Potassium sodium niobate-based lead-free piezoelectric ceramic material, and preparation method and application thereof

Abstract

The application discloses a potassium-sodium niobate-based lead-free piezoelectric ceramic material and a preparation method and application thereof, relates to the technical field of functional materials, and has a chemical formula of 0.964K 0.5 Na 0.5 Nb 0.955 Sb 0.045 O3‑0.03Bi 0.5 Na 0.5 ZrO3‑0.006BiFeO3‑xMnO2, wherein x is 0.005-0.04, and x represents a molar fraction. By means of intervention of the oxide sintering aid MnO2, microstructure, compactness, domain structure, phase boundary, loss and defect concentration of the ternary KNN-based piezoelectric ceramic material system are regulated, so that a brand-new potassium-sodium niobate (KNN)-based lead-free piezoelectric ceramic with super-high piezoelectric performance and excellent mechanical performance is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and in particular to a potassium sodium niobate-based lead-free piezoelectric ceramic material, a preparation method thereof, and applications thereof. Background Art

[0002] Piezoelectric ceramics are an important functional material that can realize the mutual conversion between mechanical energy and electrical energy. Due to its simple preparation process, low cost, excellent performance and strong controllability, it has been widely used in many consumer electronic device fields, such as piezoelectric / ferroelectric sensors, drivers, transducers, etc. Lead-based piezoelectric ceramics (such as PZT piezoelectric ceramics) have excellent electrical properties and good temperature stability. They are considered to be the most representative materials in the field of piezoelectric ceramics. They have long dominated the field of consumer electronic devices and served in industries such as civil engineering, electronic equipment, aerospace, and petrochemicals. However, the highly toxic lead element makes lead-based piezoelectric ceramics cause serious harm to human health and the earth's environment during the preparation, use and waste treatment of lead-based piezoelectric ceramics. With the improvement of people's awareness of their own health and environmental protection, vigorously developing lead-free piezoelectric ceramic materials such as potassium sodium niobate (KNN), barium titanate (BT), bismuth ferrite (BF), and bismuth titanate (BIT) has become a new trend to replace traditional lead-based piezoelectric ceramic materials. Among these lead-free piezoelectric ceramics, KNN piezoelectric ceramics have a higher Curie temperature (T c =410℃), good electrical properties (d 33 =80-120pC / N) and lower sintering temperature. However, compared with commercial lead-based PZT piezoelectric ceramics (d 33 ≥410pC / N), the piezoelectric performance of pure KNN piezoelectric ceramics is still relatively low, greatly limiting their application in high-tech consumer electronics. Therefore, to promote the development of lead-free and environmentally friendly piezoelectric / ferroelectric devices, it is particularly important to optimize and improve the piezoelectric performance of KNN piezoelectric ceramics.

[0003] Currently, various strategies have been developed to control and optimize the electrical properties of KNN piezoelectric ceramics, including doping, phase boundary engineering, domain engineering, texturing, and rapid sintering. Doping is the most effective and widely used method for optimizing the performance of KNN piezoelectric ceramics. Doping can modify the phase structure of KNN piezoelectric ceramics and manipulate the microstructure and domain structure, thereby optimizing electrical properties.

[0004] While research on KNN piezoelectric ceramics has achieved significant success, the preparation process often faces challenges such as element volatilization and stoichiometric deviations, further improving their piezoelectric performance remains challenging. Furthermore, mechanical properties, a key indicator of their service reliability and stability, are rarely reported. In practical applications, in addition to piezoelectric performance, mechanical properties, such as hardness and fracture toughness, must also be considered. Because piezoelectric ceramics are brittle materials, they are susceptible to failure due to external mechanical loads, severely limiting their service reliability and output stability in practical applications. With the advancement of modern society, piezoelectric information devices are expected to develop towards miniaturization, lightness, high sensitivity, high precision, high reliability, and high stability. This requires lead-free KNN piezoelectric ceramics to possess both enhanced piezoelectric and mechanical properties. Therefore, developing a new generation of KNN-based lead-free piezoelectric ceramic materials that combine high piezoelectric and mechanical properties has become a crucial task for the advancement and development of information technology in the new era. Summary of the Invention

[0005] Based on the problem that the high-voltage electrical properties and mechanical properties of current KNN-based lead-free piezoelectric ceramic materials are still relatively low, the purpose of the present invention is to provide a potassium sodium niobate-based lead-free piezoelectric ceramic material and its preparation method and application. The potassium sodium niobate-based lead-free piezoelectric ceramic material has both ultra-high-voltage electrical properties and excellent mechanical properties, and is expected to replace traditional lead-containing piezoelectric ceramic materials and be used in a new generation of miniature, lightweight, highly sensitive, high-precision, highly reliable and highly stable electronic information devices, making an important contribution to the development of information technology and social era in the new era.

[0006] The present invention is achieved through the following technical solutions:

[0007] In the first aspect, the present application provides a potassium sodium niobate-based lead-free piezoelectric ceramic material, the chemical formula of the potassium sodium niobate-based lead-free piezoelectric ceramic material is 0.964K 0.5 Na 0.5 Nb 0.955 Sb 0.045 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.006BiFeO3-xMnO2, wherein x = 0.005 to 0.04. Specifically, x can be 0.005, 0.01, 0.02, 0.03, or 0.04, where x represents the mole fraction.

[0008] The present invention uses the oxide sintering aid MnO2 to regulate the microstructure, density, domain structure, phase boundary, loss, and defect concentration of the ternary KNN-based piezoelectric ceramic material system, thereby obtaining a new potassium sodium niobate (KNN)-based lead-free piezoelectric ceramic with both ultra-high piezoelectric performance and excellent mechanical properties. In the present invention, when the MnO2 content is 0.01, the KNN-based piezoelectric ceramic achieves the best overall performance, namely, ultra-high piezoelectric performance d 33 =520pC / N, excellent inverse piezoelectric coefficient d 33 * =505pm / V and higher mechanical hardness H V =4.2GPa and fracture toughness K IC =1.22MPa·m 1 / 2 When the MnO2 content is 0.005, the KNN-based piezoelectric ceramics obtain higher piezoelectric performance. 33 =430pC / N and excellent fracture toughness K IC =1.34MPa·m 1 / 2 When the MnO2 content is 0.04, the KNN-based piezoelectric ceramics obtain an ultra-high mechanical hardness H v = 6.31 GPa. These performance indicators far exceed the electrical and mechanical properties of pure KNN piezoelectric ceramics and are also superior to other reported KNN piezoelectric ceramic materials. The KNN-based lead-free piezoelectric ceramic materials of this invention are expected to replace traditional lead-containing piezoelectric ceramic materials and be used in a new generation of miniature, lightweight, highly sensitive, high-precision, highly reliable, and highly stable electronic information devices, making a significant contribution to the development of information technology and society in the new era.

