Preparation method of composite ion pair modified potassium-sodium niobate ceramic

Abstract

The invention provides a preparation method of composite ion pair modified potassium-sodium niobate ceramic, and relates to the technical field of functional ceramic. The chemical general formula of the composite ion pair modified potassium-sodium niobate ceramic is (K0. 5Na0. 5) 1-x (H-V) xNbO3, H-V is a composite ion pair, x is the mole fraction of the composite ion pair, and 0 lt; x is smaller than or equal to 0.05; the composite ion pair H-V is composed of a positive ion H and an equivalent A-site vacancy V, and is used for jointly replacing A-site (K0. 5Na0. 5) 1 + in the chemical general formula and keeping the electricity price balance of a crystal structure. The potassium-sodium niobate ceramic material disclosed by the invention has excellent piezoelectric property, and the maximum piezoelectric coefficient is about 560 pC / N. The performance index is far superior to the electrical performance of pure potassium sodium niobate ceramic, and is also superior to numerous commercial lead-containing PZT piezoelectric ceramics.

Description

Technical Field

[0001] This invention relates to the field of ceramic preparation technology, and more specifically, to a method for preparing composite ion-pair modified potassium sodium niobate ceramics. Background Technology

[0002] Sodium potassium niobate ceramic is a lead-free ferroelectric piezoelectric ceramic material with a high Curie temperature, dielectric constant, and piezoelectric coefficient. It also possesses certain mechanical strength and low dielectric loss, making it suitable for fabricating ceramic capacitors, microwave ceramics, thermistors, and low-temperature co-fired ceramics. However, compared to lead zirconate titanate piezoelectric ceramics, the piezoelectric properties of pure sodium potassium niobate ceramics are still relatively low, significantly limiting its application in high-tech consumer electronics. Therefore, optimizing and improving the piezoelectric properties of sodium potassium niobate ceramics is crucial for promoting their application.

[0003] Currently, numerous strategies are used to modulate and optimize the electrical properties of sodium potassium niobate ceramics, such as doping, defect engineering, phase boundary engineering, domain engineering, texturing, and rapid sintering. Among these, doping is the most effective and widely used method for optimizing the performance of sodium potassium niobate piezoelectric ceramics. This involves substituting other elements... K , Na , Nb Alternatively, combining it with other oxide systems can alter the phase structure of potassium sodium niobate piezoelectric ceramics, thereby controlling the microstructure and domain structure to optimize electrical properties. However, this method cannot achieve a comprehensive improvement in both the piezoelectric properties and temperature stability of potassium sodium niobate ceramics. Furthermore, the relatively complex chemical composition of these material systems places high demands on the reproducibility of the preparation process. Therefore, a method for preparing composite ion-pair modified potassium sodium niobate ceramics is proposed. Summary of the Invention

[0004] The purpose of this invention is to address the problems raised in the existing background technology. To achieve the above-mentioned objective, this invention provides the following technical solution: a composite ion-pair modified potassium sodium niobate ceramic, wherein the general chemical formula of the potassium sodium niobate ceramic material is (…). K 0.5 Na 0.5 ) 1-x ( H - V ) x NbO 3， in: H - V For precisely proportioned composite ion pairs, x The mole fraction of the component. x =0.01~0.05 ( x ≠0, excluding pure potassium sodium niobate ceramics); In the complex ion pair, H +2 valent metal ions or +3 valent rare earth metal ions: +2 valent metal ions are selected from... Zn 2+ , Mg 2+ , Ca 2+ One of them, the +3 rare earth metal ion is selected from Bi 3+ , Sm 3+ , Nd 3+ One of them; V for K + / Na + Co-vacancy, its vacancy concentration and H The valence states are strictly matched, forming a charge-balanced composite ion pair: when H When the oxidation state is +2, the complex ion pair is ( V 1 / 3 1- - H 2 / 3 2+ ), empty space and H The molar ratio of ions is 1:2; when H When the oxidation state is +3, the complex ion pair is ( V 1 / 2 1- - H 1 / 2 3+ ), empty space and H The molar ratio of the ions is 1:1; The ceramic has an orthogonal-tetragonal phase transition temperature ≥210℃, a Curie temperature ≥405℃, and a maximum piezoelectric coefficient. d 33 ≥560 PC / N Residual polarization intensity ≥15.69 μC / cm 2 Fracture toughness ≥1.8 MPa · m 1 / 2 , in 10 7 The piezoelectric performance degradation rate after each cycle of loading is ≤3%.

[0005] A method for preparing composite ion-pair modified potassium sodium niobate ceramics includes the following steps: Step 1, Precise Pretreatment of Raw Materials: Verify the purity of all chemical reagents and pretreat them to remove impurities and hygroscopic components; Step 2, Integrated preparation of graded ball milling and pre-calcination powder: Through two-stage ball milling and staged calcination, the raw materials are refined and reacted in the solid phase; Step 3, Powder Plasma Surface Modification: Optimize the surface properties of powder through plasma treatment to improve compatibility with subsequent processing; Step 4: Composite adhesive granulation and gradient pressure molding: Prepare uniform granular powder and obtain a preliminary molded body by gradient pressure; Step 5: Gradient drying and cooling pre-densification of the preform: Removes moisture and increases the density of the preform, reducing sintering defects; Step 6: Multi-stage temperature rise, binder removal, sintering, and intermediate heat preservation: Thoroughly remove organic matter and optimize the grain growth basis through intermediate heat preservation; Step 7, Dynamic Atmosphere Powder Burial and Co-sintering: Densification sintering is completed under controlled atmosphere to suppress component volatilization and abnormal grain growth; Step 8: Stepped annealing for enhanced segmented pulse polarization stability: Eliminates internal stress, optimizes piezoelectric properties, and improves long-term stability; Step 9, Precision processing, performance calibration, and vacuum packaging after sintering: Surface finishing and performance screening are performed to ensure product consistency.

