NBT-based transparent high-dielectric wide-temperature lead-free capacitor ceramic material with stable bias voltage and preparation

Abstract

The invention discloses an NBT-based transparent high-dielectric wide-temperature lead-free capacitor ceramic material with stable bias voltage and preparation, and belongs to the field of capacitors. The formula of the BiAlO3-xBiAlO3 is (1-x) (0.56% of Na < 0.5 > Bi < 0.5 > TiO < 3 >-0.14% of K < 0.5 > Bi < 0.5 > Ti < 3 >-0.3% of NaNbO3)-xBiAlO3, wherein x is equal to 0.03; the preparation method comprises the following steps: weighing Bi2O3, K2CO3, Na2CO3, TiO2, Nb2O5 and Al2O3 as raw materials according to a stoichiometric ratio; the preparation method comprises the following steps: carrying out ball milling and mixing on the raw materials, drying, calcining the powder at high temperature, carrying out secondary ball milling, drying, grinding into powder, granulating by taking a polyvinyl butyral alcohol solution (PVB) as a binder, carrying out compression molding by passing through a 120-mesh sieve, discharging glue, sintering in an air atmosphere of a high-temperature furnace, and naturally cooling to room temperature along with the furnace. The operation method is simple, the preparation period is short, and good performance in multiple aspects is achieved.

Description

Technical Field

[0001] The present invention provides a high-dielectric lead-free ceramic capacitor dielectric material and preparation method constructed by multi-scale synergistic effects, which has a wide temperature range, stable bias voltage, and good mechanical and optical properties. It is mainly used in the field of multilayer ceramic capacitors in emerging industries such as AI servers and new energy vehicles. Background Art

[0002] Multilayer ceramic capacitors are indispensable basic electronic components in electronic devices. In recent years, with the rapid development of emerging fields such as AI servers and new energy vehicles, the intelligence and high performance of electronic equipment have put forward higher requirements on the reliability of dielectric materials used in multilayer ceramic capacitors (MLCCs) under complex working conditions such as extreme temperatures and dynamic bias. However, the mutual constraints between dielectric constant, breakdown field strength, bias characteristics, and temperature stability have severely limited the application of existing ceramic capacitors in these scenarios. Although Class I ceramic capacitors have excellent temperature stability and bias characteristics, the lower dielectric constant (<800) affects the improvement of the capacitance density of multilayer ceramic capacitors. Class II ceramic capacitors are mainly based on strong dielectric ferroelectrics such as BaTiO3. Although they have high dielectric constant characteristics, their breakdown field strength is small, the bias characteristics are poor, and the temperature stability is not good. According to the EIA standard formulated by the American Electronics Industry Association, the Class II ceramic X9R capacitor with the highest temperature currently used meets the capacitance temperature change rate △C / C 25 The upper operating temperature limit of 15% is only 200°C, and operation at higher temperatures is still limited. Therefore, how to design high-reliability dielectric ceramics with a high dielectric constant (>1000) and tolerance to extreme environments (high bias, high temperature, and high strength) has become a key challenge in promoting the development of a new generation of multilayer ceramic capacitors for AI servers and new energy vehicles.

