High-temperature lead-free piezoelectric ceramic material and preparation method thereof

Abstract

The present invention provides a high-temperature lead-free piezoelectric ceramic material with a chemical composition of Bi 4‑x A x Ti 2.97 (B1 1 / 3 B2 2 / 3 ) 0.03 O 12 , where 0 < x < 0.08. Here, A is a doping element of a near-Bi 3+ radius metal cation, B1 is a doping element of a low-valence metal cation, B2 is a doping element of a high-valence metal cation, and B1 and B2 form an unequal valence doping of high-valence and low-valence metal cations. The present invention uses A / B-site composite doping to replace the A-site bismuth ions and B-site titanium ions in Bi4Ti3O 12 . A near-Bi 3+ [[ID= twenty]] radius metal cation element is used for A-site doping, and at the same time, B1 element and B2 element are used for B-site unequal valence doping, so as to achieve the effect of improving piezoelectric properties while maintaining a high Curie temperature. The present invention also provides a preparation method for the high-temperature lead-free piezoelectric ceramic material.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric ceramic technology, specifically relating to a high-temperature lead-free piezoelectric ceramic material and its preparation method. Background Technology

[0002] Piezoelectric ceramics are an important class of functional materials that utilize the direct and inverse piezoelectric effects to achieve the interconversion of mechanical vibrations and electrical signals. They are widely used in sensors, filters, transformers, and ultrasonic imaging. With the rapid development of science and technology in aerospace and nuclear power fields from the 1960s to the 1990s, the demand for high-temperature applications gradually increased. Lead zirconate titanate piezoelectric ceramics (PZT) could not achieve safe monitoring at high temperatures. Therefore, researchers have focused on developing lead-free piezoelectric ceramic materials with high Curie temperatures, environmental friendliness, and high performance to replace lead-based piezoelectric materials. Among many lead-free piezoelectric materials, bismuth layered ferroelectrics (BLSFs) possess a high Curie temperature (Ti). C >600℃), low aging rate, high dielectric breakdown strength, and high mechanical quality factor (Q). m With its advantages such as high temperature piezoelectric vibration sensor properties, it is the preferred material for key piezoelectric components.

[0003] BLSFs type ceramics have the general chemical formula (Bi₂O₂). 2+ (A m-1 B m O 3m+1 ) 2- It is composed of (Bi2O2). 2+ Layers and (A) m- 1B m O 3m+1 ) 2- A specific structure ceramic formed by alternating layers along the c-axis. A is typically a twelve-coordinated monovalent, divalent, or trivalent cation or its complex ion, such as Na. + Ba 2+ Bi 3+ B represents tetravalent, pentavalent, or hexavalent cations and their complex ions suitable for octahedral coordination, such as Ti. 4+ Ta 5+ W 6+ In this context, m represents the number of perovskite-like layers, typically an integer from 1 to 5. However, this unique layered structure makes the piezoelectric properties of this type of piezoelectric ceramic material susceptible to orientation, resulting in low piezoelectric activity. Furthermore, during sintering, the Bi element in the structure is prone to volatilization, leading to an increase in carrier concentration, which also affects the electrical properties of the material.

[0004] Currently, in this field, B-site or A / B-site co-doping modification is usually adopted to improve the piezoelectric properties of bismuth-layered structure high-temperature piezoelectric ceramics. For example, piezoelectric ceramics of bismuth-layered structure Bi4Ti3O 3+ can be prepared by co-doping with Cr 5+ and Ta 12 , and its piezoelectric coefficient has been increased to 26 pC / N. Bi 3.96 Ce 0.04 Ti 2.97 W 0.015 Nb 0.015 O 12 ceramics can also be prepared by the A / B-site co-doping strategy, which increases the piezoelectric coefficient of bismuth-layered high-temperature piezoelectric ceramics to more than 34 pC / N, but the Curie temperature decreases. The properties of piezoelectric ceramics often affect each other. The higher the piezoelectric coefficient, the lower the Curie temperature tends to be. How to improve the piezoelectric properties of the material while maintaining its relatively high Curie temperature is an urgent problem to be solved. Summary of the Invention

[0005] The present invention aims to at least solve one of the above technical problems existing in the prior art. For this purpose, the present invention provides a high-temperature lead-free piezoelectric ceramic material, which can improve the piezoelectric properties of the material while maintaining a relatively high Curie temperature.

