Oxygen vacancy-trapped anti-reduction x7r barium titanate ceramic and preparation method

Abstract

The application discloses an oxygen vacancy trapped anti-reduction X7R barium titanate ceramic material, and belongs to the field of electronic ceramic materials. The ceramic is prepared from BaTiO3 with an average particle size of 80-250 nm as a main material, and contains MgCO3, MnCO3, CeO2, WO3, Yb2O3, Dy2O3, Ho2O3 and a glass sintering aid, wherein the content of CeO2 is 0.10-0.20%, the content of WO3 is 0.10%, and the total content of rare earth oxides is 0.30-0.50%. The ceramic is prepared through wet ball milling, granulation forming, reduction sintering and re-oxidation. CeO2 and WO3 cooperatively inhibit electron accumulation and oxygen vacancy migration, and the rare earth oxides and the glass sintering aid regulate the core-shell structure and the grain boundary barrier. The dielectric constant of the material is 2610-3200, and the insulation resistivity is 1.3*1012-3.1*1012 ohm*cm, so that the material meets the X7R temperature characteristics and is suitable for BME-MLCC.

Description

Technical Field

[0001] This invention belongs to the technical field of electronic ceramic materials and multilayer ceramic capacitors, specifically relating to an oxygen vacancy trapping type anti-reduction X7R barium titanate dielectric ceramic material and its preparation method, suitable for multilayer ceramic capacitors with nickel or nickel alloy base metal internal electrodes. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are characterized by their small size, high specific capacitance, and high reliability, and are widely used in consumer electronics, industrial control, communication equipment, and automotive electronics. MLCCs mainly consist of alternating layers of internal electrodes and ceramic dielectric layers, as well as terminal electrodes at both ends. Based on the temperature characteristics of the dielectric material, MLCCs can be classified into Class I and Class II ceramic capacitors. The X7R belongs to the Class II ceramic capacitor temperature characteristic class, with an operating temperature range of -55℃ to 125℃. Using the capacitance at 25℃ as a reference, the capacitance change rate should be controlled within ±15%.

[0003] Base metal internal electrode multilayer ceramic capacitors (BME-MLCCs) using nickel or nickel alloys as internal electrodes require sintering in a reducing atmosphere with low oxygen partial pressure to prevent oxidation of the internal electrodes. When BaTiO3-based ceramics are sintered in a reducing atmosphere, some Ti... 4+ Easily reduced to Ti 3+ This process, accompanied by the generation of oxygen vacancies and electron carriers, can lead to n-type semiconducting in the dielectric layer, resulting in increased dielectric loss, decreased insulation resistivity, and reduced long-term reliability. Therefore, re-oxidation treatment is usually required after reduction sintering to restore the insulation properties of the dielectric layer.

[0004] Existing reduction-resistant BaTiO3-based ceramics are typically modified using composite components of Mg, Mn, rare earth elements, and glass sintering aids. Mg components can suppress aberrant grain growth and promote core-shell structure formation; Mn components can regulate acceptor compensation states; rare earth elements such as Yb, Dy, and Ho exhibit amphoteric occupancy at A-site and B-site sites; and glass sintering aids can promote densification and regulate grain boundary states. However, acceptor doping may increase oxygen vacancy concentration, and relying solely on re-oxidation is insufficient to completely suppress oxygen vacancy migration at high temperatures and DC bias. Therefore, a composite control system that combines electron buffering, oxygen vacancy migration suppression, and grain boundary blocking is still needed.

[0005] The disclosed technologies related to this invention include: Chinese Patent Application 201811033254.8 discloses a technical solution for improving the reduction resistance of barium titanate dielectric materials through variable valence ion doping; Chinese Patent Application 202110649477.2 discloses a reduction-resistant X8R type BaTiO3-based ceramic material containing Bi2O3, MgO, and ZrO2; and Chinese Patent Application 202311044107.1 discloses BaTiO3 dielectric ceramics using BaTiO3, Bi2O3, Co2O3, and MnO2 as raw materials. These technologies can improve reduction resistance or temperature stability to a certain extent, but there is still room for further optimization in balancing high dielectric constant, low dielectric loss, insulation resistivity, and X7R temperature characteristics.

