High performance lead-free piezoelectric potassium sodium niobate based ceramics and methods of making

Abstract

The application discloses a preparation method of high-performance lead-free piezoelectric potassium-sodium niobate-based ceramics, and specifically implements the following steps: step 1, preparing pre-calcined powder; and step 2, preparing potassium-sodium niobate-based ceramics by adopting a three-step sintering method. The application further discloses the high-performance lead-free piezoelectric potassium-sodium niobate-based ceramics, which are prepared by weighing and mixing analytically pure Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2 and CaCO3 according to a stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3‑0.04Bi 0.5 Na 0.5 ZrO3‑0.003CaZrO3. The application solves the problem of low piezoelectric and mechanical properties of the existing KNN-based ceramics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of piezoelectric ceramic material preparation, and particularly relates to high-performance lead-free piezoelectric potassium-sodium niobate-based ceramics and a preparation method of the high-performance lead-free piezoelectric potassium-sodium niobate-based ceramics. BACKGROUND

[0002] Advanced piezoelectric sensing technology can realize health monitoring of high-power motors and timely elimination of soft faults in motor operation, and is an important guarantee for "strong smart grid + ubiquitous power Internet of Things". As the core technology guarantee of piezoelectric ceramic research and development for vibration sensors for motor monitoring, it directly determines the sensing accuracy, operation reliability, stability and environmental adaptability of vibration-type electrical sensing equipment.

[0003] In the current field of commercial piezoelectric materials, piezoelectric ceramics for sensing are mainly based on lead zirconate titanate (PbZrTiO3, PZT) ceramics. Taking the current advanced PZT-5 piezoelectric ceramic as an example, it has high piezoelectric performance d 1-x Ti x O3, PZT) based ceramics, for example, the current advanced PZT-5 piezoelectric ceramic has a high piezoelectric performance d 33 as high as 450 pC / N, but poor mechanical properties (nanoindentation hardness H=~3.14 GPa, Young's modulus E=~65 GPa, compressive strength=~30 MPa). PZT-based ceramics are prone to produce microcracks at the grain scale under long-term alternating mechanical load, leading to failure in industrial applications. On the other hand, with the development of green power and environmentally friendly lead-free electrical materials, the irreversible damage caused by lead to the environment and human body is gradually being taken seriously. In view of the poor mechanical properties of lead-based ceramics, it is urgent to develop high-mechanical-property lead-free piezoelectric ceramics with high piezoelectric performance.

[0004] Potassium-sodium niobate (K 0.5 Na 0.5 NbO3, KNN) has high Curie temperature T C (about 400 ℃), low driving polarization field (E dri <5 kV / mm), and environmental friendliness, and has gradually become the most potential alternative to lead-based piezoelectric ceramics. In order to modify the low piezoelectric performance of pure KNN (d 33 =40-120 pC / N), in the research, a large number of scholars have improved the piezoelectric performance of the material by constructing new polymorphic phase boundaries (PPB), for example: co-doping of the second component Bi 0.5 Na 0.5 ZrO3, although good results have been achieved (d 33>300 pC / N), but the inevitable multi-component co-doping leads to the inherent chemical heterogeneity and sensitivity to processing conditions of KNN, and causes the uneven distribution of the grain size of the sintered piezoelectric ceramic, which makes it difficult to achieve the repeatability and stability of the mechanical properties in industrial production. In the normal sintering method, a narrow sintering temperature range close to the melting point is necessary for the KNN-based ceramic to achieve sufficient densification, which brings challenges to the synergistic optimization of the electrical / mechanical properties of multiple parameters. SUMMARY

[0005] An object of the present application is to provide a preparation method of high-performance lead-free piezoelectric potassium sodium niobate-based ceramic, which solves the problem of poor piezoelectric and mechanical properties of the existing KNN-based ceramic preparation method.

[0006] Another object of the present application is to provide a high-performance lead-free piezoelectric potassium sodium niobate-based ceramic.

