Lead-free pyroelectric ceramic with high depolarization temperature as well as preparation method and application of lead-free pyroelectric ceramic

Abstract

The invention belongs to the related technical field of pyroelectric infrared detection, and discloses a high-depolarization-temperature lead-free pyroelectric ceramic and a preparation method and application thereof.The lead-free pyroelectric ceramic comprises 0.8 (Bi0. 5Na0. 5) TiO3-0. 2BaTiO3-XMn, and X is larger than 0.0 and smaller than 0.8%. By introducing the Mn element into a tetragonal-phase 0.8 (Bi0. 5Na0. 5) TiO3-0. 2BaTiO3 matrix, the depolarization temperature of the lead-free pyroelectric ceramic is increased, and the depolarization temperature of the lead-free pyroelectric ceramic is increased. And the lead-free pyroelectric material can show excellent pyroelectric performance while ensuring that the lead-free pyroelectric material has relatively high depolarization temperature. When the ceramic is prepared, firstly, the ceramic slurry is subjected to tape casting by utilizing a tape casting process to form a thin film with better quality, then the thin film is cut into a plurality of pieces to be stacked, and then the stacked thin film is subjected to hot pressing to obtain a thick film blank. According to the preparation method, cutting and thinning are not needed, and the utilization rate of the sensitive element ceramic is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to pyroelectric infrared detection, and more specifically, relates to a lead-free pyroelectric ceramic with a high depolarization temperature and a preparation method and application thereof. Background Art

[0002] Bismuth sodium titanate-based lead-free ceramics are considered to be the most promising lead-free pyroelectric materials due to their excellent pyroelectric properties. Pyroelectric infrared sensors need to undergo high-temperature processes during the preparation process, and the depolarization temperature of conventional bismuth sodium titanate-based lead-free materials is currently low. Pyroelectric sensors undergo high-temperature baking during the production process, which will cause material performance failure.

[0003] There is a common problem with the sodium bismuth titanate-based lead-free pyroelectric materials currently studied, that is, the material cannot meet the requirements of a high pyroelectric coefficient and a high depolarization temperature at the same time. If the depolarization temperature of the sodium bismuth titanate-based lead-free pyroelectric material is to be increased to adapt to high-temperature processes, it is usually necessary to sacrifice its pyroelectric coefficient. The pyroelectric coefficient is a very critical parameter of the detector. The higher the pyroelectric coefficient, the more sensitive the detection. In order to ensure the sensitivity of the detector, the pyroelectric coefficient cannot be lost excessively.

[0004] Therefore, it is urgent and of great value to develop lead-free pyroelectric materials that are compatible with the high depolarization temperature of the production process and maintain a good pyroelectric coefficient in engineering applications. Summary of the invention

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

[0006] To achieve the above object, the present invention provides a high depolarization temperature lead-free pyroelectric ceramic, which comprises 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] The present invention also provides a method for preparing a lead-free pyroelectric ceramic with a high depolarization temperature, which comprises:

[0009] Step S1: preparing raw materials according to the stoichiometric ratio of ceramics to obtain micron-sized ceramic powder;

[0010] Step S2: mixing the ceramic powder with a solvent and adding a plasticizer to obtain a ceramic slurry;

[0011] Step S3: firstly casting the ceramic slurry into a film by a casting process, then cutting the film into multiple pieces and stacking them, and then hot pressing the stacked films to obtain a thick film embryo;

[0012] Step S4: The thick film embryo is subjected to aging, isostatic pressing, plastic removal and sintering in sequence to obtain a lead-free pyroelectric ceramic.

[0013] Preferably, the solvent includes a mixture of ethanol and toluene, triolein, and polyethylene glycol, and the plasticizer includes a PVB solution and butyl benzyl phthalate;

[0014] In step S2, the ceramic powder is mixed with a solvent and a plasticizer is added, comprising:

[0015] Step S21: mixing the ceramic powder with a mixture of ethanol and toluene, triolein, and polyethylene glycol in sequence to obtain a preliminary ceramic slurry; wherein the mass fraction of ethanol in the mixture of ethanol and toluene is 40wt% to 60wt% of the mixed solution; and the mass ratio of the ceramic powder, the mixture of ethanol and toluene, the triolein, and the polyethylene glycol is 1:(0.55-0.65):(0.008-0.012):(0.005-0.007);

[0016] Step S22: adding PVB solution and butyl benzyl phthalate to the ceramic preliminary slurry to obtain ceramic slurry, wherein the viscosity of the ceramic slurry is in the range of 300 cps to 400 cps.