[0006] The present invention also provides a preparation method of the high-temperature lead-free piezoelectric ceramic material.

[0007] In the first aspect of the present invention, a high-temperature lead-free piezoelectric ceramic material is provided, with a chemical composition of Bi 4-x A x Ti 2.97 (B1 1 / 3 B2 2 / 3 ) 0.03 O 12 , where 0 < x < 0.08. Here, A is a doping element of a metal cation with a radius close to Bi 3+ , B1 is a doping element of a low-valence metal cation, B2 is a doping element of a high-valence metal cation, and B1 and B2 form an unequal valence doping of a high-valence metal cation and a low-valence metal cation.

[0008] One technical solution in the technical solution of the present invention regarding the high-temperature lead-free piezoelectric ceramic material has at least the following beneficial effects:

[0009] The present invention provides a bismuth-layered structure high-temperature piezoelectric ceramic material, which adopts A / B-site co-doping to replace the A-site bismuth ions and B-site titanium ions in Bi4Ti3O 12 , and uses a metal cation with a radius close to Bi 3+A-site doping is performed using a radius-based metal cation, while B-site inequivalent doping is performed using elements B1 and B2, introducing elements related to Bi. 3+ Near-Bi with similar ionic radii 3+ The strategy of using radius-dependent metal cations, combined with the B-site non-equivalent co-doping of high-valence and low-valence ions, effectively reduces the oxygen vacancy concentration and also adjusts the Bi4Ti3O4 concentration. 12 The degree of lattice distortion of the oxygen octahedron in the bismuth layered structure allows it to improve piezoelectric properties while maintaining a high Curie temperature.

[0010] According to some embodiments of the present invention, 0.02 ≤ x ≤ 0.06.

[0011] According to some embodiments of the present invention, the near-Bi 3+ Radius metal cations include Ce 3+ and La 3+ One of them, the high-valence metal cation includes Ta 5+ 、Nb 5+ and Sb 5+ One of them, the low-valent metal cation B1 includes Cr 3+ Mn 3+ and Mg 2+ One of them.

[0012] According to some embodiments of the present invention, when the near-Bi 3+ The radius of the metal cation is Ce 3+ The high-valence metal cation is Ta. 5+ The low-valence metal cation B1 is Cr 3+ When the chemical composition is Bi 4-x Ce x Ti 2.97 (Cr 1 / 3Ta 2 / 3 ) 0.03 O 12 (BiCTCT-100x).

[0013] For Bi 4-x Ce x Ti 2.97 (Cr 1 / 3 Ta 2 / 3 ) 0.03 O 12 In ceramics, the Ce element at site A exists in the form of Ce. 3+ The B-site composite doped ion combination is The forms of Cr and Ta are respectively Cr 3+ and Ta 5+ .

[0014] Structurally, the Curie temperature T of bismuth layered piezoelectric ceramics is... c Related to the tolerance factor t:

[0015]

[0016] Where r A r B r O These represent the radii of the A-site cation, B-site cation, and oxygen ion, respectively. Generally, the smaller t is, the higher T is. C The higher. When and replace After that, the value of t decreases, thus causing T to... C Increase. Meanwhile, generally speaking, A-site doping substitution has a significant impact on the t-value; therefore, selecting to introduce doping at the A-site... Ionic radii similar The t-value remains relatively unchanged after the replacement.

[0017] When Ta 5+ and Cr 3+ Replace Ti 4+ This can reduce the oxygen vacancy concentration, and the process is as follows:

[0018]

[0019] According to the charge compensation principle, after introducing Ta₂O₅ and Cr₂O₃, Ta 5+ and Cr 3+ Ti in ion-substituted BIT 4+ Ions can produce and Cr′ Ti Defect. Therefore, (Cr 1 / 3 / Ta 2 / 3 Doping with donors can effectively reduce oxygen vacancy concentration, which is one of the main reasons for the increase in resistivity of BiCTCT-100x ceramics.

[0020] Meanwhile, Ce at position A 3+ The ion subsequently replaced the Bi in BIT 3+ Ions, producing Defects, and to some extent inhibited Bi 3+ Ion volatilization. This process reduces the concentration of oxygen vacancies. Therefore, Ce ion donor doping effectively reduces the number of oxygen vacancies, which is one of the main reasons for the increase in resistivity of BiCTCT-100x ceramics.

