JP3042899B2 - Mixture of fine-grained barium titanate and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature sintered dielectric ceramic compound comprising fine barium titanate particles and a trace amount of cadmium silicate flux. Here, the ceramic has a high dielectric constant and a smooth dielectric constant temperature coefficient, making it particularly suitable for use as a capacitor of high quality multilayer ceramics.

[0002]

BACKGROUND OF THE INVENTION Multi-layer ceramic capacitors having a gentle X7R dielectric constant temperature coefficient represent a significant portion of the large ceramic capacitor market. There has been little work to develop better X7R ceramics with higher dielectric constants (K). Whatever is done to increase the permittivity, reducing the graduality of the temperature coefficient of the permittivity as well,
This is a well-known conflicting law. However,
Compared to large granular ceramics of the same composition (greater than 1 micron), ceramic capacitors composed of very fine particles, especially particles having a diameter of about 0.8 micron, have a higher dielectric constant (K). At the same time, the discovery of the tendency to have both a slower condenser temperature coefficient (TCC) has provided a fairly significant advance in breaking that law.

In multilayer capacitors, the fine grain structure has a higher capacitance per unit volume, ie, lower cost per microfarad, in proportion to the smaller space between adjacent buried electrode layers. . Microparticulates are made by sintering very small (eg, 0.2 micron) particles having high surface energy and advantageously sinter at low temperatures. However, for such fines, the same old conflicting rules apply. For example, hot pressed and sintered microparticulates of pure barium titanate are about 370
It has a K of 0 but is completely different from the X7R standard. To meet this X7R standard, K should be between -55 and +12
It varies by less than 15% over the usable temperature range of 5 ° C. compared to K at room temperature. However, at 1130 ° C
When sintered with 1% by weight sintering flux (CdBi ₂ Nb ₂ O ₉ ), the ceramic is densified and easily meets the X7R standard, but has a K at room temperature of around 1500. Alternatively, 15% by weight of bismuth titanate flux (Bi ₄ Ti ₃ O ₁₂ ) can be added and sintered at 1110 ° C. to achieve sufficient densification, resulting in 500 K at room temperature. And fits X7R. 1. consisting of Nb _2.5 CoO with pure and fine barium titanate
With 5% by weight of the additive, an X7R ceramic with a K of 3000 could be made, but in order to make
A sintering temperature of 0 ° C. was required. These results indicate that Hennin
g's title, "Temperature-Stable Dielectric"
s Basedon Chemically Inhomogeneous BaTiO ₃ ”(Journ
al of the American CeramicsSociety, Vol. 67, No. 4,
1984, pages 249-254).

[0004] Another well-known conflicting law demonstrated by these examples is that the addition of sintering flux to the ceramic starting mixture reduces the sintering temperature required to achieve densification, And thereby reducing the amount of noble metal required to prevent the electrodes buried during sintering from melting. The addition of flux also makes the temperature coefficient more gentle. However, such addition of flux significantly reduces the dielectric constant of the sintered ceramic. This rule applies without exception to all dielectric ceramic materials, regardless of the size of the ceramic particles.

The third contradictory law is that the addition of a sintering aid or flux in which flux is melted by liquid phase sintering during sintering involves a process in which ceramic melting and recrystallization occur simultaneously, and It is to provide a medium for promoting growth. In fact, this law states that
Just a few years ago, large particles were the goal of high dielectric constant ceramics, which was not at all conflicting. For example, U.S. Pat. No. 4,898,844 (February 6, 1990), U.S. Pat. No. 4,266,265 (May 5, 1981), U.S. Pat. No. 4,120,677 (78 October 17),
U.S. Pat. No. 4,066,426 (Jan. 3, 78) and U.S. Pat. No. 3,885,941 (May 27, 75)
Day). In U.S. Pat. No. 3,231,799 (Jan. 25, 66), a separation compound of niobium and tantalum in a starting material producing a high K ceramic having a gradual temperature coefficient (TCC) of the capacitor. Use is disclosed. These and other elements are considered grain growth inhibitors and are described, for example, in the aforementioned US Patent No. 4,120,6.
No. 77 (October 17, 78) and U.S. Pat.
No. 8,844 (February 6, 1990). Patents and patent applications having the date of grant of the patent in parentheses above are assigned to the assignee of the present invention.

