A high-throughput method for preparing a bismuth ferrite-barium titanate-based lead-free piezoelectric ceramic

Abstract

The application discloses a high-throughput preparation method of bismuth ferrite-barium titanate-based lead-free piezoelectric ceramics, and the method comprises the following steps: taking Fe2O3, Bi2O3, BaTiO3 and doped element compounds as raw materials, and preparing ceramic sample blanks through the steps of ball milling, drying and tabletting; placing the sample blanks into a muffle furnace for glue removal and calcination; taking zirconia balls or sheets as supporting pads, and stacking multiple ceramic sample blanks in a quartz tube; and placing the quartz tube into a vertical tube furnace with gradient temperature for sintering, so that the one-time high-throughput preparation of the multiple ceramic samples under different sintering temperatures is completed. Compared with a traditional preparation process, the method has the advantages of short period, short time, energy saving, and higher ceramic sample preparation efficiency under the same size and volume; and the method has the advantages of low equipment cost and simple principle compared with other high-throughput methods. The bismuth ferrite-barium titanate-based lead-free piezoelectric ceramics with the best composition, sintering temperature and electrical performance can be rapidly screened out at one time in a large temperature range.

Description

TECHNICAL FIELD

[0001] The application discloses a high-throughput preparation method of a bismuth ferrite-barium titanate (BiFeO3-BaTiO3, referred to as BF-BT) based lead-free piezoelectric ceramic, and belongs to the technical field of lead-free piezoelectric ceramic preparation. BACKGROUND

[0002] Traditional lead-based piezoelectric ceramics occupy the electronic ceramic market due to their excellent performance, but the high concentration of lead elements in the traditional lead-based piezoelectric ceramics causes serious harm to human beings and the environment. With the proposal of environment-friendly materials and the requirement of sustainable development strategies, the development of various high-performance lead-free piezoelectric ceramics has become a research hotspot at home and abroad. The BF-BT based lead-free piezoelectric ceramic which has a relatively high Curie temperature and excellent piezoelectric performance has become one of the material systems which are expected to replace lead-based high-temperature piezoelectric ceramics. Sintering is an indispensable preparation process for ceramics, and the sintering temperature seriously affects the density, microstructure and phase structure of the piezoelectric ceramic, and further affects the dielectric constant, piezoelectric coefficient and electromechanical coupling coefficient of the piezoelectric ceramic, and is an important variable for screening and optimizing the performance of the BF-BT based lead-free piezoelectric ceramic. The traditional preparation method generally uses a single-temperature-zone electric furnace to sinter the sample, and the sintering time is several hours to several tens of hours. The traditional sintering process needs to consume a large amount of time and energy, and the temperature control error in each sintering process is also easy to cause performance fluctuation. The optimization and screening of the preparation process of the piezoelectric ceramic with excellent piezoelectric performance are based on the research on the evolution law of the composition, phase structure, microstructure and piezoelectric performance with the sintering temperature, and a large number of samples need to be prepared by changing the sintering temperature, and the traditional sintering process seriously limits the research progress of the BF-BT based lead-free piezoelectric ceramic.

[0003] “Material high-throughput preparation” refers to the preparation of a large number of samples with different variables in a short time, and the core idea is to change the sequential iteration method used in traditional material research to parallel processing, so as to cause qualitative change in material research efficiency through quantitative change. “Material high-throughput preparation” can quickly provide valuable research results and accelerate the screening and optimization of material preparation processes. Song et al. realized automatic powder weighing, parallel grinding and mixing, batch molding and sintering on the basis of the traditional solid-phase sintering process, and prepared 91 Bi 0.5 Na 0.5 TiO3-BaTiO3-K 0.5 Na 0.5 NbO3 based lead-free piezoelectric ceramic samples at one time, and found that the addition of BaTiO3 and K 0.5 Na 0.5 NbO3 can promote the rhombohedral phase to tetragonal phase transition, inhibit the grain growth, and optimize the maximum piezoelectric constant d 33 33 and the inverse piezoelectric constant d 33 *ceramic composition [G. H. Song, Z. B. Liu, F. Q. Zhang, F. Liu, Y. Gu, Z. F. Liu, Y. X. Li, J. Mater. Chem. C. 2020, 8, 3655-3662]. Zhang et al. used laser molecular beam epitaxy technology to prepare stacked unit cell BaTiO3-SrTiO3(BSTO) thin films by layer-by-layer deposition method, and obtained that the dielectric constant of BSTO monotonously increases with the increase of Sr in the range of 14%<Sr<85%, and exhibits the coexistence of dielectric properties and large piezoelectric response at low Sr doping [N. Zhang, D. Wang, J. Wang, H. Fang, B. He, J. Guo, Y. Han, P. Zhang, C. Shi, Y. Chen, et al. Coatings. 2021, 11(12), 1491]. Undoubtedly, high-throughput preparation technology greatly improves the research efficiency of piezoelectric materials. SUMMARY

