Multi-element synergistically doped potassium-sodium niobate-based piezoelectric ceramic as well as preparation method and application thereof

Abstract

The invention discloses a multi-element synergistically doped potassium-sodium niobate-based piezoelectric ceramic as well as a preparation method and application thereof, and relates to the technical field of piezoelectric ceramic materials. Through synergistic doping of multiple elements Li, Sb, Bi, Hf and Ti, comprehensive improvement of high piezoelectric property, high mechanical quality factor and high-temperature stability of the potassium-sodium niobate-based piezoelectric ceramic is realized. Through A / B site element matching, the phase boundary is widened, alkali metal volatilization is inhibited, and the piezoelectric response and the structural stability are remarkably improved. The potassium-sodium niobate-based piezoelectric ceramic has excellent electrical properties and high-temperature reliability, is completely lead-free and environment-friendly, is remarkably reduced in process energy consumption and raw material cost compared with a traditional method, and is suitable for high-temperature and high-power scenes such as medical ultrasound, industrial sensing and new energy automobiles.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric ceramic materials, and in particular to a multi-element co-doped potassium sodium niobate-based piezoelectric ceramic, a preparation method thereof, and applications thereof. Background Art

[0002] Lead-based piezoelectric ceramics (such as Pb(Zr,Ti)O3, referred to as PZT) have excellent piezoelectric properties (d 33 ≥500pC / N, k≥0.6) and process maturity, it has long occupied more than 90% of the piezoelectric material market share and is widely used in core electronic devices such as ultrasonic transducers, sensors, filters, and igniters. For example, medical ultrasound probes rely on the high sensitivity of PZT to achieve precise imaging, and industrial non-destructive testing equipment uses its high-voltage electrical response to detect internal defects in materials. However, the lead oxide (PbO) content in lead-based piezoelectric ceramics is as high as 60% to 70%, posing a serious threat to the environment and human health during production, use, and disposal. Therefore, providing a lead-free piezoelectric ceramic material is an inevitable trend in the long-term development of this field.

[0003] To replace PZT, lead-free piezoelectric ceramic systems such as bismuth sodium titanate (BNT), potassium sodium niobate (KNN), and barium titanate (BT) have been developed. Among these lead-free piezoelectric ceramic systems, KNN-based piezoelectric ceramics are considered the most promising PZT replacement material due to their high-voltage electrical activity, high Curie temperature, and environmentally friendly properties.

[0004] However, the current potassium sodium niobate-based piezoelectric ceramics still face the following difficulties in the process of industrialization:

[0005] 1) The phase boundary stability of potassium sodium niobate-based piezoelectric ceramics is poor, and the morphotropic phase boundary (MPB) temperature range is narrow (<20°C), which leads to strong sensitivity to the composition of the material. Composition fluctuations can easily cause the separation of the orthorhombic phase and the tetragonal phase, making the piezoelectric ceramic performance unstable and the piezoelectric performance d 33 and mechanical quality factor Q m The discreteness is large, and the Curie temperature T c Relatively low.

[0006] 2) During the production process, K / Na elements are easily volatilized, which leads to problems such as lattice vacancies, increased porosity and decreased density in potassium sodium niobate-based piezoelectric ceramics, and is prone to the formation of pyrochlore impurity phases, such as K4Nb6O 17 , significantly reducing the mechanical quality factor of potassium sodium niobate-based piezoelectric ceramics.

[0007] 3) Higher piezoelectric performance is often accompanied by a sharp drop in the mechanical quality factor. This imbalance in the performance of high piezoelectricity and high mechanical quality factor makes it difficult to meet the needs of high-power devices.

[0008] In order to solve any of the above problems, the present invention is proposed. Summary of the Invention

[0009] The purpose of the present invention is to provide a multi-element co-doped potassium sodium niobate-based piezoelectric ceramic and its preparation method and application.

[0010] The present invention is achieved in that:

[0011] In the first aspect, the present invention provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, the chemical formula of the potassium sodium niobate-based piezoelectric ceramic material is: 0.964 (K 0.46 Na 0.54 ) 1-x Li x (Sb y Nb 1-y )O3-0.036(Bi 0.5 K 0.5 ) 0.982 (Hf z Ti 1-z ) 0.018 O3-0.2~0.3mol% B2O3-0.3~0.5mol% ZnO.

[0012] And at least two of the following conditions are met:

[0013] 1) 0.03≤x≤0.05;

[0014] 2)0.05≤y≤0.08;

[0015] 3)0.05≤z≤0.1.

[0016] In a second aspect, the present invention provides a method for preparing a piezoelectric ceramic as described in any one of the aforementioned embodiments, comprising mixing raw materials in a stoichiometric ratio, ball-milling, and pre-sintering to obtain a formulated powder, shaping the formulated powder to obtain a green body, and sintering the green body in two steps.

[0017] The raw materials include main component raw materials and sintering aids.

[0018] In a third aspect, the present invention provides an application of a piezoelectric ceramic according to any one of the aforementioned embodiments or a piezoelectric ceramic prepared by the preparation method according to any one of the aforementioned embodiments in any field of ultrasonic medical equipment, tactile feedback sensors or ultrasonic transducers.

[0019] The present invention has the following beneficial effects:

[0020] The present invention provides a multi-element co-doped potassium sodium niobate-based piezoelectric ceramic, as well as a preparation method and application. Through the co-doping of multiple elements Li, Sb, Bi, Hf, and Ti, the high piezoelectric properties, high mechanical quality factor, and high-temperature stability of potassium sodium niobate-based piezoelectric ceramics are comprehensively improved. By matching A / B site elements to broaden the phase boundary and suppress the volatilization of alkali metals, the piezoelectric response and structural stability are significantly improved. The potassium sodium niobate-based piezoelectric ceramic has both excellent electrical properties and high-temperature reliability, and is completely lead-free and environmentally friendly. The process energy consumption and raw material costs are significantly reduced compared to traditional methods. It is suitable for high-temperature and high-power scenarios such as medical ultrasound, industrial sensing, and new energy vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a scanning electron microscope (SEM) image of the potassium sodium niobate-based piezoelectric ceramic prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0024] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0025] In the first aspect, the present invention provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, the chemical formula of the potassium sodium niobate-based piezoelectric ceramic material is: 0.964 (K 0.46 Na 0.54 ) 1-x Li x (Sb y Nb 1-y )O3-0.036(Bi 0.5 K 0.5 ) 0.982 (Hf z Ti 1-z ) 0.018 O3-0.2~0.3mol% B2O3-0.3~0.5mol% ZnO.

