1 The XRD spectra of the ceramic samples prepared in Examples 1-4. As can be seen from the figure, the ceramics prepared in Examples 1-4 have a typical perovskite structure and no impurity phase is generated, indicating that all elements have successfully entered the ceramic lattice and formed a stable solid solution. In addition, a small amount of doping with CuO and Fe2O3 does not affect the ceramic phase structure. The two peaks split in the range of 45°-46° correspond to the

[002] and

[200] crystal planes, respectively, indicating that the prepared samples have a three-phase coexistence structure of rhombohedral phase-orthorhombic phase-tetragonal phase (ROT). The construction of this multi-phase coexistence structure is conducive to improving piezoelectric properties.

[0043] (2) Figure 2 The SEM images of the samples prepared in Examples 1-4 are shown in FIG. Figure 2(a), (b), (c), and (d) are microscopic morphology images at x=0.01, 0.04, 0.07, and 0.1, respectively. The prepared samples have a dense structure and cubic grain morphology. The prepared samples have a wide distribution range of grain size, showing obvious large and small grains. This may be due to the low melting points of elements such as K and Na, which are easy to volatilize, causing abnormal grain growth.

[0044] (3) Figure 3 The piezoelectric constant d of the samples prepared in Examples 1-4 33 and planar mechanical quality factor Q m Fig. Piezoelectric constant d of ceramic samples of Examples 1-4 33 The values ​​are 410, 505, 450 and 375 pC / N respectively, and the corresponding Q m The values ​​are 150, 201, 142 and 125 respectively. When the BiScO3 content is 0.04, the ceramic sample has the highest piezoelectric constant d 33 and Q m This can be attributed to its high content of rhombohedral and tetragonal phases. The similar free energy of each phase in the sample can greatly reduce the polarization anisotropy, promote polarization reversal, and thus improve the piezoelectric performance.

[0045] (4) Figure 4 The piezoelectric constant d of the samples prepared in Comparative Examples 1-3 is 33 and planar mechanical quality factor Q m Fig. Piezoelectric constant d of ceramic samples of comparative examples 1-3 33 The values ​​are 401, 473 and 435 pC / N respectively, and the corresponding Q m The values ​​are 133, 176 and 139 respectively. The piezoelectric constant d of the comparison sample 33 and Q m The values ​​are all smaller than those of the sample in Example 2, indicating that the sintering conditions in Example 2 are the optimal sintering conditions.

[0046] (5) Figure 5 Planar electromechanical coupling coefficient K of samples prepared in Examples 1-4 p Fig. Planar electromechanical coupling coefficient K of samples prepared in Examples 1-4 p The values ​​are 0.43, 0.52, 0.45 and 0.41 respectively.

[0047] (6) Figure 6The curves of the dielectric constant variation with temperature at different frequencies for the samples prepared in Examples 1-4 are shown. Near room temperature, the dielectric constant of the samples increases as the temperature decreases, indicating that there is a dielectric peak below room temperature, which can be attributed to the phase transition from the fused rhombic phase to the orthorhombic phase and the phase transition from the orthorhombic phase to the tetragonal phase. This further shows that the sample is a multi-phase coexistence structure at room temperature. The dielectric peak at high temperature indicates the transition of the ceramic from the ferroelectric phase to the paraelectric phase, and the corresponding temperature is the Curie temperature. It can be seen from the figure that the Curie temperatures of the ceramic samples of Examples 1-4 are 345°C, 341°C, 340°C and 337°C, respectively.

[0048] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A ternary potassium sodium niobate-based lead-free piezoelectric ceramic, characterized in that: The chemical composition of the potassium sodium niobate-based ternary lead-free piezoelectric ceramic is: (0.96-x)(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.04Bi 0.5 Na 0.5 Zr 0.85 Hf 0.15 O3-xBiScO3-0.85wt%CuO-0.2wt%Fe2O3, wherein x is the molar percentage of BiScO3, 0.01≤x≤0.

1.

2. The ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 1, characterized in that: The piezoelectric constant d of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic is 33 375-505pC / N, mechanical quality factor Q m The Curie temperature is 125-201 and 338-344℃.

3. The ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 1, characterized in that: The molar percentage of the BiScO3 satisfies: 0.03≤x≤0.

05.

4. The ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 1, characterized in that: The ternary potassium sodium niobate-based lead-free piezoelectric ceramic, when 0.03≤x≤0.05, has a piezoelectric constant d 33 505pC / N, mechanical quality factor Q m The Curie temperature is 201 and 338℃.

5. The ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 1, characterized in that: The planar electromechanical coupling coefficient K of the ternary potassium sodium niobate-based lead-free piezoelectric ceramic p It is 0.41-0.

52.

6. A method for preparing a ternary potassium sodium niobate-based lead-free piezoelectric ceramic, comprising the ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to any one of claims 1 to 5, characterized in that: The specific steps include: Step 1, batching and ball milling: select analytically pure reagents K2CO3, Na2CO3, Nb2O5, Sb2O5, Bi2O3, ZrO2, HfO2, Sc2O3, CuO and Fe2O3 as raw materials, weigh and ball mill them according to the stoichiometric ratio, and place the wet powder in an oven to dry to obtain a mixed powder; Step 2, pre-calcination: placing the mixed powder of step 1 in a muffle furnace and calcining at high temperature to obtain a clinker powder; Step 3, secondary ball milling: ball milling, drying and sieving the clinker powder in step 2; Step 4, granulation: adding a binder to the powder sieved in step 3, grinding it fully, granulating it and pressing it into a shape to obtain a green body; Step 5, debinding and sintering: placing the green body prepared in step 4 in a muffle furnace at 600-800° C. for 12 hours for debinding treatment, followed by two-step high-temperature sintering to obtain a ceramic block; Step 6, silver polarization: the ceramic block prepared in step 5 is polished on both sides, then silver polarized and placed in a silicone oil bath device for oil bath polarization to obtain a ternary potassium sodium niobate-based lead-free piezoelectric ceramic polarization sample.

7. The method for preparing a ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 6, characterized in that: The ball milling media used in the ball milling in step 1 are anhydrous ethanol and zirconium dioxide balls, wherein the mass ratio of the powder, anhydrous ethanol and zirconium dioxide balls is 1:2:3, the ball milling speed is 300-400rpm, and the ball milling time is 10-24h.

8. The method for preparing a ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 6, characterized in that: In step 2, the synthesis temperature is 800-900° C. and the time is 2-4 hours.

9. The method for preparing a ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 6, characterized in that: The binder in step 4 is a polyvinyl alcohol (PVA) aqueous solution with a mass fraction of 5-10wt%, and the added amount is 5-10% of the mass of the ceramic powder.

10. The method for preparing a ternary potassium sodium niobate-based lead-free piezoelectric ceramic according to claim 6, characterized in that: In the step 5, the sintering temperature of the first step is 1100-1175°C, and the time is 15-30min. The sintering temperature of the second step is 1000-1150°C, and the time is 2-4h. In the step 6, the oil bath polarization temperature is 100-150°C, the polarization field strength is 3-5kV / mm, and the polarization time is 10-30min.

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