BNT-based lead-free ferroelectric ceramic material with high pyroelectric coefficient as well as preparation method and application of BNT-based lead-free ferroelectric ceramic material

Abstract

The invention belongs to the field of functional ceramics, and particularly relates to a BNT-based pyroelectric ceramic material as well as a preparation method and application thereof. In order to obtain a lead-free pyroelectric material with excellent pyroelectric performance and good temperature stability, the invention provides a BNT-based lead-free pyroelectric ceramic material, the chemical composition of the BNT-based lead-free pyroelectric material is (Bi < 0.5-x > Pr < x > Na < 0.5 >) TiO < 3-y > wt% MnO2, x is more than or equal to 0.01 and less than or equal to 0.04, and y is more than 0 and less than or equal to 0.1. BNT is selected as a base material, the Pr element is doped, the pyroelectric coefficient can be improved, and the lead-free pyroelectric infrared detector is expected to be applied to the field of lead-free pyroelectric infrared detection.

Description

Technical Field

[0001] The present invention belongs to the field of functional ceramics, and specifically relates to a BNT-based pyroelectric ceramic material and a preparation method and application thereof, especially for lead-free BNT-based pyroelectric ceramic elements and ceramic elements for pyroelectric infrared detectors. Background Art

[0002] Over the past few decades, pyroelectric materials have been widely used in infrared detectors. Uncooled infrared detection technology has become one of the most compelling technologies in infrared focal plane imaging due to its advantages, including the lack of cooling, wide response spectrum, fast response speed, all-weather operation, low cost and power consumption, and miniaturization for wide application. It is widely used in military, defense, aerospace, industry, medicine, and daily life, playing an irreplaceable role. The operating principle of uncooled infrared detection technology is that after receiving radiation, the detector converts the radiation energy into heat, causing the temperature of the sensitive element to rise. This temperature change causes a change in the polarization intensity of the pyroelectric material in the sensitive element. This change is converted into an electrical signal through a certain conversion mechanism and then passed through a signal amplifier to detect objects. Pyroelectric materials, as the core materials of infrared detector sensors, are mainly divided into two types: dielectric thermal radiation pyroelectric materials and intrinsic pyroelectric materials. Intrinsic pyroelectric materials mainly utilize the pyroelectric effect caused by the spontaneous polarization change 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 pyroelectric detectivity figure of merit (FOMs) 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), lead magnesium niobate-lead nickel niobate (PMN-PT), etc. However, these materials contain a large amount of lead, which has long-term harm to the environment and human health. After the European Union promulgated the RoSH (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment) and WEEE (Waste Electrical and Electronic Equipment Directive) laws, countries around the world have also successively introduced various policies to restrict the use of toxic substances in electronic devices. Based on this environmental background, there is an urgent need to develop lead-free pyroelectric materials that can replace lead-based ones. In recent years, the pyroelectric properties and potential applications of some lead-free pyroelectric material systems have attracted the attention of researchers, including K 0.5 Na 0.5 NbO3-based, BaTiO3-based, SrBaNb2O6-based and Bi 0.5 Na 0.5 TiO3 based systems. 0.5 Na 0.5TiO3 has attracted extensive attention from researchers due to its high pyroelectric coefficient and depolarization temperature. However, during the modification process, the increase in pyroelectric coefficient is often accompanied by a decrease in depolarization temperature, which is extremely detrimental to the performance of the material because the material will experience high temperatures during processing, and low depolarization temperature will lead to material failure. For example, when the BT content is 0.06, 0.94BNT-0.06BT is at the MPB phase boundary, at which point the pyroelectric coefficient of the material can be increased to 3.15×10 -8 Ccm -2 K -1 , but the depolarization temperature is only 115°C. Although lead-free materials have made great progress in pyroelectric performance, their performance is still not comparable to that of lead-containing PZT materials. Therefore, further performance optimization is needed to obtain lead-free pyroelectric materials with both excellent pyroelectric performance and good temperature stability. Summary of the Invention

[0004] To address the above issues, the present invention aims to provide a BNT-based ferroelectric ceramic material for pyroelectric applications, its preparation method, and ceramic components. Designed with Pr doping, it offers simple composition and excellent performance, providing an alternative material for lead-free pyroelectric infrared detectors.

