A high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic and its preparation method

Abstract

The present invention provides a high entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic and a preparation method thereof, which belongs to the field of high-temperature piezoelectric ceramic materials. The chemical composition is Ca 1‑x‑y (Na 0.5 Bi 0.5 ) x Bi 2+y Ti y Nb 2‑y‑ z Ta z O9+u wt% MO, 0.1≤x≤0.9, 0.1≤y≤0.9, 0≤z≤5 / 3, 0<u≤0.4, where MO is selected from one or more of B2O3, Fe2O3, CuO, and MnO2. This ceramic system comprises a single orthorhombic ferroelectric phase and exhibits excellent piezoelectric properties, electrical insulation, and a high Curie temperature.

Description

Technical Field

[0001] The present invention belongs to the field of high-temperature piezoelectric ceramic materials, and specifically relates to a high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic and a preparation method thereof. Background Art

[0002] Piezoelectric ceramic materials are electronic functional materials that can realize the mutual conversion of electrical energy and mechanical energy. Various piezoelectric components such as vibration sensors and ultrasonic transducers built with piezoelectric ceramic materials as core components are widely used in many civil and military fields such as home appliances, aerospace, medical equipment, and oil exploration. With the rapid development of modern industry and the continuous changes in actual application needs, the application of piezoelectric materials has shifted from conventional use to service in extreme environments such as high temperature. The industry's demand for high-temperature piezoelectric materials is becoming more and more urgent. Generally, due to the thermal depolarization of piezoelectric materials, their safe operating temperature is above their Curie temperature T. C Less than 1 / 2-2 / 3 of the total, which requires its T C At least more than 400 ℃, and the high temperature piezoelectric ceramic materials used in high temperature piezoelectric vibration sensors used in aircraft engines have a higher operating temperature. Some devices use temperatures of ~480 ℃, and some require ultra-high temperature piezoelectric vibration sensors above 650 ℃. Regardless of environmental and health requirements or actual operating temperature restrictions, the most widely used commercial lead zirconate titanate based piezoelectric material (T C However, the high temperature (250-380℃) of lead-free piezoelectric materials has irreconcilable defects, which limits its further promotion in high-temperature piezoelectric device applications. In addition, the need for sustainable and green development has made people pay more attention to the development of lead-free piezoelectric materials.

[0003] Compared with traditional piezoelectric materials, the bismuth layered oxide CaBi2Nb2O9 structure is composed of bismuth oxide layers (Bi2O2) 2+ and two perovskite-like layers (CaNb2O7) 2- They are arranged alternately along the c-axis direction, have a high Curie temperature (~940℃), and have advantages such as good temperature stability, low dielectric loss, excellent insulation, low aging rate, and easy sintering. These characteristics make them have great potential in the field of high-temperature piezoelectricity. However, their unique layered structure leads to their piezoelectric coefficient d 33 The piezoelectric performance of CaBi2Nb2O9 is relatively low (~5.8pC / N). Moreover, during the high-temperature sintering process, the volatilization of Bi will cause the composition of CaBi2Nb2O9 to deviate from the stoichiometric ratio and even produce a second phase, further reducing its piezoelectric activity. These problems restrict its practical application in high-temperature fields. Improving its piezoelectric performance has become an urgent problem to be solved before large-scale application.

[0004] Although CaBi2Nb2O9 has some shortcomings and problems, people have improved its piezoelectric activity and expanded its potential in high-temperature piezoelectric applications through strategies such as element doping and process optimization. Among them, the piezoelectricity of CaBi2Nb2O9-based ceramics has been improved through texture engineering, chemical doping and special sintering technology. However, under the condition that the Curie temperature is greater than 900℃, the piezoelectric coefficient d 33 It is difficult to achieve or even exceed 20pC / N, which cannot meet the requirements of high voltage electrical performance and high Curie temperature. At the same time, the use of special processes is not only costly and complex, but also unsuitable for large-scale industrial production. Summary of the Invention

[0005] To solve the above problems, the present invention provides a high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic and a preparation method. The ceramic composition of this system is a single orthorhombic ferroelectric phase, which has excellent piezoelectric properties, electrical insulation and high Curie temperature.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a high entropy calcium bismuth niobate based high temperature lead-free piezoelectric ceramic, the chemical composition of which is Ca 1-x-y (Na 0.5 Bi 0.5 ) x Bi 2+y Ti y Nb 2-y-z Ta z O9+u wt%MO, 0.1≤x≤0.9, 0.1≤y≤0.9, 0≤z≤5 / 3, 0<u≤0.4, wherein MO is selected from one or more combinations of B2O3, Fe2O3, CuO, and MnO2.

