A high depolarization temperature lead-free pyroelectric ceramic, its preparation method and application

Abstract

This invention belongs to the technical field of pyroelectric infrared detection, and discloses a high depolarization temperature lead-free pyroelectric ceramic, its preparation method, and its application. The lead-free pyroelectric ceramic composition includes 0.8 (Bi) 0.5 Na 0.5 TiO3-0.2BaTiO3-XMn, 0.0<X<0.8%, through the tetragonal phase 0.8(Bi 0.5 Na 0.5 Introducing Mn into the TiO3-0.2BaTiO3 matrix can ensure high depolarization temperature for lead-free pyroelectricity while exhibiting excellent pyroelectric performance. In ceramic preparation, the ceramic slurry is first cast into a high-quality thin film using a tape casting process. The film is then cut into multiple sheets and stacked. Finally, the stacked films are hot-pressed to obtain a thick-film preform. Compared to traditional solid-state methods for preparing thick ceramic blocks, this invention eliminates the need for cutting and thinning, significantly improving the utilization rate of sensitive element ceramics.

Description

Technical Field

[0001] This invention belongs to the technical field of pyroelectric infrared detection, and more specifically, relates to a high depolarization temperature lead-free pyroelectric ceramic, its preparation method and application. Background Technology

[0002] Sodium bismuth titanate-based lead-free ceramics are considered the most promising lead-free pyroelectric materials due to their excellent pyroelectric properties. Pyroelectric infrared sensors require high-temperature processing during fabrication, but currently, conventional sodium bismuth titanate-based lead-free materials have relatively low depolarization temperatures. The high-temperature baking process during the production of pyroelectric sensors can cause material performance failure.

[0003] Existing research on sodium bismuth titanate-based lead-free pyroelectric materials generally suffers from a problem: the materials cannot simultaneously achieve a high pyroelectric coefficient and a high depolarization temperature. To increase the depolarization temperature of sodium bismuth titanate-based lead-free pyroelectric materials to adapt to high-temperature processes, it is usually necessary to sacrifice the pyroelectric coefficient. The pyroelectric coefficient is a very critical parameter for detectors; the higher the pyroelectric coefficient, the more sensitive the detection. In order to ensure the sensitivity of the detector, the pyroelectric coefficient cannot be excessively sacrificed.

[0004] Therefore, developing lead-free pyroelectric materials with high depolarization temperatures that are compatible with manufacturing processes and maintain good pyroelectric coefficients is urgent and of great value in engineering applications. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a high depolarization temperature lead-free pyroelectric ceramic, its preparation method and application, the purpose of which is to improve the polarization temperature of the lead-free pyroelectric ceramic while giving it a better pyroelectric coefficient.

[0006] To achieve the above objectives, the present invention provides a high depolarization temperature lead-free pyroelectric ceramic, the composition of which includes 0.8 (Bi) 0.5 Na 0.5 )TiO3-0.2BaTiO3-XMn, 0.0<X<0.8%.

[0007] Preferably, 0.4 ≤ X ≤ 0.6%.

[0008] This invention also provides a method for preparing a high depolarization temperature lead-free pyroelectric ceramic, comprising: Step S1: Prepare raw materials according to the stoichiometric ratio of ceramics and process them to obtain micron-sized ceramic powder; Step S2: Mix the ceramic powder with a solvent and add a plasticizer to obtain a ceramic slurry; Step S3: First, the ceramic slurry is cast into a thin film using a casting process. Then, the thin film is cut into multiple pieces and stacked. Finally, the stacked thin film is hot-pressed to obtain a thick film preform. Step S4: After the thick film preform is subjected to aging, isostatic pressing, plastic removal and sintering in sequence, lead-free pyroelectric ceramic is obtained.

[0009] Preferably, the solvent includes a mixture of ethanol and toluene, trioleic acid glyceride, and polyethylene glycol, and the plasticizer includes a PVB solution and butyl benzyl phthalate. In step S2, mixing the ceramic powder with a solvent and adding a plasticizer includes: Step S21: The ceramic powder is successively mixed with a mixture of ethanol and toluene, trioleic acid glyceride, and polyethylene glycol to obtain a preliminary ceramic slurry; wherein, the ethanol in the mixture of ethanol and toluene accounts for 40wt%~60wt% of the mass fraction of the mixed solution; the mass ratio of the ceramic powder, the mixture of ethanol and toluene, the trioleic acid glyceride, and the polyethylene glycol is 1:(0.55~0.65):(0.008~0.012):(0.005~0.007). Step S22: PVB solution and butyl benzyl phthalate are added to the preliminary ceramic slurry and mixed to obtain a ceramic slurry with a viscosity range of 300 cps to 400 cps.