[0007] The technical scheme adopted by the present application is a preparation method of high-performance lead-free piezoelectric potassium sodium niobate-based ceramic, which is implemented according to the following steps:

[0008] Step 1, preparing pre-calcined powder;

[0009] Step 2, preparing potassium sodium niobate-based ceramic by using a three-step sintering method.

[0010] The present application is characterized in that,

[0011] Step 1 is specifically: Step 1.1, weighing the raw materials according to the stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3, and the raw materials are Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2 and CaCO3 of analytical purity;

[0012] Step 1.2, placing the raw materials in step 1.1 into a ball mill, using anhydrous ethanol as the medium, rolling and ball milling for 12 h, and then drying to obtain the dry powder;

[0013] Step 1.3, high-temperature calcining the dry powder obtained in step 1.2;

[0014] Step 1.4, placing the calcined powder in step 1.3 into a ball mill, using anhydrous ethanol as the ball milling medium, and performing secondary ball milling; after the secondary ball milling is completed, the uniformly mixed slurry is dried and sieved to obtain the pre-calcined powder.

[0015] Step 1.3, the calcination temperature is 800-950 DEG C.

[0016] Both step 1.2 and step 1.4 use a planetary ball mill, and the secondary ball milling is carried out at a speed of 300-400 r / min for 24 h.

[0017] Step 2 is specifically:

[0018] Step 2.1, the pre-calcined powder obtained in step 1.4 is pressed into small round tablets using a mold, and a ceramic green body is formed by pressure molding using a cold isostatic pressing machine;

[0019] Step 2.2, the ceramic green body obtained in step 2.1 is heated to a first temperature platform T1 at a heating rate of 5 DEG C / min, and after holding for 1 h, it is heated to a second temperature platform T2 at a heating rate of 10 DEG C / min, and then cooled to a temperature platform T3 at a rate of 10 DEG C / min, and held for 5 h, and then naturally cooled to room temperature;

[0020] Step 2.3, the ceramic green body after sintering in step 2.3 is polished and polished, and the electrical and mechanical properties of the ceramic green body on both sides are tested, and the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic is obtained.

[0021] In step 2.1, the cold isostatic pressing machine is used at a pressure of 200 MPa for 10 min, and the pressure is formed into a ceramic green body with a diameter of 10 mm and a thickness of 1 mm.

[0022] T1 is in the range of 800-1000 DEG C, T2 is 1190 DEG C, and T3 is 1090 DEG C.

[0023] The ceramic green body of step 2.3 is sintered on both sides by silver plasma at a silver electrode at 600 DEG C for 30 min, and the electrical properties are tested by applying a 4-6 kV / mm electric field in silicon oil for 20-30 min, and the mechanical compression experiment is tested by using a smooth polished cuboid sample with a size of 5*5*15 mm.

[0024] The technical scheme adopted by the present application is that the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic is prepared by the preparation method of high-performance lead-free piezoelectric potassium sodium niobate-based ceramic, and the analytical pure Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2, CaCO3 are weighed and mixed according to the stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3.

[0025] The present application has the beneficial effect that the preparation method of the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic of the present application improves the grain size uniformity of the piezoelectric ceramic, suppresses internal stress caused by abnormal grain size, and promotes the grain growth of the KNN ceramic to change from two-dimensional nucleation of conventional sintering to diffusion control, thereby improving the mechanical properties of the ceramic while ensuring the piezoelectric properties of the ceramic, improving the reliability of the KNN-based ceramic and its vibration sensor during long-term service, and providing a new way for coordinated improvement of the electrical and mechanical properties of the KNN-based ceramic, thereby significantly improving the mechanical properties of the ceramic while ensuring its piezoelectric properties, and having good industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 (a) is an SEM micrograph of KNN-based bulk ceramic 800-L prepared in Example 4 with a calcination temperature of 800°C and T1 of 800°C;

[0027] Figure 1 (b) is an SEM micrograph of KNN-based bulk ceramic 850-L prepared in Example 4 with a calcination temperature of 850°C and T1 of 800°C;

