High-entropy bismuth calcium niobate-based lead-free piezoelectric ceramic material and preparation method thereof

Abstract

This invention provides a high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material and its preparation method, belonging to the field of piezoelectric ceramic materials, with a chemical composition of (Ca... x Sr y Ba z Bi u Na 1‑x‑y‑z‑u Bi2Nb 2‑ w Ta w O9, 0.2≤x≤1, 0.2≤y≤1 / 3, 0.2≤z≤1 / 3, 0≤u≤0.2, 0≤w≤1, where u and w are not simultaneously 0. The ceramic composition of this system transitions from a single orthorhombic ferroelectric phase to a tetragonal phase, and it exhibits good piezoelectric properties and temperature insensitivity.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric ceramic materials, specifically relating to a high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material and its preparation method. Background Technology

[0002] Piezoelectric ceramics are functional ceramic materials capable of converting electrical energy into mechanical energy. They are widely used as core components in various vibration sensors and ultrasonic transducers, holding a vital position in modern industry and science. With the rapid development of modern industry, the demand for piezoelectric materials to operate in extreme environments is constantly increasing. In specialized fields such as aerospace and deep well exploration, there is an urgent need for next-generation piezoelectric devices based on high-temperature piezoelectric materials, requiring piezoelectric ceramic materials that can stably operate at temperatures of 300℃ and above. Currently, the dominant piezoelectric functional material on the market is lead zirconate titanate-based ceramic material, which boasts excellent electrical properties and a Curie temperature of Ti. C ~250-380℃. On the one hand, these piezoelectric ceramics contain a large amount of lead, which will cause serious environmental pollution problems. Various countries around the world have introduced relevant laws and regulations to restrict the use of lead in electronic products. On the other hand, due to the thermal depolarization of piezoelectric materials, their safe operating temperature is limited to its T... C Lead-free high-temperature piezoelectric ceramic materials have a lead content of less than 1 / 2 to 2 / 3, making it difficult to meet the current application requirements of high-temperature piezoelectric devices. Therefore, the development of high-voltage, high-temperature resistant, low-loss, and low-cost lead-free high-temperature piezoelectric ceramic materials is urgent and of significant economic value.

[0003] The structure of bismuth layered oxide ceramics mainly consists of a perovskite-like layer (ABO3) and a bismuth-containing layer (Bi2O2). 2+ The two are arranged alternately along the c-axis, so its overall formula is (Bi₂O₂). 2+ (A m-1 B m O 3m+1 ) 2- Where m represents the number of BO6 oxygen octahedral layers in the perovskite-like structure. This unique structure gives it excellent high-temperature stability under high-temperature conditions. Compared with traditional piezoelectric materials, this bismuth layered oxide ceramic has a high Curie temperature, low relative permittivity, and high Q. m These materials possess advantages such as low aging rate, good temperature stability, and easy sintering. Among them, calcium bismuth niobate CaBi₂Nb₂O₉ (ABN) with m=2 consists of a bismuth oxide layer (Bi₂O₂). 2+ And two perovskite-like layers (CaNb2O7) 2-Composition, it possesses a very high Curie temperature (~940℃), and also exhibits advantages such as good temperature stability, excellent insulation properties, low dielectric loss, and good mechanical properties. These characteristics make it a promising candidate for high-temperature piezoelectric applications. However, due to its unique layered structure, its piezoelectric coefficient is relatively low (d). 33 (~6pC / N). Furthermore, ABN has a high coercivity field, which requires a higher electric field during polarization, increasing energy loss and reducing material efficiency, thus limiting its application in high-temperature piezoelectric fields. In addition, during the high-temperature sintering process, the volatilization of Bi element causes the composition of ABN to deviate from the stoichiometry, resulting in impurities. This is also one of the main problems of ABN-based piezoelectric ceramics.