[0010] Preferably, in step S3: The thickness of the film cast by the casting process is 25 μm to 50 μm; The stacking height of the films is 4 to 6 films; The pressure for hot pressing the stacked films is 0.8MPa ~ 1.2MPa, the temperature is 70°C ~ 80°C, and the hot pressing time is 5 ~ 7 minutes.

[0011] Preferably, in step S4, The process of removing plastic includes: The isostatically pressed thick film preform is laid flat on a flat surface. First, the temperature is increased from room temperature to 580°C to 620°C at a heating rate of 0.3°C / min to 0.5°C / min and held for 1.5h to 2.5h. Then, the temperature is reduced to room temperature at a cooling rate of 0.4°C / min to 0.5°C / min. The sintering process includes: A flat ceramic sheet of the same composition as the ceramic to be prepared is pressed onto a thick film preform after plastic removal. The thick film preform is laid flat on the flat surface, and the weight ratio of the thick film preform to the ceramic sheet is 1:(1.5~1.8). The thick film preform is sintered. The sintering process includes: raising the temperature from room temperature to 1140°C to 1150°C at a heating rate of 0.4°C / min to 0.5°C / min and holding it at that temperature for 1.5h to 2.5h, and then cooling it down to room temperature at a cooling rate of 0.4°C / min to 0.5°C / min.

[0012] Preferably, in step S4, The aging temperature is 25°C~30°C, the humidity is 50%RH~60%RH, and the aging time is 12h~24h; The isostatic pressing is performed at room temperature, with a pressure of 80MPa~120MPa and a holding time of 120s~300s.

[0013] Preferably, after sintering the thick film preform, the process further includes: Electrodes were deposited on the sintered ceramic thick film using a vapor deposition process, and then polarized under an electric field of 4kV / mm~6kV / mm for 10min~20min to excite pyroelectric properties.

[0014] Preferably, in step S1, the process of preparing raw materials according to the stoichiometric ratio of ceramics and processing them to obtain micron-sized ceramic powder includes: Step S11: Configure Bi source, Na source, Ti source, Ba source and Mn source according to the stoichiometric ratio of ceramic; Step S12: The prepared raw materials are ball-milled and dried to obtain powder. The powder is pre-sintered at a temperature of 950°C to 1020°C for 2 to 3 hours. After ball milling and drying again, micron-sized ceramic powder is obtained.

[0015] The present invention also provides a pyroelectric infrared sensor comprising a high depolarization temperature lead-free pyroelectric ceramic as described above.

[0016] In summary, compared with the prior art, the technical solutions conceived in this invention have the following main advantages: 1. The high depolarization temperature lead-free pyroelectric ceramic proposed in this invention uses a tetragonal phase 0.8(Bi) 0.5 Na 0.5 The TiO3-0.2BaTiO3 matrix enables lead-free pyroelectric ceramics to possess a depolarization temperature above 200℃, thus enabling them to adapt to the high-temperature processes in detector fabrication and ensuring device performance. Furthermore, the use of a tetragonal phase with 0.8(Bi) 0.5 Na 0.5Introducing Mn into the TiO3-0.2BaTiO3 matrix can improve the polarization characteristics and enhance the ferroelectricity of the material while ensuring a high depolarization temperature for lead-free pyroelectricity. After Mn ions occupy the B sites of the perovskite structure, defect dipoles are formed inside the material, which inhibit the movement of ferroelectric domains, enabling the lead-free material to exhibit excellent pyroelectric performance and outstanding temperature stability.

[0017] 2. The method for preparing high depolarization temperature lead-free pyroelectric ceramics proposed in this invention first uses a casting process to cast the ceramic slurry into a thin film of good quality, then cuts the film into multiple pieces and stacks them, and then hot-presses the stacked film to obtain a thick film preform. Compared with the traditional technology of preparing a thick ceramic block using a solid-state method, and then preparing the thick film for the detector by cutting, thinning, scribing, and cleaning the ceramic block, which wastes materials, the preparation of this invention can be carried out without cutting and thinning, which greatly improves the utilization rate of the sensitive element ceramic.

