High-performance lead-free textured KNN-based piezoelectric ceramic and preparation method thereof

Abstract

This invention provides a high-performance lead-free textured KNN-based piezoelectric ceramic and its preparation method, belonging to the field of electronic functional ceramics technology. The chemical formula of the lead-free textured KNN-based piezoelectric ceramic is (1-x-w)K 0.5 Na 0.5 Nb 1‑y Sb y O3-xBi 0.5 Na 0.5 ZrO3-wBiFeO3-zNaNbO3, wherein NaNbO3 serves as a seed template, with x = 0.01–0.10, y = 0.01–0.10, w = 0–0.05 mol, and z = 0.01–0.10 wt%. The NaNbO3 seed provides a template for the oriented growth of ceramic grains, allowing the ceramic grains to grow along the lamellar seed template. <001> Crystalline orientation growth is used to obtain KNN-based textured piezoelectric ceramics. 0.5 Na 0.5 ZrO3, BiFeO3 and Sb 5+ Ions are mainly used to adjust the phase transition temperatures of orthorhombic and tetragonal crystals, as well as (O-T) and rhombohedral and orthorhombic (R-O) crystals, bringing them to near room temperature. Texturing this ceramic significantly improves the piezoelectric properties of KNN-based piezoelectric materials.

Description

Technical Field

[0001] This invention belongs to the field of electronic functional ceramics technology, and specifically relates to a high-performance lead-free textured KNN-based piezoelectric ceramic and its preparation method. Background Technology

[0002] Piezoelectric ceramics are key functional materials for electronic components that can convert mechanical energy into electrical energy. They are widely used in fields such as electronic information, sensors, ultrasonic transducers, non-destructive testing, and communication technologies.

[0003] The mainstream piezoelectric ceramic material on the market is PZT lead-based ceramic. However, lead is a toxic element, and in the PZT system, the content of PbO (or Pb3O4) accounts for more than 60%. Due to the volatility of Pb and Pb... 2+ Due to their water-soluble nature, traditional lead-based piezoelectric ceramics cause varying degrees of lead pollution to the environment and human health during production, use, and disposal, seriously endangering the ecological environment and human health. With the increasing demands for environmental protection and sustainable development, the lead hazards in lead-based piezoelectric ceramics are attracting more and more attention. In this context, developing high-performance lead-free piezoelectric ceramics to replace lead-based ceramics has become an important and urgent research topic. Furthermore, given the huge market size of piezoelectric ceramics, the development of environmentally friendly lead-free piezoelectric ceramics is also of great significance.

[0004] Among many lead-free piezoelectric ceramics, KNN-based piezoelectric ceramics stand out due to their high Curie temperature (T0). c ) and excellent piezoelectric coefficient (d 33 It is considered one of the most likely lead-free piezoelectric ceramics to replace lead-based ceramics.

[0005] Since 2004, Saito et al. have used the texture template method to prepare high-performance KNN-based ceramics (d 33 Since the KNN-based lead-free piezoelectric ceramics (~416 pC / N) have received widespread attention and research, such as the work of Li Jingfeng et al. at Tsinghua University, who obtained high-voltage piezoelectric properties with good temperature stability (0-120℃, <10%) by adjusting the polymorphic phase transition temperature in KNN ceramics. 33 ~400pC / N) KNN-based lead-free piezoelectric ceramics, which have a high Curie temperature (T c > 250 ℃). In addition, Wu Jiagang et al. also achieved d-type ceramics for the first time by using multiple ion doping methods in KNN-based ceramics. 33 It has a temperature of ~650 pC / N, but its temperature coefficient (Tc) is below 160℃, which is not conducive to its practical application.

