A BNT-based lead-free pyroelectric ceramic material, its preparation method and application

Abstract

This invention relates to a BNT-based lead-free pyroelectric ceramic material, its preparation method, and its application. The chemical composition of the BNT-based lead-free pyroelectric ceramic material is: (Bi... 0.5 Na 0.5 TiO3-xMnO 2‑δ , where 0.1 mol% ≤ x ≤ 1.3 mol%, and 0.5 ≤ δ ≤ 1.

Description

Technical Field

[0001] This invention relates to a low dielectric loss (Bi) 0.5 Na 0.5 TiO3-based lead-free pyroelectric ceramic materials, their preparation methods, and applications belong to the field of infrared detection materials. Background Technology

[0002] Over the past few decades, pyroelectric materials have been widely used in infrared detectors. Uncooled infrared detection technology, due to its advantages such as no need for cooling, wide response spectrum, fast response speed, all-weather operation, low cost and low power consumption, and wide applicability, has become one of the most eye-catching technologies in current infrared focal plane imaging technology. It plays an irreplaceable role in military, defense, aerospace, industry, medical and daily life applications. The working principle of uncooled infrared detection technology is as follows: After the detector receives radiation, it can convert the radiation energy into heat energy, which causes the temperature of the sensitive element to rise. The temperature change causes the polarization intensity of the pyroelectric material in the sensitive element to change. Through a certain conversion mechanism, this can be converted into an electrical signal, which is then amplified to achieve object detection. Pyroelectric materials, as the core materials of the sensitive element of infrared detectors, are mainly divided into two types: dielectric thermal radiation pyroelectric materials and intrinsic pyroelectric materials. Among them, intrinsic pyroelectric materials mainly utilize the pyroelectric effect generated by the change of spontaneous polarization with temperature. They do not require an external electric field, have good temperature stability near room temperature, are reversible, and are conducive to miniaturization, making them the future development direction.

[0003] For practical applications, intrinsic pyroelectric materials need to meet three performance requirements: a large pyroelectric coefficient (p), a large figure of merit (FOMs) for pyroelectric detection, and excellent thermal stability. Currently, the most widely used intrinsic pyroelectric materials are perovskite-type lead-containing materials, such as lead zirconate titanate (PZT), Ca-doped lead titanate (PCT), and lead magnesium niobate-lead nickel niobate (PMN-PT). However, these materials contain large amounts of lead, posing long-term hazards to the environment and human health. Following the enactment of the EU's RoHS (Restriction of Hazardous Substances Directive) and WEEE (Waste Electrical and Electronic Equipment Directive), countries worldwide have also introduced various policies to restrict the use of toxic substances in electronic devices. Against this backdrop, there is an urgent need to develop lead-free pyroelectric materials that can replace lead-based materials. In recent years, the pyroelectric properties and potential applications of some lead-free pyroelectric material systems have attracted researchers' attention, including K... 0.5 Na 0.5 NbO3-based, BaTiO3-based, SrBaNb2O6-based, and Bi 0.5 Na 0.5 TiO3-based systems, such as Bi. 0.5 Na0.5 TiO3 has attracted widespread attention from researchers due to its high pyroelectric coefficient and depolarization temperature. However, during modification, the increase in pyroelectric coefficient is often accompanied by a decrease in depolarization temperature, which is extremely detrimental to the material's performance. This is because the material undergoes a high-temperature process during processing, and a low depolarization temperature can lead to material failure. For example, when the BT content is 0.06%, 0.94BNT-0.06BT is located at the MPB phase boundary, and the pyroelectric coefficient of the material can be increased to 3.15 × 10⁻⁶. -8 Ccm -2 K -1 However, its depolarization temperature is only 115℃. Although lead-free materials have made great progress in pyroelectric performance, their performance still cannot match that of lead-containing PZT materials. Therefore, further optimization of performance is needed to obtain lead-free pyroelectric materials that combine excellent pyroelectric performance with good temperature stability. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a BNT-based lead-free pyroelectric ceramic material with both excellent pyroelectric properties and good temperature stability, as well as its preparation method and application.

