A bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material and a method for manufacturing the same

Abstract

The application belongs to the field of pyroelectric infrared detection materials, and designs a bismuth layered structure sodium bismuth titanate-based lead-free pyroelectric ceramic material and a preparation method thereof. 0.5 Bi 4.5‑x (Li 1 / 3 Ce 2 / 3 ) x Ti4O 15 , wherein the value of x is greater than 0 and less than or equal to 0.2. The pyroelectric ceramic material is a bismuth layered structure sodium bismuth titanate-based material, has a high Curie temperature, excellent pyroelectric performance and low dielectric loss, and has the advantages of simple and stable preparation process, convenient operation and suitability for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of pyroelectric infrared detection materials, and more specifically, relates to a bismuth layered sodium titanate-based lead-free pyroelectric ceramic material and its preparation method. Background Technology

[0002] Infrared photoelectric detection technology is widely used in military, industrial, and daily life fields. Among them, uncooled pyroelectric infrared (PIR) technology has gradually become a research hotspot due to its advantages such as low power consumption, small size, and low cost.

[0003] Pyroelectric ceramic materials are commonly used as the core sensing element in uncooled infrared detectors. They generate an electrical response in response to temperature changes and are characterized by low cost, high sensitivity, and ease of fabrication. The detection capability of these uncooled pyroelectric infrared detectors depends primarily on the performance of the pyroelectric ceramic, mainly reflected in the pyroelectric coefficient (P0.05). p ) and Curie temperature ( T c The two key parameters are: the pyroelectric coefficient, determined by the polarization change caused by temperature variation, reflecting the material's ability to convert temperature fluctuations into electrical signals; and the higher Curie temperature, which ensures the operating and processing temperature range of pyroelectric materials.

[0004] Currently, the most widely used pyroelectric material is lead zirconate titanate (PZT). However, the Curie temperature of PZT (230°C) is lower than the temperature of the reflow soldering process (260°C). The high-temperature environment of reflow soldering can cause PZT to depolarize, which can lead to device failure. Therefore, it limits the use of surface mount packaging technology and makes it difficult to meet the needs of device miniaturization and integration. In addition, the use of lead-containing materials also raises issues that violate regulations on hazardous substances.

[0005] Currently, lead-free pyroelectric materials mainly include Bi0.5Na0.5TiO3 (BNT)-based, BaTiO3 (BT)-based, and K0.5Na0.5NbO3 (KNN)-based materials. While BNT-based and BT-based materials can improve their pyroelectric coefficients through doping, this comes at the cost of a significantly lower Curie temperature, making it difficult to maintain their performance at 200°C. Therefore, developing lead-free materials with high Curie temperatures as alternatives to lead-based ceramics is crucial for promoting the development of environmentally friendly electronic devices. Summary of the Invention

[0006] In view of the above defects or improvement needs of the prior art, the present application provides a bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material and a preparation method thereof.The base material of the pyroelectric ceramic material is a bismuth layer-structured sodium bismuth titanate-based material with a high Curie temperature, and part of Bi elements in the sodium bismuth titanate-based material are replaced by Li and Ce elements at the A site, thereby solving the technical problem that it is difficult to simultaneously have a high Curie temperature and a high pyroelectric coefficient in the prior art.

[0007] To achieve the above object, according to one aspect of the present application, a bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material is provided, which has a general chemical formula of Na 0.5 Bi 4.5-x (Li 1 / 3 Ce 2 / 3 ) x Ti4O 15 , wherein x is greater than 0 and less than or equal to 0.2.

[0008] As a preferred embodiment of the present application, x is 0.025-0.1.

[0009] As a preferred embodiment of the present application, the pyroelectric ceramic material has a relative dielectric constant of 100-150 and a dielectric loss of less than or equal to 0.006 under the test conditions of 25°C and 1 kHz.

[0010] As a preferred embodiment of the present application, the pyroelectric ceramic material has a Curie temperature higher than 600°C, a pyroelectric coefficient of 70-150 μCm -2 K -1 at 25°C, a current response merit factor of (0.3-0.6)×10 -10 m V -1 , a voltage response merit factor of 0.02-0.05 m 2 C -1 , and a detectivity merit factor of (1.6-4)×10 -5 Pa -1 / 2 .