[0004] Despite some drawbacks and limitations of bismuth layered oxides in high-temperature piezoelectric materials, researchers continue to strive to overcome these issues and expand their potential in high-temperature piezoelectric applications through strategies such as doping modification and process optimization. Current research mainly focuses on doping modification, including A-site doping, B-site doping, and AB-site co-doping. While ABN ceramics have shown some improvement in piezoelectric activity, they still cannot meet the requirements of both piezoelectric performance and temperature insensitivity. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material and its preparation method. The ceramic composition of this system transitions from a single orthorhombic ferroelectric phase to a tetragonal phase, and it exhibits excellent piezoelectric properties and temperature insensitivity.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material with the chemical composition (Ca... x Sr y Ba z Bi u Na 1-x-y-z-u Bi2Nb 2-w Ta w O9, 0.2≤x≤1, 0.2≤y≤1 / 3, 0.2≤z≤1 / 3, 0≤u≤0.2, 0≤w≤1, u and w are not both 0.

[0008] Furthermore, the non-zero values ​​of x, y, z, and u are the same; the A in the general formula is Ca. 2+ 、Sr 2+ Ba 2+ Bi 3+ Na + Select at least four types, and calculate the mixed entropy ΔS. mix Greater than 1.5R.

[0009] This invention provides a method for preparing the above-mentioned high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material, comprising the following steps: S1. Weighing raw materials of metal carbonate or oxide according to stoichiometric ratio, mixing and calcining once to obtain pre-synthesized powder; S2. High-energy ball milling of the pre-synthesized powder, mixing and granulating, sieving and pressing into sheets, and sintering to obtain a ceramic sample; S3. Polishing the ceramic sample, cleaning and drying it, coating both ends with silver paste, and polarizing it.

[0010] Furthermore, in step S1, the mixing process involves ball milling the metal carbonate or oxide with alcohol or water as the medium for 8-12 hours at a speed of 300-500 r / min, followed by drying after ball milling.

[0011] Furthermore, the process parameters for the first calcination are as follows: the dried mixed raw materials are calcined in an oxidizing environment at a synthesis temperature of 850-950℃ for 3-4 hours.

[0012] Furthermore, in step S2, the process parameters for the high-energy ball milling are as follows: the pre-synthesized powder is ball-milled for 8-12 hours using alcohol or water as the medium at a speed of 300-500 r / min, and then dried after high-energy ball milling.

[0013] Furthermore, after drying, the D50 particle size of the powder is 1.7-2.1 μm, and the D40 / D50 ratio is 1.1-1.2.

[0014] Furthermore, the dried powder is mixed with a binder and granulated, then passed through a 100-150 mesh sieve and cold-pressed under a pressure of 200-300 MPa to obtain a ceramic green body.

[0015] Furthermore, the ceramic ligand is sintered in an oxidizing environment under normal pressure using a powder embedding method, with the temperature increased to 500-600℃ at a heating rate of 2-4℃ / min and held for 1.5-2.5h, then increased to 1070-1120℃ at a heating rate of 4-6℃ / min and sintered for 3-4h, and then cooled in the furnace after sintering.

[0016] Furthermore, the polarization process parameters are: heat and pressure holding for 5-20 minutes in high-temperature silicone oil at 150-180℃ under a DC electric field of 18-20kV / mm.

[0017] The beneficial effects of the technical solutions provided by the embodiments of the present invention include:

[0018] 1. The ceramic composition of the present invention is a high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic with temperature insensitivity and high piezoelectric coefficient. It can be obtained using traditional piezoelectric ceramic preparation techniques and industrial raw materials. It is low in cost, has good repeatability, and is free of any other impurities, making it practical.

[0019] 2. Compared to conventional doped solid-solution ceramic compositions, this invention utilizes a high-entropy strategy to significantly enhance the piezoelectricity of bismuth calcium niobate-based lead-free piezoelectric ceramics. It prepares bismuth calcium niobate-based lead-free piezoelectric ceramics ranging from low-entropy to medium-entropy and then to high-entropy. With increasing mixing entropy, its d... 33 The method significantly improves performance and reduces coercive field, providing a new approach for designing and preparing high-performance lead-free high-temperature piezoelectric ceramics. It has extremely high performance tunability and can be applied to various bismuth layered oxide ceramic systems.

