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

Abstract

The invention relates to a perovskite type potassium-sodium niobate-based ceramic and a preparation method thereof, the general formula of the perovskite type potassium-sodium niobate-based ceramic is 0.965 (K < 0.48 > Na < 0.52 >) (Nb0. 96Sb < 0.04 >) O < 3 >-0.035 (Bi < 1-x > In < x >) Na < 0.5 > HfO < 3 >, and x is more than or equal to 0.04 and less than or equal to 0.10. In < 3 + > is introduced, and Bi < 3 + > is slightly replaced by In < 3 + > ions, so that compared with the prior art, the lead-free piezoelectric ceramic with relatively high Curie temperature and relatively high piezoelectric property is obtained on the basis of keeping the original piezoelectric property of the ceramic by introducing In < 3 + >. By a solid-phase synthesis method and a two-step sintering method, the Curie temperature of the potassium-sodium niobate-based leadless piezoelectric ceramic is improved and the temperature range for maintaining the performance is widened while the piezoelectric performance of the potassium-sodium niobate-based leadless piezoelectric ceramic is ensured, so that the temperature stability of the material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lead-free piezoelectric ceramics, and particularly relates to a perovskite-type potassium sodium niobate-based lead-free piezoelectric ceramic and a preparation method thereof. Background Art

[0002] Piezoelectric ceramics are functional materials that can convert mechanical energy and electrical energy into each other, and are widely used due to their good properties. At present, lead zirconate titanate (PZT)-based piezoelectric ceramics have always occupied a large share of the piezoelectric ceramic market due to their excellent piezoelectric properties and temperature stability, but they contain a large amount of lead in their raw materials and are highly toxic. Therefore, it is of great significance to develop a lead-free piezoelectric ceramic material comparable to traditional PZT-based piezoelectric ceramic materials. Potassium sodium niobate (KNN)-based lead-free piezoelectric ceramics have excellent piezoelectric properties and environmental friendliness, and are expected to partially replace PZT-based piezoelectric ceramics, so they have received extensive attention from researchers. Although pure potassium sodium niobate lead-free piezoelectric ceramics have a high Curie temperature, their ferroelectricity and piezoelectric properties are poor, and there is still a large gap in piezoelectric properties compared with lead-based piezoelectric ceramics. At present, the research on KNN-based lead-free piezoelectric ceramics mainly focuses on improving electrical properties and temperature stability. Among them, the electrical properties are mainly improved through phase boundary design and preparation process optimization. It is reported that incorporating perovskite minerals (such as BaZrO 3 , CaZrO 3 , (Bi, Na)ZrO 3 ) into the KNN matrix can compress the temperature region of the orthorhombic (O) phase and construct a rhombohedral (R)-tetragonal (T) phase coexistence region, thereby significantly improving the room temperature piezoelectric properties. At present, the piezoelectric properties of KNN-based ceramics are already comparable to those of commercial PZT-based ceramics. Due to the existence of a polymorphic phase boundary inside KNN-based ceramics, obvious phase structure changes will occur with temperature changes, which will lead to a sharp drop in piezoelectric properties and affect their application at higher temperatures. Piezoelectric materials will exhibit different phases at different temperatures. Generally, the temperature transition point from the T phase to the C phase is called the Curie temperature T c , which is also called the transition from the ferroelectric phase to the paraelectric phase. Piezoelectric materials have piezoelectricity in the ferroelectric phase region and lose piezoelectricity in the paraelectric phase region. Therefore, on the premise of maintaining piezoelectric properties, the temperature range of the ferroelectric phase can be broadened and the temperature stability can be improved by increasing the Curie temperature. 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 ceramic with temperature stability in view of the problems existing in the prior art. The present invention introduces In 3+ , and uses In 3+ ions to slightly replace Bi 3+After that, a lead-free piezoelectric ceramic with both a high Curie temperature and high piezoelectric properties was obtained.