[0008] Furthermore, the chemical composition is: Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 5 / 3-z Ta z O9+u wt%MO, 0≤z≤5 / 3, wherein MO is selected from one or more combinations of B2O3, Fe2O3, CuO, and MnO2.

[0009] The present invention provides a preparation method for the above-mentioned high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic, comprising the following steps: S1. weighing raw materials of metal carbonate or oxide according to a stoichiometric ratio, mixing and calcining once to obtain a pre-synthesized powder; S2. adding a sintering aid to the pre-synthesized powder according to a stoichiometric ratio, performing high-energy ball milling, mixing and granulating, sieving, pressing and sintering to obtain a ceramic sample; S3. polishing the ceramic sample, cleaning and drying it, coating both end faces with silver paste, and polarizing it.

[0010] Furthermore, in step S1, the mixing is as follows: the metal carbonate or oxide is ball-milled for 8-12 hours with alcohol or water as the medium at a rotation speed of 300-500 r / min, and then dried after the ball-milling.

[0011] Furthermore, the process parameters of the primary calcination are: calcining the dried mixed raw materials in an air environment at a synthesis temperature of 800-900° C. and keeping the temperature for 3-4 hours.

[0012] Furthermore, in step S2, the process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 12-24 hours with alcohol or water as the medium, the rotation speed is 400-600 r / min, and the high-energy ball milling is followed by drying.

[0013] Furthermore, after drying, the D50 particle size of the powder is 1.2-1.4 μm, and the D40 / D50 is 1.2-1.3.

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

[0015] Furthermore, in step S2, sintering is carried out in an air environment using a powder embedding method at normal pressure, heating the temperature to 500-600°C at a heating rate of no more than 5°C / min and keeping the temperature for at least 1 hour to remove the binder, heating the temperature to 1060-1140°C at a heating rate of no more than 6°C / min, sintering for 3-4 hours, and cooling with the furnace after sintering is completed.

[0016] Furthermore, in step S3, the polarization process parameters are: heat preservation and pressure preservation for 20-30 minutes in high-temperature silicone oil at 120-150°C and a DC electric field of 12-14 kV / mm.

[0017] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include:

[0018] 1. The ceramic composition of the present invention is a kind of ceramic composition with high voltage coefficient d 33 and high Curie temperature T CThe high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramics can be obtained using traditional piezoelectric ceramic preparation technology and industrial raw materials. The process is simple, the cost is low, and it is easy to prepare. It does not contain any other second phase, has good repeatability, and is suitable for large-scale production.

[0019] 2. Compared with the conventional doped solid solution ceramic components, the present invention uses a high entropy strategy to significantly improve the piezoelectric activity of calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramics, while maintaining its high T under the premise of improving its piezoelectricity. C Taking advantage of the advantages, a series of high-entropy bismuth calcium niobate-based high-temperature lead-free piezoelectric ceramics with excellent comprehensive piezoelectric properties were prepared. This method provides a new idea for the design and preparation of high-performance lead-free high-temperature piezoelectric ceramics. It is universal and can be applied to other bismuth layered structure oxide ceramic systems.

