High-entropy bismuth layer-structured piezoelectric material and preparation method thereof

Abstract

The application relates to a high-entropy bismuth layered piezoelectric material and a preparation method thereof. The high-entropy bismuth layered piezoelectric material is composed of (Li 0.2 Na 0.2 A 0.2 Bi 0.2 X 0.2 )Bi2Nb2O9, wherein A is one of Ca and Sr, and X is a +3-valence element.

Description

Technical Field

[0001] This invention relates to a high-performance, high-entropy bismuth layered piezoelectric material and its preparation method, belonging to the field of piezoelectric materials. Background Technology

[0002] Piezoelectric materials can convert electrical energy into mechanical energy, or vice versa, and are an important class of functional materials widely used in key fields such as aerospace, defense, and automotive electronics. Bismuth layered piezoelectric materials are a type of piezoelectric material with a unique layered structure, possessing advantages such as high Curie temperature, high breakdown field strength, and low dielectric loss. They have significant advantages in ultra-high temperature and non-volatile ferroelectric memories. For example, in the high-temperature piezoelectric vibration sensor, a key component of aero-engine health management systems, bismuth layered piezoelectric materials are the most widely used material in the 482℃ sensor. Piezoelectric properties determine the sensitivity of the sensor; therefore, improving the piezoelectric properties of bismuth layered piezoelectric materials is of great significance.

[0003] However, the piezoelectric properties of bismuth layered piezoelectric materials remain relatively low, especially for those with a Curie temperature above 850℃. For example, the CaBi₂Nb₂O₉ system has a Curie temperature exceeding 900℃, but the highest reported piezoelectric performance is only around 21 pC / N. Furthermore, because bismuth layered piezoelectric materials lack quasi-isomorphic phase boundaries similar to those in lead zirconate titanate systems, effective methods for improving their piezoelectric properties are lacking. For a long time, the main method for improving the performance of bismuth layered piezoelectric materials has been doping, i.e., introducing dopant ions into the A / B sites, or simultaneously into the A and B sites, to increase lattice distortion and improve piezoelectric properties. This method rapidly improved the performance of bismuth layered piezoelectric materials in the early stages of research, but with the continuous exploration of various doping methods, this method has gradually encountered bottlenecks in improving piezoelectric properties. Therefore, to further improve the piezoelectric properties of bismuth layered piezoelectric materials, new design approaches must be developed.

[0004] High-entropy materials have attracted increasing attention from scholars in recent years. This concept was initially applied to alloy materials and later extended to oxides, carbides, and other materials. High-entropy alloys are generally defined as solid solutions formed by five or more elements in equiatomic or near-equiatomic ratios. High-entropy alloys exhibit four main effects: the high-entropy effect, the lattice distortion effect, the hysteresis diffusion effect, and the "cocktail" effect. High-entropy alloys possess many superior properties compared to traditional materials, such as high high-temperature strength, high corrosion resistance, and good wear resistance. Therefore, the design approach for high-entropy materials holds promise for providing new avenues for developing high-performance materials.

[0005] In recent years, some scholars have attempted to improve the performance of bismuth layered piezoelectric materials using the concept of high-entropy materials, but the results have not been ideal. For example, Zhang Man et al. (M. Zhang, et al., Materials and Design, 200, 109447, 2021; M. Zhang, et al., Acta Materialia, 229, 117815, 2022) studied high-entropy bismuth layered piezoelectric materials (Ca... 0.25 Sr 0.25 Ba 0.25 Pb 0.25 Bi₂Nb₂O₉ and (Ca 0.2 Sr 0.2 Ba 0.2 Pb 0.2 Nd 0.1 Na 0.1 Bi₂Nb₂O₉ is a promising material, but its design elements are mostly +2 valence elements, resulting in a material close to a relaxor ferroelectric material, which significantly weakens its piezoelectric properties and results in a low Curie temperature (<500℃). High-entropy materials involve numerous elements (more than 5), with a wide variety of possible combinations. Furthermore, the large number of element types easily leads to relaxation tendency, severely damaging ferroelectricity and thus weakening piezoelectric properties and significantly reducing the Curie temperature. Therefore, a feasible design approach is urgently needed to obtain high-performance high-entropy bismuth layered piezoelectric materials. Summary of the Invention

[0006] To address the bottleneck issues encountered in improving the performance of current bismuth layered piezoelectric materials, this invention proposes a novel high-entropy bismuth layered piezoelectric material and its preparation method.