[0004] Another object of the present invention is to provide a preparation method of the above perovskite-type potassium sodium niobate-based ceramic. By means of the solid-phase synthesis method and the two-step sintering method, while ensuring the piezoelectric properties of the lead-free piezoelectric ceramic of potassium sodium niobate-based, its Curie temperature is increased, thereby improving the temperature stability of the material.

[0005] The following technical solutions are adopted to solve the technical problems of the present invention: A perovskite-type potassium sodium niobate-based ceramic, with the general formula 0.965(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O 3 -0.035(Bi 1-x In x )Na 0.5 HfO 3 , 0.04 ≤ x ≤ 0.10.

[0006] In the general formula of the above perovskite-type potassium sodium niobate-based ceramic x = 0.06 or 0.08.

[0007] The preparation method of the above perovskite-type potassium sodium niobate-based ceramic includes the following steps: (1) Using K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Sb 2 O 3 , Bi 2 O 3 , HfO 2 , In 2 O 3 as raw materials, calculate the mass of each raw material required according to the chemical formula ratio; (2) Mixing materials: First, dry K 2 CO 3 and Na 2 CO 3 separately, and then mix them with other raw materials and perform primary ball milling with a planetary ball mill to obtain a wet slurry; (3) Pre-sintering: After drying the wet slurry obtained in step (2), sieve it, and perform primary sintering at 800 - 900 °C for 6 - 10 h, and cool it to room temperature with the furnace to obtain pre-sintered dry materials; (4) Secondary ball milling: The pre-sintered dry material obtained in step (3) is ball milled again using a planetary ball mill to obtain a wet slurry. (5) Drying and sieving: The wet slurry obtained in step (4) is dried and then sieved to obtain ceramic powder. (6) Granulation: A polyvinyl alcohol solution with a mass fraction of 3% - 4% is added to the ceramic powder, stirred evenly, and then dried. The mass ratio of ceramic powder to polyvinyl alcohol solution is 10:3. (7) Compression molding: The dried powder is ground and sieved, then pressed into a ceramic blank using a mold and held at 500 - 700 °C for 1 - 3 h to remove the binder. (8) Two-step sintering: The ceramic blank obtained in step (7) is rapidly heated to 1180 - 1210 °C at a rate of 10 - 15 °C / min, held for 5 - 10 min, then cooled to 1070 - 1100 °C and held at this temperature for 10 - 20 h, and finally cooled to room temperature in the furnace to obtain a ceramic sheet. A ceramic sheet is obtained after cooling to room temperature in the furnace. (9) Silver coating: The ceramic sheet obtained in step (8) is coated with silver paste and held at 500 - 700 °C for 20 - 30 min for silver firing, then cooled to room temperature in the furnace. (10) Poling: The silver-coated ceramic sheet obtained in step (9) is poled to obtain a sodium potassium niobate perovskite-based ceramic.

[0008] In steps (2) and (4), the planetary ball milling uses anhydrous ethanol as the ball milling medium. The zirconia beads with diameters of 5 mm and 2 mm are mixed in a mass ratio of 1:2. The raw material, mixed beads, and anhydrous ethanol are put into the ball milling tank in a mass ratio of 1:8:5. The ball mill mills at a speed of 400 - 600 rpm for 8 - 15 h.

[0009] In steps (3), (7), (8), and (9), the heating rate is 5 - 10 °C / min.

[0010] In step (7), the diameter of the ceramic blank pressed by the mold is 8 - 10 mm, and the thickness is 1 - 1.5 mm.

[0011] In step (1), K 2 CO 3 and Na 2 CO 3 are respectively dried at 200 - 250 °C for 2 - 5 h.

[0012] In steps (3), (5), and (6), the drying temperature is 80 - 90 °C, and the drying time is 2 - 5 h.

[0013] In steps (3), (5) and (7), pass through a 75-100 mesh sieve.

