A low-loss high-curie-point bismuth titanate-barium titanate lead-free piezoelectric ceramic material and a preparation method thereof

Abstract

The application discloses a low-loss high-Curie-point bismuth ferrite-barium titanate lead-free piezoelectric ceramic material and a preparation method thereof. 1.02 FeO3-(0.25-x)BaTiO3-xCaZrO3+y%GeO2+z%MnO2; wherein x, y and z represent molar fractions, 0.005<=x<=0.020, 0.3<=y<=1, 0.5<=z<=1.5. The application introduces the third component CaZrO3, and adds GeO2 and MnO2, controls the crystal phase composition and the conductive carrier concentration, improves the microstructure, reduces the loss and improves the temperature stability, so that the Curie temperature, the depolarization temperature and the piezoelectricity are obviously improved. The lead-free piezoelectric ceramic material provided by the application has a simple synthesis process, and is expected to be applied to the preparation of high-temperature piezoelectric sensor devices.

Description

Technical Field

[0001] This invention belongs to the technical field of piezoelectric ceramics, specifically relating to a low-loss, high-Curie-point bismuth ferrite-barium titanate lead-free piezoelectric ceramic material and its preparation method. Background Technology

[0002] With the rapid development of aerospace, geological exploration, and automotive industries, there is an urgent need for high-temperature lead-free piezoelectric devices. BiFeO3 (BF) is a multifunctional material that simultaneously possesses ferroelectricity, piezoelectricity, and ferromagnetism. It exhibits a high Curie temperature (~830℃) and a high theoretical saturation polarization (~100 μC / cm²). 2 High-temperature piezoelectric materials have become a focus of widespread attention. However, synthesizing high-insulation BF ceramics with a single perovskite structure is very difficult. Introducing BaTiO3 (BT) as a second phase can stabilize the perovskite structure and suppress the generation of impurity phases. By adjusting the ratio between BF and BT, the Curie temperature can be adjusted to form high Curie temperature BiFeO3-BaTiO3 (BF-BT) ceramics with good piezoelectric properties. However, due to the large difference in sintering temperatures between BF and BT, severe Bi volatilization and Fe valence changes occur during high-temperature sintering, leading to the generation of lattice defects such as oxygen vacancies, which affects the density of the ceramic. Therefore, BF-BT piezoelectric ceramics have high leakage current and high loss, which limits their further high-voltage polarization and high-temperature applications. For this reason, many researchers have conducted extensive research on preparation techniques and chemical modification. The construction of MPB through chemical composition regulation has been proven to be a very effective strategy for improving the electrical properties of BF-BT-based ceramics, including the introduction of a third component ABO3-type perovskite structure such as K. 0.5 Na 0.5 NbO3, Bi(Ti) 0.5 Zn 0.5 O3, Bi(Mg) 0.5 Ti 0.5 It forms solid solutions with O3, BiAlO3, etc.

[0003] Chinese patent CN110128126A describes the simultaneous introduction of 0.075Bi(Ti) into 0.725BiFeO3-0.175BaTiO3 ceramics. 0.5 Zn 0.5 A multi-component system consisting of O3 and 0.025BiAlO3, with the addition of 0.01Li2CO3, 0.01MnCO3, and 0.025Bi2O3 as sintering aids, combined with calcination under pure oxygen, rapid sintering, and multi-step synthesis of intermediates, yielded superior piezoelectric properties: d 33 =137pC / N, k p =0.293%, T C =596℃, T d=580℃, tan delta =3.31%. The preparation process thereof includes multi-step synthesis, pure oxygen calcination, rapid sintering and the like, and the dielectric loss thereof is large.

[0004] The electrical properties of BF-BT ceramics are closely related to the synthesis process and material composition, and the design of composition and process control of microstructure by ion doping is still the main research method. However, the performance of piezoelectric ceramics is often mutually restricted and influenced, and the Curie temperature is also reduced by ion doping substitution modification. High-temperature piezoelectric devices require materials with high Curie temperature, especially ceramics with a Curie temperature higher than 600 DEG C and good piezoelectric properties. Therefore, how to obtain materials with high Curie temperature, low loss and good piezoelectric properties by simple and easy-to-operate methods has always been an important research content in the field of high-temperature piezoelectric ceramics. SUMMARY

[0005] In view of the above problems, the present application provides a low-loss high-Curie-point bismuth ferrite-barium titanate lead-free piezoelectric ceramic material and a preparation method thereof. The obtained ceramic material has low loss, high Curie temperature and depolarization temperature, and has good piezoelectric properties.