[0005] On one hand, the present invention provides a BNT-based lead-free pyroelectric ceramic material, wherein the chemical composition of the BNT-based lead-free pyroelectric ceramic material is: (Bi 0.5 Na 0.5 TiO3-xMnO 2-δ , where 0.1mol%≤x≤1.3mol%, 0.5≤δ≤1.

[0006] This invention designs (Bi) 0.5 Na 0.5 TiO3-xMnO 2-δ This invention yields a BNT-based lead-free pyroelectric ceramic material with high pyroelectric performance, low dielectric loss, and high depolarization temperature, which is expected to be applied in the field of uncooled infrared pyroelectric detection. The invention selects BNT, which has high pyroelectric performance, as the matrix material. Doping with Mn further enhances its ferroelectric properties while reducing the dielectric constant and loss of the ceramic. Therefore, the ceramic of this composition possesses both high pyroelectric performance and excellent temperature stability, making it a promising candidate for uncooled infrared pyroelectric detection.

[0007] Preferably, 0.1 mol % ≤ x ≤ 0.6 mol %.

[0008] Preferably, the BNT-based lead-free pyroelectric ceramic material has a relative permittivity of 290–390 (preferably 290–330) and a dielectric loss of <0.025 (preferably ≤0.015) under test conditions of 25°C and 1 kHz.

[0009] Preferably, the pyroelectric coefficient of the BNT-based lead-free pyroelectric ceramic material is (2.4–4.7) × 10⁻⁶. -8 Ccm - 2 K -1 pyroelectric voltage response figure of merit F v (3.1~6.0)×10 -2 m 2 C -1 Detection rate figure of merit F d It is (0.8~3.1)×10 -5 Pa -1 / 2 Preferably, the pyroelectric coefficient of the BNT-based lead-free pyroelectric material is (2.4–3.9) × 10⁻⁶. -8 Ccm -2 K -1 pyroelectric current response figure of merit F i It is (0.8~1.7)×10 -10 mV -1 Voltage figure of merit F v It is (3.1~4.7)×10 -2 m 2 C -1 .

[0010] On the other hand, the present invention provides a method for preparing the above-mentioned BNT-based lead-free pyroelectric ceramic material, comprising:

[0011] (1) Weigh and mix Bi source, Na source and Ti source according to the chemical composition stoichiometry of the BNT-based lead-free pyroelectric ceramic material, and calcine to obtain the early solid solution powder;

[0012] (2) The initial solid solution powder is mixed with the Mn source to obtain the final solid solution powder;

[0013] (3) The resulting final solid solution powder is mixed with a binder and granulated, then aged, shaped and extruded to obtain a ceramic blank;

[0014] (4) The obtained ceramic blank is sintered to obtain the BNT-based lead-free pyroelectric ceramic material.

[0015] Preferably, the Bi source is Bi2O3 powder; the Na source is NaHCO3 powder; the Ti source is TiO2 powder; and the Mn source is MnCO3 powder.

[0016] Preferably, the calcination temperature is 600℃~1200℃ (preferably 600~1000℃), and the time does not exceed 24 hours.

[0017] Preferably, the binder is at least one selected from polyvinyl alcohol, polyethylene glycol, polystyrene, and methylcellulose, and is added in an amount of 6-8 wt.% of the solid solution powder.

[0018] The aging temperature is room temperature, and the time is 18 to 26 hours (preferably 22 to 26 hours).

[0019] The temperature for plastic discharge is 650–850°C, and the time is 1–3 hours.

[0020] Preferably, the sintering temperature is 1000–1300°C and the time does not exceed 24 hours.

[0021] Thirdly, the present invention provides a pyroelectric ceramic element prepared from the above-mentioned BNT-based lead-free pyroelectric ceramic material.

