Anti-reduction nano BaTiO3-based X7R dielectric ceramic and preparation method thereof

Abstract

The invention discloses an anti-reduction nanometer BaTiO3-based dielectric ceramic and a preparation method of the anti-reduction nanometer BaTiO3-based dielectric ceramic. Nanometer BaTiO3 is used as a matrix, Tm2O3 and MgO are used as modifiers, the chemical expression of the BaTiO3-xTm2O3-yMgO is BaTiO3-xTm2O3-yMgO, x is 0.04-0.07, y is 0.001-0.007, and the dielectric ceramic material which has the room temperature dielectric constant of 1590-1620, meets the X7R standard and has good reduction resistance is obtained through the processes of ball milling, granulation, tabletting, sintering and the like. The dielectric ceramic is simple in component, simple in preparation process, low in cost, good in reduction resistance and stable in dielectric property in a wide temperature range, and is expected to be applied to preparation of a base metal electrode MLCC.

Description

Technical Field

[0001] The present invention designs an anti-reduction nano BaTiO 3 -based X7R dielectric ceramic and a preparation method thereof, which are mainly applied to the field of base metal multilayer ceramic capacitors. Background Art

[0002] Multilayer ceramic capacitors have become the capacitor materials with the fastest development speed and the widest application range due to their advantages such as high specific capacitance, small size, high storage density, and high insulation resistivity. In recent years, with the development of electronic devices, MLCCs have gradually developed towards the direction of large capacitance, small size, and wide temperature range. And from the perspective of cost reduction, base metals such as nickel and copper are applied to the internal electrodes of MLCCs. However, base metals are easily oxidized to corresponding oxides in the air at high temperature and lose their conductivity. Therefore, it is necessary to co-fire with the dielectric layer in a reducing atmosphere. This requires the materials in the dielectric layer to still have a high insulation resistivity in a reducing atmosphere. Due to the miniaturization trend of MLCCs, higher standards are put forward for the crystal grain size of the dielectric layer, and the crystal grain size needs to be reduced to the nanometer level.

[0003] Because barium titanate (BaTiO 3 ) has characteristics such as high dielectric constant, high insulation resistivity, low dielectric loss, and environmental friendliness, it is widely used in the field of MLCC manufacturing and is the preferred matrix material for preparing MLCCs. However, when sintered in a reducing atmosphere, barium titanate 3 produces oxygen vacancies due to the escape of lattice oxygen, thereby generating a large number of free electrons, which causes Ti 4+ to combine with free electrons and transform into Ti 3+ , resulting in an increase in the carrier concentration. This leads to the semi-conduction of the ceramic material, an abnormal increase in the dielectric constant, an increase in loss, and a deterioration of the insulation performance. In addition, barium titanate has multiple phase transitions, and the dielectric constant undergoes a sudden change at about 120 °C, which limits the application temperature range of BaTiO 3 . Therefore, it is very necessary to improve the anti-reduction ability and temperature stability of BaTiO 3 dielectric ceramics for the research of base metal electrode MLCCs and the broadening of their use temperature range. The dielectric constant of BaTiO 3 ceramics is interrelated with the grain size of the ceramic. When the grain size is reduced to the nanometer level, the dielectric constant will also decrease accordingly. To meet the requirements of large capacitance and small size of MLCCs, how to increase the dielectric constant while reducing the crystal grain size is a technical problem that needs to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an anti-reduction nano BaTiO 3X7R-based dielectric ceramics and preparation method. The crystal grain size of the dielectric ceramics is small, with good anti-reduction performance, low loss, and temperature stability meeting the X7R standard.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0006] An anti-reduction nano BaTiO 3 -based X7R dielectric ceramic, which uses nano BaTiO 3 powder as the matrix material, Tm 2 O 3 and MgO as modifiers, and its chemical formula is BaTiO 3 -xTm 2 O 3 -yMgO, where x = 0.04 - 0.07 and y = 0.001 - 0.007. This anti-reduction nano BaTiO 3 -based X7R dielectric ceramic has an insulation resistivity greater than 7.7×10 10 Ω·cm, a room temperature dielectric constant satisfying 1390 - 1620, a dielectric loss tanδ < 0.015, and a capacitance temperature change rate TCC ≤ ±15% within -55 to 125 °C, and its temperature stability meets the X7R standard.