[0004] The purpose of the present application is to provide a high-throughput preparation method of bismuth ferrite-barium titanate-based lead-free piezoelectric ceramics, which is used for the preparation process optimization and screening of ceramics with excellent piezoelectric properties. The preparation method takes Fe2O3, Bi2O3, BaTiO3 and compound of doping elements as raw materials, forms a gradient temperature field in a single temperature zone tube furnace, and screens out BF-BT-based lead-free piezoelectric ceramics with good crystallinity, dense structure and excellent electrical properties at multiple different sintering temperatures at one time.

[0005] The present application is realized by the following technical solutions:

[0006] A high-throughput preparation method of bismuth ferrite-barium titanate-based lead-free piezoelectric ceramics, which takes Fe2O3, Bi2O3 and BaTiO3 and compound of doping elements as raw materials, first prepares ceramic sample blanks through steps such as ball milling, drying and tabletting; then puts the sample blanks into a muffle furnace to remove glue and sinter, and then uses zirconia balls or sheets as supporting pads, and stacks multiple sintered ceramic sample blanks alternately in a quartz tube; puts the quartz tube into a vertical tube furnace with a gradient temperature for sintering, which can complete the one-time high-throughput preparation of multiple ceramic samples at different sintering temperatures.

[0007] The preparation method comprises the following steps:

[0008] (1) according to the chemical formula (1-x)Bi 1-y M y Fe 1-z N zO3-xBaTiO3, the mass of each raw material is calculated, and Fe2O3, Bi2O3, BaTiO3 and compound of doping elements of analytical pure or superior pure are selected and weighed, x, y and z are molar fractions, wherein 0 < x < 1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1; M is La, Ca, Sm and the like, and N is Sc, In, Co and the like;

[0009] (2) The weighed raw materials are put into a ball mill tank and placed in a planetary ball mill to perform ball milling mixing, and the mixed raw materials are dried to obtain raw material mixed powder;

[0010] (3) Polyvinyl alcohol (PVA) with a concentration of 2wt% is added to the raw material mixed powder, and after being fully ground and granulated, the raw material mixed powder is put into a metal mold and pressed into a ceramic sample body by using a hand press machine;

[0011] (4) The sample body is placed in a muffle furnace and heated to 300-600℃, and the glue is discharged and kept for 1-2h; then heated to 700-850℃, and baked and kept for 1-3h to obtain a baked ceramic sample body;

[0012] (5) The insulator and n baked ceramic sample bodies are alternately stacked in a quartz tube, n is an arbitrary integer between 10 and 40, and then the quartz tube is placed in a vertical tube furnace, and then heated to 950-1100℃ to form a required gradient temperature field, so that the sample bodies in the quartz tube are sintered at different temperatures for 6-12h.

[0013] Further, a small amount of metal oxide sintering aid such as one of MnO2, LiCO3 or CuO can be added to the raw materials in step (1). Different types of sintering aids are added in different amounts, and the amount of LiCO3 is generally 1 ‰ of all raw materials, and the amount of MnO2 is generally 1%.

[0014] Further, the ball milling medium in step (2) is selected from one of anhydrous ethanol, water and n-hexane; and the ball milling substrate is zirconium dioxide ball.

[0015] Further, the ball milling speed in step (2) is 200-450r / min, and the ball milling time is 10-16h.

[0016] Further, the heating rate in steps (4) and (5) is 5-10℃ / min.

[0017] Further, the insulator used in step (5) is a zirconia ball or sheet with a diameter of 1-6mm. The size of the zirconia ball or sheet is adjusted to adjust the temperature difference between adjacent samples and the number of samples, so as to control the sintering temperature of the samples.

[0018] Further, the vertical tube furnace forms a gradient temperature field by heat exchange with air, and the gradient temperature field in step (5) is selected from the area downward from the center of the furnace tube.

[0019] Because the temperature of the outside air is lower than that of the tube furnace, the furnace tube of the vertical tube furnace is in contact with the air in the furnace, and heat is mainly exchanged by heat conduction, resulting in that the temperature at a position deviating from the center of the furnace is lower than the temperature at the center of the furnace.

