JP2656091B2 - Dielectric ceramic with high dielectric constant, low loss factor and flat temperature coefficient - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATION The present invention relates to a high dielectric constant (K), for example, between about 4900 and about 5400, for example, a low loss factor (DF) of about 2% or more, Approximately 7000 ohms at 25 ° C-Farads and 125
A high insulation resistance (R) capacitance (C) product (RC) of about 3000 ohm-Farad or more at 25 ° C and a dielectric constant of about ± 15% or more over a temperature in the range of -55 ° C to 125 ° C and 25 ° C.
The present invention relates to a ceramic dielectric composition having a stable temperature coefficient (TC) characteristic which does not change from a base value in the above.

2. Description of the Related Art Multilayer ceramic capacitors (MLC's) are cast or molded insulating layers, usually made of dielectric ceramic powder, on which palladium / silver alloy, usually in the form of a metal paste. By forming a multilayer capacitor by laminating the resulting conductive metal electrode layers and laminating the resulting elements, and then firing to impregnate and compress the material, thus forming a multilayer ceramic capacitor. Other methods of forming MLC's are described in U.S. Patent Nos. 3,697,950 and 3,879,645 and U.S. Patent Application No. 730,711, which is incorporated herein by reference.

A high dielectric constant is important because it allows a smaller capacitor to be constructed and manufactured for a given capacitance. The electrical properties of many dielectric ceramic compositions are:
It changes substantially with increasing or decreasing temperature, but the change in insulation resistance and loss factor with dielectric constant and temperature is also an important factor to be considered in the preparation of ceramic compositions used in multilayer capacitors. .

For applications requiring dielectric constant stability over a wide temperature range, a desirable dielectric ceramic composition for multilayer capacitors has a dielectric constant above about ± 15 ° C and its base value at 25 ° C (room temperature). Does not change from. The insulation resistance and capacitance product of such a composition are 10
It should be above 00 ohm-Farad and at the maximum working temperature, in most cases at 125 ° C. above 100 ohm-Farad. Further, the loss factor should be as close to 0% as possible.

A commonly used method for manufacturing such temperature stable capacitors is the BaTiO ₃ used for high dielectric constant.
With a small number of ceramic oxide additives (dopants) consisting of trace elements or compounds that adjust the final dielectric properties. The degree of distribution of the ceramic oxide dopant throughout the unfired barium titanate is:
The degree of solid solution development during firing, grain growth, and the final fired grain composition and grain boundaries will be determined. Therefore, mixing efficiency is a key factor in the method to achieve the desired electrical properties of the final multilayer ceramic capacitor. However, until the present invention, it was very difficult to distribute very small amounts of ceramic oxide dopant homogeneously throughout the formulated ceramic dielectric composition.

To compositionally developed during the multilayer ceramic capacitor manufacturing firing process takes place, the particles of the ceramic oxide dopants of a dielectric composition, by which is in finely divided form, appropriate mixing of the ceramic oxide dopants and BaTiO ₃ It is well known that you must ensure In theory, for full compositional evolution to occur during firing of the ceramic dielectric composition, the minority components should be such that the environment around each barium titanate grain is the same throughout the bulk of the composition, and It is understood that the environment within each barium titanate grain must be dispersed such that it is the same throughout the bulk of the composition. Typically, this has been attempted by grinding the components of the composition to a particle size of about 1 micron. However, homogenous distribution is only one micron sized BaTiO ₃
Throughout the use of the particles, it may be facilitated by introducing small particles, for example, about 0.1 micron ceramic oxide dopant. By way of illustration, when using a uniformly distributed approximately 1 micron spherical powder, one unit of a mixture prepared according to the proportions disclosed in the present invention comprises 400 particles of barium titanate and 5 particles of pentoxide. Niobium and 1
It can be calculated that the particles will contain cobalt oxide. However, if barium titanate having an average particle size of about 1 micron is mixed with niobium pentoxide and cobalt oxide having a particle size of about 1 micron and these particles are completely spherical and uniformly distributed. Assuming that one unit, one unit of the mixture can be calculated to contain 400 particles of barium titanate, 5000 particles of niobium pentoxide and 1000 particles of cobalt oxide. Therefore, for each barium titanate particle, there will be about 13 niobium pentoxide particles and 3 cobalt oxide particles. Thus, the compositional evolution occurs more effectively during sintering, and the effectiveness of the addition of the ceramic oxide dopant is greater than the effect achieved by mixing a small number of 1 micron particles. Will be promoted.