[0020] 3. Using a high-entropy strategy can reduce the volatilization of Bi element, especially the higher the high-entropy value, the less Bi element volatilizes. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The XRD pattern of the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material prepared in the embodiments of the present invention;

[0023] Figure 2 The hysteresis loop of the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material prepared in the embodiments of the present invention;

[0024] Figure 3 The dielectric temperature profile of 5ABN prepared in Example 1 of this invention;

[0025] Figure 4 The dielectric temperature profile of 6ABN prepared in Example 4 of this invention;

[0026] Figure 5 The dielectric temperature profile of 3ABN prepared in Comparative Example 1 of this invention is shown. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] High-entropy alloys are broadly defined as alloys containing five or more constituent elements, with each element having an atomic fraction between 5% and 35%. This definition stems from the high mixing entropy caused by multiple principal elements. According to the Boltzmann hypothesis, the mixing entropy ΔS of a high-entropy alloy... mix The calculation formula is as follows:

[0029] ΔS mix=-R∑c i lnc i

[0030] Where R = 8.314 J / (K·mol), is the gas constant, and c i Let c1 = c2 = ... = c i At this point, the mixing entropy of the alloy will reach its maximum value.

[0031] This invention discloses a high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material with the chemical composition (Ca... x Sr y Ba z Bi u Na 1-x-y-z-u Bi2Nb 2-w Ta w O9, 0.2≤x≤1, 0.2≤y≤1 / 3, 0.2≤z≤1 / 3, 0≤u≤0.2, 0≤w≤1, u and w are not both 0.

[0032] This invention utilizes a high-entropy strategy to adjust the perovskite-like layer in ABN, further regulating its structure and properties to obtain a composition with superior piezoelectricity, thereby accelerating the practical application of lead-free ceramics in this system. The resulting piezoelectric ceramic exhibits a transformation from a single orthorhombic ferroelectric phase to a tetragonal phase, along with excellent piezoelectric properties and temperature insensitivity. Furthermore, the high-entropy strategy can reduce the volatilization of Bi, especially as the higher the high-entropy value, the less Bi volatilizes.

[0033] The non-zero values ​​of x, y, z, and u are the same; the A in the general formula is Ca. 2+ 、Sr 2+ Ba 2+ Bi 3+ Na + Select at least four types, and calculate the mixed entropy ΔS. mix Greater than 1.5R.

[0034] When the mixing entropy is greater than 1.5R, the bismuth niobate calcium-based lead-free piezoelectric ceramic material exhibits superior piezoelectricity and temperature insensitivity.

[0035] This invention also proposes a method for preparing the above-mentioned high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material, comprising the following steps:

[0036] S1. Weigh the raw materials of metal carbonate or oxide according to the stoichiometric ratio, mix them and calcine them once to obtain the pre-synthesized powder.

[0037] First, analytically pure or chemically pure carbonates or oxides are prepared and dried, preferably at 200-250℃ for 24 hours. After drying, the mixture is ball-milled for 8-12 hours at a speed of 300-500 r / min using alcohol or water as the medium. The mixture is then dried. The first calcination process parameters are as follows: the dried mixture is calcined in an oxidizing environment at a synthesis temperature of 850-950℃ for 3-4 hours to obtain the pre-synthesized powder.

[0038] This invention targets chemical compositions of (Ca) x Sr y Ba z Bi u Na 1-x-y-z-u Bi2Nb 2-w Ta w The material for O9 is selected from carbonate or oxide raw materials. In this invention, the carbonate or metal oxide raw materials can be selected from calcium carbonate, strontium carbonate, barium carbonate, bismuth trioxide, anhydrous sodium carbonate, niobium pentoxide, and tantalum pentoxide; the alcohol is preferably anhydrous ethanol.

[0039] To improve the oxidation degree of the raw materials, the preferred oxidation environment of the present invention is an oxygen flow rate of 40-50 mL / min.

[0040] S2. The pre-synthesized powder is subjected to high-energy ball milling, mixed and granulated, sieved, pressed into tablets, and sintered to obtain a ceramic sample.

[0041] The process parameters for the high-energy ball milling are as follows: the pre-synthesized powder is ball-milled for 8-12 hours with alcohol or water as the medium at a speed of 300-500 r / min, and then dried after high-energy ball milling. After drying, the D50 particle size of the powder is 1.7-2.1 μm, and the D40 / D50 ratio is 1.1-1.2. The dried powder is mixed with a binder and granulated. The binder is added at 5 wt% PVB of the powder mass. After passing through a 100-150 mesh sieve, it is cold-pressed under a pressure of 200-300 MPa to obtain a ceramic green body. The ceramic green body is a disc with a diameter of 8-10 mm and a thickness of 1-1.5 mm. The ceramic ligand is sintered in an oxidizing environment at normal pressure using the powder embedding method. The temperature is raised to 500-600℃ at a heating rate of 2-4℃ / min and held for 1.5-2.5 h. The temperature is then raised to 1070-1120℃ at a heating rate of 4-6℃ / min and sintered for 3-4 h. After sintering, the sample is cooled in the furnace to obtain the ceramic sample.