[0028] Figure 1 (c) is an SEM micrograph of KNN-based bulk ceramic 900-L prepared in Example 4 with a calcination temperature of 900°C and T1 of 800°C;

[0029] Figure 1 (d) is an SEM micrograph of KNN-based bulk ceramic 950-L prepared in Example 4 with a calcination temperature of 950°C and T1 of 800°C;

[0030] Figure 1 (e) is an SEM micrograph of KNN-based bulk ceramic 800-M prepared in Example 5 with a calcination temperature of 800°C and T1 of 900°C;

[0031] Figure 1 (f) is an SEM micrograph of KNN-based bulk ceramic 850-M prepared in Example 5 with a calcination temperature of 850°C and T1 of 900°C;

[0032] Figure 1 (g) is an SEM micrograph of KNN-based bulk ceramic 900-M prepared in Example 5 with a calcination temperature of 900°C and T1 of 900°C;

[0033] Figure 1 (h) is an SEM micrograph of KNN-based bulk ceramic 950-M prepared in Example 5 with a calcination temperature of 950°C and T1 of 900°C;

[0034] Figure 1 (i) is an SEM micrograph of KNN-based bulk ceramic 800-H made in Example 6 with a calcination temperature of 800 °C and T1 of 1000 °C;

[0035] Figure 1 (j) is an SEM micrograph of KNN-based bulk ceramic 850-H made in Example 6 with a calcination temperature of 850 °C and T1 of 1000 °C;

[0036] Figure 1 (k) is an SEM micrograph of KNN-based bulk ceramic 900-H made in Example 6 with a calcination temperature of 900 °C and T1 of 1000 °C;

[0037] Figure 1 (l) is an SEM micrograph of KNN-based bulk ceramic 950-H made in Example 6 with a calcination temperature of 950 °C and T1 of 1000 °C;

[0038] Figure 2 is a plot of the piezoelectric constant (d 33 ) of KNN-based ceramics at different T1 with different calcination temperatures in Examples 4-6;

[0039] Figure 3 is a plot of the electromechanical coupling factor (k p ) of KNN-based ceramics at different T1 with different calcination temperatures in Examples 4-6;

[0040] Figure 4 (a) is a stress-strain plot for T1 of 800 °C in Examples 4-6;

[0041] Figure 4 (b) is a stress-strain plot for T1 of 900 °C in Examples 4-6;

[0042] Figure 4 (c) is a plot of the compressive strength of samples in Example 4 and Example 5;

[0043] Figure 4 (d) is a plot of the average compressive strength of Example 4 and Example 5. DETAILED DESCRIPTION

[0044] The present application will be described in detail below with specific embodiments.

[0045] Example 1

[0046] The method for preparing high-performance lead-free piezoelectric potassium sodium niobate-based ceramics of the present application is implemented according to the following steps:

[0047] Step 1, prepare pre-calcined powder;

[0048] Step 2, prepare the potassium sodium niobate-based ceramic by a three-step sintering method.

[0049] The high-performance lead-free piezoelectric potassium sodium niobate-based ceramic prepared by the method has the following chemical composition: 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3.

[0050] Example 2

[0051] The method for preparing the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic is implemented according to the following steps:

[0052] Step 1, prepare pre-calcined powder;

[0053] Step 1.1, the raw materials are weighed according to the stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3, and the raw materials are analytical pure Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2 and CaCO3.

[0054] Step 1.2, the raw materials in step 1.1 are placed in a ball mill, anhydrous ethanol is used as the medium, and the mixture is rolled and ball milled for 12 hours, and then dried to obtain dry powder;

[0055] Step 1.3, the dry powder obtained in step 1.2 is high-temperature calcined; the calcination temperature is 800°C~950°C;

[0056] Step 1.4, the calcined powder in step 1.3 is placed in a ball mill, anhydrous ethanol is used as the ball milling medium, and secondary ball milling is performed; after the secondary ball milling is completed, the uniformly mixed slurry is dried and sieved to obtain pre-calcined powder.