[0020] 3. Use high entropy strategy to reduce the content of Bi element and introduce sintering aid to lower the sintering temperature and reduce the volatilization of Bi element. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

[0023] Figure 2 Surface morphology of the high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic material prepared in an embodiment of the present invention, a is CBN1; b is CBN2; c is CBN3; d is CBN4;

[0024] Figure 3 The dielectric temperature curve of CBN1 prepared in Example 1 of the present invention;

[0025] Figure 4 The dielectric temperature curve of CBN2 prepared in Example 2 of the present invention;

[0026] Figure 5 The dielectric temperature curve of CBN3 prepared in Example 3 of the present invention;

[0027] Figure 6 This is the dielectric temperature curve of CBN4 prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] The embodiment of the present invention discloses a high entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic, characterized in that the chemical composition is Ca 1-x-y (Na 0.5 Bi 0.5 ) x Bi 2+y Ti y Nb 2-y-z Ta z O9+u wt%MO, 0.1≤x≤0.9, 0.1≤y≤0.9, 0≤z≤5 / 3, 0<u≤0.4, wherein MO is selected from one or more combinations of B2O3, Fe2O3, CuO, and MnO2.

[0030] The present invention uses a high entropy strategy to adjust the perovskite-like layer in CaBi2Nb2O9 and further regulates the structure and performance, thereby obtaining a component with excellent comprehensive piezoelectric properties to accelerate the practical application of lead-free ceramics in this system, and obtaining a component with an orthorhombic ferroelectric phase and a high piezoelectric coefficient d 33 , high Curie temperature T C And high-temperature lead-free piezoelectric ceramics with excellent insulation performance; secondly, the high entropy strategy is used to reduce the content of Bi elements and the introduction of sintering aids to reduce the sintering temperature, which can reduce the volatilization of Bi elements. The high-temperature lead-free piezoelectric ceramics proposed in this application are used. 33 Greater than 20pC / N, Curie temperature greater than 900℃, and resistivity greater than 1×10 at 600℃ 6 Ω·cm, compared with the existing technology, the resistivity is improved by at least one order of magnitude.

[0031] Preferably, the chemical composition is: Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 5 / 3-z Ta z O9+u wt%MO,0≤z≤5 / 3, wherein MO is selected from one or more combinations of B2O3, Fe2O3, CuO, and MnO2. In this preferred technical solution, d 33 Greater than 20pC / N.

[0032] The embodiment of the present invention further provides a method for preparing the above-mentioned high-temperature lead-free piezoelectric ceramic, comprising the following steps:

[0033] S1. Weigh the raw materials of metal carbonate or oxide according to the stoichiometric ratio, mix them and calcine them once to obtain a pre-synthesized powder.

[0034] First, analytically pure or chemically pure carbonate or oxide raw materials are batched. After batching, they are preferably dried. The drying process in the embodiment of the present invention is drying at 200-250°C for at least 10 hours, which will not be described in detail below. After drying, the raw materials are mixed. The mixing is performed by ball milling. The mixing process is as follows: the metal carbonate or oxide is ball milled in alcohol or water for 8-12 hours at a speed of 300-500 r / min. After the ball milling, the raw materials are dried. The process parameters of the primary calcination are as follows: the dried mixed raw materials are calcined in an air environment at a synthesis temperature of 800-900°C and kept warm for 3-4 hours to obtain a pre-synthesized powder.

[0035] The present invention is directed to a compound having a chemical composition of Ca 1-x-y (Na 0.5 Bi 0.5 ) x Bi 2+y Ti y Nb 2-y-z Ta z The material of O9+u wt%MO is a carbonate or oxide raw material. Preferably, the carbonate or metal oxide raw material can be selected from calcium carbonate, anhydrous sodium carbonate, bismuth trioxide, titanium dioxide, niobium pentoxide, tantalum pentoxide, boron trioxide, iron trioxide, copper oxide, and manganese dioxide; the alcohol is preferably anhydrous ethanol.

[0036] S2. Add a sintering aid to the pre-synthesized powder according to a stoichiometric ratio, perform high-energy ball milling, mix and granulate, sieve, press into tablets, and sinter to obtain a ceramic sample.