[0020] According to the experience in the industry, it is assumed that the temperature field is linear, and the temperature at the center of the furnace (i.e., the position of the coil and the thermocouple) should be the set sintering temperature. However, the applicant found that the temperature at the center of the furnace is not the highest, and the temperature at a position slightly deviating from the center upward is the highest. The temperature is higher than the set sintering temperature, and the reason is currently unknown. It can be considered that there is a decreasing temperature field from the center of the furnace tube to both ends, and strictly speaking, the area downward from the center area is indeed a monotonically decreasing temperature field.

[0021] The application also provides a BF-BT-based lead-free piezoelectric ceramic material prepared by the method.

[0022] The application has the following beneficial technical effects:

[0023] The traditional preparation process cannot realize one-time high-throughput sintering preparation of multiple samples of the BF-BT-based lead-free piezoelectric ceramic in a certain sintering temperature range; the preparation method of the application can realize high-throughput sintering of different sintering temperatures and different components at one time, has a short cycle, and is helpful for quickly researching the evolution law of the microstructure and piezoelectric performance of the BF-BT-based lead-free piezoelectric ceramic under the change of composition and sintering temperature, and one-time rapid screening of the best composition, sintering temperature and piezoelectric performance of the BF-BT-based lead-free piezoelectric ceramic in a large temperature range.

[0024] Compared with the traditional sintering method of piezoelectric ceramics, the electric furnace used in the sintering method proposed in the application can be a traditional single-temperature-zone tube furnace. Compared with other same-type devices, the device has a simple structure, a small size, saves a large amount of energy cost during long-time use, and can achieve higher ceramic sample preparation efficiency under the same size and volume. Compared with other high-throughput methods, the device has low cost and simple principle.

[0025] The method proposed in the application is to form a temperature field in a conventional tube furnace for sintering, and the temperature field is continuous, and the relative continuous evolution law of the composition, microstructure and performance of the sample can be observed. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0027] Figure 1 Temperature gradient distribution map of sintering furnace and sample;

[0028] Figure 2 XRD diffraction pattern of sample after sintering at different temperatures in Example 1. DETAILED DESCRIPTION

[0029] In order to make the inventive purpose, technical solutions and beneficial technical effects of the present application more clear, the present application will be described in detail in combination with specific embodiments. It should be understood that the embodiments described in the specification are only for the purpose of explaining the present application, and are not intended to limit the present application.

[0030] The model of the vertical tube furnace in the embodiments is Hefei Kexing OTF-1200X-S-VT.

[0031] Example 1

[0032] The mass of each raw material required for calculating x=0.7, y=0, z=0 into the chemical formula (1-x)Bi 1-y M y Fe 1-z N z O3-xBaTiO3 is calculated, and Fe2O3, Bi2O3 and BaTiO3 of analytical pure or superior pure are selected and accurately weighed;

[0033] The weighed raw materials in step (1) are put into a nylon tank, anhydrous ethanol is used as the ball milling medium, and zirconium dioxide grinding balls are used as the ball milling matrix. The planetary ball mill is ball milled at a speed of 300 r / min for 16 h. Then the ball milled slurry is placed in a drying box for drying to obtain the raw material mixed powder;

[0034] The raw material mixed powder in step (2) is weighed and 2wt% polyvinyl alcohol (PVA) is added and ground and granulated. 0.4g of the granulated powder is weighed and put into a metal mold with a diameter of 10mm, and a hand-operated tablet press is used to press and form a ceramic sample body;

[0035] The ceramic sample body obtained in step (3) is placed in a muffle furnace and heated to 300℃ at a heating rate of 5℃ / min, and the glue is discharged and kept for 1h. Then it is heated to 700℃ and baked for 1h.

[0036] Zirconia balls with a diameter of 3 mm and 20 sample bodies after degassing in step (4) were alternately stacked in a quartz tube, which was placed in a vertical tube furnace. Then a gradient temperature field was formed after heating to 1067°C at a heating rate of 5°C / min, and the samples were sintered at different temperatures for 6 h. As shown in Figure 1

[0037] Example 2

[0038] The mass of each raw material required for the chemical formula (1-x)Bi 1-y M y Fe 1-z N z O3-xBaTiO3was calculated, and Fe2O3, Bi2O3, BaTiO3and Ca-doped compounds of analytical or premium purity were selected and accurately weighed.

[0039] The raw materials weighed in step (1) were placed in a nylon tank, anhydrous ethanol was used as the ball milling medium, and zirconium dioxide balls were used as the ball milling substrate. The planetary ball mill was operated at a rotation speed of 300 r / min for 16 h. The slurry after ball milling was placed in a drying box for drying to obtain the raw material mixed powder.