It is well known in the art that ceramic oxide particles can be reduced in size by grinding techniques to about 1 micron. However, it was not possible to grind the finely divided powder to the nearest 0.1 micron, because grinding technology risks increasing the level of undesirable types of contamination present in the grinding media, and Grinding efficiency is significantly reduced as the particle size of the powder reaches submicron levels.
The method according to the invention provides a means for promoting the uniformity of distribution of the minor component dopants in the ceramic mixture before sintering and for promoting the compositional development during firing. This is achieved by precipitating microparticulate dopants in finely divided form having an average particle size of about 0.1 micron in a controlled manner so as to combine with the main ceramic component particles. "Combine" used here
The term is defined as heteroaggregation of unusual particles produced by the precipitation according to the invention disclosed herein.

The surface charge properties of the particles in the liquid medium are reduced by precipitating the 0.1 micron particles in the slurry of the 1.0 micron particles of the main ceramic component so that the 0.1 micron particles dopant is combined with the 1.0 micron particles. Can be used. These surface charge properties can be quantified based on the zeta potential. This bond maximizes the contact surface area between the two types.

It is well known that the sign and magnitude of the surface charge of dispersed particles can be changed by changing the properties of the medium.
Under certain conditions, it is possible to make chemically identical particles with opposite surface charges into a dispersed state. One of the most effective methods of producing particles of opposite surface charge in an aqueous solution is the conventional method of changing the pH of a medium. See GD Palfit: "Dispersion of Powder in Liquid", Halstead Publishers, 1960, the text of which is incorporated herein by reference.

The zeta potential of a single particle can be measured by analyzing the behavior of particles dispersed in a medium at a particular pH, using an electrophoresis cell where the particle velocity is measured as a function of the applied potential gradient. . Particle velocity is proportional to the zeta potential. Therefore, by performing a series of experiments at different pH values, a zeta potential curve is obtained for geta potential and pH, which shows both the sign and magnitude of the surface charge of the dispersed particles over a range of pH values. Will be shown.

There is an important point in the zeta potential curve at which point the charge on the particle surface is zero. This point is known as the zero charge point and is sometimes referred to as the isoelectric point (IEP). It is believed that the dispersed particles in the IEP tend to aggregate together due to Van der Waals suction. In contrast, particles having the same charge, either positive or negative, tend to be separated from particles of the same charge due to the repulsive force of Coulomb. If two types of particles of opposite charges are dispersed, the first type of particles attracts the second type of particles and does not attract the same type of particles, thus forming a type of heteroaggregation right. This type of heterocoagulation effect is important because it provides a means of bonding the primary ceramic component particles with the dopant particles and prevents homogenous aggregation of the "same" particles. Furthermore, if the dopant particles are precipitated such that the 0.1 micron dopant particles thus combine with the 1.0 micron particles of the primary ceramic component, the primary ceramic component particles will become coated with the dopant particles. Therefore, prior to the sintering step in the manufacture of multilayer ceramic capacitors, the dopant particles wanted to create a uniform, dopant-rich grain boundary phase surrounding the main ceramic component core particles during sintering of the composite. Exactly in place. This maximizes the effectiveness of the dopant as a grain growth inhibitor and enhances the electrical properties of the finished dielectric ceramic capacitor.

Thus, 0.1 micron dopant particles are oppositely charged to 1.0 micron primary ceramic component particles
It is preferred to work in the pH range.

For example, if the main component is barium titanate and the dopant is niobium pentoxide, the isoelectric point of the niobium pentoxide precipitated in the method of the present invention is at pH 3.1 and the isoelectric point of barium titanate is A dot is at pH 9.0. At pH values below 3.1, the niobium pentoxide particles are positively charged, and at pH values above 3.1, the niobium pentoxide particles are negatively charged. At pH values above 9.0, barium titanate is negatively charged, and at pH values above 9.0, the barium titanate particles are positively charged. Therefore,
In the pH range between 3.1 and 9.0, the niobium pentoxide particles will be negatively charged and the barium titanate particles will be positively charged. This condition favors the coupling of two different charge types with each other, while at the same time this condition also generates the same charge type that repels each other, and thus can generate irregular particle sizes. It avoids agglomeration.