[0006] Therefore, it is necessary to provide a barium titanate-based ceramic material that can utilize the reversible redox buffering effect of CeO2 and the high-valence compensation effect of WO3 to suppress electron accumulation and oxygen vacancy migration, and stabilize the core-shell structure and grain boundary insulating barrier through rare earth oxides and glass sintering aids. Summary of the Invention

[0007] The purpose of this invention is to provide oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic and its preparation method, so as to solve the problem that existing anti-reduction BaTiO3-based ceramics cannot simultaneously achieve dielectric properties, temperature stability and insulation reliability.

[0008] To achieve the above objectives, this invention provides an oxygen vacancy trapping type reduction-resistant X7R barium titanate ceramic material. The ceramic material uses BaTiO3 with an average particle size of 80–250 nm as the main material, and comprises, by mass percentage: BaTiO3 98.00–98.80 wt%, MgCO3 0.10–0.70 wt%, MnCO3 0.10–0.70 wt%, CeO2 0.10–0.20 wt%, WO3 0.10 wt%, rare earth oxides 0.30–0.50 wt%, and glass sintering aid 0.20–0.30 wt%, with the sum of the mass percentages of all components being 100 wt%.

[0009] The rare earth oxide is one or more of Yb₂O₃, Dy₂O₃, and Ho₂O₃. Preferably, the content of Yb₂O₃ is 0–0.50 wt%, the content of Dy₂O₃ is 0–0.20 wt%, and the content of Ho₂O₃ is 0–0.20 wt%, and the content of at least one of the three is greater than 0. 3+ Dy 3+ and Ho 3+ BaTiO3 exhibits amphoteric occupancy at both A and B sites within its lattice, which can regulate the balance between donor and acceptor compensation and promote the formation of a stable core-shell structure.

[0010] The CeO2 and WO3 together constitute an oxygen vacancy trapping and redox buffer component, with a mass ratio of CeO2 to WO3 of 1:1 to 2:1. CeO2 can be used in reduction sintering and re-oxidation processes via CeO2. 4+ / Ce 3+ Valence state transition buffer electron concentration, W in WO3 6+ It can form high-valence compensation centers and reduce the effective mobility of oxygen vacancies; the synergistic effect of the two is beneficial to inhibiting Ti 4+ Excessive reduction and migration of oxygen vacancies along grains and grain boundaries.

[0011] The glass sintering aid is a low-melting-point composite oxide based on SiO2-B2O3-Al2O3-BaO-CaO or a low-melting-point composite oxide based on SiO2-B2O3-Al2O3-BaO-MgO. During sintering, the glass sintering aid promotes ceramic densification and forms a high-resistivity phase in the grain boundary thin layer and grain boundary bifurcation region, thereby increasing the grain boundary insulation barrier and reducing the probability of continuous migration of oxygen vacancies along the grain boundaries.

[0012] After sintering, the ceramic material forms a BaTiO3 core-shell structure grain. The core of the BaTiO3 core-shell structure grain is dominated by tetragonal BaTiO3, while the shell and grain boundary regions are enriched with Mg, Mn, Ce, and rare earth elements relative to the core. Preferably, the thickness of the shell is 25–80 nm, and the average grain size of the sintered ceramic material is 0.15–0.45 μm.

[0013] This invention also provides a method for preparing the oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic material, comprising the following steps:

[0014] Step S1, Ingredients: Weigh BaTiO3, MgCO3, MnCO3, CeO2, WO3, rare earth oxides and glass sintering aid according to the above mass percentages.

[0015] Step S2, ball milling, drying, granulation and molding: The components weighed in step S1 are mixed with deionized water and zirconium balls and wet ball milled to obtain a slurry; after drying the slurry, polyvinyl alcohol is added for granulation to obtain granulated material; the granulated material is pressed into shape to obtain a green body.