[0009] In a second aspect, the present application provides a method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material, comprising the following steps:

[0010] (1) According to the chemical formula of potassium sodium niobate-based lead-free piezoelectric ceramic material, chemical reagents Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2, Fe2O3 and MnO2 were weighed and prepared into powder;

[0011] (2) using the powder to granulate and form a disc body;

[0012] (3) performing debinding treatment on the disc blank;

[0013] (4) sintering the debinding disc green body to obtain a disc ceramic material;

[0014] (5) The sintered disc ceramic material is subjected to silver plating and polarization treatment to obtain a lead-free piezoelectric ceramic material.

[0015] Furthermore, when preparing the powder in step (1), the weighed chemical reagents are first ball-milled, then dried, and finally pre-calcined.

[0016] Furthermore, the temperature during the pre-firing treatment is controlled at 820° C. to 880° C., and the temperature is kept at this temperature for 240 min to 360 min.

[0017] Furthermore, in step (2), when preparing the disc body, the powder material and the polyvinyl alcohol binder are first stirred and mixed, and then dried. The dried powder particles are then placed in a forming mold and formed on a powder dry pressing machine. The forming pressure is 5MPa to 15MPa.

[0018] Furthermore, the prepared disc blank has a diameter of 10 mm and a height of 0.8 mm to 1.5 mm.

[0019] Furthermore, the formed disc body contains a large amount of PVA binder, which has a great impact on the sintering of the disc green body into porcelain. Therefore, before the green body is sintered, the PVA binder needs to be discharged. First, the formed disc body is placed on a corundum plate and placed in a muffle furnace for debinding. The debinding process in step (3) includes the following four stages:

[0020] The first stage is to raise the temperature from room temperature to 120 °C and keep it for 60 min;

[0021] The second stage is to increase the temperature from 120°C to 500°C and keep it at this temperature for 180 min;

[0022] The third stage is to increase the temperature from 500°C to 550°C;

[0023] The fourth stage is to increase the temperature from 550 °C to 850 °C and keep it at this temperature for 120 min, and then cool it naturally to room temperature.

[0024] Furthermore, the debinding disc body is placed in a muffle furnace for sintering to make it magnetic and improve the material density and mechanical strength. In step (4), the sintering process is carried out using a buried sintering method, with a sintering temperature of 1040°C to 1100°C and a holding time of 240min to 180min. The buried sintering method can reduce element volatilization during the sintering process, that is, covering the disc body with the corresponding powder.

[0025] Furthermore, the sintered disc ceramic material does not have piezoelectric functionality. To facilitate subsequent device applications, it needs to be electrically polarized. Before polarization, silver paste needs to be applied to the surface of the product to form electrodes.

[0026] The silver-plated polarization treatment method in step (5) is as follows: first, silver paste is evenly applied on both sides of the ceramic to form a continuous silver paste film; then, the ceramic piece coated with silver paste is heated to a temperature of 600° C. and kept warm for 20 to 60 minutes to ensure that the silver paste is tightly bonded to the ceramic surface and provides good conductive properties; finally, the ceramic disc with electrodes is placed in a polarization device for polarization treatment, the polarization voltage is 2.5 kV to 3.5 kV, and the pressure is maintained for 10 to 30 minutes, thereby obtaining a lead-free piezoelectric ceramic material, which meets performance testing and engineering requirements.

[0027] In a third aspect, the present application provides an application of a potassium sodium niobate-based lead-free piezoelectric ceramic material, which is prepared using the above-mentioned method, including a new generation of miniature, lightweight, highly sensitive, high-precision, highly reliable and highly stable electronic information devices, such as piezoelectric / ferroelectric sensors or drivers or transducers.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] (1) The potassium sodium niobate-based lead-free piezoelectric ceramic material of the present invention forms a unique microstructural feature: Sb, Bi and Br are added to the pure KNN lead-free piezoelectric ceramic according to a certain formula ratio. 0.5 Na 0.5 After the addition of ZrO3, BiFeO3 and MnO2, a stable RT phase boundary can be successfully constructed with more ferroelectric domain variants and flat free energy, while forming a highly densified double-peak microstructure, a fine strip-shaped domain structure and defect dipoles, which are beneficial to ferroelectric polarization and resistance to mechanical plastic deformation and crack propagation, providing a good ion doping strategy for the development of new lead-free piezoelectric ceramic materials with both high voltage and high mechanical properties.

[0030] (2) The potassium sodium niobate-based lead-free piezoelectric ceramic material of the present invention has good ferroelectric dielectric properties: by adjusting the content ratio of the oxide sintering aid MnO2, when the MnO2 content is 0.01, the KNN-based piezoelectric ceramic obtains the maximum maximum polarization intensity P max =24.7μC / cm 2 With the remnant polarization P r =19.1μC / cm 2 and the lowest coercive field E c =6.3kV / cm, and has the highest bipolar ferroelectric strain S pol =0.204%. In addition, the highest dielectric constant of 3296 and the lowest dielectric loss of 0.026 were also obtained. These findings are conducive to optimizing the piezoelectric activity of the material, thereby obtaining a KNN-based piezoelectric ceramic material with excellent piezoelectric properties.

[0031] (3) The potassium sodium niobate-based lead-free piezoelectric ceramic material of the present invention has excellent piezoelectric properties: by adjusting the content ratio of the oxide sintering aid MnO2, when the MnO2 content is 0.01, the KNN-based piezoelectric ceramics have obtained ultra-high piezoelectric performance. 33 =520pC / N and excellent inverse piezoelectric coefficient d 33 * =505pm / V. These performance indicators far exceed the electrical properties of pure KNN piezoelectric ceramics and also outperform many commercial lead-containing PZT piezoelectric ceramics. This new KNN-based lead-free piezoelectric ceramic material is expected to replace traditional lead-containing piezoelectric ceramics in a new generation of miniature, lightweight, highly sensitive, and high-precision electronic information devices.