[0022] Beneficial effects:

[0023] The BNT-based lead-free pyroelectric ceramic material prepared by this invention exhibits excellent performance and good temperature stability, making it promising for application in uncooled infrared detection. The polarized BNT-based lead-free pyroelectric ceramic material has a relative permittivity of 290–330 and a dielectric loss of less than 0.015 at a test frequency of 1 kHz and a test temperature of 25 °C. The pyroelectric coefficient of the polarized BNT-based lead-free pyroelectric ceramic material is (2.4–4.7) × 10⁻¹⁰. -8 Ccm -2 K -1 The figure of merit of the pyroelectric current response is (0.8~1.7)×10. -10 mV -1 The figure of merit of the pyroelectric voltage response is (3.1~6.0)×10. -2 m 2 C -1 The detectivity figure of merit is (3.3~8.7)×10. -5 Pa -1 / 2 In this disclosure, the depolarization temperature of BNT-based lead-free pyroelectric ceramic materials is generally higher than 150°C, and can reach up to 205°C. Attached Figure Description

[0024] Figure 1 To implement the quasi-static method for testing the pyroelectric coefficient of BNT-based lead-free pyroelectric ceramic materials after polarization treatment in sections 1-4, we present the temperature variation curves. Detailed Implementation

[0025] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0026] In this disclosure, the manganese-doped bismuth sodium titanate (BNT) lead-free pyroelectric ceramic material (BNT-based lead-free pyroelectric ceramic material) exhibits high pyroelectric performance and high depolarization temperature, and its chemical composition is: (Bi 0.5 Na 0.5 TiO3-xMnO 2-δ Where 0.1%≤x≤1.3%, x is the molar ratio, and 0.5≤δ≤1. The addition of Mn will increase the pyroelectric coefficient; therefore, the selection of x is mainly based on ensuring a relatively high pyroelectric coefficient while obtaining a relatively high T. d .

[0027] In an optional embodiment, the BNT-based lead-free pyroelectric ceramic material exhibits a high pyroelectric coefficient (2.4–4.7 × 10⁻⁶) near room temperature (25°C). -8 Ccm -2 K -1 It has a low relative permittivity (290-330), low dielectric loss (≤0.015), and excellent and stable pyroelectric performance over a wide temperature range (the detectivity figure of merit varies by ≤15% in the range of 20-80℃), making it a promising candidate for application in the field of uncooled infrared pyroelectric detection.

[0028] In a more preferred embodiment, when x = 0.184%, the material Bi 0.5 Na 0.5 TiO3-0.184%MnO 2-δ It possesses both excellent pyroelectric properties and temperature stability, with a pyroelectric coefficient p reaching 3.17 × 10⁻⁶. -8 Ccm -2 K -1 T d Temperatures can reach up to 205℃. When x = 0.553%, the Bi content of this material... 0.5 Na 0.5 TiO3-0.553%MnO 2-δ It possesses both excellent pyroelectric properties and temperature stability, with a pyroelectric coefficient p reaching 3.58 × 10⁻⁶. -8 Ccm -2 K -1 T d It can reach temperatures as high as 195℃.

[0029] In this disclosure, BNT-based lead-free pyroelectric ceramic materials are prepared through steps including ingredient preparation, mixing, synthesis, fine grinding, molding, plasticizing, and sintering. The following exemplarily illustrates the preparation method of the BNT-based lead-free pyroelectric ceramic materials provided by this invention.

[0030] Solid-phase preparation (Bi) 0.5 Na 0.5 TiO3-xMnO 2-δThe content of the mixture is 0.1% ≤ x ≤ 1.3%. Bi, Na, and Ti sources are mixed according to the stoichiometric ratio of the BNT-based lead-free pyroelectric ceramic material, and then calcined to obtain ceramic powder. Mn source is then added to the ceramic powder according to the stoichiometric ratio of the chemical composition, and mixed evenly to obtain ceramic powder again. In optional embodiments, the Bi source can be Bi₂O₃, etc. The Na source can be NaHCO₃, etc. The Ti source can be TiO₂, etc. The Mn source can be MnCO₃, etc. In optional embodiments, the calcination temperature is 600–1000°C, and the time is less than 24 hours. Preferably, the calcination temperature is 700–900°C, and the time is 1–3 hours. The heating rate during calcination is no higher than 2°C / min. After calcination, the mixture is cooled to room temperature in the furnace.