Suitable pH conditions will be those in which the species are oppositely charged and the magnitude of the difference between the zeta potential of the major component particles and the dopant particles is as large as possible. This means
It will produce the greatest attraction between the two different types, and at the same time impart a highly desirable state of dispersion of the dopant particles throughout the main component particles, producing the greatest rebound of the same type. For example, in the case of barium titanate and niobium pentoxide, the preferred conditions occur at pH 7, where the barium titanate has a zeta potential of +30 millivolts and the niobium pentoxide has a zeta potential of -45 millivolts.

The advantage of precipitating niobium pentoxide particles using suitable pH conditions so that 0.1 micron niobium pentoxide particles bind to 1.0 micron barium titanate particles and do not bind to each other is this. The purpose is to position the niobium pentoxide particles exactly where it is desired to create a uniform niobium pentoxide-rich particle boundary phase surrounding the barium titanate core particles. This location of niobium pentoxide allows for controlled grain growth during sintering of the ceramic and thus enhances the electrical properties of the dielectric ceramic capacitor. At the sintering temperatures used to produce MLC's containing barium titanate and niobium pentoxide, ie, about 1300 ° C., niobium pentoxide diffuses very slowly. Thus, if the niobium pentoxide is not evenly distributed around the barium titanate particles dispersed during the mixing and then sintering steps, this slow diffusion rate will result in the inability of the niobium pentoxide to develop in the developing microstructure. It will lead to a uniform distribution and will cause irregular grain growth and hence poor dielectric properties. When 1.0 micro niobium pentoxide particles and 1.0 micro barium titanate particles are mixed in a conventional manner by dry or wet components in a mill jar, or niobium pentoxide, barium titanate or pentoxide If the uniform condensation of niobium precipitates under favorable conditions, a non-uniform distribution can occur.

Niobium pentoxide and cobalt oxalate are precipitated in a suspension of barium titanate. For purposes of a particular embodiment of the present invention, cobalt oxalate is precipitated such that cobalt oxalate binds to barium titanate. Note that there is no need. This is true because the cobalt oxide formed from cobalt oxalate during sintering complements the unbalanced charge created by adding niobium pentoxide to barium titanate. This is because they are present as an additive and are not present as a particle growth inhibitor. Cobalt oxide diffuses very quickly at the sintering temperatures used for MLC's, and therefore its effectiveness is not necessarily reduced by being present as a 0.1 micron powder, as described in the examples.

The method described in the present invention has the advantage of producing 0.1 micron units of oxidized ceramic particles without the problems associated with current grinding technology.

A second advantage of the present invention is that it has improved electrical properties,
By the method of the conventional mixing technique, there is the production of ceramic dielectric compositions having high dielectric constant, low loss factor and high insulation resistance capacitance products. The high dielectric constant achieved by the method of the present invention, even if the capacitor manufacturer is given a constant number of effective insulating layers and the thickness of each insulating layer,
It has the significant advantage of being able to produce multilayer ceramic capacitors of higher capacitance values for a given chip size, or of the same capacitance value at reduced chip sizes. The benefit is thus reduced costs and / or miniaturization.

It is an object of the present invention to provide a mixture of one or more minor ceramic oxide component particles and primary ceramic oxide component particles, wherein at least one particle of the minor ceramic oxide component binds to the primary ceramic component particles. It is in providing.

Another object of the present invention is to provide a dielectric constant between about 4900 and 5400 at 25 ° C, a loss factor of less than about 2.0%, and a dielectric constant of 25 ° C.
In producing a ceramic composition having a stable temperature coefficient which does not change by more than about ± 15% from the reference value in the above.

Another object of the present invention is to use expensive metal internal electrodes and have a dielectric constant between about 4900 and 5400 at 25 ° C., about 2.0%
A loss factor of less than 7000 ohm-Farad at 25 ° C and an insulation resistance capacitance product of 3,000 ohm-Farad at 125 ° C and a stable dielectric constant that does not change more than about ± 15% from the reference value at 25 ° C It consists in producing a ceramic composition suitable for producing a multilayer ceramic capacitor having a temperature coefficient (TC) characteristic.