[0014] In step (10), the polarization electric field is 2-4 kV / mm and the time is 20-30 min.

[0015] The perovskite-type potassium sodium niobate-based ceramic provided by the present invention has high piezoelectric performance and a high Curie temperature. In the present invention, the composition (Bi, Na)HfO 3 (BNH) and antimony (Sb) elements are used to adjust the O-T phase transition temperature to room temperature, improve the piezoelectric performance of the piezoelectric ceramic, and at the same time introduce In 3+ , use In 3+ ions to slightly substitute Bi 3+ After that, a lead-free piezoelectric ceramic with both a high Curie temperature and high piezoelectric performance is obtained. The optimal performance is obtained at 1070-1200 °C by means of rapid heating sintering. The maximum Curie temperature is 287 °C, the maximum piezoelectric constant can reach 358 pC / N, and the maximum planar electromechanical coupling coefficient k p = 0.52. On the premise of not excessively damaging other properties, the present invention greatly increases its Curie temperature, broadens the temperature range in which the performance is maintained, and improves the temperature stability of the potassium sodium niobate-based ceramic. The preparation method of the present invention is simple, economical and practical, can be used for large-scale industrial production, has good application prospects in the fields of transducers, sensors, actuators, etc., and because it is a lead-free material, it will not cause environmental pollution during the production, use and recycling processes, and is an environmentally friendly high-performance material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the X-ray diffraction pattern of the perovskite-type potassium sodium niobate-based ceramic wafer obtained by the present invention; Figure 2 is the dielectric temperature spectrum of the perovskite-type potassium sodium niobate-based ceramic wafer obtained by the present invention; Figure 3 is the ferroelectric hysteresis loop of the perovskite-type potassium sodium niobate-based ceramic wafer obtained by the present invention; Figure 4 is the statistical chart of the piezoelectric coefficient and Curie temperature of the temperature-stable potassium sodium niobate-based textured piezoelectric ceramic in Examples 1 to 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below through specific examples. These examples are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. The protection scope of the present invention is not limited to the following examples.

[0018] Example 1 A potassium sodium niobate-based piezoelectric ceramic with a high Curie temperature has a chemical general formula of 0.965(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 ) O 3 -0.035(Bi 1-x In x ) 0.5 Na 0.5 HfO 3 , 0.04 ≤ x ≤ 0.10, where x = 0.10. The specific preparation steps are as follows: (1) Calculation: Using K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Sb 2 O 3 , Bi 2 O 3 , HfO 2 , In 2 O 3 as raw materials, calculate the required mass of each raw material according to the chemical composition; (2) Batching: Place K 2 CO 3 and Na 2 CO 3 in an oven at 220 °C and dry for 2 h to remove moisture. Then weigh according to the calculated raw material mass, put it into a ball mill pot, use a mixture of zirconia beads with a mass ratio of 1:2 and diameters of 5 mm and 2 mm as ball milling beads, add anhydrous ethanol, and perform primary ball milling in a ball mill at a speed of 400 rpm for 15 h. Discharge and dry to obtain a powder base material; (3) Pre-sintering: Pack the powder base material obtained in step (2) into a crucible, compact it, cover the crucible lid, send it into a box-type muffle furnace at 900 °C, with a heating rate of 5 °C / min, pre-sinter for 6 h, and cool to room temperature with the furnace to obtain a pre-sintered dry material; (4) Secondary ball milling: Transfer the pre-sintered dry material obtained in step (3) into a ball mill pot, add anhydrous ethanol, and ball mill in a ball mill at a speed of 400 rpm for 15 h; (5) Drying and sieving: Put the slurry obtained in step (4) into an oven at 80 °C and bake for 2 h to dry. Grind the dried powder and sieve it through a 75-mesh sieve to obtain a powder with finer particle size and uniform particles; (6) Granulation: Add the powder obtained in step (5) into a polyvinyl alcohol solution with a mass fraction of 3%. Mix the powder and the polyvinyl alcohol solution evenly, place it in an oven at 80 °C for 2 h to dry, conduct grinding treatment and pass through a 75-mesh sieve; (7) Compression molding: Press the powder obtained in step (6) into shape using a mold to obtain a disc-shaped ceramic green body with a diameter of 10 mm and a thickness of 1 mm; (8) Debinding: Place the ceramic green body obtained in step (7) into a tube furnace at 650 °C with a heating rate of 3 °C / min and burn for 2 h for debinding treatment; (9) Two-step sintering: Place the ceramic green body obtained in step (8) into a tube furnace and quickly heat it to 1210 °C at a rate of 15 °C / min, hold for 5 min, then quickly cool it to 1100 °C and hold at this temperature for 20 h. After cooling to room temperature with the furnace, obtain the ceramic finished product; (10) Silver coating and firing: Conduct silver coating treatment on the ceramic finished product obtained in step (9) and hold at 600 °C for 30 min; (11) Poling: Immerse the ceramic sample obtained in step (10) in silicone oil at room temperature for 30 min for poling with a poling electric field of 2 kV / mm to obtain a perovskite-type potassium sodium niobate-based ceramic finished product. After poling, it can be subjected to performance testing after being placed for 24 h.