[0007] According to the above scheme, the average grain size of the dielectric ceramic is 150 - 200 nm, the grains with a size greater than 250 nm are less than 10%, and the grains with a size less than 100 nm are less than 5%.

[0008] Preferably, in the chemical formula BaTiO 3 -xTm 2 O 3 -yMgO of the dielectric ceramic material, when x = 0.05 and y = 0.002 - 0.006, the insulation resistivity is about 1×10 11 - 5×10 11 Ω·cm, the room temperature dielectric constant satisfies 1391 - 1620, the dielectric loss tanδ < 0.012, the capacitance temperature change rate TCC ≤ ±15% within -55 to 125 °C, the temperature stability meets the X7R standard, and the average grain size is 170 - 180 nm. Further preferably, when x = 0.05 and y = 0.004 - 0.006, the room temperature dielectric constant is 1590 - 1620.

[0009] The preparation method of the above anti-reduction nano BaTiO 3 -based X7R dielectric ceramic mainly includes the following steps:

[0010] (1) Using nano BaTiO 3 powder, Tm 2 O3 and MgO as raw materials, according to the chemical formula BaTiO 3 -xTm 2 O 3 The raw materials were weighed according to the stoichiometric ratio of the metal atoms in the -yMgO (i.e., the raw materials BaTiO were weighed according to the molar ratio of Ba, Tm and Mg being 1:x:y). 3 、Tm 2 O 3 and MgO), wherein x=0.01-0.07, y=0.001-0.008;

[0011] (2) ball-milling and drying the raw materials weighed in step (1) to obtain ceramic powder;

[0012] (3) grinding the ceramic powder obtained in step (2) and mixing it with a binder, ball milling, granulating and screening, and dry pressing to obtain a ceramic green body;

[0013] (4) The ceramic green body obtained in step (3) is subjected to a binder removal treatment and then sintered in a reducing atmosphere at 1300-1500° C. for 2-3 hours to obtain a reduction-resistant nano BaTiO 3 Based on X7R dielectric ceramic.

[0014] According to the above scheme, the ball milling in step (2) is performed using zirconium oxide balls and anhydrous ethanol as the medium, and the ball milling is performed in a nylon planetary ball mill for 6 to 8 hours at a rotation speed of 1000 to 1200 r / min; the drying in step (2) is performed at 90 to 110° C. for 12 to 14 hours.

[0015] According to the above scheme, the binder added in step (3) is a polyvinyl alcohol aqueous solution with a concentration of 4-5%, and the binder and ceramic powder are granulated at 0.05-0.1 mL / g; the granulated powder is passed through a 100-mesh sieve; and the molding pressure is 150-200 MPa.

[0016] According to the above scheme, the debinding treatment in step (4) is to heat the mixture to 580-620°C at a heating rate of 0.5-3°C / min and keep the temperature for 1.5-3 hours to discharge the polyvinyl alcohol.

[0017] According to the above scheme, the sintering in step (4) is carried out at a heating rate of 3-5°C / min to 900-1100°C, then at a heating rate of 1.5-2.5°C / min to 1400-1500°C, and then cooled with the furnace after keeping the temperature for 2-3 hours.

[0018] According to the above scheme, the composition of the reducing atmosphere in step (4) is calculated by volume percentage: N 2 99.5%, H 2 0.5%, ventilation rate is 50L / h.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. The dielectric ceramic described in the present invention has good anti-reduction performance in the range of x = 0.04 to 0.07. By adding Tm 3 and MgO to nano BaTiO 2 O 3 to form BaTiO 3 -xTm 2 O 3 -yMgO dielectric ceramic, the insulation resistivity is between 7.7×10 10 and 5×10 11 Ω·cm, which is significantly improved compared with the pure BaTiO 3 ceramic sintered in a reducing atmosphere.