[0006] In the present application, CaZrO3 is added as the third component, which significantly reduces the leakage current and loss, and improves the depolarization temperature and temperature stability. The addition of GeO2 not only improves the sintering characteristics, but also constructs a phase structure coexisting with rhombohedral phase and tetragonal phase. The local stress generated by the ion radius mismatch between GeO2 and Fe 4+ and Fe 3+ / Ti 4+ , improves the Curie temperature, thereby realizing the optimization of structure and performance.

[0007] The purpose of the present application can be realized by the following technical solutions:

[0008] A low-loss high-Curie-point bismuth ferrite-barium titanate lead-free piezoelectric ceramic material, characterized in that the composition of the piezoelectric ceramic material is

[0009] 0.75Bi 1.02 FeO3-(0.25-x)BaTiO3-xCaZrO3+y%GeO2+z%MnO2;

[0010] Wherein x, y and z represent mole fraction, 0.005≤x≤0.020, 0.3≤y≤1, 0.5≤z≤1.5.

[0011] Preferably, x=0.01±0.005, y=0.5±0.2.

[0012] The preparation method of the low-loss high-Curie-point bismuth ferrite-barium titanate lead-free piezoelectric ceramic material according to the present application comprises the following steps:

[0013] (1) Select Bi2O3, Fe2O3, BaCO3, TiO2, CaCO3 and ZrO2 as raw materials, and take the raw materials according to the chemical formula 0.75Bi 1.02 FeO3-(0.25-x)BaTiO3-xCaZrO3 to perform ball milling, drying, pre-sintering, and obtain an intermediate powder;

[0014] (2) Take the intermediate powder and GeO2, MnO2 powder according to the chemical formula 0.75Bi 1.02 FeO3-(0.25-x)BaTiO3-xCaZrO3+y%GeO2+z%MnO2, perform ball milling, drying, granulation, molding, degassing, sintering to obtain a ceramic sheet, and then perform silver firing and polarization to obtain a piezoelectric ceramic.

[0015] Preferably, the pre-sintering temperature in step (1) is 700-900℃, the holding time is 2-8h, and the heating rate is 1-5℃ / min; the sintering temperature in step (2) is 900-1000℃, the holding time is 1-6h, and the heating rate is 1-5℃ / min.

[0016] Preferably, the pre-sintering temperature in step (1) is 750-850℃, the holding time is 3-6h, and the heating rate is 3±0.5℃ / min; the sintering temperature in step (2) is 940-980℃, the holding time is 2-4h, and the heating rate is 3±0.5℃ / min.

[0017] Preferably, the ball milling medium in step (1) is anhydrous ethanol, and the ball milling time is 8±1h; the ball milling medium in step (2) is anhydrous ethanol, and the ball milling time is 10±1h.

[0018] Preferably, the ball milling in steps (1) and (2) uses zirconium balls as grinding balls, and the mass ratio of raw materials, zirconium balls, and anhydrous ethanol is 1:(2-4):(1-2).

[0019] Preferably, the granulation in step (2) refers to adding a polyvinyl alcohol aqueous solution with a mass concentration of 5-15% as a binder; the molding in step (2) is performed by pressing into a green sheet under a pressure of 50-200MPa.

[0020] Preferably, the degassing in step (2) refers to heating the green sheet from room temperature to 600±50℃ over 4±0.5h and holding for 2±1h.

[0021] Preferably, the specific step of the silver firing in step (2) is screen printing silver paste on both sides of the ceramic sheet, and firing the silver at 750±50℃ for 20±5min; the polarization in step (2) refers to immersing the ceramic sheet into silicon oil at 100±10℃, the polarization voltage is 5±1kV / mm, and the polarization time is 20±5min.

