X7R barium titanate-based dielectric ceramic material with high bias stability and reduction resistance and preparation method thereof

Abstract

The invention discloses an X7R barium titanate-based dielectric ceramic material with high bias stability and reduction resistance, the chemical composition expression of the material is BaTiO3-aMnO2-bCaZrO3-cSiO2-xmol% Yb2O3, in the formula, a is 0.005 to 0.01, b is 0.02 to 0.06, c is 0.005 to 0.02, and 0.5 lt; xlt; 3. The particle size of the X7R barium titanate-based dielectric ceramic material after sintering can be as small as 200nm, the X7R barium titanate-based dielectric ceramic material is very beneficial to the demand of miniaturized MLCC, not only has high bias stability and reduction resistance, but also has high resistivity and low loss, the ceramic resistivity reaches 1011 omega.cm, the dielectric constant is up to 1400 or above, the temperature stability TCC is less than or equal to 15% in the range of-55 DEG C to 125 DEG C, the X7R standard is met, and the dielectric ceramic material has good application prospects. The loss is lower than 1%, and the direct-current bias stability is lower than 7%. A solid phase method is used for preparation, and the method is simple in process, environmentally friendly, good in repeatability, moderate in cost and suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic materials and devices, and particularly relates to an X7R barium titanate-based dielectric ceramic material with high bias voltage stability and anti-reduction property and a preparation method thereof. Background Art

[0002] With the rapid development of modern electronic industry, multilayer ceramic capacitors (MLCCs) are increasingly widely used in electronic devices, and the market has higher and higher requirements for their performance. It is necessary to achieve miniaturization and high reliability. According to the Electronic Industries Alliance (EIA) standard, the X7R type MLCC refers to that with the capacitance value at 25 °C as the reference, within the temperature range of -55 °C to 125 °C, the capacitance change rate (TCC) does not exceed ±15%. At present, the dielectric materials of X7R type MLCC mainly use barium titanate (BaTiO3) as the matrix. Because of its high dielectric constant, its temperature stability can be improved by means of doping modification, etc., so as to meet the performance requirements of X7R type MLCC.

[0003] In the prior art, X7R type barium titanate-based dielectric ceramic materials usually adjust their dielectric properties and temperature stability by doping rare earth elements (such as La, Nd, Sm, etc.) or transition metal elements (such as Mn, Mg, Co, etc.). For example, common chemical compositions include doping a small amount of MgO, MnO2, Y2O3, etc. in the BaTiO3 matrix to inhibit grain growth and improve the temperature stability of the dielectric constant. However, these materials still have some defects and deficiencies in practical applications. First, with the development of MLCC towards miniaturization and high capacitance, the thickness of the dielectric layer is continuously reduced (from 10 μm in the early stage to 0.3 μm currently), and the number of layers is significantly increased (from less than 100 layers to more than 1000 layers), resulting in a significant increase in the DC voltage borne by each dielectric layer. Therefore, the dielectric material needs to have excellent bias voltage stability to avoid significant degradation of dielectric properties under high electric fields. However, the X7R type barium titanate-based dielectric materials in the prior art are insufficient in bias voltage stability. Especially under high electric field conditions, the capacitance value is prone to significant changes, affecting the reliability and service life of MLCC.

[0004] Secondly, in order to reduce production costs, base metals such as copper (Cu) and nickel (Ni) are generally used as internal electrode materials in modern MLCC manufacturing. This requires the sintering process to be carried out in a reducing atmosphere to prevent oxidation of the internal electrodes. However, barium titanate-based dielectric materials are prone to semi-conduction in a reducing atmosphere, resulting in a sharp decline in dielectric properties. Although in the prior art, doping certain elements (such as Mn, Mg, etc.) can improve the anti-reduction property of the material to a certain extent, these improvements are often insufficient to meet the stability requirements under high reducing atmosphere. Especially during the high-temperature sintering process, the anti-reduction property of the material is still insufficient.

[0005] In summary, although the X7R type barium titanate-based dielectric ceramic materials in the prior art have made certain progress in dielectric constant and temperature stability, they still have obvious deficiencies in high bias stability and anti-reduction. These defects limit their application in high-end MLCCs, especially their long-term reliability under high electric field and reducing atmosphere conditions. Therefore, the development of an X7R type barium titanate-based dielectric ceramic material with both high bias stability and excellent anti-reduction has become a key technical issue that needs to be urgently solved in the current MLCC field. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reduction performance in view of the shortcomings of the above-mentioned prior art. The material is sintered in a reducing atmosphere and exhibits excellent electrical properties, with a dielectric constant greater than 1400, a dielectric loss less than 1%, and an insulation resistivity of up to 10 11 Ω·cm, the bias stability is less than 7%, and meets the X7R specification standard.