[0021] Experiments have shown that combining B-site non-equivalent co-doping to adjust the concentration of A-site ions is an effective strategy to improve the electrical properties of BIT-based ceramics. While maintaining a high Curie temperature, it can significantly improve piezoelectric properties and maintain a high Curie temperature and excellent temperature stability at high temperatures.

[0022] A second aspect of the present invention provides a method for preparing the high-temperature lead-free piezoelectric ceramic material of the first aspect of the present invention, comprising the following steps:

[0023] S1: Weigh Bi2O3, TiO2, oxides of element A, oxides of element B1, and oxides of element B2 according to the stoichiometric ratio, mix them, and then perform wet ball milling. Dry the slurry after ball milling to obtain powder.

[0024] S2: The powder is pre-fired to obtain pre-fired powder, and a portion of the pre-fired powder is granulated and pressed into tablets to obtain a green body;

[0025] S3: After debinding the green body, the green body is embedded with a portion of the pre-fired powder and then solid-phase sintered to obtain ceramic sheets.

[0026] S4: After printing electrode material on the surface of the ceramic sheet, polarization treatment is performed to obtain the high-temperature lead-free piezoelectric ceramic material.

[0027] One technical solution of the present invention relating to a method for preparing high-temperature lead-free piezoelectric ceramic materials has at least the following beneficial effects:

[0028] 1. Improved high-temperature stability and piezoelectric properties: By adopting near-Bi... 3+ Radius metal cations were used for A-site doping, and B1 and B2 elements were used for B-site non-equivalent co-doping, which effectively adjusted the properties of Bi4Ti3O4. 12 The lattice distortion in the bismuth layered structure reduces the concentration of oxygen vacancies, thereby improving the material's stability and piezoelectric properties.

[0029] 2. Enhanced Curie temperature: By employing an unequal doping strategy, a high Curie temperature (i.e., the material's ability to maintain a strong piezoelectric effect at high temperatures) is maintained, enabling the material to exhibit excellent piezoelectric properties in high-temperature environments and meet the requirements of high-temperature applications.

[0030] 3. Lead-free and environmentally friendly: It uses lead-free bismuth layered piezoelectric ceramic material, which meets environmental protection requirements and avoids the potential harm to the environment and human body caused by traditional lead-based piezoelectric materials.

[0031] 4. Controllable ceramic preparation process: Through steps such as wet ball milling, pre-firing, granulation, pressing, and sintering, the microstructure and phase composition of ceramic materials can be precisely controlled, thereby ensuring the high performance and uniformity of the materials.

[0032] 5. Simple and efficient preparation process: The entire preparation process is relatively simple and efficient, enabling the mass production of high-performance high-temperature lead-free piezoelectric ceramic materials, and possessing certain industrialization potential.

[0033] In step S1:

[0034] Bi2O3, TiO2, oxides of element A, oxides of element B1, and oxides of element B2, with a purity of 99.9%.

[0035] Considering that Bi is easily volatile at high temperatures, Bi2O3 is used in excess of 1wt%-5wt%, preferably 3wt%.

[0036] After mixing, the mixture is subjected to wet ball milling, and the milled slurry is dried to obtain powder.

[0037] The grinding jar is made of polytetrafluoroethylene and uses zirconia grinding balls. The mass ratio of the feed to the grinding balls is 1:2 to 4.

[0038] Grinding balls in large, medium, and small sizes can be in a mass ratio of 3:4:3.

[0039] According to some embodiments of the present invention, the oxide of element A includes one of CeO2 and La2O3.

[0040] According to some embodiments of the present invention, the oxide of element B1 includes one of Cr2O3 and MgO, and the oxide of element B2 includes one of Ta2O5 and Nb2O5.

[0041] According to some embodiments of the present invention, the rotational speed of the wet ball mill is 300 rpm to 400 rpm.

[0042] According to some embodiments of the present invention, the rotational speed of the wet ball mill is any value or a range formed by any two of 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, and 400 rpm, such as 340 rpm to 360 rpm.

[0043] According to some embodiments of the present invention, the wet ball milling time is 4h to 12h.

[0044] According to some embodiments of the present invention, the wet ball milling time is any value of 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or a range of any two, such as 6h to 10h.

[0045] According to some embodiments of the present invention, the ball-milled slurry is dried at a temperature of 80°C to 90°C for 1 to 2 hours, and then sieved (it can be sieved through a 60-mesh screen).