[0007] On one hand, the present invention provides a high-entropy bismuth layered piezoelectric material, wherein the high-entropy bismuth layered piezoelectric material is composed of Li 0.2 Na 0.2 A 0.2 Bi 0.2 X 0.2 Bi2Nb2O9, where A is one of Ca or Sr, and X is a +3 valence element.

[0008] This disclosure creatively introduces five equimolar amounts of ions into the A-site ions, with the molar ratio of +1, +2, and +3 ions being 2:1:2, thereby obtaining a high-entropy bismuth layered piezoelectric material that combines high piezoelectric performance and a high Curie temperature. Using the design method proposed in this invention, bismuth layered piezoelectric materials with high piezoelectric performance can be obtained while maintaining a high Curie temperature, providing a new design approach for designing high-performance bismuth layered piezoelectric materials.

[0009] Preferably, the high-entropy bismuth layered piezoelectric material has the following composition: (Li0.2 Na 0.2 Ca 0.2 Bi 0.2 X 0.2 Bi₂Nb₂O₉; where X is a rare earth element; preferably, the rare earth element is La, Pr, Nd, Sm, Pm or Eu.

[0010] Preferably, when X is La, the Curie temperature of the high-entropy bismuth layered piezoelectric material is 871℃; when X is Nd, the Curie temperature of the high-entropy bismuth layered piezoelectric material is 836℃.

[0011] On the other hand, the present invention provides a method for preparing a high-entropy bismuth layered piezoelectric material, comprising:

[0012] (1) Mix source A, source X, Li2CO3, Na2CO3, Bi2O3, and Nb2O5 powders according to the stoichiometric ratio Li 0.2 Na 0.2 A 0.2 Bi 0.2 X 0.2 Bi2Nb2O9 was weighed and mixed, and then calcined at 800–850°C to obtain raw material powder;

[0013] (2) The raw material powder and binder are mixed and then granulated to obtain granulated powder;

[0014] (3) The granulated powder is pressed into shape, plasticized and sintered to obtain the high-entropy bismuth layered piezoelectric material.

[0015] Preferably, the source A is at least one of CaCO3 and SrCO3;

[0016] The X source is at least one of La2O3, Nd2O3, Sm2O3, Pr2O3, Pm2O3, and Eu2O3.

[0017] Preferably, the binder is a polyvinyl alcohol solution with a concentration of 4-8 wt.%; the amount of the binder is 5%-10% of the raw material powder mass.

[0018] Preferably, the pressing method is dry pressing. The pressure of the dry pressing is 100-200 MPa; and the calcination time is 2-4 hours.

[0019] Preferably, the temperature for extruding the plastic is 600-700℃ and the time is 2-3 hours; more preferably, the heating rate for extruding the plastic is not higher than 2℃ / min.

[0020] Preferably, the sintering temperature is 1130–1160°C and the time is 2–4 hours; more preferably, the sintering heating rate is not higher than 2°C / min.

[0021] Preferably, electrodes are prepared on the surface of the obtained high-entropy bismuth layered piezoelectric material and polarization treatment is performed; the polarization treatment is: applying a voltage of 20-26 kV / mm at 120-200℃ for more than 10 minutes.

[0022] Furthermore, preferably, the electrode is a platinum electrode, which is prepared by coating the upper and lower surfaces of a high-entropy bismuth layered piezoelectric material with a platinum electrode slurry and then holding it at 800–900°C for 20–40 min.