[0006] Besides element substitution to regulate phase structure, texturing is an important means to significantly improve the performance of piezoelectric ceramics. This involves adding template seeds to the ceramic, causing ceramic particles to grow oriented along the direction of the template seeds, thus obtaining textured ceramics with distinct characteristic orientations. However, existing texturing modifications of KNN-based piezoelectric ceramics still cannot significantly improve their piezoelectric coefficient. Summary of the Invention

[0007] To address the technical problem of low piezoelectric coefficient in existing KNN-based ceramics, this invention provides a high-performance lead-free textured KNN-based piezoelectric ceramic and its preparation method. The technical solution is as follows:

[0008] On the one hand, the chemical formula of the lead-free textured KNN-based piezoelectric ceramic is (1-xw)K 0.5 Na 0.5 Nb 1-y Sb y O3-xBi 0.5 Na 0.5 ZrO3-wBiFeO3-zNaNbO3, where NaNbO3 serves as a seed template, and the components are: x = 0.01~0.10, y = 0.01~0.10, w = 0~0.05 mol, and z = 0.01~0.10 wt. x, y, and w correspond to the molar content of each component in the piezoelectric ceramic, and z is the mass content of NaNbO3 in the piezoelectric ceramic.

[0009] Preferably, the d of the KNN-based piezoelectric ceramic 33 ≥700 pC / N and T c > 240℃.

[0010] Preferably, the NaNbO3 seed template has a sheet-like structure with a length of about 10-20 micrometers, a width of about 10-20 micrometers, and a thickness of about 0.5-1.5 micrometers.

[0011] On the other hand, the preparation method of the lead-free textured KNN-based piezoelectric ceramic includes the following steps:

[0012] (1) Batching, mixing and calcination: Sodium carbonate (Na2CO3), potassium carbonate (K2CO3), niobium pentoxide (Nb2O5), zirconium dioxide (ZrO2), bismuth oxide (Bi2O3), antimony oxide (Sb2O3), and iron oxide (Fe2O3) are selected as initial raw materials and calcined according to the chemical formula (1-xw)K 0.5 Na 0.5 Nb 1-y Sb y O3-xBi 0.5 Na 0.5ZrO3-wBiFeO3-zNaNbO3 were weighed and ball-milled to ensure uniform mixing, where x = 0.01~0.10, y = 0.01~0.10, w = 0~0.05 mol, and z = 0.01~0.10 wt. The uniformly mixed powder was then placed in a muffle furnace for calcination. The calcined powder was then ball-milled and dried again to obtain ceramic powder A.

[0013] (2) Casting: Ceramic powder A, solvent, dispersant, binder, homogenizer, plasticizer, and NaNbO3 seed template are mixed evenly according to a certain ratio and then cast to obtain cast green film B. The purpose of casting is to make the NaNbO3 plate-shaped seed template lie flat in the substrate under the action of the scraper, so as to ensure that the ceramic grains can follow the plate-shaped seed template during the subsequent sintering process. <001> Oriented growth.

[0014] (3) Stacking: The cast green film B is sliced ​​and stacked by hot pressing to obtain the block green film C.

[0015] (4) Sintering of ceramics: The obtained bulk green body C is debonded and then sintered to obtain lead-free textured KNN-based piezoelectric ceramic D.

[0016] (5) Surface electrode preparation: The lead-free textured KNN-based piezoelectric ceramic D is polished smooth, and electrodes are printed on the ceramic surface using screen printing technology. After drying, it is placed in a muffle furnace for calcination to obtain lead-free textured KNN-based piezoelectric ceramic E with conductive electrodes plated on the upper and lower surfaces.

[0017] (6) Polarization: The lead-free textured KNN-based piezoelectric ceramic E is polarized to obtain the polarized lead-free textured KNN-based piezoelectric ceramic F, which is the high-performance lead-free textured KNN-based piezoelectric ceramic of the present invention.