SUMMARY OF THE INVENTION The first stated object is achieved by the present invention which provides a method for producing a ceramic oxide mixture comprising a main ceramic oxide component and one or more minor component dopants. In this method, at least one of the trace ceramic oxide dopants must be precipitated, and the other dopants should be precipitated.
The precipitated dopant particles are adjusted to be oppositely charged and bound to the particles of the main ceramic oxide component.

Other stated objectives include high dielectric constant, low loss factor, and stable
According to the present invention, there is provided a method for producing a ceramic composition having TC properties and comprising a main component, preferably comprising high barium titanate and a minor component dopant, preferably comprising niobium pentoxide and cobalt oxide. In the method, niobium pentoxide must be precipitated to provide the small particles of the present invention, and cobalt oxide dopant must be precipitated to provide the small particles of the present invention. Is good. The dielectric ceramic composition selected for the method according to the invention comprises:
The major components, preferably barium titanate, comprising from about 98.5 to about 98.8% by weight, and minor component dopants, preferably about
1.0 to about 1.1% and about 0.2 to about 0.3% by weight of niobium pentoxide and cobalt oxide.

The method described in the present invention provides a method for producing a dielectric ceramic having dopant particles uniformly dispersed therein, wherein the method comprises dispersing the major component particles in a liquid medium and removing the dopant precursor. Precipitating the dopant particles from the containing liquid medium, decomposing the dopant particles throughout the main component particles such that the dopant particles are associated with the main component particles, removing the liquid medium, and then sintering.

In a more preferred embodiment, the method described in the present invention provides a method for producing a dielectric ceramic having uniformly dispersed dopant particles therein, the method comprising the steps of: Is dispersed in a liquid medium, and in the precipitation of the dopant particles having a particle size smaller than the particle size of the main component particles from the liquid medium containing the precursor of the dopant particles, the pH of the main component particles and the dopant particles is controlled by controlling the pH. The dopant particles are combined with the main component particles while suppressing the coupling between the same particles by making them have opposite charges and increasing the Zeta potential difference therebetween, removing the liquid medium, and then sintering. It consists of doing.

The present invention also provides a dielectric ceramic, wherein the dielectric ceramic is combined with the primary component particles such that the dopant particles have a smaller size than the primary component particles and cover the primary component particles; By controlling the pH of the particles and the dopant particles to make them have opposite charges and increasing the zeta potential difference between them, the bonding of the same particles is very small, and the main component dielectric ceramic particles and the whole thereof Of sintered dopant particles dispersed and precipitated over the entire surface.

The present invention also provides a multilayer ceramic capacitor comprising a plurality of dielectric ceramic layers, the dielectric ceramic comprising cobalt oxide particles combined with precipitated niobium pentoxide particles and barium titanate major component particles. Consisting of punt particles, the main component particles are larger than the dopant particles, and the dopant particles are a fixed percentage of the main component particles and cover the main component particles, and the sintered dielectric ceramic has a dielectric constant between 4900 and 5400. rate,
Loss factor of 2.0% or less, insulation resistance capacitance product of more than 7000 ohm-Farad at 25 ° C and more than 3000 ohm-Farad at 125 ° C, and dielectric constant from values at 25 ° C over a temperature range of -55 ° C to 125 ° C It comprises a plurality of dielectric ceramic layers having a temperature stable temperature coefficient of less than ± 15% and a plurality of electrodes between the dielectric layers.

It will be understood by those skilled in the art that the term dopant precursor as used in the present invention refers to the type of dopant or dopant ion present in the liquid medium prior to the precipitation step.

As described below, the method of making the ceramic dielectric composition of the present invention results in substantial technical advances and has several advantages that save cost while increasing the desired physical and electrical properties. .

