Preparation method of BF-BT-BKT lead-free piezoelectric ceramic with high-temperature thermal stability and high-voltage electrical performance

Abstract

The application discloses a preparation method of BF-BT-BKT lead-free piezoelectric ceramic with high-temperature thermal stability and high-voltage electric performance. 1.02 FeO3-xBaTiO3-y(Bi 0.5 K 0.5 )TiO3+mLi2CO3+nMnO2, wherein x, y, m and n represent molar fractions of components, and 0.25

Description

Technical Field

[0001] This invention relates to the field of lead-free piezoelectric ceramics preparation technology, and in particular to a type of piezoelectric ceramic with ultra-high piezoelectric properties. 33 >450 pC / N, maximum real-time operating temperature (T) dr (greater than 350) o Specifically, this describes a method for preparing a BF-BT-BKT lead-free piezoelectric ceramic with high-temperature thermal stability and high-voltage electrical properties. Background Technology

[0002] Piezoelectric ceramics are a class of functional materials capable of converting mechanical energy into electrical energy. Due to their excellent piezoelectric effect and electromechanical coupling properties, they are widely used in sensors, actuators, ultrasonic equipment, and other fields. Traditional piezoelectric ceramics mostly use lead zirconate titanate (PZT) as their main component, which poses serious environmental pollution problems. Therefore, developing environmentally friendly, low-cost, and high-performance piezoelectric ceramics is an inevitable trend for future development.

[0003] With the continuous advancement of technology, the application of high-temperature piezoelectric materials is becoming increasingly widespread, finding extensive use in high-temperature fields such as aerospace, automotive industry, oil exploration, and 3D printing. However, existing research shows that high-temperature stability and high-voltage piezoelectric properties are contradictory; higher piezoelectric properties correspond to lower temperature stability, and higher Curie temperatures correspond to lower piezoelectric properties. Currently, the only piezoelectric ceramic system that simultaneously possesses high-voltage piezoelectric properties and high-temperature thermal stability is the bismuth scandate-lead titanate (BiScO3-PbTiO3) system. However, the high price of scandium metal and the toxicity of lead severely limit its application range. Therefore, researching and obtaining high-performance lead-free piezoelectric ceramics that simultaneously possess high-voltage piezoelectric properties and high-temperature thermal stability is of great significance.

[0004] The BiFeO3-BaTiO3 (BF-BT) system has attracted much attention due to its perovskite structure and high Curie temperature. However, current efforts to improve its performance mainly focus on phase structure modulation, making it difficult to obtain ceramics that simultaneously possess high piezoelectric properties and high-temperature thermal stability. Zuo Ruzhong of Anhui University constructed a quaternary system of bismuth ferrite-barium titanate-sodium bismuth titanate-bismuth magnesium niobate (BF-BT-BNT-BMN), achieving a room-temperature piezoelectric performance of approximately 210 pC / N. Liu Laijun et al. of Guilin University of Technology prepared BF-BT-BKT ceramics through high-temperature quenching and other processes, obtaining ceramic samples with room-temperature piezoelectric properties reaching 150 pC / N. However, the high-temperature quenching process easily forms numerous microcracks in the ceramic, leading to aging during use. Furthermore, the quenching process is prone to damaging equipment and is complex to operate, making it unsuitable for industrial production.

[0005] Existing research indicates that the thermal stability of piezoelectric ceramics is related not only to the Curie temperature but also to the phase structure; the greater the tetragonal distortion, the higher the temperature stability. Furthermore, the piezoelectric properties of piezoelectric ceramics are closely related to their microstructure. By employing texturing processes to allow grain growth to exhibit a certain degree of directional selectivity, the piezoelectric properties can be significantly enhanced. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a BiFeO3-BaTiO3-(Bi) material with high-temperature thermal stability and high-voltage electrical properties. 0.5 K 0.5 A method for preparing TiO3 (BF-BT-BKT) lead-free piezoelectric ceramics is presented. This method enhances the piezoelectric activity of the system by influencing grain growth direction through temperature gradient construction and inducing domain structure orientation using an external electric field. This method eliminates the need for high-temperature quenching and, compared to existing technologies, produces ceramics with higher piezoelectric performance and greater thermal stability.