[0037] The process parameters of the high-energy ball milling are as follows: the pre-synthesized powder and the sintering aid are ball milled for 12-24 hours with alcohol or water as the medium, the rotation speed is 400-600r / min, and the high-energy ball milling is followed by drying. Preferably, in the ball milling process, the material-to-ball ratio is 0.8-1.1, 400-450r / min ball milling is used for 4-5 hours, 500-600r / min ball milling is used for 8-19 hours, and after drying, the D50 particle size of the powder is 1.2-1.4μm, and D40 / D50 is 1.2-1.3; the particle size has a great influence on the performance of the product. Within the above particle size range, it can inhibit the burning loss of Bi during the sintering process, and facilitate the uniform mixing of the sintering aid and the pre-synthesized powder, thereby avoiding the uneven distribution of the sintering aid during the subsequent sintering process, which leads to poor local sintering properties, and the displacement of the Bi element during the sintering process due to the uneven distribution of the sintering aid. The dried powder is mixed with the binder to form The binder is added in an amount of 3wt% of the powder mass. In the embodiment of the present invention, PVB is selected as the binder. After passing through a 100-150 mesh sieve, the mixture is cold-pressed under a pressure of 100-200 MPa to obtain a ceramic green body. The ceramic green body prepared in the embodiment of the present invention is a disc with a diameter of 8-10 mm and a thickness of 1-1.4 mm. The ceramic ligand is sintered in an air environment by a powder embedding method at normal pressure, and the temperature is increased to 500-600°C at a heating rate of no more than 5°C / min, and the mixture is kept warm for at least 1 hour to remove the binder. The mixture is then heated to 1060-1140°C at a heating rate of no more than 6°C / min, and sintered for 3-4 hours. After sintering, the mixture is cooled in the furnace to obtain a ceramic sample.

[0038] S3. The ceramic sample is polished, cleaned, and dried, and then silver paste is applied to both end surfaces and polarized.

[0039] The polarization process parameters are: heat preservation and pressure preservation for 20-30 minutes in high-temperature silicone oil at 120-150° C. and a DC electric field of 12-14 kV / mm.

[0040] In order to better illustrate the embodiments of the present invention, the present invention is further described in detail below through specific examples.

[0041] Example 1

[0042] The embodiment of the present invention provides Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 5 / 3 O9 high-temperature lead-free piezoelectric ceramics and a preparation method thereof, comprising the following steps:

[0043] S1. Weigh metal carbonate or oxide raw materials according to the stoichiometric ratio, mix them, and perform a primary calcination to obtain a presynthesized powder. The metal carbonate or oxide is ball-milled in alcohol or water for 8 hours at a speed of 400 r / min, followed by drying. The process parameters for the primary calcination are as follows: the dried mixed raw materials are calcined in an air environment at a synthesis temperature of 800°C for 4 hours to obtain the presynthesized powder.

[0044] S2. Add a certain sintering aid to the pre-synthesized powder according to a stoichiometric ratio, perform high-energy ball milling, mix and granulate, press into tablets after screening, and sinter to obtain a ceramic sample. The process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 12 hours with alcohol or water as the medium, the rotation speed is 400r / min, and the powder is dried after high-energy ball milling. After drying, it is mixed with a binder and granulated, and after passing through a 100-150 mesh sieve, it is cold-pressed at a pressure of 200MPa to obtain a ceramic body; the ceramic ligand is sintered in an air environment by a powder embedding method at normal pressure, and the temperature is increased to 500℃ at a heating rate of 3℃ / min and kept at this temperature for 2h, and then increased to 1060℃ at a heating rate of 5℃ / min, and sintered for 4h. After sintering, it is cooled in the furnace to obtain a ceramic sample.

[0045] S3. After polishing, cleaning and drying the ceramic sample, apply silver paste on both ends and polarize. The polarization process parameters are: in high temperature silicone oil at 150℃, keep warm and pressurize under 14kV / mm DC electric field for 20min. 1 / 3Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 5 / 3 O9 piezoelectric ceramics are denoted as CBN1.

[0046] By calculating its mixing entropy ΔS mix is 1.78R, such as Figure 1 As shown, there is no impurity phase in CBN1, and the orthorhombic phase structure is dominant.

[0047] like Figure 2 As shown in a, the sample has a rod-like or sheet-like structure and is relatively dense; Figure 3 , Curie temperature T C is 906℃; through measurement, its d 33 The resistivity is 20.6pC / N and 1.6×10 6 Ω·cm.