[0042] By controlling the high-energy ball milling process, the particle size of the powder can be controlled within a certain range, resulting in higher density of the subsequently prepared ceramic samples, improved breakdown field strength, and a certain influence on the microstructure and antiferroelectricity of the ceramic material.

[0043] S3. Polish the ceramic sample, clean and dry it, apply silver paste to both ends, and then polarize it.

[0044] The polarization process parameters are: heat and pressure hold for 5-20 minutes in high-temperature silicone oil at 150-180℃ under a DC electric field of 18-20kV / mm.

[0045] To better illustrate the embodiments of the present invention, the present invention will be further described in detail below through specific examples.

[0046] Example 1

[0047] The embodiments of the present invention provide (Ca) 0.2 Sr 0.2 Ba 0.2 Bi 0.2 Na 0.2 The preparation method of Bi2Nb2O9 includes the following steps:

[0048] S1. Weigh the raw materials of metal carbonates or oxides according to the stoichiometric ratio, mix them, and calcine them once to obtain a pre-synthesized powder. The metal carbonates or oxides are ball-milled for 8 hours at a speed of 400 r / min using alcohol or water as the medium, and then dried after ball milling. The process parameters for the first calcination are as follows: calcine the dried mixed raw materials in an oxidizing environment at a synthesis temperature of 850℃ for 4 hours to obtain the pre-synthesized powder.

[0049] S2. The pre-synthesized powder is subjected to high-energy ball milling, mixed and granulated, sieved, pressed into tablets, and sintered to obtain a ceramic sample. The process parameters for high-energy ball milling are as follows: the pre-synthesized powder is ball-milled for 12 hours with alcohol or water as the medium at a speed of 400 r / min, and then dried after high-energy ball milling. After drying, the D50 particle size of the powder is 1.8 μm, and the D40 / D50 ratio is 1.2. The dried powder is mixed with a binder and granulated, sieved through a 100-150 mesh sieve, and then cold-pressed under a pressure of 200 MPa to obtain a ceramic green body. The ceramic ligand is sintered in an oxidizing environment at normal pressure using a powder embedding method, heated to 550℃ at a heating rate of 3℃ / min and held for 2 hours, then heated to 1100℃ at a heating rate of 5℃ / min and sintered for 4 hours. After sintering, it is cooled in the furnace to obtain the ceramic sample.

[0050] S3. After polishing, cleaning, and drying the ceramic sample, apply silver paste to both ends and then polarize it. The polarization process parameters are: holding at 180°C in high-temperature silicone oil under a DC electric field of 18kV / mm for 20 minutes. The prepared (Ca) 0.2 Sr 0.2 Ba 0.2 Bi 0.2 Na 0.2 Bi₂Nb₂O₉ piezoelectric ceramics are denoted as 5ABN.

[0051] By calculating its mixture entropy ΔS mix It is 1.61R (high entropy); such as Figure 1 As shown, 5ABN does not contain any impurities and is dominated by a tetragonal phase structure.

[0052] like Figure 2 As shown, the coercive field is 6.7 kV / mm, as Figure 3 Relative permittivity ε r The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 230-380, and the fluctuation range of dielectric loss tanσ is 0.015-0.038.

[0053] After measurement, its d 33 It is 13pC / N.

[0054] Example 2

[0055] The embodiments of the present invention provide (Ca) 0.2 Sr 0.2 Ba 0.2 Bi 0.2 Na 0.2 The preparation method of Bi2Nb2O9 includes the following steps:

[0056] S1. Weigh the raw materials of metal carbonates or oxides according to the stoichiometric ratio, mix them, and calcine them once to obtain a pre-synthesized powder. The metal carbonates or oxides are ball-milled for 8 hours at a speed of 300 r / min using alcohol or water as the medium, and then dried after ball milling. The process parameters for the first calcination are as follows: calcine the dried mixed raw materials in an oxidizing environment at a synthesis temperature of 850℃ for 3 hours to obtain the pre-synthesized powder.