[0017] Preferably, in step S3:

[0018] The thickness of the film cast by the casting process is 25 μm to 50 μm;

[0019] The films are stacked to a stacking height of 4 to 6 films;

[0020] The stacked films are hot-pressed at a pressure of 0.8 MPa to 1.2 MPa, a temperature of 70° C. to 80° C., and a hot-pressing time of 5 to 7 minutes.

[0021] Preferably, in step S4,

[0022] The process of plastic removal includes:

[0023] The isostatically pressed thick film embryo is laid flat on a flat surface, and the temperature is first 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 kept at this temperature for 1.5h to 2.5h, and then the temperature is reduced to room temperature at a cooling rate of 0.4°C / min to 0.5°C / min;

[0024] The sintering process includes:

[0025] Pressing a flat ceramic sheet with the same components as the ceramic to be prepared onto the thick film embryo after plasticizing, the thick film embryo is laid flat on a flat surface, and the weight ratio of the thick film embryo to the ceramic sheet is 1:(1.5-1.8);

[0026] The thick film embryo is sintered, and the sintering process includes: heating from room temperature to 1140°C-1150°C at a heating rate of 0.4°C / min-0.5°C / min and keeping the temperature for 1.5h-2.5h, and then cooling to room temperature at a cooling rate of 0.4°C / min-0.5°C / min.

[0027] Preferably, in step S4,

[0028] The aging temperature is 25°C to 30°C, the humidity is 50%RH to 60%RH, and the aging time is 12h to 24h;

[0029] The temperature for isostatic pressing is room temperature, the pressure is 80 MPa to 120 MPa, and the holding time is 120 s to 300 s.

[0030] Preferably, after sintering the thick film embryo, the method further comprises:

[0031] The sintered ceramic thick film is evaporated with electrodes through an evaporation process, and then polarized for 10 minutes to 20 minutes under an electric field of 4 kV / mm to 6 kV / mm to stimulate pyroelectric properties.

[0032] Preferably, in step S1, the raw materials are configured according to the stoichiometric ratio of the ceramic to obtain micron-sized ceramic powder, including:

[0033] Step S11: configuring Bi source, Na source, Ti source, Ba source and Mn source according to the stoichiometric ratio of the ceramic;

[0034] Step S12: ball-milling and drying the configured raw materials to obtain powder, pre-sintering the powder at a temperature of 950° C. to 1020° C. for 2 h to 3 h, and ball-milling and drying again to obtain micron-sized ceramic powder.

[0035] The present invention also provides a pyroelectric infrared sensor, which comprises the high depolarization temperature lead-free pyroelectric ceramic as described above.

[0036] In general, compared with the prior art, the above technical solutions conceived by the present invention mainly have the following beneficial effects:

[0037] 1. The high depolarization temperature lead-free pyroelectric ceramics of the present invention are made of 0.8 (Bi 0.5 Na0.5 )TiO3-0.2BaTiO3 matrix, the lead-free pyroelectric ceramic has a depolarization temperature of more than 200 ° C, so that it can adapt to the high temperature process in the preparation of the detector and ensure the performance of the device. 0.5 Na 0.5 )The introduction of Mn element into the TiO3-0.2BaTiO3 matrix can improve the polarization characteristics of the material and enhance the ferroelectricity of the material while ensuring that the lead-free pyroelectric has a high depolarization temperature; after the Mn ions occupy the B position of the perovskite structure, defect dipoles are formed inside the material, which inhibits the movement of ferroelectric domains, making the lead-free material exhibit excellent pyroelectric properties and outstanding temperature stability.