[0011] According to another aspect of the present application, a preparation method of a bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material is provided, which comprises the following steps:

[0012] (1) preparing a base material according to Na 0.5 Bi 4.5-x (Li 1 / 3 Ce 2 / 3 ) x Ti4O 15The stoichiometrically proportioned Na2CO3, Bi2O3, Li2CO3, CeO2 and TiO2 are weighed respectively, mixed, once ball-milled, and dried to obtain a mixed powder;

[0013] (2) The mixed powder is sequentially pre-fired, twice ball-milled, dried, granulated after adding a binder, formed, plastic-removed, and sintered to obtain the ceramic sheet;

[0014] (3) The ceramic sheet is coated with silver paste on both sides, fired and formed, placed in silicon oil for polarization under pressure, and the bismuth-layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material is obtained.

[0015] As a preferred embodiment of the present application, the conditions of the once ball-milling and the twice ball-milling are the same, specifically: anhydrous ethanol is used as the solvent, the ball-milling speed is set to 200-400 r / min, and the ball-milling time is 6-24 hours.

[0016] As a preferred embodiment of the present application, the pre-firing condition is to heat to 600-900 ℃ at a rate of 3-5 ℃ / min and keep the temperature for 1-5 h; the plastic-removing condition is to heat to 500-650 ℃ at a rate of 0.5-2 ℃ / min and keep the temperature for 1-5 h; and the sintering condition is to heat to 900-1200 ℃ at a rate of 1-5 ℃ / min and keep the temperature for 1-5 h.

[0017] As a preferred embodiment of the present application, the firing and forming condition is to keep the temperature at 500-700 ℃ for 10-30 min.

[0018] As a preferred embodiment of the present application, the method further comprises: after obtaining the bismuth-layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material, heat-treating the material, specifically: placing the polarized bismuth-layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material in an annealing furnace at 300 ℃, keeping the temperature for 5-15 min, and then taking out the material and naturally cooling it.

[0019] Overall, compared with the prior art, the above technical solution conceived by the present application mainly has the following technical advantages:

[0020] (1) The pyroelectric ceramic material of the present application is made of a bismuth-layer-structured sodium bismuth titanate matrix with a high Curie temperature (the Curie temperature is 660 ℃, and the general formula is (Bi2O2) 2+ (A n-1 B n O 3n+3 ) 2- ), and Li and Ce elements are doped at the A site of the bismuth-layer-structured sodium bismuth titanate to replace part of the Bi elements. In addition, according to the principle of charge conservation, 1 / 3 mole of Li and 2 / 3 mole of Ce are selected to replace 1 mole of Bi, and the obtained pyroelectric ceramic material has a general formula of Na 0.5 Bi 4.5-x(Li 1 / 3 Ce 2 / 3 ) x Ti4O 15 , wherein x is greater than 0 and less than or equal to 0.2, the structure is still a bismuth layer structure, and the properties of the original sodium bismuth titanate substrate are retained.

[0021] At the same time, since Li + and Ce 4+ have a large difference in ionic radius from Bi 3+ , lattice distortion is easily caused, the tilt angle of the TiO6 octahedron along the a axis is large, and the material is more sensitive to temperature changes. Meanwhile, Li + and Ce 4+ form defect dipoles, which provide additional polarization changes when the temperature changes. Thus, the pyroelectric ceramic material based on the sodium bismuth titanate substrate of the bismuth layer structure has a high Curie temperature and a high pyroelectric coefficient.

[0022] (2) When the value of x is 0.025-0.1, the relative dielectric constant of the polarized sodium bismuth titanate-based lead-free high-temperature pyroelectric ceramic under room temperature test conditions of 25 DEG C and 1 kHz is 100-150, and the dielectric loss is less than 0.006. Compared with other existing sodium bismuth titanate-based materials or pyroelectric materials of the bismuth layer structure, due to the lattice distortion caused by the introduction of Li and Ce and the combined effect of the defect dipoles between Li and Ce, the pyroelectric coefficient is increased to 70-150 mu Cm -2 K -1 ; meanwhile, the lower dielectric constant and dielectric loss value enable the current response figure of merit of the pyroelectricity to be increased to (0.3-0.6) x 10 -10 m V -1 , and the detectivity figure of merit to be increased to (1.6-4) x 10 -5 Pa -1 / 2 , so that the NBT-based lead-free high-temperature pyroelectric ceramic of the application can resist the high-temperature environment of reflow soldering without depolarization, can be packaged by surface mounting technology, and promotes the miniaturization and integration of pyroelectric devices.