[0048] Example 2

[0049] The embodiment of the present invention provides Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3Nb 5 / 3 O9 high-temperature lead-free piezoelectric ceramics and a preparation method thereof, comprising the following steps:

[0050] S1. Weigh metal carbonate or oxide raw materials according to the stoichiometric ratio, mix them, and perform a primary calcination to obtain a presynthesized powder. The metal carbonate or oxide is ball-milled in alcohol or water for 8 hours at a speed of 300 r / min, followed by drying. The process parameters for the primary calcination are as follows: the dried mixed raw materials are calcined in an air environment at a synthesis temperature of 800°C for 3 hours to obtain the presynthesized powder.

[0051] S2. Add a certain sintering aid to the pre-synthesized powder according to a stoichiometric ratio, perform high-energy ball milling, mix and granulate, press into tablets after screening, and sinter to obtain a ceramic sample. The process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 12 hours with alcohol or water as the medium, the rotation speed is 400r / min, and the powder is dried after high-energy ball milling. After drying, it is mixed with a binder and granulated, and after passing through a 100-150 mesh sieve, it is cold-pressed at a pressure of 100MPa to obtain a ceramic body; the ceramic ligand is sintered in an air environment by a powder embedding method at normal pressure, and the temperature is increased to 500℃ at a heating rate of 5℃ / min and kept at this temperature for 1h, and then increased to 1060℃ at a heating rate of 6℃ / min and sintered for 3h. After sintering, it is cooled in the furnace to obtain a ceramic sample.

[0052] S3. After polishing, cleaning and drying the ceramic sample, apply silver paste on both ends and polarize. The polarization process parameters are: in high temperature silicone oil at 120℃, keep warm and pressurize under 12kV / mm DC electric field for 20min. 1 / 3Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 5 / 3 O9 piezoelectric ceramics are recorded as CBN11.

[0053] By calculating its mixing entropy ΔS mix The Curie temperature T is 1.78, and there is no impurity phase in CBN11, which is mainly orthorhombic phase structure. C At 905℃, through measurement, its d 33 The resistivity is 20.2pC / N and 1.5×10 6 Ω·cm.

[0054] Example 3

[0055] The embodiment of the present invention provides Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb5 / 3 O9 high-temperature lead-free piezoelectric ceramics and a preparation method thereof, comprising the following steps:

[0056] S1. Weigh metal carbonate or oxide raw materials according to the stoichiometric ratio, mix, and calcine once to obtain a presynthesized powder. The metal carbonate or oxide is ball-milled in alcohol or water for 12 hours at a speed of 500 r / min, followed by drying. The process parameters for the primary calcination are as follows: calcining the dried mixed raw materials in an air environment at a synthesis temperature of 900°C for 4 hours to obtain the presynthesized powder.

[0057] S2. Add a certain sintering aid to the pre-synthesized powder according to a stoichiometric ratio, perform high-energy ball milling, mix and granulate, press into tablets after screening, and sinter to obtain a ceramic sample. The process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 24 hours with alcohol or water as the medium, the rotation speed is 600r / min, and the powder is dried after high-energy ball milling. After drying, it is mixed with a binder and granulated, and after passing through a 100-150 mesh sieve, it is cold-pressed at a pressure of 200MPa to obtain a ceramic body; the ceramic ligand is sintered in an air environment by a powder embedding method at normal pressure, and the temperature is increased to 600℃ at a heating rate of 3℃ / min and kept warm for 2h, and then increased to 1140℃ at a heating rate of 5℃ / min, sintered for 4h, and cooled with the furnace after sintering to obtain a ceramic sample.

[0058] S3. After polishing, cleaning and drying the ceramic sample, apply silver paste on both ends and polarize. The polarization process parameters are: in high temperature silicone oil at 150℃, keep warm and pressurize under 14kV / mm DC electric field for 30min. 1 / 3Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 5 / 3 O9 piezoelectric ceramics are recorded as CBN12.

[0059] By calculating its mixing entropy ΔS mix The Curie temperature T is 1.78, and there is no impurity phase in CBN12, which is mainly orthorhombic phase structure. C At 907℃, the d 33 The resistivity is 21.2pC / N and 2.3×10 6 Ω·cm.