[0040] The raw material mixed powder in step (2) was weighed and 2wt% polyvinyl alcohol (PVA) was added and ground thoroughly. 0.4 g of the granulated powder was placed in a metal mold with a diameter of 10 mm, and a hand press was used for compression molding to obtain ceramic sample bodies.

[0041] The ceramic sample bodies obtained in step (3) were placed in a muffle furnace and heated to 400°C at a heating rate of 5°C / min, degassed and kept for 2 h; then heated to 750°C and calcined for 3 h.

[0042] Zirconia balls with a diameter of 6 mm and 10 sample bodies after degassing in step (4) were alternately stacked in a quartz tube, which was placed in a vertical tube furnace. Then a gradient temperature field was formed after heating to 1089°C at a heating rate of 5°C / min, and the samples were sintered at different temperatures for 12 h.

[0043]

[0044]

[0045] ​Table 1 gives the density and d of all samples of the examples 33 According to the above method, the relative density of all samples is > 90%, and the sample obtained by the method has a dense structure and good piezoelectric performance.

[0046] Figure 2 The XRD diffraction pattern of the sample of Example 1 is given, and it can be seen that the main phase of the sample at each sintering temperature is a perovskite crystal phase. It shows that the preparation method of the application can realize high-throughput sintering of different sintering temperatures and different components at one time, and the cycle is short, which is helpful for quickly studying the evolution rule of the microstructure and piezoelectric performance of the BF-BT-based lead-free piezoelectric ceramic under the change of composition and sintering temperature.

[0047] The above is only a specific embodiment of the application, but the protection scope of the application is not limited to this. Any skilled person in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the application, and these modifications or replacements should be covered within the protection scope of the application. Therefore, the protection scope of the application should be determined by the protection scope of the claims.

Claims

1. A high-throughput preparation method of bismuth ferrite-barium titanate-based lead-free piezoelectric ceramics, the preparation method taking Fe2O3, Bi2O3 and BaTiO3 and a doped element compound as raw materials, first preparing ceramic sample blanks by ball milling, drying and tabletting; then placing the sample blanks into a muffle furnace for glue removal and calcination, and subsequently placing multiple calcined ceramic sample blanks alternately in a quartz tube with zirconia balls or sheets as spacers; placing the quartz tube into a vertical tube furnace with a gradient temperature for sintering, thereby completing the one-time high-throughput preparation of multiple ceramic samples at different sintering temperatures. The preparation method comprises the following steps: (1) according to the chemical formula (1-x) Bi 1-y M y Fe 1-z N z O3-xBaTiO3, the mass of each raw material required is calculated, and the analytically pure or premium pure Fe2O3, Bi2O3, BaTiO3 and doped element compounds are weighed, x, y and z are mole fractions, wherein 0 M is one of La, Ca and Sm, and N is one of Sc, In and Co. (2) placing the weighed raw materials into a ball mill tank and placing them in a planetary ball mill for ball milling, drying the mixed raw materials to obtain raw material mixed powder; (3) adding polyvinyl alcohol with a concentration of 2wt% to the raw material mixed powder, thoroughly grinding and granulating, and then placing the granulated product into a metal mold and pressing it into a ceramic sample blank using a hand-operated tablet press; (4) placing the sample blank into a muffle furnace, heating it to 300-600℃, removing glue and maintaining the temperature for 1-2h; then heating it to 700-850℃, calcining and maintaining the temperature for 1-3h, thereby obtaining a calcined ceramic sample blank; (5) alternately stacking the spacers and n calcined ceramic sample blanks into a quartz tube, n being any integer between 10 and 40, and then placing the quartz tube into a vertical tube furnace, subsequently heating it to 950-1100℃ to form a required gradient temperature field, and sintering the sample blanks in the quartz tube at different temperatures for 6-12h; The spacers used in step (5) are zirconia balls or sheets with a diameter of 1-6mm.

2. The method of claim 1, wherein, The raw materials in step (1) further comprise a metal oxide sintering aid, and the metal oxide sintering aid is MnO2 or CuO.

3. The method of claim 1, wherein, The ball milling medium in step (2) is selected from one of anhydrous ethanol, water and n-hexane; and the ball milling substrate is a zirconium dioxide ball.

4. The method of claim 1, wherein, The ball milling speed in step (2) is 200-450r / min, and the ball milling time is 10-16h.

5. The method of claim 1, wherein, The heating rate in steps (4) and (5) is 5-10℃ / min.

6. The method of claim 1, wherein, The gradient temperature field in step (5) is selected from the area downward from the center of the furnace tube. 7.A bismuth ferrite-barium titanate-based lead-free piezoelectric ceramic prepared by the method according to any one of claims 1 to 6.

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