[0007] The technical solution adopted by the present invention to solve the above-mentioned problems is:

[0008] A X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reduction properties, wherein the nominal chemical composition is 1BaTiO3-aMnO2-bCaZrO3-cSiO2-xmol%Yb2O3, wherein a is 0.005-0.01, b is 0.02-0.06, c is 0.005-0.02, 0.5 <x<3,a、b和c均为化学组成表达式的化学计量数,BaTiO3的化学计量数作为基准1;xmol%代表Yb2O3占BaTiO3的物质的量分数。

[0009] The method for preparing the X7R barium titanate-based dielectric ceramic material with high bias stability and reduction resistance comprises the following steps:

[0010] (1) BaTiO3, MnO2, CaZrO3, SiO2 and Yb2O3 are used as raw materials, and the ingredients are prepared according to the corresponding molar ratios in the nominal composition formula 1BaTiO3-aMnO2-bCaZrO3-cSiO2-xmol%Yb2O3, wherein a is 0.005-0.01, b is 0.02-0.06, c is 0.005-0.02, 0.5 <x<3,即配料时BaTiO3、MnO2、CaZrO3、SiO2和Yb2O3的物质的量之比(即摩尔数之比)为1:(0.005~0.01):(0.02~0.06):(0.005~0.02):x%;

[0011] (2) Ball mill and dry the raw materials weighed in step (1) to obtain ceramic powder.

[0012] (3) Mix and grind the ceramic powder obtained in step (2) with a binder, granulate and screen it, and dry-press it into a green ceramic body.

[0013] (4) Keep the green ceramic body obtained in step (3) at 500 - 700 °C in air for 1.5 - 3 hours to discharge the binder, then use zirconia as the cushion firing powder for the obtained block, and sinter it at 1200 - 1300 °C for 1 - 3 hours in a reducing atmosphere to obtain the X7R barium titanate-based dielectric ceramic material with high bias voltage stability and anti-reduction property.

[0014] According to the above scheme, in step (1), the molar ratio of BaTiO3, MnO2, CaZrO3, SiO2 and Yb2O3 during batching is preferably 1:0.007:0.03:0.01:x%, where 1.5 ≤ x ≤ 2.5.

[0015] According to the above scheme, in step (2), the ball milling uses zirconia balls and absolute ethanol as the medium, places them in a nylon planetary ball mill jar for ball milling for 12 - 14 h, and the rotation speed is 1000 - 1200 r / min; the drying is carried out at 90 - 110 °C for 12 - 24 hours.

[0016] According to the above scheme, in step (3), the binder is an aqueous solution of polyvinyl alcohol, with a concentration of 2 - 6 wt%, and its addition amount is 2 - 12% of the ceramic mass; the screening is through an 80 - 120 mesh sieve; the pressure of the dry pressing is 150 - 200 Mpa.

[0017] According to the above scheme, in step (4), the debinding is carried out by heating at a heating rate of 0.5 - 2 °C / min to 500 - 700 °C and keeping it for 1 - 3 h to discharge polyvinyl alcohol.

[0018] According to the above scheme, in step (4), the sintering is carried out by heating at a heating rate of 3 - 10 °C / min to 900 - 1100 °C, and then heating at a heating rate of 1.5 - 2.5 °C / min to 1180 °C - 1300 °C and keeping it for 1.5 - 2.5 hours, and then cooling naturally with the furnace.

[0019] According to the above scheme, in step (4), the reducing atmosphere is composed of hydrogen and an inert gas, or the reducing atmosphere is composed of hydrogen and nitrogen, where the volume fraction of hydrogen accounts for 0.4 - 0.6% of the total volume of the reducing atmosphere.

[0020] The X7R barium titanate-based dielectric ceramic material with high bias voltage stability and anti-reduction property prepared by the above method has an average grain size of 150 - 300 nm, and the insulation resistivity is at 10 11~10 12 In the range of Ω·cm, the dielectric constant is greater than 1400, the dielectric loss is lower than 1%, the temperature stability TCC≦15% at -55~125℃ meets the X7R specification standard, and the bias change rate is less than 7% under the DC bias electric field of 0~2V / μm.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] First, by adding MnO2, CaZrO3, SiO2 and Yb2O3 to BaTiO3, the present invention forms a ceramic with a nominal chemical composition of 1BaTiO3-aMnO2-bCaZrO3-cSiO2-xmol%Yb2O3, where 0.5<x<3. The present invention uses 1BaTiO3-aMnO2-bCaZrO3-cSiO2 as the basic formula, reduces the dielectric loss by Mn, reduces the sintering temperature by Si, and adjusts the Curie temperature by combining Ca and Zr; on this basis, a certain amount of Yb2O3 is added. The Yb element basically belongs to the rare earth element with the smallest ionic radius and has a relatively slow diffusion rate in barium titanate, and it is easy to form high-concentration doping or generate a second phase on the ceramic surface, which can effectively regulate the structure, morphology and properties of the barium titanate-based ceramic, and then affect its dielectric properties. The X7R barium titanate-based dielectric ceramic material described in the present invention can reach a minimum particle size of 200nm after sintering, which is very beneficial to the requirements of miniaturized MLCC. It not only has high bias stability and anti-reduction properties, but also has high resistivity and low loss. The ceramic resistivity reaches 10 11 Ω·cm, the dielectric constant is as high as more than 1400, the temperature stability TCC≦15% in the range of -55℃~125℃, meets the X7R specification standard, the loss is lower than 1%, and the DC bias stability is less than 7%. Among them, when 1.5≤x≤2.5, the X7R barium titanate-based dielectric ceramic material described in the present invention has more excellent performance, and the DC bias stability is less than 4%.