[0026] And at least two of the following conditions are met:

[0027] 1) 0.03≤x≤0.05;

[0028] 2)0.05≤y≤0.08;

[0029] 3)0.05≤z≤0.1.

[0030] Through the synergistic doping of multiple elements (Li, Sb, Bi, Hf, and Ti), the high piezoelectric properties, high mechanical quality factor, and high-temperature stability of potassium sodium niobate-based piezoelectric ceramics are comprehensively improved. By matching A / B site elements to broaden the phase boundary and suppress alkali metal volatilization, the piezoelectric response and structural stability are significantly enhanced. This potassium sodium niobate-based piezoelectric ceramic combines excellent electrical performance with high-temperature reliability, is completely lead-free and environmentally friendly, and significantly reduces process energy consumption and raw material costs compared to traditional methods. It is suitable for high-temperature, high-power applications such as medical ultrasound, industrial sensing, and new energy vehicles.

[0031] It can be understood that in the above chemical formula, the molar percentages of B2O3 and ZnO account for 0.5-0.8 mol% of the total molar weight of the potassium sodium niobate-based piezoelectric ceramic, wherein the molar percentage of B2O3 accounts for 0.2-0.3 mol% of the total molar weight of the potassium sodium niobate-based piezoelectric ceramic, and the molar percentage of ZnO accounts for 0.3-0.5 mol% of the total molar weight of the potassium sodium niobate-based piezoelectric ceramic.

[0032] In an optional embodiment, in the general chemical formula of the material of the potassium sodium niobate-based piezoelectric ceramic, x, y, and z simultaneously satisfy: 0.03≤x≤0.05; 0.05≤y≤0.08; 0.05≤z≤0.1.

[0033] The lattice distortion is adjusted by the coordinated substitution of Li, Sb and Hf at the three sites of Li+ to replace K or Na at the A site in the potassium sodium niobate base, thereby reducing the coercive electric field strength and enhancing the polarization response; Sb 5+ Substituting Nb at the B position in potassium sodium niobate, optimizing oxygen octahedral distortion, and improving the piezoelectric constant and electromechanical coupling coefficient; Hf 4+ Substituting Ti at the B' position in the potassium sodium niobate matrix enhances lattice stability and significantly raises the Curie temperature. This synergistic substitution at the A / B / B' positions balances polarization capability and structural stability, resolving the conflict between high piezoelectricity and low Curie temperature in traditional potassium sodium niobate-based piezoelectric ceramics.

[0034] In an optional embodiment, the piezoelectric constant d of the potassium sodium niobate-based piezoelectric ceramic is 33 The mechanical quality factor Qm is 230-270, the Curie temperature Tc is 290℃-350℃, and the plane electromechanical coupling coefficient k pis 0.50~0.60; dielectric loss tanδ is 1.0%~2.0%; residual polarization intensity P r 18μC / cm 2 ~25μC / cm 2 , coercive field strength E c 10kV / cm~15kV / cm; density ≥96%.

[0035] Preferably, the piezoelectric constant d of the potassium sodium niobate-based piezoelectric ceramic is 33 The mechanical quality factor Qm is 233 to 268, the Curie temperature Tc is 295 to 345 degrees Celsius, and the plane electromechanical coupling coefficient k p is 0.53~0.58; dielectric loss tanδ is 1.0%~1.8%; residual polarization intensity P r 18μC / cm 2 ~22μC / cm 2 , coercive field strength E c It is 12kV / cm~14kV / cm; the density is 96%~99%.

[0036] Preferably, the piezoelectric constant d of the potassium sodium niobate-based piezoelectric ceramic is 33 is 380pC / N~390pC / N; the mechanical quality factor Qm is 233~245, the Curie temperature Tc is 325℃~345℃, and the plane electromechanical coupling coefficient k p is 0.55~0.56; dielectric loss tanδ is 1.0%~1.5%; residual polarization intensity P r 19μC / cm 2 ~25μC / cm 2 , coercive field strength E c It is 12kV / cm~13.5kV / cm; the density is 97%~99%.

[0037] In a second aspect, the present invention provides a method for preparing a piezoelectric ceramic as described in any one of the aforementioned embodiments, comprising mixing raw materials in a stoichiometric ratio, ball-milling, and pre-sintering to obtain a formulated powder, shaping the formulated powder to obtain a green body, and sintering the green body in two steps.

[0038] The raw materials include main component raw materials and sintering aids.

[0039] In an optional embodiment, the sintering aid includes B2O3 and ZnO. By selecting B2O3 and ZnO as a composite sintering aid and combining them with a two-step sintering process, not only can the sintering temperature be reduced, but the introduction of these sintering aids can also promote high densification and uniform grain refinement of the potassium sodium niobate-based piezoelectric ceramic, thereby improving the performance of the potassium sodium niobate-based piezoelectric ceramic.

[0040] Preferably, the purity of B2O3 and ZnO in the sintering aid is ≥99.95%.

[0041] Preferably, the main component raw material includes at least one of potassium carbonate, sodium carbonate, lithium carbonate, antimony trioxide, niobium pentoxide, bismuth trioxide, hafnium dioxide and titanium pentoxide.

[0042] Preferably, among the main raw materials, the purity of potassium carbonate and sodium carbonate is ≥99.95%, and the purity of lithium carbonate, antimony trioxide, niobium pentoxide, bismuth trioxide, hafnium dioxide and titanium pentoxide is ≥99.99%.