[0023] (3) The bismuth layer structure sodium bismuth titanate-based lead-free pyroelectric ceramic material prepared by the application has a high Curie temperature and excellent pyroelectric performance. As shown in Figure 7 , the NBT-based high-temperature lead-free pyroelectric ceramic does not attenuate the pyroelectric performance after high-temperature annealing, has good stability, can be packaged by surface mounting technology, and is suitable for patch pyroelectric devices.

[0024] In conclusion, the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material has high Curie temperature, excellent pyroelectric performance, low dielectric loss, simple and stable preparation process, and convenient operation, and is suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The XRD test chart of the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic exemplified by the embodiment 1 of the present application.

[0026] Figure 2 The XRD test chart of the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic exemplified by the embodiment 2 of the present application.

[0027] Figure 3 The XRD test chart of the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic exemplified by the embodiment 3 of the present application.

[0028] Figure 4 The XRD test chart of the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic exemplified by the embodiment 4 of the present application.

[0029] Figure 5 The XRD test chart of the sodium bismuth titanate-based lead-free pyroelectric ceramic exemplified by the comparative example 1 of the present application.

[0030] Figure 6 The data chart of the pyroelectric coefficient with temperature of the embodiments and the comparative examples exemplified by the present application.

[0031] Figure 7 The pyroelectric coefficient at room temperature of the embodiments and the comparative examples exemplified by the present application after heat treatment at different temperatures. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other. And the NBT-based bismuth layer-structured sodium bismuth titanate.

[0033] Unless otherwise specified, the reagents used in the present application are commercially available, and are of commercial grade, and are used according to the received standard. The experimental tests involved in the present application all use standard experimental reagents and methods. The scientific and technical terms and abbreviations used in the present application have the meanings commonly understood by those skilled in the art.

[0034] In the present disclosure, a bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material is prepared through the steps of batching, primary ball milling, pre-sintering, secondary ball milling, granulation, molding, plastic removal, sintering, electrode preparation, polarization, etc. The following exemplary illustrates the preparation method of the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic provided by the present disclosure.

[0035] Batching: commercially available, high-purity (purity of 98.00% or more, or purity of 99.00% or more) sodium carbonate (Na2CO3), bismuth trioxide (Bi2O3), titanium dioxide (TiO2), lithium carbonate (Li2CO3), and cerium dioxide (CeO2) are weighed according to the stoichiometric ratio of Na 0.5 Bi 4.5-x (Li 1 / 3 Ce 2 / 3 ) x Ti4O 15 Chemical stoichiometric ratio weighing and mixing to obtain a powder.

[0036] Primary ball milling: the powder obtained above is uniformly mixed by ball milling, and anhydrous ethanol with the same mass as the powder is used as a solvent for ball milling for 6-24 hours, and zirconium dioxide balls are used for ball milling; after ball milling, the slurry is dried.

[0037] Pre-sintering: the dried slurry is transferred to an alumina crucible for pre-sintering to obtain a pre-sintered powder; the pre-sintering temperature is 600-900°C, the heating rate is not higher than 3-5°C / min, and the holding time is 1-5 hours.

[0038] Secondary ball milling: the pre-sintered powder is subjected to secondary ball milling, and the powder is obtained after drying, and the ball milling conditions are the same as those of the primary ball milling.

[0039] Granulation: a binder is added to the powder after secondary ball milling for granulation, for example, the binder is 5-10% of the mass of the powder, and the binder is a 4-12wt% PVA aqueous solution.

[0040] Molding: the granulated powder is placed in a die and pressed at a pressure of 4-10Mpa to obtain a green body.

[0041] Plastic removal: the green body is heated at a heating rate of 0.5-2°C / min to 500-650°C and held for 1-5 hours to remove organic matter.