[0006] As a preferred technical solution of the present invention, in step 1, the precise pretreatment of raw materials: Raw material purity verification: Inductively coupled plasma mass spectrometry (ICP-MS) was used. ICP - MS ) detection Na 2 CO 3. K 2 CO 3. Nb 2 O 5. The purity of the doped metal oxides must be ensured, with the main component purity ≥ 99.9% and the content of a single impurity element ≤ 50%. ppm ; Moisture removal treatment: Na 2 CO 3. K 2 CO 3. Place in a vacuum drying oven at 120℃ and a vacuum degree ≤ -0.095. MPa Dry under the conditions for 8-10 days h ;Will Nb 2 O 5 and doped metal oxides ( ZnO , Bi 2 O 3) Place in a muffle furnace and keep warm at 300℃ for 4 hours. h Remove adsorbed water and crystal water; Crushing of lumpy raw materials: For agglomerated or lumpy raw materials, a planetary crusher is used to crush them to a particle size ≤1 mm. mmThen, the raw materials are screened through a 100-mesh sieve to ensure uniform particle size and avoid uneven mixing during ball milling. Accurate ingredient weighing: Ingredients are weighed using a 0.01 g electronic balance according to the general chemical formula, with a weighing error ≤ ±0.1 g. wt After weighing, the raw materials are sealed in batches and stored in a desiccator to prevent moisture absorption from affecting the accuracy of the proportions.

[0007] As a preferred technical solution of the present invention, in step 2, the integrated powder preparation of graded ball milling and pre-calcination: The first stage is wet ball milling: using anhydrous ethanol as the dispersion medium (liquid-to-solid ratio 2:1, volume-to-mass ratio), adding 0.1–0.3... wt % polyethylene glycol ( PEG -6000) was used as the dispersant, and alumina balls (particle size 5-8) were used. mm The grinding media is 10:1 to 15:1, and the rotation speed is 200 to 300 rpm. r / min Ball milling time 8-12 h During the ball milling process, every 2 h 10 shutdowns min To avoid excessively high slurry temperature, the slurry particle size should be controlled between 5 and 10 mm after ball milling. μm This achieves preliminary mixing and coarsening of raw materials; Intermediate pretreatment: The slurry after the first stage ball milling is transferred to a rotary evaporator at 60–70°C and a vacuum degree ≤-0.09. MPa Concentrate the slurry to a solid content ≥70% under certain conditions, then transfer it to a vacuum drying oven at 80℃ for 12-16 minutes. h After drying, the material is crushed using a high-speed pulverizer and passed through a 200-mesh sieve to remove particles with a diameter ≥75. μm Aggregated particles; The second stage is high-energy ball milling: the pretreated intermediate is transferred to a high-energy ball mill using zirconia beads (particle size 1-3 mm). mm The grinding media is 20:1 to 25:1, and the rotation speed is 400 to 500 rpm. r / min Ball milling time 15-20 minutes h During ball milling, circulating cooling water is introduced to control the slurry temperature to ≤40℃; after ball milling, the powder particle size is refined to 1-3 mm. μm Furthermore, the composite ion pair precursor is uniformly dispersed in the powder without local agglomeration. Segmented calcination: The powder after high-energy ball milling is loaded into an alumina crucible and placed in a box-type resistance furnace; the first stage is held at 600-700℃ for 2-3 hours. h Heating rate 5℃ / min The first stage removes residual dispersion medium and adsorbed water; the second stage involves heating to 820–860℃ at a rate of 3℃ / ℃. min Insulate for 3-5 days h The solid-state reaction is completed to produce single-phase perovskite structure powder; after calcination, it is cooled to room temperature in the furnace to avoid rapid cooling that could cause lattice defects in the powder.

[0008] As a preferred technical solution of the present invention, in step 3, powder plasma surface modification: Pretreatment: The calcined powder is spread evenly on the sample holder of the plasma processing chamber, with a thickness of 1-2 mm. mm To avoid excessive powder buildup leading to uneven processing; Plasma processing parameters: Argon gas as carrier gas, purity ≥ 99.99%, carrier gas flow rate 10–15. sccm ;Pour in 5-10 vol % oxygen is used as the reactant gas, and the total gas flow rate is 20-30. sccm Processing power 100-150 W Processing time: 10-20 minutes min During the process, the vacuum level of the cavity is maintained at 10–20. Pa ; Processing effect: Through plasma etching and oxidation, a hydroxylation layer is formed on the powder surface (- OH This process enhances the hydrophilicity of the powder surface, resulting in a contact angle ≤30°. Simultaneously, it removes residual organic matter from the powder surface, improving the interfacial compatibility between the powder and the binder, as well as the subsequent sintering activity, thereby increasing the sintering driving force by more than 15%.

[0009] As a preferred technical solution of the present invention, in step 4, during the gradient pressure molding of composite adhesive granulation: Preparation of composite adhesive: Polyvinyl alcohol (VALO) PVA (degree of polymerization 1750±50) and polyethylene glycol ( PEG Mix (-4000) at a mass ratio of 8:2 to 7:3, and add deionized water to prepare a solution of 5-8... wt A % aqueous solution was stirred in an 80°C water bath for 30–60 minutes. min Dissolve completely and cool to room temperature for later use; Mixing and granulation: The modified powder and the composite binder aqueous solution are added to a twin-screw mixer in a certain proportion. The mixing temperature is 60-80℃ and the speed is 50-80. r / min Mixing time 30-60 minutes min Uniform spherical particles are formed through shearing and kneading; after granulation, the particles are screened through a double-layer sieve of 100 mesh and 200 mesh to control the particle size within 100–200 mm. μm Large particles on the sieve are crushed and regranulated, while fine powder under the sieve is recycled and reused. Gradient pressure molding: The screened granules are loaded into a circular mold (10-50 mm in diameter). mm Place it on a hydraulic forming machine; apply 50-80 g / m² of pressure in the first stage. MPa Preload 30-60 s The first stage removes air from between particles; the second stage uses 20-30... MPa / min The rate is gradually increased to 150-250. MPa Hold pressure for 2-3 seconds. min This ensures the particles are tightly bound together; preheating the mold during molding (40–60℃) reduces interfacial stress between the binder and the powder, preventing cracks or delamination in the preform; the diameter deviation of the preform after molding is ≤±0.1 mm. mm Thickness deviation ≤ ±0.05 mm .

