Barium titanate powder and method for producing same

Abstract

Provided are BaTiO3 powder having fine and uniform particle size and prescribed crystallinity, and a method for producing the same. This method for producing barium titanate (BaTiO3) powder comprises the following steps: a step of mixing titanium dioxide (TiO2) powder with barium carbonate (BaCO3) powder to obtain a first mixture having a Ba / Ti molar ratio of 0.850 or more and 1.000 or less; a step of heat-treating the first mixture at a temperature of 700 °C or more and 900 °C or less to obtain a first heat-treated product containing barium titanate (BaTiO3); a step of mixing and pulverizing the first heat-treated product and additional barium carbonate (BaCO3) powder to obtain a second mixture having a Ba / Ti molar ratio of 0.987 or more and 1.000 or less; and a step of heat-treating the second mixture at a temperature of 900 °C or more and 1200 °C or less to obtain a second heat-treated product containing barium titanate (BaTiO3). The Ba / Ti molar ratio of the second mixture is higher than that of the first mixture, and the difference therebetween is 0.142 or less.

Description

Barium Titanate Powder and Method for Producing the Same

[0001] The present invention relates to barium titanate powder and a method for producing the same.

[0002] Barium titanate (BaTiO ３ ₃) is a kind of perovskite-type compound and is characterized by a high dielectric constant. Therefore, it is used in a wide range of applications such as dielectric elements (capacitors), piezoelectric elements, optoelectronic elements, and semiconductor elements. In particular, BaTiO ３ ₃ is widely used as a material for the dielectric ceramic layer of multilayer ceramic capacitors (MLCCs). Multilayer ceramic capacitors are small in size but have a large capacitance (electrostatic capacitance), and the demand for them is increasing as electronic devices such as mobile phones are miniaturized and CPUs are made faster. Along with this, the development of BaTiO ３ powder as its raw material is progressing.

[0003] As synthesis methods for BaTiO ３ ₃ powder, various methods such as the solid-phase reaction method, the oxalate method, the hydrothermal method, the sol-gel method, and the alkoxide method have been proposed. Among these, the oxalate method synthesizes barium titanium oxalate by a liquid-phase method using barium chloride, titanium tetrachloride, and oxalic acid, and then heat-treats the obtained barium titanium oxalate to obtain BaTiO ３ ₃ powder. The oxalate method has the disadvantages that it is difficult to control the composition (Ba / Ti ratio) and hydrochloric acid is generated as a by-product, so it is necessary to provide expensive waste liquid treatment equipment. The hydrothermal method has the problem that special manufacturing equipment such as an autoclave is required. The sol-gel method and the alkoxide method have the disadvantages that the raw materials are expensive and the productivity is poor.

[0004] On the other hand, in the solid-phase reaction method, a mixture of solid raw materials such as barium carbonate (BaCO ３ ), and titanium oxide (TiO ２ ₂) is heat-treated to synthesize BaTiO ３ ₃ powder. It has the advantages that inexpensive and chemically stable raw materials can be used, expensive manufacturing equipment is not required, and it can be synthesized by a simple method. Therefore, BaTiO ３Solid-phase reaction methods are widely used as a synthesis technique for powders.

[0005] BaTiO by solid-phase reaction ３ Patent Document 1 is cited as a document disclosing powder synthesis. Patent Document 1 discloses a method for producing dielectric particles, which includes the steps of: preparing a first mixed powder by mixing titanium dioxide particles and barium compound particles; a first heat treatment step of heat-treating the first mixed powder at a temperature of 500°C or higher and less than 900°C to obtain composite oxide particles consisting only of 75 to 25 mol% barium titanate phase and 25 to 75 mol% titanium oxide phase; further mixing alkaline earth compounds, etc., with the obtained composite oxide particles to prepare a second mixed powder; and a second heat treatment step of heat-treating the second mixed powder at a temperature of 850 to 1000°C (Claim 1 of Patent Document 1).

[0006] Japanese Patent Publication No. 2009-242212

[0007] Although barium titanate powder has traditionally been synthesized using the inexpensive and simple solid-phase reaction method, there was room for improvement in this conventional method.

[0008] In other words, BaTiO ３ Powders are required to be both fine and have a uniform particle size. Here, uniform particle size means that there is little variation in the particle size of the particles contained in the powder, that is, the width of the particle size distribution is narrow (sharp). For example, thinning the dielectric ceramic layer is effective when manufacturing small, high-capacity multilayer ceramic capacitors. Also, when fabricating a thin dielectric ceramic layer, the raw material is BaTiO ３ The powder needs to be finely milled. Furthermore, powders with uneven particle size contain excessively fine particles, which can lead to abnormal grain growth during the firing process in multilayer ceramic capacitor manufacturing, causing reliability degradation. Therefore, in order to manufacture multilayer ceramic capacitors that are small, high-capacity, and highly reliable, the raw material for the dielectric ceramic layer must be BaTiO ３ The powder is required to have a fine and uniform particle size.

[0009] However, conventional technologies have been insufficient to meet these requirements. For example, Patent Document 1 describes how barium titanate particles that are fine, have uniform particle properties, and have high crystallinity can be obtained (Patent Document 1,

[0019] ). On the other hand, the thinning of multilayer ceramic capacitors is progressing, and the raw material for them is BaTiO ３ The demands for finer powders and uniform particle size have become stricter than before.