[0057] Both step 1.2 and step 1.4 use a planetary ball mill, and the secondary ball milling is performed at a speed of 300r / min~400r / min for 24 hours.

[0058] Step 2, prepare the potassium sodium niobate-based ceramic by a three-step sintering method.

[0059] Step 2.1, the pre-calcined powder obtained in step 1.4 is pressed into small round pieces using a mold, and the ceramic green body is pressure formed by a cold isostatic pressing machine; the cold isostatic pressing machine is used to press at a pressure of 200 MPa for 10 min, and the pressure forming is performed to become a ceramic green body with a diameter of 10 mm and a thickness of 1 mm.

[0060] Step 2.2, the ceramic green body obtained in step 2.1 is heated to a first temperature platform T1 at a heating rate of 5°C / min, after holding for 1 h, heated to a second temperature platform T2 at a heating rate of 10°C / min, then cooled to a temperature platform T3 at a rate of 10°C / min, and held for 5 h, and then naturally cooled to room temperature; T1 is in the range of 800°C-1000°C, T2 is 1190°C, and T3 is 1090°C.

[0061] Step 2.3, the ceramic green body after sintering in step 2.3 is polished and polished, and the electrical and mechanical properties of the ceramic green body on both sides are tested, and the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic is obtained.

[0062] Example 3

[0063] On the basis of example 2, the ceramic green body in step 2.3 of this example is sintered on both sides by silver plasma at a silver electrode at 600°C for 30 min, and the electrical performance test is performed by applying an electric field of 4kV / mm-6kV / mm in silicon oil for 20 min-30 min. The mechanical compression experiment is tested by using a smooth polished cuboid sample with a size of 5mm×5mm×15mm. The electrical properties of the obtained ceramic sheet are measured by using IEEE standard, and the mechanical properties are tested by using GB / T6569-2006 related requirements.

[0064] The preparation method of the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic of the application directly affects the grain growth behavior of the ceramic through the uniformity of the composition and the sintering conditions. In the three-step sintering, different pre-sintering temperatures and the first-stage temperature in the sintering have a significant influence on the grain size and distribution. The pre-sintering temperature and the first-stage temperature in the sintering are regulated to promote the homogenization of the composition. Under the same preparation and pre-sintering temperature, the first-stage temperature in the three-step sintering has a great influence on the grain size. Generally, compared with larger particles, smaller particles have greater curvature, similar surface energy and shorter diffusion distance, and the reaction speed with other inhomogeneous particles can be faster. Therefore, in the first stage, it grows preferentially to other particles, and the three-step sintering promotes the grain growth of the KNN ceramic to change from two-dimensional nucleation to diffusion control. By further optimizing the sintering kinetics parameters in the three-step sintering, the purpose of effectively regulating the grain growth while completing the densification of the green body is achieved, thereby effectively regulating the grain size uniformity of the piezoelectric ceramic, inhibiting the internal stress caused by abnormal grain growth, and providing the possibility of ensuring the piezoelectric performance of the ceramic while improving the mechanical performance of the ceramic.

[0065] Example 4

[0066] The preparation method of the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic of the application is specifically implemented according to the following steps:

[0067] Step 1, preparing pre-calcined powder;

[0068] Step 1.1, the raw materials are weighed according to the stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3, and the raw materials are weighed as Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2 and CaCO3 of analytical purity;

[0069] Step 1.2, the raw materials in step 1.1 are put into a ball mill, anhydrous ethanol is used as the medium, and after rolling ball milling for 12 h, the dry powder is obtained after drying;

[0070] Step 1.3, the dry powder obtained in step 1.2 is divided into four batches, and the sintering kinetics parameters of pre-calcination are regulated, and the four batches correspond to calcination at different temperatures of 800°C, 850°C, 900°C and 950°C respectively;

[0071] Step 1.4, the calcined powder is subjected to secondary ball milling at a speed of 300 r / min for 24 h with anhydrous ethanol as the ball milling medium, and after the secondary ball milling is completed, the uniformly mixed slurry is dried and sieved to obtain the pre-sintering powder.