[0042] Sintering: the green body after plastic removal is heated at a heating rate of 1-5°C / min to 900-1200°C and held for 1-5 hours, and then cooled in the furnace to obtain a bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic.

[0043] Electrode preparation: silver paste is coated on the upper and lower surfaces of the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic, and then heat-treated at a high temperature of 500-700°C for 10-30min.

[0044] Polarization: the sample is placed in silicon oil, heated to 150℃, the polarization electric field is set to 50 kV / cm, the pressure time is 10-15 min, then the voltage is increased to 80 kV / cm, and the pressure is maintained for 10-15 min, and finally the voltage is increased to 100 kV / cm, and the pressure is maintained for 10-15 min.

[0045] Specifically, the chemical composition of the bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic of the application is: Na 0.5 Bi 4.5-x (Li 1 / 3 Ce 2 / 3 ) x Ti4O 15 , wherein x The value is greater than 0 and less than or equal to 0.2. The pyroelectric ceramic has the characteristics of high pyroelectric performance, low dielectric loss and high Curie temperature, and can be used in the field of non-refrigeration infrared pyroelectric detection.

[0046] Preferably, x The value of is 0.025-0.1.

[0047] Preferably, the relative dielectric constant of the NBT-based lead-free pyroelectric ceramic material of the application under the test conditions of 25℃ and 1kHz is 100-150, and the dielectric loss is less than 0.006.

[0048] Preferably, the Curie temperature of the NBT-based lead-free pyroelectric ceramic material of the application is higher than 600℃, and the pyroelectric coefficient at room temperature is 70-150 μCm -2 K -1 , the current response merit factor of pyroelectricity is (0.3-0.6)×10 -10 m V -1 , the voltage response merit factor is 0.02-0.05 m 2 C -1 , and the detection rate merit factor is (1.6-4)×10 -5 Pa -1 / 2 . The pyroelectric ceramic does not attenuate in pyroelectric performance after annealing at 300℃.

[0049] The bismuth layer-structured sodium bismuth titanate-based lead-free pyroelectric ceramic material of the application will be further explained and described below through specific examples.

[0050] Example 1:

[0051] Batching: high-purity Na2CO3, Bi2O3, TiO2, Li2CO3, CeO2 are mixed according to Na 0.5 Bi 4.475 (Li 1 / 3 Ce2 / 3 ) 0.025 Ti4O 15 The powder is obtained by weighing and mixing according to stoichiometric ratio.

[0052] First ball milling: The powder obtained above is mixed evenly by ball milling, using anhydrous ethanol of equal mass as the solvent, and milled for 6 hours using zirconia balls. The slurry is then dried.

[0053] Pre-calcination: The dried slurry is transferred to an alumina crucible and pre-calcined to obtain pre-calcined powder. The pre-calcination temperature is 850℃, the heating rate is no higher than 5℃ / min, and the holding time is 3 hours.

[0054] Secondary ball milling: The pre-calcined powder is ball-milled a second time and dried to obtain the final powder. The ball milling conditions are the same as those for the primary ball milling.

[0055] Granulation: Add a binder to the powder after secondary ball milling for granulation. The amount of binder is 8% of the powder mass, and the binder is an 8 wt% polyvinyl alcohol solution.

[0056] Molding: The granulated powder is placed into a mold and pressed into shape using a pressure of 4 MPa to obtain a green embryo.

[0057] De-plasticizing: The green preform is heated to 600℃ at a heating rate of 5℃ / min and held at that temperature for 2 hours to remove organic matter.

[0058] Sintering: The green body after plastic removal is heated to 1100℃ at a heating rate of 3℃ / min, held for 2 hours, and then cooled in the furnace to obtain NBT-based lead-free pyroelectric ceramics.

[0059] Electrode preparation: The top and bottom surfaces of the NBT-based lead-free pyroelectric ceramic were coated with silver paste, and then kept at 600 degrees Celsius for 30 minutes.

[0060] Polarization: The sample was placed in silicone oil and heated to 150°C. The polarization electric field was set to 50 kV / cm and the pressure was applied for 15 min. Then the pressure was increased to 80 kV / cm and held for 15 min. Finally, the pressure was increased to 100 kV / cm and held for 15 min.