[0018] 3. Preferably, when desizing the thick film preform, controlling the heating and cooling rates can ensure efficient desizing of the thick film preform and minimize the damage to the material caused by temperature fluctuations during the desizing process, such as thick film cracking and incomplete desizing.

[0019] 4. Preferably, when sintering the thick film preform, controlling the weight of the ceramic sheet can prevent the thick film from bending and cracking during sintering. If the ceramic sheet is too light, the thick film preform is prone to uneven shrinkage during sintering, resulting in uneven bending. If it is too heavy, the shrinkage of the thick film preform is hindered during sintering, which can easily lead to cracking. By controlling the heating and cooling rates during sintering, the thick film preform can be ensured to shrink slowly and stably during the ceramic forming process, resulting in high-performance, high-flatness ceramics. Attached Figure Description

[0020] Figure 1 This is a flowchart of the steps in a method for preparing lead-free pyroelectric ceramics according to an embodiment of the present invention; Figure 2 This is a graph showing the change in dielectric constant of lead-free pyroelectric ceramics with temperature. Figure 3 This is a graph showing the change of the pyroelectric coefficient of lead-free pyroelectric ceramics with temperature. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] This invention provides a high depolarization temperature lead-free pyroelectric ceramic, the composition of which includes 0.8 (Bi) 0.5 Na 0.5 TiO3-0.2BaTiO3-XMn, 0.0 < X ​​< 0.8%. Among them, the tetragonal phase has 0.8% (Bi). 0.5 Na 0.5 The TiO3-0.2BaTiO3 matrix possesses a depolarization temperature above 200℃, which is suitable for the high-temperature processes in detector fabrication. However, this comes at the cost of a lower pyroelectric coefficient. Analysis revealed that by using a 0.8(Bi)-based tetragonal matrix... 0.5 Na 0.5 Introducing Mn into the TiO3-0.2BaTiO3 matrix can improve the polarization characteristics and enhance the ferroelectricity of the material while ensuring a high depolarization temperature for lead-free pyroelectricity. After Mn ions occupy the B sites of the perovskite structure, defect dipoles are formed inside the material, which inhibit the movement of ferroelectric domains, enabling the lead-free material to exhibit excellent pyroelectric performance and outstanding temperature stability.

[0023] The following examples use several sets of experimental data to illustrate this.

[0024] Example 1 X=0.2%, the composition of lead-free pyroelectric ceramic is: 0.8(Bi 0.5 Na 0.5 TiO3-0.2BaTiO3-0.2%Mn; Its depolarization temperature is 258℃, and its pyroelectric coefficient is 1.41×10⁻⁶. -4 Cm -2 K -1 .

[0025] Example 2 X=0.4%, the composition of lead-free pyroelectric ceramic is: 0.8(Bi 0.5 Na 0.5 TiO3-0.2BaTiO3-0.4%Mn; Its depolarization temperature is 260℃, and its pyroelectric coefficient is 2.11×10⁻⁶. -4 Cm -2 K -1 .

[0026] Example 3 X=0.6%, the composition of lead-free pyroelectric ceramic is: 0.8(Bi 0.5 Na 0.5TiO3-0.2BaTiO3-0.6%Mn; Its depolarization temperature is 265℃, and its pyroelectric coefficient is 2.28×10⁻⁶. -4 Cm -2 K -1 .

[0027] Comparative Example 1 X=0.0, the composition of lead-free pyroelectric ceramic is: 0.8(Bi 0.5 Na 0.5 TiO3-0.2BaTiO3; Its depolarization temperature is 250℃, and its pyroelectric coefficient is 1.12×10⁻⁶. -4 Cm -2 K -1 .

[0028] Comparative Example 2 X=0.8%, the composition of lead-free pyroelectric ceramic is: 0.8(Bi 0.5 Na 0.5 TiO3-0.2BaTiO3-0.8%Mn; Its depolarization temperature is 252℃, and its pyroelectric coefficient is 1.27×10⁻⁶. -4 Cm -2 K -1 .