The present invention provides a novel method of producing a dielectric composition having a dielectric constant between 4900 and 5400, a loss factor of less than 2.0%, and stable TC properties. The method of the present invention comprises:
Substantially different from the methods disclosed in the prior art, in the prior art, conventional mixing techniques are used and the desired dielectric properties, such as a high dielectric constant, are used to obtain materials with stable TC properties. To be sacrificed. Conventional methods use the latest inventive method to achieve higher dielectric constants, thereby producing materials with dielectric constants of about 3000 to about 4700 or less, thus limiting the same physical size. It is possible to produce multilayer ceramic capacitors with significantly lower capacitance values below, or the smallest possible physical size under the same capacitance limits. Higher dielectric constants also result from the use of significantly less ceramic and electrode materials, and thus manufacturing costs can be significantly reduced by using the methods described in the latest invention.

The method described in the present invention employs a major component powder having an average particle size of about 1.0 micron and precipitating one or two finely divided dopants having an average particle size of about 0.1 micron. Provides a means to increase the uniformity of dopant distribution in the ceramic mixture before firing, the method being controlled in such a way that the dopant particles are combined with the main ceramic component particles. Compositional development during sintering occurs more efficiently due to the increased homogeneity of the mixture, and the effectiveness of dopant addition is greater than that achieved by mixing 1.0 micron dopant particles. Enhanced.

The method of the present invention comprises the step of precipitating a dopant from a liquid medium,
Mixing the precipitated dopant with the main component slurry such that the dopant particles are evenly dispersed throughout the main component particles.

In a preferred embodiment, the main component of the ceramic composition is a slurry in a liquid medium, and then the precise amount of the solution containing the dopant precursor is added. Alternatively, the primary component can be a slurry in a solution containing the dopant precursor. The dopant is then precipitated from the solution in finely divided form in a controlled manner such that intimate contact of the dopant with the main component particles is achieved. This method can be used to introduce one or more dopants. The main component is preferably selected from the group of metal oxides forming perovskites.

In a more preferred embodiment, the main component of the ceramic composition is a slurry in a liquid medium, and then the precise amount of the solution containing the dopant precursor is added. Alternatively, the major component can be a slurry in a solution containing the dopant precursor. The dopant is then precipitated from the solution in finely divided form, while the charge of the primary ceramic component particles and the dopant particles is controlled such that intimate contact between the primary component particles and the dopant is achieved. The main component is preferably selected from the group of metal oxides forming perovskites.

In a particularly preferred embodiment, the main component is barium titanate (BaTiO ₃ ), which is slurry in water,
The two dopants are niobium pentoxide and cobalt oxide. In this embodiment, niobium pentoxide is precipitated in the presence of barium titanate, while cobalt oxide may be introduced into the slurry either in powder form or as a precipitate. The precursor solution of niobium pentoxide is a solution of niobium pentachloride in ethanol, which is precipitated with concentrated ammonium hydroxide.

Following filtration and washing, the intimate mixture of components is mixed with a suitable binder and cast into sheets by standard methods to form a multilayer capacitor structure with internal electrodes such as 70% palladium / 30% silver, Then about 1280 ° C to about 1350
C. for about 2 hours. Conventional ceramic binders, such as simply adding a vehicle, to be compatible with the other materials used and to disperse the ceramic particles and to hold them together when the solvent is removed are also contemplated by the present invention. May be used. A suitable binder composition is GY Onoda
Jr. et al., "Ceramic Method Before Firing," described in Chapter 18 of John Belay and Sands Publishing (1978). Corn syrup and polyvinyl alcohol are examples of suitable binder compositions.

The fired dielectric composition of the present invention has a high dielectric constant between about 4900 and about 5400, a low loss factor of less than 2%, and a temperature of more than 7000 ohm-Farad at 25 ° C, 50 VDC / mil, 125 ° C, 50 VDC / mil. In 3
000 ohm-Farad insulation resistance product and dielectric constant 25 ° C
It is processed into a multilayer ceramic capacitor with stable TC characteristics that does not change over ± 15% of the reference value.