[0046] In step S2:

[0047] According to some embodiments of the present invention, the pre-firing temperature is 750°C to 850°C.

[0048] According to some embodiments of the present invention, the pre-firing temperature can be any value or a range formed by any two of 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, and 850°C, such as 800°C to 830°C.

[0049] According to some embodiments of the present invention, the pre-firing time is 2h to 4h.

[0050] According to some embodiments of the present invention, the pre-firing time is any value of 2h, 2.5h, 3h, 3.5h, 4h or a range of any two, such as 2.5h to 3.5h.

[0051] Pre-calcination allows the chemical reactions between raw materials to proceed fully, synthesizing the desired phase, while also removing impurities from the raw materials and increasing density.

[0052] Preferably, the pre-firing conditions are 850°C for 2 hours.

[0053] The calcined powder is reserved for use in the sintering process for embedding powder during sintering. This serves two purposes: first, to reduce the volatilization of Bi during sintering, and second, to prevent ceramic sheets from sticking together.

[0054] Granulation and tableting of pre-calcined powder can effectively improve sample density, reduce porosity, and thus improve sample resistivity.

[0055] In this invention, a polyvinyl butyral (PVB) alcohol solution can be used as the binder. 4%-6% PVB solution is added and the mixture is thoroughly ground until the alcohol evaporates. The granulated powder is then sieved (through a 60-mesh sieve). Each batch of granulated powder is weighed at 0.40g and poured into a 10mm diameter circular tableting mold. The mold is then pressed at 5-10MPa for 10-60s to form a disc. This disc is then subjected to cold isostatic pressing at 200MPa for 10-30 minutes.

[0056] In step S3:

[0057] The green body is debonded to remove the binder added during granulation. It can be kept at 350℃ for 1 hour and then heated to 500℃ for 1 hour.

[0058] According to some embodiments of the present invention, the solid-state sintering temperature is 1080℃~1120℃.

[0059] According to some embodiments of the present invention, the holding time for solid-state sintering is 2h to 3h.

[0060] According to some embodiments of the present invention, in order to improve the quality of the sintered sheet, the solid-state sintering heating process is a segmented heating process, which raises the temperature to 850°C to 950°C at a rate of 2°C / min to 3°C / min, and then raises the temperature to the sintering temperature at a rate of 3°C / min to 5°C / min, and then holds the temperature.

[0061] In step S4:

[0062] Before polarization treatment after printing electrode material on the surface of the ceramic disc, the sintered ceramic disc is first polished, and then silver paste is printed on both sides. It is then cured at 720℃ for 15 minutes.

[0063] According to some embodiments of the present invention, the temperature of the polarization treatment is 160°C to 200°C.

[0064] According to some embodiments of the present invention, the polarization electric field of the polarization treatment is 6kV / mm to 8kV / mm.

[0065] According to some embodiments of the present invention, the polarization time of the polarization treatment is 20 min to 30 min.

[0066] According to some embodiments of the present invention, the polarization is performed by heating in an oil bath.

[0067] After polarization, the piezoelectric properties and other properties of the prepared high-temperature lead-free piezoelectric ceramic material can be tested.

[0068] A third aspect of the present invention provides a piezoelectric device comprising the high-temperature lead-free piezoelectric ceramic material of the first aspect of the present invention or the high-temperature lead-free piezoelectric ceramic material prepared by the method of the second aspect of the present invention.

[0069] One of the technical solutions of the present invention concerning piezoelectric devices has at least the following beneficial effects:

[0070] 1. High-temperature stability: The piezoelectric device made of the high-temperature lead-free piezoelectric ceramic material of the first aspect of the present invention or the material obtained by the method of the second aspect can still maintain good piezoelectric performance in high-temperature environments, and is suitable for high-temperature applications, such as automotive electronics, industrial sensors and other fields.

[0071] 2. Lead-free and environmentally friendly: This piezoelectric device uses lead-free piezoelectric ceramic material, which meets environmental protection requirements and avoids the harmful effects of traditional lead-based piezoelectric materials. It conforms to the global trend of increasingly stringent environmental standards and is suitable for use in regions and markets with strict environmental regulations.

[0072] 3. High voltage electrical performance: through near-Bi 3+ By doping with radius-determined metal cations and non-equivalent co-doping at B sites, the material of this invention significantly improves piezoelectric performance, provides stronger electrical response, enhances the efficiency of piezoelectric devices, and is widely applicable to high-precision piezoelectric applications such as sensors, actuators, and sonar systems.