[0038] 2. The preparation method of the lead-free pyroelectric ceramic with high depolarization temperature proposed in the present invention first utilizes the casting process to cast the ceramic slurry into a film of good quality, then cuts the film into multiple pieces and stacks them, and then hot presses the stacked films to obtain a thick film embryo. Compared with the traditional technology of using the solid phase method to prepare thicker ceramic blocks, and then cutting, thinning, slicing, cleaning and other processes to prepare the ceramic blocks into thick films used in detectors, which causes waste of materials, the preparation method of the present invention does not require cutting and thinning, greatly improving the utilization rate of sensitive element ceramics.

[0039] 3. Preferably, when debonding the thick film body, the heating rate and the cooling rate are controlled to ensure efficient debonding of the thick film body, and to minimize the damage to the material caused by temperature fluctuations during the debonding process, such as cracking of the thick film and incomplete debonding.

[0040] 4. Preferably, when sintering the thick film embryo, the weight of the ceramic sheet is controlled to prevent the thick film from bending and cracking during the sintering process. If the ceramic sheet is too light, the thick film embryo is prone to uneven shrinkage during the sintering process, resulting in uneven bending of the ceramic sheet. If it is too heavy, the shrinkage of the thick film embryo is hindered during the sintering process and is prone to cracking. By controlling the heating rate and cooling rate during sintering, it is possible to ensure that the thick film embryo shrinks slowly and steadily during the ceramic forming process, thereby obtaining high-performance and high-flatness ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a flow chart of the steps of a method for preparing lead-free pyroelectric ceramics in one embodiment of the present invention;

[0042] Figure 2 This is a graph showing the change in dielectric constant of lead-free pyroelectric ceramics with temperature;

[0043] Figure 3 This is a graph showing the change in pyroelectric coefficient of lead-free pyroelectric ceramics with temperature. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] The present invention provides a high depolarization temperature lead-free pyroelectric ceramic, which comprises 0.8 (Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3-XMn, 0.0<X<0.8%. Among them, the 0.8 (Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3 matrix has a depolarization temperature of more than 200℃, which can adapt to the high temperature process in the preparation of detectors. However, it sacrifices the pyroelectric coefficient, making the pyroelectric coefficient low. 0.5 Na 0.5 )The introduction of Mn element into the TiO3-0.2BaTiO3 matrix can improve the polarization characteristics of the material and enhance the ferroelectricity of the material while ensuring that the lead-free pyroelectric has a high depolarization temperature; after the Mn ions occupy the B position of the perovskite structure, defect dipoles are formed inside the material, which inhibits the movement of ferroelectric domains, making the lead-free material exhibit excellent pyroelectric properties and outstanding temperature stability.

[0046] The following is an explanation using several sets of experimental data as examples.

[0047] Example 1

[0048] X = 0.2%, the composition of lead-free pyroelectric ceramics is:

[0049] 0.8(Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3-0.2%Mn;

[0050] Its depolarization temperature is 258℃ and its pyroelectric coefficient is 1.41×10 -4 Cm -2 K -1 .

[0051] Example 2

[0052] X = 0.4%, the composition of lead-free pyroelectric ceramics is:

[0053] 0.8(Bi 0.5 Na 0.5)TiO3-0.2BaTiO3-0.4%Mn;

[0054] Its depolarization temperature is 260℃ and its pyroelectric coefficient is 2.11×10 -4 Cm -2 K -1 .

[0055] Example 3

[0056] X = 0.6%, the composition of lead-free pyroelectric ceramics is:

[0057] 0.8(Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3-0.6%Mn;

[0058] Its depolarization temperature is 265℃ and its pyroelectric coefficient is 2.28×10 -4 Cm -2 K -1 .

[0059] Comparative Example 1

[0060] X=0.0, the composition of lead-free pyroelectric ceramics is:

[0061] 0.8(Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3;

[0062] Its depolarization temperature is 250℃ and its pyroelectric coefficient is 1.12×10 -4 Cm -2 K -1 .

[0063] Comparative Example 2

[0064] X = 0.8%, the composition of lead-free pyroelectric ceramics is:

[0065] 0.8(Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3-0.8%Mn;

[0066] Its depolarization temperature is 252℃ and its pyroelectric coefficient is 1.27×10 -4 Cm -2 K -1 .

[0067] Table 1 below is a comparison of the experimental data of the above examples.

[0068]

[0069] like Figure 2The figure 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.