[0016] Step S3, reduction sintering: The green body is placed in a H2-N2 reducing atmosphere and sintered at 1270-1330 °C for 2-4 h to obtain a sintered body.

[0017] Step S4, re-oxidation: The sintered body is placed in an N2 atmosphere containing 10-200 ppm O2 and re-oxidized at 900-1100℃ for 2 h to obtain the oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic material.

[0018] Preferably, in step S2, the ratio of the total mass of deionized water, zirconium balls, and the components weighed in step S1 is 2:1:1, the wet ball milling speed is 280 r / min, and the wet ball milling time is 3 to 16 h; the slurry is dried at 100 °C, the amount of polyvinyl alcohol added is 15% of the mass of the dried powder, the particle size of the granulated material is 80 to 250 mesh, and the pressing pressure is 12 MPa.

[0019] Preferably, in step S3, the H2-N2 reducing atmosphere is a 1% H2-99% N2 atmosphere or a 2% H2-98% N2 atmosphere, the gas flow rate is 50-70 sccm, the heating rate is 3 ℃ / min, and the cooling rate is 4 ℃ / min; in step S4, the gas flow rate of the N2 atmosphere containing 10-200 ppm O2 is 50-70 sccm.

[0020] Beneficial effects of the present invention

[0021] 1. CeO2 and WO3 together constitute oxygen vacancy trapping and redox buffer components, which can synergistically suppress electron accumulation and oxygen vacancy migration during reduction sintering and re-oxidation, thereby reducing the risk of semiconductorization of the dielectric layer.

[0022] 2. One or more of Yb2O3, Dy2O3 and Ho2O3, together with MgCO3 and MnCO3, can synergistically regulate the lattice occupancy and defect compensation of BaTiO3, which is beneficial to stabilizing the core-shell structure and satisfying the X7R temperature characteristics.

[0023] 3. Glass sintering aids promote ceramic densification and increase the grain boundary insulation barrier, which helps reduce leakage current and improve insulation reliability.

[0024] 4. The present invention employs wet ball milling, conventional granulation molding, reducing atmosphere sintering, and re-oxidation treatment, and the process flow is highly compatible with the production of BME-MLCC dielectric ceramics.

[0025] 5. The ceramic material prepared in the examples exhibits a dielectric constant of 2610–3200, a dielectric loss of 0.5%–1.6%, and an insulation resistivity of 1.3 × 10⁻⁶ under conditions of 25 °C and 1 kHz. 12 ~3.1×10 12 Ω·cm, and meets the X7R temperature characteristics in the range of -55 ℃ to 125 ℃. Attached Figure Description

[0026] Figure 1 This is a schematic flowchart of the preparation method of the reduction-resistant high-performance X7R type ceramic material of the present invention;

[0027] Figure 2These are characteristic curves showing the change of dielectric constant as a function of temperature for the samples in Examples 1-8 of this invention.

[0028] Figure 3 This is a characteristic curve of the dielectric constant of the samples in Examples 1-8 of the present invention as a function of temperature. Detailed Implementation

[0029] Examples 1-8

[0030] Step S1, Ingredients: Weigh BaTiO3, MgCO3, MnCO3, CeO2, Yb2O3, Dy2O3, Ho2O3, WO3, and glass sintering aid according to the mass percentages listed in Table 1. "—" in Table 1 indicates no addition, and the corresponding content is calculated as 0; the sum of the mass percentages of the components in each embodiment is 100 wt%.

[0031] Step S2, ball milling: Add the components weighed in step S1 into a ball mill jar, mix them according to the mass ratio of deionized water, zirconium balls and powder of 2:1:1, and wet ball mill at 280 r / min for 10 h to obtain a uniform slurry.

[0032] Step S3, drying, granulation and molding: The slurry obtained in step S2 is dried in an oven at 100 ℃, and polyvinyl alcohol accounting for 15% of the mass of the dried powder is added for granulation. The particle size of the granulated material is controlled to be 80-250 mesh. It is pressed into a green body with a diameter of about 10 mm and a thickness of about 1 mm under a pressure of 12 MPa.

