A hard potassium-sodium niobate lead-free piezoelectric ceramic and a preparation method thereof

Abstract

This invention discloses a hard sodium potassium niobate lead-free piezoelectric ceramic and its preparation method. The lead-free piezoelectric ceramic is based on sodium potassium niobate ceramic by introducing two metal oxides, CuO and MnO2. The preparation method involves synthesizing sodium potassium niobate ceramic powder, then introducing CuO and MnO2, followed by secondary ball milling, drying and sieving, dry pressing, and sintering. This successfully prepares a hard sodium potassium niobate lead-free piezoelectric ceramic with high piezoelectric constant, low loss, and high mechanical quality factor. d 33 It is 335 pC / N. k p Reaching 0.51, Q m For 363, tan d =0.0103. The introduction of bimetallic cation doping not only ensured sintering quality but also effectively improved [the quality] through defect design. Q m This achieves the effect of hardening ceramics.

Description

Technical Field

[0001] This invention belongs to the field of lead-free piezoelectric ceramic technology, specifically relating to a hard potassium sodium niobate lead-free piezoelectric ceramic and its preparation. Background Technology

[0002] Piezoelectric ceramics possess unique electromechanical coupling properties and have wide applications in the fields of electronics, artificial intelligence, and medical technology. However, due to the high lead content of lead-based ceramics (PZT), which pose potential hazards to human health and the environment, their commercial use is gradually being phased out. Potassium sodium niobate (KNN)-based lead-free piezoelectric ceramics exhibit excellent piezoelectric response and high Curie temperature, making them one of the most promising alternatives to PZT-based ceramics. In recent years, numerous researchers have successfully increased the piezoelectric constant of KNN ceramics to over 700 pC / N through compositional manipulation, grain boundary engineering, defect engineering, and other innovative methods.

[0003] Despite significant improvements in piezoelectric properties, high piezoelectricity alone cannot meet the demands of practical applications. Factors such as dielectric loss, temperature stability, and mechanical quality factor of ceramics also need to be considered. Q m The improvement in piezoelectric properties has a significant impact on the application of ceramics in transducers, resonators, and other fields. While the piezoelectric properties of ceramics are improved, their mechanical quality factor also increases. Q m It will decrease. When piezoelectric devices operate at high frequencies, the lower... Q m This can lead to excessively high dielectric losses. Therefore, in KNN-based ceramics, it is necessary to improve the material's dielectric properties while maintaining high piezoelectric performance. Q m This is a crucial task. Simultaneously optimizing the piezoelectric properties, dielectric loss, and... Q m This is the key to realizing its practical application. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a hard sodium potassium niobate lead-free piezoelectric ceramic with excellent piezoelectric properties, low dielectric loss and high mechanical quality factor, in order to overcome the shortcomings of the prior art.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned hard sodium potassium niobate lead-free piezoelectric ceramic.

[0006] The following technical solution is adopted to solve the technical problem of the present invention: A hard potassium sodium niobate lead-free piezoelectric ceramic, with the general formula (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb0.04 ,Hf 0.035 O3- x %molCuO- y %mol MnO2, x =0.5-2、 y =0.5-2, synthesized by solid-state method with chemical formula (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 The ceramic raw powder is made of O3, then CuO and MnO2 are introduced, and then it is dry-pressed and sintered at 1000-1150℃ for 10-20 h.

[0007] The preferred solution is: x =0.5, 1, 1.5, 2, y =0.5, 1, 1.5, 2.

[0008] A method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic, comprising, (1) Calculation: Using K2CO3, Na2CO3, Nb2O5, Sb2O3, Bi2O3, and HfO2 as raw materials, according to (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 )Calculate the O3 ratio and weigh the required mass of each raw material; (2) Mixing: K2CO3 and Na2CO3 are dried separately, then mixed with other raw materials and ball-milled using a planetary ball mill to obtain a slurry; (3) Synthesis: The slurry obtained in step (2) is dried, sieved, and then kept at 800-900 ℃ for 3-10 h for synthesis. The raw ceramic powder is obtained by cooling it to room temperature in the furnace. (4) Add CuO and MnO2: Calculate the required amounts of CuO and MnO2 according to the chemical formula ratio, and weigh them; (5) Ball milling: The ceramic raw powder obtained in steps (3) and (4) is mixed with CuO and MnO2 and then ball milled again using a planetary ball mill. (6) Drying and sieving: The ball milling material obtained in step (5) is dried and then sieved to obtain ceramic precursor; (7) Granulation: Add 4%-6% polyvinyl alcohol solution by mass to the ceramic precursor obtained in step (6), stir evenly, and then dry. The mass ratio of ceramic precursor to polyvinyl alcohol solution is 5:1. (8) Dry pressing: Grind and sieve the dried powder from step (7), press it into a ceramic body using a mold, and then keep it at 550-700 ℃ for 1-4 h to remove the glue; (9) Sintering: The ceramic preform after debinding is heated to 1000-1150℃ at a heating rate of 10℃ / min and sintered for 10-20 h. After cooling to room temperature in the furnace, ceramic samples are obtained. (10) Polarization: The ceramic sample from step (9) is treated with silver, specifically by holding it at 500-700 ℃ for 20-30 min, cooling it in the furnace, and then polarizing it in silicone oil at 120 ℃ for 10-60 min with a polarization electric field of 3 kV / mm to obtain a hard potassium sodium niobate lead-free piezoelectric ceramic product.