[0073] 4. Optimized crystal structure: Because the crystal structure of the material of this invention is optimized through a specific doping strategy during the preparation process, the oxygen vacancy concentration is reduced and the lattice distortion of the oxygen octahedron is adjusted, the piezoelectric device has better stability and reliability and can maintain excellent performance in long-term use.

[0074] 5. Broad application prospects: This piezoelectric device is suitable for a variety of industrial and consumer electronics fields, especially in applications requiring high-temperature piezoelectric performance, such as high-temperature sensors, energy harvesting devices, and acoustic sensors, meeting the growing technical demands for high efficiency, environmental protection, and high temperature resistance. Attached Figure Description

[0075] Figure 1 The present invention relates to a high-temperature lead-free piezoelectric ceramic material Bi. 4-x Ce x Ti 2.97 (Cr 1 / 3 Ta 2 / 3 ) 0.03 O 12 The preparation process flow chart.

[0076] Figure 2 The results show the piezoelectric coefficient of the BiCTCT-100x sample after annealing at various temperatures.

[0077] Figure 3 The ceramic of this invention exhibits superior performance compared to other Bi4Ti3O-based ceramics. 12 Comparison results of ceramic doping and modification products. Detailed Implementation

[0078] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0079] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0080] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0081] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0082] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0083] In an embodiment of the present invention, Bi 4-x A x Ti 2.97 (B1 1 / 3 B2 2 / 3 ) 0.03 O 12 It is abbreviated as BiCTCT-100x.

[0084] Example

[0085] A high-temperature lead-free piezoelectric ceramic material Bi was prepared. 4-x Ce x Ti 2.97 (Cr 1 / 3 Ta 2 / 3 ) 0.03 O 12 , where x = 0, 0.02, 0.04, 0.06, 0.08.

[0086] Preparation process as follows Figure 1 As shown, the specific process is as follows:

[0087] Weigh Bi₂O₃ (99.9%), CeO₂ (99.9%), TiO₂ (99%), Cr₂O₃ (99.99%), and Ta₂O₅ (99.99%) powders according to stoichiometric ratios. Considering that Bi is volatile at high temperatures, Bi₂O₃ is added in excess by 3 wt%.

[0088] Pour the prepared raw materials into a polytetrafluoroethylene (PTFE) ball mill jar, and add zirconia grinding balls at a mass ratio of 1:3. Use large, medium, and small grinding balls in a mass ratio of 3:4:3. Add enough anhydrous ethanol to almost completely submerge the grinding balls. Finally, cover the jar and perform wet ball milling. The milling conditions are 350 rpm for 6 hours. Dry the milled slurry at 85°C for 1 hour, then sieve it (through a 60-mesh sieve).

[0089] The powder is poured into an alumina crucible for pre-firing at 800℃ for 3 hours. Pre-firing allows for sufficient chemical reactions between the raw materials to synthesize the desired phase, while also removing impurities and increasing density. Preferably, the pre-firing conditions are 850℃ for 2 hours. The calcined powder is reserved for embedding during the sintering process, which reduces Bi volatilization and prevents ceramic sheets from sticking together.

[0090] Using pre-calcined powder for granulation and tableting can effectively improve sample density, reduce porosity, and thus improve sample resistivity. In this embodiment, the binder used is an alcoholic solution of polyvinyl butyral (PVB). 5% PVB solution is added and thoroughly ground until the alcohol evaporates. The granulated powder is then sieved (through a 60-mesh sieve). 0.40g of the granulated powder is weighed each time and poured into a 10mm diameter circular tableting mold. The mold is pressed at 5-10MPa for 10-60s to form round tablets. Then, cold isostatic pressing is performed at 200MPa for 10-30 minutes.

[0091] The green body is subjected to a debinding process to remove the binder added during granulation, which involves holding it at 350℃ for 1 hour and then raising the temperature to 500℃ and holding it for another hour.

[0092] The pre-fired powder was used to embed the debinding sample, followed by solid-state sintering at 1000℃ for 2 hours at a heating rate of 3℃ / min. Notably, to improve the quality of the sintered sheet, a segmented heating method was adopted: the temperature was increased to 900℃ at a rate of 2℃ / min, and then increased to the sintering temperature at a rate of 4℃ / min, followed by a holding period.