[0010] As a preferred technical solution of the present invention, in step 5, gradient drying-cooling and pre-densification of the embryo: Gradient temperature drying: The molded preform is placed in a forced-air drying oven, and a three-stage temperature increase is adopted: room temperature 60℃ (heating rate 5~10℃ / h ), insulation 2 h 60℃→90℃ (heating rate 10℃ / h ), insulation 3 h ; 90℃→120℃ (heating rate 15℃ / h Insulation 4-6 h During the drying process, regular ventilation is required to remove moisture and prevent cracking caused by inconsistent drying rates between the surface and interior of the embryo; the moisture content of the embryo after drying should be ≤0.5%. Cooling and pre-densification: The dried preform is sealed with a polyethylene film and placed in the high-pressure chamber of a cooling press, using nitrogen (purity ≥99.9%) as the pressure medium; first, at 50... MPa / min The rate of boosting to 100 MPa , holding pressure 2 min Then 30 MPa / min The rate of voltage boosting is 300-400 MPa Hold pressure 5-10 min Finally, with 50 MPa / min The pressure was released to atmospheric pressure at a certain rate; after pre-densification, the density of the preform increased from 60%–65% after molding to 75%–80%, the internal porosity was ≤20%, and the pores were uniformly distributed with no obvious large-sized pores (pore diameter ≤1). μm ).

[0011] As a preferred technical solution of the present invention, step 6 involves multi-segment programmed heating and binder removal followed by intermediate heat preservation during sintering. Multi-stage temperature-controlled debinding: The pre-densified preform is placed in an alumina boat and then into a tube furnace; the first stage is at room temperature of 200℃ (heating rate 5℃ / ...). min ), insulation 1 h Remove free water from the embryo; second stage: 200℃ to 300℃ (heating rate 3℃ / min ), insulation 2 h Preliminary decomposition PVA Adhesive (decomposition rate ≥60%); Third stage 300℃ to 550~580℃ (heating rate 2℃ / min Insulation 6-10 h Completely decomposes adhesives and residual organic matter (total decomposition rate ≥99%); air is introduced during the adhesive discharge process (flow rate 0.5). L / min ), taking away the decomposition products ( CO 2. H 2 O To avoid product residue causing ceramic contamination; Sintering Intermediate Temperature Insulation: After the binder is removed, maintain a temperature of 3℃ / min The temperature is increased to 900℃ at a certain rate and held for 1-2 hours. h The process involves holding the powder particles at a constant temperature during sintering. This step helps to homogenize the internal temperature of the pellet, reducing stress caused by temperature gradients. It also promotes diffusion on the surface of powder particles, forming initial neck bonding, laying a uniform foundation for grain growth during subsequent high-temperature sintering, and preventing abnormal grain growth at high temperatures.

[0012] As a preferred technical solution of the present invention, in step 7, dynamic atmosphere-powder co-sintering: Powder preparation: Pre-fired powder with the same composition as ceramic powder (calcined at 820-860℃ for 3 minutes) h ) and 5-10 wt %of ZrO 2. Powder (particle size 1-3) μm Mix thoroughly and use as a embedding powder; ZrO 2. The powder can reduce the interfacial adhesion between the powder and the ceramic body, thus playing an anti-sticking role; Powder embedding process: Place the preform, which has undergone intermediate heat preservation, into an alumina crucible, and fill the surrounding area with powder. The powder thickness should be 3 to 5 times the thickness of the ceramic preform, ensuring that the preform is completely covered by the powder to reduce the risk of sintering defects. K , Na The volatilization of elements; Dynamic mixing atmosphere control: adopts O 2 and N The ratio of the 2-gas mixture is precisely controlled by a mass flow controller: Early stage of sintering (room temperature ~ 900℃): O 2: N2:4:6 (volume ratio), gas flow rate 0.5~1 L / min This promotes the complete oxidation of residual organic matter; Mid-sintering stage (900℃~1100℃): O 2: N 2:3:7 (volume ratio), gas flow rate 0.8~1.2 L / min To balance grain growth and compositional stability; Later stage of sintering (from 1100℃ to cooling down to 600℃): O 2: N 2:8 (volume ratio), gas flow rate 0.5~1 L / min ,inhibition K , Na Elemental volatilization and the generation of lattice oxygen defects; Warm sintering process: After intermediate heat preservation, sinter at 2-3℃ / min The temperature is increased to 1080–1100℃ at a rate of [unspecified rate], and held for 3–4 [unspecified periods]. h During the heat preservation process, every 1 h Record the furnace temperature once, and control the temperature fluctuation within ±5℃; after sintering, maintain a temperature of 5℃ / min The temperature was reduced to 600℃ at a rate of [missing information], and then cooled to room temperature in the furnace; finally, a ceramic green body with a density ≥97% and uniform grain size (1-3 [missing information]) was obtained. μm No obvious abnormally large grains (grain size ≤5) μm ).