[0009] In steps (2) and (5), the planetary ball mill uses anhydrous ethanol as the milling medium. Zirconia balls with a diameter of 5 mm and a diameter of 2 mm are mixed at a mass ratio of 1:3. The raw materials, mixed balls and anhydrous ethanol are mixed at a mass ratio of 1:3:2 and placed in the ball milling jar. The ball mill is run at 300-600 rpm for 1-15 hours.

[0010] The temperature conditions in steps (3), (8) and (10) are obtained by uniform heating, with a heating rate of 1-5 ℃ / min.

[0011] In step (8), the ceramic blank is pressed by the mold with a diameter of 8-24 mm and a thickness of 1-2 mm.

[0012] In step (2), K2CO3 and Na2CO3 are dried at 120-220 ℃ for 2-12 h.

[0013] The drying temperature in steps (3) and (6) is 90-120℃, and the drying time is 1-3 h.

[0014] In steps (3) and (6), the sieving is done through a 75-100 mesh screen.

[0015] The beneficial effects of this invention are as follows: The prepared hard sodium potassium niobate lead-free piezoelectric ceramics possess high piezoelectric performance, low dielectric loss, and high mechanical quality factor. Traditional solid-state synthesis methods are low-cost and simple, suitable for industrial mass production. This invention introduces low-valence metal cations after synthesis. Compared with existing ceramic preparation technologies, this can act as a sintering aid, lowering the sintering temperature and optimizing the sintering quality. Furthermore, the low-valence metal cations, when doped into the ceramic interior, create B-site defects, simultaneously achieving excellent piezoelectric constants and... Q m This reduces ceramic losses. Simultaneously, it achieves optimal performance at 1020℃, with a piezoelectric constant...d 33 =335 pC / N, planar electromechanical coupling coefficient k p =0.51, Mechanical Quality Factor Q m For 363, tan δ =0.0103. While maintaining the piezoelectric properties of lead-free potassium sodium niobate piezoelectric ceramics, losses were reduced and improvements were increased. Q m This provides a broad application prospect for piezoelectrically sensitive sensors, filters, and drivers. Attached Figure Description

[0016] Figure 1 Different results obtained in this invention x , y X-ray diffraction pattern of sodium potassium niobate ceramics; Figure 2 Different results obtained in this invention x , y Comparison of high-temperature dielectric temperature spectra of sodium potassium niobate ceramics; Figure 3 Different results obtained in this invention x , y Hysteresis loop diagram of lower hard sodium niobate ceramic. Detailed Implementation

[0017] The present invention will be described in detail and completely below with reference to the embodiments and accompanying drawings. The embodiments are only some examples and not all examples.