[0021] 2. The dielectric ceramic described in the present invention exhibits good anti-reduction performance. In the range of x = 0.04 to 0.07 and y = 0.001 to 0.007, the insulation resistivity is not less than 7.7×10 10 Ω·cm, the room temperature dielectric constant satisfies 1390 to 1620, the dielectric loss tanδ < 0.015, and the capacitance-temperature change rate TCC ≤ ±15% within -55 to 125°C, and the temperature stability meets the X7R standard; preferably, in the range of x = 0.05 and y = 0.002 to 0.006, it has better dielectric loss and insulation resistivity, the dielectric loss tanδ < 0.012, and the insulation resistivity is greater than 1×10 11 Ω·cm; among them, when x = 0.05 and y = 0.004 to 0.006, the room temperature dielectric constant reaches 1590 to 1620.

[0022] 3. The dielectric ceramic described in the present invention exhibits a relatively small crystal grain size, and the average crystal grain size is distributed between 150 and 200 nm.

[0023] 4. The preparation method of the dielectric ceramic described in the present invention is simple. It is sintered in a reducing atmosphere, the raw material components are simple, easy to obtain and low in cost; there are no volatile elements and no lead-containing substances in the raw materials, which is green, environmentally friendly and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is the XRD pattern of the anti-reduction nano BaTiO 3 -based dielectric ceramics prepared in Comparative Examples 2 to 3 and Examples 1 to 3 of the present invention;

[0025] Figure 2 FIG. is the XRD pattern of the anti-reduction nano BaTiO 3SEM pattern of the base dielectric ceramic; when x = 0.05 and y = 0, 0.002, 0.004, 0.006, 0.008 respectively, it corresponds to Figure 2 (a), Figure 2 (b), Figure 2 (c), Figure 2 (d), Figure 2 (e);

[0026] Figure 3 is the graph of the change of dielectric constant with temperature of the dielectric ceramic of Comparative Example 2 of the present invention at different frequencies (-60 to 180 °C);

[0027] Figure 4 is the graph of the change of dielectric constant with temperature of the dielectric ceramic of Example 1 of the present invention at different frequencies (-60 to 180 °C);

[0028] Figure 5 is the graph of the change of dielectric constant with temperature of the dielectric ceramic of Example 2 of the present invention at different frequencies (-60 to 180 °C);

[0029] Figure 6 is the graph of the change of dielectric constant with temperature of the dielectric ceramic of Example 3 of the present invention at different frequencies (-60 to 180 °C);

[0030] Figure 7 is the graph of the change of dielectric constant with temperature of the dielectric ceramic of Comparative Example 3 of the present invention at different frequencies (-60 to 180 °C);

[0031] Figure 8 is the change of dielectric constant with temperature of the dielectric ceramics prepared in Comparative Examples 2-3 and Examples 1-3 of the present invention at 1 kHz frequency;

[0032] Figure 9 is the graph of the capacitance-temperature change rate of the dielectric ceramics prepared in Comparative Examples 2-3 and Examples 1-3 of the present invention at 1 kHz frequency. Detailed implementation manners

[0033] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0034] Comparative Example 1

[0035] Prepare pure BaTiO 3 ceramics as a blank group for control experiments, and its preparation method specifically includes the following steps:

[0036] (1) Weigh nano BaTiO 3 powder as the experimental raw material;

[0037] (2) Weigh the raw materials and put them into a nylon planetary ball milling jar. Using anhydrous ethanol and zirconia balls as the ball milling media, ball mill for 8 h on a planetary ball mill at a rotational speed of 1200 r / min. Then dry at 100 °C for 24 h to obtain ceramic powder.

[0038] (3) Add a 5 wt% aqueous solution of polyvinyl alcohol binder to the ceramic powder obtained in step (2). The binder and the ceramic powder are mixed at 0.08 mL / g. After mixing evenly, granulate and pass through a 100-mesh sieve. The sieved ceramic powder is aged for 24 h, and then dry-pressed into 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.

[0039] (4) Heat the green ceramic obtained in step (3) in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min, hold for 2 h, and then cool with the furnace. The purpose is to remove polyvinyl alcohol. Pass a reducing atmosphere (by volume percentage: N 2 99.5%, H 2 0.5%, ventilation rate of 40 - 80 L / h) into a tubular furnace and heat to 1000 °C at a heating rate of 5 °C / min, then heat to 1300 °C at a heating rate of 2 °C / min, hold for 2 hours, and then cool with the furnace to obtain a BaTiO 3 ceramic sample.

