Perovskite type potassium-sodium niobate-based composite ceramic and preparation method thereof

Abstract

The invention discloses a perovskite-type potassium-sodium niobate-based composite ceramic and a preparation method thereof, the perovskite-type potassium-sodium niobate-based composite ceramic is prepared from two kinds of lead-free piezoelectric ceramics, which are 0.965 (K < 0.48 > Na < 0.52 >) (Nb0.955 Sb < 0.045 >) O < 3 >-0.035 (Bi < 0.5 >, Na < 0.5 >) HfO3 and (K < 0.5 > Na < 0.5 >) NbO < 3 >-1% mol Cu, and the two kinds of lead-free piezoelectric ceramics are firstly pre-synthesized into powder and then mixed, dried and sintered to prepare the perovskite-type potassium-sodium niobate-based composite ceramic. The potassium-sodium niobate-based composite ceramic prepared by mixing potassium-sodium niobate-based ceramic powder of two different systems according to different molar ratios, dry-pressing and sintering has excellent piezoelectric property, good temperature stability and good mechanical quality factor, the piezoelectric constant d33 of the potassium-sodium niobate-based composite ceramic is 254 pC / N, kp reaches 0.51, Qm is 173, and Tc is 304 DEG C.

Description

Technical Field

[0001] The invention belongs to the technical field of lead-free piezoelectric ceramics, and in particular relates to a method for preparing a perovskite-type potassium sodium niobate-based composite ceramic. Background Art

[0002] Lead zirconate titanate (PZT)-based ceramics are commercially used due to their excellent piezoelectric properties. However, PZT-based piezoelectric ceramics contain a large amount of lead. Therefore, potassium sodium niobate (KNN)-based ceramics with good piezoelectric properties and high Curie temperature have been widely studied as a strong alternative to lead zirconate titanate (PZT)-based ceramics. At present, researchers are committed to improving the piezoelectric properties of potassium sodium niobate (KNN)-based ceramics. Through ion doping and multi-component design, potassium sodium niobate (KNN)-based ceramics are modified to have a multi-phase coexistence structure at room temperature, which can obtain high piezoelectric properties. At the same time, Li + Partially replace Na at position A + / K + , or use Sb 5+ Nb instead of B 5+ To reduce the OT phase transition point, construct the coexistence of OT phases at room temperature to obtain high d 33 Alternatively, doping ABO3 oxides such as (Bi, Na)ZrO3 or (Bi, Na)HfO3 into (K, Na)NbO3 or (K, Na)(Nb, Sb)O3 can reduce the OT phase transition point or increase the RO phase transition point, thereby compressing the O phase temperature range, constructing the RT phase transition at room temperature or constructing the coexistence of the ROT three phases, and improving the ceramic d 33 However, high piezoelectricity alone cannot meet the needs of devices in practical applications. The temperature stability and mechanical quality factor of ceramics Q m The improvement has an important impact on the application of ceramics in transducers, resonators and other fields. The phase boundary in the KNN-based ceramics where multiple phases coexist is different from the quasi-modular phase boundary (MPB) in lead zirconate titanate (PZT), and is called the polymorphic phase boundary (PPB). The quasi-modular phase boundary (MPB) is a phase boundary whose composition does not change with temperature. Therefore, at different temperatures, the two-phase content of PZT-based piezoelectric ceramics remains unchanged, allowing it to maintain excellent piezoelectric properties. However, the composition of the polymorphic phase boundary (PPB) reported so far is greatly affected by temperature, and the change in the ratio of the two coexisting phases with temperature makes its piezoelectric performance unstable. At the same time, while the piezoelectric performance of the ceramic is improved, its mechanical quality factor Q m When piezoelectric devices operate at high frequencies, the lower Q mThis will lead to excessively high dielectric loss. Therefore, in potassium sodium niobate (KNN), the material's Q m It is also a crucial task to simultaneously optimize the piezoelectric properties, Curie temperature and Q m, is the key to realize its practicality. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a perovskite-type potassium sodium niobate-based composite ceramic with excellent piezoelectric properties, good temperature stability and high mechanical quality factor in view of the shortcomings of the prior art.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned perovskite-type potassium sodium niobate-based composite ceramic.