[0013] As a preferred technical solution of the present invention, in step 8, stepped annealing-segmented pulse polarization-stability enhancement: Stepped annealing: The sintered ceramic green body is placed in a box-type resistance furnace and annealed in three stages: holding at 300℃ for 3 minutes. h (Heating rate 5℃ / min ), 400℃ heat preservation 2 h (Heating rate 3℃ / min ), 600℃ heat preservation 1 h (Heating rate 2℃ / min ); then at 5℃ / min The rate of annealing is as the furnace cools to room temperature; the thermal stress and lattice distortion generated during annealing are eliminated, lattice integrity is improved by more than 20%, and the fracture toughness of the ceramic increases from 1.5... MPa · m 1 / 2 Increase to ≥1.8 MPa · m 1 / 2 ; Segmented pulse polarization process: Pretreatment before polarization: The annealed ceramic blank is polished on both sides to remove the surface oxide layer, coated with silver paste, and fired at 600℃ for 30 minutes. min To form electrodes; Polarizing medium: High-temperature silicone oil (temperature 120~140℃) is used, and the insulation resistance of the silicone oil is ≥10. 12 Ω · cm ; Polarization steps: First stage applies 2 kV / mm Pre-polarization voltage, heat preservation 5 min This allows for the initial orientation of the electrical domains within the ceramic; the second stage uses 0.5... kV / mm The increment gradually increases to 3-5 kV / mm Maintain a pulse frequency of 50-100. Hz (Pulse duty cycle 50%), polarization time 15–20 seconds min This promotes the complete directional alignment of electric domains; the third stage reduces the voltage to 2. kV / mm Insulation 5 min Then slowly cut off the power (voltage reduction rate 0.2). kV / mm · min ), and allow to cool naturally to room temperature in silicone oil; Stability enhancement: The polarized ceramic was placed in a constant temperature and humidity chamber and aged for 24 hours at 85℃ and 85% relative humidity. h Products with stable performance are selected through accelerated aging; the piezoelectric coefficient after aging d 33 With a decay rate of ≤1%, the ceramic material is guaranteed to maintain long-term stability under harsh environments. Step 9: Precision processing after sintering - performance calibration - vacuum packaging in progress. Precision surface grinding and polishing: A two-step polishing method is used: The first step uses diamond polishing paste (particle size 1-5). μm Mechanical grinding on a grinding machine at a speed of 300-500 rpm. r / min Grinding pressure: 0.1–0.2 MPa The first step is to remove impurities and unevenness from the electrode layer surface; the second step is to use colloidal silica polishing slurry (particle size 50-100 μm). nm Perform chemical mechanical polishing at a speed of 800–1000 rpm. r / min Polishing pressure: 0.05–0.1 rpm MPa Polishing time 30-60 seconds minSurface roughness of ceramics after polishing Ra ≤0.05 μm , parallelism ≤ 0.01 mm Flatness ≤ 0.005 mm ; Multi-dimensional performance calibration: The polished ceramic was placed in a high-precision piezoelectric performance testing system and tested at 25℃ and 50% relative humidity: piezoelectric coefficient d 33 (Error ≤ ±1) PC / N ), dielectric constant ε r With dielectric loss tanδ (1) kHz (Lower), Residual Polarization Intensity P r The piezoelectric coefficient was tested at -50℃, 0℃, 100℃, and 200℃. d 33 Ensure that temperature stability meets the standards; eliminate products whose deviation from any performance indicator exceeds ±2%; Vacuum sealing: Pack qualified products in polyester film, place them in a vacuum packaging machine, and evacuate to a vacuum level of ≤-0.095. MPa The product is sealed and encapsulated; after encapsulation, it is stored in a dry environment (humidity ≤30%) to avoid surface oxidation or moisture absorption that could affect its performance.

[0014] Compared with existing technologies, the beneficial effects of this invention are as follows: The potassium sodium niobate ceramic material of this invention achieves excellent ferroelectric dielectric properties. By controlling the composition and content of the composite ion pairs, a saturated hysteresis loop is obtained, with a maximum polarization intensity and a remanent polarization intensity of 22.94. μC / cm 2 and 15.69 μC / cm 2 The dielectric constant is approximately 4866, and the orthorhombic-tetragonal phase transition temperature is increased to 210°C. C Curie temperature rises to 405°C C These findings are beneficial for optimizing the piezoelectric activity of materials, thereby obtaining a potassium sodium niobate ceramic material with excellent piezoelectric properties.

[0015] The potassium sodium niobate ceramic material of this invention exhibits excellent piezoelectric properties, with a maximum piezoelectric coefficient of approximately 560. PC / N These performance indicators far exceed the electrical properties of pure potassium sodium niobate ceramics, and are also superior to many commercially available lead-containing ceramics. PZTPiezoelectric ceramics. This novel potassium sodium niobate ceramic material is expected to replace traditional lead-containing piezoelectric ceramic materials and be applied in a new generation of miniature, lightweight, highly sensitive, and high-precision electronic information devices, making an important contribution to the development of information technology and society in the new era. Attached Figure Description

[0016] Picture 1 The potassium sodium niobate ceramics obtained in Examples 1-4 XRD Figure, in which ( a ) is 2 θ ~20-80° XRD Full spectrum, ( b ) is 2 θ ~45° magnified view of a specific area.

[0017] Picture 2 The potassium sodium niobate ceramics obtained in Examples 1-4 SEM picture.

[0018] Picture 3 The dielectric properties of the potassium sodium niobate ceramics obtained in Examples 1-4 are shown in the diagram.

[0019] Picture 4 The phase transition temperatures are the potassium sodium niobate ceramics obtained in Examples 1-4.

[0020] Picture 5 The hysteresis loops of the potassium sodium niobate ceramics obtained in Examples 1-4 are shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely illustrates some embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features and technical solutions in the embodiments of the present invention can be combined with each other. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0023] Example 1 This embodiment provides a ( K 0.5 Na0.5 ) NbO 3. The preparation method of ceramic materials, the specific steps are as follows: (1) Powder preparation: Weigh out according to the chemical formula of potassium sodium niobate ceramic. Na 2 CO 3. K 2 CO 3. Nb 2 O 5. Chemical reagents: First, ball mill the weighed raw materials, then dry the resulting slurry, and finally calcine it at 800°C. C Insulation 2 h (2) Granulation and tableting: The above powder is mixed with 5 wt After grinding and mixing the % concentration of polyvinyl alcohol adhesive, it was dried. Then, the dried powder was placed in a mold and subjected to a 150°C test. MPa The ceramic blank is formed by dry pressing; (3) Debinding and sintering: Place the ceramic body in a high-temperature furnace and slowly heat it to 600°C. C Insulation 4 h The sample was then subjected to a debinding process; the debinded sample was then subjected to powder embedding and sintering at a temperature of 1100°C. C Insulation 4 h Round ceramic discs are produced by sintering powder.

[0024] Experimental results show that: The ceramic samples at room temperature exhibited an orthorhombic phase structure with no impurities present; the ceramic grain size was approximately 1.04 mm. μm The maximum dielectric constant of the ceramic is 4823; the orthorhombic-tetragonal phase transition temperature and Curie temperature of the ceramic are 198°C and 198°C, respectively. C and 396° C The hysteresis loop of ceramics does not exhibit a relatively regular shape; the piezoelectric coefficient of ceramics is 168; ceramics XRD The results are as follows Picture 1 The curve shown in Example 1 is for ceramics. SEM The results are as follows Picture 2 middle( a As shown in the figure; the dielectric temperature spectrum of the ceramic is as follows. Picture 3 middle( a As shown in the figure; the orthorhombic-tetragonal phase transformation temperature and Curie temperature of ceramics are as follows. Picture 4 Data from Example 1; Ferroelectric properties of the ceramic, such as Picture 5 As shown in Example 1.