[0072] Step 2, the three-step sintering method was used to prepare the potassium sodium niobate-based ceramic.

[0073] Step 2.1, the pre-calcined powder obtained by calcination at 800°C was pressed into small discs using a mold, and the ceramic green body was pressure-formed by a cold isostatic pressing machine; the cold isostatic pressing machine was used to press at a pressure of 200 MPa for 10 min, and the pressure-formed ceramic green body had a diameter of 10 mm and a thickness of 1 mm.

[0074] Step 2.2, the ceramic green body obtained in step 2.1 was heated to a first temperature platform T1 at a heating rate of 5°C / min, and after holding for 1 h, it was heated to a second temperature platform T2 at a heating rate of 10°C / min, and then cooled to a temperature platform T3 at a rate of 10°C / min, and held for 5 h, and then naturally cooled to room temperature; T1 was 800°C, abbreviated as L, T2 was 1190°C, and T3 was 1090°C.

[0075] Step 2.3, the ceramic green body sintered in step 2.3 was polished and polished, and the electrical and mechanical properties were tested on both sides of the ceramic green body, thereby obtaining high-performance lead-free piezoelectric potassium sodium niobate-based ceramic, denoted as 800-L; the SEM micrograph of KNN-based bulk ceramic 800-L prepared at a calcination temperature of 800°C and T1 of 800°C is shown in Figure 1 (a), which is a micrograph of the grain morphology of 800-L, reflecting that the uniformity of grain size distribution is general.

[0076] On this basis, the pre-calcined powders obtained by calcination at 850°C, 900°C and 950°C respectively were subjected to three-step sintering using the same three-step sintering process parameters, and the obtained high-performance lead-free piezoelectric potassium sodium niobate-based ceramic was named 850-L, 900-L and 950-L, and the corresponding SEM micrographs are shown in Figure 1 (b)-(d), which are micrographs of the grain morphology of 850-L, 900-L and 950-L, reflecting that the uniformity of grain size distribution is general.

[0077] The two sides of the ceramic green body were sintered in silver electrodes by silver plasma at 600°C for 30 min, and the electrical performance test was carried out in silicon oil under an electric field of 4kV / mm-6kV / mm for 20 min-30 min, and the mechanical compression experiment was carried out on a smooth and polished cuboid sample with a size of 5mm×5mm×15mm. The electrical properties of the obtained ceramic sheet were measured according to the IEEE standard, and the mechanical properties were tested according to the requirements of GB / T6569-2006.

[0078] Example 5

[0079] The application discloses a preparation method of high-performance lead-free piezoelectric potassium-sodium niobate-based ceramics.

[0080] Step 1, preparing pre-calcined powder;

[0081] Step 1.1, according to the stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3, raw materials are weighed, and the raw materials are Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2 and CaCO3 of analytical purity;

[0082] Step 1.2, the raw materials in step 1.1 are put into a ball mill, anhydrous ethanol is used as a medium, and rolling ball milling is performed for 12 h, and then the dry powder is obtained after drying;

[0083] Step 1.3, the dry powder obtained in step 1.2 is divided into four batches, and the sintering kinetics parameters of pre-calcination are controlled, and the four batches correspond to calcination at different temperatures of 800°C, 850°C, 900°C and 950°C respectively;

[0084] Step 1.4, the calcined powder in step 1.3 is put into a ball mill, anhydrous ethanol is used as a ball milling medium, and secondary ball milling is performed; after the secondary ball milling is completed, the uniformly mixed slurry is dried and sieved to obtain pre-calcined powder.

[0085] Both step 1.2 and step 1.4 adopt a planetary ball mill, and the secondary ball milling is performed at a rotating speed of 400 r / min for 24 h.

[0086] Step 2, a three-step sintering method is used to prepare potassium-sodium niobate-based ceramics.