[0007] To improve piezoelectric properties and thermal stability while maintaining a high Curie temperature, this invention selects BF-BT, which has a high Curie temperature and a perovskite structure, as the matrix material. Near the MPB composition point, it utilizes (Bi) with a high Curie temperature and a tetragonal phase structure. 0.5 K 0.5 TiO3 (BKT) was used to modulate the phase structure of BF-BT to construct a BF-BT-BKT lead-free piezoelectric ceramic with a trigonal-tetragonal MPB structure near the tetragonal phase structure and close to the tetragonal phase structure.

[0008] To obtain textured ceramics, this invention employs two techniques to influence grain growth and domain structure orientation:

[0009] (1) During the sintering process, sintering aids are added and sintering is carried out using a temperature gradient. During the sintering process, the low-temperature liquid phase generated by the low-temperature sintering aids can effectively promote grain boundary movement, causing ceramic grains to grow along the temperature gradient direction;

[0010] (2) Apply a DC electric field along the direction of the temperature gradient to influence the distribution of the domain structure of the grains using an external electric field, see Appendix. Figure 1 .

[0011] This invention achieves the goal of simultaneously improving thermal stability and piezoelectric properties by influencing and inducing grain growth and domain structure distribution through phase structure control, temperature gradient field sintering, and external electric field, thereby obtaining the Curie temperature T. c > 480℃, in-situ depolarization temperature T dr Piezoelectric properties at temperatures >350℃ 33>460pC / N, high-performance lead-free piezoelectric ceramics usable at temperatures above 300°C, see attached image. Figure 2 .

[0012] The technical solution to achieve the objective of this invention is:

[0013] A lead-free piezoelectric ceramic, BF-BT-BKT, exhibiting high-temperature thermal stability and high-voltage electrical properties, has the general formula (1-x)BiFeO3-xBaTiO3-y(Bi 0.5 K 0.5 TiO3+mLi2CO3+nMnO2, where x, y, m and n represent the mole fractions of the components, and 0.25≤x≤0.35, 0 <y <0.05, 0 <m <0.01, 0 <n≤0.01.

[0014] The preparation method of the BF-BT-BKT lead-free piezoelectric ceramic with high-temperature thermal stability and high-voltage electrical properties includes the following steps:

[0015] 1) Using analytically pure Bi₂O₃, Fe₂O₃, BaCO₃, TiO₂, K₂CO₃, Li₂CO₃, and MnO₂ as raw materials, according to (1-x)Bi 1.02 FeO3-xBaTiO3-y(Bi 0.5 K 0.5 The materials are prepared in the ratio of TiO3 + mLi2CO3 + nMnO2, with Bi element in excess at 2.0% mol to compensate for the volatilization of Bi element during sintering. Here, x, y, m, and n represent the mole fraction of the components, and 0.25 ≤ x ≤ 0.35, 0 < y < 0.05, 0 < m < 0.01, and 0 < n ≤ 0.01.

[0016] 2) After ball milling the above mixed powder with anhydrous ethanol for 24 hours, take it out, dry it in a drying oven at 100°C, pass it through a 200-mesh sieve, then put the powder into a high-alumina crucible, compact it, cover it, put it in a muffle furnace and heat it rapidly to 780°C at a heating rate of 300°C / h for pre-calcination, hold it at the temperature for 4 hours, then turn off the power, cool it with the furnace, and take it out for use.

[0017] 3) Take out the pre-calcined powder, ball mill it again for 12 hours, then take it out, dry it, sieve it, add 5% PVA solution to granulate it, and compress it into tablets under 25MPa pressure in a tablet press to obtain cylindrical tablets with a diameter of 11.0mm and a height of 20.0mm.