[0005] In order to solve the technical problem of the present invention, the following technical solution is adopted: A perovskite-type potassium sodium niobate-based composite ceramic is composed of a general formula of 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 ) Two ceramic powders of NbO3-1%molCu are mechanically mixed in a molar ratio of 1-5:1, dry-pressed and sintered at 1080-1200°C for 10-20h.

[0006] The preparation method of the above-mentioned perovskite-type potassium sodium niobate-based composite ceramic comprises the following process: Step (1) synthesize 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder; Step (2) takes 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na0.5 ) NbO3-1%molCu ceramic powder, after mechanical mixing, fully ground and sieved; Step (3) after dry pressing, heat preservation at 500-700° C. for 1-3 hours to remove binder and obtain potassium sodium niobate-based ceramic green body; Step (4) sintering the potassium sodium niobate-based ceramic green body prepared in step (3) at 1080-1200° C. for 10-20 h at a heating rate of 30° C. / min, and cooling the green body to room temperature to obtain a perovskite-type potassium sodium niobate-based composite ceramic.

[0007] In the above step (1), 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder method: K2CO3, Na2CO3, Nb2O5, Sb2O3, Bi2O3, HfO2 are used as raw materials, and the mass of each raw material required is calculated according to the chemical formula ratio; then K2CO3 and Na2CO3 are dried separately, mixed with other raw materials, and then ball-milled with a planetary ball mill to obtain a slurry; the obtained slurry is dried and kept at 830-900℃ for 5-9h, cooled to room temperature with the furnace, and the obtained material is ball-milled again with a planetary ball mill, and then dried and sieved to obtain 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder; In step (1), (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder method: K2CO3, Na2CO3, Nb2O5, CuO are used as raw materials, and the mass of each raw material required is calculated according to the chemical formula ratio; then K2CO3 and Na2CO3 are dried separately, mixed with other raw materials, and then ball-milled with a planetary ball mill to obtain a slurry; the obtained slurry is dried and kept at 830-900℃ for 5-9h for synthesis, and the obtained material is ball-milled again with a planetary ball mill, dried, sieved, and obtained (K 0.5 Na 0.5 )NbO3-1%molCu; In step (2), the grinding and sieving is to place the two ceramic powders in the same mortar, fully mix and grind and sieve to obtain potassium sodium niobate-based composite ceramic raw powder; The method of step (3) is to add a polyvinyl alcohol solution with a mass fraction of 3%-4% to the potassium sodium niobate-based composite ceramic raw powder, stir evenly, and then dry, wherein the mass ratio of the potassium sodium niobate-based composite ceramic raw powder to the polyvinyl alcohol solution is 10:3; then use a planetary ball mill to ball mill, dry and sieve, and use a mold to dry press to obtain a potassium sodium niobate-based ceramic green embryo.

[0008] The planetary ball mills involved all use anhydrous ethanol as the ball milling medium, and are mixed with 5mm and 2mm diameter zirconium oxide beads in a mass ratio of 1:2. The material to be ball milled: ball milling beads: anhydrous ethanol in a mass ratio of 1:10:4 are put into the ball milling jar, and the ball mill is milled at a speed of 300-600rpm for 1-15h.

[0009] Synthesized 0.965(K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder slurry after drying heat preservation operation, the heating rate of the heat preservation container is 3-5℃ / min, the synthesis (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder slurry is kept warm after drying, and the heating rate of the insulation container is 3-5℃ / min.

[0010] The potassium sodium niobate-based ceramic green body obtained in step (3) has a diameter of 8-15 mm, a thickness of 1-2 mm, an applied pressure of 6-12 MPa, and a holding time of 2-5 min.

[0011] In step (1), 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 ) K2CO3 and Na2CO3 used in NbO3-1%molCu ceramic powder are both dried at 180-220℃ for 2-12h.

[0012] When it comes to screening operations, 75-100 mesh screens are used.