[0023] Beneficial effects:

[0024] This invention combines the design principles of high-entropy materials with the characteristics of bismuth layered piezoelectric materials. It proposes introducing five equimolar amounts of ions at the A-site, with a +1, +2, and +3 ion ratio of 2:1:2. This method enhances the piezoelectric performance while maintaining a high Curie temperature, resulting in a bismuth layered piezoelectric material with both high piezoelectric performance and a high Curie temperature. The material involved in this invention has a piezoelectric coefficient of up to 25 pC / N, while maintaining a Curie temperature above 850°C. It is currently the high-temperature piezoelectric material with the highest piezoelectric performance among materials with a Curie temperature above 850°C (the highest reported piezoelectric coefficient internationally is 21.1 pC / N, obtained based on traditional doping methods), making it a leading material internationally. Attached Figure Description

[0025] Figure 1 The powder X-ray diffraction pattern of LNCB-Nd / La prepared in this invention shows that it forms a single bismuth layered perovskite structure.

[0026] Figure 2 The change in dielectric constant of LNCB-Nd / La with temperature indicates that the Curie temperature of LNCB-Nd is 836°C and the Curie temperature of LNCB-La is 871°C. Detailed Implementation

[0027] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0028] The key to this invention lies in introducing five equimolar amounts of ions into the A-site, wherein the molar ratio of +1, +2, and +3 ions is 2:1:2. Utilizing the high-entropy effect, a high-entropy bismuth layered piezoelectric material with high piezoelectric properties is obtained. Preferably, the designed material chemical composition is (Li... 0.2 Na 0.2 Ca 0.2 Bi 0.2 X 0.2Bi₂Nb₂O₉ (abbreviated as LNCB-X), where X is a +3 valence element such as La or Nd. The ceramic is characterized by both high entropy bismuth layered materials and high piezoelectric properties. In the design of high-entropy bismuth layered materials, due to the large number of elements involved (five or more), the possible combinations are extremely diverse. Furthermore, the excessive number of elements in the composition design easily leads to relaxation tendency, which destroys ferroelectricity, thereby weakening piezoelectric properties and significantly reducing the Curie temperature (e.g., M. Zhang, et al., Materials and Design, 200, 109447, 2021; M. Zhang, et al., Acta Materialia, 229, 117815, 2022). Therefore, obtaining materials that simultaneously possess high Curie temperature and high piezoelectric properties is very difficult, requiring careful selection of the types and proportions of elements. Specifically, Li and Na are irreplaceable. For example, choosing potassium (K) results in a large ionic radius and a greater tendency for relaxation; its addition would significantly weaken piezoelectricity and lower the Curie temperature. While calcium (Ca) can be replaced by sr, Mg is not feasible because its ionic radius is too small to form a perovskite structure. For instance, MgBi₂Nb₂O₉ has a pyrochlore structure, not a perovskite structure.

[0029] This invention also discloses a preparation process for high-entropy bismuth layered piezoelectric materials, including batching, primary ball milling, pre-calcination, secondary ball milling, granulation, briquetting, plasticizing, sintering, electrode preparation, and polarization. The following exemplarily illustrates the preparation method of high-entropy bismuth layered piezoelectric materials.

[0030] Ingredients. High-purity Li2CO3, Na2CO3, CaCO3, La2O3, Nd2O3, Sm2O3, Pr2O3, Pm2O3, Eu2O3, Bi2O3, and Nb2O5 powders are mixed according to stoichiometric ratios to obtain a mixed powder.

[0031] The mixing method is ball milling, referred to as one ball milling cycle. Specifically, wet ball milling is used to mix the prepared raw materials. The prepared raw materials are ball milled for 12-18 hours using anhydrous ethanol as the medium in a planetary ball mill. Zirconia balls are used as the milling balls. After ball milling, the raw materials are dried.

[0032] Pre-calcination. The dried raw material (i.e., the mixed powder) is pressed into briquettes and then placed in an alumina crucible for pre-calcination in a box-type resistance furnace to obtain the raw material powder. Preferably, the temperature is raised to 800-850°C at a rate not exceeding 2°C / min and calcined for 2 hours, and then cooled to room temperature in the furnace.

[0033] Preferably, a second ball milling is performed after pre-calcination. Specifically, the pre-calcined raw material powder is ground into powder and then placed in a ball mill jar for a second ball milling, with the milling conditions being the same as during the first ball milling. After the ball milling is completed, the powder is dried.

