A CaTiO3-based relaxor ferroelectric ceramic material and its preparation method

Abstract

This invention relates to the field of dielectric energy storage ceramic materials, specifically to a CaTiO3-based relaxor ferroelectric ceramic material and its preparation method. The general chemical formula of the CaTiO3-based composite relaxor ferroelectric ceramic material is: (1-x)Ca 0.5 Bi 0.25 Na 0.25 TiO3-xBaZrO3, where 0 < x ≤ 0.30, is produced by solid-state reaction method, in which Bi2O3, Na2CO3, CaCO3, TiO2, BaCO3, and ZrO2 are stoichiometrically proportioned, followed by wet ball milling, pre-calcination, granulation, tableting, debinding, and sintering. This invention, by constructing a relaxor ferroelectric heterojunction, synergistically optimizes the breakdown field strength, polarization intensity, and dielectric loss, solving the problems of polarization saturation and low energy storage efficiency in traditional ferroelectrics.

Description

Technical Field

[0001] This invention relates to the field of dielectric energy storage ceramic materials, specifically to a CaTiO3-based relaxor ferroelectric ceramic material and its preparation method. Background Technology

[0002] Dielectric capacitors are widely used in devices such as defibrillators and multilayer ceramic capacitors (MLCCs) due to their high power density and fast charging and discharging speed. With the expansion of application scenarios, they need to maintain good energy storage performance over a wide temperature range while meeting the requirements of miniaturization and integration.

[0003] Among lead-free energy storage ceramics, CaTiO3 (CT) stands out due to its wide bandgap (3.4 eV) and low dielectric loss (~10⁻⁻⁶ eV). 5 With its moderate dielectric constant, Ca exhibits a high intrinsic breakdown field strength. 0.5 Bi 0.25 Na 0.25 TiO3 (BNCT) has a high proportion of polar ions, but suffers from low polarization and low breakdown field strength. BaZrO3 (BZ), as a cubic paraelectric perovskite material, has a large band gap and perovskite unit cell, and a tolerance factor of 0.987, which can increase the breakdown field strength and excite high polarization.

[0004] Traditional ferroelectric materials often face the challenges of polarization saturation and low energy storage efficiency. It is difficult to achieve high breakdown field strength, high polarization intensity and low polarization hysteresis simultaneously through single material modification. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention aims to provide a CaTiO3-based relaxor ferroelectric ceramic material and its preparation method. The CaTiO3-based relaxor ferroelectric ceramic material has high breakdown field strength, high effective energy storage density, high energy storage efficiency, and excellent temperature and frequency stability.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A type of Ca 0.5 Bi 0.25 Na 0.25 TiO3 matrix material, which consists of 0.5CaTiO3- 0.5 Bi 0.5 Na 0.5 TiO3 solid solution formation was used as a benchmark for performance comparison of relaxor ferroelectric ceramics after the introduction of BaZrO3.

[0007] (1-x)Ca0.5Bi was synthesized by introducing BaZrO3 (BZ) into the matrix material and using a solid-state method. 0.25 Na 0.25 TiO 3-x BaZrO3((1 - x)BNCT - xBZ, 0 < x ≤ 0.30) solid solution.

[0008] A CaTiO3 - based composite relaxor ferroelectric ceramic material with the chemical general formula: (1 - x)Ca 0.5 Bi 0.25 Na 0.25 TiO3 - xBaZrO3, where 0 < x ≤ 0.30.

[0009] Furthermore, x is 0.10.

[0010] In the above preferred x - value scheme, the effective energy storage density of the ceramic reaches 14.98 J / cm 3 , the energy storage efficiency is 89.95%, the maximum polarization intensity (Pmax) reaches 37.28 μC / cm 2 , and the polarization saturation field strength is increased to >120 kV / mm. The main reasons are as follows: The wide bandgap of the linear dielectric CaTiO3 can suppress leakage current and increase the breakdown field strength; the tolerance factor of the paraelectric phase BaZrO3 is about 0.987, which can stabilize the perovskite lattice, and the Ba 2+ (r = 1.61 Å), Zr 4+ (r = 0.72 Å) have size differences with the matrix ions. After doping, it intensifies local disorder, promotes the relaxation of the ferroelectric body, and forms smaller nano - polar micro - regions (PNRs) to dominate the polarization response, greatly reducing polarization hysteresis. At the same time, the smaller PNRs are easy to re - orient under the electric field, taking into account both high energy storage density and high energy storage efficiency.