[0013] The present invention is made by mixing and sintering two different ceramic powders in different molar ratios. Compared with the existing single-component technology, on the one hand, it can construct a dispersed phase boundary to maintain the piezoelectric properties of the piezoelectric ceramic, and on the other hand, it can improve the piezoelectric performance system and high Q mSystem mixing can simultaneously obtain excellent piezoelectric properties and Q m , and obtain a higher Curie temperature. At the same time, the rapid heating sintering method is used to obtain the best performance at 1080-1200℃. Its piezoelectric constant d 33 =254pC / N, Planar Electromechanical Coupling Coefficient k p =0.51, mechanical quality factor Q m The Curie temperature is 173 T c The Curie temperature and Q m , providing a broad application prospect for it in piezoelectrically sensitive sensors, filters, drivers, etc. The perovskite-type potassium sodium niobate-based composite ceramic provided by the present invention has high piezoelectric performance, good temperature stability and high mechanical quality factor, and is prepared by a traditional solid phase synthesis method. Compared with the existing multi-layer casting technology, the preparation of multiple ceramics in different proportions is more convenient, with a high repetition rate, easy to implement, low cost, simple process, and can be used for industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 X-ray diffraction patterns of the perovskite-type potassium sodium niobate-based composite ceramic and two single-component ceramics obtained in the present invention; Figure 2 A comparison diagram of high-temperature dielectric temperature spectra of the perovskite-type potassium sodium niobate-based composite ceramic and two single-component ceramics obtained by the present invention; Figure 3 The hysteresis loop diagrams of the perovskite-type potassium sodium niobate-based composite ceramic and two single-component ceramics obtained by the present invention are shown. DETAILED DESCRIPTION

[0015] The present invention is described in detail and completely below through embodiments in conjunction with the accompanying drawings. The embodiments are only partial embodiments, not all embodiments.

[0016] Two single components 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 )Preparation method of NbO3-1%molCu ceramics. Example 1

[0017] 0.965(K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 ) The preparation method of HfO3 ceramics, the specific steps are as follows: (1) Using K2CO3, Na2CO3, Nb2O5, Sb2O3, Bi2O3 and HfO2 as raw materials, calculate the mass of each raw material required according to the chemical formula ratio; dry K2CO3 and Na2CO3 at 180℃ for 12h respectively; (2) Preparation: The raw materials were placed in a ball mill, anhydrous ethanol was used as the ball milling medium, and a mixture of zirconia beads with a diameter of 5 mm and a diameter of 2 mm in a mass ratio of 1:2 was used as ball milling beads. The mass ratio of raw materials: ball milling beads: anhydrous ethanol was 1:10:4. The raw materials were initially ball milled at 400 rpm for 1 h in a planetary ball mill to obtain a wet slurry. (3) Primary sintering: The obtained slurry is placed in an oven and baked at 120°C for 1 h to obtain dry powder, which is then placed in a crucible and pressed tightly. The crucible is covered and placed in a box-type muffle furnace at 860°C with a heating rate of 5°C / min. The slurry is pre-sintered for 6 h and cooled to room temperature in the furnace to obtain pre-sintered dry material. (4) Ball milling: The pre-sintered dry material was transferred into a ball milling jar, and anhydrous ethanol was used as the ball milling medium. Zirconia beads with a mass ratio of 1:2 and a diameter of 5 mm and a diameter of 2 mm were mixed as ball milling beads for the second ball milling. The mass ratio of pre-sintered dry material: ball milling beads: anhydrous ethanol was 1:10:4. The ball milling was carried out at a speed of 400 rpm in a planetary ball mill for 15 h. (5) Drying and sieving: The slurry obtained by ball milling is placed in an oven and dried at 90°C for 3 hours. The dried powder is ground and passed through a 75-mesh sieve to obtain a 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder; (6) Granulation: at 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder was added with 3% polyvinyl alcohol solution by mass, stirred evenly, and then placed in an oven at 80℃ for 2h to dry to obtain pellets. The pellets were subjected to planetary ball milling and passed through a 75-mesh sieve, of which 0.965 (K 0.48Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder: polyvinyl alcohol solution mass ratio is 10:3; wherein the planetary ball mill uses anhydrous ethanol as the ball milling medium, and a mixture of zirconia beads with a diameter of 5 mm and a diameter of 2 mm with a mass ratio of 1:2 is used as the ball milling beads, and the pellets: ball milling beads: anhydrous ethanol mass ratio of 1:10:4 are placed in the ball milling jar, and the ball mill is milled at a speed of 600 rpm for 1 hour; (7) Dry pressing: Use a mold to press into a disc-shaped ceramic body with a diameter of 10 mm and a thickness of 1.5 mm, apply a pressure of 8 MPa, hold the pressure for 3 min, and then keep the temperature at 650 °C for 2 h for debinding, with a heating rate of 3 °C / min; (8) Rapid heating sintering: The ceramic body after debinding is rapidly heated to 1100°C at 30°C / min and sintered for 15 h. The ceramic sample is obtained after cooling to room temperature in the furnace. (9) Polarization: The ceramic sample was treated with silver, specifically, kept at 600°C for 30 min, cooled with the furnace, and then polarized in silicone oil for 30 min at room temperature. The polarization electric field was 3 kV / mm, and a 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic finished products can be tested for performance after being placed for 24 hours after polarization. Example 2