[0010] In light of these problems, the inventors conducted thorough research. As a result, they found that BaTiO ３ When manufacturing the powder, the barium carbonate (BaCO3) contained in the raw materials ３ We came to the conclusion that BaCO2 in the material being treated is prone to grain growth during heat treatment, and if it is present in large quantities, abnormal grain growth occurs during heat treatment, which may hinder finer grain size and uniform particle size. ３ I thought that controlling the quantity might suppress the occurrence of abnormal grain growth.

[0011] Then, heat treatment is performed multiple times at a predetermined temperature, and BaCO4 is added after each heat treatment. ３ A method was discovered in which the composition of the material to be treated is controlled to a predetermined range by adding powder. According to this method, BaTiO has a fine and uniform particle size and predetermined crystallinity. ３ We have gained the insight that a powder can be obtained from this BaTiO. ３ We also gained insights into the fact that using powders makes it possible to manufacture electronic components that exhibit particularly excellent characteristics in terms of reliability.

[0012] The present invention was completed based on such findings, and comprises BaTiO having a fine and uniform particle size and predetermined crystallinity. ３ The objective is to provide a powder and a method for producing the same.

[0013] The present invention encompasses the following embodiments. In this specification, the expression "~" includes the numerical values ​​at both ends. That is, "X ~ Y" is synonymous with "X or more and Y or less".

[0014] According to one aspect of the present invention, barium titanate (BaTiO３ A method for producing the powder, comprising the following steps: barium carbonate (BaCO3) ３ ) powder and titanium dioxide (TiO ２ ) A step of mixing powders to obtain a first mixture having a Ba / Ti molar ratio of 0.850 or more and 1.000 or less; The first mixture is heat-treated at a temperature of 700°C or more and 900°C or less to obtain barium titanate (BaTiO ３ A step to obtain a first heat-treated product containing ), and the first heat-treated product and additional barium carbonate (BaCO3). ３ The process involves mixing and grinding the powder to obtain a second mixture having a Ba / Ti molar ratio of 0.987 or more and 1.010 or less, and heat-treating the second mixture at a temperature of 900°C or more and 1200°C or less to obtain barium titanate (BaTiO ３ A method is provided which includes the step of obtaining a second heat-treated product containing ), wherein the Ba / Ti molar ratio of the second mixture is greater than the Ba / Ti molar ratio of the first mixture and the difference is 0.142 or less.

[0015] According to another aspect of the present invention, barium titanate powder is provided in which the cumulative 50% diameter (Dv50) in the volume particle size distribution is 100 nm or more and 250 nm or less, the ratio of the cumulative 10% diameter (Dn10) in the number particle size distribution to Dv50 (Dn10 / Dv50) is 0.38 or more, and the integral width (B) of the (222) plane diffraction peak determined by X-ray diffraction and Dv50 satisfy the following relationship (1).

[0016]

[0017] According to the present invention, BaTiO has a fine and uniform particle size and predetermined crystallinity. ３ A powder and a method for producing the same are provided.

[0018] This is a schematic diagram showing the internal structure of a multilayer ceramic capacitor. ３ This figure shows the relationship between the cumulative 50% diameter (Dv50) of the powder and the integrated width (B) of the XRD diffraction peak.

[0019] Specific embodiments of the present invention (hereinafter referred to as "these embodiments") are described below. However, the present invention is not limited to the following embodiments, and various modifications are possible without altering the essence of the invention. Furthermore, in this specification, any combination of preferred embodiments can be adopted as long as technical consistency can be maintained. For example, one of the preferred numerical ranges can be arbitrarily combined with the other.

[0020] <<1. Method for producing barium titanate powder>> Barium titanate (BaTiO) of this embodiment ３ The method for producing the powder is as follows: Barium carbonate (BaCO3) ３ ) powder and titanium dioxide (TiO ２ ) A step of mixing powders to obtain a first mixture having a Ba / Ti molar ratio of 0.850 or more and 1.000 or less (first mixing step), a step of heat treating the obtained first mixture at a temperature of 700°C or more and 900°C or less to obtain a first heat-treated product containing barium titanate (first heat treatment step), and the obtained first heat-treated product and additional barium carbonate (BaCO3) ３ The process includes a step of mixing and grinding the powder to obtain a second mixture having a Ba / Ti molar ratio of 0.987 or more and 1.010 or less (second mixing step), and a step of heat-treating the obtained second mixture at a temperature of 900°C or more and 1200°C or less to obtain a second heat-treated product containing barium titanate (second heat treatment step). Furthermore, the Ba / Ti molar ratio of the second mixture is greater than the Ba / Ti molar ratio of the first mixture, and the difference is 0.142 or less. Details of each step are described below.

[0021] <First Mixing Process> In the first mixing process, barium carbonate (BaCO3) is used. ３ ) powder and titanium dioxide (TiO ２ The powders are mixed to obtain a first mixture having a Ba / Ti molar ratio of 0.850 to 1.000. ３ Powder and TiO ２ Each powder is the final product, BaTiO ３ These are powdered Ba and Ti raw materials. BaCO ３ Powder and TiO ２Any known raw materials can be used as the powder. Furthermore, the particle size (specific surface area) is not limited as long as it can be mixed. However, fine BaCO3 is not suitable. ３ powder and TiO ２ The powder is highly reactive, and the resulting BaTiO ３ It contributes to further finening of the powder. On the other hand, excessively fine raw material powders are difficult to handle. While maintaining high handlingability, BaTiO ３ From the perspective of reducing the fineness of the powder, BaCO ３ The specific surface area (SSA) of the powder is 2 m². ２ / g or more 30m ２ Preferably less than / g, and 10m ２ / g or more 30m ２ Less than / g is more preferable. Also, from a similar viewpoint, TiO ２ The specific surface area (SSA) of the powder is 20 m². ２ Preferably 30 m ２ / g or more 100m ２ A value of less than / g is more preferable.