[0018] Example 1: A method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic, the specific steps of which are as follows: (1) Calculation: Using K2CO3, Na2CO3, Nb2O5, Sb2O3, Bi2O3, and HfO2 as raw materials, calculate according to the chemical formula (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 )O3 Calculate the required mass of each raw material; (2) Batching: K2CO3 and Na2CO3 were dried in an oven at 150 ℃ for 4 h to remove moisture. Then, according to the calculation results, each raw material was weighed and placed in a ball mill jar. Anhydrous ethanol was used as the medium, and zirconia beads with a mass ratio of 1:2, a diameter of 5 mm and a diameter of 2 mm were mixed as the ball mill beads. The mass ratio of raw material: ball mill beads: anhydrous ethanol was 1:3:2. The ball mill was initially ball milled at 400 rpm for 1 h in a planetary ball mill to obtain wet slurry. (3) Synthesis: The obtained slurry was placed in an oven and baked at 120 ℃ for 2 h to obtain dry powder. Then it was packed into a crucible and pressed tightly. The crucible lid was closed and it was sent into a box-type muffle furnace at 850 ℃ with a heating rate of 3 ℃ / min. After pre-firing for 6 h, it was cooled to room temperature with the furnace to obtain ceramic raw powder. (4) Add CuO and MnO2: according to the chemical formula (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 Calculate the required amounts of CuO and MnO2, and weigh them. (5) Ball milling: The ceramic raw powder, CuO, and MnO2 were transferred into a ball milling jar. Anhydrous ethanol was used as the ball milling medium. Zirconia beads with a diameter of 5 mm and a diameter of 2 mm were mixed in a mass ratio of 1:2 and ball milling was carried out for a second time. The mass ratio of raw material: ball milling beads: anhydrous ethanol was 1:3:2. The mixture was ball milled for 2 h at a speed of 400 rpm in a planetary ball mill. (6) Drying and sieving: The slurry obtained from ball milling is placed in an oven at 120 ℃ for 1 h to dry. The dried powder is then ground and passed through an 80-mesh sieve to obtain fine and uniform powder. (7) Granulation: Add 6% polyvinyl alcohol solution to ceramic powder, stir evenly, put it in an 80 ℃ oven for 2 hours to dry, grind and pass through an 80 mesh sieve, wherein the mass ratio of ceramic powder to polyvinyl alcohol solution is 5:1; (8) Dry pressing: The ceramic blank with a diameter of 24 mm and a thickness of 1.5 mm is pressed using a mold, and then the glue is removed after being kept at 660 ℃ for 2 h, wherein the heating rate is 1℃ / min; (9) Sintering: The ceramic preform after debinding was rapidly heated to 1020 °C at 10 °C / min and sintered for 15 h. After cooling to room temperature in the furnace, ceramic samples were obtained. (10) Polarization: The ceramic product is silver-treated, specifically by holding it at 600 ℃ for 30 min with a heating rate of 5 ℃ / min. After cooling in the furnace, it is polarized in silicone oil at 120 ℃ for 30 min with a polarization electric field of 3 kV / mm to obtain a hard potassium sodium niobate lead-free piezoelectric ceramic product. After polarization, it can be placed for 24 h before performance testing.

[0019] Example 2: A method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic, the specific steps of which are as follows: The chemical formula of step (4) is (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 The remaining steps are the same as in Example 1, consisting of O3-1%molCuO-0.5%molMnO2.

[0020] Example 3: A method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic, the specific steps of which are as follows: The chemical formula of step (4) is (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 The remaining steps are the same as in Example 1: O3-1.5%molCuO-1%molMnO2.

[0021] Comparative Example 1: Preparation of potassium sodium niobate ceramics without the addition of CuO and MnO2, the specific steps are as follows: Among them, the chemical formula is (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 The method is O3-0%molCuO-0%molMnO2. Unlike Example 1, there is no step (4), step (5) only involves transferring the ceramic raw powder into the ball mill jar, and the sintering temperature of step (9) is 1150℃. The remaining steps are the same as in Example 1.

[0022] The structure and properties of the lead-free potassium sodium niobate piezoelectric ceramics prepared in Examples 1-3 and Comparative Example 1 are analyzed as follows: (I) Structural Analysis Figure 1The figures show room-temperature X-ray diffraction patterns of the potassium sodium niobate lead-free piezoelectric ceramic discs prepared by sintering in Examples 1-3 and Comparative Example 1. As can be seen from the figures, all samples exhibit a perovskite structure without any impurity phases, indicating that CuO and MnO2 are well dissolved in the lattice of the potassium sodium niobate lead-free piezoelectric ceramic. θ The peak shape at 45.5 ° can be used to analyze the phase composition inside the potassium sodium niobate lead-free piezoelectric ceramic. The results show that all samples have the coexistence of the O and T phases at room temperature, and the peak shapes are basically consistent, indicating that the introduction of CuO and MnO2 will not cause significant changes in the lattice and phase structure of the potassium sodium niobate lead-free piezoelectric ceramic.

[0023] (II) Performance Analysis Figure 2 The high-temperature dielectric temperature spectra of the potassium sodium niobate lead-free piezoelectric ceramics of Examples 1-3 and Comparative Example 1 were measured at a frequency of 1 kHz. It can be clearly seen that after CuO and MnO2 doping, the Curie temperature of the ceramics is slightly reduced, but all are above 200℃, which meets the requirements of some applications. Figure 3 The hysteresis loops of the lead-free potassium sodium niobate piezoelectric ceramics of Examples 1-3 and Comparative Example 1 were measured at a frequency of 1 Hz. As Cu... 2+ Mn 4+ As ion doping deepens, its hysteresis loop shifts horizontally to the right, which causes the absolute values ​​of the positive and negative coercive fields to change. E i Increase E i For internal bias field, E i The gradual increase in Cu indicates an increase in the amount of space charge inside the ceramic, which also represents the increase in Cu content. 2+ Mn 4+ Deeper doping leads to an increase in internal defects in ceramics. Excessive defect dipoles pin domain walls, disrupting the long-range order of ferroelectricity and refining the domain structure. This undoubtedly weakens polarization and increases the ceramic's... Q m Table 1 shows the performance data of each sample. It can be seen from the table that as Cu... 2+ Mn 4+ With deeper ion doping, the piezoelectric constant decreases slightly, but still remains above 300 pC / N. Q m The value increased significantly, and the dielectric loss... tanδ The decline was significant, returning to the 0.01 level. x = 1, y Optimal performance is achieved when = 1.