[0060] Example 4

[0061] Unlike Example 1, in step S2 of this embodiment, the material-to-ball ratio in the ball milling process was 0.8, and ball milling was performed at 400 rpm for 4 hours and 500 rpm for 8 hours. After drying, the powder had a D50 particle size of 1.4 μm and a D40 / D50 ratio of 1.2. The prepared piezoelectric ceramic was designated CBN13.

[0062] By calculating its mixing entropy ΔS mix The Curie temperature T is 1.78, and there is no impurity phase in CBN13, which is mainly orthorhombic phase structure. C At 910℃, through measurement, its d 33 The resistivity is 23.2pC / N and 4.3×10 6 Ω·cm.

[0063] Example 5

[0064] Unlike Example 1, in step S2 of this embodiment, the ball-to-material ratio in the ball milling process was 1.1. Ball milling was performed at 450 rpm for 5 hours and 600 rpm for 19 hours. After drying, the powder had a D50 particle size of 1.2 μm and a D40 / D50 ratio of 1.3. The prepared piezoelectric ceramic was designated CBN14.

[0065] By calculating its mixing entropy ΔS mix The Curie temperature T is 1.78, and there is no impurity phase in CBN14, which is mainly orthorhombic phase structure. C At 910℃, through measurement, its d 33 The resistivity is 24.6pC / N and 3.9×10 6 Ω·cm.

[0066] Example 6

[0067] The embodiment of the present invention provides Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 NbTa 2 / 3 The preparation method of O9 comprises the following steps:

[0068] S1. Weigh metal carbonate or oxide raw materials according to the stoichiometric ratio, mix them, and perform a primary calcination to obtain a presynthesized powder. The metal carbonate or oxide is ball-milled in alcohol or water for 8 hours at a speed of 300 r / min, followed by drying. The process parameters for the primary calcination are as follows: calcining the dried mixed raw materials in an air environment at a synthesis temperature of 850°C for 3 hours to obtain the presynthesized powder.

[0069] S2. Add a certain sintering aid to the pre-synthesized powder according to a stoichiometric ratio, perform high-energy ball milling, mix and granulate, press into tablets after screening, and sinter to obtain a ceramic sample. The process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 8 hours with alcohol or water as the medium, the rotation speed is 300r / min, and the powder is dried after high-energy ball milling. After drying, it is mixed with a binder and granulated, and after passing through a 100-150 mesh sieve, it is cold-pressed at a pressure of 200MPa to obtain a ceramic body; the ceramic ligand is sintered in an air environment by a powder embedding method at normal pressure, and the temperature is increased to 550℃ at a heating rate of 3℃ / min and kept at this temperature for 1h, and then increased to 1100℃ at a heating rate of 5℃ / min and sintered for 3h. After sintering, it is cooled with the furnace to obtain a ceramic sample.

[0070] S3. After polishing, cleaning and drying the ceramic sample, apply silver paste on both ends and polarize. The polarization process parameters are: in high temperature silicone oil at 150℃, keep warm and pressurize under 14kV / mm DC electric field for 20min. 1 / 3Na 1 / 6 Bi 5 / 2 Ti 1 / 3 NbTa 2 / 3 O9 piezoelectric ceramics are recorded as CBN2.

[0071] By calculating its mixing entropy ΔS mix is 2.34R (high entropy); Figure 1 As shown, the piezoelectric ceramic prepared in this embodiment does not contain any impurity phase and is mainly composed of an orthorhombic phase structure.

[0072] like Figure 2 As shown in b, the sample has a rod-like or sheet-like structure and is relatively dense; Figure 4 , Curie temperature T C is 901℃. After measurement, its d 33 The resistivity is 22.7pC / N and 1.2×10 7 Ω·cm.

[0073] Example 7

[0074] The embodiment of the present invention provides Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 1 / 3 Ta 4 / 3 The preparation method of O9 comprises the following steps:

[0075] S1. Weigh metal carbonate or oxide raw materials according to the stoichiometric ratio, mix them, and perform a primary calcination to obtain a presynthesized powder. The metal carbonate or oxide is ball-milled in alcohol or water for 8 hours at a speed of 300 r / min, followed by drying. The process parameters for the primary calcination are as follows: the dried mixed raw materials are calcined in an air environment at a synthesis temperature of 900°C for 3 hours to obtain the presynthesized powder.