[0003] Na 0.5 Bi 0.5 TiO3-K 0.5 Bi 0.5 TiO3 (abbreviated as NBT-KBT) is a binary solid solution with relaxor ferroelectric properties. Recently, researchers have introduced the component NaTaO3 (NT) into the NBT-KBT matrix to construct NBT-KBT-0.31NT wide-temperature capacitor ceramic. This material maintains excellent capacitance temperature stability (△C / C) over a wide temperature range (-60℃~277℃). 25℃≤±15%) and low dielectric loss (≤0.025) (Liu et al., JOURNAL OF MATERIOMICS Volume: 10 Issue: 4 Pages: 751-761 Publication Year: JULY 2024). It should be noted that although the temperature characteristics of this material are better than those of existing commercial X9R capacitor porcelain, there are still the following problems: First, the relative dielectric constant at room temperature is low (840), and the low dielectric constant is not conducive to the high capacitance density of multilayer ceramic capacitors; second, the maximum temperature that meets the working stability is 277℃, and its application in extreme temperature scenarios above 300℃ is still limited; third, the grain size of the material is large (2.06μm) and uneven, which is not conducive to enhancing the anti-breakdown capability. Tests show that the breakdown field strength of the material is less than 250kV / cm, and the effective energy storage density is only 2.2J / cm 3 Therefore, it is necessary to explore high-dielectric, wide-temperature dielectric materials with a service temperature exceeding 300°C and excellent anti-puncture capabilities to meet the demand for high-quality multilayer ceramic capacitors in emerging fields such as AI servers and new energy vehicles.

[0004] The present invention reports a quaternary material system (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3 (abbreviated as NBT-KBT-NN-xBA). This system combines wide temperature stability, high dielectric constant, low dielectric loss, and good bias characteristics. Furthermore, the ceramic material's fine-grained structure ensures high breakdown strength and excellent optical properties, making it potentially useful in transparent electronic devices. Summary of the Invention

[0005] The present invention is characterized by introducing BiAlO3 (BA) modified components into the NBT-KBT-NN matrix to obtain a high-k dielectric material for lead-free ceramic capacitors with wide temperature range, bias stability, and good mechanical and optical properties. BA is a metastable perovskite compound with a high Curie temperature (>520°C). Its introduction into the NBT-KBT-NN matrix can improve the electrical quality of capacitor ceramics based on multi-scale synergistic effects. From the perspective of ion occupancy, the Al in BA 3+ Ions entering the B site of the NBT-KBT-NN matrix perovskite lattice will destroy the original long-range ferroelectric order and increase the relaxivity, thereby improving the wide temperature stability of the dielectric ceramic; at the same time, it has a 6s 2 Bi with lone electron pairs 3+ The ions will occupy the A site of the perovskite lattice, which is beneficial to increase the dielectric constant of the dielectric ceramic. From the perspective of defect chemistry, the low-valent Al in BA 3+ Ion substitution of high-charge Ti in NBT-KBT-NN matrix4+ and Nb 5+ Ions will act as negative charge centers to bind oxygen vacancies, thereby inhibiting the electrical insulation of the conductivity-enhancing material. From the perspective of ceramic sintering, BA as a modifier helps to obtain high-density fine-grained ceramics. The refinement of grain size and the reduction of porosity will help to obtain dielectric ceramics with high Vickers hardness, high breakdown strength and excellent light transmittance. The relative dielectric constant of NBT-KBT-NN-BA ceramics at 25°C is as high as 1361, and it maintains excellent capacitance temperature stability (△C / C) in an ultra-wide temperature range (5°C-318°C). 25 ℃ ≤ ± 15%) and low dielectric loss (≤ 0.025). The material has good bias stability (capacitance change rate ≤ ± 10%) in a wide DC electric field (0kV / cm ~ 90kV / cm) and a variable temperature environment (25℃-150℃). At the same time, the material has a fine-grained structure (average grain size 1.09μm), high breakdown strength (315kV / cm), and an effective energy storage density of 3.43J / cm 3 , efficiency is 85.3%, Vickers hardness can reach 6.5GPa, and optical transmittance reaches 70% at a wavelength of 780nm.

[0006] The present invention is achieved through the following technical solutions.

[0007] A high dielectric material for lead-free ceramic capacitors with excellent properties in many aspects, the chemical composition of which is (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3, wherein x is preferably 0.05.