[0057] S2. The pre-synthesized powder is subjected to high-energy ball milling, mixed and granulated, sieved, pressed into tablets, and sintered to obtain a ceramic sample. The process parameters for high-energy ball milling are as follows: the pre-synthesized powder is ball-milled for 8 hours with alcohol or water as the medium at a speed of 300 r / min, and then dried after high-energy ball milling. After drying, the D50 particle size of the powder is 2.1 μm, and the D40 / D50 ratio is 1.1. The dried powder is mixed with a binder and granulated, sieved through a 100-150 mesh sieve, and then cold-pressed under a pressure of 200 MPa to obtain a ceramic green body. The ceramic ligand is sintered in an oxidizing environment at normal pressure using a powder embedding method, heated to 500℃ at a heating rate of 2℃ / min and held for 1.5 hours, then heated to 1070℃ at a heating rate of 5℃ / min and sintered for 3 hours. After sintering, the sample is cooled in the furnace to obtain the ceramic sample.

[0058] S3. Polish the ceramic sample, clean and dry it, apply silver paste to both ends, and then polarize it. The polarization process parameters are: heat and pressure hold for 5 minutes in high-temperature silicone oil at 150℃ under a DC electric field of 18kV / mm.

[0059] By calculating its mixture entropy ΔS mix It has an entropy of 1.61R (high entropy); there are no impurities, and the structure is mainly tetragonal.

[0060] The coercive field of the prepared piezoelectric ceramic material was measured to be 6.7 kV / mm, and the relative permittivity ε was [value missing] over a temperature range from room temperature to 500 °C. r The fluctuation range is 240-400, and the fluctuation range of dielectric loss tanσ is 0.016-0.040.

[0061] After measurement, its d 33 It is 11pC / N.

[0062] Example 3

[0063] The embodiments of the present invention provide (Ca) 0.2 Sr 0.2 Ba 0.2 Bi 0.2 Na 0.2 The preparation method of Bi2Nb2O9 includes the following steps:

[0064] S1. Weigh the raw materials of metal carbonates or oxides according to the stoichiometric ratio, mix them, and calcine them once to obtain a pre-synthesized powder. The metal carbonates or oxides are ball-milled for 8 hours at a speed of 300 r / min using alcohol or water as the medium, and then dried after ball milling. The process parameters for the first calcination are as follows: calcine the dried mixed raw materials in an oxidizing environment at a synthesis temperature of 950℃ for 4 hours to obtain the pre-synthesized powder.

[0065] S2. The pre-synthesized powder is subjected to high-energy ball milling, mixed and granulated, sieved, pressed into tablets, and sintered to obtain a ceramic sample. The process parameters for high-energy ball milling are as follows: the pre-synthesized powder is ball-milled for 12 hours with alcohol or water as the medium at a speed of 500 r / min, and then dried after high-energy ball milling. After drying, the D50 particle size of the powder is 1.7 μm, and the D40 / D50 ratio is 1.1. The dried powder is mixed with a binder and granulated, sieved through a 100-150 mesh sieve, and then cold-pressed under a pressure of 300 MPa to obtain a ceramic green body. The ceramic ligand is sintered in an oxidizing environment at normal pressure using a powder embedding method, heated to 600℃ at a heating rate of 4℃ / min and held for 2.5 hours, then heated to 1120℃ at a heating rate of 6℃ / min and sintered for 4 hours. After sintering, it is cooled in the furnace to obtain the ceramic sample.

[0066] S3. Polish the ceramic sample, clean and dry it, apply silver paste to both ends, and then polarize it. The polarization process parameters are: heat and pressure hold for 20 minutes in high-temperature silicone oil at 180℃ under a DC electric field of 20kV / mm.

[0067] By calculating its mixture entropy ΔS mix The value is 1.61R; there are no impurities, and the structure is mainly tetragonal.

[0068] The coercive field of the prepared piezoelectric ceramic material was measured to be 7.1 kV / mm. The relative permittivity εr and dielectric loss tanσ were measured at temperatures ranging from room temperature to 500 °C. r The fluctuation range is 220-390, and the fluctuation range of dielectric loss tanσ is 0.015-0.040.