[0076] S2. Add a certain sintering aid to the pre-synthesized powder according to a stoichiometric ratio, perform high-energy ball milling, mix and granulate, press into tablets after screening, and sinter to obtain a ceramic sample. The process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 12 hours with alcohol or water as the medium, the rotation speed is 500r / min, and the powder is dried after high-energy ball milling. After drying, the D50 particle size of the powder is 1.4μm, and D40 / D50 is 1.2; the dried powder is mixed with a binder and granulated, and after passing through a 100-150 mesh sieve, it is cold-pressed at a pressure of 100MPa to obtain a ceramic body; the ceramic ligand is sintered in an air environment by a powder embedding method at normal pressure, and the temperature is increased to 550℃ at a heating rate of 3℃ / min and kept at this temperature for 2h, and then increased to 1120℃ at a heating rate of 4℃ / min, sintered for 4h, and cooled with the furnace after sintering to obtain a ceramic sample.

[0077] S3. After polishing, cleaning and drying the ceramic sample, apply silver paste on both ends and polarize. The polarization process parameters are: in high temperature silicone oil at 180℃, keep warm and pressurize under 12kV / mm DC electric field for 20min. 1 / 3Na 1 / 6 Bi 5 / 2 Ti 1 / Nb 1 / 3 Ta 4 / 3 O9 piezoelectric ceramics are recorded as CBN3.

[0078] By calculating its mixing entropy ΔS mix is 2.20R; Figure 1 The prepared piezoelectric ceramic CBN3 does not contain any impurity phase and is mainly composed of an orthorhombic phase structure.

[0079] like Figure 2 As shown in c, the sample has a rod-like or sheet-like structure and is relatively dense; Figure 5 , Curie temperature T C is 903℃. After measurement, its d 33 The resistivity is 31.5pC / N and 1.6×10 7 Ω·cm.

[0080] Example 8

[0081] The embodiment of the present invention provides Ca1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Ta 5 / 3 The preparation method of O9 comprises the following steps:

[0082] S1. Weigh metal carbonate or oxide raw materials according to the stoichiometric ratio, mix them, and perform a primary calcination to obtain a presynthesized powder. The metal carbonate or oxide is ball-milled in alcohol or water for 8 hours at a speed of 300 r / min, followed by drying. The process parameters for the primary calcination are as follows: the dried mixed raw materials are calcined in an air environment at a synthesis temperature of 900°C for 4 hours to obtain the presynthesized powder.

[0083] S2. Add a certain sintering aid to the pre-synthesized powder according to a stoichiometric ratio, perform high-energy ball milling, mix and granulate, press into tablets after screening, and sinter to obtain a ceramic sample. The process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 12 hours with alcohol or water as the medium, the rotation speed is 500r / min, and the powder is dried after high-energy ball milling. After drying, the D50 particle size of the powder is 1.4μm, and D40 / D50 is 1.2; the dried powder is mixed with a binder and granulated, and after passing through a 100-150 mesh sieve, it is cold-pressed at a pressure of 100MPa to obtain a ceramic body; the ceramic ligand is sintered in an air environment by a powder embedding method at normal pressure, and the temperature is increased to 600℃ at a heating rate of 4℃ / min and kept at this temperature for 2h, and then increased to 1140℃ at a heating rate of 4℃ / min, sintered for 4h, and cooled with the furnace after sintering to obtain a ceramic sample.

[0084] S3. After polishing, cleaning and drying the ceramic sample, apply silver paste on both ends and polarize. The polarization process parameters are: in high temperature silicone oil at 180℃, keep warm and pressurize under 13kV / mm DC electric field for 20min. 1 / 3Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Ta 5 / 3 O9 piezoelectric ceramics are recorded as CBN4.

[0085] By calculating its mixing entropy ΔS mix is 1.78R; Figure 1 The prepared piezoelectric ceramic CBN4 does not contain any impurity phase and is mainly composed of an orthorhombic phase structure. Figure 2 As shown in d, the sample has a rod-like or sheet-like structure and is relatively dense; Figure 6 , Curie temperature T C is 908℃. After measurement, its d 33 The resistivity is 26.5pC / N and 4.0×10 6Ω·cm.