[0022] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0023] (1) Low loss and high Curie point: the present application utilizes CaZrO3 to stabilize the perovskite structure of the piezoelectric material, reduces the oxygen vacancy concentration and leakage current, improves the polarization voltage, and improves the temperature stability; then GeO2 and MnO2 are added to adjust the crystal phase composition, optimize the microstructure, and improve the Curie temperature, thereby effectively improving the piezoelectric properties and working temperature of the bismuth ferrite-barium titanate ceramic, and the piezoelectric ceramic T c >610℃, and the dielectric loss is ≤1.5%.

[0024] (2) The lead-free piezoelectric ceramic prepared by the present application has mature process and low cost, does not need high temperature and high pressure, atmosphere, annealing, quenching, and additional production conditions such as multi-step synthesis, and has good repeatability and stability, and has strong practical value. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the room temperature XRD graph of the piezoelectric ceramic material prepared in example 1 and example 2 of the present application.

[0026] Figure 2 is the scanning electron microscope (SEM) photo of the piezoelectric ceramic material prepared in example 1 of the present application.

[0027] Figure 3 is the scanning electron microscope (SEM) photo of the piezoelectric ceramic material prepared in example 2 of the present application.

[0028] Figure 4 is the dielectric temperature curve of the piezoelectric ceramic material prepared in example 1 of the present application at 10kHz, 20kHz, 100kHz and 1MHz.

[0029] Figure 5 is the dielectric temperature curve of the piezoelectric ceramic material prepared in example 2 of the present application at 10kHz, 20kHz, 100kHz and 1MHz.

[0030] Figure 6 is the curve of the direct current resistivity of the piezoelectric ceramic material prepared in example 1 and example 2 of the present application with temperature.

[0031] Figure 7is the depolarization curve of the piezoelectric ceramic material prepared in Example 1 and Example 2 of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described in conjunction with specific examples. It is to be understood that the examples described herein are intended to explain, but not limit, the scope of the present application.

[0033] Example 1

[0034] Composition: 0.75Bi 1.02 FeO3-0.245BaTiO3-0.005CaZrO3+0.3% GeO2+0.5% MnO2

[0035] The preparation method is as follows:

[0036] Analytically pure Bi2O3, Fe2O3, BaCO3, TiO2, CaCO3 and ZrO2 are used as raw materials, and are weighed according to the chemical formula 0.75Bi 1.02 FeO3-0.245BaTiO3-0.005CaZrO3. The raw materials, zirconium balls and anhydrous ethanol are mixed in a ratio of 1:3:1.2, and are planetary ball-milled for 8h. After being dried at 85°C for 10h and sieved, the mixture is pre-fired at a rate of 3°C / min to 800°C, and is kept at this temperature for 4h. After the pre-fired intermediate is sieved and weighed, 0.3% GeO2 and 0.5% MnO2 powders are weighed according to the molar ratio and added. The raw materials, zirconium balls and anhydrous ethanol are mixed again in a ratio of 1:3:1.2, and are ball-milled for 10h. After being dried at 85°C for 10h and sieved, the mixture is granulated by adding a polyvinyl alcohol solution with a mass concentration of 8%, and is pressed into a green sheet with a diameter of 10mm and a thickness of 1.2mm under a pressure of 150MPa. The green sheet is placed in a high-alumina crucible, is covered and sealed, and is subjected to degassing by being heated to 600°C at a rate of 4h / h and kept at this temperature for 2h. Then, the green sheet is sintered by being heated to 980°C at a rate of 3°C / min and kept at this temperature for 2h, and is naturally cooled to room temperature. The ceramic sheet is ground into a thin sheet with a thickness of about 0.8cm, and silver paste is screen-printed on both sides of the thin sheet. The thin sheet is then fired at 750°C for 20min to form silver electrodes. Finally, the ceramic sheet is immersed in silicon oil at 100°C, and is polarized under a direct current voltage of 5kV / mm for 20min. After being cooled to room temperature for 24h, the piezoelectric properties of the ceramic sheet are measured.

[0037] Example 2

[0038] Composition: 0.75Bi 1.02 FeO3-0.245BaTiO3-0.005CaZrO3+0.5% GeO2+0.5% MnO2

[0039] Example 2 and Example 1 have substantially the same preparation method, except that the sintering temperature is 960°C, and the sintering time is 3h.

