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

Abstract

The invention belongs to the field of functional ceramics, and particularly relates to a BNT-based pyroelectric ceramic material with a high depolarization temperature as well as a preparation method and application of the BNT-based pyroelectric ceramic material. In order to obtain the lead-free pyroelectric material with excellent pyroelectric performance and good temperature stability, the invention provides the BNT-based lead-free pyroelectric ceramic material, and the chemical composition of the BNT-based lead-free pyroelectric material is (Bi < 0.5 > Na < 0.5 >) Ti < 1-x > Fe < x > O < 3-delta >, wherein 0 < x < = 0.003, and 0 < delta < = 0.003. BNT is selected as a base material, low-valence Fe is adopted to replace high-valence Ti, the depolarization temperature can be increased, and the method 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 with a high depolarization temperature, a preparation method and an application thereof, and is especially applicable to 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 Na0.5 TiO3 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 these issues, the present invention aims to provide a BNT-based pyroelectric ceramic material, its preparation method, and ceramic components. This material utilizes low-valent Fe to replace high-valent Ti, introducing oxygen vacancies to suppress domain motion and increase the depolarization temperature. The material boasts 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 Na 0.5 )Ti 1-x Fe x O 3-δ ;Wherein 0<x≤0.003, 0<δ≤0.003.

[0006] The present invention is designed (Bi 0.5 Na 0.5 )Ti 1-x Fe x O 3-δ The composition of the material, in which Fe exists mostly as +3, causes a violation of overall charge conservation in the material, generating a certain amount of oxygen vacancies, which in turn form defect dipoles. This has a pinning effect on the ferroelectric domains, raising the depolarization temperature. Ultimately, a BNT-based lead-free pyroelectric ceramic material with a high depolarization temperature is obtained, which is expected to be used in the field of lead-free pyroelectric infrared detection. The present invention selects BNT as the matrix material and replaces the high-valent Ti with low-valent Fe to increase the depolarization temperature, which is expected to be used in the field of lead-free pyroelectric infrared detection.

[0007] Preferably, 0.0005≤x≤0.002.

[0008] Preferably, the BNT-based lead-free pyroelectric ceramic material has a relative dielectric constant of 300-400 and a dielectric loss of less than 0.03 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) mixing a Bi source, an Fe source, a Na source, and a Ti source according to the chemical composition ratio of the BNT-based lead-free pyroelectric ceramic material, and calcining the mixture to obtain a solid solution powder; (2) mixing the solid solution powder and the binder and granulating them, and then aging, molding and extruding them to obtain a ceramic green body; (3) Sintering the ceramic green body to obtain the BNT-based lead-free pyroelectric material.

[0010] Preferably, the Bi source is Bi2O3; the Fe source is Fe2O3; the Na source is NaHCO3; and the Ti source is TiO2.

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

[0012] Preferably, the binder is at least one of polyvinyl alcohol, polyethylene glycol, polystyrene and methyl cellulose; and the amount of the binder added is 6 to 8 wt.% of the mass of the solid solution powder.

[0013] Preferably, the aging temperature is room temperature and the aging time is 18 to 26 hours.

[0014] Preferably, the temperature of the plastic removal is 650-850° C., and the time is 1-3 hours.

[0015] Preferably, the sintering temperature is 1000-1300° C. and the sintering time does not exceed 24 hours.

[0016] In another aspect, the present invention provides a ceramic component made of the above-mentioned BNT-based lead-free pyroelectric ceramic material.

[0017] Preferably, the ceramic material is processed into a desired size and then silvered and sintered to obtain the ceramic material.

[0018] 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 depolarization temperature and high pyroelectric coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is Example 1 of the present invention (Bi 0.5Na 0.5 )Ti 0.999 Fe 0.001 O 3-δ 、Example 2 (Bi 0.5 Na 0.5 )Ti 0.9995 Fe 0.0005 O 3-δ 、Example 3 (Bi 0.5 Na 0.5 )Ti 0.998 Fe 0.002 O 3-δ 、Example 4 (Bi 0.5 Na 0.5 )Ti 0.997 Fe 0.003 O 3-δ X-ray diffraction pattern of; Figure 2 1 is a comparison chart of dielectric temperature spectra of Example 1, Example 2, Example 3 and Example 4 of the present invention; Figure 3 4 is a comparison chart of pyroelectric coefficients of Example 1, Example 2, Example 3 and Example 4 of the present invention. DETAILED DESCRIPTION

[0020] 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.

[0021] In the present invention, the chemical composition of the BNT-based pyroelectric ceramic material is (Bi 0.5 Na 0.5 )Ti 1-x Fe x O 3-δ , wherein 0<x≤0.003, x is a mole percentage, 0<δ≤0.003. Preferably, the composition range of 0.0005≤x≤0.002 has a higher depolarization temperature and a larger pyroelectric coefficient.