[0018] 4) Place the formed raw sheet into a tube furnace. The cylindrical raw sheet is placed horizontally, with its two ends in two temperature zones set at sintering temperatures T1 and T2, respectively, where 850℃≤T1≤900℃ and 960℃≤T2≤1010℃. Two electrode plates are set at both ends of the tube furnace and connected to the positive and negative terminals of a DC power supply, respectively. The temperature is slowly increased to 600℃ at a rate of 60℃ / h and held for 4 hours to remove the binder. Then, the temperature of the two temperature zones is rapidly increased to T1 and T2 at a rate of 5℃ / min. At the same time, a DC voltage U is applied to the electrode plates at both ends of the tube furnace, where 12V≤U≤36V, to form a stable DC electric field in the tube furnace. The electric field is kept constant, and the sample is sintered at this temperature for 240 minutes. After that, the power is turned off, and the external electric field remains unchanged. The sample is then cooled to room temperature with the furnace.

[0019] 5) Cut the sintered ceramic sheet horizontally along the direction perpendicular to the length of the cylinder. The cut sample is coin-shaped, with a thickness of 1.0 mm and a diameter of 10.0 mm. Grind and polish the surface of the cut sample, coat both ends with silver paste, and fire at 550℃ for 15 min.

[0020] 6) Polarize the silver-fired ceramic sheet in silicone oil with a polarization electric field of 6000V / mm, a polarization temperature of 120℃, and a time of 15min. Maintain the polarization electric field and remove the sheet after cooling to room temperature.

[0021] Performance was measured after the sample was left to stand in air at room temperature for 24 hours.

[0022] The positive effects of this invention are:

[0023] 1. By using BKT to regulate the phase structure of BF-BT, the phase structure of BF-BT near the tetragonal phase in the MPB area is obtained, thereby improving the thermal stability of the ceramic by increasing the tetragonal distortion of the ceramic structure.

[0024] 2. By utilizing temperature gradient field construction and adding low-temperature sintering aids, the grain growth of BF-BT-BKT ceramics is controlled to obtain BF-BT-BKT piezoelectric ceramics with textured structure that grow along the temperature gradient direction.

[0025] 3. During the high-temperature sintering process, the distribution of ceramic domain structure at high temperature is influenced by an external electric field to obtain higher piezoelectric properties.

[0026] Through the combination of the above technologies, the BF-BT-BKT ceramic prepared using the technology of this invention possesses a textured microstructure and exhibits excellent thermal stability and piezoelectric properties at high temperatures. In-situ depolarization testing shows that the ceramic prepared using the process and formulation described in this invention, under operating conditions at T=350℃, has d 33With a high voltage performance of 460 pC / N, the above real-time high voltage performance indicates that it can be used in high-temperature conditions above 300°C. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the temperature gradient field and external electric field structure distribution during ceramic sintering in this invention;

[0028] Figure 2 The Td of the BF-BT-BKT lead-free piezoelectric ceramic sample of this invention 33 In-situ depolarization curve.

[0029] In the figure, 1-1. First furnace baffle; 1-2. Second furnace baffle; 1-3. Firing platform; 2-1. Negative electrode of electrode plate; 2-2. Positive electrode of electrode plate; 2-3. DC power supply; 2-4. Switch; 3-1. First temperature zone; 3-2. Second temperature zone; 4. Sample; 5. Partition layer. Detailed Implementation

[0030] The present invention will be further illustrated below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, the tube furnace used in step (4) of the embodiment is a two-temperature zone tube furnace, including a first furnace baffle 1-1 and a second furnace baffle 1-2 set at both ends of the furnace body; a firing platform 1-3 is provided in the middle of the furnace body, and the sample 4 is placed in the hollow part of the partition layer 5. The sample 4 and the partition layer 5 are placed on the firing platform 1-3, and the partition layer 5 divides the interior of the tube furnace into two temperature zones, namely the first temperature zone 3-1 and the second temperature zone 3-2. The two ends of the sample 4 are respectively in the first temperature zone 3-1 and the second temperature zone 3-2.

[0032] The first temperature zone 3-1 is equipped with a negative electrode 2-1, and the second temperature zone 3-2 is equipped with a positive electrode 2-2. The negative electrode 2-1 is electrically connected to the negative terminal of the DC power supply 2-3, and the positive electrode 2-2 is electrically connected to the positive terminal of the DC power supply 2-3. A power switch 2-4 is provided in the connecting wire.

[0033] The partition layer 5 is a circular cylindrical body, and the sample 4 is placed in the hollow part of the circular cylindrical body. The partition layer 5 serves to isolate the two temperature zones and maintain the temperature gradient (temperature difference) at both ends of the sample.