[0040] Grind and polish both sides of the BaTiO 3 ceramic prepared in Comparative Example 1, coat silver electrodes, and test its dielectric properties. The BaTiO 3 ceramic has a dielectric constant as high as 67513 and a dielectric loss of about 0.1391 at frequencies of 1 kHz, 10 kHz, 100 kHz, 1 MHz, and room temperature.

[0041] Measure the insulation resistivity of the BaTiO 3 ceramic prepared in Comparative Example 1 under an AC electric field of 1 kV / mm. As shown in Table 1, the insulation resistivity at room temperature is 6.4×10 5 Ω·cm, and semi-conduction occurs.

[0042] Comparative Example 2

[0043] A reduction-resistant nano BaTiO 3 -based dielectric ceramic with a chemical composition expression of BaTiO 3 -0.05Tm 2 O 3 , and its preparation method specifically includes the following steps:

[0044] (1) According to the composition expression, nano BaTiO 3 powder, Tm2 O 3 Weigh according to a molar ratio of 1:0.05;

[0045] (2) Put the weighed raw materials into a nylon planetary ball milling jar, use absolute ethanol and zirconia balls as ball milling media, ball mill on a planetary ball mill for 8 h at a rotation speed of 1200 r / min; then dry at 100 °C for 24 h to obtain ceramic powder;

[0046] (3) Add an aqueous solution binder of polyvinyl alcohol with a concentration of 5 wt% to the ceramic powder obtained in step (2), mix the binder and the ceramic powder at 0.08 mL / g, granulate after mixing evenly and pass through a 100-mesh sieve, age the sieved ceramic powder for 24 h, and then dry-press it into a shape with a tableting machine 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;

[0047] (4) Heat the green ceramic obtained in step (3) from room temperature to 600 °C at a heating rate of 1 °C / min in a muffle furnace, hold for 2 h, and then cool with the furnace. The purpose is to remove polyvinyl alcohol; introduce a reducing atmosphere (by volume percentage: N 2 99.5%, H 2 0.5%, and the gas flow rate is 40 - 80 L / h) in a tubular furnace, heat it to 1000 °C at a heating rate of 5 °C / min, and then heat it to 1300 °C at a heating rate of 2 °C / min, hold for 2 hours, and then cool with the furnace to obtain a BaTiO 3 ceramic sample.

[0048] Perform X-ray diffraction (XRD) tests on the BaTiO 3 -based dielectric ceramics prepared in Comparative Example 2. The XRD pattern is as Figure 1 shown. It can be seen from the XRD pattern that the dielectric ceramic material presents a pure perovskite structure, no second phase is generated, and it has a cubic phase structure.

[0049] Grind and polish both sides of the BaTiO 3 ceramics prepared in Comparative Example 2, coat silver electrodes, and test the dielectric properties. As Figure 3 shown, the dielectric constant of the BaTiO3 ceramic is 3091 at frequencies of 1 kHz, 10 kHz, 100 kHz, and 1 MHz at room temperature, the dielectric loss is about 0.0188, and the temperature stability is as Figure 9 shown. The temperature range that satisfies TCC ≤ 15% is -30 to 142 °C.

[0050] Test the insulation resistivity of the BaTiO 3 ceramics prepared in Comparative Example 2 under an AC electric field of 1 kV / mm. As shown in Table 1, the insulation resistivity at room temperature is 7.7×1010 Ω·cm, no semiconductivity occurs.

[0051] Example 1

[0052] A kind of anti-reduction nano BaTiO 3 Base dielectric ceramic, chemical composition expression is BaTiO 3 -0.05Tm 2 O 3 -0.002MgO, the preparation method thereof specifically comprises the following steps:

[0053] (1) According to the composition expression, nano BaTiO 3 Powder, Tm 2 O 3 , MgO is weighed according to the molar ratio of 1:0.05:0.002;

[0054] (2) The weighed raw materials were placed in a nylon planetary ball mill, anhydrous ethanol and zirconium oxide balls were used as ball milling media, and the raw materials were ball milled for 8 h at a speed of 1200 r / min; then the raw materials were dried at 100° C. for 24 h to obtain ceramic powder;