[0043] The inventors have discovered that the current sintering temperature of potassium sodium niobate-based piezoelectric ceramics is relatively high, generally >1100°C, which is the main problem leading to alkali metal volatilization. Therefore, the present invention designs a two-step sintering process to reduce the sintering temperature of potassium sodium niobate-based piezoelectric ceramics. Combined with the synergistic doping of Sb, Ta, Li, Bi, and Hf, the morphotropic phase boundary of potassium sodium niobate-based piezoelectric ceramics is broadened, further suppressing alkali metal volatilization. As a result, the potassium sodium niobate-based piezoelectric ceramics produced by the present invention have high piezoelectric properties, high mechanical quality factor, and high-temperature stability.

[0044] In an optional embodiment, the preparation method of potassium sodium niobate-based piezoelectric ceramics comprises the following steps:

[0045] S01. Prepare formula powder

[0046] In an optional embodiment, the method for preparing the formula powder includes: adding raw materials into a ball mill, then adding grinding balls and a solvent to perform wet ball milling, and drying the slurry obtained by the wet ball milling and then pre-calcining it.

[0047] That is, preferably, wet ball milling is used in the process of preparing the formula powder. The traditional production process of potassium sodium niobate-based piezoelectric ceramics mostly adopts the solid-phase method, which has high process sensitivity, especially to parameters such as raw material purity, ball milling time, and sintering curve. As a result, it is difficult to ensure the consistency of potassium sodium niobate-based piezoelectric ceramics in the mass production process. The present invention reduces the process sensitivity by adopting wet ball milling, and then pre-burns the slurry obtained by ball milling after drying, so that the uniformly mixed raw materials undergo a chemical reaction to generate KNN phase, thereby avoiding component segregation.

[0048] Preferably, the mass ratio of the raw materials, the solvent, and the grinding balls is 1.8-2.2:4.8-5.2:9.8-10.2, wherein the total mass of the main component raw materials and the sintering aid is the mass of the raw materials.

[0049] Preferably, the grinding balls include any one of zirconium oxide grinding balls and aluminum oxide balls; and the solvent includes anhydrous ethanol.

[0050] Preferably, the ball milling speed is 260 r / min to 360 r / min, and the time is 12 h to 16 h.

[0051] Preferably, the pre-firing temperature is 820° C. to 850° C., and the holding time is 3 h to 8 h.

[0052] Preferably, the method further comprises sieving the powder obtained by pre-calcination for standby use, wherein the mesh number of the sieve is 60 to 100 meshes.

[0053] S02. Preparation of green body

[0054] In an optional embodiment, in order to ensure the uniformity of the green body structure, such as the uniformity of the composition between particles and the uniformity of the chemical composition, the green body preparation method includes: grinding, granulating, molding and debinding the formula powder in sequence.

[0055] S021, Grinding

[0056] Preferably, the grinding is slurry grinding, which can further reduce the process sensitivity of the raw materials and ensure the stability of the element ratio of the potassium sodium niobate-based piezoelectric ceramics.

[0057] Slurry grinding includes mixing the formula powder, water, grinding dispersant and binder to obtain a mixed slurry, and adding grinding beads to the mixed slurry for grinding.

[0058] The mixed slurry obtained after grinding is a submicron slurry, the particle size distribution of which satisfies the normal distribution, and D50=500nm~800nm.

[0059] Preferably, in the mixed slurry, the mass ratio of the formula powder to water is 1:0.8-1.2, the mass of the grinding dispersant is 0.1wt.%-2.5wt.% of the total weight of the mixed slurry, and the mass of the binder is 0.7wt.%-1wt.% of the total weight of the mixed slurry.

[0060] Preferably, the grinding dispersant includes at least one of polyacrylamide, styrene-maleic anhydride copolymer and tetramethylammonium hydroxide.

[0061] Preferably, the binder includes at least one of polyvinyl alcohol and polyacrylic acid amine with a concentration of 5 to 6 wt.%.

[0062] Preferably, the mass ratio of the mixed slurry to the grinding beads is 1:0.8-1.2, the particle size of the grinding beads is 1 mm-3 mm, and the material of the grinding beads includes at least one of zirconium oxide and aluminum oxide.

[0063] Preferably, the grinding parameters include: a grinding rod speed of 1300 r / min to 1800 r / min, a circulating pump speed of 80 r / min to 120 r / min, and a grinding time of 1 h to 4 h.

[0064] Preferably, the water used in the grinding process is deionized water.

[0065] S022, Granulation

[0066] Preferably, the granulation is spray granulation, and the spray granulation obtains spherical granulation powder, and the particle size distribution of the spherical granulation powder is D50=30μm~50μm.

[0067] Preferably, the spray granulation adopts a spray granulation tower, the inlet temperature of the spray drying tower is 200°C to 250°C, and the outlet temperature is 100°C to 120°C.

[0068] S023, Molding

[0069] Preferably, the molding is compression molding, wherein the spherical granulated powder obtained by granulation is put into a mold and dry-pressed, and the compression molding pressure is 18 MPa to 25 MPa.

[0070] Preferably, the shape of the blank obtained by press molding is any one of a disc, a cylinder, a square or a prism.

[0071] Preferably, the blank obtained by compression molding is in the shape of a disc with a diameter of 15 mm to 25 mm and a thickness of 0.5 mm to 1.5 mm.

[0072] S024, glue removal

[0073] Preferably, debinding includes firing the green body obtained by pressing to completely remove organic materials such as binders and dispersants in the grinding process.

[0074] Preferably, the firing parameters include: heating to 600° C. to 700° C. at 2° C. / min to 4° C. / min, and keeping the temperature for 2 h to 4 h.

[0075] S03, two-step sintering

[0076] In an alternative embodiment, the two-step sintering includes sealing the green body before performing the first stage sintering and the second stage sintering. Sealing can also reduce the possibility of alkali metal volatilization.

[0077] The first stage sintering includes: heating to 1050°C to 1100°C at a heating rate of 6°C / min to 8°C / min, and keeping the temperature for 20 to 40 minutes.

[0078] The second stage sintering includes: cooling to 940°C to 1020°C at a rate of 3°C / min to 5°C / min, and keeping the temperature for 4 to 6 hours.