[0034] Granulation. A binder is added to the dried raw material powder for granulation. The amount of binder is 5% to 10% of the powder mass. The binder is a 4-8 wt.% polyvinyl alcohol solution.

[0035] Briquetting. The prepared pellets are pressed into green bodies under a pressure of 200 MPa.

[0036] Demolding. Heat the green body to 600-700℃ at a rate not exceeding 2℃ / min, hold for 2-3 hours, and then demold.

[0037] Sintering. The green blank after plastic removal is heated to 1130-1160℃ at a heating rate not exceeding 2℃ / min and held for 2 hours, and then cooled to room temperature in the furnace.

[0038] Electrode preparation. Platinum electrodes were coated on both the upper and lower surfaces of the ceramic, and sintered at 800–900℃ for 20–40 min.

[0039] Polarization. The sample is polarized by applying a voltage of 20–26 kV / mm at 120–200 °C for at least 10 minutes.

[0040] The high-entropy bismuth layered piezoelectric material of the present invention has the characteristics of high piezoelectric coefficient (16 pC / N or more, preferably 23 pC / N or more, more preferably 23 to 25 pC / N), high Curie temperature (741 to 871 °C) and low dielectric loss (<2% @ 1 kHz). It is synthesized by solid-state method, which is simple and suitable for production and promotion.

[0041] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0042] Example 1

[0043] (1) Ingredients: High-purity Li2CO3, Na2CO3, CaCO3, La2O3, Bi2O3, and Nb2O5 powders are mixed according to the stoichiometric ratio (Li 0.2 Na 0.2 Ca 0.2Bi 0.2 La 0.2 Bi2Nb2O9 was used as an ingredient in the batch;

[0044] (2) Single-stage ball milling: The prepared raw materials are mixed using wet ball milling. The prepared raw materials are ball milled for 12-18 hours using anhydrous ethanol as the medium in a planetary ball mill. Zirconia balls are used as the milling balls. After ball milling, the raw materials are dried.

[0045] (3) Pre-firing: The dried raw material is pressed into blocks and then placed in an alumina crucible for pre-firing in a box-type resistance furnace. The temperature is increased to 850°C at a rate of 2°C / min, held for 2 hours, and then cooled to room temperature with the furnace.

[0046] (4) Secondary ball milling: The pre-calcined raw material is ground into powder and then placed in a ball mill jar for secondary ball milling. The ball milling conditions are the same as those for the primary ball milling. After ball milling, the powder is dried.

[0047] (5) Granulation: A binder is added to the dried powder for granulation. The amount of binder is 5% to 10% of the powder mass. Preferably, the binder is a 4 to 8 wt.% polyvinyl alcohol solution.

[0048] (6) Briquetting: The prepared granules are pressed into green bodies under a pressure of 200 MPa;

[0049] (7) Demolding: Heat the green body to 600℃ at a rate of 2℃ / min, hold for 2 hours, and then demold;

[0050] (8) Sintering: The green compact after plastic removal is heated to 1150℃ at a heating rate of 2℃ / min and held at that temperature for 2 hours, then cooled to room temperature in the furnace. The resulting high-entropy bismuth layered piezoelectric material is denoted as LNCB-La;

[0051] (9) Electrode preparation: Platinum electrodes were coated on both the upper and lower surfaces of the ceramic and sintered at 850℃ for 30 min.

[0052] (10) Polarization: The sample was polarized for 10 min at 180℃ by applying a voltage of 24kV / mm.

[0053] Example 2

[0054] In this Example 2, the preparation process of the high-entropy bismuth layered piezoelectric material is the same as in Example 1, except that in step (1), the high-purity Li2CO3, Na2CO3, CaCO3, Nd2O3, Bi2O3, and Nb2O5 powders are prepared in a stoichiometric ratio (Li 0.2 Na 0.2 Ca 0.2 Bi 0.2 Nd 0.2Bi₂Nb₂O₉ was used as the raw material. The resulting high-entropy bismuth layered piezoelectric material is denoted as LNCB-Nd.

[0055] Figure 1 The powder X-ray diffraction pattern of LNCB-X is shown, indicating that it has formed a single phase and the phase structure is a bismuth layered perovskite structure.