[0018] (K 0.5 Na 0.5 ) The preparation method of NbO3-1%molCu ceramics, the specific steps are as follows: (1) Take K2CO3, Na2CO3, Nb2O5 and CuO as raw materials, and calculate the mass of each raw material required according to the chemical formula ratio; dry K2CO3 and Na2CO3 at 220℃ for 2h respectively; (2) Preparation: The raw materials were placed in a ball mill, anhydrous ethanol was used as the ball milling medium, and a mixture of zirconia beads with a diameter of 5 mm and a diameter of 2 mm in a mass ratio of 1:2 was used as ball milling beads. The mass ratio of raw materials: ball milling beads: anhydrous ethanol was 1:10:4. The raw materials were initially ball milled at 400 rpm for 1 h in a planetary ball mill to obtain a wet slurry. (3) Primary sintering: The obtained slurry is placed in an oven and baked at 120°C for 1 h to obtain dry powder, which is then placed in a crucible and pressed tightly. The crucible is covered and placed in a box-type muffle furnace at 860°C with a heating rate of 5°C / min. The slurry is pre-sintered for 6 h and cooled to room temperature in the furnace to obtain pre-sintered dry material. (4) Ball milling: The pre-sintered dry material was transferred into a ball milling jar, and anhydrous ethanol was used as the ball milling medium. Zirconia beads with a mass ratio of 1:2 and a diameter of 5 mm and a diameter of 2 mm were mixed as ball milling beads for the second ball milling. The mass ratio of pre-sintered dry material: ball milling beads: anhydrous ethanol was 1:10:4. The ball milling was carried out at a speed of 400 rpm in a planetary ball mill for 15 h. (5) Drying and sieving: The slurry obtained by ball milling is placed in an oven and baked at 120°C for 2 hours to dry. The dried powder is ground and passed through a 100-mesh sieve to obtain (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder; (6) Granulation: 0.5 Na 0.5 )NbO3-1%molCu ceramic powder was added with 3% polyvinyl alcohol solution by mass, stirred evenly, and then placed in an oven at 80℃ for 2h to obtain pellets. The pellets were subjected to planetary ball milling and passed through a 100-mesh sieve. 0.5 Na 0.5 )NbO3-1%molCu powder: polyvinyl alcohol solution mass ratio is 10:3; wherein the planetary ball mill uses anhydrous ethanol as the ball milling medium, and a mixture of zirconia beads with a mass ratio of 1:2, a diameter of 5 mm and a diameter of 2 mm is used as the ball milling beads, and the pellets: ball milling beads: anhydrous ethanol mass ratio of 1:10:4 are put into the ball milling tank, and the ball mill is milled at a speed of 600 rpm for 1 hour; (7) Dry pressing: The ceramic body is pressed into a disc-shaped body with a diameter of 10 mm and a thickness of 1.5 mm using a mold. The applied pressure is 8 MPa and the holding time is 3 min. Then, the body is kept at 650 °C for 2 h for debinding. The heating rate is 5 °C / min. (8) Rapid heating sintering: The ceramic body after debinding is rapidly heated to 1100°C at 30°C / min and sintered for 15 h. The ceramic sample is obtained after cooling to room temperature in the furnace. (9) Polarization: The ceramic sample was treated with silver, specifically, kept at 600°C for 30 min, cooled in the furnace, and then polarized in silicone oil for 30 min at room temperature with a polarization electric field of 3 kV / mm to obtain (K 0.5 Na 0.5 )NbO3-1%molCu ceramic finished product can be tested for performance after being placed for 24 hours after polarization. Example 3