[0005] On the one hand, the present invention provides a BNT-based lead-free pyroelectric ceramic material, the chemical composition of the BNT-based lead-free pyroelectric material is (Bi 0.5-x Pr x Na 0.5 )TiO3-ywt%MnO2, where 0.01≤x≤0.04, 0<y≤0.1.

[0006] The present invention is designed (Bi 0.5-x Pr x Na 0.5 )TiO3-ywt% MnO2 composition, resulting in a BNT-based lead-free pyroelectric ceramic material with a high pyroelectric coefficient, which is expected to be used in the field of lead-free pyroelectric infrared detection. The present invention uses BNT as the matrix material and doping it with the element Pr can increase the pyroelectric coefficient, which is expected to be used in the field of lead-free pyroelectric infrared detection.

[0007] Preferably, 0.01≤x≤0.03; or / and, y=0.0756.

[0008] Preferably, the BNT-based lead-free pyroelectric ceramic material has a relative dielectric constant of 300 to 900 and a dielectric loss of less than 0.10 under test conditions of 25° C. and 1 kHz.

[0009] In another aspect, the present invention provides a method for preparing a BNT-based lead-free pyroelectric ceramic material, comprising: (1) weighing a Bi source, a Pr source, a Na source, and a Ti source according to the chemical composition of the BNT-based lead-free pyroelectric ceramic material, mixing the mixture, and calcining the mixture to obtain a solid solution powder; (2) mixing the solid solution powder and the Mn source to obtain a mixed powder; (3) mixing the obtained mixed powder with a binder, granulating, aging, molding and molding to obtain a ceramic green body; (4) Sintering the obtained ceramic body to obtain the BNT-based lead-free pyroelectric ceramic material.

[0010] Preferably, in step (1): the Bi source is Bi2O3; the Pr source is Pr6O 11 ; The Na source is NaHCO3; The Ti source is TiO2.

[0011] Preferably, in step (1), the calcination temperature is 600° C. to 1000° C., and the calcination time does not exceed 24 hours.

[0012] Preferably, in step (2): the Mn source is MnCO3.

[0013] Preferably, in step (3): the binder is at least one of polyvinyl alcohol, polyethylene glycol, polystyrene and methyl cellulose; the amount of the binder added is 6 to 8 wt.% of the mixed powder; The aging temperature is room temperature and the time is 18 to 26 hours; The temperature of the plastic removal is 650-850° C., and the time is 1-3 hours.

[0014] Preferably, in step (4): the sintering temperature is 1000-1300°C and the sintering time does not exceed 24 hours.

[0015] In another aspect, the present invention provides a ceramic component made of the BNT-based lead-free pyroelectric ceramic material.

[0016] Preferably, the ceramic material is processed into a desired size and then silvered and sintered to obtain the ceramic material.

[0017] Beneficial effects of the present invention: The technical solution of the present invention prepares lead-free BNT-based pyroelectric ceramics with high pyroelectric coefficients through component regulation and process optimization. Measurements show that the lead-free BNT-based pyroelectric ceramics have the characteristics of high pyroelectric coefficients and high depolarization temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is Example 1 of the present invention (Bi 0.48 Pr 0.02 Na 0.5)TiO3-0.0756%MnO2, Example 2 (Bi 0.49 Pr 0.01 Na 0.5 )TiO3-0.0756%MnO2, Example 3 (Bi 0.47 Pr 0.03 Na 0.5 )TiO3-0.0756%MnO2, Comparative Example 1 (Bi 0.46 Pr 0.04 Na 0.5 ) X-ray diffraction pattern of TiO3-0.0756% MnO2; Figure 2 1 is a comparison diagram of hysteresis loops of Example 1, Example 2, Example 3, and Comparative Example 1 of the present invention; Figure 3 4 is a comparison chart of pyroelectric coefficients of Examples 1, 2 and 3 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0020] In the present disclosure, the chemical composition of the BNT-based pyroelectric ceramic material is (Bi 0.5-x Pr x Na 0.5 )TiO3-y wt% MnO2, where 0.01≤x≤0.04, x is a molar percentage; preferably 0.06≤y≤0.08, y is a mass percentage. The present invention addresses the pyroelectric properties of BNTs by using Pr doping to disrupt the long-range order of the BNTs, enhancing the activity of the polar nanodomains and thereby improving the pyroelectric coefficient.