[0070] like Figure 3 The figure shows the change of pyroelectric coefficient of lead-free pyroelectric ceramics with temperature. As a detector, we only focus on the pyroelectric coefficient at room temperature.

[0071] From the above data, it can be seen that if Mn is not added, 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 -4 Cm -2 K -1 , in the tetragonal phase of 0.8 (Bi 0.5 Na 0.5 )After the Mn element is introduced into the TiO3-0.2BaTiO3 matrix, its depolarization temperature and pyroelectric coefficient are improved to a certain extent. When the Mn element reaches X≥0.8%, the improvement effect is basically not obvious. Moreover, when X is between 0.4% and 0.6%, its depolarization temperature is as high as 260°C and the pyroelectric coefficient is significantly improved. Therefore, preferably, 0.4≤X≤0.6%.

[0072] The pyroelectric ceramics prepared by the traditional solid phase method need to be mechanically processed before they can be used as pyroelectric sensitive elements in devices. During the processing, the comprehensive utilization rate of the ceramic block after cutting, thinning, slicing, cleaning and other processes is often less than 30%, and the loss is extremely large. The present invention uses a tape casting process to prepare the ceramic into a thick film (90-120μm). Under the premise of not needing to cut and thin, its thickness can be well suitable for devices, greatly improving the utilization rate of sensitive element ceramics.

[0073] like Figure 1 FIG. 1 is a flow chart showing the steps of a method for preparing lead-free pyroelectric ceramics in an embodiment of the present invention, which mainly includes steps S1 to S4. Each step is described below.

[0074] Step S1: raw materials are prepared according to the stoichiometric ratio of ceramics, and processed to obtain micron-sized ceramic powder.

[0075] Please follow the steps below to do this.

[0076] Step S11: configuring Bi source, Na source, Ti source, Ba source and Mn source according to the stoichiometric ratio of the ceramic.

[0077] According to the ceramic composition 0.8 (Bi 0.5 Na 0.5)TiO3-0.2BaTiO3-XMn stoichiometric ratio Bi source, Na source, Ti source, Ba source, and Mn source with purity higher than 99.5% are dried at 150-200°C for 1h to 2h and then weighed. In one embodiment, the Bi source may be Bi2O3, the Na source may be NaHCO3, the Ti source may be TiO2, the Ba source may be BaCO3, and the Mn source may be MnCO3, and the purity of the above raw materials is higher than 99.5%. All raw materials are baked at 150-200°C for more than 1h before weighing to prevent moisture.

[0078] Step S12: ball-milling and drying the configured raw materials to obtain powder, pre-sintering the powder at a temperature of 950° C. to 1020° C. for 2 h to 3 h, and ball-milling and drying again to obtain micron-sized ceramic powder.

[0079] Specifically, the weighed raw material powder is ball-milled and dried, the powder is sieved and loaded into a crucible for compaction, and the crucible is opened for pre-sintering preparation. After pre-sintering at 950°C to 1020°C for 2h to 3h, it is ball-milled and dried to obtain a micron-sized target ceramic powder.

[0080] Step S2: Mixing ceramic powder with a solvent and adding a plasticizer to obtain a ceramic slurry.

[0081] Mixing with solvent and adding plasticizer to adjust viscosity are necessary steps for preparing casting slurry. In this embodiment, the solvent used includes ethanol and toluene mixture, triolein, polyethylene glycol, and the plasticizer used includes PVB solution and butyl benzyl phthalate.

[0082] Step S2 can be performed as follows.

[0083] Step S21: Mixing ceramic powder with a mixture of ethanol and toluene, triolein, and polyethylene glycol in sequence to obtain a preliminary ceramic slurry; wherein the mass fraction of ethanol in the mixture of ethanol and toluene accounts for 40wt% to 60wt% of the mixed solution; and the mass ratio of ceramic powder, ethanol and toluene mixture, triolein, and polyethylene glycol is 1:(0.55-0.65):(0.008-0.012):(0.005-0.007).