[0055] (3) adding a 5 wt% polyvinyl alcohol aqueous solution binder to the ceramic powder obtained in step (2), mixing the binder and the ceramic powder at a concentration of 0.08 mL / g, granulating and passing through a 100-mesh sieve after mixing evenly, aging the sieved ceramic powder for 24 hours, and then dry-pressing it with a tablet press at a molding pressure of 150 MPa to obtain a ceramic green disc with a diameter of 12 mm and a thickness of about 1 mm;

[0056] (4) heating the ceramic green body obtained in step (3) from room temperature to 600° C. in a muffle furnace at a heating rate of 1° C. / min and keeping the temperature for 2 h, and then cooling the green body in the muffle furnace, the purpose of which is to remove the polyvinyl alcohol; introducing a reducing atmosphere (calculated by volume percentage: N 2 99.5%, H 2 0.5%, ventilation speed 40-80L / h) was heated to 1000°C at a rate of 5°C / min, then heated to 1300°C at a rate of 2°C / min, kept at this temperature for 2 hours and then cooled in the furnace to obtain BaTiO 3 Ceramic samples.

[0057] The BaTiO3-based dielectric ceramic prepared in Example 1 was subjected to X-ray diffraction (XRD) testing, and the XRD pattern was as follows: Figure 1 As shown, it can be seen from the XRD spectrum that the ceramic material presents a pure perovskite structure, does not produce a second phase, and presents a cubic phase structure.

[0058] The BaTiO prepared in Example 1 3Both sides of the ceramic are ground, polished, and coated with silver electrodes, and the dielectric properties are tested. As Figure 4 shown, for the BaTiO3 ceramic, at frequencies of 1 kHz, 10 kHz, 100 kHz, and 1 MHz and at room temperature, the dielectric constant is 1397 and the dielectric loss is 0.0110. The temperature stability is as Figure 9 shown. In the temperature range of -60 to 148 °C, the temperature coefficient of capacitance (TCC) ≤ 15%, meeting the X7R standard.

[0059] The BaTiO 3 ceramic prepared in Example 1 is tested for its insulation resistivity under an AC electric field of 1 kV / mm. As shown in Table 1, at room temperature, the insulation resistivity is 5.0×10 11 Ω·cm, and no semi-conduction occurs.

[0060] Example 2

[0061] A reduction-resistant nano BaTiO 3 -based dielectric ceramic with a chemical composition expression of BaTiO 3 -0.05Tm 2 O 3 -0.004MgO. Its preparation method specifically includes the following steps:

[0062] (1) According to the composition expression, nano BaTiO 3 powder, Tm 2 O 3 and MgO are weighed according to a molar ratio of 1:0.05:0.004;

[0063] (2) The weighed raw materials are put into a nylon planetary ball mill pot, and anhydrous ethanol and zirconia balls are used as ball milling media. Ball milling is carried out on a planetary ball mill for 8 h at a rotation speed of 1200 r / min; then it is dried at 100 °C for 24 h to obtain ceramic powder;

[0064] (3) A 5 wt% aqueous solution of polyvinyl alcohol binder is added to the ceramic powder obtained in step (2). The binder and the ceramic powder are mixed at 0.08 mL / g. After mixing evenly, granulation is carried out and sieved through a 100-mesh sieve. The sieved ceramic powder is aged for 24 h, and then dry-pressed into a shape using a tablet press with a forming pressure of 150 MPa to obtain a ceramic green wafer with a diameter of 12 mm and a thickness of about 1 mm;

[0065] (4) The ceramic green obtained in step (3) is heated in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min, held for 2 h, and then cooled with the furnace. The purpose is to remove polyvinyl alcohol; a reducing atmosphere (by volume percentage: N 2 99.5%, H 20.5%, with an aeration rate of 40 - 80 L / h, was heated to 1000 °C at a heating rate of 5 °C / min, and then to 1300 °C at a heating rate of 2 °C / min. After holding for 2 hours, it was cooled in the furnace to obtain BaTiO 3 ceramic samples.

[0066] The BaTiO 3 - based dielectric ceramics prepared in Example 2 were subjected to X - ray diffraction (XRD) tests. The XRD pattern is as Figure 1 shown. It can be seen from the XRD pattern that the ceramic material exhibits a pure perovskite structure, without the formation of a second phase, and has a cubic phase structure.