[0031] In an optional embodiment, the ceramic powder can also be pressed into shape before calcination, at a pressure of 4–6 MPa. As an example, Bi₂O₃, NaHCO₃, and TiO₂ are prepared according to the stoichiometric ratio of BNT-based lead-free pyroelectric ceramic material to obtain a mixed powder (raw material). The mixed powder is ball-milled, pressed into shape, and calcined to obtain block ceramic. The block material is ground into powder, mixed with MnCO₃, and then ball-milled and dried to obtain ceramic powder. In an optional embodiment, the mixing method for the primary and secondary ball milling is wet ball milling. As an example of wet ball milling, the mixing time is 20–26 hours according to the mass ratio of raw material:balls:alcohol = 1:(3–5):(0.6–1.0). The ball milling media used in the wet ball milling method is zirconium balls. In this disclosure, the ceramic powder has a small particle size and narrow particle size distribution.

[0032] Preparation of ceramic green bodies. A binder is added to ceramic powder, and the mixture is granulated to obtain granulated powder. The granulated powder is then aged, shaped, and desizing to obtain ceramic green bodies. In optional embodiments, the binder may be polyvinyl alcohol (PVA), polyethylene glycol, polystyrene, or methylcellulose, etc. The amount of binder added may be 6-8 wt.% of the weight of the ceramic powder. In optional embodiments, the desizing conditions may be: heating to 700-900°C at a heating rate not exceeding 2°C / min, and then holding at that temperature for 1-3 hours. In optional embodiments, the aging temperature is room temperature (e.g., room temperature 25°C), and the time is 22-26 hours. As an example, a binder is added to ceramic powder that has undergone secondary ball milling and drying, followed by granulation, aging, and pressing, and then desizing to obtain ceramic green bodies. In optional embodiments, before aging, the granulated powder may be pressed into shape at a pressure of 4-6 MPa. After aging, it is pressed and shaped under pressure of 1.4 to 1.6 MPa.

[0033] BNT-based lead-free pyroelectric ceramic materials are obtained by sintering a ceramic green blank. In optional embodiments, the sintering temperature can be 1000–1300°C, and the time can be less than 24 hours. Preferably, the sintering temperature is 1000–1200°C, and the time is 1–3 hours. The heating rate during sintering is no higher than 2°C / min. After sintering, the green blank is cooled to room temperature in the furnace. Alternatively, the ceramic green blank can be placed in a high-temperature furnace (sintering furnace), first covered with ceramic powder having the same composition as the ceramic powder, and then sintered to obtain BNT-based lead-free pyroelectric ceramic materials.

[0034] BNT-based lead-free pyroelectric ceramic material is processed to the required size, ultrasonically cleaned, silver-coated using a screen, dried, and then calcined to obtain the pyroelectric ceramic element. The calcination conditions are 700–800℃ and held for 5–40 minutes.

[0035] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0036] Example 1: The material composition is (Bi) 0.5 Na 0.5 TiO3-0.184 mol%MnO 2-δ

[0037] (1) Using Bi2O3, NaHCO3, and TiO2 powders as raw materials, the mixture was prepared according to the stoichiometric ratio and mixed by wet ball milling at a mass ratio of raw material:ball:alcohol = 1:4:1 for 24 hours to ensure uniform mixing of all components. After drying, the mixture was passed through a 40-mesh sieve, pressed into large blocks at 5 MPa, and heated to 850°C at a heating rate not exceeding 2°C / min, and held at that temperature for 2 hours to synthesize ceramic powder.

[0038] (2) Grind the ceramic powder from step (1) and pass it through a 40-mesh sieve. Mix MnCO3 with the ceramic powder at a molar ratio (0.184%), and then further mix the powder evenly by wet ball milling. Grind the powder for 24 hours at a mass ratio of raw material:ball:alcohol = 1:4:1. Dry the finely ground ceramic powder. Then add 7wt.% PVA binder, granulate, press and age for 24 hours, pass through a 40-mesh sieve, press and shape under a pressure of 1.4-1.6MPa, and then heat to 800℃ and hold for 2 hours to remove the plastic, thus obtaining a ceramic green body.

[0039] (3) Place the ceramic blank into an alumina crucible. In order to prevent the volatilization of elements such as bismuth and sodium, cover the blank with ceramic powder with the same composition as in step (1), cover it with a ground end plate, raise the temperature to 1140°C at a heating rate of 2°C / min, hold for 2 hours, and cool with the furnace to obtain BNT-based lead-free pyroelectric ceramic material.