[0018] Preferably, the raw materials mentioned in step (1), namely sodium carbonate (Na2CO3), potassium carbonate (K2CO3), niobium pentoxide (Nb2O5), zirconium dioxide (ZrO2), bismuth oxide (Bi2O3), antimony oxide (Sb2O3), and iron oxide (Fe2O3), all have a purity greater than 99%; anhydrous ethanol or water is used as the ball milling medium, the rotation speed is 200-300 rpm, and the time is 6-12 hours, wherein the grinding balls used are zirconium oxide balls or agate balls; the calcination temperature of the powder is 800-950°C. o C, the heat preservation time is 3 to 10 hours.

[0019] Preferably, the casting slurry formulation in step (2) is as follows: powder is 100 wt%, binder PVB is 4-10 wt%, solvent is 40-60 wt%, dispersant is 0.8-1.5 wt%, plasticizer is 4-6 wt%, and homogenizer is 0.5-1.0 wt%. The molecular weight of PVB is 70,000-270,000; the solvent is a mixture of p-xylene (30%) and anhydrous ethanol (70%), or a mixture of butanone (40%) and anhydrous ethanol (60%), or a mixture of butanone (88.6%) and water (11.4%), or a mixture of anhydrous ethanol (68%) and toluene (32%), or a mixture of anhydrous ethanol (27%) and trichloroethylene (63%), or a mixture of n-acetone (88%) and butanone (12%), or a mixture of acetone (88%) and methane. The solvent is a mixture of benzene (12%) or a mixture of p-xylene (17%) and n-acetone (83%), all percentages being volume fractions; the dispersant is soybean oil, peanut oil, or fish oil; the plasticizer is a mixture of dibutyl phthalate (DBP) and polyethylene glycol (PEG-400), or a mixture of butyl benzyl phthalate (BBP) and polyethylene glycol (PEG-400), with the mass ratio of DBP to PEG-400 and the mass ratio of BBP to PEG-400 both being 1:1; the homogenizer is cyclohexanone.

[0020] Preferably, in step (3), the hot pressing temperature is 70~85 ℃ and the holding time is 5~10 min.

[0021] Preferably, the temperature for debinding in step (4) is 400~600℃ and the time is 1~2 hours; the sintering in step (4) adopts a two-step sintering process, including heating to 1100-1260℃ at room temperature at a heating rate of 3~5℃ / min and holding for 10~30min; then cooling to 1050~1150℃ at a cooling rate of 8~15℃ / min and holding for 5~10 hours.

[0022] Preferably, the surface electrode in step (5) is a nickel electrode, a copper electrode, or a silver electrode. The calcination temperature is 400~600℃. o C, keep warm for 1 hour.

[0023] Preferably, in step (6), the polarization electric field is 20-40 kV / mm and the time is 10-30 min.

[0024] The beneficial effects of the technical solution provided by this invention include at least the following:

[0025] The chemical formula of the lead-free textured KNN-based piezoelectric ceramic of this invention is (1-xw)K 0.5 Na 0.5 Nb 1-y Sby O3-xBi 0.5 Na 0.5 ZrO3-wBiFeO3-zNaNbO3, wherein the NaNbO3 seed crystals provide a template for the orientation and growth of ceramic grains, allowing the ceramic grains to grow along the lamellar template seed crystals. <001> Crystalline orientation growth is used to obtain KNN-based textured piezoelectric ceramics.

[0026] Bi 0.5 Na 0.5 ZrO3, BiFeO3 and Sb 5+ Ions are mainly used to adjust the phase transition temperatures of orthorhombic and tetragonal crystals, as well as (OT) and rhombohedral and orthorhombic (RO) crystals, bringing them to near room temperature. In addition, Bi... 0.5 Na 0.5 ZrO3, BiFeO3 and Sb 5+ Ions and other substances can also help regulate domain structure and reduce domain size, and improve ceramic density. Texturing this ceramic can significantly enhance the piezoelectric properties of KNN-based piezoelectric materials. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 For comparative examples 1-3 and example 1, k p and d 33 Performance comparison chart;

[0029] Figure 2 This is the XRD pattern for Comparative Example 1;

[0030] Figure 3 The XRD pattern is shown in Comparative Example 2.