[0067] The two sides of the BaTiO 3 ceramics prepared in Example 2 were ground and polished, and silver electrodes were coated to test the dielectric properties. As Figure 5 shown, the BaTiO 3 ceramics have a dielectric constant of 1615, a dielectric loss of 0.0099 at frequencies of 1 kHz, 10 kHz, 100 kHz, and 1 MHz at room temperature. The temperature stability is as Figure 9 shown, and the temperature coefficient of capacitance (TCC) ≤ 15% within - 60 - 128 °C, meeting the X7R standard.

[0068] The BaTiO 3 ceramics prepared in Example 2 were tested for their insulation resistivity under an AC electric field of 1 kV / mm. As shown in Table 1, the insulation resistivity at room temperature is 1.9×10 11 Ω·cm, and no semi - conduction occurred.

[0069] Example 3

[0070] A reduction - resistant nano - BaTiO 3 - based dielectric ceramic, with a chemical composition expression of BaTiO 3 - 0.05Tm 2 O 3 - 0.006MgO. Its preparation method specifically includes the following steps:

[0071] (1) According to the composition expression, nano - BaTiO 3 powder, Tm 2 O 3 and MgO were weighed according to a molar ratio of 1:0.05:0.006;

[0072] (2) The weighed raw materials were put into a nylon planetary ball - milling tank, with anhydrous ethanol and zirconia balls as ball - milling media, and ball - milled on a planetary ball mill for 8 h at a rotation speed of 1200 r / min; then dried at 100 °C for 24 h to obtain ceramic powder;

[0073] (3) Add an aqueous polyvinyl alcohol binder with a concentration of 5 wt% to the ceramic powder obtained in step (2). The binder and the ceramic powder are mixed at 0.08 mL / g. After mixing evenly, granulation is carried out and the mixture is passed through a 100-mesh sieve. The sieved ceramic powder is aged for 24 h, and then dry-pressed into a shape using a tablet press with 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;

[0074] (4) Heat the green ceramic obtained in step (3) in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min, hold for 2 h, and then cool with the furnace. The purpose is to remove polyvinyl alcohol. Introduce a reducing atmosphere (by volume percentage: N 2 99.5%, H 2 0.5%, with a gas flow rate of 40 - 80 L / h) in a tubular furnace and heat it to 1000 °C at a heating rate of 5 °C / min, then heat it to 1300 °C at a heating rate of 2 °C / min, hold for 2 hours, and then cool with the furnace to obtain a BaTiO 3 ceramic sample.

[0075] The BaTiO 3 -based dielectric ceramic prepared in Example 3 was subjected to X-ray diffraction (XRD) testing. The XRD pattern is as Figure 1 shown. It can be seen from the XRD pattern that the ceramic material exhibits a pure perovskite structure, no second phase is generated, and it has a cubic phase structure.

[0076] Grind and polish both sides of the BaTiO 3 ceramic prepared in Example 3, coat silver electrodes, and test its dielectric properties. As Figure 6 shown, the BaTiO 3 ceramic has a dielectric constant of 1591, a dielectric loss of 0.0103 at frequencies of 1 kHz, 10 kHz, 100 kHz, and 1 MHz at room temperature, and its temperature stability is as Figure 9 shown. The temperature coefficient of capacitance TCC ≤ 15% within -60 to 125 °C, meeting the X7R standard.

[0077] Measure the insulation resistivity of the BaTiO 3 ceramic prepared in Example 3 under an AC electric field of 1 kV / mm. As shown in Table 1, the insulation resistivity at room temperature is 1.1×10 11 Ω·cm, and no semi-conduction occurs.

[0078] Comparative Example 3

[0079] A reduction-resistant nano BaTiO 3 -based dielectric ceramic with a chemical composition expressed as BaTiO 3 - 0.05Tm 2 O3 -0.008 MgO, and its preparation method specifically includes the following steps:

[0080] (1) According to the composition expression, nano BaTiO 3 powder, Tm 2 O 3 and MgO are weighed according to a molar ratio of 1:0.05:0.008;

[0081] (2) The weighed raw materials are put into a nylon planetary ball milling tank, and anhydrous ethanol and zirconia balls are used as ball milling media. Ball milling is carried out on a planetary ball mill for 8 h at a rotation speed of 1200 r / min; then it is dried at 100 °C for 24 h to obtain ceramic powder;