[0019] Example 2 A potassium sodium niobate-based piezoelectric ceramic with a high Curie temperature has a chemical general formula of 0.965(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 ) O 3 -0.035(Bi 1-x In x ) 0.5 Na 0.5 HfO 3 , 0.04 ≤ x ≤ 0.10, where x = 0.08, and the specific preparation steps are as follows: (1) Calculation: Based on K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Sb 2 O 3 , Bi 2 O 3 , HfO 2 , In 2 O 3Using [raw materials] as raw materials, calculate the required mass of each raw material according to the chemical composition; (2)Batching: Place K 2 CO 3 and Na 2 CO 3 in an oven at 200 °C for 5 h to remove moisture. Then, weigh according to the calculated raw material mass, put it into a ball milling tank, use a mixture of zirconia beads with a mass ratio of 1:2, diameters of 5 mm and 2 mm as ball milling beads, add anhydrous ethanol, and put it into a ball mill for the first ball milling at a speed of 600 rpm for 8 h. Discharge and dry to obtain a powder base material; (3)Pre-sintering: Pack the powder base material obtained in step (2) into a crucible, press it tightly, cover the crucible lid, send it into a box-type muffle furnace at 800 °C, with a heating rate of 5 °C / min, pre-sinter for 10 h, and cool to room temperature with the furnace to obtain a pre-sintered dry material; (4)Secondary ball milling: Transfer the pre-sintered dry material obtained in step (3) into a ball milling tank, add anhydrous ethanol, and ball mill in a ball mill at a speed of 600 rpm for 8 h; (5)Drying and sieving: Put the slurry obtained in step (4) into an oven at 90 °C and bake for 2 h to dry it. Grind the dried powder and pass it through a 75-mesh sieve to obtain a powder with finer particle size and uniform particles; (6)Granulation: Add a 3% polyvinyl alcohol solution to the powder obtained in step (5), mix the powder and the polyvinyl alcohol solution evenly, put it into an oven at 90 °C and bake for 2 h to dry it, and then grind and pass it through a 75-mesh sieve; (7)Pressing and forming: Use a mold to press and form the powder obtained in step (6) to obtain a circular ceramic green body with a diameter of 10 mm and a thickness of 1 mm; (8)Debinding: Put the ceramic green body obtained in step (7) into a tube furnace at 650 °C, with a heating rate of 3 °C / min, and burn for 2 h for debinding treatment; (9)Two-step sintering: Put the ceramic green body obtained in step (8) into a tube furnace, quickly heat it to 1210 °C at a rate of 15 °C / min and hold for 5 min, then quickly cool it to 1100 °C, hold at this temperature for 20 h, and cool to room temperature with the furnace to obtain a ceramic product; (10)Silver coating and firing: Perform silver coating treatment on the ceramic product obtained in step (9) and hold at 600 °C for 30 min; (11)Polarization: Immerse the ceramic sample obtained in step (10) in silicone oil at room temperature and polarize it for 30 min with a polarization electric field of 2 kV / mm to obtain a perovskite-type potassium sodium niobate-based ceramic product. After polarization, it can be placed for 24 h and then subjected to performance testing.