[0031] Figure 4 The XRD pattern is shown in Comparative Example 3.

[0032] Figure 5 The XRD pattern is shown in Example 1.

[0033] Figure 6 The dielectric spectra are for Comparative Examples 1-3 and Example 1.

[0034] Figure 7 The NaNbO3 seed template used in Comparative Example 3 and Example 1, wherein Figure 7 (a) is a scanning electron microscope image of the seed template; Figure 7 (b) is Figure 7 (a) Enlarged view of the portion within the frame. Figure 7 (c) is a particle size distribution diagram of the seed template. Detailed Implementation

[0035] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0036] Comparative Example 1: 0.97 (K) 0.5 Na 0.5 NbO3-0.03Bi 0.5 Na 0.5 ZrO3-0.002BiFeO3-based piezoelectric ceramics.

[0037] The specific preparation steps are as follows:

[0038] According to the stoichiometric ratio 0.97 (K) 0.5 Na 0.5 NbO3-0.03Bi 0.5 Na 0.5 Weigh out dried K₂CO₃, Na₂CO₃, Nb₂O₅, Bi₂O₃, ZrO₂, and Fe₂O₃ raw materials. Place the weighed raw materials in a nylon jar and add an appropriate amount of anhydrous ethanol for ball milling at 250 r / min for 8 h. Place the mixed slurry in an oven to dry at 90℃. Grind the dried mixed powder using an agate mortar and pestle and place it in a crucible for calcination at 850℃ for 5 h. Place the calcined powder back into the ball mill jar, add an appropriate amount of anhydrous ethanol, and ball mill a second time at 300 r / min for 12 h. Place the crushed powder in an oven to dry again at 90℃ to obtain calcined powder.

[0039] PVB was added to the above calcined powder for granulation. The granulated powder was then placed into a mold with a diameter of 10 mm and pressed into sheets to obtain piezoelectric ceramic green bodies with a viscose content.

[0040] The piezoelectric ceramic green body with the above-mentioned adhesive content was placed in a muffle furnace for adhesive removal at a temperature of 600℃ for 2 hours to obtain the ceramic green body. The ceramic green body was then sintered again in a muffle furnace using a two-step sintering process. In the first step, the temperature was rapidly increased (5℃ / min) to 1200℃, held for 10-30 minutes, and then rapidly decreased to 1100℃ for 3-5 hours. Finally, the green body was cooled to room temperature in the furnace.

[0041] The surface of the sintered ceramic sample was polished, silver electrodes were screen-printed, and the sample was placed in a muffle furnace for silver baking at a sintering temperature of 600℃ for 20 minutes.

[0042] The silver-baked ceramic sample was placed in an oil bath crucible for polarization. The polarization voltage was 30 kV / cm and the polarization time was 20 min.

[0043] Comparative Example 2: 0.97(K) 0.5 Na 0.5 (Nb) 0.95 Sb 0.05 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.002BiFeO3-based piezoelectric ceramics were prepared using a method similar to that of Comparative Example 1.

[0044] Comparative Example 3: 0.97(K) 0.5 Na 0.5 NbO3-0.03Bi 0.5 Na 0.5 ZrO3-0.002BiFeO3-3%wt NaNbO3-based textured piezoelectric ceramics; the specific preparation steps are as follows:

[0045] Similar to Example 1, calcined powder was obtained by ball milling, calcination and other means.

[0046] Weigh 12g of calcined powder and prepare a casting slurry according to the mass ratio of ceramic powder:PVB:solvent:dispersant:plasticizer:homogenizer:100:6.4:60:1.4:6:0.5. Place the casting slurry in a ball mill and stir for 10 hours at 200 r / min. Then add a NaNbO3 seed template (z = 3%wt) to the slurry and stir until homogeneous to obtain the casting slurry. Pour the casting slurry into a casting machine for casting into a film. After the film dries, remove it, cut it to the same size, and stack it. Hot-press it at 75℃ and 15MPa for 5 minutes to obtain a blank.