[0082] (3) A 5 wt% aqueous solution of polyvinyl alcohol binder is added to the ceramic powder obtained in step (2). The binder and the ceramic powder are mixed at 0.08 mL / g. After mixing evenly, granulation is carried out and sieved through a 100-mesh sieve. The sieved ceramic powder is aged for 24 h, and then dry-pressed 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;

[0083] (4) The green ceramic obtained in step (3) is heated in a muffle furnace from room temperature to 600 °C at a heating rate of 1 °C / min and held for 2 h, and then cooled with the furnace. The purpose is to remove polyvinyl alcohol; A reducing atmosphere (by volume percentage: N 2 99.5%, H 2 0.5%, and the gas flow rate is 40 - 80 L / h) is introduced into a tube furnace and heated to 1000 °C at a heating rate of 5 °C / min, and then heated to 1300 °C at a heating rate of 2 °C / min, held for 2 hours, and then cooled with the furnace to obtain a BaTiO 3 ceramic sample.

[0084] The BaTiO3-based dielectric ceramic prepared in Comparative Example 3 was tested by X-ray diffraction (XRD). The XRD pattern is as Figure 1 shown. It can be seen from the XRD pattern that the ceramic material presents a pure perovskite structure, no second phase is generated, and it is in a cubic phase structure.

[0085] The two sides of the BaTiO 3 ceramic prepared in Comparative Example 3 were ground and polished, and silver electrodes were coated to test the dielectric properties. As Figure 7 shown, the dielectric constant of the BaTiO3 ceramic is 1842, the dielectric loss is 0.0112 at frequencies of 1 kHz, 10 kHz, 100 kHz, 1 MHz, and room temperature. The temperature stability is as Figure 9 shown, and the temperature coefficient of capacitance (TCC) ≤ 15% within -60 to 73 °C.

[0086] The BaTiO prepared in Comparative Example 3 3 ceramics were tested for their insulation resistivity under an AC electric field of 1 kV / mm. As shown in Table 1, the insulation resistivity at room temperature was 2.3×10 11 Ω·cm, and no semi-conduction occurred.

[0087] From Figure 2 it can be seen that when x = 0.05 and y = 0.002 - 0.008, the obtained BaTiO 3 ceramics had uniform grain sizes, with an average grain size ≤ 200 nm. The grain sizes were mainly concentrated in the range of 150 - 200 nm, accounting for more than 50%. The grains with a diameter greater than 250 nm were less than 10%, and the grains with a diameter less than 100 nm were less than 5%. Among them, when x = 0.05 and y = 0.002 - 0.006, the average grain diameter was between 175 - 180 nm. In Comparative Example 2, when x = 0.05 and y = 0, the average diameter was about 3.27 μm, and the grain diameters of the ceramics were very large.

[0088] Table 1 lists the dielectric properties and insulation resistivity at 1 kHz of the ceramics prepared in each comparative example and example.

[0089] Table 1

[0090]

[0091]

[0092] Combined with Table 1, it can be seen that the BaTiO 3 -based X7R dielectric ceramics provided in the examples had better performance in all aspects compared with the comparative examples. Specifically, the room temperature dielectric constant satisfied 1391 - 1615, the dielectric loss tanδ was reduced to less than 0.012, the insulation resistivity reached the order of magnitude of 10 11 Ω·cm, and the capacitance temperature change rate TCC ≤ ±15% was satisfied within -55 - 125°C. The anti-reducing nano BaTiO 3 -based X7R dielectric ceramics of the present invention captured free electrons due to the introduction of Tm 3+ , effectively reducing the concentration of free electrons, reducing the possibility of the transformation of Ti 4+ to Ti 3+ , significantly increasing the insulation resistivity of the ceramics in a reducing atmosphere, and improving the anti-reducing ability of the BaTiO 3 -based dielectric ceramics; the addition of Mg 2+ further increased the insulation resistivity, and MgO, as a broadening agent, depressed the dielectric peak and increased the dielectric constant at the low temperature end, improving the temperature stability of the BaTiO 3 -based dielectric ceramics.