[0061] For well-polarized pyroelectric ceramics, the pyroelectric coefficient is... p =77μC m -2 K -1 The figure of merit of the current response of pyroelectricity. F i 0.32×10 -10 m V -1 Voltage response figure of merit F v It is 0.027×m 2 C-1 , probe rate merit factor F d 1.62 x 10 -5 Pa -1 / 2 .

[0062] Example 2:

[0063] Ingredients: high-purity Na2CO3, Bi2O3, TiO2, Li2CO3, CeO2 are mixed according to the stoichiometric ratio of Na 0.5 Bi 4.45 (Li 1 / 3 Ce 2 / 3 ) 0.05 Ti4O 15 Chemical stoichiometric ratio weighing and mixing to obtain a powder.

[0064] First ball milling: the above obtained powder is uniformly mixed by ball milling, and anhydrous ethanol with the same mass as the powder is used as a solvent, and ball milling is performed for 6 hours, and zirconium dioxide balls are used for ball milling. After ball milling, the slurry is dried.

[0065] Pre-sintering: the dried slurry is transferred to an alumina crucible, and a pre-sintered powder is obtained by pre-sintering. The pre-sintering temperature is 850°C, the heating rate is not higher than 5°C / min, and the holding time is 3 hours.

[0066] Second ball milling: the pre-sintered powder is subjected to secondary ball milling, and the powder is obtained by drying, and the ball milling conditions are the same as those of the first ball milling.

[0067] Granulation: a binder is added to the powder after the second ball milling for granulation, and the amount of the binder is 8% of the mass of the powder, and the binder is a 8wt% polyvinyl alcohol solution.

[0068] Molding: the granulated powder is placed in a die and pressed into a green body under a pressure of 4Mpa.

[0069] Plastic removal: the green body is heated to 600°C at a heating rate of 5°C / min, and the organic matter is removed after holding for 2 hours.

[0070] Sintering: the green body after plastic removal is heated to 1100°C at a heating rate of 3°C / min, and held for 2 hours, and then cooled in the furnace to obtain an NBT-based lead-free pyroelectric ceramic.

[0071] Electrode preparation: silver paste is coated on the upper and lower surfaces of the NBT-based lead-free pyroelectric ceramic, and then heat treated at 600°C for 30 minutes.

[0072] Polarization: The sample was placed in silicon oil and heated to 150℃, the polarization electric field was set to 50 kV / cm, the pressure time was 15 min, then the voltage was increased to 80 kV / cm, and the pressure was maintained for 15 min, and finally the voltage was increased to 100 kV / cm, and the pressure was maintained for 15 min.

[0073] The pyroelectric ceramic after polarization was tested, and the pyroelectric coefficient was p =103μC m -2 K -1 The current response merit factor of the pyroelectricity F i was 0.43×10 -10 m V -1 , the voltage response merit factor F v was 0.036×m 2 C -1 , and the detection rate merit factor F d was 2.39×10 -5 Pa -1 / 2 .

[0074] Example 3:

[0075] Batching: high-purity Na2CO3, Bi2O3, TiO2, Li2CO3, CeO2 were weighed according to the stoichiometric ratio of Na 0.5 Bi 4.5-0.075 (Li 1 / 3Ce 2 / 3 ) 0.075 Ti4O 15 , and mixed to obtain a powder.

[0076] Primary ball milling: the powder obtained above was uniformly mixed by ball milling, and anhydrous ethanol with the same mass as the powder was used as a solvent, and ball milling was performed for 6 hours, and zirconium dioxide balls were used for ball milling. After ball milling, the slurry was dried.

[0077] Pre-sintering: the dried slurry was transferred to an alumina crucible, and pre-sintering was performed to obtain a pre-sintered powder. The pre-sintering temperature was 850℃, the heating rate was not higher than 5℃ / min, and the holding time was 3 hours.

[0078] Secondary ball milling: the pre-sintered powder was subjected to secondary ball milling, and the powder was obtained after drying, and the ball milling conditions were the same as those of the primary ball milling.

[0079] Granulation: a binder was added to the powder after secondary ball milling for granulation, and the amount of the binder was 8% of the mass of the powder, and the binder was a 8wt% polyvinyl alcohol solution.