[0079] By controlling the process parameters of the two-step sintering within the above range, the first-stage sintering can quickly eliminate the pores formed after the green body is debinded and achieve initial densification; the second-stage sintering can inhibit grain coarsening, so that the grain size is controlled at 0.8μm to 1.5μm, and the density is further improved. At the same time, the two-step sintering process can also effectively improve the piezoelectric constant of potassium sodium niobate-based piezoelectric ceramics. In addition, the sintering temperature of the two-step sintering is less than or equal to 1100°C, which avoids the loss of potassium and sodium ions and ensures that the element ratio of potassium sodium niobate-based piezoelectric ceramics is consistent with the theoretical stoichiometric ratio. At the same time, the low-temperature two-step sintering process has lower energy consumption and lower costs than the traditional high-temperature sintering process, which is conducive to increasing production capacity.

[0080] Preferably, the blank is laminated before sealing.

[0081] By selecting B2O3 and ZnO as composite sintering aids and combining them with a low-temperature two-step sintering process, not only can the sintering temperature be reduced, but the introduction of the above-mentioned sintering aids can also promote the high densification and uniform grain refinement of potassium sodium niobate-based piezoelectric ceramics, which is beneficial to improving the performance of potassium sodium niobate-based piezoelectric ceramics.

[0082] S04, post-processing

[0083] In an optional embodiment, in order to impart piezoelectric function to the sintered body after sintering, the sintered body obtained after the two-step sintering is further subjected to post-processing, wherein the post-processing includes preparing an electrode layer and high-voltage polarization.

[0084] S041. Preparation of electrode layer

[0085] Preferably, the method for preparing the electrode layer includes covering the surface of the sintered body with electrode slurry and then performing a sintering treatment.

[0086] Preferably, the electrode slurry includes metal and its dispersion, wherein the metal material includes any one of silver, copper and gold.

[0087] Preferably, the metal content in the electrode slurry is 80 wt.% to 90 wt.%.

[0088] Preferably, the sintering temperature is 700° C. to 750° C., and the sintering time is 20 min to 30 min.

[0089] Preferably, before the surface of the sintered body is covered with the electrode slurry, the sintered body is polished and cleaned to ensure a stable connection between the electrode layer and the sintered body.

[0090] Preferably, the electrode slurry can be applied by screen printing, for example, as long as the electrode slurry can be evenly applied to the surface of the sintered body.

[0091] S042, high voltage polarization

[0092] Preferably, the high-voltage polarization includes immersing the sintered body having the electrode layer in a silicone oil bath and applying an electric field to perform polarization treatment.

[0093] Preferably, the electric field for high-voltage polarization is a direct current electric field, the electric field strength is 3 kV / mm to 4.5 kV / mm, and the holding time is 25 min to 45 min.

[0094] The potassium sodium niobate-based piezoelectric ceramics prepared by the preparation method of the present invention have mass production compatibility, do not require complex equipment, and have batch consistency deviation of less than 5%.

[0095] In a third aspect, the present invention provides an application of a piezoelectric ceramic according to any one of the aforementioned embodiments or a piezoelectric ceramic prepared by the preparation method according to any one of the aforementioned embodiments in any field of ultrasonic medical equipment, tactile feedback sensors or ultrasonic transducers.

[0096] Example 1

[0097] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi and Ti, and the general chemical formula is:

[0098] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.06 Nb 0.94 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.06, z=0.

[0099] This embodiment also provides a method for preparing the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, comprising the following steps:

[0100] S01. Prepare formula powder

[0101] Calculated according to the chemical formula, 137.574 g of sodium carbonate, 159.162 g of potassium carbonate, 625.373 g of niobium pentoxide, 7.398 g of lithium carbonate, 43.778 g of antimony oxide, 0.000 g of hafnium oxide, 21.384 g of bismuth oxide, 3.732 g of titanium oxide, 0.542 g of boron oxide, and 1.057 g of zinc oxide were used as raw materials.

[0102] The raw materials and 5000g of zirconium oxide grinding balls were placed in a ball mill. 2500g of anhydrous ethanol was added and wet-milled at 300r / min for 16 hours. The milled slurry was then poured out and dried to obtain a mechanically mixed powder. The mechanically mixed powder was poured into a crucible and pre-calcined in a muffle furnace at 850°C for 5 hours. The resulting formula powder was then passed through an 80-mesh sieve for later use.

[0103] S02. Preparation of green body

[0104] S021, Grinding

[0105] The formula powder obtained after pre-calcination in step S01 was evenly mixed with 620 g of deionized water, 36 g of polyacrylamide and 400 g of PVA binder with a concentration of 5 wt.% were added, and 1000 g of zirconia beads (particle size 1 mm to 3 mm) were added. The grinding rod speed was set to 1600 r / min, the circulation pump speed was 100 r / min, and the sanding time was 2 h to obtain a submicron mixed slurry whose particle size distribution satisfied the normal distribution and D50 = 520 nm.

[0106] S022, Granulation

[0107] The mixed slurry obtained in step S021 was spray granulated using a spray drying tower. The inlet temperature of the spray drying tower was 230° C., and the outlet temperature was 110° C. Spherical granulated powder was obtained by spray granulation. The particle size distribution of the spherical granulated powder was D50=34 μm.

[0108] S023, Molding

[0109] The spherical granulated powder obtained in step S022 is placed into a mold and dry pressed at 23 MPa to a size of round wafer blank.

[0110] S024, glue removal

[0111] The disc blanks obtained in step S023 are placed on a setter plate at a certain interval, heated to 650° C. at a rate of 4° C. / min and kept at this temperature for 3 hours to remove the organic binder and dispersant.

[0112] S03, two-step sintering

[0113] The disc blanks after debinding in step S024 are stacked and sealed with a sagger, and then sintered in two steps to obtain a sintered body.

[0114] In the first stage of sintering, the temperature was raised to 1050°C at 8°C / min and kept at this temperature for 40 minutes; in the second stage of sintering, the temperature was lowered to 1020°C at 5°C / min and kept at this temperature for 4 hours.

[0115] S04, post-processing

[0116] S041. Preparation of electrode layer

[0117] After polishing and cleaning the sintered body obtained in step S03, silver paste (silver content is 85 wt.%) is evenly covered on both sides of the ceramic sheet using screen printing, and sintered at 720° C. for 30 minutes to form an electrode layer.