[0008] A method for preparing a novel dielectric material for multilayer ceramic capacitors comprises the following steps:

[0009] (1): According to the chemical formula (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3, where x = 0.05, weigh appropriate amounts of Bi2O3, Na2CO3, K2CO3, TiO2, Al2O3, and Nb2O5 as starting materials, and dry these materials at 100°C for 8h;

[0010] (2): According to the stoichiometric ratio of the metal atoms in the expression, Na2CO3, Nb2O5, K2CO3, TiO2, Bi2O3 and Al2O3 were weighed and placed in a ball mill. Anhydrous ethanol was used as the ball milling medium. The mixture was ball milled for 12 h to mix evenly. The mixture was taken out and dried. Then, the mixture was heated to 900 °C and pre-calcined for 3 h at a heating rate of 3 °C / min.

[0011] (3) The powder obtained after pre-sintering in step (2) is crushed, ball-milled for 12 hours to mix evenly, dried at 100°C for 8 hours, and then ground into powder. Polyvinyl butyral alcohol solution (PVB) (preferably at a concentration of 10wt%) is used as a binder to form granules, and then pressed into shape after passing through a 120-mesh sieve. The granules are kept at 650°C for 3 hours to discharge the colloid, and then sintered at 1150°C in an air atmosphere in a high-temperature furnace. After keeping the granules for 3 hours, the granules are naturally cooled to room temperature in the furnace to obtain a high-k lead-free ceramic capacitor dielectric material with a wide temperature range, stable bias voltage, and good mechanical and optical properties.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] The BiAlO3-doped NBT-KBT-NN-based ceramics developed in this work significantly surpass traditional BaTiO3-based and NBT-based ceramics in comprehensive performance: its relative dielectric constant can reach 1361 at room temperature, which is conducive to the miniaturization of MLCC and the improvement of capacitance density. It maintains capacitance temperature stability (△C / C 25 ℃≤±15%) and low dielectric loss (≤0.025). At the same time, the material has high mechanical strength, excellent optical properties and voltage resistance. The Vickers hardness can reach 6.5GPa, the transmittance at 780nm is 70%, and the breakdown field strength is as high as 315kV / cm. In addition, the material has excellent bias characteristics, and the capacitance change rate is ≤±10% under the conditions of 0kV / cm~90kV / cm and 25℃~150℃. Compared with traditional material systems, the comprehensive performance of the dielectric ceramics obtained by this invention has been comprehensively improved, providing an innovative material solution for MLCCs working under high voltage and extreme temperature scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The phase structure of the samples was determined using a D8-Advance X-ray diffractometer from Bruker, Germany. The grain size, grain boundaries, porosity, and other characteristics of the ceramics were observed using a FEIQuanta 650 field emission scanning electron microscope from FEI, USA. The Vickers hardness of the dielectric material was measured using an HXD-1000TMC / LCD digital microhardness tester produced by Shanghai Taiming Optical Instrument Co., Ltd., China. The transmittance of the dielectric material was measured using a UH-4150 spectrophotometer produced by Hitachi, Japan. A precision digital bridge (Agilent E4980A) was used to test the dielectric material's capacitance-temperature change rate at 1 kHz, as well as the relationship between the dielectric constant and dielectric loss as a function of temperature. A Premier II ferroelectric tester produced by Radiant, USA, was used to test the DC bias characteristics, breakdown electric field, and energy storage characteristics of the dielectric material.

[0015] Figure 1 : XRD patterns of the ceramic dielectric materials prepared in Example 1 and Comparative Examples 1, 2, and 3.

[0016] Figure 2 : SEM images of ceramic dielectric materials prepared in Example 1 and Comparative Examples 1, 2, and 3.

[0017] Figure 3 : Vickers hardness of the ceramic dielectric materials prepared in Example 1 and Comparative Examples 1, 2, and 3.

[0018] Figure 4 : Transmittance of ceramic dielectric materials prepared in Example 1 and Comparative Example 1. The insets are optical photographs of the samples.

[0019] Figure 5 : Surface temperature variation diagram of the ceramic dielectric materials prepared in Example 1 and Comparative Example 1.