[0034] Example 1:

[0035] A lead-free piezoelectric ceramic, BF-BT-BKT, with high-temperature thermal stability and high-voltage electrical properties, has the chemical formula: 0.70BiFeO3-0.30BaTiO3+0.015BKT+0.006Li2CO3+0.005MnO2.

[0036] The preparation method includes the following steps:

[0037] (1) Using analytical grade Bi2O3, Fe2O3, BaCO3, TiO2, K2CO3, Li2CO3 and MnO2 as raw materials, according to 0.70Bi 1.02 The ingredients were prepared using the formula FeO3-0.30BaTiO3+0.015BKT+0.006Li2CO3+0.005MnO2, with Bi element in excess at 2.0%mol to compensate for the volatilization of Bi element during sintering.

[0038] (2) The above mixed powder was ball-milled with anhydrous ethanol for 24 hours, then dried in a drying oven at 100°C and passed through a 200-mesh sieve. The powder was then placed in a high-alumina crucible, compacted, covered, and placed in a muffle furnace and rapidly heated to 780°C at a heating rate of 300°C / h. o C is pre-fired, kept at a temperature for 4 hours, then the power is turned off, and the furnace is cooled down before being taken out for use.

[0039] (3) Take out the pre-calcined powder, ball mill it for 12 hours, dry it, sieve it, add 5% PVA solution to granulate it, and feed it into a tablet press under 25MPa pressure to form a cylindrical tablet with a diameter of 10.0mm and a height of about 20.0-25.0mm.

[0040] (4) such as Figure 1 As shown, the formed raw sheet sample 4 was placed in a tube furnace. The cylindrical raw sheet was placed horizontally, with its two ends in two temperature zones with sintering temperatures set to T1 and T2, respectively. The temperature was slowly increased to 600℃ at a heating rate of 60℃ / h, and the binder was removed after holding at that temperature for 4h. Then, the two temperature zones were rapidly heated to T1=900℃ and T2=990℃ at a heating rate of 5℃ / min. The negative electrode 2-1 and positive electrode 2-2 of the electrode plates at both ends of the tube furnace were then connected to a DC power supply 2-3. The voltage was increased to 24V and kept constant. After holding at that temperature for 240min, the power was turned off, and the external electric field remained unchanged. The sample was cooled to room temperature with the furnace.

[0041] (5) Cut the sintered ceramic sheet radially into coin-shaped round samples with a thickness of 1.0 mm and a diameter of 10.0 mm. After grinding and polishing the surface of the cut sample, apply silver paste to both ends and fire it at 550℃ for 15 min.

[0042] (6) Polarize the piezoelectric ceramic sheet after silver firing in silicone oil with a polarization electric field of 6000V / mm and a polarization temperature of 120℃. Hold the temperature and pressure for 15 minutes, keep the voltage constant, turn off the power and cool down. Take it out after the temperature drops to room temperature.

[0043] Performance was measured after the sample was left to stand in air at room temperature for 24 hours.

[0044] The performance measurement results are as follows:

[0045]

[0046] Example 2:

[0047] A lead-free piezoelectric ceramic, BF-BT-BKT, with high-temperature thermal stability and high-voltage electrical properties, has the chemical formula: 0.72BiFeO3-0.28BaTiO3+0.025BKT+0.006Li2CO3+0.005MnO2.

[0048] The preparation method and steps are the same as in Example 1.

[0049] The difference is:

[0050] In step (1), the ingredients are prepared according to the formula 0.72BiFeO3-0.28BaTiO3+0.025BKT+0.006Li2CO3+0.005MnO2;

[0051] In step (4), T1 = 880 o C, T2 = 970 o C.

[0052] The performance measurement results are as follows:

[0053]

[0054] Example 3:

[0055] A lead-free piezoelectric ceramic, BF-BT-BKT, with high-temperature thermal stability and high-voltage electrical properties, has the chemical formula: 0.70BiFeO3-0.30BaTiO3+0.010BKT+0.006Li2CO3+0.005MnO2.