[0040] Example 3

[0041] Composition: 0.75Bi 1.02 FeO3-0.24BaTiO3-0.01CaZrO3+0.5% GeO2+1% MnO2

[0042] Example 3 is basically the same as the preparation method of Example 1, except that the pre-sintering temperature is 850°C, and the holding time is 3h; the sintering temperature is 960°C, and the holding time is 2h.

[0043] Example 4

[0044] Composition: 0.75Bi 1.02 FeO3-0.245BaTiO3-0.005CaZrO3+0.7% GeO2+0.5% MnO2

[0045] Example 4 is basically the same as the preparation method of Example 1, except that the pre-sintering temperature is 750°C, and the holding time is 6h; the sintering temperature is 940°C, and the holding time is 4h.

[0046] Example 5

[0047] Composition: 0.75Bi 1.02 FeO3-0.235BaTiO3-0.015CaZrO3+0.5% GeO2+1% MnO2

[0048] Example 5 is basically the same as the preparation method of Example 1, except that the sintering temperature is 960°C, and the holding time is 2h.

[0049] Comparative Example 1

[0050] Composition: 0.75Bi 1.02 FeO3-0.25BaTiO3+0.3% GeO2+0.5% MnO2

[0051] Comparative Example 1 is basically the same as the preparation method of Example 1, except that the sintering temperature is 960°C, and the holding time is 2h.

[0052] Comparative Example 2

[0053] Composition: 0.75Bi 1.02 FeO3-0.24BaTiO3-0.01CaZrO3+1% MnO2

[0054] Comparative Example 2 is basically the same as the preparation method of Example 1, except that the sintering temperature is 960°C, and the holding time is 3h.

[0055] Table 1 lists the piezoelectric properties of the piezoelectric ceramics prepared in Examples 1-5 and Comparative Examples 1-2, including piezoelectric constant d 33 , planar electromechanical coupling factor k p , Curie temperature T c , depolarization temperature T d , and dielectric loss tan δ at 1 kHz. It can be seen that Examples 1-5 all have high Curie temperature T c (>610℃) and depolarization temperature T d (>548℃), and low loss tan δ (<1.5%), and maintain good piezoelectric properties. The increase of CaZrO3 slightly reduces the Curie temperature, but significantly reduces the dielectric loss, and increases T d , and enhances the piezoelectric properties. The Curie temperature of the ceramic after adding GeO2 is significantly increased. Comparative Example 1 has a similar Curie temperature to each of the examples, but T d is too low (~485℃), and the loss is large (~4.8%). Comparative Example 2 has similar d 33 and k p values to each of the examples, especially a low dielectric loss (~1.3%), but T c and T d are low; the low T d is not conducive to the application of piezoelectric ceramics in high temperature fields.

[0056] Table 1 Piezoelectric properties of piezoelectric ceramics

[0057]

[0058] Figure 1 Fig. 1 is a room temperature XRD pattern of the piezoelectric ceramic material prepared in Example 1 and Example 2 of the present application, and the ceramic shows a single perovskite structure without other impurity phase peaks. Figure 1 The insert shows an enlarged view of the main peak at diffraction angle 2θ = 31.3-32.0°, and it can be seen that the typical doublet of the rhombohedral phase is no longer obvious, and a broadened diffraction peak showing coexistence of rhombohedral and tetragonal phases is shown.

[0059] Figure 2 and Figure 3 Fig. 2 is an SEM image of the surface of the piezoelectric ceramic prepared in Example 1 and Example 2 of the present application after grinding, polishing and thermal etching, and the ceramic material shows a dense and uniform microstructure.

[0060] Figure 4 and Figure 5The dielectric temperature curves of piezoelectric ceramic materials prepared in Example 1 and Example 2 of the present application at 10 kHz, 20 kHz, 100 kHz and 1 MHz, respectively, both of which have two dielectric abnormal peaks, the high-temperature dielectric peak corresponds to the ferroelectric-paraelectric phase transition, and the corresponding temperature is the Curie temperature T c Both of which show high values, 618℃ and 628℃, respectively.

[0061] Figure 6 The DC resistivity-temperature curves of piezoelectric ceramic materials prepared in Example 1 and Example 2 of the present application, the DC resistivity p still remains in the order of 10 7 Ω·cm at 300℃, which indicates that the material has good high-temperature insulation.