[0086] Comparative Example 1

[0087] Different from Example 1, this comparative example prepares CaBi2Nb2O9 piezoelectric ceramics.

[0088] Its mixing entropy ΔS mix 0; CBN0 does not have any impurity phase and is mainly composed of an orthorhombic phase structure.

[0089] After measurement, its d 33 The resistivity is 5.8 pC / N and 4.3×10 5 Ω·cm.

[0090] Comparative Example 2

[0091] Different from Example 1, the powder prepared in this comparative example has a D50 particle size of 2.6 μm and a D40 / D50 ratio of 1.2.

[0092] By calculating its mixing entropy ΔS mix is 1.78R; there is no impurity phase, and the orthorhombic phase structure is the main one. After measurement, its d 33 The resistivity is 17.4 pC / N and 1.2×10 6 Ω·cm.

[0093] By comparing the embodiment with comparative example 1, it can be seen that the phase structure remains unchanged when the high entropy strategy is introduced. 33 Significantly improved, maintain high T C By comparing Examples 1, 4, and 5 with Comparative Example 2, it can be seen that when the D50 particle size of the powder is 1.2-1.4 μm and D40 / D50 is 1.2-1.3, d 33 Significant improvement.

[0094] 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 in the scope of protection of the present invention.

Claims

1. A high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic, characterized in that: Chemical composition: Ca 1 / 3 Na 1 / 6 Bi 5 / 2 Ti 1 / 3 Nb 5 / 3-z Ta z O9+u wt% MO, 0≤z≤5 / 3, 0<u≤0.4, wherein MO is selected from one or more combinations of B2O3, Fe2O3, CuO, and MnO2.

2. A method for preparing the high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic according to claim 1, characterized in that: The following steps are involved: S1. Weigh the metal carbonate or oxide raw materials according to the stoichiometric ratio, mix and calcine once to obtain a pre-synthesized powder; S2. The pre-synthesized powder was added with a sintering aid in a stoichiometric ratio, subjected to high-energy ball milling, mixed and granulated, sieved, pressed and sintered to obtain a ceramic sample; S3. The ceramic sample is polished, cleaned, and dried, and then silver paste is applied to both end surfaces and polarized.

3. The method for preparing high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic according to claim 2, characterized in that: In step S1, the mixing is as follows: the metal carbonate or oxide is ball-milled for 8-12 hours with alcohol or water as the medium at a rotation speed of 300-500 r / min, and then dried after the ball-milling.

4. The method for preparing high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic according to claim 2, characterized in that: The process parameters of the primary calcination are as follows: calcining the dried mixed raw materials in an air environment at a synthesis temperature of 800-900° C. and keeping the temperature for 3-4 hours.

5. The method for preparing high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramics according to claim 2, characterized in that: In step S2, the process parameters of the high-energy ball milling are as follows: the pre-synthesized powder is ball milled for 12-24 hours with alcohol or water as the medium, the rotation speed is 400-600 r / min, and the high-energy ball milling is followed by drying.

6. The method for preparing high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic according to claim 5, characterized in that: After drying, the D50 particle size of the powder is 1.2-1.4 μm, and the D40 / D50 is 1.2-1.

3.

7. The method for preparing high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramics according to claim 5, characterized in that: The dried powder is mixed with a binder to form granules, passed through a 100-150 mesh sieve, and then cold-pressed at a pressure of 100-200 MPa to obtain a ceramic body.

8. The method for preparing high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramics according to claim 2, characterized in that: In step S2, sintering is carried out in an air environment using a powder embedding method at normal pressure, heating the temperature to 500-600°C at a heating rate of no more than 5°C / min, keeping the temperature for at least 1 hour to remove the binder, heating the temperature to 1060-1140°C at a heating rate of no more than 6°C / min, sintering for 3-4 hours, and cooling the furnace after sintering.

9. The method for preparing high-entropy calcium bismuth niobate-based high-temperature lead-free piezoelectric ceramic according to claim 2, characterized in that: In step S3, the polarization process parameters are: heat preservation and pressure preservation for 20-30 minutes in high-temperature silicone oil at 120-150°C and a DC electric field of 12-14 kV / mm.

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