[0023] Second, the present invention realizes the regulation of the particle size of the BT ceramic through Yb2O3. The particle size of the ceramic prepared by the system of the present invention shows a positive correlation with the content of Yb2O3. This is because when introducing the Yb2O3 component into the matrix of 1BaTiO3-aMnO2-bCaZrO3-cSiO2, a second phase of Yb2Ti2O7 is generated, and the Zener effect occurs, inhibiting the growth of grains, so that a barium titanate matrix ceramic material with a small particle size can be prepared; at the same time, precisely because the small grain size increases the domain wall density, the bias stability of the material is well improved, and the doping of Yb belongs to the acceptor doping at the Ti site, which can introduce oxygen vacancies and improve the anti-reduction performance of the material.

[0024] Thirdly, the present invention uses a solid-phase method for preparation, which has a simple process, is green and environmentally friendly, has good repeatability, a moderate cost, and is suitable for industrial production.

[0025] Description of the Drawings

[0026] Figure 1 It is the X-ray diffraction pattern of the barium titanate-based dielectric ceramic material samples prepared in Comparative Examples 1-2 and Examples 1-4 of the present invention.

[0027] Figure 2 It is the scanning electron microscope photograph of the barium titanate-based dielectric ceramic material samples prepared in Comparative Examples 1-2 and Examples 1-4 of the present invention.

[0028] Figure 3 It is the capacitance-temperature change rate diagram (a) and TCC diagram (b) (-55°C to 125°C) of the barium titanate-based dielectric ceramic material samples prepared in Comparative Examples 1-2 and Examples 1-4 of the present invention.

[0029] Figure 4 It is the relationship diagram (a) and change rate diagram (b) (0 to 2 V / μm) of the DC bias voltage applied to the barium titanate-based dielectric ceramic material samples prepared in Comparative Examples 1-2 and Examples 1-4 of the present invention and the dielectric constant.

[0030] In the above drawings, 0Yb represents Comparative Example 1 (i.e., x = 0 mol%), 1Yb represents Comparative Example 2 (i.e., x = 0.5 mol%), 2Yb represents Example 1 (i.e., x = 1 mol%), 3Yb represents Example 2 (i.e., x = 1.5 mol%), 4Yb represents Example 3 (i.e., x = 2 mol%), and 5Yb represents Example 4 (i.e., x = 2.5 mol%). Detailed Embodiments

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the embodiments and the drawings.

[0032] In the following embodiments and comparative examples, each raw material is in powder form, and the average particle size is about 100 nm.

[0033] Example 1

[0034] An X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reducibility, whose chemical composition expression is 1BaTiO3 - 0.03CaZrO3 - 0.007MnO - 0.01SiO2 - 1 mol% Yb2O3, and its preparation method specifically includes the following steps:

[0035] (1) According to the chemical composition expression, using BaTiO3, CaZrO3, MnO2, SiO2, and Yb2O3 as raw materials, weigh each raw material according to the molar ratio of BaTiO3, CaZrO3, MnO2, SiO2, and Yb2O3 being 1:0.03:0.007:0.01:0.01;

[0036] (2) Put the five raw materials weighed in step (1) into a material tank, use zirconia balls and absolute ethanol as media, ball mill on a planetary ball mill for 6 h at a rotational speed of 1200 r / min, and then dry at 110 °C for 24 h. After drying, ceramic powder is obtained;

[0037] (3) Add a 5 wt% aqueous solution of polyvinyl alcohol as a binder to the ceramic powder obtained in step (2), add the binder at 2 drops / g of the ceramic powder, mix evenly and then granulate, pass through a 100-mesh sieve, age for 24 h after sieving, and then dry-press it into shape with a tablet press at a molding pressure of 150 MPa to obtain a green ceramic disc with a diameter of 12 mm and a thickness of about 1 mm;

[0038] (4) Heat the green ceramic disc obtained in step (3) in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min and hold for 2 hours, then cool naturally with the furnace to discharge polyvinyl alcohol organic impurities; subsequently, introduce a reducing atmosphere (composed of 99.5% N2 + 0.5% H2 by volume percentage) into a tubular furnace, and heat it to 1000 °C at a heating rate of 2 °C / min, then heat it to 1220 °C at a heating rate of 2 °C / min, and hold for 2 h, and then cool to 800 °C at a rate of 2 °C / min and cool naturally with the furnace to obtain the sample of the X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reducibility.

[0039] Perform X-ray diffraction (XRD) testing on the X7R barium titanate-based dielectric ceramic material prepared in Example 1. The XRD pattern is as Figure 1 shown. It can be seen that the ceramic material is a pure perovskite structure without obvious second phases.

[0040] After crushing the X7R barium titanate-based dielectric ceramic material prepared in Example 1, select a ceramic block with a suitable shape and perform thermal etching in a reducing atmosphere (99.5% N2 + 0.5% H2) at 1170 °C for 30 min, then clean and dry the sample after thermal etching with absolute ethanol, and test its cross-sectional microstructure, as Figure 2 shown. The ceramic samples after thermal etching all show high crystallinity, uniform grain size, no second phases, and the average grain size is 276 nm.