[0011] The energy storage density of the energy - storage ceramic depends on the synergistic improvement of the dielectric constant and the breakdown field strength, and it is often difficult for a single component to take both into account. The main phase BNCT has a high dielectric constant due to the disordered distribution of cations, but the low breakdown field strength limits the energy storage density; BZO is the second phase formed in the BNCT matrix, and BZO has excellent insulation and high breakdown field strength, but the dielectric constant is low. Through the synergistic effect, the BZO second phase forms a uniformly dispersed "insulating barrier network" in the BNCT matrix: on the one hand, a charge depletion layer is formed at the interface between BZO and BNCT, suppressing leakage current and increasing the overall breakdown field strength, thus increasing the breakdown field strength of the composite system; on the other hand, the high dielectric property of the BNCT main phase weakens the dilution effect of BZO on the overall dielectric constant through interface polarization coupling, keeping the dielectric constant of the composite system at a high level.

[0012] A preparation method of a CaTiO3 - based composite relaxor ferroelectric ceramic material, comprising the following steps: Weigh the raw materials Bi2O3, Na2CO3, CaCO3, TiO2, BaCO3 and ZrO2 according to the stoichiometric ratio of the chemical general formula, and carry out wet ball milling and mixing to obtain a mixed powder.

[0013] Pre-calcine the mixed powder to obtain a perovskite phase precursor powder.

[0014] Add a binder to the perovskite phase precursor powder, grind and granulate it, then press it into a green body. After degumming the green body, sinter it to obtain the CaTiO3-based composite relaxor ferroelectric.

[0015] In a preferred embodiment of the present invention, the time for wet ball milling is 12 h, and the ball milling medium is ethanol.

[0016] In a preferred embodiment of the present invention, the pre-calcination temperature is 800 °C and the time is 3 h.

[0017] In a preferred embodiment of the present invention, the binder is polyvinyl alcohol, the mass fraction is 0.5%, the pressure for pressing into shape is 10 MPa, and a powder of equal components for protection is covered around the green body before sintering.

[0018] In a preferred embodiment of the present invention, the temperature for degumming treatment is 550 °C and the time is 2.5 h.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The CaTiO3-based composite relaxor ferroelectric ceramic material described in the present invention has a chemical general formula: (1 - x)Ca 0.5 Bi 0.25 Na 0.25 TiO3 - xBaZrO3, where 0 < x ≤ 0.30. The CaTiO3-based relaxor ferroelectric ceramic material has a high energy storage density, a high energy storage efficiency and excellent environmental stability.

[0020] 2. The CaTiO3-based composite relaxor ferroelectric ceramic material described in the present invention, especially the preferred component BNCT-10BZ (x = 0.10), has excellent comprehensive energy storage performance; the dielectric loss tanδ < 0.02 in a wide frequency range, which is beneficial to reducing energy loss. In terms of environmental stability, under the test conditions of 30 - 120 °C, the variation ranges of the energy storage density and efficiency are respectively controlled within 0.06 J / cm 3 and 4.8%; under the test conditions of 10 - 200 Hz, the average value of the effective energy storage density is 10.8 J / cm 3 , the dispersion is ±0.1 J / cm 3 , and the efficiency fluctuation is lower than 2.1%; at the same time, it has a fast discharge characteristic (the time t corresponding to 90% of the saturated discharge energy density 0.9(≈ 27 ns), suitable for dielectric capacitor applications under extreme conditions. Attached Figure Description

[0021] Figure 1 The XRD patterns of BNCT-BZ-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 are shown.

[0022] Figure 2 The image shows a SEM image of the BNCT-BZ-based lead-free relaxor ferroelectric ceramic from Example 2.

[0023] Figure 3 This is the unipolar energy storage loop of the BNCT-BZ-based lead-free relaxor ferroelectric ceramic in Example 2.

[0024] Figure 4 The total energy storage density of the BNCT-BZ-based lead-free relaxor ferroelectric ceramic in Example 2 under different electric field strengths is ( W total ), effective energy storage density ( W rec ) and energy storage efficiency ( ƞ ). Detailed Implementation

[0025] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0027] A CaTiO3-based composite relaxor ferroelectric ceramic material with the general chemical formula: (1-x)Ca 0.5 Bi 0.25 Na 0.25 TiO3-xBaZrO3, where 0 <x≤0.30。

[0028] Furthermore, x is 0.10.

[0029] A method for preparing a CaTiO3-based composite relaxor ferroelectric ceramic material includes the following steps: According to the stoichiometric ratio of the general chemical formula, raw materials Bi2O3, Na2CO3, CaCO3, TiO2, BaCO3 and ZrO2 were weighed and mixed by wet ball milling to obtain a mixed powder.

[0030] The mixed powder was pre-calcined to obtain perovskite phase precursor powder.

[0031] A binder is added to the perovskite phase precursor powder, and the powder is ground, granulated, and pressed into a green body. After debinding the green body, it is sintered to obtain the CaTiO3-based composite relaxor ferroelectric.