[0032] (4) The potassium sodium niobate-based lead-free piezoelectric ceramic material of the present invention has obtained ultra-high mechanical properties: by regulating the content ratio of the oxide sintering aid MnO2, when the MnO2 content is 0.005, the KNN-based piezoelectric ceramic obtains ultra-high fracture toughness K IC =1.34MPa·m 1 / 2 When the MnO2 content is 0.04, the KNN-based piezoelectric ceramics obtain an ultra-high mechanical hardness H v =6.31GPa. When the MnO2 content is 0.01, the KNN-based piezoelectric ceramics also obtain excellent mechanical hardness H v =4.2GPa and fracture toughness K IC =1.22MPa·m 1 / 2 . These performance indicators far exceed the mechanical properties of pure KNN piezoelectric ceramics, and are also better than other KNN piezoelectric ceramic materials reported so far. Excellent mechanical behavior enables the ceramic material to maintain its structural integrity and stability when disturbed by external forces, thereby effectively resisting the influence of various working environments. Combined with its excellent piezoelectric properties, this new KNN-based lead-free piezoelectric ceramic material (especially when the MnO2 content is 0.01) is expected to replace traditional lead-containing piezoelectric ceramic materials and be used in a new generation of miniature, lightweight, highly sensitive, high-precision, highly reliable and highly stable electronic information devices, making important contributions to the development of information technology and social era in the new era. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0034] Figure 1 The technical roadmap and performance comparison chart of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic in the embodiment of the present application; wherein (a) is the technical roadmap of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic; (b) is the domain structure morphology chart of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic system, and the fine bar-shaped domain and the rich domain wall optimize the electrical and mechanical properties of the material; (c) and (d) are the electrical properties and mechanical properties of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic material in the present application, and the performance comparison with other KNN-based piezoelectric ceramics and commercialized lead-based PZT ceramics reported at present;

[0035] Figure 2 The crystal structure and microstructure chart of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic in the embodiment of the present application; wherein (a) is the XRD pattern of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic; (b) is the high-magnification transmission electron microscope chart of the KNNS-BNZ-BF-0.01Mn ceramic under the

[001] crystal band axis; (c) is the SEM microstructure chart of the KNNS-BNZ-BF-0.01Mn ceramic; (d) is the PFM phase chart of the KNNS-BNZ-BF-0.01Mn ceramic;

[0036] Figure 3 The dielectric behavior and phase diagram of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic in the embodiment of the present application, wherein (a) and (b) are the dielectric temperature curves of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic at low temperature and high temperature, respectively; (c) is the phase diagram of the KNNS-BNZ-BF-xMn ceramic;

[0037] Figure 4 The ferroelectric performance curve chart of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic in the embodiment of the present application; wherein (a) is the ferroelectric hysteresis curve of the KNNS-BNZ-BF-xMn ceramic; (b) is the maximum polarization intensity (P max ), the residual polarization intensity (P r ), and the coercive field (E c ) of the KNNS-BNZ-BF-xMn ceramic; (c) is the ferroelectric butterfly curve of the KNNS-BNZ-BF-xMn ceramic; (d) is the positive strain (S pos ), the negative strain (S neg ), and the total strain (S pol ) of the KNNS-BNZ-BF-xMn ceramic; (e) is the unipolar strain curve of the KNNS-BNZ-BF-xMn ceramic; (f) is the unipolar strain (S uni ) and the inverse piezoelectric coefficient (d33 * );

[0038] Figure 5 The dielectric properties and piezoelectric properties of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics in the embodiment of the present invention are shown in FIG. 1 , wherein (a) is the dielectric constant (ε) of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics. r ) and dielectric loss (tanθ); (b) is the piezoelectric constant (d 33 ) and electromechanical coupling coefficient (k p );

[0039] Figure 6 Figure 1 is a graph showing the mechanical plastic deformation resistance test results of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics in the embodiment of the present invention; (a, b, c, d, e) are the load-displacement curves of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics under nanoindentation; (f) is the indentation penetration depth of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics;

[0040] Figure 7 These are the hardness and fracture toughness test results of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics in the implementation of the present invention; (a, c) are the Vickers indentation morphology SEM images of the unpolarized and polarized KNNS-BNZ-BF-0.02Mn lead-free piezoelectric ceramics, respectively; (b, d) are the hardness and fracture toughness of the unpolarized and polarized KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics, respectively. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0042] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0043] The present invention successfully synthesized the ternary system KNNS-BNZ-BF-xMn lead-free piezoelectric ceramic material through the "chemical doping" strategy, and simultaneously obtained excellent electrical properties and ultra-high mechanical properties in the ceramic sample with component x = 0.01 ( Figure 1), by adding Sb, Bi 0.5 Na 0.5 ZrO3and BiFeO3into pure KNN lead-free piezoelectric ceramics, a ternary system KNNS-BNZ-BF lead-free piezoelectric ceramics with high electrical performance potential is formed. Then, by adding oxide sintering aid MnO2into the ternary system KNN-based lead-free piezoelectric ceramics, through regulating the content ratio of the sintering aid, a stable R-T phase boundary can be successfully constructed, more ferroelectric domain variants and flat free energy are obtained, at the same time, a double-peak microstructure with high densification, small strip domain structure and defect dipoles are formed, which is beneficial to ferroelectric polarization and resistance to mechanical plastic deformation and crack propagation, finally, a new type of lead-free piezoelectric ceramic with high piezoelectricity and high mechanical performance is obtained, from Figure 1 It can be seen from Fig. (b) that the small strip domain and the rich domain wall optimize the electrical and mechanical properties of the material, from Figure 1 It can be seen from Figs. (c) and (d) that the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics have excellent piezoelectric and mechanical properties at the same time, which is expected to replace traditional lead-containing piezoelectric ceramic materials and be applied to a new generation of micro, light, high sensitivity, high precision, high reliability and high stability electronic information devices, making important contributions to the development of information technology and social era. The specific embodiments of the KNNS-BNZ-BF-xMn lead-free piezoelectric ceramics under each component are as follows:

[0044] Example 1

[0045] The embodiment provides a preparation method of a KNNS-BNZ-BF-0.005Mn lead-free piezoelectric ceramic material, which is performed according to the following steps:

[0046] S1, preparing chemical reagents: Na2CO3(AR 99.8%), K2CO3(AR 99%), Nb2O5(AR 99.95%), Sb2O3(AR 99.99%), Bi2O3(AR 99.99%), ZrO2(AR 99%), Fe2O3(99.99%) and MnO2(AR 99.95%).

[0047] S2, the chemical reagents in step S1 are mixed according to the stoichiometric formula 0.964K 0.5 Na 0.5 Nb 0.955 Sb 0.045 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.006BiFeO3-0.005MnO2

[0048] (KNNS-BNZ-BF-0.005Mn) were weighed and proportioned on a high-precision balance. The weighed chemical reagents were poured into a polytetrafluoroethylene ball mill. Anhydrous ethanol was added as a dispersion medium. The mixture was ball milled for 720 min on a planetary ball mill at a speed of 580 r / min to ensure that the chemical reagents were fully mixed.

