KR100390469B1 - Process for Preparing Ultrafine Barium Titanate Dielectric Ceramic Material - Google Patents

Abstract

The present invention relates to a method for producing ultrafine dielectric ceramic material for low temperature firing, which can produce ultrafine BaTiO ₃ dielectric ceramics at low temperature.

The present invention is characterized by coating the ultrafine BaTiO ₃ powder with a solution of Cu-2 ethylhexanoate metal organic compound.

According to the present invention, the grain size is 120 to 130 nm and fired at 1000 ° C., the average particle diameter of 280 to 420 nm, the density of 5.61 to 5.80 g / cm ³ , and the temperature range of -14 to 61 ° C. at -55 to 125 ° C. A Cu-coated BaTiO ₃ powder capable of producing high density ultrafine BaTiO ₃ dielectric ceramics having a dielectric constant change of% can be obtained.

Description

Process for Preparing Ultrafine Barium Titanate Dielectric Ceramic Material

The present invention relates to a method for producing an ultrafine dielectric ceramic material, and more specifically, to ultrafine BaTiO which can obtain ultrafine dielectric ceramics having good dielectric properties by coating the ultrafine BaTiO ₃ powder with a Cu metal organic compound solution. ₃ relates to a method for producing a dielectric ceramic material.

Multi-Layer Ceramic Capacitors (MLCCs) are essential passive components for building small, lightweight electronic circuits. Recently, due to the miniaturization of components due to the miniaturization of various electronic devices and the high integration of electronic circuits, multilayer ceramic capacitors also need to develop ultra-small devices. In order to manufacture a micro multilayer ceramic capacitor, the thickness of one layer of the dielectric ceramic after firing should preferably be 2 m or less. In order to reliably manufacture a multilayer ceramic capacitor made of dielectric ceramics having such a thickness, the average particle diameter of the dielectric ceramics after firing should preferably be no more than 1/4 of the thickness of one layer, that is, 0.5 μm or less and high density. .

On the other hand, multilayer ceramic capacitors are manufactured by stacking dielectric ceramics and internal electrodes up to several hundred layers alternately and simultaneously firing them. Therefore, the internal electrode material must be able to withstand the firing temperature of the dielectric ceramics. Titanate based on barium titanate (BaTiO ₃ ), which requires a high firing temperature of 1300 ° C. or more, has been mainly used as a dielectric ceramic for multilayer ceramic capacitors. These materials require expensive high melting point precious metal internal electrodes such as Pd, Pt and the like. In order to reduce the cost of using such an expensive electrode, a low temperature firing technique of a low-temperature firing dielectric ceramic composition or ultra-fine dielectric ceramics using an inexpensive electrode such as Ag or Pd-Ag is required.

Attempts have been made to produce ultrafine dielectric ceramics by adding an additive such as Pb-based, Cd-based, Bi-based, B-based, or Li-based to BaTiO ₃ to lower the firing temperature (see Japan Nippon Teki 5-120915,日本 特 開平 1-192762). However, these additives all have problems such as toxicity, non-environmental affinity, chemical reactivity with dielectric materials, water reactivity with water used as a solvent in water. In order to eliminate such a problem, an environmentally friendly and chemically stable ultrafine dielectric ceramic composition for low temperature firing or low temperature baking technology of ultrafine dielectric ceramics is required.

An environmentally friendly, chemically stable, low-cost BaTiO ₃ dielectric ceramic composition for the addition of cheap Cu has been proposed. (Reference: Japanese Patent No. 8-203702, Korean Patent Publication No. 94-3970) This is understood because calcination is promoted at low temperature due to the liquid phase produced by addition of Cu. However, even in the BaTiO ₃ dielectric ceramic composition for low temperature sintering with Cu as described above, an average particle diameter of 1 μm or less cannot be obtained, and because of the irregular distribution of the liquid phase, abnormal grain growth (abnormal or exaggerated grain growth) often occurs. It is not widely used for the manufacture of multilayer ceramic capacitors. (Reference: Jo, Man et al., "Dielectric Properties of BaTiO ₃ Ceramics with Abnormal Grain Growth," Journal of the Korean Ceramic Society, 36 [8], 965-973 (1999))

Accordingly, an object of the present invention is to uniformly coat the ultrafine BaTiO ₃ powder with a Cu metal organic compound solution so that the above-mentioned problems can be solved, so that ultrafine BaTiO ₃ dielectric ceramics having good dielectric properties can be manufactured at low temperature. The present invention provides a method for producing an ultrafine dielectric ceramic material for low temperature firing.

In order to achieve this object, according to the present invention, preparing a mixed slurry of ultra-fine BaTiO ₃ powder, Cu metal organic compound solution and anhydrous solvent, drying the mixed slurry, and heat-treated the dried mixed slurry There is provided a method for producing an ultra-fine BaTiO ₃ dielectric ceramic material comprising the step of decomposing the residual organic matter to obtain a Cu-coated ultra-fine BaTiO ₃ powder.