[0084] Specifically, ceramic powder is mixed with ethanol and toluene mixed solution, triolein, and polyethylene glycol in turn and ball-milled to obtain a ceramic preliminary slurry. The mass ratio of ceramic powder to ethanol and toluene mixed solution (wherein the mass fraction of ethanol in the mixed solution is 40wt% to 60wt%) is 1:0.55 to 0.65, and the specific optional ratio is 1:0.6. The mass ratio of ceramic powder to triolein is 1:(0.008 to 0.012), and the specific optional ratio is 1:0.01. The mass ratio of ceramic powder to polyethylene glycol is 1:(0.005 to 0.007), and the specific optional ratio is 1:0.006.

[0085] Step S22: adding PVB solution and butyl benzyl phthalate to the preliminary ceramic slurry to obtain a ceramic slurry, wherein the viscosity of the ceramic slurry is in the range of 300 cps to 400 cps.

[0086] Specifically, in order to make the thick film plastic, an appropriate amount of PVB solution and butyl benzyl phthalate are added to the obtained ceramic preliminary slurry and then ball-milled to mix into a ceramic slurry, and the slurry viscosity is controlled to be 300cps to 400cps. In one embodiment, the concentration of the PVB solution is 20wt%-25wt%, the amount of the PVB solution added is controlled to be 25wt%-30wt% of the mass of the ceramic powder, and the amount of butyl benzyl phthalate added is controlled to be 0.6wt% of the mass of the ceramic powder.

[0087] Step S3: firstly, the ceramic slurry is cast into a film by a casting process, then the film is cut into multiple pieces and stacked, and then the stacked films are hot pressed to obtain a thick film embryo.

[0088] The tape casting process can produce good quality films with a thickness of tens of microns, but if a thicker film layer is produced, it is difficult to guarantee the quality of the film layer by directly using the tape casting process. The ceramic sheets used in the detector are generally hundreds of microns thick. In order to ensure the quality of the thick film, the conventional method is to prepare thicker ceramic blocks by solid phase method, and then the ceramic blocks are cut, thinned, sliced, cleaned and other processes to prepare the thick film used in the detector. After cutting, thinning, slicing, cleaning and other processes, the comprehensive utilization rate of the material is often less than 30%, and the loss is extremely large.

[0089] In the present invention, the ceramic slurry is first cast into a film of good quality using a casting process, and then the film is cut into multiple pieces and stacked, and then the stacked films are hot pressed to obtain a thick film embryo. In this way, the thickness can be well suitable for the device without the need for cutting and thinning, thereby greatly improving the utilization rate of the sensitive element ceramic.

[0090] In a specific embodiment, step S3 can be performed as follows.

[0091] Step S31: using a casting process to cast a film with a thickness of 25 μm to 50 μm, and then cutting the cast film into square pieces with a side length of 30 mm to 50 mm.

[0092] Specifically, the operating environment temperature is maintained at 20° C. to 30° C., and the humidity is maintained at 50% RH to 70% RH.

[0093] Step S32: stack the cut square pieces into 4 to 6 pieces.

[0094] Step S33: hot pressing the stacked films, with a pressure of 0.8 MPa to 1.2 MPa, specifically 1 MPa, a temperature of 70° C. to 80° C., specifically 75° C., and a hot pressing time of 5 to 7 minutes.

[0095] Specifically, a thick film embryo with a thickness of 110 μm to 150 μm can be obtained.

[0096] Preferably, all operations from casting to hot pressing should be completed within 15 minutes.

[0097] Step S4: The thick film embryo is subjected to aging, isostatic pressing, plastic removal and sintering in sequence to obtain a lead-free pyroelectric ceramic.

[0098] Aging, isostatic pressing, demolding and sintering are all necessary processing steps for the film layer produced by the casting process.

[0099] Step S41: aging the thick film embryos in sequence.

[0100] Specifically, the aging temperature is 25°C to 30°C, the humidity is 50%RH to 60%RH, and the aging time is 12h to 24h; through the aging process, it can be ensured that the thick film stably removes volatile additives, increases the solid content of the thick film, and obtains a high-quality uniform ceramic thick film.

[0101] Step S42: isostatically pressing the aged thick film embryo.

[0102] Specifically, cold isostatic pressing can be used. The temperature for isostatic pressing 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 discharged, making the thick film stronger and improving the density of the ceramic after sintering.