[0032] In a preferred embodiment of the present invention, the wet ball milling time is 12 hours, and the ball milling medium is ethanol.

[0033] In a preferred embodiment of the present invention, the pre-firing temperature is 800°C and the time is 3 hours.

[0034] In a preferred embodiment of the present invention, the binder is polyvinyl alcohol with a mass fraction of 0.5%, the compression molding pressure is 10 MPa, and a protective powder of equal components is covered around the green body before sintering.

[0035] In a preferred embodiment of the present invention, the temperature of the glue removal treatment is 550°C and the time is 2.5 hours.

[0036] Example 1 Preparation of BNCT-10BZ ceramics (x = 0.1, preferred composition) (1) According to (1-0.1)Ca 0.5 Bi 0.25 Na 0.25 The stoichiometric ratio of TiO3-0.1BaZrO3 was used to weigh Bi2O3, Na2CO3, CaCO3, TiO2, BaCO3, and ZrO2 (weighing error 0 to +0.0005 g). The subsequent ball milling, drying, pre-calcination, granulation, tableting, and sintering steps were the same as in Example 1.

[0037] (2) The sintered ceramic sheet is finely ground to a thickness of 30-50 μm, and a gold layer is sputtered to cover one side completely. A 0.8 mm thick layer is prepared on the other side. 2 Micro-area gold electrodes are used for energy storage testing.

[0038] (3) Test results show that the effective energy storage density reaches 14.98 J / cm² under an electric field of 95 kV / mm. 3 The energy storage efficiency is 89.95%; within the temperature range of 30-120℃, the variation range of energy storage density and efficiency is controlled within 0.06 J / cm³. 3 Within 4.8%; at frequencies of 10-200 Hz, the average energy storage density is 10.8 J / cm³.3 After 106 charge-discharge cycles, the energy storage performance degradation does not exceed 0.2 J / cm². 3 The efficiency reduction was ≤3.8%. Simultaneously, discharge performance tests were conducted on the ceramic: at room temperature, as the electric field increased from 10 kV / mm to 18 kV / mm, the underdamped discharge current density increased from 680 A / cm² to 1224 A / cm², and the power density increased from 34 MW / cm². 3 Increased to 110 MW / cm 3 In overdamped discharge, the time (t0.9) corresponding to 90% saturation discharge energy density is about 27 ns, indicating a fast discharge speed. Within the temperature range of 30-160 ℃, the peak discharge current, CD, PD, and (t0.9) all change by less than 10%, demonstrating excellent thermal stability.

[0039] Example 2 Preparation of BNCT-20BZ ceramics (x = 0.2) According to (1-0.2) Ca 0.5 Bi 0.25 Na 0.25 TiO 3-0.2 BaZrO3 was prepared by weighing the raw materials according to the stoichiometric ratio, and the preparation steps were the same as in Example 1.

[0040] The ceramic XRD pattern shows a broad dielectric constant plateau, indicating a cubic phase at room temperature. It exhibits low dielectric loss and good temperature stability. The hysteresis loop is nearly linear, and the remanent polarization is low. However, compared to the x = 0.1 composition, its energy storage density and environmental stability are slightly lower.

[0041] Example 3 Preparation of BNCT-30BZ ceramics (x = 0.3) According to (1-0.3) Ca 0.5 Bi 0.25 Na 0.25 TiO 3-0.3 BaZrO3 was prepared by weighing the raw materials according to the stoichiometric ratio, and the preparation steps were the same as in Example 1.

[0042] XRD patterns show that the ceramic has a distinct second phase. Although the microstructure is still relatively dense, the average grain size has increased to 2.5 μm, the breakdown field strength has decreased, and the energy storage performance and stability have been reduced.

[0043] Comparative Example 1 Preparation of pure BNCT ceramics (x = 0) (1) Weigh the corresponding amounts of Bi2O3, Na2CO3, CaCO3 and TiO2 according to the stoichiometric ratio (weighing error 0 to +0.0005g), pour them into a ball mill jar, add ethanol and wet ball mill for 12 h.

[0044] (2) After drying the slurry at 100℃ for 3 h, it was pre-calcined at 800℃ for 3 h to obtain the perovskite phase precursor.

[0045] (3) Add 0.5wt.% PVA to granulate, press into a circular green body with a diameter of 10 mm and a thickness of 1 mm at 10 MPa; cover the green body with protective powder of equal composition, heat to 550℃ at 5℃ / min and hold for 2.5 h to remove the binder, then heat to 1080℃ and sinter for 2 h, and obtain pure BNCT ceramic after cooling.