[0029] The table below shows a comparison of the experimental data for the above examples.

[0030]

[0031] like Figure 2 The graph shows the change of dielectric constant of lead-free pyroelectric ceramics with temperature, from which the depolarization temperature of different lead-free pyroelectric ceramics can be seen.

[0032] like Figure 3 The graph shows the change of the pyroelectric coefficient of lead-free pyroelectric ceramic with temperature. As a detector, we only focus on the pyroelectric coefficient at room temperature.

[0033] The data above shows that without Mn doping, 0.8 (Bi) 0.5 Na 0.5 The depolarization temperature of TiO3-0.2BaTiO3 can reach 250℃, but its pyroelectric coefficient is low, only 1.12×10⁻⁶. -4 Cm -2 K -1 In the tetragonal phase of 0.8 (Bi) 0.5 Na 0.5Introducing Mn into the TiO3-0.2BaTiO3 matrix increases both its depolarization temperature and pyroelectric coefficient to some extent. However, when the Mn content (X) reaches ≥0.8%, the improvement is not significant. Furthermore, when X is between 0.4% and 0.6%, the depolarization temperature reaches 260℃ and the pyroelectric coefficient increases very significantly. Therefore, preferably, 0.4 ≤ X ≤ 0.6%.

[0034] Pyroelectric ceramics prepared by traditional solid-state methods require mechanical processing before they can be used as pyroelectric sensing elements in devices. During processing, the ceramic block undergoes cutting, thinning, dicing, and cleaning, resulting in a material utilization rate of less than 30% and significant losses. This invention utilizes a casting process to prepare thick films (90-120 μm) of ceramic. Without requiring cutting or thinning, the thickness is well-suited for device applications, greatly improving the utilization rate of the sensing element ceramic.

[0035] like Figure 1 The diagram shows a flowchart of the preparation method of lead-free pyroelectric ceramics in one embodiment of the present invention, which mainly includes steps S1 to S4. Each step is described below.

[0036] Step S1: Prepare raw materials according to the stoichiometric ratio of ceramics and process them to obtain micron-sized ceramic powder.

[0037] The specific steps are as follows.

[0038] Step S11: Configure Bi source, Na source, Ti source, Ba source and Mn source according to the stoichiometric ratio of ceramic.

[0039] According to the ceramic composition 0.8 (Bi 0.5 Na 0.5 The stoichiometric ratio of TiO3-0.2BaTiO3-XMn involves drying Bi, Na, Ti, Ba, and Mn sources with a purity higher than 99.5% at 150-200°C for 1-2 hours, followed by weighing. In one embodiment, the Bi source can be Bi2O3, the Na source can be NaHCO3, the Ti source can be TiO2, the Ba source can be BaCO3, and the Mn source can be MnCO3. All raw materials have a purity higher than 99.5%. All raw materials are baked at 150-200°C for at least 1 hour before weighing to prevent moisture absorption.

[0040] Step S12: The prepared raw materials are ball-milled and dried to obtain powder. The powder is pre-sintered at a temperature of 950°C to 1020°C for 2 to 3 hours. After ball milling and drying again, micron-sized ceramic powder is obtained.

[0041] Specifically, the weighed raw material powder is ball-milled and dried, then sieved and packed into a crucible for compaction. The crucible is then left open for pre-sintering. After pre-sintering at 950°C~1020°C for 2~3 hours, the powder is ball-milled and dried to obtain micron-sized target ceramic powder.

[0042] Step S2: Mix ceramic powder with solvent and add plasticizer to obtain ceramic slurry.

[0043] Mixing with a solvent and adding a plasticizer to adjust the viscosity are necessary steps in preparing the casting paste. In this embodiment, the solvents used include a mixture of ethanol and toluene, trioleic acid glyceride, and polyethylene glycol, and the plasticizers used include PVB solution and butyl benzyl phthalate.

[0044] Step S2 can be performed as follows.

[0045] Step S21: The ceramic powder is mixed with a mixture of ethanol and toluene, trioleic acid glyceride and polyethylene glycol to obtain a preliminary ceramic slurry; wherein, the ethanol in the mixture of ethanol and toluene accounts for 40wt%~60wt% of the mass fraction of the mixed solution; the mass ratio of ceramic powder, ethanol and toluene mixture, trioleic acid glyceride and polyethylene glycol is 1:(0.55~0.65):(0.008~0.012):(0.005~0.007).