[0080] Molding: the granulated powder was placed in a die, and a pressure of 4Mpa was applied to press and form a green body.

[0081] Deplasticization: The green body was heated to 600℃ at a heating rate of 5℃ / min, and held for 2 hours to remove the organic matter.

[0082] Sintering: The deplasticized green body was heated to 1100℃ at a heating rate of 3℃ / min, and held for 2 hours to obtain NBT-based lead-free pyroelectric ceramic.

[0083] Electrode preparation: The NBT-based lead-free pyroelectric ceramic was coated with silver paste on both sides, and then heat-treated at 600℃ for 30 minutes.

[0084] Polarization: The sample was placed in silicone oil and heated to 150℃, and the polarization electric field was set to 50kV / cm for 15 minutes, then increased to 80kV / cm for 15 minutes, and finally increased to 100kV / cm for 15 minutes.

[0085] The pyroelectric ceramic after polarization was tested, and the pyroelectric coefficient was p =142μC m -2 K -1 The current response merit factor of pyroelectricity F i was 0.59×10 -10 m V -1 , the voltage response merit factor F v was 0.049×m 2 C -1 , and the detection rate merit factor F d was 3.47×10 -5 Pa -1 / 2 .

[0086] Example 4:

[0087] Batching: High-purity Na2CO3, Bi2O3, TiO2, Li2CO3, and CeO2 were weighed according to the stoichiometric ratio of Na 0.5 Bi 4.5-0.1 (Li 1 / 3 Ce 2 / 3 ) 0.1 Ti4O 15 to obtain a powder.

[0088] Primary ball milling: The powder obtained above was uniformly mixed by ball milling, and anhydrous ethanol with the same mass as the powder was used as a solvent, and ball milling was performed for 6 hours, and zirconium dioxide balls were used for ball milling. After ball milling, the slurry was dried.

[0089] Pre-burning: The dried slurry was transferred into an alumina crucible and pre-burned to obtain pre-burned powder. The pre-burning temperature was 850℃, the heating rate was not higher than 5℃ / min, and the holding time was 3 hours.

[0090] Secondary ball milling: The pre-burned powder was subjected to secondary ball milling, and the powder was dried to obtain a powder. The ball milling conditions were the same as those of the primary ball milling.

[0091] Granulation: A binder was added to the powder after secondary ball milling for granulation. The amount of the binder was 8% of the mass of the powder, and the binder was a 8wt% polyvinyl alcohol solution.

[0092] Molding: The granulated powder was placed into a die and pressed to obtain a green body under a pressure of 4Mpa.

[0093] Plastic removal: The green body was heated to 600℃ at a heating rate of 5℃ / min and held for 2 hours to remove organic matter.

[0094] Sintering: The green body after plastic removal was heated to 1100℃ at a heating rate of 3℃ / min and held for 2 hours, and then cooled in the furnace to obtain an NBT-based lead-free pyroelectric ceramic.

[0095] Electrode preparation: Silver paste was coated on the upper and lower surfaces of the NBT-based lead-free pyroelectric ceramic, and then heat-treated at a high temperature of 600℃ for 30min.

[0096] Polarization: The sample was placed in silicone oil and heated to 150℃, and the polarization electric field was set to 50 kV / cm for 15min, then increased to 80 kV / cm for 15min, and finally increased to 100 kV / cm for 15min.

[0097] The pyroelectric ceramic after polarization was tested, and the pyroelectric coefficient was p =126μC m -2 K -1 . The current response merit factor of the pyroelectricity was F i 0.52×10 -10 m V -1 , the voltage response merit factor of the pyroelectricity was F v 0.045×m 2 C -1 , and the detection rate merit factor of the pyroelectricity was F d 2.23×10 -5 Pa -1 / 2 .

[0098] Comparative Example 1:

[0099] Ingredients: high-purity Na2CO3, Bi2O3, TiO2, Li2CO3, CeO2 are mixed according to Na 0.5 Bi 4.5 Ti4O 15 The stoichiometric ratio is weighed and mixed to obtain a powder.

[0100] First ball milling: the above obtained powder is uniformly mixed by ball milling, and anhydrous ethanol with the same mass as the powder is used as a solvent, and ball milling is performed for 6 hours, and zirconium dioxide balls are used for ball milling. After ball milling, the slurry is dried.