[0069] After measurement, its d 33 It is 10 pC / N.

[0070] Example 4

[0071] Unlike Example 1, this example prepares (Ca) 0.2 Sr 0.2 Ba 0.2 Bi 0.2 Na 0.2 Bi2NbTaO9 piezoelectric ceramic, denoted as 6ABN.

[0072] By calculating its mixture entropy ΔS mix It is 2.3R (high entropy); such as Figure 1 As shown, 6ABN does not contain any impurities and is dominated by a tetragonal phase structure.

[0073] like Figure 2 As shown, the coercive field of the prepared piezoelectric ceramic material was measured to be 7.7 kV / mm. Figure 4 As shown, the relative permittivity εr The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 154-467, and the fluctuation range of dielectric loss tanσ is 0.047-0.110.

[0074] After measurement, its d 33 It is 14pC / N.

[0075] Example 5

[0076] Unlike Example 2, this example prepares (Ca) 0.2 Sr 0.2 Ba 0.2 Bi 0.2 Na 0.2 Bi2NbTaO9 piezoelectric ceramic.

[0077] By calculating its mixture entropy ΔS mix It has an entropy of 2.3R (high entropy); there are no impurities, and the structure is mainly tetragonal.

[0078] The coercive field of the prepared piezoelectric ceramic material was measured to be 7.7 kV / mm, and the relative permittivity ε was [missing value]. r The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 165-482, and the fluctuation range of dielectric loss tanσ is 0.05-0.12.

[0079] After measurement, its d 33 It is 12pC / N.

[0080] Example 6

[0081] Unlike Example 3, this example prepares (Ca) 0.2 Sr 0.2 Ba 0.2 Bi 0.2 Na 0.2 Bi2NbTaO9 piezoelectric ceramic.

[0082] By calculating its mixture entropy ΔS mix It has an entropy of 2.3R (high entropy); there are no impurities, and the structure is mainly tetragonal.

[0083] The coercive field of the prepared piezoelectric ceramic material was measured to be 7.9 kV / mm, and the relative permittivity ε was [missing value]. r The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 143-457, and the fluctuation range of dielectric loss tanσ is 0.049-0.111.

[0084] After measurement, its d 33 It is 11pC / N.

[0085] Comparative Example 1

[0086] Unlike Example 1, this comparative example prepares CaBi₂Nb₂O₉ piezoelectric ceramics. The prepared CaBi₂Nb₂O₉ piezoelectric ceramics are denoted as ABN.

[0087] Its mixing entropy ΔS mix =0 (low entropy); such as Figure 1 As shown, ABN does not contain any impurities and is dominated by a tetragonal phase structure.

[0088] like Figure 2 As shown, the coercive field of the prepared piezoelectric ceramic material was measured to be 8.0 kV / mm, and the relative permittivity ε was... r The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 119-139, and the fluctuation range of dielectric loss tanσ is 0.005-0.032.

[0089] After measurement, its d 33 It is 5pC / N.

[0090] Comparative Example 2

[0091] Unlike Example 1, this comparative example prepared (Ca 1 / 3 Sr 1 / 3 Ba 1 / 3 Bi₂Nb₂O₉ piezoelectric ceramics. The prepared (Ca) 1 / 3 Sr 1 / 3 Ba 1 / 3 Bi₂Nb₂O₉ piezoelectric ceramics are denoted as 3ABN.

[0092] Its mixing entropy ΔS mix It is 1.1R (medium entropy); such as Figure 1 As shown, 3ABN does not contain any impurities and is dominated by a tetragonal phase structure.

[0093] like Figure 2 As shown, the coercive field of the prepared piezoelectric ceramic material was measured to be 4.9 kV / mm. Figure 5 As shown, the relative permittivity ε r The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 273-381, and the fluctuation range of dielectric loss tanσ is 0.038-0.058.

[0094] After measurement, its d 33 It is 8pC / N.

[0095] Comparative Example 3

[0096] Unlike Example 1, in this comparative example, the powder prepared in step S2 has a D50 particle size of 3.1 μm and a D40 / D50 ratio of 1.1.

[0097] Its mixing entropy ΔS mix It has an entropy of 1.61R (high entropy); there are no impurities, and the structure is mainly tetragonal.