[0022] BaCO ３ Powder and TiO ２ The powder mixing may be carried out either dry or wet. Also, when mixing, the material to be treated (BaTiO ３ Powder and TiO ２ The powder may be ground. For wet mixing, known wet mixing equipment such as a ball mill, bead mill, attritor, vibratory mill, disper mill, sand grind mill, or wet jet mill may be used. As the mixed solvent, known solvents such as water, methanol, ethanol, propanol, butanol, toluene, xylene, acetone, methyl ethyl ketone, methylene chloride, ethyl acetate, dimethylformamide, or dimethyl ether may be used. The mixed solvent may be one solvent alone or a combination of multiple solvents. For dry mixing, known dry mixing equipment such as a Henschel mixer, Nauter mixer, ribbon blender, V-type mixer, high-speed mixer, super mixer, turbosphere mixer, or jet mill may be used.

[0023] In the manufacturing method of this embodiment, the Ba / Ti molar ratio of the obtained first mixture is 0.850 or more and 1.000 or less. If the Ba / Ti molar ratio is greater than 1.000, BaCO2 in the first mixture ３ Because the quantity becomes excessively large, the resulting BaTiO ３ There is a risk that the particle size of the powder will be uneven. This is because BaCO ３ ga TiO ２ This is because it promotes easier grain growth. BaCO3 promotes easier grain growth. ３ If a large amount is present, in the subsequent first heat treatment step, BaTiO ３ Before formation, BaCO ３ Grain growth progresses. ３ The presence of BaTiO reduces the uniformity of the distribution of Ba and Ti in the heat-treated material, resulting in BaTiO ３ This results in a non-uniform Ba / Ti ratio. In other words, in the first heat treatment step, Ba-rich BaTiO ３ Particles and Ti-rich BaTiO ３ A state in which particles are mixed is formed. Ba-rich BaTiO ３ Particles and Ti-rich BaTiO ３ Because the particles have different grain growth rates, the BaTiO synthesized in the first heat treatment step ３ The particle size variation increases, and this is the final product, BaTiO ３ This can lead to variations in the particle size of the powder.

[0024] If the Ba / Ti molar ratio is less than 0.850, the amount of Ba in the first mixture becomes excessively low, so BaTiO ３ There is a risk that the particle size of the powder will be non-uniform. That is, because the amount of Ba in the first mixture is excessively low, the final product (BaTiO) will have the desired Ba / Ti molar ratio. ３ To obtain the powder, a large amount of BaCO4 is added in the subsequent second mixing step. ３ It becomes necessary to add BaCO2, which is prone to grain growth in the second heat treatment step after the second mixing step. ３ Because a large amount of it will be present, the final product obtained in the second heat treatment step (BaTiO ３ The particle size variation of the powder increases.

[0025] On the other hand, if the Ba / Ti molar ratio of the first mixture is 0.850 or more and 1.000 or less, in combination with the effects in the subsequent steps (the first heat treatment step, the second mixing step, the second heat treatment step), the final product BaTiO ３ It becomes possible to enhance the effects of the refinement and size uniformity of the powder. From the viewpoint of further enhancing this effect, the Ba / Ti molar ratio of the first mixture is more preferably 0.987 or more and 0.992 or less. The addition amount of the BaCO ３ powder that is liable to grain growth added in the subsequent second mixing step can be suppressed, and the Ba / Ti molar ratio of the final product (BaTiO ３ powder) can be stabilized. Therefore, the Ba / Ti molar ratio of the final product can be precisely and easily controlled. The Ba / Ti molar ratio of the first mixture can be controlled by adjusting the mixing ratio of the BaCO ３ powder and the TiO ２ powder.

[0026] <First Heat Treatment Step> In the first heat treatment step, the first mixture is heat-treated (first heat treatment) to obtain a first heat-treated product containing barium titanate (BaTiO ３ ). By the heat treatment, carbon dioxide gas (CO ３ powder from the BaCO ２ ) is desorbed and changed to barium oxide (BaO). Then BaO reacts with the TiO ２ powder to form BaTiO ３ . The first heat-treated product contains BaTiO ３ , and further, in some cases, unreacted products (BaO, TiO ２ , etc.) and heterogeneous phases (BaTi ２ O ５ , BaTi ４ O ９ , etc.) may be included.

[0027] In the manufacturing method of the present embodiment, the heat treatment temperature in the first heat treatment step is 700°C or more and 900°C or less. If the heat treatment temperature exceeds 900°C, BaTiO in the first heat treatment step ３Grain growth progresses excessively. At this stage, particles having variations in the Ba / Ti ratio and the particles obtained by grain growth thereof are generated, and the effect of reducing the particle size variation in the subsequent steps (second mixing step, second heat treatment step) becomes insufficient. Further, since the crystallite diameter of BaTiO ３ becomes excessively large, it becomes difficult to obtain BaTiO ３ powder having a desired crystallinity. Further, when the heat treatment temperature is less than 700 ° C, the synthesis of BaTiO ３ becomes insufficient. Since a large amount of unreacted BaCO ３ remains, the amount of BaCO ３ in the subsequent second heat treatment step becomes excessively large. As a result, the grain growth of BaCO ３ progresses and the particle size variation of the final product (BaTiO ３ powder) becomes large. By setting the heat treatment temperature to 700 ° C or higher and 900 ° C or lower, it becomes possible to obtain a final product (BaTiO ３ powder) that is fine, has a uniform particle size, has a high degree of synthesis, and has a small crystallite diameter. From the viewpoint of further enhancing the effect of refining and uniformizing the particle size of the final product (BaTiO ３ powder), the heat treatment temperature is more preferably 800 ° C or higher and 900 ° C or lower. In this temperature range, the reaction between BaCO ３ powder and TiO ２ powder proceeds more stably.