[0024] Table 1 Performance data of each sample

[0025] In summary, the hard sodium potassium niobate lead-free piezoelectric ceramic provided by this invention exhibits excellent piezoelectric properties. Q m With high dielectric value and low dielectric loss, it can be applied in power devices such as resonators and piezoelectric motors, and is of great significance in replacing lead-based piezoelectric ceramics in the future.

Claims

1. A hard sodium potassium niobate lead-free piezoelectric ceramic, characterized in that: The general formula is (K) 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 O3- x %molCuO- y %mol MnO2, x =0.5-2、 y =0.5-2, synthesized by solid-state method with chemical formula (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 The ceramic raw powder is made of O3, then CuO and MnO2 are introduced, and then it is dry-pressed and sintered at 1000-1150℃ for 10-20 h.

2. The hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 1, characterized in that: x =0.5、1、1.5、2， y =0.5、1、1.5、2。 3. The method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 1 or 2, characterized in that... Includes the following steps: (1) Calculation: Using K2CO3, Na2CO3, Nb2O5, Sb2O3, Bi2O3, and HfO2 as raw materials, according to (K 0.46 Na 0.5225 ,Bi 0.0175 (Nb) 0.925 ,Sb 0.04 ,Hf 0.035 )Calculate the O3 ratio and weigh the required mass of each raw material; (2) Mixing: K2CO3 and Na2CO3 are dried separately, then mixed with other raw materials and ball-milled using a planetary ball mill to obtain a slurry; (3) Synthesis: The slurry obtained in step (2) is dried, sieved, and then kept at 800-900 ℃ for 3-10 h for synthesis. The raw ceramic powder is obtained by cooling it to room temperature in the furnace. (4) Add CuO and MnO2: Calculate the required amounts of CuO and MnO2 according to the chemical formula ratio, and weigh them; (5) Ball milling: The ceramic raw powder obtained in steps (3) and (4) is mixed with CuO and MnO2 and then ball milled again using a planetary ball mill. (6) Drying and sieving: The ball milling material obtained in step (5) is dried and then sieved to obtain ceramic precursor; (7) Granulation: Add 4%-6% polyvinyl alcohol solution by mass to the ceramic precursor obtained in step (6), stir evenly, and then dry. The mass ratio of ceramic precursor to polyvinyl alcohol solution is 5:

1. (8) Dry pressing: Grind and sieve the dried powder from step (7), press it into a ceramic body using a mold, and then keep it at 550-700℃ for 1-4 hours to remove the glue. (9) Sintering: The ceramic preform after debinding is heated to 1000-1150℃ at a heating rate of 10℃ / min and sintered for 10-20 h. After cooling to room temperature in the furnace, ceramic samples are obtained. (10) Polarization: The ceramic sample from step (9) is treated with silver, specifically by holding it at 500-700 ℃ for 20-30 min, cooling it in the furnace, and then polarizing it in silicone oil at 120 ℃ for 10-60 min with a polarization electric field of 3 kV / mm to obtain a hard potassium sodium niobate lead-free piezoelectric ceramic product.

4. The method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 3, characterized in that: In steps (2) and (5), the planetary ball mill uses anhydrous ethanol as the milling medium. Zirconia balls with a diameter of 5 mm and a diameter of 2 mm are mixed at a mass ratio of 1:

3. The raw materials, mixed balls and anhydrous ethanol are mixed at a mass ratio of 1:3:2 and placed in the ball milling jar. The ball mill is run at 300-600 rpm for 1-15 hours.

5. The method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 3, characterized in that: The temperature conditions in steps (3), (8) and (10) are obtained by uniform heating, with a heating rate of 1-5 ℃ / min.

6. The method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 3, characterized in that: In step (8), the mold presses the ceramic blank to a diameter of 8-24 mm and a thickness of 1-2 mm.

7. The method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 3, characterized in that: In step (2), K2CO3 and Na2CO3 are dried at 120-220 ℃ for 2-12 h.

8. The method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 3, characterized in that: The drying temperature in steps (3) and (6) is 90-120℃, and the drying time is 1-3 h.

9. The method for preparing a hard sodium potassium niobate lead-free piezoelectric ceramic according to claim 3, characterized in that: In steps (3) and (6), the sieving is done through a 75-100 mesh screen.

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