In the present invention, as a starting material for producing the ultrafine BaTiO ₃ dielectric ceramic material, the ultrafine BaTiO ₃ powder manufactured by hydrothermal synthesis, which is about 99.9% or more in purity, is preferable.

The Cu metal organic compound is preferably Cu-2 ethylhexanoate, and its amount is 5% by weight, preferably 2-5% by weight, based on the BaTiO ₃ raw material powder. If the addition amount is less than 2% by weight, the effect of lowering the firing temperature is insignificant, and even when it exceeds 5% by weight, there is no significant change in the firing density obtained after firing.

According to the present invention, the BaTiO ₃ powder is uniformly coated with Cu by the addition of the Cu metal organic compound, and thus the BaTiO ₃ powder coated with Cu is baked at 800 to 1100 ° C. for 0.5 to 1.5 hours, but the firing temperature is increased. As a result, it is possible to bake in a form in which the average particle diameter is gradually increased without accompanying abnormal grain growth, thereby obtaining an ultrafine BaTiO ₃ dielectric ceramic material.

The slurry prepared by mixing BaTiO ₃ powder and Cu metal organic compound solution together with anhydrous solvent is preferably dried at about 100 hours at 100 ° C. and then heat treated at about 500 ° C. for 2 hours to completely decompose the organic matter remaining after drying. This yields an ultrafine BaTiO ₃ dielectric ceramic powder uniformly coated with Cu.

Prepared according to the method of the present invention, BaTiO ₃ powder having an average particle diameter of about 120 ~ 130 nm and the Cu coating amount of 2 to a density when 5 wt% of BaTiO ₃ powder sikyeoteul fired at 1000 ℃ for 0.5 hours from about 5.61 - 5.79 It is an ultrafine BaTiO ₃ powder capable of obtaining dielectric ceramics having a g / cm ³ , an average particle diameter of 0.31 to 0.47 μm, and a dielectric constant change of −14 to 52% in a temperature range of −55 to 125 ° C.

Hereinafter, the present invention will be described in more detail with reference to Examples.

<Examples 1-7>

First, 0 to 6 wt% of Cu-2ethylhexanoate (STREM, USA) was added to ultrafine BaTiO ₃ powder (specific surface area = 8.65 m ² / g, BT-8, Cabot, USA) of about 99.9% or more purity prepared by hydrothermal synthesis. It is added and charged into a Teflon jar and wet mixed for about 12 hours using anhydrous 1-Butanol (Aldrich, USA) and zirconia balls with a purity of at least about 99.8%. At this time, the ratio of the mixture: anhydrous 1-Butanol: zirconia ball is 1: 2: 2 by weight ratio.

The mixed slurry thus prepared is dried at about 100 ° C. for about 12 hours and then heat-treated at about 500 ° C. for about 2 hours to decompose the residual organic material to obtain a Cu-coated ultrafine dielectric ceramic BaTiO ₃ powder.

The specific surface area of the BaTiO ₃ powder thus prepared was measured using a BET specific surface area analyzer (Quantachrome, model name Autosorb-1), from which an ideal spherical particle having a density of 6.0 g / cm ³ was assumed and crystallite size was determined. Saved.

The results are shown in Table 1 below.

No. Coating amount (wt%) Specific surface area (m ² / g) Crystallite size (nm) One 0 8.65 116 2 One 8.39 119 3 2 8.32 120 4 3 8.04 124 5 4 7.89 127 6 5 7.69 130 7 6 7.64 131

In the results of Table 1, as the coating amount was increased, the BaTiO ₃ powder with slightly increased crystallite size was obtained. This phenomenon appears to be due to the coating of Cu on the surface of the BaTiO ₃ powder. That is, the ultrafine BaTiO ₃ powder and 0-6 wt% Cu-2ethylhexanoate were wet mixed with anhydrous 1-Butanol as a solvent and subjected to proper post-treatment, thereby uniformly coating Cu on the surface of the powder so that the grain size was 116-131. Ultrafine BaTiO ₃ powders of nm could be obtained.

<Examples 8 to 46>

On the other hand, BaTiO ₃ powder obtained in order to investigate plasticity and dielectric properties was uniaxially press-molded at a pressure of 1 ton / cm ² in a mold having a diameter of 10 mm, and then hydrostatically molded at a pressure of 3 ton / cm ² and It baked by heating up to 800-1300 degreeC at about 360 degreeC / hr, and holding for 2 hours.

After that, the firing density was measured, and one surface was polished with an SiC abrasive paper (# 2000) and a diamond paste (9, 3, 1 µm), and the average of the fired bodies was measured by a scanning electron microscope (S-4200, manufactured by Hitachi). The particle diameter was measured.