[0049] S3. Remove the highly mixed KNNS-BNZ-BF-0.005Mn slurry from the ball mill and dry it under a heat lamp. Then, pour the dried slurry into an alumina crucible, cover the crucible, and pre-calculate it in a muffle furnace at 850°C for 360 minutes. Finally, through the solid-phase reaction process during pre-calcination, a KNNS-BNZ-BF-0.005Mn solid solution compound with a specific structure is formed.

[0050] S4. The pre-calcined KNNS-BNZ-BF-0.005Mn solid solution was transferred to a mortar and granulated with 7% wt of polyvinyl alcohol (PVA) binder. The dried KNNS-BNZ-BF-0.005Mn granules were then compacted on a powder dry compactor at a compacting pressure of 10 MPa, resulting in KNNS-BNZ-BF-0.005Mn discs with a diameter of 10 mm and a height of 1 mm.

[0051] S5. The formed KNNS-BNZ-BF-0.005Mn disc body is placed in a muffle furnace for debinding. The debinding temperature setting process includes: first, the muffle furnace temperature is raised from room temperature to 120°C and held for 60 minutes; second, the muffle furnace temperature is raised from 120°C to 500°C and held for 180 minutes; then, the muffle furnace temperature is raised from 500°C to 550°C; finally, the muffle furnace temperature is raised from 550°C to 850°C and held for 120 minutes, followed by natural cooling to room temperature. Next, the debinded KNNS-BNZ-BF-0.005Mn disc body is placed in the muffle furnace again for sintering to make it magnetic and improve the material density and mechanical strength. During the sintering process, the buried burning method is usually used to reduce element volatilization, that is, covering the disc body with the corresponding powder. The sintering temperature was 1070° C., and the temperature was kept for 180 min. The sintering temperature was then naturally cooled to room temperature to obtain a KNNS-BNZ-BF-0.005Mn ceramic disc material.

[0052] S6. Use a brush to dip a small amount of silver paste and evenly apply it to both sides of the sintered KNNS-BNZ-BF-0.005Mn ceramic disc to form a continuous silver paste film. Then place it in a muffle furnace for heating to ensure that the silver paste is tightly bonded to the ceramic surface and forms an electrode. The heating temperature is 600°C and the temperature is kept for 30 minutes. Finally, the KNNS-BNZ-BF-0.005Mn ceramic disc with electrodes is placed in a polarization device for polarization treatment. The polarization voltage is 3kV and the pressure is maintained for 10 minutes. Finally, the KNNS-BNZ-BF-0.005Mn lead-free piezoelectric ceramic material that meets the performance test is obtained.

[0053] The following performance characterizations were performed on the KNNS-BNZ-BF-0.005Mn lead-free piezoelectric ceramic material prepared by the method of this embodiment.

[0054] 1) XRD and temperature-varying dielectric tests were performed on KNNS-BNZ-BF-0.005Mn ceramics, demonstrating the structural characteristics of the coexistence of RT phases ( Figure 2 and Figure 3 ), and also obtained a higher dielectric constant (ε r =3139) and lower dielectric loss (tanθ=0.029)( Figure 5 ).

[0055] 2) The hysteresis curve and butterfly curve of KNNS-BNZ-BF-0.005Mn ceramic sample were tested by ferroelectric analyzer, and the maximum ferroelectric polarization intensity (P max =24.1μC / cm 2 ), a larger residual polarization intensity (P r =18μC / cm 2 ), smaller coercive field (E c =7.5kV / cm), a large bipolar ferroelectric total strain (S pol =0.179%), a large unipolar ferroelectric strain (S uni =0.113%) and a larger inverse piezoelectric coefficient (d 33 * =417pm / V)( Figure 4 ).

[0056] 3) Use quasi-static d 33 The piezoelectric constant and electromechanical coupling coefficient of KNNS-BNZ-BF-0.005Mn ceramic material were tested by measuring instrument and impedance analyzer, and the larger piezoelectric constant (d 33 =430pC / N) and a higher electromechanical coupling coefficient (k p =0.45)( Figure 5 ).

[0057] 4) The load-displacement curve of KNNS-BNZ-BF-0.005Mn ceramic material was obtained by nanoindentation, and the maximum indentation depth (H m =643nm)( Figure 6 ). In addition, the hardness and fracture toughness of KNNS-BNZ-BF-0.005Mn ceramic material were obtained by using Vickers indenter, where the hardness value is: v =3.6Gpa, polarization H v =3.4GPa; fracture toughness value: unpolarized K IC =1.32MPa·m 1 / 2 , polarization K IC =1.34MPa·m 1 / 2 ( Figure 7 ).

[0058] from Figure 7 As can be seen from Figures (b, d), when the MnO2 content is 0.005, the KNN-based piezoelectric ceramics obtain an ultra-high fracture toughness K IC =1.34MPa·m 1 / 2 .

[0059] Example 2

[0060] This embodiment provides a method for preparing a KNNS-BNZ-BF-0.01Mn lead-free piezoelectric ceramic material, which is carried out according to the following steps:

[0061] S1. Prepare chemical reagents: Na2CO3 (AR 99.8%), K2CO3 (AR 99%), Nb2O5 (AR 99.95%), Sb2O3 (AR 99.99%), Bi2O3 (AR 99.99%), ZrO2 (AR 99%), Fe2O3 (99.99%) and MnO2 (AR99.95%).

[0062] S2, the above experimental materials were mixed according to the stoichiometric formula 0.964K 0.5 Na 0.5 Nb 0.955 Sb 0.045 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.006BiFeO3-0.01MnO2 (KNNS-BNZ-BF-0.01Mn) was weighed and proportioned on a high-precision balance. The weighed chemical reagents were poured into a polytetrafluoroethylene ball mill jar, and anhydrous ethanol was added as a dispersion medium. The mixture was ball milled for 720 minutes on a planetary ball mill at a speed of 580 r / min to ensure that the chemical reagents were fully mixed.

[0063] S3. Remove the highly mixed KNNS-BNZ-BF-0.01Mn slurry from the ball mill and dry it under a heat lamp. Then, pour the dried slurry into an alumina crucible, cover the crucible, and pre-calculate it in a muffle furnace at 850°C for 360 minutes. Finally, through the solid-phase reaction process during pre-calcination, a KNNS-BNZ-BF-0.01Mn solid solution compound with a specific structure is formed.

[0064] S4. The pre-calcined KNNS-BNZ-BF-0.01Mn solid solution was transferred to a mortar and granulated with 7% wt of polyvinyl alcohol (PVA) binder. The dried KNNS-BNZ-BF-0.01Mn granules were then compacted on a powder dry compactor at a compacting pressure of 10 MPa, resulting in KNNS-BNZ-BF-0.01Mn discs with a diameter of 10 mm and a height of 1 mm.