[0020] Example 3 A potassium sodium niobate-based piezoelectric ceramic with a high Curie temperature has a chemical general formula of 0.965(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 ) O 3 -0.035(Bi 1-x In x ) 0.5 Na 0.5 HfO 3 , 0.04 ≤ x ≤ 0.10, where x = 0.06, and the specific preparation steps are as follows: (1) Calculation: Using K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Sb 2 O 3 , Bi 2 O 3 , HfO 2 , In 2 O 3 as raw materials, calculate the required mass of each raw material according to the chemical composition; (2) Batching: Place K 2 CO 3 and Na 2 CO 3 in an oven and dry them at 200 °C for 5 h to remove moisture. Then weigh them according to the calculated raw material mass, put them into a ball mill jar, use a mixture of zirconia beads with a mass ratio of 1:2 and diameters of 5 mm and 2 mm as ball milling beads, add anhydrous ethanol, and carry out primary ball milling in a ball mill at a speed of 600 rpm for 8 h. Discharge and dry to obtain a powder base material; (3) Pre-sintering: Put the powder base material obtained in step (2) into a crucible, compact it, cover the crucible lid, send it into a box-type muffle furnace at 800 °C, with a heating rate of 5 °C / min, pre-sinter for 10 h, and cool to room temperature with the furnace to obtain a pre-sintered dry material; (4) Secondary ball milling: Transfer the pre-sintered dry material obtained in step (3) into a ball mill jar, add anhydrous ethanol, and ball mill in a ball mill at a speed of 600 rpm for 8 h; (5) Drying and sieving: Put the slurry obtained in step (4) into an oven and bake it at 90 °C for 2 h to dry it. Grind the dried powder and sieve it through a 75-mesh sieve to obtain a powder with finer particle size and uniform particles; (6) Granulation: Add the powder obtained in step (5) into a polyvinyl alcohol solution with a mass fraction of 3%. Mix the powder and the polyvinyl alcohol solution evenly, put it in an oven at 90 °C for 2 h to dry, conduct grinding treatment and pass through a 75-mesh sieve; (7) Compression molding: Press the powder obtained in step (6) into a mold to obtain a disc-shaped ceramic green body with a diameter of 10 mm and a thickness of 1 mm; (8) Debinding: Put the ceramic green body obtained in step (7) into a tubular furnace at 500 °C with a heating rate of 3 °C / min and burn for 3 h for debinding treatment; (9) Two-step sintering: Put the ceramic green body obtained in step (8) into a tubular furnace and rapidly heat it to 1180 °C at a rate of 10 °C / min, hold for 10 min, then rapidly cool it to 1100 °C, hold at this temperature for 20 h, and cool it to room temperature with the furnace to obtain a ceramic product; (10) Silver coating and firing: Conduct silver coating treatment on the ceramic product obtained in step (9) and hold at 500 °C for 30 min; (11) Poling: Immerse the ceramic sample obtained in step (10) in silicone oil at room temperature for 30 min for poling, with a poling electric field of 2 kV / mm, to obtain a perovskite-type potassium sodium niobate-based ceramic product. After poling, it can be placed for 24 h and then the performance can be tested.