[0028] Firing may be performed by a known method. As the firing furnace, a batch-type or continuous electric furnace or gas furnace, for example, a roller hearth kiln, a rotary kiln, a pusher furnace, etc. can be used. The firing time may be, for example, 10 minutes or more and 24 hours or less. Further, firing may be performed in an air atmosphere, an inert gas atmosphere, a reduced pressure atmosphere, a vacuum atmosphere or a pressurized atmosphere.

[0029] Preferably, the Ti reaction rate in the first heat treatment step is 40% or more and 100% or less. Here, the Ti reaction rate is the molar ratio of Ti that reacts with BaCO ３ powder by heat treatment to form BaTiO ３ among the Ti contained in the first mixture. In other words, as shown in the following formula (2), TiO ２The amount of Ti contained in the powder is relative to the amount of BaTiO in the first heat-treated product. ３ This is the percentage of Ti contained in [the material].

[0030]

[0031] By increasing the Ti reaction rate, the BaCO3 contained in the first heat-treated product can be increased. ３ The amount can be kept low. Therefore, the amount of BaCO in the second heat-treated product subjected to the subsequent second heat treatment process is reduced. ３ The amount is suppressed, and as a result, the final product is BaTiO ３ This makes it possible to exhibit an even more pronounced effect of uniformizing the particle size of the powder. From the viewpoint of enhancing the effect of uniformizing the particle size, a Ti reaction rate of 40% to 100% is more preferable, and 80% to 100% is even more preferable.

[0032] <Second Mixing Step> In the second mixing step, the obtained first heat-treated product is mixed with additional barium carbonate (BaCO3). ３ The powders are mixed and ground to obtain a second mixture. At this time, the Ba / Ti molar ratio of the obtained second mixture is adjusted to be between 0.987 and 1.010.

[0033] In the second mixing step, the final product is BaTiO ３ To control the composition of the powder, an additional BaCO2 is used. ３ Add the powder to obtain the second mixture. If the Ba / Ti molar ratio of the second mixture is less than 0.987, the composition will be excessively Ti-rich, so BaTiO ３ The tetragonal degree of the powder decreases, and consequently, the dielectric properties decrease. Also, if the Ba / Ti molar ratio of the second mixture exceeds 1.010, the composition becomes excessively Ba-rich, and therefore BaTiO ３ The tetragonal crystallinity of the powder decreases. BaTiO has a high tetragonal crystallinity and excellent dielectric properties. ３ From the viewpoint of obtaining a powder, the Ba / Ti molar ratio of the second mixture is preferably 0.987 or more and 1.010 or less, and more preferably 0.987 or more and 0.994 or less.

[0034] In the manufacturing method of this embodiment, the Ba / Ti molar ratio of the second mixture is greater than the Ba / Ti molar ratio of the first mixture, and the difference (Ba / Ti molar ratio of the second mixture - Ba / Ti molar ratio of the first mixture) is 0.142 or less. In the second mixing step, BaCO ３ Because powder is added, the Ba / Ti molar ratio of the second mixture is inevitably greater than that of the first mixture. Furthermore, by keeping the difference in the Ba / Ti molar ratio between the second and first mixtures within a predetermined range (0.142 or less), the final product BaTiO is obtained, in conjunction with the effects of other processes (first mixing process, first heat treatment process, second heat treatment process). ３ This makes it possible to enhance the effects of fine powdering and uniform particle size.

[0035] In contrast, if the difference in the Ba / Ti molar ratio between the second mixture and the first mixture is greater than 0.142, additional BaCO added in the second mixing step ３ The quantity is excessively large. BaCO4 is prone to grain growth in the subsequent second heat treatment process. ３ Because a large amount of it will be present, the final product is BaTiO ３ The particle size variation of the powder increases. BaTiO ３ From the viewpoint of suppressing variations in powder particle size, the difference in the Ba / Ti molar ratio between the second mixture and the first mixture is preferably 0.005 or more and 0.112 or less. By limiting the difference in the Ba / Ti molar ratio to the above range, the BaCO2 produced during the heat treatment in the subsequent second heat treatment step is suppressed. ３ This can more effectively suppress grain growth and the resulting non-uniformity of composition (Ba, Ti).

[0036] First heat-treated product and BaCO ３Powder mixing and grinding may be carried out by either a dry or wet method. However, a wet method is preferred as it allows for more uniform and finer mixing and grinding. Wet mixing can be carried out using known wet mixing equipment such as a ball mill, bead mill, attritor, vibratory mill, sand grind mill, or wet jet mill. As the grinding solvent, known solvents such as water, methanol, ethanol, propanol, butanol, toluene, xylene, acetone, methyl ethyl ketone, methylene chloride, ethyl acetate, dimethylformamide, and dimethyl ether may be used. The grinding solvent may be a single solvent or a combination of multiple solvents.