[0033] Step S4, reduction sintering: The green blank obtained in step S3 is placed in a 1% H2-99% N2 atmosphere or a 2% H2-98% N2 atmosphere, heated to 1270-1320 ℃ at a heating rate of 3 ℃ / min, held at that temperature for 2-3 h, and then cooled at a cooling rate of 4 ℃ / min; the gas flow rate of the reducing atmosphere is 50-70 sccm.

[0034] Step S5, re-oxidation: The sintered body obtained in step S4 is placed in an N2 atmosphere containing 10-200 ppm O2 and re-oxidized at 900-1000 °C for 2 h to obtain oxygen vacancy trapping type reduction-resistant X7R barium titanate ceramic material. The specific ingredients, process parameters and performance test results of each embodiment are shown in Tables 1, 2 and 3, respectively.

[0035] Table 1. Ingredients (wt%) of Oxygen Vacancy Trapping Type Reduction-Resistant X7R Barium Titanate Ceramic Materials in Examples 1-8

[0036]

[0037] Table 2 Process parameters for oxygen vacancy trapping type reduction-resistant X7R barium titanate ceramic materials (Examples 1-8)

[0038]

[0039] Table 3 Performance of Oxygen Vacancy Trapping Reduction-Resistant X7R Barium Titanate Ceramic Materials (Examples 1-8)

[0040] .

Claims

1. An oxygen vacancy-trapping, reduction-resistant barium X7R titanate ceramic material, characterized in that, The ceramic material is based on BaTiO3 with an average particle size of 80–250 nm as the main material, and by mass percentage comprises BaTiO3 98.00–98.80 wt%, MgCO3 0.10–0.70 wt%, MnCO3 0.10–0.70 wt%, CeO2 0.10–0.20 wt%, WO3 0.10 wt%, rare earth oxides 0.30–0.50 wt%, and glass sintering aid 0.20–0.30 wt%, with the sum of the mass percentages of all components being 100 wt%; the rare earth oxides are one or more of Yb2O3, Dy2O3, and Ho2O3.

2. The oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic material according to claim 1, characterized in that, The rare earth oxides include 0-0.50 wt% Yb2O3, 0-0.20 wt% Dy2O3, and 0-0.20 wt% Ho2O3, and the content of at least one of Yb2O3, Dy2O3, and Ho2O3 is greater than 0.

3. The oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic material according to claim 1 or 2, characterized in that, The CeO2 and the WO3 together constitute an oxygen vacancy trapping and redox buffer component, and the mass ratio of the CeO2 to the WO3 is 1:1 to 2:

1.

4. The oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic material according to any one of claims 1 to 3, characterized in that, The glass sintering aid is a low-melting-point composite oxide based on SiO2-B2O3-Al2O3-BaO-CaO or a low-melting-point composite oxide based on SiO2-B2O3-Al2O3-BaO-MgO.

5. The oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic material according to any one of claims 1 to 4, characterized in that, The ceramic material has a BaTiO3 core-shell structure grain, wherein the core of the BaTiO3 core-shell structure grain is mainly composed of tetragonal BaTiO3, and the shell and grain boundary regions are enriched with Mg, Mn, Ce and rare earth elements relative to the core; the thickness of the shell is 25-80 nm, and the average grain size of the ceramic material after sintering is 0.15-0.45 μm.

6. The oxygen vacancy trapping type anti-reduction X7R barium titanate ceramic material according to any one of claims 1 to 5, characterized in that, The ceramic material exhibits a dielectric constant of 2610–3200, a dielectric loss of 0.5%–1.6%, and an insulation resistivity of 1.3 × 10⁻⁶ under conditions of 25 °C and 1 kHz. 12 ~3.1×10 12 Ω·cm; with the capacitance at 25 °C as a reference, the capacitance change rate of the ceramic material in the range of -55 °C to 125 °C does not exceed ±15%.

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