[0019] A method for preparing a perovskite-type potassium sodium niobate-based composite ceramic, the specific steps are as follows: (1) According to 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3:(K 0.5 Na 0.5 )NbO3-1%molCu=1 molar ratio Weigh 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder; (2) Mechanical mixing: 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 ) NbO3-1% molCu ceramic powder is placed in the same mortar, fully mixed and ground through a 100-mesh sieve to obtain potassium sodium niobate-based composite ceramic raw powder; (3) Granulation: Add 3% polyvinyl alcohol solution by mass to the potassium sodium niobate-based composite ceramic raw powder, stir evenly, and then put it into an oven at 80°C for 2 hours to dry to obtain granules. The granules are ball-milled with a planetary ball mill and passed through a 75-mesh sieve, wherein the mass ratio of potassium sodium niobate-based composite ceramic raw powder to polyvinyl alcohol solution is 10:3; wherein the planetary ball mill uses anhydrous ethanol as the ball milling medium, and a mixture of zirconia beads with a mass ratio of 1:2 and a diameter of 5 mm and a diameter of 2 mm is used as the ball milling beads, and the granules: ball milling beads: anhydrous ethanol are placed in a ball milling jar in a mass ratio of 1:10:4, and the ball mill is milled at 600 rpm for 1 hour; (4) Dry pressing: The ceramic body is pressed into a disc-shaped body with a diameter of 10 mm and a thickness of 1.5 mm using a mold. The applied pressure is 8 MPa and the holding time is 3 min. Then, the body is heated at 650 °C for 2 h for debinding. The heating rate is 3 °C / min. (5) Rapid heating sintering: The ceramic body after debinding is rapidly heated to 1100°C at 30°C / min and sintered for 15 hours. After cooling to room temperature in the furnace, a perovskite-type potassium sodium niobate-based composite ceramic is obtained. (6) Polarization: After cooling to room temperature, the perovskite-type potassium sodium niobate-based composite ceramic is treated with silver. Specifically, the ceramic is kept at 600°C for 30 minutes. After cooling, the ceramic is polarized in silicone oil at room temperature for 30 minutes. The polarization electric field is 3 kV / mm to obtain a finished perovskite-type potassium sodium niobate-based composite ceramic. After polarization, the ceramic is placed for 24 hours before performance testing. Example 4

[0020] A method for preparing a perovskite-type potassium sodium niobate-based composite ceramic, the specific steps are as follows: (1) According to 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3:(K 0.5 Na 0.5 )NbO3-1%molCu=2 molar ratio Weigh 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder; (2) Mechanical mixing: 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 ) NbO3-1% molCu ceramic powder is placed in the same mortar, fully mixed and ground through a 100-mesh sieve to obtain potassium sodium niobate-based composite ceramic raw powder; (3) Granulation: Add 3% polyvinyl alcohol solution by mass to the potassium sodium niobate-based composite ceramic raw powder, stir evenly, and then put it into a 120°C oven for 2 hours to dry to obtain granules. The granules are ball-milled with a planetary ball mill and passed through a 100-mesh sieve, wherein the mass ratio of potassium sodium niobate-based composite ceramic raw powder to polyvinyl alcohol solution is 10:3; wherein the planetary ball mill uses anhydrous ethanol as the ball milling medium, and a mixture of zirconia beads with a mass ratio of 1:2 and a diameter of 5 mm and a diameter of 2 mm is used as the ball milling beads, and the granules: ball milling beads: anhydrous ethanol are placed in a ball milling jar in a mass ratio of 1:10:4, and the ball mill is milled at 500 rpm for 12 hours; (4) Dry pressing: Use a mold to press into a disc-shaped ceramic body with a diameter of 8 mm and a thickness of 1 mm, apply a pressure of 6 MPa, hold the pressure for 5 min, and then keep the temperature at 700 °C for 1 h for debinding, with a heating rate of 5 °C / min; (5) Rapid heating sintering: The ceramic body after debinding is rapidly heated to 1080°C at 30°C / min and sintered for 20 hours. After cooling to room temperature, the perovskite-type potassium sodium niobate-based composite ceramic is obtained. (6) Polarization: After cooling to room temperature, the perovskite-type potassium sodium niobate-based composite ceramic is treated with silver. Specifically, the ceramic is kept at 600°C for 30 minutes. After cooling, the ceramic is polarized in silicone oil at room temperature for 30 minutes. The polarization electric field is 3 kV / mm to obtain a finished perovskite-type potassium sodium niobate-based composite ceramic. After polarization, the ceramic is placed for 24 hours before performance testing. Example 5