[0087] Step 2.1, the pre-calcined powder obtained in step 1.4 is pressed into small round pieces by using a mold, and a cold isostatic pressing machine is used for pressure forming of a ceramic blank; the cold isostatic pressing machine is used for pressure forming at a pressure of 200 MPa for 10 min, so that a ceramic blank with a diameter of 10 mm and a thickness of 1 mm is formed.

[0088] Step 2.2, the ceramic blank obtained in step 2.1 is heated to a first temperature platform T1 at a heating rate of 5°C / min, after being kept at the first temperature platform T1 for 1 h, the temperature is increased to a second temperature platform T2 at a heating rate of 10°C / min, then the temperature is cooled to a temperature platform T3 at a rate of 10°C / min, and the temperature platform T3 is kept for 5 h, and then the temperature is naturally cooled to room temperature; T1 is 900°C, and is abbreviated as M, T2 is 1190°C, and T3 is 1090°C.

[0089] Step 2.3, the sintered ceramic green body of step 2.3 is polished and polished, and the test electrical and mechanical properties are tested on both sides of the ceramic green body, thereby obtaining high-performance lead-free piezoelectric potassium sodium niobate-based ceramics, denoted as 800-M; the SEM micrograph of KNN-based bulk ceramics 800-M prepared at a calcination temperature of 800°C and T1 of 900°C is shown in Fig. Figure 1 (e) is a 800-M grain micro-morphology diagram, and the uniform distribution of grain size is reflected.

[0090] On this basis, the pre-calcined powders calcined at 850°C, 900°C and 950°C respectively in step 2.1 are sintered by the same three-step sintering process parameters, and the obtained high-performance lead-free piezoelectric potassium sodium niobate-based ceramics are denoted as 850-M, 900-M and 950-M. The corresponding SEM micrographs are shown in Figs. Figure 1 (f)-(h) are 850-M, 900-M and 950-M grain micro-morphology diagrams, which show that the grain size is uniformly distributed.

[0091] The ceramic green body is sintered on both sides by silver plasma at a silver electrode at 600°C for 30 min, and the electrical performance test is carried out in silicon oil under an electric field of 4kV / mm-6kV / mm for 20 min-30 min. The mechanical compression experiment is tested by using a smooth and polished cuboid sample of 5mmx5mmx15mm. The electrical properties of the obtained ceramic sheet are measured by using IEEE standard, and the mechanical properties are tested by using GB / T6569-2006 related requirements.

[0092] Example 6

[0093] The preparation method of the high-performance lead-free piezoelectric potassium sodium niobate-based ceramics is specifically implemented according to the following steps:

[0094] Step 1, preparing pre-calcined powders;

[0095] Step 1.1, the raw materials are weighed according to the stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3, and the raw materials are weighed as Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2 and CaCO3 of analytical purity;

[0096] Step 1.2, the raw materials in step 1.1 are put into a ball mill, anhydrous ethanol is used as medium, and the obtained dry powder is dried after rolling ball milling for 12 h;

[0097] Step 1.3, the dry powder obtained in step 1.2 is divided into four batches to control the sintering kinetics parameters of pre-calcination, and the four batches are calcined at different temperatures of 800°C, 850°C, 900°C and 950°C respectively;

[0098] Step 1.4, the calcined powder in step 1.3 is put into a ball mill with anhydrous ethanol as the ball milling medium for secondary ball milling. After the secondary ball milling, the uniformly mixed slurry is dried and sieved to obtain the pre-calcined powder.

[0099] Both step 1.2 and step 1.4 use a planetary ball mill, and the secondary ball milling is carried out at a speed of 350r / min for 24h.

[0100] Step 2, the potassium sodium niobate-based ceramic is prepared by a three-step sintering method.

[0101] Step 2.1, the pre-calcined powder obtained in step 1.4 is pressed into small round pieces using a mold, and the ceramic green body is formed by cold isostatic pressing. The cold isostatic pressing machine is used to press at a pressure of 200MPa for 10min, and the pressure forming is carried out to become a ceramic green body with a diameter of 10mm and a thickness of 1mm.