[0118] S042, high voltage polarization

[0119] The sintered body with the electrode layer obtained in step S041 was immersed in a silicone oil bath and a DC electric field of 4.5 kV / mm was applied for a holding time of 35 minutes to obtain a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic.

[0120] The cross-sectional microstructure of the potassium sodium niobate-based piezoelectric ceramics prepared in this embodiment is as follows: Figure 1 As shown, from Figure 1 It can be seen from the SEM photograph of the piezoelectric ceramic that the grain size of the ceramic prepared in this embodiment is about 4-7 μm, the grain growth and accumulation are relatively sufficient, and there are no obvious pores.

[0121] Example 2

[0122] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi and Ti, and the general chemical formula is:

[0123] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.07 Nb 0.93 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.07, z=0.

[0124] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this embodiment is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.485 g of sodium carbonate, 159.059 g of potassium carbonate, 618.322 g of niobium pentoxide, 7.393 g of lithium carbonate, 51.042 g of antimony oxide, 0.000 g of hafnium oxide, 21.371 g of bismuth oxide, 3.730 g of titanium oxide, 0.542 g of boron oxide, and 1.056 g of zinc oxide.

[0125] Example 3

[0126] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi and Ti, and the general chemical formula is:

[0127] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.08 Nb 0.92 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.08, z=0.

[0128] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this embodiment is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.397 g of sodium carbonate, 158.957 g of potassium carbonate, 611.281 g of niobium pentoxide, 7.388 g of lithium carbonate, 58.296 g of antimony oxide, 0.000 g of hafnium oxide, 21.357 g of bismuth oxide, 3.728 g of titanium oxide, 0.542 g of boron oxide, and 1.056 g of zinc oxide.

[0129] Example 4

[0130] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi, Hf, and Ti, and the general chemical formula is:

[0131] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.07 Nb 0.93 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 (Hf 0.05 Ti 0.05 ) 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.07, z=0.05.

[0132] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this embodiment is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.508 g of sodium carbonate, 159.086 g of potassium carbonate, 618.427 g of niobium pentoxide, 7.394 g of lithium carbonate, 51.050 g of antimony oxide, 0.018 g of hafnium oxide, 21.374 g of bismuth oxide, 3.544 g of titanium oxide, 0.542 g of boron oxide, and 1.056 g of zinc oxide.

[0133] Example 5

[0134] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi, Hf, and Ti, and the general chemical formula is:

[0135] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.07 Nb 0.93 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 (Hf 0.08 Ti 0.02 ) 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.07, z=0.08.

[0136] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this embodiment is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.522 g of sodium carbonate, 159.102 g of potassium carbonate, 618.489 g of niobium pentoxide, 7.395 g of lithium carbonate, 51.055 g of antimony oxide, 0.028 g of hafnium oxide, 21.376 g of bismuth oxide, 3.433 g of titanium oxide, 0.542 g of boron oxide, and 1.056 g of zinc oxide.

[0137] Example 6

[0138] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi, Hf, and Ti, and the general chemical formula is:

[0139] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.07 Nb 0.93 )O3-0.036(Bi0.5 K 0.5 ) 0.982 (Hf 0.1 Ti 0.9 ) 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.07, z=0.1.

[0140] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this embodiment is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.522 g of sodium carbonate, 159.102 g of potassium carbonate, 618.489 g of niobium pentoxide, 7.395 g of lithium carbonate, 51.055 g of antimony oxide, 0.028 g of hafnium oxide, 21.376 g of bismuth oxide, 3.433 g of titanium oxide, 0.542 g of boron oxide, and 1.056 g of zinc oxide.

[0141] Example 7

[0142] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, whose general chemical formula is the same as that of Example 6, and the preparation method is similar to that of Example 6, with the only difference being that: in the two-step sintering in step S03, the first stage sintering is carried out by heating the temperature to 1070°C at 8°C / min and keeping the temperature for 40 minutes; the second stage sintering is carried out by cooling the temperature to 980°C at 5°C / min and keeping the temperature for 5 hours.

[0143] Example 8

[0144] This embodiment provides a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, whose general chemical formula is the same as that of Example 6, and the preparation method is similar to that of Example 6, with the only difference being that: in the two-step sintering in step S03, the first stage sintering is heating to 1100°C at 8°C / min and keeping warm for 40 minutes; the second stage sintering is cooling to 940°C at 5°C / min and keeping warm for 6 hours.

[0145] Comparative Example 1

[0146] This comparative example is a multi-element synergistically doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Bi and Ti, and the general chemical formula is:

[0147] 0.964(K 0.46 Na 0.54 ) 0.97 Li 0.03 -0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.03, y=0, z=0.

[0148] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this comparative example is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 139.381 g of sodium carbonate, 161.186 g of potassium carbonate, 667.082 g of niobium pentoxide, 5.563 g of lithium carbonate, 0.000 g of antimony oxide, 0.000 g of hafnium oxide, 21.442 g of bismuth oxide, 3.743 g of titanium oxide, 0.544 g of boron oxide and 1.060 g of zinc oxide.

[0149] Comparative Example 2

[0150] This comparative example is a multi-element synergistically doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Bi and Ti, and the general chemical formula is:

[0151] 0.964(K 0.46 Na 0.54 ) 0.94 Li 0.06 -0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0, z=0.

[0152] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this comparative example is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 138.107 g of sodium carbonate, 159.778 g of potassium carbonate, 667.869 g of niobium pentoxide, 7.426 g of lithium carbonate, 0.000 g of antimony oxide, 0.000 g of hafnium oxide, 21.467 g of bismuth oxide, 3.747 g of titanium oxide, 0.545 g of boron oxide, and 1.061 g of zinc oxide.

[0153] Comparative Example 3

[0154] This comparative example is a multi-element synergistically doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Bi and Ti, and the general chemical formula is:

[0155] 0.964(K 0.46 Na 0.54 ) 0.95 Li 0.05 -0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.05, y=0, z=0.

[0156] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this comparative example is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 136.830 g of sodium carbonate, 158.367 g of potassium carbonate, 668.658 g of niobium pentoxide, 9.294 g of lithium carbonate, 0.000 g of antimony oxide, 0.000 g of hafnium oxide, 21.493 g of bismuth oxide, 3.751 g of titanium oxide, 0.545 g of boron oxide and 1.062 g of zinc oxide.