[0021] A method for preparing a perovskite-type potassium sodium niobate-based composite ceramic, the specific steps are as follows: (1) According to 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3:(K 0.5 Na 0.5 )NbO3-1%molCu=3 molar ratio Weigh 0.965(K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder; (2) Mechanical mixing: 0.965 (K0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 ) NbO3-1% molCu ceramic powder is placed in the same mortar, fully mixed and ground through a 100-mesh sieve to obtain potassium sodium niobate-based composite ceramic raw powder; (3) Granulation: Add 3% polyvinyl alcohol solution by mass to the potassium sodium niobate-based composite ceramic raw powder, stir evenly, and then put it into a 120°C oven for 2 hours to dry to obtain granules. The granules are ball-milled with a planetary ball mill and passed through a 100-mesh sieve, wherein the mass ratio of potassium sodium niobate-based composite ceramic raw powder to polyvinyl alcohol solution is 10:3; wherein the planetary ball mill uses anhydrous ethanol as the ball milling medium, and a mixture of zirconia beads with a mass ratio of 1:2 and a diameter of 5 mm and a diameter of 2 mm is used as the ball milling beads, and the granules: ball milling beads: anhydrous ethanol are placed in a ball milling jar in a mass ratio of 1:10:4, and the ball mill is milled at 500 rpm for 12 hours; (4) Dry pressing: Use a mold to press into a disc-shaped ceramic body with a diameter of 8 mm and a thickness of 1 mm, apply a pressure of 8 MPa, hold the pressure for 3 min, and then keep the temperature at 700 °C for 1 h for debinding, with a heating rate of 5 °C / min; (5) Rapid heating sintering: The ceramic body after debinding is rapidly heated to 1080°C at 30°C / min and sintered for 20 hours. After cooling to room temperature, the perovskite-type potassium sodium niobate-based composite ceramic is obtained. (6) Polarization: After cooling to room temperature, the perovskite-type potassium sodium niobate-based composite ceramic is treated with silver. Specifically, the ceramic is kept at 600°C for 30 minutes. After cooling, the ceramic is polarized in silicone oil at room temperature for 30 minutes. The polarization electric field is 3 kV / mm to obtain a finished perovskite-type potassium sodium niobate-based composite ceramic. After polarization, the ceramic is placed for 24 hours before performance testing. Example 6

[0022] A method for preparing a perovskite-type potassium sodium niobate-based composite ceramic, the specific steps are as follows: (1) According to 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3:(K 0.5 Na 0.5)NbO3-1%molCu=5 molar ratio Weigh 0.965(K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder; (2) Mechanical mixing: 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder and (K 0.5 Na 0.5 ) NbO3-1% molCu ceramic powder is placed in the same mortar, fully mixed and ground through a 100-mesh sieve to obtain potassium sodium niobate-based composite ceramic raw powder; (3) Granulation: Add 3% polyvinyl alcohol solution by mass to the potassium sodium niobate-based composite ceramic raw powder, stir evenly, and then put it into a 120°C oven for 2 hours to dry to obtain granules. The granules are ball-milled with a planetary ball mill and passed through a 100-mesh sieve, wherein the mass ratio of potassium sodium niobate-based composite ceramic raw powder to polyvinyl alcohol solution is 10:3; wherein the planetary ball mill uses anhydrous ethanol as the ball milling medium, and a mixture of zirconia beads with a mass ratio of 1:2 and a diameter of 5 mm and a diameter of 2 mm is used as the ball milling beads, and the granules: ball milling beads: anhydrous ethanol are placed in a ball milling jar in a mass ratio of 1:10:4, and the ball mill is milled at 300 rpm for 15 hours; (4) Dry pressing: Use a mold to press into a disc-shaped ceramic body with a diameter of 15 mm and a thickness of 2 mm. Apply a pressure of 12 MPa for 2 min, and then heat at 500 °C for 3 h for debinding. The heating rate is 5 °C / min. (5) Rapid heating sintering: The ceramic body after debinding is rapidly heated to 1200°C at 30°C / min and sintered for 10 hours. After cooling to room temperature in the furnace, a perovskite-type potassium sodium niobate-based composite ceramic is obtained. (6) Polarization: After cooling to room temperature, the perovskite-type potassium sodium niobate-based composite ceramic is treated with silver. Specifically, the ceramic is kept at 600°C for 30 minutes. After cooling, the ceramic is polarized in silicone oil at room temperature for 30 minutes. The polarization electric field is 3 kV / mm to obtain a finished perovskite-type potassium sodium niobate-based composite ceramic. After polarization, the ceramic is placed for 24 hours before performance testing.