[0102] Step 2.2, the ceramic green body obtained in step 2.1 is heated to a first temperature platform T1 at a heating rate of 5°C / min, and then heated to a second temperature platform T2 at a heating rate of 10°C / min after holding for 1h. Then, it is cooled to a temperature platform T3 at a rate of 10°C / min, and held for 5h, and then naturally cooled to room temperature. T1 temperature is 1000°C, referred to as H, T2 temperature is 1190°C, and T3 temperature is 1090°C.

[0103] Step 2.3, the ceramic green body after sintering in step 2.3 is polished and polished, and the electrical and mechanical properties are tested on both sides of the ceramic green body, and the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic is obtained, which is marked as 800-H. The SEM micrograph of KNN-based bulk ceramic 800-H prepared by calcining at 800°C and T1 at 1000°C is shown in Figure 1 (i), which shows the grain micro-morphology of 800-H, and the uniformity of grain size distribution is generally good.

[0104] On this basis, the pre-calcined powders calcined at 850°C, 900°C and 950°C respectively in step 2.1 are sintered by the same three-step sintering process parameters, and the obtained high-performance lead-free piezoelectric potassium sodium niobate-based ceramics are named as 850-H, 900-H and 950-H. The corresponding SEM micrographs are shown in Figure 1 (j)-(l), which are the grain micro-morphology of 850-H, 900-H and 950-H, compared withFigure 1 (f-h), the reaction of grain size uniform distribution is general.

[0105] The ceramic green body is sintered by silver plasma at both sides of silver electrode at 600 DEG C for 30 min, and the polarization is carried out in silicon oil under an electric field of 4kV / mm-6kV / mm for 20 min-30 min for electrical performance test, and the mechanical compression experiment is carried out on the smooth and polished cuboid sample with a size of 5mm*5mm*15mm. The electrical performance of the obtained ceramic sheet is measured according to IEEE standard, and the mechanical performance test is carried out according to the related requirements of GB / T6569-2006.

[0106] The piezoelectric performance of the ceramic prepared in examples 4, 5 and 6 is shown in Figure 2 , Figure 3 , wherein the ordinate d 33 , k p are piezoelectric constant and electromechanical coupling coefficient respectively, and the abscissa is the name of different samples, and it is shown that the sample in example 5 has the optimal piezoelectric performance.

[0107] The compression performance of the ceramic prepared in examples 4, 5 and 6 is shown in Figure 4 (a), wherein the stress-strain diagram is shown when the first temperature platform T1 is 800 DEG C, the ordinate is stress, and the abscissa is strain; as shown in Figure 4 (b), the stress-strain diagram is shown when the first temperature platform T1 is 900 DEG C, the ordinate is stress, and the abscissa is strain; as shown in Figure 4 (c), the compression strength comparison diagram of the samples in examples 4 and 5 is shown; the ordinate is compression strength, and the abscissa is the name of different samples; as shown in Figure 4 (d), the average compression strength diagram of examples 4 and 5 is shown, the ordinate is average compression strength (ACS), and the abscissa is the name of different samples. It is shown that the sample in example 5 has the optimal mechanical performance, the compression strength and the average compression strength are the largest, and the mechanical performance fluctuation is small.

[0108] The high-performance lead-free piezoelectric potassium sodium niobate ceramic of the application has the composition of: 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5ZrO3-0.003CaZrO3 ceramics, the powder pre-calcination treatment is carried out at different temperatures (800-950 DEG C), the particle size uniformity and chemical heterogeneity of the pre-sintered powder are regulated, the polymorphic phase boundary (PPB) at room temperature is realized, the sintering temperature (800-1000 DEG C) of the first stage of three-step sintering is adjusted, the thermal homogenization process is effectively realized before the grain boundary diffusion, and the uniform grain size distribution and highly dense microstructure are obtained.