[0021] Theoretical research and multiple experimental verifications have shown that the ferroelectric properties of BNT-based ceramics can be achieved by small-scale substitution, given the similar ionic radii of Pr and Bi. A square hysteresis loop can be observed within the composition range of 0.01 ≤ x ≤ 0.03, demonstrating typical ferroelectric characteristics, high remanent polarization, and a high depolarization temperature.

[0022] The preparation method of the BNT-based pyroelectric ceramic material disclosed herein can be prepared through a solid-phase reaction process, which may include, for example, batching, mixing, briquetting, synthesis, pulverization, fine grinding, molding, demolding, and sintering. The following describes an exemplary preparation method for the BNT pyroelectric ceramic material.

[0023] The solid phase method is used to prepare ceramic powder. Specifically, Na source, Pr source, Bi source and Ti source are added in the form of (Bi 0.5- xPr x Na0.5)TiO3-0.0756%MnO2 are uniformly mixed in a stoichiometric ratio to synthesize the required ceramic powder. The Bi source can be Bi2O3. The Pr source can be Pr6O 11 The Na source may be NaHCO 3 . The Ti source may be TiO 2 .

[0024] In an optional embodiment, the raw materials can be uniformly mixed using ball milling. The mass ratio of raw materials: balls: alcohol can be 1:(4-8):(0.8-1.3). The ball milling medium can be zirconium balls, agate balls, etc. The ball milling (mixing) time can be 24-48 hours. After ball milling, the raw materials can be dried and sieved (e.g., 20-80 mesh). After drying, the raw materials can be briquette-pressed, for example, at a pressure of 100-300 MPa.

[0025] In an alternative embodiment, the synthesis (calcination) temperature may be 800-1000°C. Preferably, the temperature is raised to the synthesis temperature at a rate of no more than 2°C / min. This allows the reaction to fully occur. The holding time at the synthesis temperature may be 1-24 hours, preferably 2-6 hours.

[0026] After calcination, the powder can be cooled to room temperature in the furnace. The resulting powder can be placed in a sealed container (e.g., a sealed alumina crucible) for synthesis, thereby reducing the volatilization of Bi and Na components and slag contamination. After synthesis, the powder can be crushed and sieved (e.g., 20-80 mesh) to improve the efficiency of the subsequent ball milling process and save preparation time. A Mn source is added to the synthesized powder, followed by fine grinding. The Mn source is MnCO3.

[0027] In an optional embodiment, the resulting BNT-based ceramic powder is shaped and extruded to produce a ceramic green body. The BNT-based ceramic powder may be finely ground before forming. The fine grinding method may be wet ball milling. The mass ratio of ceramic powder: balls: alcohol may be 1:(4-8):(0.6-1.2). The ball milling media may be zirconium balls, agate balls, or the like. The ball milling time may be 24-48 hours. After fine grinding, the product may be dried.