[0040] (4) Grind the sintered ceramic sheet to 0.5 mm, clean it, dry it, screen print silver paste, dry it again, raise the temperature to 800°C at a rate of 2°C / min, hold it for 30 minutes and fire it to obtain the pyroelectric ceramic element.

[0041] The pyroelectric ceramic element prepared in Example 1 was polarized under the following conditions: 100℃, 7kV / mm voltage, and polarization time of 30 min. To ensure sufficient polarization, a voltage holding and cooling method was adopted. The dielectric and pyroelectric properties of the polarized ceramic were tested, and the results are shown in Table 1. Figure 1 .

[0042] Example 2: The material composition is (Bi) 0.5 Na 0.5 TiO3-0.553 mol%MnO 2-δ

[0043] The polarized pyroelectric ceramic element was obtained by repeating the preparation method of Example 1 according to the above formula.

[0044] The dielectric and pyroelectric properties of the polarized pyroelectric ceramic element were tested, and the results are shown in Table 1. Figure 1 This component still exhibits high pyroelectric properties near room temperature, with a pyroelectric coefficient p reaching 3.581 × 10⁻⁶. -8 Ccm -2 K -1 pyroelectric current response figure of merit F i It is 1.269×10 -10 mV -1 pyroelectric voltage response figure of merit F v It is 4.781×10 -2 m 2 C -1 Detection rate figure of merit F d It is 2.549×10 -5 Pa -1 / 2 Meanwhile, the pyroelectricity remains stable within the range of 20–80℃, and the depolarization temperature of the material can reach 186℃.

[0045] Example 3: The material composition is (Bi) 0.5 Na 0.5 TiO3-0.922 mol%MnO 2-δThe polarized pyroelectric ceramic element was obtained by repeating the preparation method of Example 1 according to the above formula.

[0046] The dielectric and pyroelectric properties of the polarized pyroelectric ceramic element were tested, and the results are shown in Table 1. Figure 1 This component still exhibits high pyroelectric properties near room temperature, with a pyroelectric coefficient p reaching 3.590 × 10⁻⁶. -8 Ccm -2 K -1 pyroelectric current response figure of merit F i It is 1.278×10 -10 mV -1 pyroelectric voltage response figure of merit F v It is 4.426×10 -2 m 2 C -1 Detection rate figure of merit F d 2.492×10 -5 Pa -1 / 2 Meanwhile, the pyroelectricity remains stable within the range of 20–80℃, and the depolarization temperature of the material can reach 186℃.

[0047] Example 4: The material composition is (Bi) 0.5 Na 0.5 TiO3-1.291 mol% MnO 2-δ The polarized pyroelectric ceramic element was obtained by repeating the preparation method of Example 1 according to the above formula.

[0048] The dielectric and pyroelectric properties of the polarized pyroelectric ceramic element were tested, and the results are shown in Table 1. Figure 1 This component exhibits optimal overall pyroelectric performance, maintaining high pyroelectric activity even near room temperature. The pyroelectric coefficient p reaches 4.643 × 10⁻⁶. -8 Ccm -2 K -1 pyroelectric current response figure of merit F i 1.652×10 -10 mV -1 The pyroelectric voltage response figure of merit Fv is 5.989 × 10⁻⁶. -2 m 2 C -1 Detection rate figure of merit F d It is 2.751×10 -5 Pa -1 / 2 Meanwhile, the pyroelectricity remains stable within the range of 20–80℃, and the depolarization temperature of the material can reach 182℃.

[0049] Comparative Example 1: The material composition is (Bi) 0.5 Na 0.5 TiO3

[0050] The polarized pyroelectric ceramic element was obtained by repeating the preparation method of Example 1 according to the above formula. The dielectric and pyroelectric properties of the polarized pyroelectric ceramic element were tested, and the results are shown in Table 1.

[0051] Figure 1 The figures shown are the temperature-dependent curves of the BNT-based lead-free pyroelectric coefficient, tested using a quasi-static method after polarization treatment in Examples 1-4. Figure 1 It can be seen from this that the series of component ceramics has a high pyroelectric coefficient p of (3.2~4.7)×10 -8 Ccm -2 K -1 It remains stable within the temperature range of 20–80℃.