[0022] The present invention has been verified through theoretical research and multiple experiments. For BNT ceramics, low-valent Fe is used to replace high-valent Ti to introduce oxygen vacancies, pin ferroelectric domains, and increase the depolarization temperature.

[0023] 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.

[0024] The solid phase method is used to prepare ceramic powder. Specifically, Na source, Fe source, Bi source and Ti source are mixed in the form of (Bi 0.5 Na0.5 )Ti 1-x Fe x O 3-δ The desired ceramic powder is uniformly mixed in a stoichiometric ratio to synthesize the Bi source is Bi2O3, the Fe source is Fe2O3, the Na source is NaHCO3, and the Ti source is TiO2.

[0025] 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.

[0026] In an optional embodiment, the synthesis (calcination) temperature may be 800-1000°C. Preferably, the temperature is raised to the synthesis temperature at a heating rate of no more than 2°C / min. This allows the reaction to fully occur. The holding time at the synthesis temperature may be selected to be 1-24 hours, preferably 2-6 hours. The present invention adds an Fe source during the batching process. According to the batching table and experimental results, Fe enters the B site, and acceptor substitution introduces oxygen vacancies, forming defect dipoles that have a pinning effect on the ferroelectric domain, thereby increasing the depolarization temperature.

[0027] In an alternative embodiment, after calcination, the powder can be cooled to room temperature in the furnace. The resulting bulk powder can be placed in a sealed container (e.g., a sealed alumina crucible) for synthesis, thereby reducing volatilization of the 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.

[0028] The BNT-based ceramic powder is formed and extruded to obtain a ceramic green body. The BNT-based ceramic powder can be finely ground before forming. The fine grinding method can be wet ball milling. The mass ratio of ceramic powder: balls: alcohol can be 1:(4-8):(0.6-1.2). The ball milling media can be zirconium balls, agate balls, etc. The ball milling time can be 24-48 hours. After fine grinding, the product can be dried.

[0029] In an optional embodiment, a binder is added 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 desired 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.

[0030] The ceramic green body is sintered. The sintering temperature can be 1000-1300°C, and the holding time can be 1-24 hours, preferably 2-6 hours. In a preferred embodiment, the temperature is raised to 1000-1300°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.

[0031] According to the preparation process of the present invention, by controlling the mixing time and fine grinding time within 24 hours and 48 hours respectively, a ceramic sample with an average grain size of 10 to 40 μm is obtained. Figure 1 According to the XRD pattern, no obvious second phase was found, and it can be preliminarily judged that Fe entered the B site (Ti site). Figure 2 In the dielectric temperature spectrum, as the doping amount increases, the loss changes more obviously with temperature, and the leakage conduction phenomenon of the material is serious, which further determines that Fe has entered the B site (Ti site).

[0032] 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.

[0033] The lead-free BNT-based pyroelectric ceramic material of the embodiment of the present invention has the characteristics of high depolarization temperature, high pyroelectric coefficient, etc., and has a typical square hysteresis loop characteristic at room temperature.

[0034] 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.

[0035] Example 1 In this embodiment 1, the BNT-based ferroelectric ceramic material used for pyroelectricity has the molecular formula (Bi 0.5 Na 0.5 )Ti 1-x Fe x O 3-δ , wherein x=0.001. 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 Na 0.5 )Ti 1-x Fe x O 3-δ , where x = 0.001 for ingredient calculation, the required raw materials are: sodium bicarbonate with a purity of 99.5%, bismuth oxide with a purity of 99.999%, titanium oxide with a purity of 99.8%; iron oxide with a purity of 99%, weighed using an electronic balance with an accuracy of 0.001g; (2) The weighed raw materials were mixed and placed in a nylon jar, anhydrous ethanol was added to the jar, and the nylon jar was 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 included two different sizes of 15 mm diameter × 15 mm height and 7.5 mm diameter × 7.5 mm height, and the zirconia balls included one size: 10 mm diameter; the mass ratio of the three zirconia columns and balls was 4:2:3 respectively; then the mixture was poured out and dried in a baking oven, and then sieved with a 40-mesh nylon sieve, and the sieved mixed powder was 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 ceramic powder; (3) The obtained powder was placed in a nylon jar again, and anhydrous ethanol was added to the jar to a level not higher than 2 / 3 of the jar height. The nylon jar was placed on a planetary ball mill with zirconia columns and zirconia balls of different sizes as the medium and mixed for 6 hours. The mixture was 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) The obtained green body after plastic removal was sintered in an atmospheric atmosphere at a sintering temperature of 1140°C for 2 hours, and the sample was taken out after natural cooling to room temperature; (6) The sintered ceramic sample is processed, cleaned, dried, and electroded to obtain a ceramic element.

[0036] 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 ceramic obtained in Example 1 is pure phase. The dielectric properties of the ceramic element prepared in Example 1 were tested, and the results are shown in the attached Figure 2 The ceramic element prepared in Example 1 was polarized and the pyroelectric coefficient was tested. The results are shown in the attached Figure 3 .