[0023] The structure and performance of the potassium sodium niobate lead-free piezoelectric ceramics prepared in Examples 1-6 are analyzed as follows: 1. Structural analysis Figure 1 X-ray diffraction patterns of perovskite potassium niobate ceramic discs prepared by sintering of Examples 1-3, 5, and 6. It can be seen from the figure that all the samples of the examples are perovskite structures and do not contain any impurities. The diffraction peak shape of the BNH sample can be seen at 2θ=45.5°, indicating that the BNH sample is a coexistence of OT phases. The data of the KNNC ceramic sample show that it is in the O phase at room temperature. As the mixing molar ratio of the two ceramic raw powders increases, the sample gradually changes from the O phase to the coexistence of the OT phases, and the proportion of the T phase gradually increases. The increase in the T phase is beneficial to improving the piezoelectric properties of the ceramic sample.

[0024] 2. Performance Analysis Figure 2 The high temperature dielectric temperature spectra of the perovskite potassium niobate ceramics of Examples 1-6 measured at a frequency of 1 kHz show that the Curie temperature of the BNH sample is the lowest, 246°C, while the Curie temperature of the KNNC sample is the highest, 407°C. The data of the perovskite potassium sodium niobate-based composite ceramics with different molar ratios show that 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3(BNH) and (K 0.5 Na 0.5 )When the proportion of NbO3-1%molCu=5 (KNNC) gradually increases, the Curie temperature gradually decreases, indicating that the component with a large proportion will play a dominant role in the performance change of the ceramic. Figure 3 The hysteresis loops of the perovskite potassium niobate ceramics of Examples 1-3, 5-6 measured at a frequency of 1 Hz show that the maximum polarization intensity and residual polarization intensity of the BNH sample are the largest, and the ferroelectricity is the best, while the residual polarization and maximum polarization intensity of the KNNC sample are the smallest, and the ferroelectricity is the worst. As the ratio of BNH:KNNC gradually increases, the maximum polarization and residual polarization intensity of the sample gradually increase, indicating that the ferroelectricity gradually increases, which is exactly the opposite of the change law of the Curie temperature. Table 1 shows the performance data of each sample. It can be seen from the table that the sample with BNH:KNNC=3 has the best comprehensive performance. d 33 =254pC / N, Planar Electromechanical Coupling Coefficient k p =0.51, mechanical quality factor Q m The Curie temperature is 173 T cIt is 304℃.

[0025] In summary, the perovskite-type potassium sodium niobate-based composite ceramic provided by the present invention, which is a mixture of two ceramic raw powders in different molar ratios, has excellent piezoelectric properties, a high Curie temperature, and good temperature stability. It can be used in sensors and is of great significance to replace lead-based piezoelectric ceramics in the future.

[0026] Table 1 Performance data of each sample .

Claims

1. A perovskite-type potassium sodium niobate-based composite ceramic, characterized in that: The general formula is 0.965(K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 ) Two ceramic powders of NbO3-1%molCu are mechanically mixed in a molar ratio of 1-5:1, dry-pressed and sintered at 1080-1200°C for 10-20h.