[0046] Specifically, ceramic powder is successively mixed with a mixture of ethanol and toluene, trioleic acid ester, and polyethylene glycol and ball-milled to obtain a preliminary ceramic slurry. The mass ratio of ceramic powder to the ethanol and toluene mixture (where ethanol accounts for 40wt%~60wt% of the mixture by mass) is 1:0.55~0.65, with a specific optional ratio of 1:0.6. The mass ratio of ceramic powder to trioleic acid ester is 1:(0.008~0.012), with a specific optional ratio of 1:0.01. The mass ratio of ceramic powder to polyethylene glycol is 1:(0.005~0.007), with a specific optional ratio of 1:0.006.

[0047] Step S22: PVB solution and butyl benzyl phthalate are added to the initial ceramic slurry and mixed to obtain a ceramic slurry with a viscosity range of 300 cps to 400 cps.

[0048] Specifically, to make the thick film plastic, an appropriate amount of PVB solution and butyl benzyl phthalate are added to the obtained preliminary ceramic slurry and then ball-milled to form a ceramic slurry, with the slurry viscosity controlled at 300 cps~400 cps. In one embodiment, the concentration of the PVB solution is 20wt%-25wt%, the amount of PVB solution added is controlled at 25wt%-30wt% of the ceramic powder mass, and the amount of butyl benzyl phthalate added is controlled at 0.6wt% of the ceramic powder mass.

[0049] Step S3: First, the ceramic slurry is cast into a thin film using a casting process. Then, the film is cut into multiple pieces and stacked. Finally, the stacked film is hot-pressed to obtain a thick film preform.

[0050] Casting can produce thin films with a thickness of tens of micrometers and good quality. However, if a thicker film layer is to be produced, it is difficult to guarantee the quality of the film layer by directly using the casting process. The ceramic sheets used in detectors are generally hundreds of micrometers thick. To ensure the quality of the thick film, a thick ceramic block is usually prepared by solid-state method. Then, the ceramic block is processed by cutting, thinning, dicing, and cleaning to prepare the thick film used in the detector. After cutting, thinning, dicing, and cleaning, the overall utilization rate of the material is often less than 30%, resulting in extremely high losses.

[0051] In this invention, ceramic slurry is first cast into a thin film of good quality using a casting process. The film is then cut into multiple pieces and stacked. The stacked film is then hot-pressed to obtain a thick film preform. In this way, the thickness can be well adapted to the device without cutting and thinning, which greatly improves the utilization rate of sensitive element ceramics.

[0052] In one specific embodiment, step S3 can be performed as follows.

[0053] Step S31: Cast a film with a thickness of 25μm to 50μm using a casting process, and then cut the cast film into square pieces with a side length of 30mm to 50mm.

[0054] Specifically, the operating environment temperature is maintained at 20°C to 30°C, and the humidity is maintained at 50%RH to 70%RH.

[0055] Step S32: Stack the cut square pieces in groups of 4 to 6.

[0056] Step S33: Hot-press the stacked film at a pressure of 0.8MPa ~ 1.2MPa (specifically 1 MPa), a temperature of 70°C ~ 80°C (specifically 75°C), and a hot-pressing time of 5 ~ 7 minutes.

[0057] Specifically, thick film preforms with a thickness of 110μm to 150μm can be obtained.

[0058] Preferably, all operations from casting to hot pressing should be completed within 15 minutes.

[0059] Step S4: After aging, isostatic pressing, plasticizing, and sintering the thick film preform, lead-free pyroelectric ceramic is obtained.

[0060] Aging, isostatic pressing, desizing, and sintering are all necessary processing steps for the film layer generated by the casting process.

[0061] Step S41: The thick film preform is aged sequentially.

[0062] Specifically, the aging temperature is 25°C~30°C, the humidity is 50%RH~60%RH, and the aging time is 12h~24h. Through the aging process, it is possible to ensure that the volatile additives are stably removed from the thick film, increase the solid content of the thick film, and obtain a high-quality uniform ceramic thick film.

[0063] Step S42: Perform isostatic pressing on the aged thick film preform.