[0025] Example 2: This embodiment provides a ( K 0.5 Na 0.5 )0.995 ( Bi - V ) 0.005 NbO 3. The preparation method of ceramic materials, the specific steps are as follows: (1) Powder preparation: Weigh out according to the chemical formula of potassium sodium niobate ceramic. Na 2 CO 3. K 2 CO 3. Bi 2 O 3. Nb 2 O 5. Chemical reagents: First, ball mill the weighed raw materials, then dry the resulting slurry, and finally calcine it at 850°C. C Insulation 6 h (2) Granulation and tableting: The above powder is mixed with 10 wt The polyvinyl alcohol adhesive of a certain concentration was ground, mixed thoroughly, and dried. The dried powder was then placed in a mold and subjected to a 100% [method / process]. MPa The ceramic blank is formed by dry pressing; (3) Debinding and sintering: Place the ceramic body in a high-temperature furnace and slowly heat it to 550°C. C Insulation 20 h The sample underwent debinding treatment; after debinding, it was subjected to powder embedding and sintering treatment at a temperature of 1080°C. C Insulation 6 h Round ceramic discs are produced by sintering powder.

[0026] Experimental results show that: The ceramic samples at room temperature exhibited an orthorhombic phase structure with no impurities present; the ceramic grain size was approximately 2.53 mm. μm The maximum dielectric constant of the ceramic is 4404; the orthorhombic-tetragonal phase transition temperature and Curie temperature of the ceramic are 205°C. C and 403° C The hysteresis loop of the ceramic does not exhibit a regular shape; the piezoelectric coefficient of the ceramic is 144; ceramic XRD The results are as follows Picture 1 The curve shown in Example 2 is for ceramics. SEM The results are as follows Picture 2 middle( b As shown in the figure; the dielectric temperature spectrum of the ceramic is as follows. Picture 3 middle( b As shown in the figure; the orthorhombic-tetragonal phase transformation temperature and Curie temperature of ceramics are as follows. Picture 4 Data from Example 2; Ferroelectric properties of the ceramic, such as Picture 5 As shown in Example 2.

[0027] Example 3: This embodiment provides a ( K 0.5 Na 0.5 ) 0.99 ( Zn - V ) 0.01 NbO 3. The preparation method of ceramic materials, the specific steps are as follows: (1) Powder preparation: Weigh out according to the chemical formula of potassium sodium niobate ceramic. Na 2 CO 3. K 2 CO 3. ZnO , Nb 2 O 5. Chemical reagents: First, ball mill the weighed raw materials, then dry the milled slurry, and finally calcine it at 820°C. C Insulation 4 h (2) Granulation and tableting: The above powder is mixed with 8 wt The polyvinyl alcohol adhesive of a certain concentration was ground, mixed thoroughly, and dried. The dried powder was then placed in a mold and subjected to a 240°C process. MPa The ceramic blank is formed by dry pressing; (3) Debinding and sintering: Place the ceramic body in a high-temperature furnace and slowly heat it to 500°C. C Insulation 8 h The sample underwent debinding treatment; after debinding, it was subjected to powder embedding and sintering treatment at a temperature of 1060°C. C Insulation 2 h Round ceramic discs are produced by sintering powder.

[0028] Experimental results show that: The ceramic samples at room temperature exhibited an orthorhombic phase structure with no impurities present; the ceramic grain size was approximately 3.11 mm. μm The maximum dielectric constant of the ceramic is 3305; the orthorhombic-tetragonal phase transition temperature and Curie temperature of the ceramic are 210°C. C and 405° C The hysteresis loop of the ceramic is rectangular in shape, with a maximum polarization and a remanent polarization of 22.94. μC / cm 2 and 15.69 μC / cm 2 The piezoelectric coefficient of the ceramic is 560; ceramic XRD The results are as follows Picture 1 The curve shown in Example 3 is for ceramics. SEM The results are as follows Picture 2 middle(c As shown in the figure; the dielectric temperature spectrum of the ceramic is as follows. Picture 3 middle( c As shown in the figure; the orthorhombic-tetragonal phase transformation temperature and Curie temperature of ceramics are as follows. Picture 4 Data from Example 3; Ferroelectric properties of the ceramic, such as Picture 5 As shown in Example 3.

[0029] Example 4: This embodiment provides a ( K 0.5 Na 0.5 ) 0.95 ( Sm - V ) 0.05 NbO 3. The preparation method of ceramic materials, the specific steps are as follows: (1) Powder preparation: Weigh out according to the chemical formula of potassium sodium niobate ceramic. Na 2 CO 3. K 2 CO 3. Sm 2 O 3. Nb 2 O 5. Chemical reagents: First, ball mill the weighed raw materials, then dry the resulting slurry, and finally calcine it at 880°C. C Insulation 3 h (2) Granulation and tableting: The above powder is mixed with 6 wt The polyvinyl alcohol adhesive of a certain concentration was ground, mixed thoroughly, and dried. The dried powder was then placed in a mold and subjected to a 300-degree rotation. MPa The ceramic blank is formed by dry pressing; (3) Debinding and sintering: Place the ceramic body in a high-temperature furnace and slowly heat it to 550°C. C Insulation 10 h The sample underwent debinding treatment; after debinding, it was subjected to powder embedding and sintering treatment at a temperature of 1120°C. C Insulation 3 h Round ceramic discs are produced by sintering powder.