[0157] Comparative Example 4

[0158] This comparative example is a multi-element synergistically doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Bi and Ti, and the general chemical formula is:

[0159] 0.964(K 0.46 Na 0.54 ) 0.94 Li 0.06 -0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.06, y=0, z=0.

[0160] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this comparative example is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 135.550 g of sodium carbonate, 156.953 g of potassium carbonate, 669.449 g of niobium pentoxide, 11.166 g of lithium carbonate, 0.000 g of antimony oxide, 0.000 g of hafnium oxide, 21.518 g of bismuth oxide, 3.75 g of titanium oxide, 0.546 g of boron oxide and 1.063 g of zinc oxide.

[0161] Comparative Example 5

[0162] This comparative example is a multi-element synergistically doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi and Ti, and the general chemical formula is:

[0163] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.09 Nb 0.91 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 Ti 0.018O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.09, z=0.

[0164] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this comparative example is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.309 g of sodium carbonate, 158.855 g of potassium carbonate, 604.248 g of niobium pentoxide, 7.383 g of lithium carbonate, 65.541 g of antimony oxide, 0.000 g of hafnium oxide, 21.343 g of bismuth oxide, 3.725 g of titanium oxide, 0.541 g of boron oxide and 1.055 g of zinc oxide.

[0165] Comparative Example 6

[0166] This comparative example is a multi-element synergistically doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi, Hf and Ti, and the general chemical formula is:

[0167] 0.964(K 0.46 Na 0.54 ) 0.96 Li 0.04 (Sb 0.07 Nb 0.93 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 (Hf 0.11 Ti 0.89 ) 0.018 O3-0.3mol%B2O3-0.5mol%ZnO, wherein x=0.04, y=0.07, z=0.11.

[0168] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this comparative example is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.536 g of sodium carbonate, 159.118 g of potassium carbonate, 618.552 g of niobium pentoxide, 7.396 g of lithium carbonate, 51.061 g of antimony oxide, 0.039 g of hafnium oxide, 21.378 g of bismuth oxide, 3.321 g of titanium oxide, 0.542 g of boron oxide and 1.057 g of zinc oxide.

[0169] Comparative Example 7

[0170] This comparative example discloses a multi-element synergistically doped potassium sodium niobate-based lead-free piezoelectric ceramic, wherein the doping elements are Li, Sb, Bi, Hf, and Ti, but no sintering aid is added. The general chemical formula is:

[0171] 0.964(K 0.46 Na 0.54 )0.96 Li 0.04 (Sb 0.07 Nb 0.93 )O3-0.036(Bi 0.5 K 0.5 ) 0.982 (Hf 0.1 Ti 0.9 ) 0.018 O3, where x=0.04, y=0.07, z=0.1.

[0172] In addition, the preparation method of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in this comparative example is the same as that in Example 1, with the only difference being that the raw material composition in step S01 is: 137.752 g of sodium carbonate, 159.368 g of potassium carbonate, 619.522 g of niobium pentoxide, 7.407 g of lithium carbonate, 51.141 g of antimony oxide, 0.035 g of hafnium oxide, 21.412 g of bismuth oxide, 3.364 g of titanium oxide, 0.000 g of boron oxide, and 0.000 g of zinc oxide.

[0173] Comparative Example 8

[0174] This comparative example discloses a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, the general chemical formula of which is the same as that of Example 6, and the preparation method is similar to that of Example 6, with the only difference being that in the two-step sintering in step S03, the temperature is raised to 980°C at 8°C / min in the first stage and kept at this temperature for 40 minutes; and the temperature is further raised to 1070°C at 5°C / min in the second stage, kept at this temperature for 6 hours, and then cooled with the furnace.

[0175] Comparative Example 9

[0176] This comparative example is a multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, whose chemical formula is the same as that of Example 6, and the preparation method is similar to that of Example 6, with the only difference being that step S03 is replaced by a one-step sintering, specifically, heating to 1100°C at 8°C / min, keeping the temperature for 6 hours, and cooling with the furnace.

[0177] Test Example 1

[0178] The performance of the multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramics provided in Examples 1 to 8 and Comparative Examples 1 to 9 was tested, wherein the piezoelectric constant d 33 , Mechanical quality factor Q m , Curie temperature T c , Planar electromechanical coupling coefficient k p , dielectric loss tanδ, residual polarization intensity P r And the coercive electric field strength E cThe tests were carried out in accordance with the standard GB / T 3389-2008, and the density was tested in accordance with the standard GB / T 25995-2010, and the results are shown in Table 1.

[0179] Table 1 Properties of potassium sodium niobate-based piezoelectric ceramics

[0180]

[0181]

[0182] As shown in Table 1, in Comparative Examples 1 to 4, when y and z in the chemical formula are both 0, that is, when Sb, Hf and Ti are not doped, the piezoelectric constant d 33 The mechanical quality factor Q is significantly lower than that of the embodiment. m The level is equivalent to that of Example 1, which shows that the potassium sodium niobate-based piezoelectric ceramics of Comparative Examples 1 to 4 are difficult to achieve both high piezoelectricity and high mechanical quality factor. However, the embodiments of the present invention can improve the piezoelectric constant d while ensuring that the potassium sodium niobate-based piezoelectric ceramics have a high mechanical quality factor. 33 In addition, the potassium sodium niobate-based piezoelectric ceramics of Comparative Examples 1 to 4 also have a Curie temperature T c and the planar electromechanical coupling coefficient k p The performance is worse than that of the embodiment when the dielectric loss tanδ increases and the density decreases.

[0183] It can be seen from Examples 1 to 3 and Comparative Example 5 that, compared with Comparative Examples 1 to 4, the piezoelectric activity of the potassium sodium niobate-based piezoelectric ceramics is significantly improved by doping Sb in the potassium sodium niobate-based piezoelectric ceramics. When y = 0.07, that is, the potassium sodium niobate-based piezoelectric ceramics of Example 2, its d 33 Reach 365pC / N,k p =0.56, tanδ=1.2%, the performance is close to the upper limit, which meets the requirements of high response and low loss; when y=0.09, that is, the potassium sodium niobate-based piezoelectric ceramic of comparative example 5, its phase separation is obvious, specifically manifested as d 33 Drop, E c It increases to 16.5kV / cm, indicating that excessive Sb doping will damage the stability of the potassium sodium niobate-based piezoelectric ceramic structure.