In another particularly preferred embodiment, high purity barium titanate (99.9-99.95% purity) of fine particle size (0.8-1.3 microns) is stirred into deionized water. 0.8 ~
Add 1.3 micron fine particles of cobalt oxide and then continuously stir the mixture for 30 minutes to 33 hours to ensure that the two reagents are well mixed. An ethanolic solution of niobium pentachloride is added to the barium titanate / cobalt oxide slurry. The ratio of barium titanate, cobalt oxide and niobium pentachloride is such that barium titanate: niobium pentoxide: cobalt oxide in the obtained ceramic composition
9871: 107: 22. The resulting slurry is stirred for 10-60 minutes and concentrated ammonium hydroxide is added to precipitate the aqueous niobium pentoxide. The composite slurry is filtered, then washed with deionized water, and the washing is continued until silver chloride precipitation is completely eliminated when tested with a silver nitrate / nitric acid solution. The cleaning mixture of ceramic oxide is then dried at 110 ° C. in a laboratory open. Next, the uniformly blended ceramic composition was uniformly mixed with dioctyl phthalate “NUOSTABE
V-1444 ^{TM "1} / ethanol, toluene and" BUTVAR B-
Load the ball mill with the binder solution prepared by uniformly mixing the ^76TM " ² / vinyl resin. The ratio of ceramic composition to binder is 400: 218.

1: "NUOSTABE V-1444 ^TM" is an organic solvent dispersion agent with no alkali ions that can be obtained from the New jar Sea province of Nuodekkusu company.

2: "BUTVAR B-76 ^™ " is a binder available from Monsanto and comprising a mixture of polyvinyl butyrate, polyvinyl alcohol and vinyl acetate.

The resulting slurry is mixed for 5-20 hours, removed and then filtered through a 44 micron sieve. This slurry is
It has a viscosity of about 1500 centipoise and is then degassed and then cast by standard techniques to about 1.5 mil thick tape. This tape is converted to a multilayer ceramic capacitor with 70% palladium and 30% silver electrodes by conventional methods well known in the industry. Preheat the capacitor at 260 ° C for 48 hours, place on a zircon setter, then 1280 ° C
Sinter at 11340 ° C. for 1-3 hours. The sintered capacitor has ten effective dielectric layers having a dielectric thickness of about 1.1 to about 1.2 mil. Terminal electrodes of DuPont ^™ silver paint No. 4822, a mixture of silver and glass frit in a binder, are applied to the opposite ends of the multilayer capacitors and the capacitors are fired at 815 ° C. in a tunnel furnace. The resulting multilayer capacitor has a dielectric constant of about 5400 and a loss factor of about 1.57% measured at 1 KHz at 1 VRMS, and a dielectric constant of about ± 9.9% or more between -55 ° C and + 125 ° C at 25 ° C. It has TC characteristics that do not change from the dielectric constant value.

(Examples) The present invention will be further described by the following examples, but the present invention is not intended to be limited thereto. The values shown in the following examples may be changed based on factors known in the art.

Example 1 500 g of high purity barium titanate was stirred in 500 g of deionized water. 1.122 g of fine particle size (1.0 micron) cobalt oxide (CoO) was added, followed by continuous stirring for 3 hours to ensure thorough mixing of the two reagents. 188.9 g of a 28.74 g per liter solution of niobium pentachloride in ethanol was added to the barium titanate / cobalt oxide slurry via burette. Stir the resulting slurry for 30 minutes, then 20 ml
Of concentrated ammonium hydroxide with a burette to pH 7.0
Then, hydrous niobium pentoxide was precipitated. The composite slurry was filtered, washed with deionized water, and washed completely free of silver chloride precipitation when tested with a silver nitrate / nitric acid solution.
The ceramic oxide wash mixture was then dried in a laboratory oven at 110 ° C.

The uniformly blended ceramic composition was then mixed with 186 g of dioctyl phthalate, 90 g of NUOSTABE V-1444 ^™ , 597 ml.
Of ethanol and 270 ml of toluene, and 273 g of BUTVAR
B-76 ^TM vinyl resin was loaded into a ball mill with 218 g of the binder solution obtained by mixing homogeneously.