[0101] Pre-sintering: the dried slurry is transferred to an alumina crucible, and a pre-sintered powder is obtained by pre-sintering. The pre-sintering temperature is 850°C, the heating rate is not higher than 5°C / min, and the holding time is 3 hours.

[0102] Second ball milling: the pre-sintered powder is subjected to secondary ball milling, and the powder is obtained by drying, and the ball milling conditions are the same as those of the first ball milling.

[0103] Granulation: a binder is added to the powder after the second ball milling for granulation, and the amount of the binder is 8% of the mass of the powder, and the binder is a 8wt% polyvinyl alcohol solution.

[0104] Molding: the granulated powder is placed in a die and pressed to form a green body under a pressure of 4Mpa.

[0105] Plastic removal: the green body is heated to 600°C at a heating rate of 5°C / min, and the organic matter is removed after holding for 2 hours.

[0106] Sintering: the green body after plastic removal is heated to 1100°C at a heating rate of 3°C / min, and held for 2 hours, and then cooled in the furnace to obtain an NBT-based lead-free pyroelectric ceramic.

[0107] Electrode preparation: silver paste is coated on the upper and lower surfaces of the NBT-based lead-free pyroelectric ceramic, and then heat treated at 600°C for 30 minutes.

[0108] Polarization: the sample is placed in silicone oil and heated to 150°C, the polarization electric field is set to 50 kV / cm, the pressure time is 15 minutes, then the voltage is increased to 80 kV / cm, and the pressure is maintained for 15 minutes, and finally the voltage is increased to 100 kV / cm, and the pressure is maintained for 15 minutes.

[0109] The polarized pyroelectric ceramic is tested, and the pyroelectric coefficient is p =50μC m -2 K -1 The current response merit factor of the pyroelectricity F i is 0.21×10 -10 m V -1 , and the voltage response merit factorF v 0.019 x m 2 C -1 , figure of merit F d 0.79 x 10 -5 Pa -1 / 2 .

[0110] Table 1 is the pyroelectric performance parameters of the polarized comparative examples and examples, as follows:

[0111]

[0112] Figures 1 to 5 The XRD patterns of the ceramic sheets prepared in Examples 1-4 and Comparative Example, respectively, can be seen from the XRD patterns that all the ceramic sheets have obvious (119) peaks, indicating that all are bismuth layer structures. In addition, the (200) / (020) peaks in different samples have different trends, and the peaks are obviously separated in the comparative example, and the separation gradually weakens with the increase of the Li and Ce doping amount, indicating that the crystal structure is obviously distorted with the incorporation of Li and Ce.

[0113] Figure 6 is the graph of the pyroelectric coefficient of Examples 1-4 and Comparative Example with temperature. The pyroelectric coefficient of the comparative example at room temperature is 50 μC m -2 K -1 , and the pyroelectric coefficient of Example 3 is 142 μC m -2 K -1 . It shows that the pyroelectric coefficient is effectively improved.

[0114] Figure 7 is the pyroelectric coefficient of Examples 1-4 and Comparative Example at room temperature after annealing at different temperatures. It can be shown that after annealing at 300℃, the pyroelectric coefficient does not attenuate. It shows that it can be packaged in surface mount form using reflow soldering process.

[0115] Table 1 summarizes the pyroelectric coefficient and pyroelectric quality factor of Examples 1-4 and Comparative Example, showing that the pyroelectric coefficient and the value of the pyroelectric quality factor are all improved after doping LiCe.

[0116] In summary, the present application provides such bismuth layer structure of sodium bismuth titanate-based lead-free pyroelectric ceramic, by introducing Li, Ce elements into the NBT matrix, lattice distortion is produced, which is more sensitive to temperature change. The pyroelectric performance is improved, combined with low dielectric loss, good pyroelectric quality factor value is obtained. At the same time, it has very high Curie temperature, which ensures that it does not depolarize during reflow soldering process, which is conducive to the realization of surface mount packaging technology, and realizes the miniaturization and integration of the device.