[0065] S5. The formed KNNS-BNZ-BF-0.01Mn disc body is placed in a muffle furnace for debinding. The debinding temperature setting process includes: first, the muffle furnace temperature is raised from room temperature to 120°C and held for 60 minutes; second, the muffle furnace temperature is raised from 120°C to 500°C and held for 180 minutes; then, the muffle furnace temperature is raised from 500°C to 550°C; finally, the muffle furnace temperature is raised from 550°C to 850°C and held for 120 minutes, followed by natural cooling to room temperature. Next, the debinded KNNS-BNZ-BF-0.01Mn disc body is placed in the muffle furnace again for sintering to make it magnetic and improve the material density and mechanical strength. During the sintering process, the buried burning method is usually used to reduce element volatilization, that is, covering the disc body with the corresponding powder. The sintering temperature was 1070° C. and the temperature was kept for 180 min. The sintering temperature was then naturally cooled to room temperature to obtain a KNNS-BNZ-BF-0.01Mn ceramic disc material.

[0066] S6. Use a brush to dip a small amount of silver paste and evenly apply it to both sides of the sintered KNNS-BNZ-BF-0.01Mn ceramic disc to form a continuous silver paste film. Then place it in a muffle furnace for heating to ensure that the silver paste is tightly bonded to the ceramic surface and forms an electrode. The heating temperature is 600°C and the temperature is kept for 30 minutes. Finally, the KNNS-BNZ-BF-0.01Mn ceramic disc with electrodes is placed in a polarization device for polarization treatment. The polarization voltage is 3kV and the pressure is maintained for 10 minutes. Finally, the KNNS-BNZ-BF-0.01Mn lead-free piezoelectric ceramic material that meets the performance test is obtained.

[0067] The following performance characterizations were performed on the KNNS-BNZ-BF-0.01Mn lead-free piezoelectric ceramic material prepared by the method of this embodiment.

[0068] 1) XRD and temperature-varying dielectric tests were performed on KNNS-BNZ-BF-0.01Mn ceramics, demonstrating the structural characteristics of the coexistence of RT phases ( Figure 2 and Figure 3 ). The crystal structure of KNNS-BNZ-BF-0.01Mn ceramics was observed using HRTEM, revealing the neatly arranged atomic morphology and high-quality crystallinity ( Figure 2 ). At the same time, the microstructure was observed by SEM, which showed a bimodal grain distribution characteristic and excellent density. Moreover, the domain structure of the ceramic was observed by PFM, which revealed a smaller strip domain structure with lower free energy, which helps to improve the piezoelectric performance. Finally, the ceramic obtained the highest dielectric constant (ε r =3296) and the lowest dielectric loss (tanθ=0.026)( Figure 5 ).

[0069] 2) The hysteresis curve and butterfly curve of KNNS-BNZ-BF-0.01Mn ceramic sample were tested by ferroelectric analyzer, and the maximum ferroelectric maximum polarization intensity (P max =24.7μC / cm 2 ), the maximum remnant polarization intensity (P r =19.1μC / cm 2 ), smaller coercive field (E c =6.9kV / cm), the maximum bipolar ferroelectric total strain (S pol =0.205%), the maximum unipolar ferroelectric strain (S uni =0.136%) and the maximum inverse piezoelectric coefficient (d 33 * =505pm / V)( Figure 4 ).

[0070] from Figure 4 As can be seen from Figure (b), when x = 0.01, the ceramic system obtains the best maximum polarization intensity (P max =24.7μC / cm 2 ) and the remanent polarization intensity (P r =19.1μC / cm 2 ), and also has a smaller coercive field (E c =6.3kV / cm).

[0071] from Figure 4 As can be seen from Figure (d), when x = 0.01, the ceramic system obtains the best positive strain (Spos =0.137%), negative strain (S pos =0.067%) and the total strain (S pol =0.204%).

[0072] from Figure 4 As can be seen from Figure (f), when x = 0.01, the ceramic system obtains the best unipolar strain (S uni =0.136%) and the inverse piezoelectric coefficient (d 33 * =505pm / V).

[0073] 3) Use quasi-static d 33 The piezoelectric constant and electromechanical coupling coefficient of KNNS-BNZ-BF-0.01Mn ceramic material were tested by measuring instrument and impedance analyzer, and the maximum piezoelectric constant (d 33 =520pC / N) and the maximum electromechanical coupling coefficient (k p =0.526)( Figure 5 ).

[0074] from Figure 5 As can be seen from Figure (a), when x = 0.01, the ceramic system obtains the best dielectric constant (ε r =3296) and minimum dielectric loss (tanθ=0.026).

[0075] from Figure 5 As can be seen from Figure (b), when x = 0.01, the ceramic system obtains the best piezoelectric constant (d 33 =520pC / N) and electromechanical coupling coefficient (k p =0.526).

[0076] 4) The load-displacement curve of KNNS-BNZ-BF-0.01Mn ceramic material was obtained by nanoindentation, and the minimum indentation depth (H) of the ceramic was obtained. m =609nm)( Figure 6 ), showing good resistance to plastic deformation. In addition, the hardness and fracture toughness of KNNS-BNZ-BF-0.01Mn ceramic material were obtained by Vickers indentation instrument, where the hardness value is: v =4.2Gpa, polarization H v =4.0GPa; fracture toughness value: unpolarized K IC =1.19MPa·m 1 / 2 , polarization K IC =1.22MPa·m 1 / 2 ( Figure 7 ).

[0077] from Figure 7 As can be seen from Figures (b, d), when the MnO2 content is 0.01, the electrical properties of the KNN-based piezoelectric ceramics are the best, and at the same time, excellent mechanical hardness H is obtained. v =4.2GPa and fracture toughness K IC =1.22MPa·m 1 / 2 .

[0078] Example 3

[0079] This embodiment provides a method for preparing a KNNS-BNZ-BF-0.02Mn lead-free piezoelectric ceramic material, which is carried out according to the following steps:

[0080] S1. Prepare chemical reagents: Na2CO3 (AR 99.8%), K2CO3 (AR 99%), Nb2O5 (AR 99.95%), Sb2O3 (AR 99.99%), Bi2O3 (AR 99.99%), ZrO2 (AR 99%), Fe2O3 (99.99%) and MnO2 (AR99.95%).

[0081] S2, the above experimental materials were mixed according to the stoichiometric formula 0.964K 0.5 Na 0.5 Nb 0.955 Sb 0.045 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.006BiFeO3-0.02MnO2 (KNNS-BNZ-BF-0.02Mn) was weighed and proportioned on a high-precision balance. The weighed chemical reagents were poured into a polytetrafluoroethylene ball mill jar, and anhydrous ethanol was added as a dispersion medium. The mixture was ball milled for 720 minutes on a planetary ball mill at a speed of 580 r / min to ensure that the chemical reagents were fully mixed.