[0041] The two sides of the X7R barium titanate-based dielectric ceramic material prepared in Example 1 were ground flat, polished, and coated with silver electrodes. The specific method was as follows: a small brush was used to apply silver paste on the upper and lower surfaces of the X7R barium titanate-based dielectric ceramic material, then it was dried in an oven at 100 °C, and then sintered in a muffle furnace at 580 °C for 30 minutes. Its dielectric properties were tested as Figure 3 (a) shown. The X7R barium titanate-based dielectric ceramic material had a dielectric constant (25 °C) of approximately 1440 and a dielectric loss (Tanδ) of approximately 0.83% at a frequency of 1 kHz and room temperature; its temperature stability was as Figure 3 (b) shown. The TCC was ≤ ±15% in the temperature range of -55 °C to 125 °C, meeting the X7R specification standard.

[0042] The insulation resistivity of the X7R barium titanate-based dielectric ceramic material prepared in Example 1 was tested under an AC electric field of 1 kV / mm. As shown in Table 1, its insulation resistivity (Resistivity(25 °C)) at room temperature reached 4.54×10 11 Ω·cm.

[0043] The DC bias performance of the X7R barium titanate-based dielectric ceramic material prepared in Example 1 was tested by applying a DC voltage at 1 kHz. As Figure 4 (a) shown, at a frequency of 1 kHz, its dielectric constant was between 3000 and 1800 in the range of 0 to 2 V / μm, and the change rate was as Figure 4 (b) shown. The bias change rate in the range of 0 to 2 V / μm was 6.59%.

[0044] Example 2

[0045] An X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reduction properties, whose chemical composition expression is 1BaTiO3 - 0.03CaZrO3 - 0.007MnO2 - 0.01SiO2 - 1.5 mol% Yb2O3. Its preparation method specifically includes the following steps:

[0046] (1) According to the chemical composition expression, using BaTiO3, CaZrO3, MnO2, SiO2, and Yb2O3 as raw materials, each raw material was weighed according to the molar ratio of BaTiO3, CaZrO3, MnO2, SiO2, and Yb2O3 of 1:0.03:0.007:0.01:0.015;

[0047] (2) The five raw materials weighed in step (1) were put into a material tank, using zirconia balls and anhydrous ethanol as media, ball-milled on a planetary ball mill for 6 h at a rotation speed of 1200 r / min, and then dried at 110 °C for 24 h. After drying, ceramic powder was obtained;

[0048] (3) Add an aqueous solution of polyvinyl alcohol with a concentration of 5 wt% as a binder to the ceramic powder obtained in step (2). Add the binder at a rate of 2 drops / g of the ceramic powder. After mixing evenly, granulate the mixture, sieve it through a 100-mesh sieve, age it for 24 h after sieving, and then dry-press it into a shape using a tablet press at a forming pressure of 150 MPa to obtain a green ceramic disc with a diameter of 12 mm and a thickness of about 1 mm;

[0049] (4) Heat the green ceramic disc obtained in step (3) in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min and hold for 2 hours, then cool it naturally in the furnace to remove polyvinyl alcohol organic impurities; Subsequently, introduce a reducing atmosphere (99.5% N2 + 0.5% H2) into a tubular furnace, and heat it to 1000 °C at a heating rate of 2 °C / min, then heat it to 1220 °C at a heating rate of 2 °C / min, and hold for 2 h. After that, cool it to 800 °C at a rate of 2 °C / min and cool it naturally in the furnace to obtain the sample of the X7R barium titanate-based dielectric ceramic material with high bias voltage stability and anti-reduction property.

[0050] Perform X-ray diffraction (XRD) testing on the X7R barium titanate-based dielectric ceramic material prepared in Example 2. The XRD pattern is as Figure 1 shown. It can be seen that the ceramic material is a pure perovskite structure without obvious secondary phases.

[0051] After crushing the X7R barium titanate-based dielectric ceramic material prepared in Example 2, select a ceramic block with a suitable shape and perform thermal etching at 1170 °C for 30 min in a reducing atmosphere (99.5% N2 + 0.5% H2). Then, clean the thermally etched sample with absolute ethanol and dry it, and test its cross-sectional microstructure, as Figure 2 shown. The thermally etched ceramic samples all show high crystallinity, uniform grain size, no secondary phases, and an average grain size of 201 nm.

[0052] Grind and polish both sides of the X7R barium titanate-based dielectric ceramic material prepared in Example 2 and coat silver electrodes, and test its dielectric properties as Figure 3 (a) shown. At a frequency of 1 kHz and room temperature, the dielectric constant (25 °C) is about 1623, and the dielectric loss (Tanδ) is about 0.76%; The temperature stability is as Figure 3 (b) shown. In the temperature range of -55 °C to 125 °C, TCC ≤ ±15%, meeting the X7R specification standard.

[0053] Test the insulation resistivity of the X7R barium titanate-based dielectric ceramic material prepared in Example 2 under an AC electric field of 1 kV / mm. As shown in Table 1, its insulation resistivity at room temperature (Resistivity(25 °C)) reaches 7.76×10 11 Ω·cm.