[0021] Example 4 A potassium sodium niobate-based piezoelectric ceramic with a high Curie temperature has a chemical general formula of 0.965(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 ) O 3 -0.035(Bi 1-x In x ) 0.5 Na 0.5 HfO 3 , 0.04 ≤ x ≤ 0.10, where x = 0.04, and the specific preparation steps are as follows: (1) Calculation: Using K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Sb 2 O 3 , Bi 2 O 3 , HfO 2 , In 2 O 3Using [raw materials] as raw materials, calculate the required mass of each raw material according to the chemical composition; (2)Batching: Place K 2 CO 3 and Na 2 CO 3 in an oven at 250 °C and dry for 2 h to remove moisture. Then weigh according to the calculated raw material mass, put it into a ball milling tank, use a mixture of zirconia beads with diameters of 5 mm and 2 mm in a mass ratio of 1:2 as ball milling beads, add anhydrous ethanol, and perform primary ball milling in a ball mill at a speed of 400 rpm for 15 h. Discharge and dry to obtain a powder base material; (3)Pre-sintering: Put the powder base material obtained in step (2) into a crucible, compact it, cover the crucible lid, send it into a box-type muffle furnace at 900 °C, with a heating rate of 10 °C / min, pre-sinter for 10 h, and cool to room temperature with the furnace to obtain a pre-sintered dry material; (4)Secondary ball milling: Transfer the pre-sintered dry material obtained in step (3) into a ball milling tank, add anhydrous ethanol, and ball mill in a ball mill at a speed of 400 rpm for 15 h; (5)Drying and sieving: Put the slurry obtained in step (4) into an oven at 90 °C and bake for 2 h to dry. Grind the dried powder and pass it through a 75-mesh sieve to obtain a powder with finer particle size and uniform particles; (6)Granulation: Add a 3% by mass polyvinyl alcohol solution to the powder obtained in step (5), mix the powder and the polyvinyl alcohol solution evenly, put it into an oven at 90 °C and bake for 2 h to dry, perform grinding treatment and pass it through a 75-mesh sieve; (7)Pressing into shape: Press the powder obtained in step (6) into shape using a mold to obtain a disc-shaped ceramic green body with a diameter of 8 mm and a thickness of 1.5 mm; (8)Debinding: Put the ceramic green body obtained in step (7) into a tubular furnace at 700 °C, with a heating rate of 3 °C / min, and burn for 1 h for debinding treatment; (9)Two-step sintering: Put the ceramic green body obtained in step (8) into a tubular furnace and quickly heat it to 1210 °C at a rate of 15 °C / min, hold for 5 min, then quickly cool to 1070 °C, hold at this temperature for 10 h, and cool to room temperature with the furnace to obtain a ceramic product; (10)Silver coating and silver firing: Perform silver coating treatment on the ceramic product obtained in step (9) and hold at 700 °C for 20 min; (11)Polarization: Immerse the ceramic sample obtained in step (10) in silicone oil at room temperature and polarize it for 20 min with a polarization electric field of 4 kV / mm to obtain a perovskite-type potassium sodium niobate-based ceramic product. After polarization, it can be placed for 24 h and then subjected to performance testing.