2. The method for preparing a perovskite-type potassium sodium niobate-based composite ceramic according to claim 1, characterized in that Including the following processes: Step (1) synthesize 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder; Step (2) takes 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 ) NbO3-1%molCu ceramic powder, after mechanical mixing, fully ground and sieved; Step (3) after dry pressing, heat preservation at 500-700° C. for 1-3 hours to remove binder and obtain potassium sodium niobate-based ceramic green body; Step (4) sintering the potassium sodium niobate-based ceramic green body prepared in step (3) at 1080-1200° C. for 10-20 h at a heating rate of 30° C. / min, and cooling the green body to room temperature to obtain a perovskite-type potassium sodium niobate-based composite ceramic.

3. The method for preparing a perovskite-type potassium sodium niobate-based composite ceramic according to claim 2, characterized in that The steps include: In step (1), 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder method: K2CO3, Na2CO3, Nb2O5, Sb2O3, Bi2O3, HfO2 are used as raw materials, and the mass of each raw material required is calculated according to the chemical formula ratio; then K2CO3 and Na2CO3 are dried separately, mixed with other raw materials, and then ball-milled with a planetary ball mill to obtain a slurry; the obtained slurry is dried and kept at 830-900℃ for 5-9h, cooled to room temperature with the furnace, and the obtained material is ball-milled again with a planetary ball mill, and then dried and sieved to obtain 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder; In step (1), (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder method: K2CO3, Na2CO3, Nb2O5, CuO are used as raw materials, and the mass of each raw material required is calculated according to the chemical formula ratio; then K2CO3 and Na2CO3 are dried separately, mixed with other raw materials, and then ball-milled with a planetary ball mill to obtain a slurry; the obtained slurry is dried and kept at 830-900℃ for 5-9h for synthesis, and the obtained material is ball-milled again with a planetary ball mill, dried, sieved, and obtained (K 0.5 Na 0.5 )NbO3-1%molCu; In step (2), the grinding and sieving is to place the two ceramic powders in the same mortar, fully mix and grind and sieve to obtain potassium sodium niobate-based composite ceramic raw powder; The method of step (3) is to add a polyvinyl alcohol solution with a mass fraction of 3%-4% to the potassium sodium niobate-based composite ceramic raw powder, stir evenly, and then dry, wherein the mass ratio of the potassium sodium niobate-based composite ceramic raw powder to the polyvinyl alcohol solution is 10:3; then use a planetary ball mill to ball mill, dry and sieve, and use a mold to dry press to obtain a potassium sodium niobate-based ceramic green embryo.

4. The method for preparing a perovskite-type potassium sodium niobate-based composite ceramic according to claim 3, characterized in that: The planetary ball mills involved all use anhydrous ethanol as the ball milling medium, and are mixed with 5mm and 2mm diameter zirconium oxide beads in a mass ratio of 1:

2. The material to be ball milled: ball milling beads: anhydrous ethanol in a mass ratio of 1:10:4 are put into the ball milling jar, and the ball mill is milled at a speed of 300-600rpm for 1-15h.

5. The method for preparing a perovskite-type potassium sodium niobate-based composite ceramic according to claim 3, characterized in that: Synthesized 0.965(K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 ceramic powder slurry after drying heat preservation operation, the heating rate of the heat preservation container is 3-5℃ / min, the synthesis (K 0.5 Na 0.5 )NbO3-1%molCu ceramic powder slurry is kept warm after drying, and the heating rate of the insulation container is 3-5℃ / min.

6. The method for preparing a perovskite-type potassium sodium niobate-based composite ceramic according to claim 2 or 3, characterized in that: The potassium sodium niobate-based ceramic green body obtained in step (3) has a diameter of 8-15 mm, a thickness of 1-2 mm, an applied pressure of 6-12 MPa, and a holding time of 2-5 min.

7. The method for preparing a perovskite-type potassium sodium niobate-based composite ceramic according to claim 3, characterized in that: In step (1), 0.965 (K 0.48 Na 0.52 )(Nb 0.955 Sb 0.045 )O3-0.035(Bi 0.5 ,Na 0.5 )HfO3 and (K 0.5 Na 0.5 ) K2CO3 and Na2CO3 used in NbO3-1%molCu ceramic powder are both dried at 180-220℃ for 2-12h.

8. The method for preparing a perovskite-type potassium sodium niobate-based composite ceramic according to claim 2 or 3, characterized in that: When it comes to screening operations, 75-100 mesh screens are used.

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