[0062] Figure 7 The d 33 emf polarization curves of piezoelectric ceramic materials prepared in Example 1 and Example 2 of the present application, when the d 33 emf sharply decreases, the corresponding annealing temperature is the depolarization temperature T d . The d 33 emf of Example 1 and Example 2 both remain high values below ≈535℃, and rapidly decrease at ≈550℃, which indicates that the d 33 emf has high temperature stability and can maintain stable piezoelectric properties in high-temperature operating environments, which is inseparable from the decrease in dielectric loss and the change in crystal phase structure. The XRD pattern, SEM pattern, dielectric temperature curve, DC resistivity-temperature curve and depolarization curve of the piezoelectric ceramic prepared in Example 3-5 are similar to those of Example 1 and Example 2, and will not be specifically described.

[0063] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods, and all shall be included in the protection scope of the present application.

Claims

1. A low-loss high Curie point BiTiO3-BaTiO3 lead-free piezoelectric ceramic material, characterized by, The piezoelectric ceramic material has a composition of 0.75Bi 1.02 FeO3-(0.25-x)BaTiO3-xCaZrO3+y%GeO2+z%MnO2; wherein x, y and z represent mole fraction, 0.005≤x≤0.020, 0.3≤y≤1, 0.5≤z≤1.

5.

2. A low loss high Curie point Bi- BaTiO3 lead-free piezoelectric ceramic material according to claim 1, characterized in that, x=0.01±0.005, y=0.5±0.

2.

3. The method of producing a low-loss high Curie point Bi- based barium titanate free piezoelectric ceramic material according to claim 1 or 2, characterized in that, The method comprises the following steps: (1) Select Bi2O3, Fe2O3, BaCO3, TiO2, CaCO3 and ZrO2 as raw materials, and 0.75Bi 1.02 FeO3-(0.25-x)BaTiO3-xCaZrO3 The raw materials are weighed, ball milled, dried, pre-fired, and the intermediate powder is obtained. (2) 0.75 Bi 1.02 FeO3-(0.25-x)BaTiO3-xCaZrO3+y%GeO2+z%MnO2 intermediate powder and GeO2, MnO2 powder are weighed, ball-milled, dried, granulated, molded, de-gassed, sintered to obtain ceramic sheets, and then silvered and polarized to obtain piezoelectric ceramics.

4. The production method according to claim 3, characterized by, The pre-burning temperature in step (1) is 700-900℃, the holding time is 2-8h, and the heating rate is 1-5℃ / min; the sintering temperature in step (2) is 900-1000℃, the holding time is 1-6h, and the heating rate is 1-5℃ / min.

5. The preparation method according to claim 4, characterized in that, The pre-burning temperature in step (1) is 750-850℃, the holding time is 3-6h, and the heating rate is 3±0.5℃ / min; the sintering temperature in step (2) is 940-980℃, the holding time is 2-4h, and the heating rate is 3±0.5℃ / min.

6. The method of any one of claims 3 to 5, wherein the method further comprises, The ball milling medium in step (1) is anhydrous ethanol, and the ball milling time is 8±1h; the ball milling medium in step (2) is anhydrous ethanol, and the ball milling time is 10±1h.

7. The preparation method according to claim 6, characterized in that, The ball milling in steps (1) and (2) uses zirconium balls as the grinding balls, and the mass ratio of the raw material, the zirconium balls and the anhydrous ethanol is 1:(2-4):(1-2).

8. The method of any one of claims 3 to 5, wherein the method further comprises, The granulation in step (2) refers to adding a polyvinyl alcohol aqueous solution with a mass concentration of 5-15% as a binder; the molding in step (2) is to press into a green sheet under a pressure of 50-200MPa.

9. The preparation method according to claim 8, characterized in that, The degumming in step (2) refers to heating the green sheet from room temperature to 600±50℃ for 4±0.5h and then holding for 2±1h.

10. The method of claim 9, wherein, The silver firing in step (2) comprises the following specific steps: screen printing silver paste on both sides of the ceramic sheet, and firing the silver at 750±50℃ for 20±5min; the polarization in step (2) refers to immersing the ceramic sheet into silicon oil at 100±10℃, the polarization voltage is 5±1kV / mm, and the polarization time is 20±5min.

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