[0184] From Examples 4 to 6 and Comparative Example 6, it can be seen that continuing to dope Hf on the basis of Example 2 can further optimize the high temperature stability of potassium sodium niobate-based piezoelectric ceramics. When z = 0.08, that is, the potassium sodium niobate-based piezoelectric ceramics of Example 5, its T c =330℃,d 33 =390pC / N, tanδ=1.1%, the comprehensive performance is the best, meeting the requirements of high response and low loss; when z=0.11, that is, the potassium sodium niobate-based piezoelectric ceramic of comparative example 6, d33 decreased to 275pC / N, tanδ increased to 2.2%, Q m It approaches the lower limit, indicating that excessive Hf doping will cause performance defects in potassium sodium niobate-based piezoelectric ceramics.

[0185] From Example 6 and Comparative Example 7, it can be seen that the sintering temperature required for preparing potassium sodium niobate-based piezoelectric ceramics cannot be reduced by not adding a sintering aid in Comparative Example 7. Therefore, at the same sintering temperature as Example 6, Comparative Example 7 is not sintered sufficiently, and the piezoelectric constant d of the prepared potassium sodium niobate-based piezoelectric ceramics is 33 , Curie temperature T c , Planar electromechanical coupling coefficient k p and the remnant polarization intensity P r Both the dielectric loss tanδ and the coercive electric field strength E c The sintering density also decreased significantly, and the performance of potassium sodium niobate-based piezoelectric ceramics decreased significantly.

[0186] From Examples 6 to 8 and Comparative Examples 8 to 9, it can be seen that the two-stage sintering process has significant advantages. 33 =390pC / N, tanδ=1.0%, the density is increased to 98.5%; in comparative example 8, the temperature is still increased during the second sintering, and the piezoelectric constant d 33 , Planar electromechanical coupling coefficient k p and the remnant polarization intensity P r Decreases, dielectric loss tanδ increases; Comparative Example 9 uses one-time sintering, density decreases piezoelectric constant d 33 and the planar electromechanical coupling coefficient k p decreases, and the dielectric loss tanδ increases.

[0187] In summary, the present invention provides a multi-element co-doped potassium sodium niobate-based piezoelectric ceramic, a preparation method, and an application thereof, which have at least the following advantages:

[0188] (1) Using a multi-element synergistic doping strategy, Li, Sb and Hf are synergistically substituted at three sites: Li+ replaces K or Na at the A site in the potassium sodium niobate base to adjust the lattice distortion, reduce the coercive electric field strength, and enhance the polarization response; Sb 5+ Substituting Nb at the B position in potassium sodium niobate, optimizing oxygen octahedral distortion, and improving the piezoelectric constant and electromechanical coupling coefficient; Hf 4+ Substituting Ti at the B' position in the potassium sodium niobate matrix enhances lattice stability and significantly raises the Curie temperature. This synergistic substitution at the A / B / B' positions balances polarization capability and structural stability, resolving the conflict between high piezoelectricity and low Curie temperature in traditional potassium sodium niobate-based piezoelectric ceramics.

[0189] (2) Through a two-stage gradient sintering process, the first stage uses high temperature (1050-1100°C) to rapidly densify the green body to promote rapid grain growth and eliminate porosity; the second stage uses low temperature (940-1020°C) to control the grain boundaries, inhibit grain coarsening, refine the grain boundaries, and reduce dielectric loss. Compared with traditional single-stage sintering, this process significantly improves density and improves the piezoelectric constant by 20%-30% compared with traditional potassium sodium niobate-based piezoelectric ceramics.

[0190] (3) The B2O3 / ZnO composite sintering aid enables the formation of a low-temperature liquid phase during the sintering process. 0.3 mol% B2O3 and 0.5 mol% ZnO form a low-viscosity liquid phase at 800-900°C, accelerating particle rearrangement and lowering the sintering temperature from the traditional 1200°C to 1050°C. At the same time, it can play a role in grain boundary passivation, reduce oxygen vacancy concentration, suppress leakage current, and make tanδ ≤1.0%, thereby improving the performance of potassium sodium niobate-based piezoelectric ceramics.

[0191] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A multi-element co-doped potassium sodium niobate-based lead-free piezoelectric ceramic, characterized in that: The general chemical formula of potassium sodium niobate-based piezoelectric ceramics is: 0.964 (K 0.46 Na 0.54 ) 1-x Li x (Sb y Nb 1-y )O3-0.036(Bi 0.5 K 0.5 ) 0.982 (Hf z Ti 1-z ) 0.018 O3-0.2~0.3mol%B2O3-0.3~0.5mol%ZnO; And at least two of the following conditions are met: 1)0.03≤x≤0.05； 2)0.05≤y≤0.08； 3)0.05≤z≤0.1。 2. The piezoelectric ceramic according to claim 1, characterized in that In the general chemical formula of the potassium sodium niobate-based piezoelectric ceramic material, x, y and z simultaneously satisfy the following: 0.03≤x≤0.05; 0.05≤y≤0.08; 0.05≤z≤0.

1.