[0109] The preparation method of the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic adopts a three-step sintering method, the ceramic body is rapidly heated to a certain temperature first, the small particles are grown, the uniformity of the powder particle size is improved, the ceramic body is rapidly heated to high temperature again, then the furnace temperature is rapidly reduced to a lower temperature, and long-time heat preservation is carried out. By optimizing the sintering kinetics parameters of the ceramic in the method, the grain size and uniformity of the piezoelectric ceramic are controlled, and the internal stress caused by abnormal grain growth is effectively inhibited. By using the difference between the grain boundary diffusion energy and the grain boundary migration energy, densification is prior to grain boundary movement, so that the purpose of effectively regulating the grain growth and completing the densification of the body is achieved, which provides the possibility for improving the mechanical properties and stability of the KNN-based ceramic on the basis of stable piezoelectric properties.

Claims

1. A method for preparing high-performance lead-free piezoelectric potassium sodium niobate-based ceramics, characterized in that: Please follow the steps below to implement: Step 1, preparing pre-calcined powder; Step 2, preparing potassium sodium niobate-based ceramics by a three-step sintering method; Step 1 is as follows: Step 1.1, according to the stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 ZrO3-0.003CaZrO3 is used to proportion and weigh the raw materials, and the weighed raw materials are analytically pure Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2, and CaCO3; Step 1.2: Place the raw materials in step 1.1 into a ball mill, use anhydrous ethanol as the medium, and perform rolling ball milling for 12 h, followed by drying to obtain a dry powder; Step 1.3, calcining the dry powder obtained in step 1.2 at high temperature; Step 1.4: placing the powder calcined in step 1.3 into a ball mill and performing a second ball milling using anhydrous ethanol as a ball milling medium; after the second ball milling is completed, drying and sieving the mixed slurry to obtain a pre-calcined powder; The calcination temperature in step 1.3 is 900°C; Step 2 is as follows: Step 2.1: The pre-calcined powder obtained in step 1.4 is pressed into small discs using a mold, and then formed into a ceramic blank using a cold isostatic press; Step 2.2: The ceramic blank obtained in step 2.1 is heated to the first temperature platform T1 at a heating rate of 5°C / min. After holding at this temperature for 1 hour, the temperature is increased to the second temperature platform T2 at a heating rate of 10°C / min. The ceramic blank is then cooled to the temperature platform T3 at a rate of 10°C / min, held at this temperature for 5 hours, and then naturally cooled to room temperature. Step 2.3, grinding and polishing the ceramic blank sintered in step 2.3, and testing the electrical and mechanical properties on both sides of the ceramic blank to obtain a high-performance lead-free piezoelectric potassium sodium niobate-based ceramic; The T1 temperature range is 900°C, the T2 temperature is 1190°C, and the T3 temperature is 1090°C.

2. The method for preparing high-performance lead-free piezoelectric potassium sodium niobate-based ceramics according to claim 1, wherein: Steps 1.2 and 1.4 were both performed using a planetary ball mill, with the secondary ball milling being performed at a speed of 300 rpm to 400 rpm for 24 h.

3. The method for preparing high-performance lead-free piezoelectric potassium sodium niobate-based ceramics according to claim 1, characterized in that: In step 2.1, the isostatic press is used to press at a pressure of 200 MPa for 10 minutes to form a ceramic blank with a diameter of 10 mm and a thickness of 1 mm.

4. The method for preparing high-performance lead-free piezoelectric potassium sodium niobate-based ceramics according to claim 1, wherein: The ceramic blanks in step 2.3 were fired on both sides of the silver electrode with silver plasma and kept at 600°C for 30 minutes. The electrical properties were tested by polarizing in silicone oil with an electric field of 4kV / mm-6kV / mm for 20-30 minutes. The mechanical compression test was conducted using a 5mm×5mm×15mm smooth and polished rectangular sample.

5. A high-performance lead-free piezoelectric potassium sodium niobate-based ceramic, produced by the method for preparing the high-performance lead-free piezoelectric potassium sodium niobate-based ceramic according to claim 1, characterized in that: Analytical pure Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2, CaCO3 were mixed in a stoichiometric ratio of 0.957K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O3-0.04Bi 0.5 Na 0.5 It is prepared by weighing and mixing ZrO3-0.003CaZrO3.

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