[0054] The X7R barium titanate-based dielectric ceramic material prepared in Example 2 was tested for DC bias performance by applying a DC voltage at 1 kHz, as Figure 4 (a) shows. At a frequency of 1 kHz, the dielectric constant is between 3000 and 1800 at 0 - 2 V / μm, and the change rate is as Figure 4 (b) shows. The bias change rate at 0 - 2 V / μm is 3.27%.

[0055] Example 3

[0056] An X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reduction property, whose chemical composition expression is 1BaTiO3 - 0.03CaZrO3 - 0.007MnO2 - 0.01SiO2 - 2mol% Yb2O3. Its preparation method specifically includes the following steps:

[0057] (1) According to the chemical composition expression, using BaTiO3, CaZrO3, MnO2, SiO2, and Yb2O3 as raw materials, weigh each raw material according to the molar ratio of BaTiO3:CaZrO3:MnO2:SiO2:Yb2O3 being 1:0.03:0.007:0.01:0.02;

[0058] (2) Put the five raw materials weighed in step (1) into a material tank, use zirconia balls and absolute ethanol as media, ball mill for 6 h on a planetary ball mill at a rotation speed of 1200 r / min, and then dry at 110 °C for 24 h. After drying, ceramic powder is obtained;

[0059] (3) Add a 5wt% aqueous solution of polyvinyl alcohol as a binder to the ceramic powder obtained in step (2), add the binder at 2 drops / g of ceramic powder, mix evenly and then granulate, pass through a 100-mesh sieve, age for 24 h after sieving, and then dry-press it into shape with a tablet press at a forming pressure of 150 MPa to obtain a green ceramic disc with a diameter of 12 mm and a thickness of about 1 mm;

[0060] (4) Heat the green ceramic disc obtained in step (3) in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min and hold for 2 hours, then cool naturally with the furnace to remove polyvinyl alcohol organic impurities; subsequently, introduce a reducing atmosphere (99.5% N2 + 0.5% H2) into a tube furnace, and heat it to 1000 °C at a heating rate of 2 °C / min, then heat it to 1220 °C at a heating rate of 2 °C / min, hold for 2 h, and then cool to 800 °C at a rate of 2 °C / min and cool naturally with the furnace to obtain the sample of the X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reduction property.

[0061] The X7R barium titanate-based dielectric ceramic material prepared in Example 3 was subjected to X-ray diffraction (XRD) testing. The XRD pattern is as Figure 1 shown. It can be seen that the ceramic material has a pure perovskite structure and no obvious secondary phase.

[0062] After the X7R barium titanate-based dielectric ceramic material prepared in Example 3 was crushed, ceramic blocks with appropriate shapes were selected and thermally etched at 1170 °C for 30 min in a reducing atmosphere (99.5% N2 + 0.5% H2). Then, the samples after thermal etching were cleaned with absolute ethanol and dried, and their cross-sectional microtopographies were tested. As Figure 2 shown, the ceramic samples after thermal etching all showed high crystallinity, uniform grain sizes, no secondary phase, and the average grain size was 191 nm.

[0063] Both sides of the X7R barium titanate-based dielectric ceramic material prepared in Example 3 were ground, polished, and coated with silver electrodes, and its dielectric properties were tested. As Figure 3 (a) shown, at a frequency of 1 kHz and room temperature, the dielectric constant (25 °C) was approximately 1510, and the dielectric loss (Tanδ) was approximately 0.86%; the temperature stability was as Figure 3 (b) shown. In the temperature range of -55 °C to 125 °C, TCC ≤ ±15%, meeting the X7R specification standard.

[0064] The insulation resistivity of the X7R barium titanate-based dielectric ceramic material prepared in Example 3 was tested under an AC electric field of 1 kV / mm. As shown in Table 1, its insulation resistivity at room temperature (Resistivity(25 °C)) reached 8.68×10 11 Ω·cm.

[0065] The DC bias performance of the X7R barium titanate-based dielectric ceramic material prepared in Example 3 was tested by applying a DC voltage at 1 kHz. As Figure 4 (a) shown, at a frequency of 1 kHz, the dielectric constant was between 3000 and 1800 in the range of 0 to 2 V / μm, and the change rate was as Figure 4 (b) shown. The bias change rate in the range of 0 to 2 V / μm was 3.80%.

[0066] Example 4

[0067] An X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reducibility, whose chemical composition expression is 1BaTiO3 - 0.03CaZrO3 - 0.007MnO2 - 0.01SiO2 - 2.5 mol% Yb2O3. Its preparation method specifically includes the following steps:

[0068] (1) According to the chemical composition expression, using BaTiO3, CaZrO3, MnO2, SiO2, and Yb2O3 as raw materials, weigh each raw material according to the molar ratio of BaTiO3, CaZrO3, MnO2, SiO2, and Yb2O3 being 1:0.03:0.007:0.01:0.025;

[0069] (2) Put the five raw materials weighed in step (1) into a material tank, use zirconia balls and anhydrous ethanol as media, ball mill for 6 h on a planetary ball mill at a rotation speed of 1200 r / min, and then dry at 110 °C for 24 h. After drying, ceramic powder is obtained;