The results are shown in Table 2 below.

Plasticity of Coated BaTiO ₃ Powder ¹ . No. Coating amount (wt%) Firing temperature (℃) Plastic density (g / cm ³ ) Average particle size (㎛) 8 0 1000 3.87 0.18 9 0 1100 4.35 0.25 10 0 1200 5.23 0.34 11 0 1300 5.81 13.68 12 One 900 4.73 0.19 13 One 1000 4.97 0.27 14 One 1100 5.16 0.32 15 One 1200 5.25 0.90 16 One 1300 5.38 1.68 17 2 800 4.95 0.18 18 2 900 5.11 0.25 19 2 1000 5.36 0.31 20 2 1100 5.54 0.36 21 2 1200 5.56 0.94 22 2 1300 5.57 1.75 23 3 800 5.23 0.18 24 3 900 5.46 0.27 25 3 1000 5.63 0.34 26 3 1100 5.81 0.40 27 3 1200 5.82 1.01 28 3 1300 5.82 2.13 29 4 800 5.38 0.19 30 4 900 5.54 0.29 31 4 1000 5.70 0.37 32 4 1100 5.89 0.44 33 4 1200 5.89 1.05 34 4 1300 5.90 2.58 35 5 800 5.43 0.20 36 5 900 5.59 0.30 37 5 1000 5.82 0.47 38 5 1100 5.96 0.49 39 5 1200 5.95 1.12 40 5 1300 5.96 2.85 41 6 800 5.48 0.25 42 6 900 5.58 0.38 43 6 1000 5.84 0.56 44 6 1100 5.96 0.83 45 6 1200 5.96 1.40 46 6 1300 5.95 3.25 ¹ Firing time = 2.0 hr

In the results of Table 2, in the case of BaTiO ₃ powder that is not coated with copper, only a density of 5.23 g / cm ³ can be obtained even when calcined at 1200 ° C. When it was wt%, BaTiO ₃ dielectric ceramics having a high density of 5.36 to 5.94 g / cm ³ were obtained even when fired at 1000 ° C. Firing is promoted even when the amount of Cu coating is 1 wt%, but the effect is relatively insignificant, and when the coating amount is more than 5 wt%, no further densification is achieved. On the other hand, when the amount of Cu coating was constant, the firing density also increased as the firing temperature was increased at 800 to 1100 ° C, but the firing density did not increase significantly even when the firing temperature was increased above 1100 ° C.

When the firing temperature of Cu-coated BaTiO ₃ powder is 800 to 1100 ° C, the average particle size gradually increases as the firing temperature increases. When the Cu coating amount is 2 to 5 wt%, ultrafine BaTiO ₃ having an average particle diameter of 0.5 μm or less Dielectric ceramics were obtained. However, above 1100 ° C, as the firing temperature increased, the average particle diameter rapidly increased.

As the BaTiO ₃ powder is coated with Cu, low-temperature plasticization and ultra-fine atomization of BaTiO ₃ dielectric ceramics are possible. The uniformly coated Cu on the surface of the BaTiO ₃ powder has a spatial uniformity in the liquid phase, which is a mass transfer path at the firing temperature. It is believed to be due to the formation of metals in order to promote plasticity. In addition, at the firing temperature of 1100 ° C or higher, no increase in density is achieved and only the average particle size is rapidly increased. Densification of the Cu-coated BaTiO ₃ powder occurs at a temperature of 1100 ° C or lower, and grain growth is at a temperature of 1100 ° C or higher. It seems to be due to happening in.

<Examples 47-64>

Meanwhile, BaTiO ₃ powder was uniaxially squeezed at a pressure of 1 ton / cm ² in a mold having a diameter of 10 mm to confirm the conditions under which the Cu coated on the surface of the ultrafine BaTiO ₃ powder forms BaTiO ₃ and the core shell structure at the firing temperature. After press molding, hydrostatic pressure molding was carried out again at a pressure of 3 ton / cm ² , and the resultant was calcined by raising the temperature to 800 to 1300 ° C. at about 360 ° C./hr from normal temperature and maintaining for 0.5 to 4.0 hours.

After firing, polishing was performed using SiC abrasive paper (# 1000) so that the final specimen thickness was 1 mm. After polishing, silver paste was applied to both sides of the specimen and heat treated at about 600 ° C. for about 10 minutes to form electrodes. The specimen thus prepared was mounted in a temperature control chamber (Delta Design, USA) and the dielectric constant was measured using an LCR meter (model name 4263B manufactured by Hewlett Packard) in the temperature range of -55 to 125 ° C. (1.0 V _rms , 1 KHz)

Subsequently, after removing all the electrodes on both sides of the specimen, the plastic density was measured, and one side was polished with SiC abrasive paper (# 2000) and diamond paste (9, 3, 1 μm), followed by scanning electron microscopy (manufactured by Hitachi, S-4200), the average particle diameter of the fired body was measured.