[0030] Experimental results show that: The ceramic samples at room temperature exhibited an orthorhombic phase structure with no impurities present; the ceramic grain size was approximately 3.35 mm. μm The maximum dielectric constant of the ceramic is 4866; the orthorhombic-tetragonal phase transition temperature and Curie temperature of the ceramic are 200°C. C and 399° C The hysteresis loop of ceramics does not exhibit a relatively regular shape; the piezoelectric coefficient of ceramics is 242; ceramics XRD The results are as follows Picture 1 The curve shown in Example 4 is for ceramics. SEM The results are as follows Picture 2 middle( d As shown in the figure; the dielectric temperature spectrum of the ceramic is as follows. Picture 3 middle( d As shown in the figure; the orthorhombic-tetragonal phase transformation temperature and Curie temperature of ceramics are as follows. Picture 4 Data from Example 4; Ferroelectric properties of the ceramic, such as Picture 5 As shown in Example 4.

[0031] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described herein. Although the present invention has been described in detail with reference to the above embodiments, the present invention is not limited to the specific embodiments described above. Therefore, any modifications or substitutions to the present invention, as well as all technical solutions and improvements that do not depart from the spirit and scope of the invention, are covered within the scope of the claims of the present invention.

Claims

1. A composite ion-pair modified potassium sodium niobate ceramic, characterized in that, The general chemical formula of the potassium sodium niobate ceramic material is ( K 0.5 Na 0.5 ) 1-x ( H - V ) x NbO 3， in: H - V For precisely proportioned composite ion pairs, x The mole fraction of the component. x =0.01~0.05 ( x ≠0, excluding pure potassium sodium niobate ceramics); In the complex ion pair, H +2 valent metal ions or +3 valent rare earth metal ions: +2 valent metal ions are selected from... Zn 2+ , Mg 2+ , Ca 2+ One of them, the +3 rare earth metal ion is selected from Bi 3+ , Sm 3+ , Nd 3+ One of them; V for K + / Na + Co-vacancy, its vacancy concentration and H The valence states are strictly matched, forming a charge-balanced composite ion pair: when H When the oxidation state is +2, the complex ion pair is ( V 1 / 3 1- - H 2 / 3 2+ ), empty space and H The molar ratio of the ions is 1:2; when H When the oxidation state is +3, the complex ion pair is ( V 1 / 2 1- - H 1 / 2 3+ ), empty space and H The molar ratio of the ions is 1:1; The ceramic has an orthogonal-tetragonal phase transition temperature ≥210℃, a Curie temperature ≥405℃, and a maximum piezoelectric coefficient. d 33 ≥560 pC / N Residual polarization intensity ≥15.69 μC / cm 2 Fracture toughness ≥1.8 MPa · m 1 / 2 , in 10 7 The piezoelectric performance degradation rate after each cycle of loading is ≤3%.

2. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 1, characterized in that, Includes the following steps: Step 1, Precise Pretreatment of Raw Materials: Verify the purity of all chemical reagents and pretreat them to remove impurities and hygroscopic components; Step 2, Integrated preparation of graded ball milling and pre-calcination powder: Through two-stage ball milling and staged calcination, the raw materials are refined and reacted in the solid phase; Step 3, Powder Plasma Surface Modification: Optimize the surface properties of powder through plasma treatment to improve compatibility with subsequent processing; Step 4: Composite adhesive granulation and gradient pressure molding: Prepare uniform granular powder and obtain a preliminary molded body by gradient pressure; Step 5: Gradient drying and cooling pre-densification of the preform: Removes moisture and increases the density of the preform, reducing sintering defects; Step 6: Multi-stage temperature rise, binder removal, sintering, and intermediate heat preservation: Thoroughly remove organic matter and optimize the grain growth basis through intermediate heat preservation; Step 7, Dynamic Atmosphere Powder Burial and Co-sintering: Densification sintering is completed under controlled atmosphere to suppress component volatilization and abnormal grain growth; Step 8: Stepped annealing for enhanced segmented pulse polarization stability: Eliminates internal stress, optimizes piezoelectric properties, and improves long-term stability; Step 9, Precision processing, performance calibration, and vacuum packaging after sintering: Surface finishing and performance screening are performed to ensure product consistency.

3. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 2, characterized in that, Step 1: Precise pretreatment of raw materials Raw material purity verification: Inductively coupled plasma mass spectrometry (ICP-MS) was used. ICP - MS ) detection Na 2 CO 3. K 2 CO 3. Nb 2 O 5. The purity of the doped metal oxides must be ensured, with the main component purity ≥ 99.9% and the content of a single impurity element ≤ 50%. ppm ; Moisture removal treatment: Na 2 CO 3. K 2 CO 3. Place in a vacuum drying oven at 120℃ and a vacuum degree ≤ -0.

095. MPa Dry under the conditions for 8-10 days h ;Will Nb 2 O 5 and doped metal oxides ( ZnO , Bi 2 O 3) Place in a muffle furnace and keep warm at 300℃ for 4 hours. h Remove adsorbed water and crystal water; Crushing of lumpy raw materials: For agglomerated or lumpy raw materials, a planetary crusher is used to crush them to a particle size ≤1 mm. mm Then, the raw materials are screened through a 100-mesh sieve to ensure uniform particle size. Accurate ingredient weighing: Ingredients are weighed using a 0.01 g electronic balance according to the general chemical formula, with a weighing error ≤ ±0.1 g. wt After weighing, the raw materials are sealed and stored in a desiccator in batches.

4. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 3, characterized in that, Step 2: Integrated powder preparation via classifying ball milling and pre-calcination. The first stage is wet ball milling: using anhydrous ethanol as the dispersion medium (liquid-to-solid ratio 2:1, volume-to-mass ratio), adding 0.1–0.3... wt % polyethylene glycol ( PEG -6000) was used as the dispersant, and alumina balls (particle size 5-8) were used. mm The grinding media is 10:1 to 15:1, and the rotation speed is 200 to 300 rpm. r / min Ball milling time 8-12 h During the ball milling process, every 2 h 10 shutdowns min The particle size of the slurry after ball milling is controlled at 5-10 mm. μm The raw materials are initially mixed and refined. Intermediate pretreatment: The slurry after the first stage ball milling is transferred to a rotary evaporator at 60–70°C and a vacuum degree ≤-0.