[0070] (3) Add an aqueous solution of polyvinyl alcohol with a concentration of 5 wt% as a binder to the ceramic powder obtained in step (2), add the binder at 2 drops / g of the ceramic powder, mix evenly and then granulate, pass through a 100-mesh sieve, age for 24 h after sieving, and then dry-press it into shape with a tablet press at a forming pressure of 150 MPa to obtain a green ceramic disc with a diameter of 12 mm and a thickness of about 1 mm;

[0071] (4) Heat the green ceramic disc obtained in step (3) in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min and hold for 2 hours, and then cool naturally with the furnace to discharge polyvinyl alcohol organic impurities; then introduce a reducing atmosphere (99.5% N2 + 0.5% H2) into a tubular furnace, and heat it to 1000 °C at a heating rate of 2 °C / min, then heat it to 1220 °C at a heating rate of 2 °C / min, and hold for 2 h, and then cool to 800 °C at a rate of 2 °C / min and cool naturally with the furnace to obtain the sample of the X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reducibility.

[0072] Perform X-ray diffraction (XRD) testing on the X7R barium titanate-based dielectric ceramic material prepared in Example 4. The XRD pattern is as Figure 1 shown. It can be seen that the ceramic material is a pure-phase perovskite structure without obvious secondary phases.

[0073] After crushing the X7R barium titanate-based dielectric ceramic material prepared in Example 4, select a ceramic block with a suitable shape and perform thermal etching at 1170 °C for 30 min in a reducing atmosphere (99.5% N2 + 0.5% H2), then clean and dry the sample after thermal etching with anhydrous ethanol, and test its cross-sectional microstructure, as Figure 2 shown. The ceramic samples after thermal etching all show high crystallinity, uniform grain size, no secondary phases, and the average grain size is 221 nm.

[0074] Grind and polish both sides of the X7R barium titanate-based dielectric ceramic material prepared in Example 4 and coat silver electrodes, and test its dielectric properties asFigure 3 As shown in (a), at a frequency of 1 kHz and room temperature, the dielectric constant (25 °C) is approximately 1475, and the dielectric loss (Tanδ) is approximately 0.77%; the temperature stability is as Figure 3 shown in (b). In the temperature range of -55 °C to 125 °C, TCC ≤ ±15%, meeting the X7R specification standard.

[0075] The X7R barium titanate-based dielectric ceramic material prepared in Example 4 was tested for its insulation resistivity under an AC electric field of 1 kV / mm. As shown in Table 1, its insulation resistivity at room temperature (Resistivity(25 °C)) reached 8.86×10 11 Ω·cm.

[0076] The X7R barium titanate-based dielectric ceramic material prepared in Example 4 was tested for its DC bias performance under a DC voltage at 1 kHz. As Figure 4 shown in (a), at a frequency of 1 kHz, the dielectric constant is between 3000 and 1800 in the range of 0 to 2 V / μm, and the change rate is as Figure 4 shown in (b). The bias change rate in the range of 0 to 2 V / μm is 2.53%.

[0077] Comparative Example 1

[0078] A BaTiO3-based dielectric ceramic with a chemical composition expression of BaTiO3, CaZrO3, SiO2, and MnO2. Its preparation method specifically includes the following steps:

[0079] (1) According to the composition expression, raw materials of BaTiO3, CaZrO3, MnO2, and SiO2 were weighed according to a molar ratio of 1:0.03:0.007:0.01.

[0080] (2) The same as step (2) of Example 1;

[0081] (3) The same as step (3) of Example 1;

[0082] (4) The same as step (4) of Example 1.

[0083] The BaTiO3-based dielectric ceramic prepared in Comparative Example 1 was tested by X-ray diffraction (XRD). The XRD pattern is as Figure 1 shown in (). It can be seen from the XRD pattern that the ceramic sample is a pure perovskite structure without obvious secondary phases.

[0084] The BaTiO3-based dielectric ceramic prepared in Comparative Example 1 was crushed, and a ceramic block with a suitable shape was selected for thermal etching at 1170 °C for 30 min in a reducing atmosphere. Then the thermally etched sample was cleaned with anhydrous ethanol and dried, and its cross-sectional microstructure was tested. As Figure 2As shown, the ceramic samples all exhibit high crystallinity, uniform grain size, no second phase, and an average grain size of 1.56 μm.

[0085] The two sides of the BaTiO3-based dielectric ceramic prepared in Comparative Example 1 were ground, polished, and silver electrodes were coated, and the dielectric properties were tested. As Figure 3 (a) shows, the dielectric constant (25 °C) of this BaTiO3-based dielectric ceramic is about 1457 and the dielectric loss (Tanδ) is about 1.21% at a frequency of 1 kHz and room temperature; the temperature stability is as Figure 3 (b) shows, the temperature range with TCC ≤ ±15% is -55 °C to 125 °C, which does not meet the X7R specification standard.

[0086] The insulation resistivity of the BaTiO3-based dielectric ceramic prepared in Comparative Example 1 was tested under an AC electric field of 1 kV / mm. As shown in Table 1, the insulation resistivity (Resistivity(25 °C)) reaches 1.17×10 10 Ω·cm at room temperature.

[0087] The DC bias performance of the BaTiO3-based dielectric ceramic prepared in Comparative Example 1 was tested by applying a DC voltage at 1 kHz. The relationship between the dielectric constant and the change rate with the applied DC bias is as Figure 4 shown. The dielectric constant of this BaTiO3-based dielectric ceramic is in the range of 1400 - 2400 and the change rate is 35.7% at a frequency of 1 kHz and in the range of 0 V / μm - 2 V / μm.