[0098] The coercive field of the prepared piezoelectric ceramic material was measured to be 4.9 kV / mm, and the relative permittivity ε was [missing value]. r The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 285-396, and the fluctuation range of dielectric loss tanσ is 0.041-0.068.

[0099] After measurement, its d 33 It is 11pC / N.

[0100] Comparative Example 4

[0101] Unlike Example 1, in this comparative example, the powder prepared in step S2 has a D50 particle size of 4.5 μm and a D40 / D50 ratio of 1.2.

[0102] Its mixing entropy ΔS mix It has an entropy of 1.61R (high entropy); there are no impurities, and the structure is mainly tetragonal.

[0103] The coercive field of the prepared piezoelectric ceramic material was measured to be 5.1 kV / mm, and the relative permittivity ε was [missing value]. r The dielectric loss tanσ and the relative permittivity ε at temperatures ranging from room temperature to 500°C r The fluctuation range is 261-375, and the fluctuation range of dielectric loss tanσ is 0.038-0.061.

[0104] After measurement, its d 33 It is 10 pC / N.

[0105] By comparing Examples 1 and 4, and Comparative Examples 1 and 2, it can be seen that as the entropy value increases, d 33 Significant improvement and a significant reduction in coercive field; by comparing Example 1, Comparative Examples 3 and 4, it can be seen that when the D50 particle size of the powder is 1.7-2.1 μm and the D40 / D50 is 1.1-1.2, d 33 Significant improvement, reduced coercive field, and reduced dielectric loss tanσ.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material, characterized in that, The chemical composition is (Ca x Sr y Ba z Bi u Na 1-x-y-z-u Bi2Nb 2-w Ta w O9, 0.2≤x≤1, 0.2≤y≤1 / 3, 0.2≤z≤1 / 3, 0≤u≤0.2, 0≤w≤1, u and w are not both 0.

2. The high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 1, characterized in that, The values ​​of x, y, z, and u are the same; The Ca in the chemical composition 2+ 、Sr 2+ Ba 2+ Bi 3+ Na + Choose at least four.

3. A method for preparing a high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Weigh the raw materials of metal carbonate or oxide according to the stoichiometric ratio, mix them and calcine them once to obtain the pre-synthesized powder; S2. The pre-synthesized powder is subjected to high-energy ball milling, mixed and granulated, sieved, pressed into tablets, and sintered to obtain a ceramic sample; S3. Polish the ceramic sample, clean and dry it, apply silver paste to both ends, and then polarize it.

4. The method for preparing the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 3, characterized in that, In step S1, the mixing process involves ball milling the metal carbonate or oxide with alcohol or water as the medium for 8-12 hours at a speed of 300-500 r / min, followed by drying after ball milling.

5. The method for preparing the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 4, characterized in that, The process parameters for the first calcination are as follows: the dried mixed raw materials are calcined in an oxidizing environment at a synthesis temperature of 850-950℃ for 3-4 hours.

6. The method for preparing the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 3, characterized in that, In step S2, the process parameters for high-energy ball milling are as follows: the pre-synthesized powder is ball-milled for 8-12 hours with alcohol or water as the medium at a speed of 300-500 r / min, and then dried after high-energy ball milling.

7. The method for preparing the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 6, characterized in that, After drying, the D50 particle size of the powder is 1.7-2.1 μm, and the D40 / D50 ratio is 1.1-1.

2.

8. The method for preparing the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 6, characterized in that, The dried powder is mixed with a binder and granulated. After passing through a 100-150 mesh sieve, it is cold-pressed under a pressure of 200-300 MPa to obtain a ceramic green body.

9. The method for preparing the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 8, characterized in that, The ceramic green body is sintered in an oxidizing environment under normal pressure using the powder embedding method. The temperature is increased to 500-600℃ at a heating rate of 2-4℃ / min and held for 1.5-2.5h. The temperature is then increased to 1070-1120℃ at a heating rate of 4-6℃ / min and sintered for 3-4h. After sintering, the green body is cooled in the furnace.

10. The method for preparing the high-entropy bismuth niobate calcium-based lead-free piezoelectric ceramic material according to claim 3, characterized in that, The polarization process parameters are: heat and pressure hold for 5-20 minutes in high-temperature silicone oil at 150-180℃ under a DC electric field of 18-20kV / mm.

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