[0047] The above-mentioned blanks were placed in a muffle furnace for debinding at a temperature of 600℃ for 2 hours to obtain ceramic green bodies. The ceramic green bodies were then sintered in the muffle furnace using a two-step sintering process. The first step involved rapidly heating to 1200℃ (heating rate 5℃ / min), holding for 10–30 minutes, and then rapidly cooling to 1100℃ and holding for 10 hours. After sintering, the green bodies were cooled to room temperature in the furnace.

[0048] The surface of the sintered ceramic sample was polished, silver electrodes were screen-printed, and the sample was placed in a muffle furnace for silver baking at a sintering temperature of 600℃ for 20 minutes.

[0049] The silver-baked ceramic sample was placed in an oil bath crucible for polarization. The polarization voltage was 30 kV / cm and the polarization time was 20 min.

[0050] Example 1: 0.97 (K) 0.5 Na 0.5 )Nb 0.95 Sb 0.05 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.002BiFeO3-3 %wtNaNbO3-based textured piezoelectric ceramics; the specific preparation steps are similar to those of Comparative Example 3.

[0051] Table 1

[0052]

[0053] Table 1 compares the performance parameters of different comparative examples and embodiments. Comparative example 1 did not include a seed template or Sb. 5+ Comparative Example 2: Add Sb 5+ Without the addition of a seed template, the performance was improved compared to Comparative Example 1. This is mainly due to the Sb 5+ The introduction of [a specific ingredient] shifts the OT phase transition temperature towards room temperature. Comparative Example 3, compared to Comparative Example 1, incorporates a seed template, demonstrating oriented growth of the ceramic and a significant improvement in its properties. Example 1 incorporates a seed template and Sb [a specific ingredient]. 5+ Because Sb 5+ By adjusting the OT phase transition temperature to room temperature and using a seed template to induce oriented growth of ceramic grains, the sample from Example 1 ultimately achieved high piezoelectric properties. 33 =750 pC / N.

[0054] Figure 1 For comparative examples 1-3 and example 1, k p and d 33 The performance comparison chart can intuitively illustrate the performance differences between the above comparative examples and Example 1.

[0055] Figure 2 This is the XRD pattern for Comparative Example 1. Figure 3 The XRD patterns for Comparative Example 2 show that the products have a pure perovskite structure. Figure 4 The XRD pattern of Comparative Example 3 shows that after adding the seed template, the ceramic samples all follow the... <001> Oriented growth.

[0056] Figure 5The XRD pattern of Example 1 shows that after adding the seed template, the ceramic sample also exhibits obvious texture orientation characteristics, and along... <001> Oriented growth.

[0057] Figure 6 Diothermal spectra of Comparative Examples 1-3 and Example 1; Comparative Examples 1 and 3 did not contain Sb. 5+ Sb was added to both Comparative Example 2 and Example 1. 5+ It can be found that Sb 5+ The introduction of this technology shifts the OT phase transition temperature towards room temperature. This is beneficial for improving the d-phase properties of piezoelectric ceramics. 33 and k p Performance, i.e., d in Comparative Example 2 33 and k p Superior performance compared to Comparative Example 1; d of Example 1 33 and k p Its performance is superior to that of Comparative Example 3.

[0058] Figure 7 The NaNbO3 seed template used in Comparative Example 3 and Example 1, wherein Figure 7 (a) is a scanning electron microscope image of the seed template. Figure 7 (b) is Figure 7 (a) An enlarged view of the part within the frame shows that the NaNbO3 seed template has a sheet-like structure with a length of about 10-20 micrometers, a width of about 10-20 micrometers, and a thickness of about 0.5-1.5 micrometers. Figure 7 (c) is a particle size distribution diagram of the seed template.