[0037] First heat-treated product and BaCO ３ During the mixing and grinding of the powder, the first heat-treated material to be treated and BaCO3 ３ The combined powder (mixture) is pulverized, increasing its specific surface area (SSA). Preferably, the SSA increase rate is between 8% and 70%. The SSA increase rate is the percentage increase in the SSA of the treated material before and after mixing and pulverization, and is determined according to the following formula (3).

[0038]

[0039] Increasing the SSA increase rate to 8% or more disperses the aggregated particles of added barium carbonate, resulting in a more uniform dispersion of elements. However, excessive grinding of the particles can generate very fine particles, which may grow into coarser particles during the subsequent second heat treatment, or they may remain fine even after the second heat treatment. This can worsen the particle size distribution, but keeping the SSA increase rate below 70% can suppress the generation of very fine particles.

[0040] <Second Heat Treatment Step> In the second heat treatment step, the obtained second mixture is heat-treated (second heat treatment) to produce barium titanate (BaTiO ３ A second heat-treated product containing ) is obtained. The second heat treatment yields a second mixture containing BaTiO ３ The proportion increases. In other words, the second mixture subjected to the second heat treatment consists of the first heat-treated product and the additionally added BaCO3. ３It contains powder. Also, as mentioned above, the first heat-treated product is BaTiO ３ It also contains unreacted products (BaO, TiO ２ etc.) or different phases (BaTi ２ O ５ , BaTi ４ O ９ It may include (etc.). Therefore, when the second mixture is subjected to high-temperature heat treatment, the additionally added BaCO ３ The reaction proceeds between the powder, unreacted product, and other phases to produce BaTiO ３ The proportion (degree of synthesis) of [the element] increases.

[0041] In the manufacturing method of this embodiment, the heat treatment temperature in the second heat treatment step is 900°C or higher and 1200°C or lower. If the heat treatment temperature is less than 900°C, BaTiO in the second mixture ３ The formation reaction is insufficient. The final product is BaTiO ３ The powder will contain many unreacted products and other phases, making it difficult to obtain the desired properties. Also, if the heat treatment temperature exceeds 1200°C, BaTiO ３ Although the formation reaction proceeds sufficiently, grain growth proceeds excessively. Final product (BaTiO) ３ The particles in the powder may become coarser. Final product (BaTiO ３ From the viewpoint of significantly enhancing the effects of finer particle size and uniform particle size of the powder, the heat treatment temperature in the second heat treatment step is preferably 900°C to 1000°C. By setting the heat treatment temperature within the above range, the final product BaTiO ３ The particle size (Dv50) of the powder can be controlled to a more desirable range.

[0042] In this way, the barium titanate (BaTiO) of this embodiment ３ ) Powder can be obtained. That is, the second heat-treated product obtained in the second heat treatment step can be used as is. ３ It can be used as a powder. Alternatively, if necessary, the second heat-treated product can be subjected to post-treatment such as crushing, classification, or washing, and the resulting processed product can be converted into BaTiO ３ It may also be used as a powder.

[0043] In the manufacturing method of this embodiment, heat treatment at a predetermined temperature is performed multiple times, and BaCO3 is also produced. ３ This method is characterized by the addition of powder in two stages (or more) – the raw material mixing stage and the intermediate stage – and by controlling the composition of the raw material mixture and the intermediate product within a predetermined range. Therefore, it is characterized by the large amount of BaCO3 that causes abnormal grain growth in the material subjected to heat treatment. ３ Because its presence is suppressed, BaTiO has a fine and uniform particle size. ３ A powder can be obtained. Also, the obtained BaTiO ３ Because the powder possesses a predetermined crystalline structure, it enables the manufacture of electronic components with superior properties in terms of reliability and other characteristics.

[0044] The resulting BaTiO ３ The powder preferably has a cumulative 50% diameter (Dv50) in its volume particle size distribution of 100 nm to 250 nm. ３ Powders enable the fabrication of electronic components exhibiting superior properties. For example, fine BaTiO ３ The powder enables the formation of a thin dielectric ceramic layer, which can then be used to obtain a small, high-capacity multilayer ceramic capacitor. Dv50 is preferably between 100 nm and 250 nm.

[0045] <<2. Barium titanate powder>> Barium titanate (BaTiO) of this embodiment ３ The powder is characterized by having fine and uniform particle size. Specifically, the cumulative 50% diameter (Dv50) in the volume particle size distribution is between 100 nm and 250 nm, and the ratio of the cumulative 10% diameter (Dn10) in the number particle size distribution to Dv50 (Dn10 / Dv50) is 0.38 or higher.

[0046] BaTiO ３ The powder, when used as a raw material, enables the manufacture of electronic components that exhibit particularly excellent characteristics in terms of reliability. For example, it enables the manufacture of small, high-capacity multilayer ceramic capacitors that exhibit superior reliability.

[0047] Dv50 is preferably between 100 nm and 250 nm. Furthermore, Dn10 / Dv50 is preferably 0.38 or higher, and more preferably 0.42 or higher. There is no upper limit to Dn10 / Dv50. However, the upper limit of Dn10 / Dv50 may be 1 or less.

[0048] The BaTiO of this embodiment ３ The powder has the characteristic of possessing a predetermined crystalline structure in relation to its particle size. Specifically, the integral width (B) of the (222) plane diffraction peak obtained by X-ray diffraction and Dv50 satisfy the following relationship (1).