[0088] Comparative Example 2

[0089] A barium titanate-based dielectric ceramic material, whose chemical composition expression is 1BaTiO3 - 0.03CaZrO3 - 0.007MnO - 0.01SiO2 - 0.5 mol% Yb2O3, and its preparation method specifically includes the following steps:

[0090] (1) According to the chemical composition expression, using BaTiO3, CaZrO3, MnO, SiO2, Yb2O3 as raw materials, each raw material was weighed according to the molar ratio of BaTiO3, CaZrO3, MnO, SiO2, Yb2O3 being 1:0.03:0.007:0.01:0.005;

[0091] (2) The same as step (2) of Example 1;

[0092] (3) The same as step (3) of Example 1;

[0093] (4) The same as step (4) of Example 1.

[0094] The barium titanate-based dielectric ceramic material prepared in Comparative Example 2 was tested by X-ray diffraction (XRD), and the XRD pattern is asFigure 1 As shown in (1Yb), it can be seen that the ceramic material is a pure perovskite structure without obvious secondary phases.

[0095] After crushing the barium titanate-based dielectric ceramic material prepared in Comparative Example 2, a ceramic block with a suitable shape was selected and thermally etched at 1170 °C for 30 min in a reducing atmosphere (99.5% N2 + 0.5% H2), and then the thermally etched sample was cleaned with anhydrous ethanol and dried, and its cross-sectional microstructure was tested. As Figure 2 shown in (a), the thermally etched ceramic samples all showed high crystallinity, uniform grain size, no secondary phases, and the average grain size was 1.21 μm.

[0096] The two sides of the barium titanate-based dielectric ceramic material prepared in Comparative Example 2 were ground, polished and coated with silver electrodes, and its dielectric properties were tested. As Figure 3 shown in (left), at a frequency of 1 kHz and at room temperature, the dielectric constant (25 °C) was about 2160, and the dielectric loss (Tanδ) was about 1.12%; the temperature stability was as Figure 3 shown in (right), the temperature range satisfying TCC ≤ ±15% was 22 °C to 68 °C, which did not meet the X7R specification standard.

[0097] The insulation resistivity of the barium titanate-based dielectric ceramic material prepared in Comparative Example 2 was tested under an AC electric field of 1 kV / mm. As shown in Table 1, its insulation resistivity at room temperature (Resistivity(25 °C)) reached 1.17×10 10 Ω·cm.

[0098] The DC bias performance of the barium titanate-based dielectric ceramic material prepared in Comparative Example 2 was tested by applying a DC voltage at 1 kHz. As Figure 4 shown in a(1Yb), at a frequency of 1 kHz, the dielectric constant was between 3000 and 1800 at 0 to 2 V / μm, and the change rate was as Figure 4 shown in b(1Yb), the bias change rate at 0 to 2 V / μm was 40.6%.

[0099] Table 1 gives the comprehensive performance (raw material particle size, whether X7R, bias stability, dielectric constant, loss, resistivity) of the comparative examples and the examples.

[0100] Table 1

[0101]

[0102] Comparing the results of the examples and the comparative examples, it can be seen that: the comparative examples all did not meet the X7R specification standard, and the average grains were relatively large, reaching the micron level; moreover, the resistivity could only reach 10 10Ω·cm, one order of magnitude lower than that of the embodiment; the bias stability is particularly poor, 5 to 15 times that of the embodiment, reaching more than 35%.

[0103] Under the chemical composition (0.5 < x < 3) required by the present invention, the X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reduction property prepared in the embodiment has an average grain size of 150 - 300 nm, an insulation resistivity in the range of 10 11 -10 12 Ω·cm, a dielectric constant greater than 1400, a dielectric loss lower than 1%, a temperature stability TCC ≤ 15% at -55 to 125 °C meeting the X7R specification standard, and a bias change rate less than 7% under a 0 - 2 V / μm DC bias electric field. In particular, when x = 1.5, the dielectric constant of the ceramic is as high as 1623, the loss is only 0.76%, and the resistivity is 7.70×10 11 Ω·cm, meeting the requirements of the X7R specification, and under a DC voltage of 2 V / μm, the change rate of the DC bias stability is only 3.27%, which is the best case. Of course, when x = 2, the dielectric constant is 1510, the loss is 0.86%, and the resistivity is 8.68×10 11 Ω·cm, meeting the requirements of the X7R specification. Under a DC voltage of 2 V / μm, the change rate of the DC bias stability is 3.8%, which is also a better case. Based on the 1BaTiO3-aCaZrO3-bMnO2-cSiO2 basic formula of the present invention, by introducing the Yb2O3 component, first, the acceptor doping of the Yb element at the Ti site introduces oxygen vacancies, inhibits the release of essential oxygen, and improves the anti-reduction performance of the ceramic dielectric in a reducing atmosphere. Second, due to the gradually formed Yb2Ti2O7 pyrochlore phase, the grain growth is inhibited through the Zener effect, and the prepared small-particle-size nano-ceramics are beneficial to the miniaturization of MLCC. Finally, due to the gradual decrease in the grain size, the domains become smaller and the domain wall density increases, and the temperature stability and DC bias stability are well improved.