[0103] Step S43: Demolding the thick film embryo after isostatic pressing.

[0104] Specifically, the thick film embryo after isostatic pressing is laid flat on a flat surface, firstly the temperature is raised from room temperature to 580℃~620℃ at a heating rate of 0.3C / min~0.5℃ / min and kept at that temperature for 1.5h~2.5h, and then the temperature is lowered to room temperature at a cooling rate of 0.4C / min~0.5℃ / min. Through plastic removal, the organic additives in the thick film can be removed to obtain pure ceramic components, wherein, by controlling the heating rate and the cooling rate, the efficient debinding of the thick film embryo can be ensured, and the damage to the material caused by temperature fluctuations, such as cracking of the thick film and incomplete debinding, can be minimized during the debinding process.

[0105] Step S44: sintering the thick film embryo after plastic removal.

[0106] Specifically, a flat ceramic sheet with the same component as the ceramic to be prepared is first pressed onto the thick film embryo after plastic removal, the thick film embryo is spread flat on a flat surface, the weight ratio of the thick film embryo to the ceramic sheet is 1:(1.5~1.8), and then the thick film embryo is sintered. The sintering process includes: increasing the temperature from room temperature to 1140℃~1150℃ at a heating rate of 0.4℃ / min~0.5℃ / min and keeping it warm for 1.5h~2.5h, and then cooling it to room temperature at a cooling rate of 0.4C / min~0.5℃ / min. Through sintering, the thick film embryo can be prepared into a high-quality ceramic sheet. Among them, controlling the weight of the ceramic sheet can prevent the thick film from bending and cracking during the sintering process. If the ceramic sheet is too light, the thick film embryo is prone to uneven shrinkage during the sintering process, resulting in uneven bending of the ceramic sheet. If it is too heavy, the shrinkage of the thick film embryo is hindered during the sintering process and it is easy to crack. By controlling the heating rate and the cooling rate, the thick film embryo can be guaranteed to shrink slowly and steadily during the ceramic forming process, thereby obtaining high-performance and high-flatness ceramics.

[0107] Specifically, after sintering, a ceramic thick film of 90 μm to 120 μm can be obtained.

[0108] Furthermore, it also includes:

[0109] Step S45: depositing electrodes on the sintered ceramic thick film through a vapor deposition process.

[0110] Specifically, after electrodes are evaporated on both sides of the lead-free ceramic thick film, the lead-free pyroelectric ceramic thick film with good pyroelectric properties and high depolarization temperature is obtained by polarizing for 10 to 20 minutes under an electric field of 4 to 6 kV / mm.

[0111] By means of the above-mentioned preparation method, lead-free pyroelectric ceramics with a good depolarization temperature can be prepared. Moreover, in the present invention, the ceramic slurry is firstly cast into a film of good quality by means of a casting process, and then the film is cut into multiple pieces and stacked, and then the stacked films are hot pressed to obtain a thick film embryo. In this way, the thickness can be well suitable for the device without the need for cutting and thinning, thereby greatly improving the utilization rate of the sensitive element ceramics.

[0112] The present invention also provides a pyroelectric infrared sensor, which comprises the high depolarization temperature lead-free pyroelectric ceramics described above, and a tetragonal 0.8 (Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3 matrix, so that its depolarization temperature is as high as 200℃, which can withstand the high temperature process in device preparation and ensure the performance of the device. 0.5 Na 0.5 )Mn is doped into the TiO3-0.2BaTiO3 matrix, which can improve the pyroelectric coefficient to a certain extent, thereby ensuring the sensitivity of the device. Therefore, the pyroelectric infrared sensor provided by the present invention has good comprehensive performance.

[0113] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. It should be noted that "in one embodiment", "for example", "for example", etc. of the present invention are intended to illustrate the present invention, rather than to limit the present invention.

[0114] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A high depolarization temperature lead-free pyroelectric ceramic, characterized in that: Its composition includes 0.8(Bi 0.5 Na 0.5 )TiO3-0.2BaTiO3-XMn, 0.0<X<0.8%.