[0093] The sintered ceramic discs are polished, then silver paste is printed on both sides, and then cured at 720℃ for 15 minutes.

[0094] The sample was polarized by oil bath heating at a temperature of 180℃, a polarization electric field of 7kV / mm, and a polarization time of 25min.

[0095] The piezoelectric properties and other properties of the polarized ceramic sheet were tested.

[0096] This invention is in position B. Based on unequal doping, introducing Ce ions with similar radii to Bi ions at the A-site can effectively reduce the impact on the Curie temperature. BiCTCT-100x ceramics were prepared by solid-state sintering. By reducing Bi volatilization and decreasing the concentration of oxygen vacancies, the resistivity of the ceramic was improved, thus enhancing the Bi₄Ti₃O₃ content while maintaining a high Curie temperature. 12 The piezoelectric properties and stability of the base ceramic.

[0097] Table 1 shows the Bi content at different doping levels x. 4-x Ce x Ti 2.97 (Cr 1 / 3 Ta 2 / 3 ) 0.03 O 12 Performance parameters of ceramics.

[0098] Table 1

[0099]

[0100] Table 1 shows that co-doping at sites A / B can improve the performance of Bi4Ti3O4. 12 Comprehensive electrical properties of the base ceramic (pure Bi4Ti3O prepared by conventional methods) 12 The piezoelectric coefficient of the ceramic is approximately 3.5 pC / N. When x = 0.04, the BiCTCT-100x ceramic exhibits the highest piezoelectric coefficient at 37 pC / N, which is significantly better than that of pure Bi4Ti3O. 12 This represents an improvement of approximately 11 times. Simultaneously, at 500℃, it possesses the lowest dielectric loss (tanδ=0.078) and a relatively high resistivity, reaching 6.6×10⁻⁶. 6 Ω·cm, relative to pure Bi4Ti3O 12 For ceramics, the high-temperature resistivity is increased by two orders of magnitude (compared to pure Bi4Ti3O prepared by traditional solid-state sintering). 12 The high-temperature resistivity of ceramics is approximately 10. 4 (Approximately Ω·cm)

[0101] Ce 3+ Substitution causes lattice distortion and simultaneously modulates the distribution of oxygen vacancies, thereby improving piezoelectric properties. Furthermore, the Curie temperature of BiCTCT-4 ceramics is higher than that of pure Bi4Ti3O. 12 ceramics (T) C =675℃). When B position and replace After that, the value of t decreases, thus causing T to... C Increase.

[0102] Meanwhile, unlike other technologies where Ce ions have a +4 valence, causing greater lattice distortion, in this invention, due to the synergistic effect of unequal doping at the B site, Ce ions at the A site only have a +3 valence. and The ionic radii are similar, so the t-value remains relatively unchanged after substitution. However, with increasing Ce content, the orthogonality of the crystal decreases, leading to a change in T. C The value gradually decreases. Therefore, based on the non-equivalent doping at the B site, the introduction of Ce ions with a radius similar to that of Bi ions at the A site effectively minimizes the impact on T. C The influence can maintain a relatively high T C value.

[0103] Figure 2 The figures show the piezoelectric coefficients of the BiCTCT-100x sample after annealing at various temperatures. It can be seen that the sample exhibits good piezoelectric stability, maintaining a high piezoelectric coefficient even after annealing at 500℃. Furthermore, the piezoelectric coefficients above T... c After annealing at the specified temperature, the ceramic undergoes a transformation from a ferroelectric phase to a paraelectric phase. 33 It is almost zero.

[0104] The piezoelectric properties and Curie temperature of this invention are compared with those based on Bi4Ti3O. 12 Comparing the invention work on ceramic doping modification, the results are as follows: Figure 3 As shown. Figure 3 middle, Figure 3 In this context, W / Nb refers to Bi4Ti. 2.9 W 0.05 Nb 0.05 O 12 ;

[0105] W / Cr refers to Bi4Ti 2.95 W 0.05 O 12.05 +0.2wt.%Cr2O3;

[0106] Ce / W / Nb refers to Bi 3.96 Ce 0.04 Ti 2.97 W 0.015 Nb 0.015 O 12 ;

[0107] Mg / Nb refers to Bi4Ti 2.95 (Mg 1 / 3 Nb 2 / 3 ) 0.05 O 12 ;

[0108] Ce / W / Ta refers to Bi 3.96 Ce0.04 Ti 2.94 W 0.03 Ta 0.03 O 12 ;