[0037] Example 2 In this embodiment 2, the BNT-based ferroelectric ceramic material used for pyroelectricity has a molecular formula of (Bi 0.5 Na 0.5 )Ti 1-x Fe x O 3-δ , wherein x = 0.0005. The preparation method of Example 1 was repeated according to the above chemical formula.

[0038] 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 2 has no impurity phase. The dielectric properties of the prepared ceramic are tested. Figure 2 The dielectric temperature spectrum of Example 2 is shown. The pyroelectric coefficient of the ceramic element prepared in Example 2 was tested after polarization treatment. The results are shown in the attached Figure 3 .

[0039] Example 3 In this embodiment 3, the BNT-based ferroelectric ceramic material used for pyroelectricity has the molecular formula (Bi 0.5 Na 0.5 )Ti 1-x Fe x O 3-δ , wherein x = 0.002. The preparation method of Example 1 was repeated according to the above chemical formula.

[0040] The prepared BNT-based ferroelectric ceramic material was subjected to X-ray diffraction test. Figure 1The X-ray diffraction pattern of Example 3 is shown. It can be seen that the obtained ceramic has no impurity phase. The dielectric properties of the prepared ceramic are tested. Figure 2 The dielectric temperature spectrum of Example 3 is shown. The pyroelectric coefficient of the ceramic element prepared in Example 3 was tested after polarization treatment. The results are shown in the attached Figure 3 .

[0041] Example 4 The BNT-based pyroelectric ceramic material in this embodiment 4 has the molecular formula (Bi 0.5 Na 0.5 )Ti 1-x Fe x O 3-δ , wherein x = 0.003. The preparation method of Example 1 was repeated according to the above chemical formula.

[0042] The prepared BNT-based relaxor ferroelectric ceramic material was subjected to X-ray diffraction test. Figure 1 The X-ray diffraction pattern of Example 4 is shown. It can be seen that the obtained ceramic has no impurity phase. The dielectric properties of the prepared ceramic are tested. Figure 2 The dielectric temperature spectrum of Example 4 is shown. The pyroelectric coefficient of the ceramic element prepared in Example 4 was tested after polarization treatment. The results are shown in the attached Figure 3 When the Fe content continues to increase, more oxygen vacancies will appear, the resistivity of the material will decrease, leakage conduction will be obvious, polarization will be difficult, and subsequent testing will be affected.

[0043] Result analysis: from Figure 1 It can be seen that Examples 1-4 of the low-cost substituted BNT ceramics are all pure phase; Figure 2 The dielectric temperature spectra of Examples 1-4 are shown in FIG. It can be seen that Examples 1-4 all have relatively high depolarization temperatures, with the depolarization temperature of Example 1 reaching 213°C. The variation of the pyroelectric coefficient of Examples 1-4 with temperature is shown in the figure below. Figure 3 As shown in the figure, the pyroelectric coefficient changes slightly in the temperature range of 20℃-80℃. At 25℃, the pyroelectric coefficient of Example 1 can reach 2.88×10 -4 Cm -2 K -1 .

[0044] Table 1 lists the relevant performance parameters of Examples 1-4, among which Example 1 has a higher depolarization temperature.

[0045] Table 1: Dielectric parameters of BNT-based lead-free pyroelectric ceramic materials after polarization:

[0046] The depolarization temperature of all components in the present invention is improved, but the dielectric constant and loss of other components are large, the pyroelectric coefficient is small, and the overall pyroelectric performance is poor, making the component with x = 0.001 the optimal component. In summary, the embodiments of the present invention form a simple BNT-based pyroelectric ceramic component. By replacing high-valent Ti with low-valent Fe, the depolarization temperature of BNT-based ceramics is increased, making them suitable for lead-free pyroelectric infrared detection.

[0047] 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 Na 0.5 )Ti 1-x Fe x O 3-δ ;Wherein 0<x≤0.003, 0<δ≤0.

003.

2. The BNT-based lead-free pyroelectric material according to claim 1, characterized in that: 0.0005≤x≤0.002。 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 300-400 and a dielectric loss of less than 0.03 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) mixing a Bi source, an Fe source, a Na source, and a Ti source according to the chemical composition ratio of the BNT-based lead-free pyroelectric ceramic material, and calcining the mixture to obtain a solid solution powder; (2) mixing the solid solution powder and the binder and granulating them, and then aging, molding and extruding them to obtain a ceramic green body; (3) Sintering the ceramic green body to obtain the BNT-based lead-free pyroelectric material.

5. The preparation method according to claim 5, characterized in that The Bi source is Bi2O3; the Fe source is Fe2O3; the Na source is NaHCO3; and the Ti source is TiO2.

6. The preparation method according to claim 4 or 5, characterized in that 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 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 mass of the solid solution 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.

8. The preparation method according to any one of claims 4 to 7, characterized in that The sintering temperature is 1000-1300° C. and the sintering time does not exceed 24 hours.

9. 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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