[0082] S3. Remove the highly mixed KNNS-BNZ-BF-0.02Mn slurry from the ball mill and dry it under a heat lamp. Then, pour the dried slurry into an alumina crucible, cover the crucible, and pre-calculate it in a muffle furnace at 850°C for 360 minutes. Finally, through the solid-phase reaction process during pre-calcination, a KNNS-BNZ-BF-0.02Mn solid solution compound with a specific structure is formed.

[0083] S4. The pre-calcined KNNS-BNZ-BF-0.02Mn solid solution was transferred to a mortar and granulated with 7% wt of polyvinyl alcohol (PVA) binder. The dried KNNS-BNZ-BF-0.02Mn granules were then compacted on a powder dry compactor at a compacting pressure of 10 MPa, resulting in KNNS-BNZ-BF-0.02Mn discs with a diameter of 10 mm and a height of 1 mm.

[0084] S5. The formed KNNS-BNZ-BF-0.02Mn disc body is placed in a muffle furnace for debinding. The debinding temperature setting process includes: first, the muffle furnace temperature is raised from room temperature to 120°C and held for 60 minutes; second, the muffle furnace temperature is raised from 120°C to 500°C and held for 180 minutes; then, the muffle furnace temperature is raised from 500°C to 550°C; finally, the muffle furnace temperature is raised from 550°C to 850°C and held for 120 minutes, followed by natural cooling to room temperature. Next, the debinded KNNS-BNZ-BF-0.02Mn disc body is placed in the muffle furnace again for sintering to make it magnetic and improve the material density and mechanical strength. During the sintering process, the buried burning method is usually used to reduce element volatilization, that is, covering the disc body with the corresponding powder. The sintering temperature was 1070° C. and the temperature was kept for 180 min. The sintering temperature was then naturally cooled to room temperature to obtain a KNNS-BNZ-BF-0.02Mn ceramic disc material.

[0085] S6. Use a brush to dip a small amount of silver paste and evenly apply it to both sides of the sintered KNNS-BNZ-BF-0.02Mn ceramic disc to form a continuous silver paste film. Then place it in a muffle furnace for heating to ensure that the silver paste is tightly bonded to the ceramic surface and forms an electrode. The heating temperature is 600°C and the temperature is kept for 30 minutes. Finally, the KNNS-BNZ-BF-0.02Mn ceramic disc with electrodes is placed in a polarization device for polarization treatment. The polarization voltage is 3kV and the pressure is maintained for 10 minutes. Finally, the KNNS-BNZ-BF-0.02Mn lead-free piezoelectric ceramic material that meets the performance test is obtained.

[0086] The following performance characterizations were performed on the KNNS-BNZ-BF-0.02Mn lead-free piezoelectric ceramic material prepared by the method of this embodiment.

[0087] 1) XRD and temperature-varying dielectric tests were performed on KNNS-BNZ-BF-0.02Mn ceramics, demonstrating the structural characteristics of the coexistence of RT phases ( Figure 2 and Figure 3 ). At the same time, a higher dielectric constant (ε r =3001) and lower dielectric loss (tanθ=0.028)( Figure 5 ).

[0088] 2) The hysteresis curve and butterfly curve of KNNS-BNZ-BF-0.02Mn ceramic sample were tested by ferroelectric analyzer, and the maximum ferroelectric polarization intensity (P max =20.9μC / cm 2 ), a larger residual polarization intensity (P r =14.7μC / cm 2 ), smaller coercive field (E c =8.1kV / cm), a large bipolar ferroelectric total strain (S pol =0.176%), a large unipolar ferroelectric strain (S uni =0.135%) and a larger inverse piezoelectric coefficient (d 33 * =500pm / V)( Figure 4 ).

[0089] 3) Use quasi-static d 33 The piezoelectric constant and electromechanical coupling coefficient of KNNS-BNZ-BF-0.02Mn ceramic material were tested by measuring instrument and impedance analyzer, and the larger piezoelectric constant (d 33 =409pC / N) and a higher electromechanical coupling coefficient (k p =0.433)( Figure 5 ).

[0090] 4) The load-displacement curve of KNNS-BNZ-BF-0.02Mn ceramic material was obtained by nanoindentation, and the minimum indentation depth (H m =594nm)( Figure 6 ). In addition, the indentation and crack extension morphology, hardness and fracture toughness of KNNS-BNZ-BF-0.02Mn ceramic material were obtained by Vickers indentation instrument, where the hardness value is: v =4.5Gpa, polarization H v =4.35GPa; fracture toughness value: unpolarized K IC =1.213MPa·m 1 / 2 , polarization K IC =1.245MPa·m 1 / 2 ( Figure 7 ).

[0091] Example 4

[0092] This embodiment provides a method for preparing a KNNS-BNZ-BF-0.03Mn lead-free piezoelectric ceramic material, which is carried out according to the following steps:

[0093] S1. Prepare chemical reagents: Na2CO3 (AR 99.8%), K2CO3 (AR 99%), Nb2O5 (AR 99.95%), Sb2O3 (AR 99.99%), Bi2O3 (AR 99.99%), ZrO2 (AR 99%), Fe2O3 (99.99%) and MnO2 (AR99.95%).

[0094] S2, the above experimental materials were mixed according to the stoichiometric formula 0.964K 0.5 Na 0.5 Nb 0.955 Sb 0.045 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.006BiFeO3-0.03MnO2 (KNNS-BNZ-BF-0.03Mn) was weighed and proportioned on a high-precision balance. The weighed chemical reagents were poured into a polytetrafluoroethylene ball mill jar, and anhydrous ethanol was added as a dispersion medium. The mixture was ball milled for 720 minutes on a planetary ball mill at a speed of 580 r / min to ensure that the chemical reagents were fully mixed.

[0095] S3. Remove the highly mixed KNNS-BNZ-BF-0.03Mn slurry from the ball mill and dry it under a heat lamp. Then, pour the dried slurry into an alumina crucible, cover the crucible, and pre-calculate it in a muffle furnace at 850°C for 360 minutes. Finally, through the solid-phase reaction process during pre-calcination, a KNNS-BNZ-BF-0.03Mn solid solution compound with a specific structure is formed.

[0096] S4. The pre-calcined KNNS-BNZ-BF-0.03Mn solid solution was transferred to a mortar and granulated with 7% wt of polyvinyl alcohol (PVA) binder. The dried KNNS-BNZ-BF-0.03Mn granules were then compacted on a powder dry compactor at a compacting pressure of 10 MPa, resulting in KNNS-BNZ-BF-0.03Mn discs with a diameter of 10 mm and a height of 1 mm.