[0020] Figure 6 : Relationship curves of dielectric constant and dielectric loss versus temperature at 1 kHz for the ceramic dielectric materials prepared in Example 1 and Comparative Examples 1, 2, and 3.

[0021] Figure 7 : Curves showing the relationship between the capacitance-temperature change rate and dielectric loss of the ceramic dielectric materials prepared in Example 1 and Comparative Examples 1, 2, and 3 and temperature.

[0022] Figure 8 : Capacitance change rate of Example 1 at different temperatures and different bias voltages.

[0023] Figure 9 : The effective energy storage density and efficiency of the ceramic dielectric materials prepared in Example 1 and Comparative Example 1 under their respective near-breakdown electric fields. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the examples, but the present invention is not limited to the following examples.

[0025] Example 1:

[0026] (1): According to the chemical formula (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3, where x = 0.05. Weigh appropriate amounts of Bi2O3, Na2CO3, K2CO3, TiO2, Al2O3, and Nb2O5 as starting materials and dry them at 100°C for 8 hours;

[0027] (2): According to the stoichiometric ratio of the metal atoms in the expression, Na2CO3, Nb2O5, K2CO3, TiO2, Bi2O3 and Al2O3 were weighed and placed in a ball mill. Anhydrous ethanol was used as the ball milling medium. The mixture was ball milled for 12 h to mix evenly. The mixture was taken out and dried. Then, the mixture was heated to 900 °C and pre-calcined for 3 h at a heating rate of 3 °C / min.

[0028] (3) The powder obtained after pre-sintering in step (2) is ground into powder, ball-milled for 12 hours to mix evenly, dried at 100°C for 8 hours, and then ground into powder. A polyvinyl butyral alcohol solution (PVB) with a preferred concentration of 10wt% is used as a binder to form granules, and then pressed into shape after passing through a 120-mesh sieve. The powder is kept at 650°C for 3 hours to discharge the colloid, and then sintered at 1150°C in an air atmosphere in a high-temperature furnace. After keeping the temperature for 3 hours, the material is naturally cooled to room temperature in the furnace to obtain a high-k lead-free ceramic capacitor dielectric material with a wide temperature range, stable bias voltage, and good mechanical and optical properties.

[0029] Comparative Example 1:

[0030] (1): According to the chemical formula (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3, where x = 0. Weigh appropriate amounts of Bi2O3, Na2CO3, K2CO3, TiO2, Al2O3, and Nb2O5 as starting materials and dry them at 100°C for 8 hours;

[0031] (2): According to the stoichiometric ratio of the metal atoms in the expression, Na2CO3, Nb2O5, K2CO3, TiO2, Bi2O3 and Al2O3 were weighed and placed in a ball mill. Anhydrous ethanol was used as the ball milling medium. The mixture was ball milled for 12 h to mix evenly. The mixture was taken out and dried. Then, the mixture was heated to 900 °C and pre-calcined for 3 h at a heating rate of 3 °C / min.

[0032] (3) The powder obtained after pre-calcining in step (2) is ground into powder, ball-milled for 12 hours to mix evenly, dried at 100°C for 8 hours, and then ground into powder. A polyvinyl butyral alcohol solution (PVB) with a preferred concentration of 10 wt% is used as a binder for granulation. The powder is then passed through a 120-mesh sieve and pressed into shape. The powder is kept at 650°C for 3 hours to discharge the colloid. The powder is then sintered at 1150°C in an air atmosphere in a high-temperature furnace. After keeping the temperature for 3 hours, the powder is naturally cooled to room temperature in the furnace.

[0033] Comparative Example 2:

[0034] (1): According to the chemical formula (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3, where x = 0.03. Weigh appropriate amounts of Bi2O3, Na2CO3, K2CO3, TiO2, Al2O3, and Nb2O5 as starting materials and dry them at 100°C for 8 hours;

[0035] (2): According to the stoichiometric ratio of the metal atoms in the expression, Na2CO3, Nb2O5, K2CO3, TiO2, Bi2O3 and Al2O3 were weighed and placed in a ball mill. Anhydrous ethanol was used as the ball milling medium. The mixture was ball milled for 12 h to mix evenly. The mixture was taken out and dried. Then, the mixture was heated to 900 °C and pre-calcined for 3 h at a heating rate of 3 °C / min.