The resulting slurry was mixed for 16 hours, removed, and then
Filtered through a 44 micron sieve. The filtered slurry is
It has a viscosity of about 1500 centipoise and is then degassed and then cast by standard techniques to about 1.5 mil thick tape. This tape is converted into a multilayer ceramic capacitor with 70% palladium / 30% silver electrodes by conventional methods well known in the industry. The capacitor was preheated at 260 ° C. for 48 hours, placed on a zircon niacet, and then
Sinter at 80 ° C to 1340 ° C for 1 to 3 hours. The sintered capacitor has ten effective dielectric layers having a dielectric thickness of about 1.1 to about 1.2 mil. Terminal electrodes of DuPont ^™ silver paint No. 4822, a mixture of silver and glass frit in a binder, are applied to the opposite ends of the multilayer capacitors and the capacitors are fired at 815 ° C. in a tunnel furnace. The obtained multilayer capacitor is measured at a measurement frequency of 1 KHz by a model ESI 2110 capacitance bridge, at an interval of about 20 ° C. from −55 ° C. to + 12 ° C.
5 ° C capacitance (C), loss factor (DF), and 25
The capacitance change in capacitance versus temperature at ° C. was measured. Insulation resistance was measured at 25 ° C. and 125 ° C. after charging the capacitors at 50 VDC for 2 minutes using a Megohmmeter M16 ^™ manufactured by London, Ontario.

Examples 2-6 Table 1 summarizes the weight percent addition of niobium pentoxide and cobalt oxide to barium titanate for a series of compositions prepared by the method described in Example 1 using conventional mixing of 1 micron ceramic powder. A series of compositions (A to
H). In addition, the surface area in m ² / g, the average particle size (d50) measured using Micromeritics Cedigraph ^™ is shown for both series of compositions and is prepared by the method according to the invention. 1 shows a clear difference in the physical properties of the composition prepared and the composition prepared by conventional mixing of 1 micron ceramic oxide particles.

The dielectric properties of these compositions and of the composition described in Example 1 are shown in Table 2 together with the dielectric properties obtained with a similar series of compositions (AH). Was prepared by conventional mixing of 1 micron ceramic oxide particles. The results clearly demonstrate the excellent performance of the composition prepared by the method according to the invention. Dielectric constant is 4900 ~ 54
00, higher, with a loss factor of about 1.6%,
Lower, the RC product is higher at about 7500 ohm-Farad.

Examples 7 to 8 In Example 7, 500 g of high-purity barium titanate was used.
Of cobalt oxide (CoO) per liter of deionized water
The solution was stirred into 500 ml of a cobalt acetate solution containing an equivalent of 2.1674 g.
Stirring is continued for 30 minutes, then 2 per 500 ml of deionized water.
Oxalic acid solution 3 containing 30.3 g of water oxalic acid [(CO OH) ₂ 2H ₂ O]
0 ml was added to precipitate the finely divided form of cobalt oxalate. 28.0 niobium pentoxide per liter of deionized water
186.8 ml of an ethanol solution of niobium pentachloride containing 8 g equivalent
Was added to the barium titanate / cobalt oxalate suspension and the mixture was stirred for 30 minutes. Concentrated ammonium hydroxide 20ml
Was added dropwise to adjust the pH to 7.0, whereby aqueous niobium pentoxide was precipitated. The resulting composite slurry was filtered and washed with deionized water, and finally the wash water was confirmed to be free of chloride ions. The wash mixture was then dried in an oven at 110 ° C.

A multilayer ceramic capacitor was prepared as described in Example 1. The results of the electrical tests are shown in Table 3 together with the capacitors obtained for Example 8, where the capacitors for Example 8 contained only 2.
The preparation was carried out in the same manner as in Example 7 except that an ethanol solution of 179.25 g of niobium pentachloride containing an equivalent of 28.08 g of niobium pentoxide per liter of water was used.

Electrical results again showed that a dielectric constant of 5,000 or more could be obtained by dopant precipitation. In addition, the loss factor is less than 2% and the temperature stability of the dielectric constant has been proven over the temperature range of 55 ° C to 125 ° C since the dielectric constant is more than ± 15% of its reference value at 25 ° C. .

Example 9 500 g of high purity BaCO ₃ and 202 g of high purity TiO ₂ were thoroughly mixed and then dispersed in about 175 ml of deionized water until a uniform dispersion slurry was obtained. 4% by weight of "DARVAN C ^TM " ³
Until then, it may be added to the slurry to help disperse the powder particles. The slurry was then removed to a drying pan and dried in an oven at about 150 ° C. with forced air circulation.