[0109] W / Mn refers to Bi4Ti 2.9 W 0.1 O 12 +4wt.%Mn2O3;

[0110] W / Ta refers to Bi4Ti 2.92 W 0.04 Ta 0.04 O 12 ;

[0111] Mn / Nb refers to Bi4Ti 2.95 (Mn 1 / 3 Nb 2 / 3 ) 0.05 O 12 ;

[0112] Zn / Nb refers to Bi4Ti 2.93 (Zn 1 / 3 Nb 2 / 3 ) 0.07 O 12 ;

[0113] Nb / Ta refers to Bi4Ti 2.98 Nb 0.01 Ta 0.01 O 12 ;

[0114] Cu / Sb refers to Bi4Ti 2.965 (Cu 1 / 3 Sb 2 / 3 ) 0.035 O 12 ;

[0115] Cu / Nb refers to Bi4Ti 2.95 (Cu 1 / 3 Nb 2 / 3 ) 0.05 O 12 .

[0116] It can be observed that Bi4Ti3O from other works 12 While improving the piezoelectric properties, the Curie temperature of the ceramic sample also decreased significantly, both being lower than that of pure Bi₄Ti₃O. 12The Curie temperature of ceramics is 675℃, while the BiCTCT-4 sample in this invention maintains an excellent Curie temperature (681℃) while achieving excellent piezoelectric properties (37 pC / N). This result confirms that modifying the A-site with equivalent ions based on non-equivalent doping at the B-site is an effective way to enhance the properties of Bi4Ti3O4. 12 The strategy for modifying the comprehensive electrical properties of ceramics will provide some reference directions for subsequent work on modifying piezoelectric ceramics.

[0117] Comparative Example

[0118] Typically, Ce ions incorporated into the A-site exist in a mixed state of +3 and +4 valences, which leads to increased lattice distortion and a significant decrease in the Curie temperature. However, in this invention, through the synergistic effect of unequal doping at the B-site, Ce ions in the ceramic sample exist only in a single +3 valence state, effectively reducing the impact of A-site doping on the Curie temperature. Table 2 shows the high-temperature lead-free piezoelectric ceramic material Bi of this invention. 4-x Ce x Ti 2.97 (Cr 1 / 3 Ta 2 / 3 ) 0.03 O 12 (x = 0.04, abbreviated as Ce / Cr / Ta) Comparison with other works.

[0119] Table 2

[0120]

[0121] In Table 2, Ce / W / Ta represents Bi 3.96 Ce 0.04 Ti 2.94 W 0.03 Ta 0.03 O 12 ;Ce / W / Nb represents Bi 3.96 Ce 0.04 Ti 2.9 7W 0.015 Nb 0.015 O 12 .

[0122] This invention proposes a modification strategy that introduces atoms of the same valence at the A site into the base layer of non-equivalent doping at the B site. The A / B site composite doping in this invention replaces Bi₄Ti₃O₂. 12The invention employs cerium, chromium, and tantalum doping. Notably, unlike traditional methods where the incorporation of mixed +3 and +4 valence Ce ions at the A-site leads to a significant drop in the Curie temperature, the B-site non-equivalent doping strategy in this invention ensures that the A-site Ce ion is a single +3 valence ion, effectively reducing its impact on the Curie temperature. Simultaneously, this strategy effectively reduces oxygen vacancy concentration, resulting in a B-site composite non-equivalent dopant ion combination. That is, the composition is Bi 4-x Ce x Ti 2.97 (Cr 1 / 3 Ta 2 / 3 ) 0.03 O 12 By inducing lattice distortion and simultaneously regulating the distribution of oxygen vacancies, the piezoelectric properties are improved, which is within the scope of protection of this invention.

[0123] Considering Bi volatilization, Bi is in excess in the raw materials, preferably 3% excess. Pre-calcined powder is used for granulation and tableting. Pre-calcination effectively removes impurities from the powder and generates BIT powder. Furthermore, the pre-calcined powder is also used for embedding in sintering to reduce Bi volatilization during sintering and prevent ceramic sheets from sticking together. Samples are then prepared using solid-state sintering, with staged heating to improve the sintering quality. For this experimental scheme, the preferred sintering process is 1120℃-2h, with a heating / cooling rate of 3℃ / min. The temperature is first raised to 900℃ at 2℃ / min, and then raised to the sintering temperature at 3℃ / min, within the scope of this patent protection.