3. The piezoelectric ceramic according to claim 1, wherein The piezoelectric constant d of the potassium sodium niobate-based piezoelectric ceramic is 33 The mechanical quality factor Qm is 230-270, the Curie temperature Tc is 290℃-350℃, and the plane electromechanical coupling coefficient k p is 0.50~0.60; dielectric loss tanδ is 1.0%~2.0%; residual polarization intensity P r 18μC / cm 2 ~25μC / cm 2 , coercive field strength E c 10kV / cm~15kV / cm; density ≥96%; Preferably, the piezoelectric constant d of the potassium sodium niobate-based piezoelectric ceramic is 33 The mechanical quality factor Qm is 233 to 268, the Curie temperature Tc is 295 to 345 degrees Celsius, and the plane electromechanical coupling coefficient k p is 0.53~0.58; dielectric loss tanδ is 1.0%~1.8%; residual polarization intensity P r 18μC / cm 2 ~22μC / cm 2 , coercive field strength E c 12kV / cm~14kV / cm; density is 96%~99%; Preferably, the piezoelectric constant d of the potassium sodium niobate-based piezoelectric ceramic is 33 is 380pC / N~390pC / N; the mechanical quality factor Qm is 233~245, the Curie temperature Tc is 325℃~345℃, and the plane electromechanical coupling coefficient k p is 0.55~0.56; dielectric loss tanδ is 1.0%~1.5%; residual polarization intensity P r 19μC / cm 2 ~25μC / cm 2 , coercive field strength E c It is 12kV / cm~13.5kV / cm; the density is 97%~99%.

4. A method for preparing a piezoelectric ceramic according to any one of claims 1 to 3, characterized in that: The method comprises mixing raw materials according to a stoichiometric ratio, ball-milling the raw materials, and then pre-sintering the raw materials to obtain a formula powder, shaping the formula powder to obtain a green body, and performing two-step sintering on the green body; The raw materials include main component raw materials and sintering aids.

5. The preparation method according to claim 4, characterized in that The two-step sintering includes sealing the green body and then performing first-stage sintering and second-stage sintering; The first stage sintering includes: heating to 1050°C to 1100°C at a heating rate of 6°C / min to 8°C / min, and keeping the temperature for 20 to 40 minutes; The second stage sintering includes: cooling to 940° C. to 1020° C. at a rate of 3° C. / min to 5° C. / min, and keeping the temperature for 4 to 6 hours.

6. The preparation method according to claim 4, characterized in that The sintering aid includes B2O3 and ZnO; Preferably, in the sintering aid, the purity of the B2O3 and the ZnO is ≥99.95%; Preferably, the main component raw material includes at least one of potassium carbonate, sodium carbonate, lithium carbonate, antimony trioxide, niobium pentoxide, bismuth trioxide, hafnium dioxide and titanium pentoxide; Preferably, among the main component raw materials, the purity of potassium carbonate and sodium carbonate is ≥99.95%, and the purity of lithium carbonate, antimony trioxide, niobium pentoxide, bismuth trioxide, hafnium dioxide and titanium pentoxide is ≥99.99%.

7. The preparation method according to claim 4 or 6, characterized in that: The preparation method of the formula powder comprises: adding the raw materials into a ball mill, adding grinding balls and a solvent to perform wet ball milling, drying the slurry obtained by the wet ball milling, and then pre-calcining; Preferably, the mass ratio of the raw material, the solvent and the grinding balls is 1.8-2.2:4.8-5.2:9.8-10.2; Preferably, the grinding balls include any one of zirconium oxide grinding balls and aluminum oxide balls; the solvent includes anhydrous ethanol; Preferably, the ball milling speed is 260 r / min to 360 r / min, and the time is 12 h to 16 h; Preferably, the pre-firing temperature is 820° C. to 850° C., and the holding time is 3 h to 8 h.

8. The preparation method according to claim 4, characterized in that The method for preparing the green body comprises: sequentially grinding, granulating, molding and debinding the formulated powder; Preferably, the grinding is slurry grinding, which includes mixing the formula powder, water, a grinding dispersant and a binder to obtain a mixed slurry, adding grinding beads to the mixed slurry for grinding, and the particle size distribution of the mixed slurry obtained after grinding satisfies the normal distribution, and D50=500nm~800nm; Preferably, in the mixed slurry, the mass ratio of the formula powder to water is 1:0.8-1.2, the mass of the grinding dispersant is 0.1wt.%-2.5wt.% of the total weight of the mixed slurry, and the mass of the binder is 0.7wt.%-1wt.% of the total weight of the mixed slurry; Preferably, the grinding dispersant comprises at least one of polyacrylamide, styrene-maleic anhydride copolymer and tetramethylammonium hydroxide; Preferably, the binder comprises at least one of polyvinyl alcohol and polyacrylic acid amine at a concentration of 5 to 6 wt.%; Preferably, the mass ratio of the mixed slurry to the grinding beads is 1:0.8-1.2, the particle size of the grinding beads is 1mm-3mm, and the material of the grinding beads includes at least one of zirconium oxide and aluminum oxide; Preferably, the grinding parameters include: a grinding rod speed of 1300 r / min to 1800 r / min, a circulating pump speed of 80 r / min to 120 r / min, and a grinding time of 1 h to 4 h; Preferably, the granulation is spray granulation, and the spray granulation obtains spherical granulation powder, and the particle size distribution of the spherical granulation powder is D50=30μm~50μm; Preferably, the inlet temperature of the spray drying tower for spray granulation is 200°C to 250°C, and the outlet temperature is 100°C to 120°C; Preferably, the forming is compression molding, and the pressure of the compression molding is 18 MPa to 25 MPa; Preferably, the debinding process includes firing the green body obtained by pressing, and the firing parameters include: heating to 600° C. to 700° C. at a rate of 2° C. / min to 4° C. / min, and keeping the temperature for 2 h to 4 h.

9. The preparation method according to claim 4, characterized in that The invention also includes post-processing the sintered body obtained after the two-step sintering, wherein the post-processing includes preparing an electrode layer and high-voltage polarization; Preferably, the method for preparing the electrode layer comprises covering the surface of the sintered body with electrode slurry and then performing a sintering treatment; Preferably, the electrode slurry comprises a metal and a dispersant thereof, wherein the metal comprises any one of silver, copper and gold; Preferably, the metal content in the electrode slurry is 80 wt.% to 90 wt.%; Preferably, the sintering temperature is 700°C to 750°C, and the time is 20min to 30min; Preferably, the electric field for high-voltage polarization is a direct current electric field, the electric field strength is 3 kV / mm to 4.5 kV / mm, and the holding time is 25 min to 45 min.

10. Use of the piezoelectric ceramic according to any one of claims 1 to 3 or the piezoelectric ceramic produced by the preparation method according to any one of claims 4 to 9 in any field of ultrasonic medical equipment, tactile feedback sensor or ultrasonic transducer.

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