[0064] Specifically, cold isostatic pressing can be used. The isostatic pressing temperature is room temperature, the pressure is 80MPa~120MPa, and the holding time is 120s~300s. Through isostatic pressing, tiny pores in the thick film can be expelled, making the thick film more robust and improving the density of the ceramic after sintering. Step S43: De-plasticize the isostatically pressed thick film preform.

[0065] Specifically, the isostatically pressed thick film preform is laid flat on a smooth surface. It is first heated from room temperature to 580°C to 620°C at a heating rate of 0.3°C / min to 0.5°C / min and held at that temperature for 1.5 to 2.5 hours. Then, it is cooled to room temperature at a cooling rate of 0.4°C / min to 0.5°C / min. Through debinding, organic additives in the thick film can be removed, yielding a pure ceramic component. By controlling the heating and cooling rates, efficient debinding of the thick film preform can be ensured, and the damage caused by temperature fluctuations during debinding, such as cracking of the thick film and incomplete debinding, can be minimized.

[0066] Step S44: Sinter the thick film preform after plastic removal.

[0067] Specifically, firstly, flat ceramic sheets of the same composition as the ceramic to be prepared are pressed onto the thick film preform after plastic removal. The thick film preform is laid flat on the flat surface, and the weight ratio of the thick film preform to the ceramic sheet is 1:(1.5~1.8). Then, the thick film preform is sintered. The sintering process includes: raising the temperature from room temperature to 1140°C~1150°C at a heating rate of 0.4°C / min~0.5°C / min and holding it at that temperature for 1.5h~2.5h, and then cooling it down to room temperature at a cooling rate of 0.4°C / min~0.5°C / min. Sintering allows thick-film preforms to be prepared into high-quality ceramic sheets. Controlling the weight of the ceramic sheets prevents the thick film from bending and cracking during sintering. If the ceramic sheets are too light, uneven shrinkage during sintering can lead to unevenness and bending. If they are too heavy, shrinkage is hindered, making cracking more likely. By controlling the heating and cooling rates, the thick-film preform can shrink slowly and steadily during ceramic formation, resulting in high-performance, high-flatness ceramics.

[0068] Specifically, a ceramic thick film of 90μm to 120μm can be obtained after sintering.

[0069] Furthermore, it also includes: Step S45: Deposit electrodes onto the sintered ceramic thick film using a vapor deposition process.

[0070] Specifically, after the lead-free ceramic thick film is deposited with electrodes on both sides, it is polarized under an electric field of 4-6kV / mm for 10-20 minutes to obtain a lead-free pyroelectric ceramic thick film with good pyroelectric performance and high depolarization temperature.

[0071] The above preparation method can produce high-quality lead-free pyroelectric ceramics with good depolarization temperature. Moreover, in this invention, the ceramic slurry is first cast into a thin film with good quality using a casting process. The film is then cut into multiple pieces and stacked. The stacked film is then hot-pressed to obtain a thick film preform. In this way, the thickness can be well adapted to the device without cutting and thinning, which greatly improves the utilization rate of the sensitive element ceramic.

[0072] This invention also provides a pyroelectric infrared sensor, comprising the high depolarization temperature lead-free pyroelectric ceramic described above, using a tetragonal 0.8(Bi) phase. 0.5 Na 0.5 The TiO3-0.2BaTiO3 matrix provides a depolarization temperature exceeding 200℃, enabling it to withstand high-temperature processes in device fabrication and ensuring device performance. Furthermore, the presence of a tetragonal 0.8(Bi) phase further enhances its performance. 0.5 Na 0.5Doping Mn into the TiO3-0.2BaTiO3 matrix can improve the pyroelectric coefficient to a certain extent, thereby ensuring the sensitivity of the device. Therefore, the pyroelectric infrared sensor provided by this invention has good overall performance.

[0073] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. It should be noted that the terms "in one embodiment," "for example," and "again" are intended to illustrate the present invention and are not intended to limit the present invention.