[0049]

[0050] The integrated width of the X-ray diffraction peak is an indicator of crystallinity. That is, the more crystallinity the powder, the smaller the integrated width, and the less crystallinity the powder, the larger the integrated width. The BaTiO of this embodiment satisfies the relationship in equation (1) above. ３ The powder has a large integral width B in relation to the cumulative 50% diameter Dv50, and therefore can be said to have low crystallinity or a small crystallite size.

[0051] The BaTiO of this embodiment has low crystallinity. ３ Powders are highly reactive, and using them as raw materials can sometimes improve the properties of electronic components manufactured using them. For example, multilayer ceramic capacitors use BaTiO as the main component raw material for the dielectric ceramic layer. ３ The dielectric green sheet is prepared by adding additive components, including rare earth elements (Re), to the powder. After printing an electrode pattern on the upper surface of the obtained dielectric green sheet, it is manufactured by lamination and firing. During firing, the additive elements (Re, etc.) are used to substitute for Ba or Ti, such as BaTiO. ３ It is incorporated into the crystal, thereby improving the characteristics (reliability, temperature characteristics, etc.) of the multilayer ceramic capacitor. The BaTiO of this embodiment has low crystallinity and high reactivity. ３ Powder readily incorporates additive elements (such as Re). Therefore, it contributes to improving the characteristics of multilayer ceramic capacitors.

[0052] The BaTiO of this embodiment ３The Ba / Ti molar ratio of the powder is preferably 0.987 or more and 1.010 or less, and more preferably 0.990 or more and 0.994 or less.

[0053] The BaTiO of this embodiment has the following features ３ The powder is particularly suitable as a raw material for the dielectric ceramic layer of a multilayer ceramic capacitor. In this embodiment, BaTiO ３ By using powder, it becomes possible to manufacture small, high-capacity multilayer ceramic capacitors that exhibit particularly excellent characteristics in terms of reliability.

[0054] Figure 1 schematically shows the internal structure of a multilayer ceramic capacitor. The multilayer ceramic capacitor 1 has a laminate 4 in which a plurality of stacked dielectric ceramic layers 2 and a plurality of internal electrode layers 3 extending between the dielectric ceramic layers 2 are alternately stacked. A pair of external electrodes 5, which function as terminal electrodes, are provided at both ends of the laminate 4. One of the pair of external electrodes 5 is electrically connected to the other such that adjacent internal electrode layers 3 are electrically separated from each other.

[0055] When a voltage is applied between one external electrode 5 and the other, a potential difference is generated between the internal electrodes 3 connected to each external electrode 5. As a result, capacitance is generated in the dielectric ceramic layer 3 sandwiched between the internal electrode layers 3, and the multilayer ceramic capacitor functions as a capacitive element (dielectric element).

[0056] However, the BaTiO of this embodiment ３ The powder is not limited to applications in the manufacture of multilayer ceramic capacitors. It goes without saying that it is also applicable to other known applications such as dielectric elements, piezoelectric elements, optoelectronic elements, and / or semiconductor elements.

[0057] The present invention will be described in more detail using the following examples. However, the present invention is not limited to the following examples.

[0058] (1) Production of barium titanate powder [Examples 1-4] In Examples 1-4, barium carbonate (BaCO3) was used. ３ ) powder and titanium dioxide (TiO２ Using the powder as a raw material, the process involves a first mixing step, a first heat treatment step, a second mixing step, and a second heat treatment step to produce barium titanate (BaTiO). ３ The powder was synthesized.

[0059] First, the specific surface area is 30 m². ２ / g BaCO ３ Powder with a specific surface area of ​​30 m² ２ / g of TiO ２ The powder is zirconia (ZrO ２ Using a ball mill equipped with media, ekinen® or water was wet-mixed and then dried to obtain a mixed powder (first mixture) (first mixing step). At this time, the Ba / Ti molar ratio of the first mixture was set to the values ​​shown in Table 1 below, using BaCO ３ Powder and TiO ２ The amount of powder used was adjusted.

[0060] The obtained first mixture was heat-treated in an air atmosphere using an electric furnace (batch furnace), and then allowed to cool naturally to obtain a heat-treated product (first heat-treated product) (first heat treatment step). In this process, the heat treatment (first heat treatment) was performed at the temperatures shown in Table 1 below, for 20 minutes for Example 1 and for 1 hour for Examples 2 to 4.

[0061] Next, the obtained first heat-treated material has a specific surface area of ​​30 m². ２ / g BaCO ３ Add the powder, ZrO ２ Using a ball mill equipped with media, ekinen® or water was wet-mixed and dispersed (ground), and then dried to obtain a dry powder (second mixture) (second mixing step). At this time, BaCO₃ was added so that the Ba / Ti molar ratio of the second mixture was the value shown in Table 1 below. ３ I adjusted the amount of powder.

[0062] The obtained second mixture was heat-treated in an air atmosphere using an electric furnace, and then allowed to cool naturally to obtain a heat-treated product (second heat-treated product) (second heat treatment step). In this case, the heat treatment (second heat treatment) was performed for 1 hour at the temperatures shown in Table 1 below. The obtained second heat-treated product was then treated with barium titanate (BaTiO2). ３ ) It was evaluated as a powder.

[0063] The Ba / Ti molar ratio of the mixtures (first mixture and second mixture) was determined by X-ray fluorescence analysis (XRF). Specifically, the composition of each mixture was examined using XRF, and the Ba / Ti molar ratio of the mixture was calculated based on the obtained analytical results.