[0097] S5, the formed KNNS-BNZ-BF-0.03Mn wafer blank is placed in a muffle furnace for degassing treatment, and the degassing temperature setting process includes: first, the temperature of the muffle furnace is raised from room temperature to 120°C and kept for 60 min; second, the temperature of the muffle furnace is raised from 120°C to 500°C and kept for 180 min; then, the temperature of the muffle furnace is raised from 500°C to 550°C; finally, the temperature of the muffle furnace is raised from 550°C to 850°C, and kept for 120 min, and then naturally cooled to room temperature. Next, the KNNS-BNZ-BF-0.03Mn wafer blank after degassing treatment is placed in the muffle furnace again for sintering treatment to make it magnetized, and at the same time to improve the material density and mechanical strength. In the sintering process, the buried sintering method is usually used to reduce element volatilization, that is, the wafer blank is covered with the corresponding powder. The sintering temperature is 1070°C, and the temperature is kept for 180 min, and then naturally cooled to room temperature to obtain the KNNS-BNZ-BF-0.03Mn ceramic wafer material.

[0098] S6, a small amount of silver paste is taken with a brush and evenly applied to both sides of the sintered KNNS-BNZ-BF-0.03Mn ceramic wafer to form a continuous silver paste film. Then it is placed in a muffle furnace for heating to ensure that the silver paste is tightly combined with the ceramic surface and forms an electrode. The heating temperature is 600°C, and the temperature is kept for 30 min. Finally, the KNNS-BNZ-BF-0.03Mn ceramic wafer with electrode is placed in a polarization device for polarization treatment. The polarization voltage is 3kV, and the pressure is kept for 10 min, and finally the KNNS-BNZ-BF-0.03Mn lead-free piezoelectric ceramic material that meets the performance test is obtained.

[0099] The KNNS-BNZ-BF-0.03Mn lead-free piezoelectric ceramic material prepared by the method of this embodiment is characterized by the following properties.

[0100] 1) The KNNS-BNZ-BF-0.03Mn ceramic is tested by XRD and variable temperature dielectric instrument, which proves the structural characteristics of R-T phase coexistence ( Figure 2 and Figure 3 ). At the same time, a higher dielectric constant (ε r = 2898) and a lower dielectric loss (tanθ = 0.029) ( Figure 5 ) are obtained.

[0101] 2) The hysteresis curve and butterfly curve of the KNNS-BNZ-BF-0.03Mn ceramic sample are tested by a ferroelectric analyzer, and a larger ferroelectric maximum polarization strength (P max = 20.2μC / cm 2 ), a larger remanent polarization strength (P r = 12μC / cm 2), smaller coercive field (E c =8.15kV / cm), a large bipolar ferroelectric total strain (S pol =0.171%), a large unipolar ferroelectric strain (S uni =0.128%) and a larger inverse piezoelectric coefficient (d 33 * =474pm / V)( Figure 4 ).

[0102] 3) Use quasi-static d 33 The piezoelectric constant and electromechanical coupling coefficient of KNNS-BNZ-BF-0.03Mn ceramic material were tested by measuring instrument and impedance analyzer, and the larger piezoelectric constant (d 33 =371pC / N) and a higher electromechanical coupling coefficient (k p =0.429)( Figure 5 ).

[0103] 4) The load-displacement curve of KNNS-BNZ-BF-0.03Mn ceramic material was obtained by nanoindentation, and the minimum indentation depth (H) of the ceramic was obtained. m =608nm)( Figure 6 ). In addition, the hardness and fracture toughness of KNNS-BNZ-BF-0.03Mn ceramic material were obtained by using Vickers indenter, where the hardness value is: v =4.34Gpa, polarization H v =4.1GPa; fracture toughness value: unpolarized K IC =1.233MPa·m 1 / 2 , polarization K IC =1.254MPa·m 1 / 2 ( Figure 7 ).

[0104] Example 5

[0105] This embodiment provides a method for preparing a KNNS-BNZ-BF-0.04Mn lead-free piezoelectric ceramic material, which is carried out according to the following steps:

[0106] S1. Prepare chemical reagents: Na2CO3 (AR 99.8%), K2CO3 (AR 99%), Nb2O5 (AR 99.95%), Sb2O3 (AR 99.99%), Bi2O3 (AR 99.99%), ZrO2 (AR 99%), Fe2O3 (99.99%) and MnO2 (AR99.95%).

[0107] S2, the above experimental materials were mixed according to the stoichiometric formula 0.964K 0.5 Na0.5 Nb 0.955 Sb 0.045 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.006BiFeO3-0.04MnO2 (KNNS-BNZ-BF-0.04Mn) was weighed and proportioned on a high-precision balance. The weighed chemical reagents were poured into a polytetrafluoroethylene ball mill jar, and anhydrous ethanol was added as a dispersion medium. The mixture was ball milled for 720 minutes on a planetary ball mill at a speed of 580 r / min to ensure that the chemical reagents were fully mixed.

[0108] S3. Remove the highly mixed KNNS-BNZ-BF-0.04Mn slurry from the ball mill and dry it under a heat lamp. Then, pour the dried slurry into an alumina crucible, cover the crucible, and pre-calculate it in a muffle furnace at 850°C for 360 minutes. Finally, through the solid-phase reaction process during pre-calcination, a KNNS-BNZ-BF-0.04Mn solid solution compound with a specific structure is formed.

[0109] S4. The pre-calcined KNNS-BNZ-BF-0.04Mn solid solution was transferred to a mortar and granulated with 7% wt of polyvinyl alcohol (PVA) binder. The dried KNNS-BNZ-BF-0.04Mn granules were then compacted on a powder dry compactor at a compacting pressure of 10 MPa, resulting in KNNS-BNZ-BF-0.04Mn discs with a diameter of 10 mm and a height of 1 mm.

[0110] S5. The formed KNNS-BNZ-BF-0.04Mn disc body is placed in a muffle furnace for debinding. The debinding temperature setting process includes: first, the muffle furnace temperature is raised from room temperature to 120°C and held at this temperature for 60 minutes; second, the muffle furnace temperature is raised from 120°C to 500°C and held at this temperature for 180 minutes; then, the muffle furnace temperature is raised from 500°C to 550°C; finally, the muffle furnace temperature is raised from 550°C to 850°C and held at this temperature for 120 minutes, followed by natural cooling to room temperature. Next, the debinded KNNS-BNZ-BF-0.04Mn disc body is placed in the muffle furnace again for sintering to make it magnetic and improve the material density and mechanical strength. During the sintering process, the buried burning method is usually used to reduce element volatilization, that is, covering the disc body with the corresponding powder. The sintering temperature was 1070° C. and the temperature was kept for 180 min. The sintering temperature was then naturally cooled to room temperature to obtain a KNNS-BNZ-BF-0.04Mn ceramic disc material.