[0074] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high depolarization temperature lead-free pyroelectric ceramic, characterized in that, include: The high depolarization temperature lead-free pyroelectric ceramic has a composition including 0.8 (Bi) 0.5 Na 0.5 TiO3-0.2BaTiO3-XMn, 0.8(Bi 0.5 Na 0.5 TiO3-0.2BaTiO3 forms a tetragonal matrix with a content of 0.4% ≤ X ≤ 0.6%. After Mn ions occupy the B sites in the perovskite structure, defect dipoles are formed inside the material, which inhibit the movement of ferroelectric domains and optimize the pyroelectric properties and temperature stability of the lead-free material. Step S1: Prepare raw materials according to the stoichiometric ratio of ceramics and process them to obtain micron-sized ceramic powder; Step S2: Mix the ceramic powder with a solvent and add a plasticizer to obtain a ceramic slurry; Step S3: First, the ceramic slurry is cast into a thin film using a casting process. Then, the thin film is cut into multiple pieces and stacked. Finally, the stacked thin film is hot-pressed to obtain a thick film preform. Step S4: After the thick film preform is subjected to aging, isostatic pressing, plastic removal and sintering in sequence, lead-free pyroelectric ceramic is obtained; In step S2, mixing the ceramic powder with a solvent and adding a plasticizer includes: Step S21: The ceramic powder is successively mixed with a mixture of ethanol and toluene, trioleic acid glyceride, and polyethylene glycol to obtain a preliminary ceramic slurry; wherein, the ethanol in the mixture of ethanol and toluene accounts for 40wt%~60wt% of the mass fraction of the mixed solution; the mass ratio of the ceramic powder, the mixture of ethanol and toluene, the trioleic acid glyceride, and the polyethylene glycol is 1:(0.55~0.65):(0.008~0.012):(0.005~0.007). Step S22: PVB solution and butyl benzyl phthalate are added to the preliminary ceramic slurry and mixed to obtain a ceramic slurry with a viscosity range of 300 cps to 400 cps. The solvent includes a mixture of ethanol and toluene, trioleic acid glyceride, and polyethylene glycol; the plasticizer includes a PVB solution and butyl benzyl phthalate. In step S3: The thickness of the film cast by the casting process is 25 μm to 50 μm; The stacking height of the films is 4 to 6 films; The pressure for hot pressing the stacked films is 0.8 MPa ~ 1.2 MPa, the temperature is 70 °C ~ 80 °C, and the hot pressing time is 5 ~ 7 min; In step S4, The aging temperature is 25 °C~30 °C, the humidity is 50%RH~60%RH, and the aging time is 12 h~24 h; The isostatic pressing was performed at room temperature, with a pressure of 80 MPa to 120 MPa and a holding time of 120 s to 300 s. The process of removing plastic includes: laying the isostatically pressed thick film preform flat on a flat surface, first raising the temperature from room temperature to 580 °C to 620 °C at a heating rate of 0.3 °C / min to 0.5 °C / min and holding it at that temperature for 1.5 h to 2.5 h, and then lowering it to room temperature at a cooling rate of 0.4 °C / min to 0.5 °C / min; The sintering process includes: pressing a flat ceramic sheet of the same composition as the ceramic to be prepared onto a thick film preform after plastic removal. The thick film preform is laid flat on a flat surface, and the weight ratio of the thick film preform to the ceramic sheet is 1:(1.5~1.8). The thick film preform is sintered. The sintering process includes: raising the temperature from room temperature to 1140 °C to 1150 °C at a heating rate of 0.4 °C / min to 0.5 °C / min and holding it at that temperature for 1.5 h to 2.5 h, and then cooling it down to room temperature at a cooling rate of 0.4 °C / min to 0.5 °C / min. After sintering the thick film preform, the process further includes: Electrodes were deposited on the sintered ceramic thick film using a vapor deposition process, and then polarized for 10 to 20 minutes under an electric field of 4 kV / mm to 6 kV / mm to excite pyroelectric properties.

2. The preparation method according to claim 1, characterized in that, In step S1, the process of preparing raw materials according to the stoichiometric ratio of ceramics and processing them to obtain micron-sized ceramic powder includes: Step S11: Configure Bi source, Na source, Ti source, Ba source and Mn source according to the stoichiometric ratio of ceramic; Step S12: The prepared raw materials are ball-milled and dried to obtain powder. The powder is pre-sintered at a temperature of 950 °C to 1020 °C for 2 h to 3 h, and then ball-milled and dried again to obtain micron-sized ceramic powder.

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