[0036] (3) The powder obtained after pre-calcining in step (2) is ground into powder, ball-milled for 12 hours to mix evenly, dried at 100°C for 8 hours, and then ground into powder. A polyvinyl butyral alcohol solution (PVB) with a preferred concentration of 10 wt% is used as a binder for granulation. The powder is then passed through a 120-mesh sieve and pressed into shape. The powder is kept at 650°C for 3 hours to discharge the colloid. The powder is then sintered at 1150°C in an air atmosphere in a high-temperature furnace. After keeping the temperature for 3 hours, the powder is naturally cooled to room temperature in the furnace.

[0037] Comparative Example 3:

[0038] (1): According to the chemical formula (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5TiO3-0.3NaNbO3)-xBiAlO3, where x = 0.07. Weigh appropriate amounts of Bi2O3, Na2CO3, K2CO3, TiO2, Al2O3, and Nb2O5 as starting materials and dry them at 100°C for 8 hours;

[0039] (2): According to the stoichiometric ratio of the metal atoms in the expression, Na2CO3, Nb2O5, K2CO3, TiO2, Bi2O3 and Al2O3 were weighed and placed in a ball mill. Anhydrous ethanol was used as the ball milling medium. The mixture was ball milled for 12 h to mix evenly. The mixture was taken out and dried. Then, the mixture was heated to 900 °C and pre-calcined for 3 h at a heating rate of 3 °C / min.

[0040] (3) The powder obtained after pre-calcining in step (2) is ground into powder, ball-milled for 12 hours to mix evenly, dried at 100°C for 8 hours, and then ground into powder. A polyvinyl butyral alcohol solution (PVB) with a preferred concentration of 10 wt% is used as a binder for granulation. The powder is then passed through a 120-mesh sieve and pressed into shape. The powder is kept at 650°C for 3 hours to discharge the colloid. The powder is then sintered at 1150°C in an air atmosphere in a high-temperature furnace. After keeping the temperature for 3 hours, the powder is naturally cooled to room temperature in the furnace.

[0041] Depend on Figure 1 It can be seen that the prepared ceramic samples all present a perovskite structure without the generation of a second phase.

[0042] Depend on Figure 2 It can be seen that with the addition of BiAlO3, the grain size first decreases and then increases, and a dense fine-grained ceramic (average grain size 1.09 μm) is obtained in the embodiment. The refinement of the grain size and the reduction of the porosity contribute to the improvement of the breakdown electric field and mechanical properties, and enhance the transparency of the ceramic.

[0043] Depend on Figure 3 It can be seen that the Vickers hardness of the embodiment is the highest. High hardness can effectively resist mechanical stress, reduce internal damage, and improve the reliability of ceramic capacitors.

[0044] Depend on Figure 4 It can be seen that compared with Comparative Example 1, the transmittance of the embodiment is greatly improved, and the improvement of the transmittance is beneficial to the heat dissipation of the capacitor and prolongs its life.

[0045] Depend on Figure 5 It can be seen that compared with Comparative Example 1, the embodiment takes a shorter time to reach the same temperature as Comparative Example 1, has a stronger thermal conductivity, and is conducive to heat dissipation of the capacitor.

[0046] Depend on Figure 6It can be seen that with the addition of BiAlO3, the material's relaxivity is enhanced, the Curie peak is broadened, and the Curie temperature moves to the high temperature region, which is conducive to its use as a high-temperature capacitor porcelain. The dielectric loss starting temperature of Example 1 is the highest, indicating that it has the ability to suppress high-temperature loss.