[0111] S6. Use a brush to dip a small amount of silver paste and evenly apply it to both sides of the sintered KNNS-BNZ-BF-0.04Mn ceramic disc to form a continuous silver paste film. Then place it in a muffle furnace for heating to ensure that the silver paste is tightly bonded to the ceramic surface and forms an electrode. The heating temperature is 600°C and the temperature is kept for 30 minutes. Finally, the KNNS-BNZ-BF-0.04Mn ceramic disc with electrodes is placed in a polarization device for polarization treatment. The polarization voltage is 3kV and the pressure is maintained for 10 minutes. Finally, the KNNS-BNZ-BF-0.04Mn lead-free piezoelectric ceramic material that meets the performance test is obtained.

[0112] The following performance characterizations were performed on the KNNS-BNZ-BF-0.04Mn lead-free piezoelectric ceramic material prepared by the method of this embodiment.

[0113] 1) XRD and variable temperature dielectric test were used to test KNNS-BNZ-BF-0.04Mn ceramics, proving the pseudo cubic phase structure characteristics ( Figure 2 and Figure 3 ),from Figure 3 It can be seen that the addition of MnO2 has a great influence on the dielectric properties of ceramics. When the doping is low, there is a stable RT phase boundary. When the doping is high, the RT phase boundary disappears and a pseudo cubic phase structure is formed. At the same time, a lower dielectric constant (ε r =2217) and higher dielectric loss (tanθ=0.035)( Figure 5 ).

[0114] 2) The hysteresis curve and butterfly curve of KNNS-BNZ-BF-0.04Mn ceramic sample were tested by ferroelectric analyzer, and the smaller ferroelectric maximum polarization intensity (P max =13.9μC / cm 2 ), smaller residual polarization intensity (P r =4.01μC / cm 2 ), smaller coercive field (E c =5.9kV / cm), smaller bipolar ferroelectric total strain (S pol =0.065%), smaller unipolar ferroelectric strain (S uni =0.063%) and a larger inverse piezoelectric coefficient (d 33 * =233pm / V)( Figure 4 ).

[0115] 3) Use quasi-static d 33 The piezoelectric constant and electromechanical coupling coefficient of KNNS-BNZ-BF-0.04Mn ceramic material were tested by measuring instrument and impedance analyzer, and a smaller piezoelectric constant (d 33=86pC / N) and a smaller electromechanical coupling coefficient (k p =0.16)( Figure 5 ).

[0116] 4) The load-displacement curve of KNNS-BNZ-BF-0.04Mn ceramic material was obtained by nanoindentation, and the minimum indentation depth (H m =566nm)( Figure 6 ), indicating excellent resistance to plastic deformation. In addition, the hardness and fracture toughness of KNNS-BNZ-BF-0.04Mn ceramic material were obtained using a Vickers indenter, where the hardness value is: v =6.3Gpa, polarization H v =5.7GPa; fracture toughness value: unpolarized K IC =1.101MPa·m 1 / 2 , polarization K IC =1.147MPa·m 1 / 2 ( Figure 7 ).

[0117] from Figure 7 As can be seen from Figures (b, d), when the MnO2 content is 0.04, the KNN-based piezoelectric ceramics obtain an ultra-high mechanical hardness H v =6.31Gpa.

[0118] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A potassium sodium niobate-based lead-free piezoelectric ceramic material, characterized in that: The chemical formula of the potassium sodium niobate-based lead-free piezoelectric ceramic material is 0.964K 0.5 Na 0.5 Nb 0.955 Sb 0.045 O3-0.03Bi 0.5 Na 0.5 ZrO3-0.006BiFeO3-xMnO2, wherein x=0.005~0.04, and x represents the molar fraction.

2. A method for preparing the potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 1, characterized in that: The following steps are involved: (1) According to the chemical formula of potassium sodium niobate-based lead-free piezoelectric ceramic material, chemical reagents Na2CO3, K2CO3, Nb2O5, Sb2O3, Bi2O3, ZrO2, Fe2O3 and MnO2 were weighed and prepared into powder; (2) using the powder to granulate and form a disc body; (3) performing debinding treatment on the disc blank; (4) sintering the debinding disc green body to obtain a disc ceramic material; (5) The sintered disc ceramic material is subjected to silver plating and polarization treatment to obtain a lead-free piezoelectric ceramic material.

3. The method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 2, characterized in that: When preparing the powder in step (1), the weighed chemical reagents are first ball-milled, then dried, and finally pre-calcined.

4. The method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 3, characterized in that: The temperature during the pre-firing treatment is controlled at 820°C to 880°C, and the temperature is kept at this temperature for 240min to 360min.

5. The method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 2, characterized in that: When preparing the disc body in step (2), the powder and the polyvinyl alcohol binder are first stirred and mixed and then dried. Then, the dried powder particles are placed in a forming mold and formed on a powder dry pressing machine.

6. The method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 5, characterized in that: The prepared disc blank has a diameter of 10 mm and a height of 0.8 mm to 1.5 mm.

7. The method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 2, characterized in that: The debinding process in step (3) includes the following four stages: The first stage is to raise the temperature from room temperature to 120°C and keep it for 60 min; The second stage is to increase the temperature from 120°C to 500°C and keep it at this temperature for 180 min; The third stage is to increase the temperature from 500°C to 550°C; The fourth stage is to increase the temperature from 550 °C to 850 °C and keep it at this temperature for 120 min, and then cool it naturally to room temperature.

8. The method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 2, characterized in that: In step (4), the sintering treatment is carried out by the buried firing method, the sintering temperature is 1040° C. to 1100° C., and the heat preservation time is 180 min to 240 min.

9. The method for preparing a potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 2, characterized in that: The silver plating polarization treatment method in step (5) is as follows: first, silver paste is evenly applied on both sides of the ceramic to form a continuous silver paste film; then, the ceramic sheet coated with silver paste is heated to ensure that the silver paste is tightly bonded to the ceramic surface and provides good conductive properties; finally, the ceramic disc with electrodes is placed in a polarization device for polarization treatment to obtain a lead-free piezoelectric ceramic material.

10. Use of the potassium sodium niobate-based lead-free piezoelectric ceramic material according to claim 1 or the potassium sodium niobate-based lead-free piezoelectric ceramic material prepared by the preparation method according to any one of claims 2 to 9, characterized in that: This includes piezoelectric / ferroelectric sensors or actuators or transducers.

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