[0056] The preparation method and steps are the same as in Example 1, except that:

[0057] In step (1), the ingredients are prepared according to the formula 0.70BiFeO3-0.30BaTiO3+0.010BKT+0.006Li2CO3+0.005MnO2;

[0058] In step (4), T1 = 890 oC, T2 = 980 o C.

[0059] The performance measurement results are as follows:

[0060]

[0061] Example 4:

[0062] A lead-free piezoelectric ceramic, BF-BT-BKT, with high-temperature thermal stability and high-voltage electrical properties, has the chemical formula: 0.68BiFeO3-0.32BaTiO3+0.010BKT+0.010Li2CO3+0.005MnO2.

[0063] The preparation method and steps are the same as in Example 1, except that:

[0064] In step (1), the ingredients are prepared according to the formula 0.68BiFeO3-0.32BaTiO3+0.010BKT+0.010Li2CO3+0.005MnO2;

[0065] In step (4), T1 = 910 o C, T2 = 1000 o C.

[0066] The performance measurement results are as follows:

[0067]

[0068] Example 5:

[0069] A lead-free piezoelectric ceramic, BF-BT-BKT, with high-temperature thermal stability and high-voltage electrical properties, has the chemical formula: 0.75BiFeO3-0.25BaTiO3+0.025BKT+0.005Li2CO3+0.005MnO2.

[0070] The preparation method and steps are the same as in Example 1, except that:

[0071] In step (1), the ingredients are prepared according to the formula 0.75BiFeO3-0.25BaTiO3+0.025BKT+0.005Li2CO3+0.005MnO2;

[0072] In step (4), T1 = 850 o C, T2 = 960 o C.

[0073] The performance measurement results are as follows:

[0074]

[0075] The upper and lower limits and ranges of the components listed in this invention, as well as the upper and lower limits and ranges of the process parameters, can all realize this invention, and will not be listed one by one here.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing BF-BT-BKT lead-free piezoelectric ceramics with high-temperature thermal stability and high-voltage electrical properties, characterized in that, The preparation method includes steps such as temperature gradient sintering to control the grain growth direction and external electric field influencing the domain structure; The preparation method includes the following steps: 1) Using analytically pure Bi₂O₃, Fe₂O₃, BaCO₃, TiO₂, K₂CO₃, Li₂CO₃, and MnO₂ as raw materials, according to (1-x)Bi 1.02 FeO3-xBaTiO3-y(Bi 0.5 K 0.5 The materials are prepared in the ratio of TiO3 + mLi2CO3 + nMnO2, with Bi element in excess at 2.0% mol to compensate for the volatilization of Bi element during sintering. Here, x, y, m, and n represent the mole fraction of the components, and 0.25 ≤ x ≤ 0.35, 0 < y < 0.05, 0 < m < 0.01, and 0 < n ≤ 0.

01. 2) After ball milling the above raw materials with anhydrous ethanol for 24 hours, take them out, dry them in a drying oven at 100°C, pass them through a 200-mesh sieve, then put the powder into a high-alumina crucible, compact it, cover it, put it into a muffle furnace and heat it rapidly to 780°C at a heating rate of 300°C / h for pre-calcination, keep it at the temperature for 4 hours, then turn off the power, cool it with the furnace and take it out for later use. 3) Take out the pre-calcined powder, ball mill it again for 12 hours, then take it out, dry it, sieve it, add 5% PVA solution to granulate it, and compress it into tablets under 25MPa pressure in a tablet press to obtain cylindrical tablets with a diameter of 11.0mm and a height of 20.0mm. 4) Place the formed raw sheet into a tube furnace. The cylindrical raw sheet is placed horizontally, with its two ends in two temperature zones set at sintering temperatures T1 and T2, respectively, where 850℃≤T1≤900℃ and 960℃≤T2≤1010℃. Two electrode plates are set at both ends of the tube furnace and connected to the positive and negative terminals of a DC power supply, respectively. The temperature is slowly increased to 600℃ at a rate of 60℃ / h and held for 4 hours to remove the binder. Then, the temperature of the two temperature zones is rapidly increased to T1 and T2 at a rate of 5℃ / min. At the same time, a DC voltage U is applied to the electrode plates at both ends of the tube furnace, where 12V≤U≤36V, to form a stable DC electric field in the tube furnace. The electric field is kept constant, and the sample is sintered at this temperature for 240 minutes. After that, the power is turned off, and the external electric field remains unchanged. The sample is then cooled to room temperature with the furnace. 5) Cut the sintered ceramic sheet horizontally along the direction perpendicular to the length of the cylinder. The cut sample is coin-shaped with a thickness of 1.0 mm and a diameter of 10.0 mm. Grind and polish the surface of the cut sample, plate silver paste on both ends, and fire at 550℃ for 15 min. 6) Polarize the silver-fired ceramic sheet in silicone oil with a polarization electric field of 6000V / mm, a polarization temperature of 120℃, and a time of 15min. Maintain the polarization electric field and remove the sheet after cooling to room temperature.