The results are shown in Table 3 below.

Plasticity Characteristics ¹ and Dielectric Properties of Coated BaTiO ₃ Powders. No. Coating amount (wt%) Firing time (hr) Firing Density (g / cm ³ ) Average particle size (㎛) Room temperature dielectric constant Dielectric constant change (%) ² 47 3 0.5 5.61 0.28 2054 -12 to 42 48 3 1.0 5.62 0.31 2042 -12 to 45 49 3 1.5 5.62 0.31 2025 -13 to 49 50 3 2.0 5.63 0.34 1988 -14 to 57 51 3 3.0 5.63 0.56 1994 -14 to 60 52 3 4.0 5.63 0.80 1990 -15 to 61 53 4 0.5 5.67 0.30 2105 -12 to 48 54 4 1.0 5.68 0.33 2077 -13 to 50 55 4 1.5 5.69 0.34 2052 -14 to 56 56 4 2.0 5.70 0.37 2037 -14 to 62 57 4 3.0 5.70 0.66 2010 -15 to 64 58 4 4.0 5.70 0.99 2045 -15 to 66 59 5 0.5 5.79 0.41 2143 -11 to 52 60 5 1.0 5.80 0.40 2124 -12 to 55 61 5 1.5 5.80 0.42 2111 -13 to 61 62 5 2.0 5.82 0.47 2076 -14 to 76 63 5 3.0 5.82 0.78 2097 -15 to 78 64 5 4.0 5.82 1.13 2088 -15 to 80 ¹ firing temperature = 1000 ° C, ^{2 relative to} room temperature dielectric constant, temperature range = -55 to 125 ° C

In the results of Table 3, the firing density hardly changes regardless of the firing time. The average particle diameter does not change significantly until the firing time is 1.5 hours, but at higher firing times, it rapidly increases as the firing time increases. As the firing time increases, the room temperature dielectric constant slowly decreases until the firing time is 1.5 hours, but does not change significantly at further firing times. As the firing time increases, the change in dielectric constant gradually increases until the firing time is 1.5 hours, but the firing time rapidly increases from 1.5 to 2.0 hours, and does not change significantly over the firing time.

This phenomenon is explained by the fact that Cu coated on the surface of ultrafine BaTiO ₃ powder forms a core shell structure with BaTiO ₃ when the firing time is 0.5 to 1.5 hours, and a solid solution with BaTiO _{3 when} the firing time is 2.0 to 4.0 hours. Seems to be due to the formation of.

According to the present invention, ultrafine BaTiO ₃ powders are uniformly coated with a Cu metal organic compound solution to obtain ultrafine dielectric ceramic powders for low temperature firing capable of producing ultrafine BaTiO ₃ dielectric ceramics having good dielectric properties at low temperatures. Can be.

Claims (9)

Preparing a mixed slurry of ultra-fine BaTiO ₃ powder, Cu metal organic compound solution and anhydrous solvent, Drying the mixed slurry, and A method of manufacturing an ultrafine BaTiO ₃ dielectric ceramic material, comprising the step of obtaining a Cu-coated ultrafine BaTiO ₃ powder by thermally decomposing and removing residual organic materials contained in the dried mixed slurry. The method of claim 1, wherein the ultra fine BaTiO ₃ Method for producing a dielectric ceramic material, characterized in that the Cu-metal-organic compound is 2 Cu-ethylhexanoate. The method of claim 1 wherein the anhydrous solvent is ultra fine BaTiO ₃ The method for producing a dielectric ceramic material characterized in that the anhydrous 1-butanol. The method of claim 1, wherein the ultra fine BaTiO ₃ The method for producing a dielectric ceramic material, characterized in that the production of the mixed slurry by ball-milling. The method of claim 1, wherein the ultra fine BaTiO ₃ The method for producing a dielectric ceramic material, characterized in that the heat treatment temperature is about 500 ℃. The method of claim 1, wherein the drying temperature is 100 ° C. ₃ . The method of producing an ultrafine BaTiO ₃ dielectric ceramic material according to claim 1 or 2, wherein the addition amount of the Cu metal organic compound is 2 to 5% by weight of the BaTiO ₃ powder. The method of claim 1, wherein the ultra fine BaTiO ₃ The method for producing a dielectric ceramic material according to claim 1, further comprising the step of firing the Cu coated ultra fine BaTiO ₃ powder in 800~1100 ℃. The method of claim 8, wherein the firing step of the method for producing ultra fine BaTiO ₃ dielectric ceramic material, characterized in that is carried out during the 0.5~1.5 hours.