3: “DARVAN C ^™ ” is an alkali ion-free dispersant solution consisting of a mixture of polyelectrolyte, ammonia and sulfur, available from WP Vanderbilt, Connecticut. The dried cake was then ground, placed in a ceramic sheath, and sintered at a temperature of about 1900 ° F to about 2200 ° F for about 1 to 5 hours. X-ray diffraction and BaO alkaline test on the sample
Complete reaction and the formation of high purity BaTiO ₃ were shown. The sintered powder was then ground with a ZrO ₂ medium in a vibration energy mill until the average particle size was reduced to 1.0 microns. Alternatives to reducing to 1.0 micron size would include ball mill or jet mill.

Next, 500 g of high-purity barium titanate prepared by the method described above was mixed with cobalt acetate and niobium pentoxide, and treated in the same manner as described in Example 7 to obtain a composite mixture of oxides.

A multilayer ceramic capacitor was prepared as described in Example 1. The electrical results are shown in Table 4 and compare 500 g of the same barium titanate with 1.0 micron of cobalt oxide and niobium pentoxide in the same proportions by conventional mixing. Again, the results show a significant improvement in the dielectric constant as a result of controlling the dopant component and precipitating in finely divided form.

Examples 10-11 In Example 10, 500 ml of a cobalt acetate solution containing 500 g of high-purity barium titanate and niobium pentoxide having a fine particle size (1.0 micron) of 2.1674 g of cobalt oxide (CoO) per liter of deionized water. And then continuously stirred for 3 hours to ensure thorough mixing of the reagents. Deionized water
30 ml of an oxalic acid solution containing 30.3 g of oxalic acid [(COOH) ₂ .2H ₂ O] per 500 ml was added to precipitate cobalt oxide in a finely divided form. Filtering and washing the composite slurry;
Dried in an oven at 110 ° C.

A multilayer ceramic capacitor was prepared from the composite slurry as described in Example 1. Table 5 shows the electrical test results. 500 g of high-purity barium titanate and 5.03331 g of niobium pentoxide having a fine particle size (1.0 μm) of deionized water 5
Cobalt acetate 5 containing 2.0798 g equivalent of cobalt oxide per 00 ml
Example prepared in the same manner as Example 10 except for addition to 00 ml
It is shown with the result obtained for 11.

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Claims (3)

(57) [Claims] 1. A method for dispersing a dielectric ceramic particle of a main component in a liquid medium and precipitating dopant particles having a particle size smaller than the particle size of the main component particle from a liquid medium containing a precursor of the dopant particle. By controlling the pH of the particles and the dopant particles, they are made to have opposite charges, and the zeta potential difference between them is increased so as to suppress the bonding between the same particles and to separate the dopant particles from the main component particles. A method for producing a dielectric ceramic having uniformly dispersed dopant particles, comprising bonding, removing a liquid medium, and then sintering. 2. The method according to claim 1, wherein the dopant particles have a particle size smaller than that of the main component particles and bind to the main component particles so as to cover the main component particles.
The main component dielectric ceramic particles and the dopants dispersed and precipitated throughout the main component, by making them have opposite charges and by increasing the zeta potential difference between them, the bonding between the same particles is very small. A dielectric ceramic composition comprising a sintered body of particles, wherein the dielectric ceramic composition is produced by the method according to claim 1. 3. A multilayer ceramic capacitor comprising a plurality of dielectric ceramic layers and a plurality of electrodes between dielectric layers, wherein the dielectric ceramic comprises precipitated niobium pentoxide particles and cobalt oxide dopant particles combined with barium titanate main component particles. The main component particles are larger in size than the dopant particles, the dopant particles are at a constant ratio to the main component particles and cover the main component particles, and the sintered dielectric ceramic is between 4900 and 5400 Dielectric constant, loss factor less than 2.0%, insulation resistance capacitance product of more than 7000 ohm-Farad at 25 ° C and more than 3000 ohm-Farad at 125 ° C, and dielectric constant of -55 ° C to 125
A multilayer ceramic capacitor having a temperature stable temperature coefficient that is less than ± 15% from a value at 25 ° C over a temperature range of 25 ° C.