09. MPa Concentrate the slurry to a solid content ≥70% under certain conditions, then transfer it to a vacuum drying oven at 80℃ for 12-16 minutes. h ; After drying, the material is crushed using a high-speed pulverizer and passed through a 200-mesh sieve to remove particles with a diameter ≥75. μm Aggregated particles; The second stage is high-energy ball milling: the pretreated intermediate is transferred to a high-energy ball mill using zirconia beads (particle size 1-3 mm). mm The grinding media is 20:1 to 25:1, and the rotation speed is 400 to 500 rpm. r / min Ball milling time 15-20 minutes h During ball milling, circulating cooling water is introduced to control the slurry temperature to ≤40℃; after ball milling, the powder particle size is refined to 1-3 mm. μm Furthermore, the composite ion pair precursor is uniformly dispersed in the powder without local agglomeration. Segmented calcination: The powder after high-energy ball milling is loaded into an alumina crucible and placed in a box-type resistance furnace; the first stage is held at 600-700℃ for 2-3 hours. h Heating rate 5℃ / min Remove residual dispersion medium and adsorbed water; The second stage involves heating to 820–860℃ at a rate of 3℃ / ℃. min Insulate for 3-5 days h The solid-phase reaction is completed to produce single-phase perovskite structure powder; after calcination, it is cooled to room temperature in the furnace.

5. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 4, characterized in that, Step 3: Surface modification of powder plasma: Pretreatment: The calcined powder is spread evenly on the sample holder of the plasma processing chamber, with a thickness of 1-2 mm. mm To avoid excessive powder buildup leading to uneven processing; Plasma processing parameters: Argon gas as carrier gas, purity ≥ 99.99%, carrier gas flow rate 10–15. sccm ;Pour in 5-10 vol % oxygen is used as the reactant gas, and the total gas flow rate is 20-30. sccm Processing power 100-150 W Processing time: 10-20 minutes min During the process, the vacuum level of the cavity is maintained at 10–20. Pa ; Processing effect: Through plasma etching and oxidation, a hydroxylation layer is formed on the powder surface (- OH This process enhances the hydrophilicity of the powder surface, resulting in a contact angle ≤30°. Simultaneously, it removes residual organic matter from the powder surface, improving the interfacial compatibility between the powder and the binder, as well as the subsequent sintering activity, thereby increasing the sintering driving force by more than 15%.

6. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 5, characterized in that, Step 4: Composite adhesive granulation gradient pressure molding: Preparation of composite adhesive: Polyvinyl alcohol (VALO) PVA (degree of polymerization 1750±50) and polyethylene glycol ( PEG Mix (-4000) at a mass ratio of 8:2 to 7:3, and add deionized water to prepare a solution of 5-8... wt A % aqueous solution was stirred in an 80°C water bath for 30–60 minutes. min Dissolve completely and cool to room temperature for later use; Mixing and granulation: The modified powder and the composite binder aqueous solution are added to a twin-screw mixer in a certain proportion. The mixing temperature is 60-80℃ and the speed is 50-80. r / min Mixing time 30-60 minutes min Uniform spherical particles are formed through shearing and kneading; after granulation, the particles are screened through a double-layer sieve of 100 mesh and 200 mesh to control the particle size within 100–200 mm. μm Large particles on the sieve are crushed and regranulated, while fine powder under the sieve is recycled and reused. Gradient pressure molding: The screened granules are loaded into a circular mold (10-50 mm in diameter). mm Place it on a hydraulic forming machine; apply 50-80 g / m² of pressure in the first stage. MPa Preload 30-60 s Expel air from between particles; The second stage is 20-30 MPa / min The rate is gradually increased to 150-250. MPa Hold pressure for 2-3 seconds. min This ensures the particles are tightly bound together; preheating the mold during molding (40–60℃) reduces interfacial stress between the binder and the powder, preventing cracks or delamination in the preform; the diameter deviation of the preform after molding is ≤±0.1 mm. mm Thickness deviation ≤ ±0.05 mm .

7. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 6, characterized in that, Step 5: Preform gradient drying - cooling and pre-densification under pressure. Gradient temperature drying: The molded preform is placed in a forced-air drying oven, and a three-stage temperature increase is adopted: room temperature 60℃ (heating rate 5~10℃ / h ), insulation 2 h 60℃→90℃ (heating rate 10℃ / h ), insulation 3 h ; 90℃→120℃ (heating rate 15℃ / h Insulation 4-6 h During the drying process, regular ventilation is required to remove moisture; the moisture content of the embryo after drying should be ≤0.5%. Cooling and pre-densification: The dried preform is sealed with a polyethylene film and placed in the high-pressure chamber of a cooling press, using nitrogen (purity ≥99.9%) as the pressure medium; first, at 50... MPa / min The rate of boosting to 100 MPa , holding pressure 2 min Then 30 MPa / min The rate of voltage boosting is 300-400 MPa Hold pressure 5-10 min Finally, with 50 MPa / min The pressure was released to atmospheric pressure at a certain rate; after pre-densification, the density of the preform increased from 60%–65% after molding to 75%–80%, the internal porosity was ≤20%, and the pores were uniformly distributed with no obvious large-sized pores (pore diameter ≤1). μm ).

8. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 7, characterized in that, Step 6: Multi-stage temperature rise and binder removal - intermediate heat preservation during sintering: Multi-stage temperature-controlled debinding: The pre-densified preform is placed in an alumina boat and then into a tube furnace; the first stage is at room temperature of 200℃ (heating rate 5℃ / ...). min ), insulation 1 h Remove free water from the embryo; second stage: 200℃ to 300℃ (heating rate 3℃ / min ), insulation 2 h Preliminary decomposition PVA Adhesive (decomposition rate ≥60%); Third stage 300℃ to 550~580℃ (heating rate 2℃ / min Insulation 6-10 h Completely decomposes adhesives and residual organic matter (total decomposition rate ≥99%); air is introduced during the adhesive discharge process (flow rate 0.5). L / min ), taking away the decomposition products CO 2. H 2 O ; Intermediate heat preservation during sintering: After the binder is removed, maintain a temperature of 3℃ / min The temperature is increased to 900℃ at a certain rate and held for 1-2 hours. h During sintering, the intermediate temperature is maintained. This step can homogenize the internal temperature of the preform, reduce the stress caused by the temperature gradient, and at the same time promote the diffusion of powder particles on the surface, forming preliminary neck bonding, laying a uniform grain growth foundation for subsequent high-temperature sintering, and avoiding abnormal grain growth in the high-temperature stage.

9. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 8, characterized in that, Step 7: Dynamic Atmosphere - Powder Co-sintering Powder preparation: Pre-fired powder with the same composition as ceramic powder (calcined at 820-860℃ for 3 minutes) h ) and 5-10 wt %of ZrO 2. Powder (particle size 1-3) μm Mix thoroughly and use as a embedding powder; ZrO 2. The powder can reduce the interfacial adhesion between the powder and the ceramic body, thus playing an anti-sticking role; Powder embedding process: Place the preform, which has undergone intermediate heat preservation, into an alumina crucible, and fill the surrounding area with powder. The powder thickness should be 3 to 5 times the thickness of the ceramic preform, ensuring that the preform is completely covered by the powder to reduce the risk of sintering defects. K , Na The volatilization of elements; Dynamic mixing atmosphere control: adopts O 2 and N The ratio of the 2-gas mixture is precisely controlled by a mass flow controller: Early stage of sintering (room temperature ~ 900℃): O 2: N 2:4:6 (volume ratio), gas flow rate 0.5~1 L / min This promotes the complete oxidation of residual organic matter; Mid-sintering stage (900℃~1100℃): O 2: N 2:3:7 (volume ratio), gas flow rate 0.8~1.2 L / min To balance grain growth and compositional stability; Later stage of sintering (from 1100℃ to cooling down to 600℃): O 2: N 2:8 (volume ratio), gas flow rate 0.5~1 L / min ,inhibition K , Na Elemental volatilization and the generation of lattice oxygen defects; Warm sintering process: After intermediate heat preservation, sinter at 2-3℃ / min The temperature is increased to 1080–1100℃ at a rate of [unspecified rate], and held for 3–4 [unspecified periods]. h During the heat preservation process, every 1 h Record the furnace temperature once, and control the temperature fluctuation within ±5℃; after sintering, maintain a temperature of 5℃ / min The temperature was reduced to 600℃ at a rate of [missing information], and then cooled to room temperature in the furnace; finally, a ceramic green body with a density ≥97% and uniform grain size (1-3 [missing information]) was obtained. μm No obvious abnormally large grains (grain size ≤5) μm ).

10. The method for preparing composite ion-pair modified potassium sodium niobate ceramic according to claim 9, characterized in that, Step (8) Stepped annealing - segmented pulse polarization - stability enhancement in progress: Stepped annealing: The sintered ceramic green body is placed in a box-type resistance furnace and annealed in three stages: holding at 300℃ for 3 minutes. h (Heating rate 5℃ / min ), 400℃ heat preservation 2 h (Heating rate 3℃ / min ), 600℃ heat preservation 1 h (Heating rate 2℃ / min ); then at 5℃ / min The rate of annealing is as the furnace cools to room temperature; the thermal stress and lattice distortion generated during annealing are eliminated, lattice integrity is improved by more than 20%, and the fracture toughness of the ceramic increases from 1.5... MPa · m 1 / 2 Increase to ≥1.8 MPa · m 1 / 2 ; Segmented pulse polarization process: Pretreatment before polarization: The annealed ceramic blank is polished on both sides to remove the surface oxide layer, coated with silver paste, and fired at 600℃ for 30 minutes. min To form electrodes; Polarizing medium: High-temperature silicone oil (temperature 120~140℃) is used, and the insulation resistance of the silicone oil is ≥10. 12 Ω · cm ; Polarization steps: First stage applies 2 kV / mm Pre-polarization voltage, heat preservation 5 min This allows for the initial orientation of the electrical domains within the ceramic; the second stage uses 0.5... kV / mm The increment gradually increases to 3-5 kV / mm Maintain a pulse frequency of 50-100. Hz (Pulse duty cycle 50%), polarization time 15–20 seconds min This promotes the complete directional alignment of electric domains; the third stage reduces the voltage to 2. kV / mm Insulation 5 min Then slowly cut off the power (voltage reduction rate 0.2). kV / mm · min ), and allow to cool naturally to room temperature in silicone oil; Stability enhancement: The polarized ceramic was placed in a constant temperature and humidity chamber and aged for 24 hours at 85℃ and 85% relative humidity. h Products with stable performance are selected through accelerated aging; the piezoelectric coefficient after aging d 33 With a decay rate of ≤1%, the ceramic material is guaranteed to maintain long-term stability under harsh environments. Step 9: Precision processing after sintering - performance calibration - vacuum packaging in progress. Precision surface grinding and polishing: A two-step polishing method is used: The first step uses diamond polishing paste (particle size 1-5). μm Mechanical grinding on a grinding machine at a speed of 300-500 rpm. r / min Grinding pressure: 0.1–0.2 MPa The first step is to remove impurities and unevenness from the electrode layer surface; the second step is to use colloidal silica polishing slurry (particle size 50-100 μm). nm Perform chemical mechanical polishing at a speed of 800–1000 rpm. r / min Polishing pressure: 0.05–0.1 rpm MPa Polishing time 30-60 seconds min Surface roughness of ceramics after polishing Ra ≤0.05 μm , parallelism ≤ 0.01 mm Flatness ≤ 0.005 mm ; Multi-dimensional performance calibration: The polished ceramic was placed in a high-precision piezoelectric performance testing system and tested at 25℃ and 50% relative humidity: piezoelectric coefficient d 33 (Error ≤ ±1) pC / N ), dielectric constant ε r With dielectric loss tanδ (1) kHz (Lower), Residual Polarization Intensity P r The piezoelectric coefficient was tested at -50℃, 0℃, 100℃, and 200℃. d 33 To ensure that temperature stability meets the standards; Products with any performance index deviation exceeding ±2% will be excluded; Vacuum sealing: Pack qualified products in polyester film, place them in a vacuum packaging machine, and evacuate to a vacuum level of ≤-0.

095. MPa The product is sealed and encapsulated; after encapsulation, it is stored in a dry environment (humidity ≤30%) to avoid surface oxidation or moisture absorption that could affect its performance.

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