[0117] Obviously, various modifications and changes are possible in the present application without departing from the spirit and scope of the application. It is intended that the application encompass such modifications and changes as fall within the scope of the appended claims and their equivalents. The above-described embodiments are intended to be illustrative only. Changes can be made by one having ordinary skill in the art without departing from the spirit and scope of the application. Equivalents which do not depart from the spirit and scope of the application are intended to be covered.

Claims

1. A bismuth-layered sodium titanate-based lead-free pyroelectric ceramic material, characterized in that, The chemical formula of this pyroelectric ceramic material is Na. 0.5 Bi 4.5-x (Li 1 / 3 Ce 2 / 3 ) x Ti4O 15 ,in x The value ranges from 0.025 to 0.

1.

2. The bismuth-layered sodium titanate-based lead-free pyroelectric ceramic material according to claim 1, characterized in that, The pyroelectric ceramic material has a relative permittivity of 100-150 and a dielectric loss of less than or equal to 0.006 under test conditions of 25°C and 1kHz.

3. The bismuth-layered sodium titanate-based lead-free pyroelectric ceramic material according to claim 1, characterized in that, The pyroelectric ceramic material has a Curie temperature higher than 600℃; and at 25℃, its pyroelectric coefficient is 70–150 μC / m. -2 K -1 The figure of merit of the current response of pyroelectricity is (0.3~0.6)×10 -10 m V -1 The voltage response figure of merit is 0.02 to 0.05m. 2 C -1 The detectivity figure of merit is (1.6–4) × 10⁻⁶. -5 Pa -1 / 2 .

4. The method for preparing the bismuth layered sodium titanate-based lead-free pyroelectric ceramic material according to any one of claims 1-3, characterized in that, The method includes the following steps: (1) According to Na 0.5 Bi 4.5-x (Li 1 / 3 Ce 2 / 3 ) x Ti4O 15 Na2CO3, Bi2O3, Li2CO3, CeO2 and TiO2 were weighed out according to the stoichiometric ratio, mixed, ball-milled once, and dried to obtain mixed powder; (2) The mixed powder is subjected to pre-firing, secondary ball milling, drying, granulation after adding binder, molding, plasticizing and sintering to obtain ceramic sheets; (3) Coat both sides of the ceramic sheet with silver paste, fire and shape it, place it in silicone oil and apply pressure to polarize it, so as to obtain the bismuth layered structure sodium titanate-based lead-free pyroelectric ceramic material.

5. The method for preparing the bismuth layered sodium titanate-based lead-free pyroelectric ceramic material according to claim 4, characterized in that, The conditions for the first ball milling and the second ball milling are the same: anhydrous ethanol is used as the solvent, the ball milling speed is set to 200-400 r / min, and the ball milling time is 6-24 hours.

6. The method for preparing the bismuth layered sodium titanate-based lead-free pyroelectric ceramic material according to claim 4, characterized in that, The pre-firing conditions are: heating at 3-5℃ / min to 600-900℃ and holding for 1-5 hours; the descaling conditions are: heating at 0.5-2℃ / min to 500-650℃ and holding for 1-5 hours; and the sintering conditions are: heating at 1-5℃ / min to 900-1200℃ and holding for 1-5 hours.

7. The method for preparing the bismuth layered sodium titanate-based lead-free pyroelectric ceramic material according to claim 4, characterized in that, The firing and shaping conditions are to hold the temperature at 500–700°C for 10–30 minutes.

8. The method for preparing the bismuth layered sodium titanate-based lead-free pyroelectric ceramic material according to claim 4, characterized in that, The polarization conditions are as follows: place the product in silicone oil and heat it to 150°C, set the polarization electric field to 50 kV / cm, pressurize for 10-15 min, then increase the pressure to 80 kV / cm and hold for 10-15 min, and finally increase the pressure to 100 kV / cm and hold for 10-15 min.

9. The method for preparing the bismuth layered sodium titanate-based lead-free pyroelectric ceramic material according to claim 4, characterized in that, The method further includes: after obtaining the bismuth layered sodium titanate-based lead-free pyroelectric ceramic material, heat treatment is performed on it, specifically: the polarized bismuth layered sodium titanate-based lead-free pyroelectric ceramic material is placed in an annealing furnace at 300°C, held for 5 to 15 minutes, and then taken out and allowed to cool naturally.

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