[0056] Figure 2 The curves showing the dielectric constant of LNCB-X versus temperature are shown. It can be seen that LNCB-Nd and LNCB-La have dielectric peaks at 836℃ and 871℃, respectively, indicating that ferroelectric phase transitions occur. These two temperatures also mark the Curie temperatures of the two materials.

[0057] Example 3

[0058] In this Example 3, the preparation process of the high-entropy bismuth layered piezoelectric material is the same as in Example 1, except that in step (1), the high-purity Li2CO3, Na2CO3, CaCO3, Sm2O3, Bi2O3, and Nb2O5 powders are prepared in a stoichiometric ratio (Li 0.2 Na 0.2 Ca 0.2 Bi 0.2 Sm 0.2 Bi₂Nb₂O₉ was used as the raw material. The resulting high-entropy bismuth layered piezoelectric material is denoted as LNCB-Sm.

[0059] Table 1 shows the main performance parameters of LNCB-Nd / La / Sm:

[0060] composition Piezoelectric coefficient (pC / N) Curie temperature / °C Dielectric loss tanδ (@1kHz) Example 1 LNCB-La 25 871 0.0095 Example 2 LNCB-Nd 23 836 0.0114 Example 3 LNCB-Sm 16 741 0.0169 .

[0061] Comparative Example 1

[0062] With (Li 0.2 Bi 0.2 Ca 0.6 Bi₂Nb₂O₉ (LBC) was used as Comparative Example 1, and its preparation process followed that of Example 1. The Curie temperature of the obtained LBC was 928°C, but the piezoelectric coefficient d 33 It has a dielectric loss of only about 14 pC / N and a dielectric loss of 0.00565 at 1 kHz.

Claims

1. A high-entropy bismuth layer structured piezoelectric material, characterized in that, The high-entropy bismuth layered piezoelectric material has a composition of (Li 0.2 Na 0.2 A 0.2 Bi 0.2 X 0.2 )Bi2Nb2O9, wherein A is one of Ca and Sr, X is a +3-valence element; X is a rare earth element; and the rare earth element is La, Pr, Nd, Sm, Pm or Eu.

2. The high-entropy bismuth layer structured piezoelectric material of claim 1, wherein, When X is La, the Curie temperature of the high-entropy bismuth layered piezoelectric material is 871 DEG C; when X is Nd, the Curie temperature of the high-entropy bismuth layered piezoelectric material is 836 DEG C.

3. A method of producing a high-entropy bismuth layer structured piezoelectric material according to any one of claims 1-2, characterized in that, The application relates to a high-entropy bismuth layered piezoelectric material and a preparation method thereof. (1) A source, X source, Li2CO3, Na2CO3, Bi2O3, Nb2O5 powder according to the stoichiometric ratio Li 0.2 Na 0.2 Bi 0.2 A 0.2 X 0.2 Bi2Nb2O9 are weighed and mixed, and calcined at 800-850°C to obtain raw material powder; The application relates to a high-entropy bismuth layered piezoelectric material and a preparation method thereof. The A source is one of CaCO3 and SrCO3; 4. The production method according to claim 3, characterized by, The X source is one of La2O3, Nd2O3, Sm2O3, Pr2O3, Pm2O3 and Eu2O3. The binder is a polyvinyl alcohol solution with a concentration of 4-8 wt.%; the amount of the binder is 5%-10% of the mass of the raw material powder.

5. The preparation method according to claim 3, characterized in that, The dry pressing forming mode is dry pressing; the dry pressing forming pressure is 100-200 MPa; and the calcining time is 2-4 hours.

6. The production method according to claim 3, characterized by, The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; 7. The preparation method according to claim 3, characterized in that, The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; 8. The preparation method according to claim 7, characterized in that, The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours.

9. The production method according to any one of claims 3 to 8, characterized by, The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; 10. The method of claim 9, wherein, The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C, and the time is 2-3 hours; The sintering temperature is 1130-1160 DEG C, and the time is 2-4 hours. The plastic removal temperature is 600-700 DEG C

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