2. A method for preparing BF-BT-BKT lead-free piezoelectric ceramics with high-temperature thermal stability and high-voltage electrical properties, characterized in that, Includes the following steps: (1) Using analytical grade Bi2O3, Fe2O3, BaCO3, TiO2, K2CO3, Li2CO3 and MnO2 as raw materials, according to 0.70Bi 1.02 The ingredients were prepared using the formula FeO3-0.30BaTiO3+0.015BKT+0.006Li2CO3+0.005MnO2, with Bi element in excess at 2.0%mol to compensate for the volatilization of Bi element during sintering. (2) After ball milling the above raw materials with anhydrous ethanol for 24 hours, remove them, dry them in a drying oven at 100°C, and pass them through a 200-mesh sieve. Then, put the powder into a high-alumina crucible, compact it, cover it, and put it into a muffle furnace to rapidly heat it to 780°C at a heating rate of 300°C / h. o C is pre-fired, kept at a temperature for 4 hours, then the power is turned off, and the furnace is cooled down before being taken out for use. (3) Take out the pre-calcined powder, ball mill it for 12 hours, dry it, sieve it, add 5% PVA solution to granulate it, and feed it into a tablet press under 25MPa pressure to form a cylindrical tablet with a diameter of 10.0mm and a height of 20.0-25.0mm. (4) Place the formed raw sheet into the tube furnace. The cylindrical raw sheet is placed horizontally, and the two ends of the cylindrical raw sheet are respectively in two temperature zones with set sintering temperatures of T1 and T2. The temperature was slowly increased to 600℃ at a rate of 60℃ / h, and the sample was held at that temperature for 4 hours before the glue was removed. Then, the two temperature zones were rapidly increased to T1=900℃ and T2=990℃ at a rate of 5℃ / min. The electrode plates at both ends of the tube furnace were then connected to a DC power supply, and the voltage was increased to 24V and kept constant. The temperature was held for 240 minutes before the power was turned off. The external electric field remained constant, and the sample was cooled to room temperature with the furnace. (5) Cut the sintered ceramic sheet radially into coin-shaped round samples with a thickness of 1.0 mm and a diameter of 10.0 mm. After grinding and polishing the surface of the cut sample, apply silver paste to both ends and fire it at 550℃ for 15 min. (6) Polarize the piezoelectric ceramic sheet after silver firing in silicone oil with a polarization electric field of 6000V / mm and a polarization temperature of 120℃. Hold the temperature and pressure for 15 minutes, keep the voltage constant, turn off the power and cool down. Take it out after the temperature drops to room temperature.

3. The ceramic prepared by the method of claim 1, which describes the BF-BT-BKT lead-free piezoelectric ceramic with high-temperature thermal stability and high-voltage electrical properties, has the following general formula: (1-x)BiFeO3-xBaTiO3-y(Bi 0.5 K 0.5 TiO3+mLi2CO3+nMnO2, where x, y, m and n represent the mole fractions of the components, and 0.25≤x≤0.35, 0 <y <0.05, 0 <m <0.01, 0 <n≤0.

01.

4. The ceramic prepared by the method of claim 2, which describes the BF-BT-BKT lead-free piezoelectric ceramic with high temperature thermal stability and high voltage electrical properties, has the following chemical formula: 0.70BiFeO3-0.30BaTiO3+0.015BKT+0.006Li2CO3+0.005MnO2.

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