[0022] Example 5 A potassium sodium niobate-based piezoelectric ceramic with a high Curie temperature has a chemical general formula of 0.965(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 ) O 3 -0.035(Bi 1-x In x ) 0.5 Na 0.5 HfO 3 , 0.04 ≤ x ≤ 0.10, where x = 0, and the specific preparation steps are as follows: (1) Calculation: Using K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Sb 2 O 3 , Bi 2 O 3 , and HfO as raw materials, calculate the required mass of each raw material according to the chemical composition; (2) Batching: Place K 2 CO 3 and Na 2 CO 3 in an oven and dry them at 200 °C for 5 h to remove moisture. Then, weigh them according to the calculated raw material mass, put them into a ball milling tank, use a mixture of zirconia beads with diameters of 5 mm and 2 mm in a mass ratio of 1:2 as ball milling beads, add anhydrous ethanol, and perform primary ball milling in a ball mill at a speed of 600 rpm for 8 h. Discharge and dry to obtain a powder base material; (3) Pre-sintering: Put the powder base material obtained in step (2) into a crucible, compact it, cover the crucible lid, send it into a box-type muffle furnace at 800 °C, with a heating rate of 5 °C / min, pre-sinter for 10 h, and cool it to room temperature with the furnace to obtain a pre-sintered dry material; (4) Secondary ball milling: Transfer the pre-sintered dry material obtained in step (3) into a ball milling tank, add anhydrous ethanol, and ball mill in a ball mill at a speed of 600 rpm for 8 h; (5) Drying and sieving: Put the slurry obtained in step (4) into an oven and bake it at 90 °C for 2 h to dry it. Grind the dried powder and sieve it through a 75-mesh sieve to obtain a powder with finer particle size and uniform particles; (6)Granulation: Add the powder obtained in step (5) to a polyvinyl alcohol solution with a mass fraction of 3%. Mix the powder and the polyvinyl alcohol solution evenly, place it in an oven at 90 °C for 2 h to dry, conduct grinding treatment and pass through a 75-mesh sieve; (7)Compression molding: Press the powder obtained in step (6) into a shape using a mold to obtain a disc-shaped ceramic green body. The diameter of the ceramic green body is 10 mm and the thickness is 1 mm; (8)Debinding: Place the ceramic green body obtained in step (7) into a tube furnace at 650 °C with a heating rate of 3 °C / min and burn for 2 h for debinding treatment; (9)Two-step sintering: Place the ceramic green body obtained in step (8) into a tube furnace and rapidly heat it to 1210 °C at a rate of 15 °C / min, hold for 5 min, then rapidly cool to 1100 °C, hold at this temperature for 20 h, and cool to room temperature with the furnace to obtain a ceramic product; (10)Silver coating and firing: Conduct silver coating treatment on the ceramic product obtained in step (9) and hold at 600 °C for 30 min; (11)Polarization: Immerse the ceramic sample obtained in step (10) in silicone oil at room temperature for polarization for 30 min, with a polarization electric field of 2 kV / mm, to obtain a perovskite-type sodium potassium niobate-based ceramic product. After polarization, it can be placed for 24 h and then performance testing can be carried out.

[0023] The analysis of the lead-free piezoelectric sodium potassium niobate prepared in Examples 1-5 is as follows Figure 1 is the X-ray diffraction pattern of the sodium potassium niobate-based ceramic discs sintered for the examples. As can be seen from the figure, all the samples of the examples are perovskite structures and there are no any impurity phases. At 2θ = 45.5 °, it can be seen that In 3+ The doping concentration of significantly affects the position and shape of the diffraction peaks, indicating that In 3+ doping generates a phase transformation. Figure 2 is the dielectric temperature spectrum measured for the ceramic discs prepared in the examples at a frequency of 1 kHz. It can be seen that the doping of In 3+ substitutes for part of Bi 3+ The main role is to increase the Curie temperature. The prepared samples have a relatively high Curie temperature, all above two hundred. At x in the range of 0.04 - 0.06, its Curie temperature increases with the increase of x , and the Curie temperature decreases in the range of 0.06 - 0.10. Among them, when x = 0.06, the Curie temperature reaches the maximum, reaching 287 °C. Figure 3 is the ferroelectric hysteresis loop of the ceramic discs prepared in the examples. From Figure 3It can be seen that the prepared samples exhibit a very saturated ferroelectric hysteresis loop, and the remanent polarization and saturation polarization are relatively large, so they have excellent ferroelectric properties. From Figure 4 it can be seen that after In 3+ doping replaces part of Bi 3+ , the Curie temperature increases, and at the same time, a relatively high piezoelectric constant can be ensured.