[0064] [Comparative Example 1] In Comparative Example 1, BaCO2 ３ Powder and TiO ２ Using powder as a raw material, BaTiO is produced through only the first mixing step and the first heat treatment step. ３ The powder was synthesized. In other words, the second mixing step and the second heat treatment step were omitted.

[0065] First, the specific surface area is 30 m². ２ / g BaCO ３ Powder with a specific surface area of ​​30 m² ２ / g of TiO ２ The powder is ZrO ２ A mixed powder (first mixture) was obtained by wet mixing with ekinen® or water using a ball mill equipped with media, followed by drying. At this time, the Ba / Ti molar ratio of the first mixture was set to the values ​​shown in Table 1 below, using BaCO3. ３ Powder and TiO ２ The amount of powder used was adjusted.

[0066] The resulting mixture was heat-treated in an air atmosphere using an electric furnace (batch furnace), and then allowed to cool naturally to obtain a heat-treated product (first heat-treated product). During this process, the heat treatment was carried out for 1 hour at the temperatures shown in Table 1 below. The resulting first heat-treated product was then prepared using BaTiO2. ３ It was evaluated as a powder.

[0067]

[0068] [Comparative Examples 2-6] In Comparative Examples 2-6, BaTiO was synthesized by hydrothermal synthesis. ３ The powder was synthesized. Specifically, barium hydroxide and titanium dioxide were reacted hydrothermally under high temperature and pressure (150-250°C) and then dried.

[0069] (2) Evaluation: The BaTiO obtained in Examples 1 to 4 and Comparative Examples 1 to 6 ３ The various properties of the powder were evaluated using the following procedure.

[0070] <Particle Size (Dn10, Dv50)> Barium titanate powder was observed using a scanning electron microscope (SEM), and the resulting SEM images were analyzed to determine the particle size of the primary particles constituting the powder. The SEM observation was performed at a magnification of 30,000x. During the image analysis, more than 300 particles were extracted, and the particle size of each particle was determined. Based on the obtained particle sizes, the particle size distribution based on the number of particles was determined, and the cumulative 10% from the finest particle side was determined as Dn10. In addition, the volume of each particle was calculated from the particle size to a spherical value, and based on the obtained volume, the particle size distribution based on the volume was determined, and the cumulative 50% diameter from the finest particle side was determined as Dv50.

[0071] Furthermore, based on the obtained Dv50, F(Dv50) was calculated according to the following formula (4).

[0072]

[0073] <XRD (integral width B)> BaTiO ３ The powder was analyzed by powder X-ray diffraction (XRD). The sample used for XRD analysis was BaTiO ３ The sample was prepared by leveling and molding the powder. XRD analysis was performed under the following conditions.

[0074] - Radiation source: CuKα - Background correction: Yes - Integration time: 1.0 s / step - X-ray output intensity: 1.6 kW - Step width: 0.01° / step

[0075] Then, in the obtained XRD profile, the integral width (B) of the (222) plane diffraction peak appearing at 2θ = 81 to 85° was determined. Specifically, the area (integral intensity) and peak intensity of the (222) plane diffraction peak were determined, and the integral width (B) was calculated by dividing the area (integral intensity) by the peak intensity. Then, the difference between the integral width (B) and F(Dv50) (B - F(Dv50)) was calculated.

[0076] <Capacitor Characteristics (MTTF)> BaTiO ３ Multilayer ceramic capacitors were fabricated using powder and their characteristics were evaluated. First, BaTiO ３ Add a predetermined amount of MgO and Dy to the powder as an additive. ２ O ３ SiO ２ MnCO３ BaCO ３ Adding, and further using polyvinyl butyral resin as an organic binder, ethanol as an organic solvent, and partially stabilized ZrO ２ The material was placed in a PVC pot along with the media (2 mm in diameter), mixed, and crushed to form a slurry.

[0077] The obtained slurry was formed into a sheet using the doctor blade method, and then punched out to a predetermined size to obtain a rectangular green sheet. The thickness of the green sheet was adjusted to 1 μm after firing. Next, a conductive paste with Ni powder as the conductive component was screen printed onto the obtained green sheet to form a conductive paste layer (internal electrode pattern) that would become the internal electrode layer after firing.

[0078] Then, a laminated block was fabricated by laminating green sheets with internal electrode patterns formed on them, and further laminating green sheets without internal electrode patterns as outer layers on both the upper and lower sides, and then pressing them together. The unfired laminate obtained by cutting this laminated block to the predetermined dimensions was heat-treated in air (350°C, 3 hours) to remove the binder, and then 10 －１０ MPa H ２ -N ２ -H ２ The laminate (ceramic laminate) was fired at 1200°C for 2 hours in a reducing atmosphere consisting of oxygen gas.

[0079] A conductive paste for forming external electrodes was applied to both ends of the fired laminate and baked, and then Ni and Sn were electroplated to form external electrodes that were electrically connected to the internal electrodes. A multilayer ceramic capacitor was fabricated in this manner. The fabricated multilayer ceramic capacitor had dimensions of length (L): 1.6 mm, width (W): 0.8 mm, and thickness (T): 0.8 mm, with an element thickness (thickness of the dielectric ceramic layer) of 1 μm and 320 layers of dielectric ceramic layers.