[0047] Depend on Figure 7 It can be seen that the embodiment maintains the capacitance temperature stability (ΔC / C 25 ℃≤±15%) and low dielectric loss (≤0.025).

[0048] Depend on Figure 8 It can be seen that the capacitance change rate of the embodiment is ≤±10% under the conditions of 25°C to 150°C and 0kV / cm to 90kV / cm. The stable bias characteristic is beneficial for the use of this material under extreme conditions of high temperature and high pressure.

[0049] Depend on Figure 9 It can be seen that the effective energy storage density, efficiency and breakdown electric field of the embodiment are greatly improved compared with the comparative example 1.

Claims

1. A sodium bismuth titanate-based quaternary high-dielectric lead-free ceramic capacitor dielectric material, characterized in that: The nominal chemical formula of the ceramic dielectric material is (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3, where x=0.

05.

2. The sodium bismuth titanate-based quaternary high-dielectric lead-free ceramic capacitor dielectric material according to claim 1, characterized in that: The relative dielectric constant of this material reaches 1361 at room temperature, and the capacitance temperature stability △C / C is maintained in an ultra-wide temperature range of 5℃-318℃ 25 ℃≤±15% and low dielectric loss ≤0.025; effective energy storage density is 3.43J / cm 3 , efficiency is 85.3%, breakdown field strength is 315kV / cm; it has good stability under high temperature and high pressure, and the capacitance change rate is ≤±10% at 0kV / cm~90kV / cm and 25℃~150℃; it has good mechanical and optical properties, Vickers hardness can reach 6.5GPa, and optical transmittance can reach 70% at a wavelength of 780nm.

3. The method for preparing a sodium bismuth titanate-based quaternary high-dielectric lead-free ceramic capacitor dielectric material according to claim 1 or 2, characterized in that: The following steps are involved: (1): According to the chemical formula (1-x)(0.56Na 0.5 Bi 0.5 TiO3-0.14K 0.5 Bi 0.5 TiO3-0.3NaNbO3)-xBiAlO3 Weigh appropriate amounts of Na2CO3, Nb2O5, K2CO3, TiO2, Bi2O3, and Al2O3 as starting materials, and dry them at 100°C for 8h; (2): According to the stoichiometric ratio of the metal atoms in the expression, Na2CO3, Nb2O5, K2CO3, TiO2, Bi2O3 and Al2O3 were weighed and placed in a ball mill. Anhydrous ethanol was used as the ball milling medium. The mixture was ball milled for 12 h to mix evenly. The mixture was taken out and dried. Then, the mixture was heated to 900 °C and pre-calcined for 3 h at a heating rate of 3 °C / min. (3) The powder obtained after pre-calcining in step (2) is ground into powder, ball-milled for 12 hours to mix evenly, dried at 100°C for 8 hours, and then ground into powder. The powder is granulated with polyvinyl butyral alcohol solution (PVB) as a binder, and then pressed into shape after passing through a 120-mesh sieve. The powder is kept at 650°C for 3 hours to discharge the colloid, and then sintered at 1150°C in an air atmosphere in a high-temperature furnace. After keeping the temperature for 3 hours, the powder is naturally cooled to room temperature in the furnace to obtain a high-k lead-free ceramic capacitor dielectric material with wide temperature range, bias stability, and good mechanical and optical properties.

4. The method according to claim 3, characterized in that The concentration of the polyvinyl butyral alcohol solution (PVB) is 10 wt %.

5. Use of the sodium bismuth titanate-based quaternary high-dielectric lead-free ceramic capacitor dielectric material according to claim 1 or 2 in ceramic capacitors.

6. The use according to claim 5, wherein the operating temperature range is 5°C-318°C.

7. The use according to claim 5, wherein the operating temperature range is 25°C-150°C.

8. Application of the sodium bismuth titanate-based quaternary high-dielectric lead-free ceramic capacitor dielectric material according to claim 1 or 2 for AI servers and new energy vehicles.

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