[0028] Add a binder for granulation. The binder used in granulation can be polyvinyl alcohol (PVA) or the like, the concentration of the binder is 6-8%, and the amount added can be 5-7% of the weight of the ceramic powder. After granulation, it can be aged for a period of time, and then pressed into shape after aging. The aging time can be 24-48 hours. The molding process can include: dry-pressing the prepared powder to obtain a green body of the required size. The pressing pressure can be 100-300 MPa. After molding, the temperature is increased and the plastic is discharged. The plastic discharge conditions can be: heating to 600-800°C at a heating rate of not more than 2°C / min, keeping warm for 1-24 hours, preferably 2-6 hours, and cooling to room temperature with the furnace.

[0029] The ceramic green body is sintered. The sintering temperature can be 1100-1300°C, and the holding time can be 1-24 hours, preferably 2-6 hours. In a preferred embodiment, the temperature is raised to 1100-1300°C at a heating rate of no more than 2°C / minute, which facilitates the formation of the ceramic without causing component segregation. Sintering can be performed in a high-temperature furnace, and after sintering, the ceramic body can be cooled to room temperature in the furnace.

[0030] According to the preparation process of the present invention, by controlling the mixing time and the fine grinding time to be within 24 hours and 48 hours respectively, a ceramic sample with an average grain size of 10 to 40 μm is obtained.

[0031] Also disclosed herein is a BNT-based pyroelectric ceramic component made using the aforementioned BNT-based pyroelectric ceramic material. In one example, the ceramic material is processed into desired dimensions, cleaned (e.g., ultrasonically cleaned), dried, silver-coated, and silver-sintered to obtain the BNT-based pyroelectric ceramic component. Silver-sintering conditions can include maintaining the temperature at 600-900°C for 10-30 minutes, and then increasing the temperature to 600-900°C at a rate of no more than 2°C / minute.

[0032] The lead-free BNT-based pyroelectric ceramic material of the embodiment of the present invention has the characteristics of high remnant polarization, high pyroelectric coefficient, etc. It has a typical square hysteresis loop characteristic at room temperature.

[0033] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values ​​exemplified below.

[0034] Example 1 In this embodiment 1, the BNT-based ferroelectric ceramic material used for pyroelectricity has the molecular formula (Bi 0.5-x Pr x Na 0.5 )TiO3-0.0756% MnO2, wherein x=0.02. The present invention is prepared by a solid phase sintering method, specifically according to the following steps: (1) According to the molecular formula (Bi 0.5-x Pr x Na 0.5) TiO3-0.0756% MnO2, where x = 0.02. The required raw materials are: 99.5% pure sodium bicarbonate, 99.999% pure bismuth oxide, 99.8% pure titanium oxide, and 99.9% pure praseodymium oxide, weighed to the nearest 0.001 g using an electronic balance; (2) The weighed raw materials are mixed and placed in a nylon jar, anhydrous ethanol is added to the jar, and the nylon jar is placed on a planetary ball mill with zirconia columns and zirconia balls of different sizes as the medium for mixing for 6 hours. The zirconia columns include two different sizes of 15 mm diameter × 15 mm height and 7.5 mm diameter × 7.5 mm height, and the zirconia balls include one size: 10 mm diameter; the mass ratio of the three zirconia columns and balls is 4:2:3; then the mixture is poured out and dried in a baking oven, and then sieved with a 40-mesh nylon sieve, and the sieved mixed powder is pressed into a cylindrical block with a size of 65 mm diameter × 20 mm height on a press; synthesized at 850°C for 4 hours, and then crushed through a 40-mesh sieve to obtain a ceramic powder (or solid solution powder); (3) The obtained ceramic powder is placed in a nylon jar again, and manganese carbonate powder is added at 0.1% by weight of the powder. Anhydrous ethanol is added to the jar to a level not higher than 2 / 3 of the jar height. The nylon jar is placed on a planetary ball mill with zirconia columns and zirconia balls of different sizes as a medium and mixed for 6 hours. The nylon jar is then poured out and dried in a baking oven, and then sieved with a 40-mesh nylon sieve to obtain a finely ground powder. (4) adding a 7 wt.% polyvinyl alcohol aqueous solution to the ground ceramic powder, where the amount of the polyvinyl alcohol aqueous solution added is 6% of the mass of the ceramic powder, and then uniformly granulating the powder, passing it through a 40-mesh sieve, and molding it into small cylinders with a size of 13 mm in diameter and 1 mm in height, and then performing plastic molding; (5) Sintering the obtained green body after plastic removal in an atmospheric atmosphere at a sintering temperature of 1200°C for 4 hours, and then taking out the sample after naturally cooling to room temperature; (6) The sintered ceramic sample is processed, cleaned, dried, and electroded to obtain a ceramic element.