[0080] High-accelerated life (HALT) testing was performed on 100 multilayer ceramic capacitors fabricated in each example and comparative example. The HALT test was conducted under conditions of an ambient temperature of 150°C and a DC applied voltage of 16V. In the test, the insulation resistance was 10 ５ A failure was defined as the point at which the impedance fell below Ω, and the obtained data was analyzed using Weibull analysis to calculate the mean time to failure (MTTF). Based on the MTF value, reliability was determined according to the following criteria.

[0081] MTF: 300 hours or more: Good (G) MTF: Less than 300 hours: Poor (NG)

[0082] (3) Evaluation results <Powder properties> BaTiO of Examples 1 to 4 and Comparative Examples 1 to 6 ３ The physical properties of the powder are shown in Table 2 below. Also, BaTiO ３ Figure 2 shows the relationship between the cumulative 50% diameter (Dv50) of the powder and the integrated width (B) of the XRD diffraction peak.

[0083] BaTiO of Examples 1-4 ３ The powder had a Dv50 of 100 nm to 250 nm and a Dn10 / Dv50 of 0.38 or higher. This indicates that it has a fine and uniform particle size. Furthermore, in the relationship between the integral width B and Dv50, B - F(Dv50) was a positive value (+), and the integral width B was relatively large. Therefore, it was found that it has a certain degree of crystallinity, that is, relatively low crystallinity.

[0084] In contrast, the BaTiO of Comparative Example 1 ３ The powder had a Dn10 / Dv50 of less than 0.38 and exhibited non-uniform particle size. Furthermore, the BaTiO2 of Comparative Examples 2-6, synthesized by hydrothermal synthesis, also exhibited non-uniform particle size. ３ Although the powder had a Dn10 / Dv50 ratio of 0.38 or higher, the relationship between the integral width B and Dv50, B-F(Dv50), was negative. Therefore, it did not possess the required crystallinity.

[0085]

[0086] <Capacitor Characteristics> BaTiO of Example 1 and Comparative Example 6 ３Table 3 below shows the mean time to failure (MTTF) of multilayer ceramic capacitors (MLCCs) fabricated using powder.

[0087] The multilayer ceramic capacitor of Example 1 had a relatively long MTF of 358 hours, indicating excellent reliability. In contrast, the multilayer ceramic capacitor of Comparative Example 6 had a relatively short MTF of 282 hours, resulting in lower reliability compared to Example 1.

[0088]

[0089] From the above results, according to this embodiment, BaTiO has a fine and uniform particle size and a predetermined crystallinity. ３ It is understood that a powder and a method for producing the same are provided.

Claims

1. Barium titanate (BaTiO) ３ A method for producing the powder, comprising the following steps: barium carbonate (BaCO3) ３ ) powder and titanium dioxide (TiO ２ ) A step of mixing powders to obtain a first mixture having a Ba / Ti molar ratio of 0.850 or more and 1.000 or less; The first mixture is heat-treated at a temperature of 700°C or more and 900°C or less to obtain barium titanate (BaTiO ３ A step to obtain a first heat-treated product containing ), and the first heat-treated product and additional barium carbonate (BaCO3). ３ The process involves mixing and grinding the powder to obtain a second mixture having a Ba / Ti molar ratio of 0.987 or more and 1.010 or less, and heat-treating the second mixture at a temperature of 900°C or more and 1200°C or less to obtain barium titanate (BaTiO ３ A method comprising the step of obtaining a second heat-treated product containing ), wherein the Ba / Ti molar ratio of the second mixture is greater than the Ba / Ti molar ratio of the first mixture and the difference is 0.142 or less.

2. The method according to claim 1, wherein in the step of obtaining the second mixture, the first heat-treated product and additional barium carbonate powder are mixed and pulverized by a wet method.

3. The method according to claim 1 or 2, wherein in the step of obtaining the second mixture, the rate of increase in the specific surface area (SSA) of the treated material during the mixed grinding of the first heat-treated material and additional barium carbonate powder is 8% or more and 70% or less.

4. The method according to claim 1 or 2, wherein the barium titanate powder has a cumulative 50% diameter (Dv50) in its volume particle size distribution of 100 nm or more and 250 nm or less.

5. In the process of obtaining the first heat-treated product, among the titanium (Ti) contained in the first mixture, barium carbonate (BaCO3) is obtained by heat treatment. ３ ) reacts with the powder to form barium titanate (BaTiO ３ The method according to claim 1 or 2, wherein the titanium (Ti) reaction rate, which is the molar ratio of titanium (Ti) that forms the ) is 40% or more and 100% or less.

6. The method according to claim 1 or 2, wherein the Ba / Ti molar ratio of the first mixture is 0.987 or more and 0.992 or less.

7. The method according to claim 1 or 2, wherein in the step of obtaining the first heat-treated product, the heat treatment of the first mixture is carried out at a temperature of 800°C or more and 900°C or less.

8. The method according to claim 1 or 2, wherein the difference between the Ba / Ti molar ratio of the second mixture and the Ba / Ti molar ratio of the first mixture is 0.005 or more and 0.112 or less.

9. The method according to claim 1 or 2, wherein in the step of obtaining the second heat-treated product, the heat treatment of the second mixture is carried out at a temperature of 900°C or more and 1000°C or less.

10. Barium titanate powder having a cumulative 50% diameter (Dv50) in the volume particle size distribution of 100 nm or more and 250 nm or less, and a ratio of the cumulative 10% diameter (Dn10) in the number particle size distribution to Dv50 (Dn10 / Dv50) of 0.38 or more, and the integral width (B) of the (222) plane diffraction peak determined by X-ray diffraction and Dv50 satisfy the relationship in equation (1) below.

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