[0024] In summary, the potassium sodium niobate-based ceramics with a high Curie temperature provided by the present invention have excellent piezoelectric properties, a relatively high Curie temperature, and good temperature stability, and can be applied in the field of sensors. It is of great significance to replace lead-based piezoelectric ceramics in the future.

Claims

1. A perovskite-type potassium sodium niobate-based ceramic, characterized in that: General formula 0.965(K 0.48 Na 0.52 )(Nb 0.96 Sb 0.04 )O3-0.035(Bi 1-x In x )Na 0.5 HfO3, 0.04≤ x ≤0.

10.

2. The perovskite-type potassium sodium niobate-based ceramic according to claim 1, characterized in that: x = 0.06 or 0.

08.

3. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 1 or 2, characterized in that The following steps are involved: (1) Take K2CO3, Na2CO3, Nb2O5, Sb2O3, Bi2O3, HfO2 and In2O3 as raw materials and calculate the mass of each raw material required according to the chemical formula ratio; (2) Mixing: First, K2CO3 and Na2CO3 are dried separately, then mixed with other raw materials and initially ball-milled in a planetary ball mill to obtain a wet slurry; (3) Pre-sintering: drying the wet slurry obtained in step (2), sieving it, and performing primary sintering at 800-900°C for 6-10 hours, followed by cooling to room temperature to obtain pre-sintered dry material; (4) Secondary ball milling: The pre-sintered dry material obtained in step (3) is again ball milled using a planetary ball mill to obtain a wet slurry; (5) Drying and sieving: drying the wet slurry obtained in step (4) and sieving to obtain ceramic powder; (6) Granulation: Add 3%-4% polyvinyl alcohol solution by mass into the ceramic powder, stir evenly and then dry. The mass ratio of ceramic powder to polyvinyl alcohol solution is 10:

3. (7) Pressing: Grind and sieve the dried powder, press it into a ceramic body with a mold, and then keep it at 500-700 °C for 1-3 hours to debind; (8) Two-step sintering: the ceramic body obtained in step (7) is rapidly heated to 1180-1210°C at a rate of 10-15°C / min and kept at this temperature for 5-10 min, then cooled to 1070-1100°C and kept at this temperature for 10-20 h, and then cooled to room temperature in the furnace to obtain a ceramic sheet; (9) Silver coating: coating the ceramic sheet obtained in step (8) with silver paste and heating at 500-700°C for 20-30 min to sinter the silver, and then cooling the furnace to room temperature; (10) Polarization: The silver-coated ceramic sheet obtained in step (9) is polarized to obtain a perovskite-type potassium sodium niobate-based ceramic.

4. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 3, characterized in that: In the step (2) and the step (4), the planetary ball mill uses anhydrous ethanol as the ball milling medium, and the balls are mixed in a mass ratio of 1:2 of 5 mm diameter zirconia balls: 2 mm diameter zirconia balls. The raw materials: mixed balls: anhydrous ethanol are placed in a ball milling jar in a mass ratio of 1:8:5, and the ball mill is milled at a speed of 400-600 rpm for 8-15 hours.

5. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 3 or 4, characterized in that: The heating rate in steps (3), (7), (8) and (9) is 5-10°C / min.

6. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 5, characterized in that: In step (7), the mold is pressed into a ceramic body with a diameter of 8-10 mm and a thickness of 1-1.5 mm.

7. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 3 or 6, characterized in that: In the step (1), K2CO3 and Na2CO3 are dried at 200-250°C for 2-5 hours respectively.

8. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 7, characterized in that: In the steps (3), (5) and (6), the drying temperature is 80-90° C. and the drying time is 2-5 h.

9. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 3 or 8, characterized in that: In the steps (3), (5) and (7), the mixture is sieved through a 75-100 mesh screen.

10. The method for preparing a perovskite-type potassium sodium niobate-based ceramic according to claim 9, characterized in that: In the step (10), the polarization electric field is 2-4 kV / mm and the time is 20-30 min.

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