2. The high depolarization temperature lead-free pyroelectric ceramic according to claim 1, characterized in that: 0.4≤X≤0.6％。 3. A method for preparing a lead-free pyroelectric ceramic with a high depolarization temperature as claimed in claim 1 or 2, characterized in that: include: Step S1: preparing raw materials according to the stoichiometric ratio of ceramics to obtain micron-sized ceramic powder; Step S2: mixing the ceramic powder with a solvent and adding a plasticizer to obtain a ceramic slurry; Step S3: firstly casting the ceramic slurry into a film by a casting process, then cutting the film into multiple pieces and stacking them, and then hot pressing the stacked films to obtain a thick film embryo; Step S4: The thick film embryo is subjected to aging, isostatic pressing, plastic removal and sintering in sequence to obtain a lead-free pyroelectric ceramic.

4. The preparation method according to claim 3, characterized in that: The solvent includes a mixture of ethanol and toluene, triolein, and polyethylene glycol, and the plasticizer includes a PVB solution and butyl benzyl phthalate; In step S2, the ceramic powder is mixed with a solvent and a plasticizer is added, comprising: Step S21: mixing the ceramic powder with a mixture of ethanol and toluene, triolein, and polyethylene glycol in sequence to obtain a preliminary ceramic slurry; wherein the mass fraction of ethanol in the mixture of ethanol and toluene is 40wt% to 60wt% of the mixed solution; and the mass ratio of the ceramic powder, the mixture of ethanol and toluene, the triolein, and the polyethylene glycol is 1:(0.55-0.65):(0.008-0.012):(0.005-0.007); Step S22: adding PVB solution and butyl benzyl phthalate to the ceramic preliminary slurry to obtain ceramic slurry, wherein the viscosity of the ceramic slurry is in the range of 300 cps to 400 cps.

5. The preparation method according to claim 3, characterized in that: In step S3: The thickness of the film cast by the casting process is 25 μm to 50 μm; The films are stacked to a stacking height of 4 to 6 films; The stacked films are hot-pressed at a pressure of 0.8 MPa to 1.2 MPa, a temperature of 70° C. to 80° C., and a hot-pressing time of 5 to 7 minutes.

6. The preparation method according to claim 3, characterized in that: In step S4, The process of plastic removal includes: The isostatically pressed thick film embryo is laid flat on a flat surface, and the temperature is first 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 kept at this temperature for 1.5h to 2.5h, and 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: Pressing a flat ceramic sheet with the same components as the ceramic to be prepared onto the thick film embryo after plasticizing, the thick film embryo is laid flat on a flat surface, and the weight ratio of the thick film embryo to the ceramic sheet is 1:(1.5-1.8); The thick film embryo is sintered, and the sintering process includes: heating from room temperature to 1140°C-1150°C at a heating rate of 0.4°C / min-0.5°C / min and keeping the temperature for 1.5h-2.5h, and then cooling to room temperature at a cooling rate of 0.4°C / min-0.5°C / min.

7. The preparation method according to claim 3, characterized in that: In step S4, The aging temperature is 25°C to 30°C, the humidity is 50%RH to 60%RH, and the aging time is 12h to 24h; The temperature for isostatic pressing is room temperature, the pressure is 80 MPa to 120 MPa, and the holding time is 120 s to 300 s.

8. The preparation method according to claim 3, characterized in that: After sintering the thick film embryo, the method further comprises: The sintered ceramic thick film is evaporated with electrodes through an evaporation process, and then polarized for 10 minutes to 20 minutes under an electric field of 4 kV / mm to 6 kV / mm to stimulate pyroelectric properties.

9. The preparation method according to claim 3, characterized in that: In step S1, the raw materials are configured according to the stoichiometric ratio of the ceramics to obtain micron-sized ceramic powder, including: Step S11: configuring Bi source, Na source, Ti source, Ba source and Mn source according to the stoichiometric ratio of the ceramic; Step S12: ball-milling and drying the configured raw materials to obtain powder, pre-sintering the powder at a temperature of 950° C. to 1020° C. for 2 h to 3 h, and ball-milling and drying again to obtain micron-sized ceramic powder.

10. A pyroelectric infrared sensor, characterized in that: The invention comprises the high depolarization temperature lead-free pyroelectric ceramic as claimed in claim 1 or 2.

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