[0059] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. A high-performance lead-free textured KNN-based piezoelectric ceramic, characterized in that, The chemical formula of the lead-free textured KNN-based piezoelectric ceramic is (1-xw)K 0.5 Na 0.5 Nb 1-y Sb y O3-xBi 0.5 Na 0.5 ZrO3-wBiFeO3-zNaNbO3, wherein NaNbO3 is a seed template, and the values ​​of x = 0.01~0.10, y = 0.01~0.10, w = 0.002~0.05 mol, and z = 0.01~0.10 wt; The preparation method of the high-performance lead-free textured KNN-based piezoelectric ceramic includes the following steps: (1) Ingredients, mixing and calcination: Sodium carbonate, potassium carbonate, niobium pentoxide, zirconium dioxide, bismuth oxide, antimony oxide and iron oxide are selected as initial raw materials. They are weighed according to the chemical formula and ball-milled to make them evenly mixed. The evenly mixed powder is placed in a muffle furnace for calcination. The calcined powder is ball-milled and dried again to obtain ceramic powder A. (2) Casting: Ceramic powder A, solvent, dispersant, binder, homogenizer and plasticizer, and NaNbO3 seed template are mixed evenly according to a certain ratio and then cast to obtain cast green film B; (3) Stacking: The cast green film B is sliced ​​and stacked by hot pressing to obtain a block green film C; (4) Sintering of ceramics: The obtained bulk green body C was debinded and then sintered to obtain lead-free textured KNN-based piezoelectric ceramic D; (5) Surface electrode preparation: The lead-free textured KNN-based piezoelectric ceramic D is polished smooth, and electrodes are printed on the ceramic surface using screen printing technology. After drying, it is placed in a muffle furnace for calcination to obtain lead-free textured KNN-based piezoelectric ceramic E with conductive electrodes plated on the upper and lower surfaces. (6) Polarization: The lead-free textured KNN-based piezoelectric ceramic E is polarized to obtain the polarized lead-free textured KNN-based piezoelectric ceramic F, which is the high-performance lead-free textured KNN-based piezoelectric ceramic.

2. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, The d of the KNN-based piezoelectric ceramic 33 ≥700 pC / N and T c > 240℃.

3. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, The NaNbO3 seed template has a sheet-like structure with a length of 10-20 micrometers, a width of 10-20 micrometers, and a thickness of 0.5-1.5 micrometers.

4. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, The raw materials mentioned in step (1), namely sodium carbonate, potassium carbonate, niobium pentoxide, zirconium dioxide, bismuth oxide, antimony oxide, and iron oxide, all have a purity greater than 99%; anhydrous ethanol or water is used as the ball milling medium, the rotation speed is 200-300 rpm, and the time is 6-12 hours, wherein the grinding balls used are zirconium oxide balls or agate balls; the calcination temperature of the powder is 800-950°C. o C, the heat preservation time is 3 to 10 hours.

5. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, In step (2), the proportion of the cast slurry is as follows: the powder is 100 wt%, the amount of PVB binder is 4~10 wt%, the amount of solvent is 40~60 wt%, the amount of dispersant is 0.8~1.5 wt%, the amount of plasticizer is 4~6 wt%, and the amount of homogenizer is 0.5~1.0 wt%.

6. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, In step (3), the hot pressing temperature is 70~85 ℃ and the holding time is 5~10 min.

7. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, In step (4), the temperature for debinding is 400-600℃ and the time is 1-2 hours. The sintering in step (4) adopts a two-step sintering process, including heating to 1100-1260℃ at a heating rate of 3-5℃ / min at room temperature and holding for 10-30 min; then cooling to 1050-1150℃ at a cooling rate of 8-15℃ / min and holding for 5-10 hours.

8. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, In step (5), the surface electrode is a nickel electrode, a copper electrode, or a silver electrode; the calcination temperature is 400~600℃. o C, keep warm for 1 hour.

9. The high-performance lead-free textured KNN-based piezoelectric ceramic according to claim 1, characterized in that, In step (6), the polarization electric field is 20-40 kV / mm and the time is 10-30 min.

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