[0035] The prepared BNT-based pyroelectric ceramic material was subjected to X-ray diffraction test. Figure 1 The X-ray diffraction pattern of Example 1 is shown. It can be seen that the obtained ceramic of Example 1 is a pure phase.

[0036] The hysteresis loop test of the prepared ceramic element was carried out at room temperature and 1Hz. The results are shown in the attached Figure 2 .

[0037] The prepared ceramic element was polarized and the pyroelectric coefficient was tested. The results are shown in the attached Figure 3 .

[0038] Example 2 In this embodiment 2, the BNT-based ferroelectric ceramic material used for pyroelectricity has a molecular formula of (Bi 0.5-x Pr x Na 0.5 )TiO3-0.0756% MnO2, wherein x = 0.01. The preparation method of Example 1 was repeated according to the above chemical formula; except for the different value of x in step (1), the other steps were the same as those of Example 1.

[0039] The prepared BNT-based ferroelectric ceramic material was subjected to X-ray diffraction test. Figure 1 The X-ray diffraction pattern of Example 2 is shown. It can be seen that the obtained ceramic of Example has no impurity phase.

[0040] The hysteresis loop test of the prepared ceramics was carried out. Figure 2 The PE curve of Example 2 is shown. It can be seen that the ceramic has typical ferroelectric properties.

[0041] The ceramic element prepared in Example 2 was polarized and the pyroelectric coefficient was tested. The results are shown in the attached Figure 3 .

[0042] Example 3 In this embodiment 3, the BNT-based ferroelectric ceramic material used for pyroelectricity has the molecular formula (Bi 0.5-x Pr x Na 0.5 )TiO3-0.0756% MnO2, wherein x = 0.03. The preparation method of Example 1 was repeated according to the above chemical formula; except for the different value of x in step (1), the other steps were the same as those of Example 1.

[0043] The prepared BNT-based ferroelectric ceramic material was subjected to X-ray diffraction test. Figure 1 The X-ray diffraction pattern of Example 2 is shown. It can be seen that the obtained ceramic has no impurity phase.

[0044] The hysteresis loop test of the prepared ceramics was carried out. Figure 2 The PE curve of Example 3 is shown. It can be seen that the ceramic has typical ferroelectric properties.

[0045] The ceramic element prepared in Example 3 was polarized and the pyroelectric coefficient was tested. The results are shown in the attached Figure 3 .

[0046] Comparative Example 1 The BNT-based pyroelectric ceramic material in Comparative Example 1 has the molecular formula (Bi 0.5-x Pr x Na 0.5)TiO3-0.0756% MnO2, wherein x = 0.04. The preparation method of Example 1 was repeated according to the above chemical formula; except for the different value of x in step (1), the other steps were the same as those of Example 1.

[0047] The prepared BNT-based relaxor ferroelectric ceramic material was subjected to X-ray diffraction test. Figure 1 The X-ray diffraction pattern of Comparative Example 1 is shown. It can be seen that the obtained ceramic has no impurity phase.

[0048] The hysteresis loop of the prepared ceramics was carried out. Figure 2 The PE curve of Example 3 is shown. It can be seen that the ceramic begins to show relaxation characteristics.