[0052] Table 1 lists the dielectric and pyroelectric properties of the polarized BNT-based lead-free pyroelectric ceramic materials prepared in Examples 1-4 and Comparative Examples 1-2, respectively.

[0053] Table 1 shows the dielectric parameters of the polarized BNT-based lead-free pyroelectric ceramic materials:

[0054] sample <![CDATA[ε r (1kHz)]]> Tanδ(1kHz) <![CDATA[p(10 -4 Cm -2 K -1 )]]> <![CDATA[F i (10 -10 m / V)]]> <![CDATA[F v (10 -2 m 2 / C)]]> <![CDATA[F d (10 -5 Well -1 / 2 )]]> Td(℃) Example 1 292 0.0117 3.168 1.127 4.370 1.861 205 Example 2 310 0.0113 3.581 1.269 4.781 2.549 195 Example 3 321 0.0110 3.590 1.278 4.426 2.492 186 Example 4 311 0.0112 4.643 1.652 5.989 2.751 182 Comparative Example 1 397 0.0231 2.301 0.971 2.330 0.909 193

Claims

1. A BNT-based lead-free pyroelectric ceramic material, characterized by, The BNT-based lead-free pyroelectric ceramic material has a chemical composition of: (Bi 0.5 Na 0.5 )TiO3-xMnO 2-δ wherein 0.184 mol %≤x≤1.291 mol %, 0.5≤δ≤1. The pyroelectric coefficient of the BNT-based lead-free pyroelectric ceramic material is (3.168-4.643) x 10 -8 C cm -2 K -1 , and the depolarization temperature is 182-205 DEG C.

2. The BNT-based lead-free pyroelectric ceramic material of claim 1, wherein, The BNT-based lead-free pyroelectric ceramic material has a relative dielectric constant of 290-390 and a dielectric loss of <0.025 under a test condition of 25 DEG C and 1 kHz.

3. The BNT-based lead-free pyroelectric ceramic material according to claim 1 or 2, characterized in that, The pyroelectric current response merit factor F of the BNT-based lead-free pyroelectric material i is (0.8-1.7) x 10 -10 mV -1 , the voltage merit factor F v is (3.1-6.0) x 10 -2 m 2 C -1 , the detectivity merit factor F d is (0.8-3.1) x 10 -5 Pa -1 / 2 .

4. A method of producing the BNT-based lead-free pyroelectric ceramic material according to any one of claims 1 to 3, characterized by, The method comprises the following steps: (1) measuring and mixing Bi source, Na source and Ti source according to the stoichiometric ratio of the chemical composition of the BNT-based lead-free pyroelectric ceramic material, and calcining to obtain a pre-stage solid solution powder; (2) mixing the pre-stage solid solution powder with a Mn source to obtain a final solid solution powder; (3) mixing the obtained final solid solution powder with a binder and granulating, aging, molding and plastic removal to obtain a ceramic green body; (4) sintering the obtained ceramic green body to obtain the BNT-based lead-free pyroelectric ceramic material.

5. The preparation method according to claim 4, characterized in that, The Bi source is Bi2O3 powder; the Na source is NaHCO3 powder; the Ti source is TiO2 powder; and the Mn source is MnCO3 powder.

6. The preparation method according to claim 4, characterized in that, The calcining temperature is 600 DEG C-1200 DEG C, and the time is not more than 24 hours.

7. The preparation method according to claim 4, characterized in that, The binder is at least one of polyvinyl alcohol, polyethylene glycol, polystyrene and methyl cellulose, and the addition amount is 6-8 wt.% of the solid solution powder; The aging temperature is room temperature, and the time is 18-26 hours; The plastic removal temperature is 650 DEG C-850 DEG C, and the time is 1-3 hours.

8. The preparation method according to claim 4, characterized in that, The sintering temperature is 1000 DEG C-1300 DEG C, and the time is not more than 24 hours.

9. A pyroelectric ceramic element, characterized by, The BNT-based lead-free pyroelectric ceramic material is prepared by the method according to any one of claims 1-3.

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