[0104] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several improvements and transformations can be made, and these all belong to the protection scope of the present invention.

Claims

1. A X7R barium titanate-based dielectric ceramic material with high bias stability and anti-reduction properties, characterized in that: The chemical composition expression of the X7R barium titanate-based dielectric ceramic material is BaTiO3-aMnO2-bCaZrO3-cSiO2-xmol%Yb2O3, where a is 0.005 to 0.01, b is 0.02 to 0.06, c is 0.005 to 0.02, 0.5 < x < 3, and a, b, and c are all stoichiometric coefficients in the chemical composition expression, and xmol% represents the mole fraction of Yb2O3 in BaTiO3.

2. The X7R barium titanate-based dielectric ceramic material with high bias stability and reduction resistance according to claim 1, characterized in that: The insulation resistivity of the X7R barium titanate-based dielectric ceramic material is 10 11 ~10 12 In the Ω·cm range, the dielectric constant is greater than 1400, the dielectric loss is less than 1%, the temperature stability TCC is ≤ 15% at -55 to 125°C, meeting the X7R specification standard, and the bias voltage change rate is less than 7% under a 0 to 2V / μm DC bias electric field.

3. The X7R barium titanate-based dielectric ceramic material with high bias stability and reduction resistance according to claim 1, characterized in that: When 1.5≤x≤2.5, the insulation resistivity of the X7R barium titanate-based dielectric ceramic material is 10 11 ~10 12 In the range of Ω·cm, the dielectric constant is greater than 1450, the dielectric loss is less than 0.85%, the temperature stability TCC is ≤15% at -55~125℃, meeting the X7R specification standard, and the bias voltage change rate is less than 4% under a DC bias electric field of 0~2V / μm.

4. The X7R barium titanate-based dielectric ceramic material with high bias stability and reduction resistance according to claim 1, characterized in that: The average grain size of the X7R barium titanate-based dielectric ceramic material is 150 to 300 nm.

5. The method for preparing the X7R barium titanate-based dielectric ceramic material according to any one of claims 1 to 4, characterized in that: It includes the following steps: (1) Using BaTiO3, MnO2, CaZrO3, SiO2, and Yb2O3 as raw materials, proportioning according to the corresponding molar ratios in the composition chemical expression 1BaTiO3--aMnO2-bCaZrO3-cSiO2-xmol%Yb2O3. When proportioning, the molar ratios of BaTiO3, MnO2, CaZrO3, SiO2, and Yb2O3 are 1:(0.005 to 0.01):(0.02 to 0.06):(0.005 to 0.02):x%; (2) Ball-milling and drying the raw materials weighed in step (1) to obtain ceramic powder; (3) Mixing and grinding the ceramic powder obtained in step (2) with a binder, granulating and sieving, and dry-pressing to form a ceramic green body; (4) Calcining the ceramic green body obtained in step (3) to discharge the binder, and then using zirconia as the cushion firing powder to sinter in a reducing atmosphere to obtain the X7R barium titanate-based dielectric ceramic material with high bias voltage stability and anti-reduction property.

6. The method for preparing the X7R barium titanate-based dielectric ceramic material according to claim 5, characterized in that: In step (1), when proportioning, the molar ratios of BaTiO3, MnO2, CaZrO3, SiO2, and Yb2O3 are 1:0.007:0.03:0.01:x%, where 1.5 ≤ x ≤ 2.

5.

7. The method for preparing the X7R barium titanate-based dielectric ceramic material according to claim 5, characterized in that: In step (2), the ball-milling uses zirconia balls and anhydrous ethanol as media, places them in a nylon planetary ball-milling tank for ball-milling for 12 to 14 h, and the rotation speed is 1000 to 1200 r / min; the drying is carried out at 90 to 110 °C for heat preservation for 12 to 24 hours; In step (3), the binder is an aqueous solution of polyvinyl alcohol with a concentration of 2 to 6 wt%, and its addition amount is 2 to 12% of the ceramic mass; the sieving is through an 80 to 120 mesh sieve; the pressure of the dry pressing is 150 to 200 Mpa; In step (4), the degumming is to raise the temperature at a heating rate of 0.5 to 2 °C / min to 500 to 700 °C for heat preservation for 1 to 3 h to discharge polyvinyl alcohol.

8. The method for preparing the X7R barium titanate-based dielectric ceramic material according to claim 5, characterized in that: In step (4), the sintering is to raise the temperature at a heating rate of 3 to 10 °C / min to 900 to 1100 °C, and then raise the temperature at a heating rate of 1.5 to 2.5 °C / min to 1180 °C to 1300 °C for heat preservation for 1.5 to 2.5 hours, and then cool naturally with the furnace.

9. The method for preparing the X7R barium titanate-based dielectric ceramic material according to claim 5, characterized in that: In step (4), the reducing atmosphere is composed of hydrogen and an inert gas, or the reducing atmosphere is composed of hydrogen and nitrogen, where the volume fraction of hydrogen accounts for 0.4 to 0.6% of the total volume of the reducing atmosphere.

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