[0046] (4) The ceramic hysteresis loop is square, with obvious ferroelectric domain reversal characteristics. The dielectric constant has two abnormal peaks with temperature change, the energy storage density is low, and the environmental stability is poor.

[0047] Results Analysis Table 1 compares the ceramic performance of Comparative Example 1 (X=0) and Example 1 (X=0.1). As shown in the table, when comparing the energy storage performance of the ceramic with x=0.10 with the undoped matrix, Eb increases from 350 kV / mm to 950 kV / mm, and η increases from 80% to 90%, resulting in Wrec increasing dramatically from 1.87 J / cm3 to 14.98 J / cm3, an increase of 700%.

[0048] Table 1 compares the ceramic properties of Comparative Example 1 (X=0) and Example 1 (X=0.1). Figure 1 (XRD) verified the successful formation of the perovskite solid solution and clarified the optimal doping range of BZ (x=0.10), providing a structural basis for improving energy storage performance.

[0049] Figure 2 (SEM) confirmed the excellent microstructure of the x=0.10 sample with high density and fine grains, ensuring high breakdown field strength and low leakage loss.

[0050] Figure 3 The energy storage loop exhibits excellent polarization characteristics of "high Pmax + low Pr", which is the core prerequisite for achieving a high energy storage density of 14.98 J / cm³ and a high energy storage efficiency of 89.95%.

[0051] Figure 4 The energy storage performance curve quantifies the electric field dependence of energy storage performance, verifies the performance stability over a wide electric field range, and provides parameter support for practical applications.

[0052] The CaTiO3-based composite relaxor ferroelectric ceramic material of this invention has the general chemical formula: (1-x)Ca 0.5 Bi0.25 Na 0.25 TiO3-xBaZrO3, where 0 < x ≤ 0.30, the CaTiO3-based relaxor ferroelectric ceramic material has high energy storage density, high energy storage efficiency and excellent environmental stability.

[0053] For the CaTiO3-based composite relaxor ferroelectric ceramic material described in the present invention, especially the preferred component BNCT-10BZ (x = 0.10), the comprehensive energy storage performance is excellent; the dielectric loss tanδ < 0.02 in the wide frequency range, which is beneficial to reducing energy loss. In terms of environmental stability, under the test conditions of 30 - 120 °C, the variation ranges of the energy storage density and efficiency are controlled within 0.06 J / cm 3 and 4.8% respectively; under the test conditions of 10 - 200 Hz, the average value of the effective energy storage density is 10.8 J / cm 3 , and the dispersion is ±0.1 J / cm 3 , and the efficiency fluctuation is less than 2.1%; at the same time, it has the characteristics of fast discharge (the time t corresponding to 90% of the saturated discharge energy density 0.9 ≈27 ns), which is suitable for dielectric capacitor applications under extreme conditions.

[0054] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the adopted step methods are the same as those in the embodiments, in order to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0055] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A CaTiO3-based composite relaxor ferroelectric ceramic material, characterized in that, The general chemical formula is: (1-x)Ca 0.5 Bi 0.25 Na 0.25 TiO 3-x BaZrO3, where 0 < x≤0.

30.

2. The CaTiO3-based composite relaxor ferroelectric ceramic material according to claim 1, characterized in that, x is 0.

10.

3. The method for preparing CaTiO3-based composite relaxor ferroelectric ceramic material according to claim 1, characterized in that, Includes the following steps: According to the stoichiometric ratio of the general chemical formula, raw materials Bi2O3, Na2CO3, CaCO3, TiO2, BaCO3 and ZrO2 were weighed and mixed by wet ball milling to obtain a mixed powder; The mixed powder was pre-calcined to obtain perovskite phase precursor powder; A binder is added to the perovskite phase precursor powder, and the powder is ground, granulated, and pressed into a green body. After debinding the green body, it is sintered to obtain the CaTiO3-based composite relaxor ferroelectric.

4. The method for preparing CaTiO3-based composite relaxor ferroelectric ceramic material according to claim 3, characterized in that, The wet ball milling time is 11-13 hours, and the ball milling medium is ethanol.

5. The method for preparing CaTiO3-based composite relaxor ferroelectric ceramic material according to claim 3, characterized in that, The preheating temperature is 700-900℃, and the time is 1-4 hours.

6. The method for preparing CaTiO3-based composite relaxor ferroelectric ceramic material according to claim 3, characterized in that, The binder is polyvinyl alcohol with a mass fraction of 0.3-0.6%, the compression molding pressure is 9-11 MPa, and a protective powder of equal components is covered around the green body before sintering.

7. The method for preparing CaTiO3-based composite relaxor ferroelectric ceramic material according to claim 3, characterized in that, The temperature for debinding is 500-600℃, and the time is 2-3 hours.

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