[0093] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and modifications can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. An anti-reduction nano-BaTiO3-based X7R dielectric ceramic, characterized in that: Nano-BaTiO3 powder is used as the matrix material, Tm2O3 and MgO are used as modifiers, and its chemical expression is BaTiO3-xTm2O3-yMgO, wherein x=0.04-0.07, y=0.001-0.

007.

2. The anti-reduction nano-BaTiO3-based X7R dielectric ceramic according to claim 1, characterized in that The insulation resistivity of the dielectric ceramic is not less than 7.7×10 10 Ω·cm, the room temperature dielectric constant meets 1390~1620, the dielectric loss tanδ<0.015, the capacitance temperature change rate TCC≤±15% within -55~125℃, and the temperature stability meets the X7R standard.

3. The anti-reduction nano-BaTiO3-based X7R dielectric ceramic according to claim 1, characterized in that The average grain size of the dielectric ceramic is distributed in the range of 150 to 200 nm.

4. The anti-reduction nano-BaTiO3-based X7R dielectric ceramic according to claim 1, characterized in that In the chemical expression of the dielectric ceramic, x=0.05, y=0.002-0.006, and the insulation resistivity is greater than 1×10 11 Ω·cm, the room temperature dielectric constant meets 1391~1620, the dielectric loss tanδ<0.012, the capacitance temperature change rate TCC≤±15% within -55~125℃, the temperature stability meets the X7R standard, and the average grain size is 175~180nm.

5. The anti-reduction nano-BaTiO3-based X7R dielectric ceramic according to claim 4, characterized in that In its chemical expression, x=0.05, y=0.004~0.006, and the room temperature dielectric constant is 1590~1620.

6. The method for preparing the reduction-resistant nano-BaTiO3-based X7R dielectric ceramic according to any one of claims 1 to 5, characterized in that: The steps include: (1) Using nano-BaTiO3 powder, Tm2O3 and MgO as raw materials, weigh each raw material according to the stoichiometric ratio of metal atoms in the chemical expression BaTiO3-xTm2O3-yMgO; (2) ball-milling and drying the raw materials weighed in step (1) to obtain ceramic powder; (3) grinding the ceramic powder obtained in step (2) and mixing it with a binder, ball milling, granulating and screening, and dry pressing to obtain a ceramic green body; (4) After debinding treatment, the ceramic green body obtained in step (3) is sintered in a reducing atmosphere at 1400-1500° C. for 2-3 hours to obtain a reduction-resistant nano-BaTiO3-based X7R dielectric ceramic; wherein the composition of the reducing atmosphere is, by volume percentage, N2 99.2-99.7%, H2 0.3-0.8%, and the ventilation rate is 40-80 L / h.

7. The method for preparing a reduction-resistant nano-BaTiO3-based X7R dielectric ceramic according to claim 6, characterized in that: The ball milling in step (2) is performed by using zirconium oxide balls and anhydrous ethanol as the medium in a nylon planetary ball mill for 6 to 8 hours at a rotation speed of 1000 to 1200 r / min; the drying in step (2) is performed by keeping the temperature at 90 to 110° C. for 12 to 14 hours.

8. The method for preparing a reduction-resistant nano-BaTiO3-based X7R dielectric ceramic according to claim 6, characterized in that: The binder added in the step (3) is a polyvinyl alcohol aqueous solution with a concentration of 4-5%, and 0.05-0.1 mL of the binder is added to each gram of ceramic powder for granulation; the powder after granulation is sieved, and the average particle size does not exceed 200 microns; the molding pressure is 150-200 MPa.

9. The method for preparing a reduction-resistant nano-BaTiO3-based X7R dielectric ceramic according to claim 6, characterized in that: The debinding treatment in step (4) is to heat the mixture to 580-620° C. at a heating rate of 0.5-3° C. / min and keep the temperature for 1.5-3 hours to discharge the polyvinyl alcohol.

10. The method for preparing a reduction-resistant nano-BaTiO3-based X7R dielectric ceramic according to claim 6, characterized in that: The sintering in step (4) is carried out by heating the temperature to 900-1100° C. at a heating rate of 3-5° C. / min, and then heating the temperature to 1400-1500° C. at a heating rate of 1.5-2.5° C. / min, keeping the temperature for 2-3 hours, and then cooling with the furnace.

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