[0124] Based on the experimental results, through position A (Ce) and position B... Composite substitution improves the piezoelectric properties of ceramics. Furthermore, with increasing A-site doping concentration, the Curie temperature generally ranges from 671 to 682 °C, approaching that of pure Bi₄Ti₃O₂. 12 Curie temperature of ceramics (T) C =675℃). Therefore, by adopting an ion strategy with similar ionic radii at the A site combined with unequal doping at the B site, it is possible to effectively improve piezoelectric performance while reducing the impact on the Curie temperature, and simultaneously achieve high resistivity and excellent temperature stability at high temperatures.

[0125] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A high-temperature lead-free piezoelectric ceramic material, characterized in that, The chemical composition is Bi 4-x A x Ti 2.97 (B1 1 / 3 B2 2 / 3 ) 0.03 O 12 , 0.02≤x≤0.06, where A is the nearest Bi 3+ The doping element for the radius metal cation is selected from Ce. 3+ Or La 3+ B1 is a low-valence metal cation doping element selected from Cr. 3+ Mn 3+ or Mg 2+ B2 is a dopant element of a high-valence metal cation, selected from Ta. 5+ 、Nb 5+ or Sb 5+ B1 and B2 form unequal co-doping of high-valence and low-valence metal cations.

2. The high-temperature lead-free piezoelectric ceramic material according to claim 1, characterized in that, When the near-Bi 3+ The radius of the metal cation is Ce 3+ The high-valence metal cation is Ta. 5+ The low-valence metal cation is Cr. 3+ When the chemical composition is Bi 4-x Ce x Ti 2.97 (Cr 1 / 3 Ta 2 / 3 ) 0.03 O 12 .

3. A method for preparing the high-temperature lead-free piezoelectric ceramic material as described in claim 1 or 2, characterized in that, Includes the following steps: S1: Weigh Bi2O3, TiO2, oxides of element A, oxides of element B1, and oxides of element B2 according to the stoichiometric ratio, mix them, and then perform wet ball milling. Dry the slurry after ball milling to obtain powder. S2: The powder is pre-fired to obtain pre-fired powder, and a portion of the pre-fired powder is granulated and pressed into tablets to obtain a green body; S3: After debinding the green body, the green body is embedded with a portion of the pre-fired powder and then solid-phase sintered to obtain ceramic sheets. S4: After printing electrode material on the surface of the ceramic sheet, polarization treatment is performed to obtain the high-temperature lead-free piezoelectric ceramic material.

4. The method according to claim 3, characterized in that, The oxide of element A includes one of CeO2 and La2O3.

5. The method according to claim 3, characterized in that, The oxide of element B1 includes one of Cr2O3 and MgO, and the oxide of element B2 includes one of Ta2O5 and Nb2O5.

6. The method according to claim 3, characterized in that, The solvent used in the wet ball milling includes ethanol.

7. The method according to claim 3, characterized in that, The rotation speed of the wet ball mill is 300 rpm to 400 rpm.

8. The method according to claim 3, characterized in that, The wet ball milling time is 4h to 12h.

9. The method according to claim 3, characterized in that, The preheating temperature is 750℃~850℃.

10. The method according to claim 3, characterized in that, The preheating time is 2 to 4 hours.

11. The method according to claim 3, characterized in that, The solid-state sintering temperature is 1080℃~1120℃.

12. The method according to claim 3, characterized in that, The holding time for solid-state sintering is 2h to 3h.

13. The method according to claim 3, characterized in that, The solid-state sintering heating process is a segmented heating process, where the temperature is raised to 850℃~950℃ at a rate of 2℃ / min~3℃ / min, and then raised to the sintering temperature at a rate of 3℃ / min~5℃ / min, followed by holding at that temperature.

14. The method according to claim 3, characterized in that, The polarization treatment temperature is 160℃~200℃.

15. The method according to claim 3, characterized in that, The polarization electric field of the polarization treatment is 6kV / mm to 8kV / mm.

16. The method according to claim 3, characterized in that, The polarization time for the polarization treatment is 20 min to 30 min.

17. A piezoelectric device, characterized in that, The high-temperature lead-free piezoelectric ceramic material includes the high-temperature lead-free piezoelectric ceramic material as described in claim 1 or 2, or the high-temperature lead-free piezoelectric ceramic material prepared by the method described in any one of claims 3 to 16.

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