[0049] Result analysis: Figure 1 It can be seen that the Pr-doped BNT ceramics of Examples 1, 2, 3, and Comparative Example 1 are all pure phases; Figure 2 The hysteresis loop diagrams of Example 1, Example 2, Example 3, and Comparative Example 1 are shown. It can be seen that the PE curves of Example 1, Example 2, and Example 3 are all square, indicating that they have good ferroelectric properties. The PE curve of Comparative Example 1 begins to show a waist state, indicating that the component has begun to relax. The variation of pyroelectric coefficient with temperature in Example 1, Example 2 and Example 3 is shown in FIG. Figure 3 As shown in FIG1 , the pyroelectric coefficient increases with the increase of temperature. At 25°C, the pyroelectric coefficient of Example 1 can reach 4.47×10 -4 Cm -2 K -1 .

[0050] Table 1 lists the relevant performance parameters of Example 1 (0.02), Example 2 (0.01), Example 3 (0.03) and Comparative Example 1 (0.04), among which Example 1 has a higher pyroelectric coefficient: The p value in Table 1 is measured, and the following Fi, Fv, and Fd are calculated based on p. In Comparative Example 1, p could not be measured, so the subsequent performance data are blank. This is primarily because polarization is difficult at room temperature when the Pr content is 0.04, making p impossible to measure.

[0051] In summary, the embodiments of the present invention form a simple BNT-based pyroelectric ceramic component, and the pyroelectric coefficient of the BNT-based ceramic is improved by doping with the Pr element, and is suitable for the field of lead-free pyroelectric infrared detection.

[0052] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A BNT-based lead-free pyroelectric ceramic material, characterized in that: The chemical composition of the BNT-based lead-free pyroelectric material is (Bi 0.5-x Pr x Na 0.5 )TiO3-y wt%MnO2, wherein 0.01≤x≤0.04, 0<y≤0.

1.

2. The BNT-based lead-free pyroelectric material according to claim 1, characterized in that: 0.01≤x≤0.03; or / and, y=0.0756.

3. The BNT-based lead-free pyroelectric material according to claim 1 or 2, characterized in that: The BNT-based lead-free pyroelectric ceramic material has a relative dielectric constant of 300 to 900 and a dielectric loss of less than 0.10 under test conditions of 25° C. and 1 kHz.

4. A method for preparing the BNT-based lead-free pyroelectric ceramic material according to any one of claims 1 to 3, characterized in that: include: (1) weighing a Bi source, a Pr source, a Na source, and a Ti source according to the chemical composition of the BNT-based lead-free pyroelectric ceramic material, mixing the mixture, and calcining the mixture to obtain a solid solution powder; (2) mixing the solid solution powder and the Mn source to obtain a mixed powder; (3) mixing the obtained mixed powder with a binder, granulating, aging, molding and molding to obtain a ceramic green body; (4) Sintering the obtained ceramic body to obtain the BNT-based lead-free pyroelectric ceramic material.

5. The preparation method according to claim 4, characterized in that In step (1): the Bi source is Bi2O3; the Pr source is Pr6O 11 ; The Na source is NaHCO3; The Ti source is TiO2.

6. The preparation method according to claim 4 or 5, characterized in that In step (1): the calcination temperature is 600° C. to 1000° C., and the calcination time is no more than 24 hours.

7. The preparation method according to any one of claims 4 to 6, characterized in that In step (2): the Mn source is MnCO3.

8. The preparation method according to any one of claims 4 to 7, characterized in that In step (3): the binder is at least one of polyvinyl alcohol, polyethylene glycol, polystyrene and methyl cellulose; the amount of the binder added is 6 to 8 wt.% of the mixed powder; The aging temperature is room temperature and the time is 18 to 26 hours; The temperature of the plastic removal is 650-850° C., and the time is 1-3 hours.

9. The preparation method according to any one of claims 4 to 8, characterized in that In step (4): the sintering temperature is 1000-1300° C. and the sintering time does not exceed 24 hours.

10. A ceramic component, characterized in that: The invention is made from the BNT-based lead-free pyroelectric ceramic material according to any one of claims 1 to 3.

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