[0006] Mechanical pulverization of ceramic powder particles to reduce particle size is not effective when less than about 1 micron, and the particles are uneven and non-spherical in shape. More recently, methods for making finer powders have become known.
See, for example, U.S. Pat. No. 4,654,075 (March 31, 1987). The microparticles thus "manufactured" are advantageously spherical, have a relatively narrow particle size distribution, and have an average particle size distribution above 0.1 micron during the manufacturing process. Such particles have a very high energy density and will consequently sinter at a lower temperature than a collection of large particles of the same composition. They are also susceptible to sintering with other compounds in the ceramic starting material.

[0007]

The object of the present invention is to provide a.
An object of the present invention is to provide a ceramic powder mixture for use in producing a sintered dielectric ceramic having particles of an average particle size of less than 9 microns and having a high dielectric constant and a temperature coefficient of gradual dielectric constant of X7R. .

[0008]

SUMMARY OF THE INVENTION A mixture of ceramic powders consists of agglomerates containing a group of three types of powder particles. 95-98% by weight of very fine barium titanate particles, 1.5-3.5% by weight of cadmium silicate,
And 0.5-1.5% by weight of a particle growth inhibitor. The mixture of particles in these agglomerates is lightly calcined and co-reacted on the outer surface with their adjacent surfaces,
Combine with each other. The very fine barium titanate particles in the agglomerate are essentially spherical and 0.2-0.7
It has an average diameter of microns. The average size of the agglomerates can be reduced, for example by pulverization after the firing step.
It can be smaller than 5 microns.

The present invention relates to a cadmium silicate sintering aid combined with a fine barium titanate powder having an average particle size of less than about 0.7 microns and a small amount of a reactive inhibitor. During this period, it is possible to produce an X7R type capacitor having a high dielectric constant, exhibiting unexpected synergistic action. In particular, cadmium silicate, which has a characteristic melting point above the sintering temperature, takes up a small amount of barium from the titanate and melts to form a eutectic flux that acts as a medium in which liquid phase sintering can occur. Furthermore, silicate fluxes, which are known to be less reactive than borate fluxes, nevertheless have an additional advantage. That is, the silicate flux, unlike the borate flux, clearly forms droplets that wet the barium titanate in the larger interstices of the grain boundaries, resulting in a substantially higher dielectric constant than when using borate. Is very small barium titanate ceramic.

[0010] The powder of the present invention is further characterized and characterized by the fact that there is essentially no variation in the Curie temperature of barium titanate during the sintering process in capacitors made from this powder. Therefore, the reaction of barium titanate with reactive inhibitor elements, such as niobium, and cations in the flux, such as cadmium, zinc, bismuth, etc., is less likely to occur. No matter how small the reaction between the barium titanate and the additive that occurs, there is no difference only on the outer surface. This is probably due to the limited solubility of this combination of additives in either the surface or the flux of the barium titanate particles.
Such cations that have reacted with barium titanate during sintering typically result in Curie temperature fluctuations, but with the sintered powders of the present invention, essentially no usable temperature at the usable temperature at which the dielectric constant is maximized. Does not fluctuate.

Among the cadmium silicates used as powders according to the invention, the composition 3CdO.SiO ₂ has the highest composition of capacitors having the highest dielectric constant and the smoothest TCC over the temperature range of -55 to 125 ° C. produce.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A number of related tests were conducted on dielectric ceramic (10) and ceramic (1) as shown in FIG.
A disk-shaped sample capacitor having conductive electrodes on the large surface facing 0) was implemented in each case. According to the procedure used in each condition, a completed barium titanate disk or chip of about 35 mils (1.4 mm) was formed, followed by the formation of electrodes on two opposite large surfaces of the chip. I do. In particular, the slip suspension is composed of essentially pure and high amounts of barium titanate powder, about 1% by weight of niobium oxide powder (Nb ₂ O ₅ ), and various amounts of powdered glass sintered flux. It was made by mixing the powder in an organic vehicle.

The starting powder containing pentavalent niobium had an average particle size of about 1 micron. The starting cadmium silicate powder is cadmium oxide (CdO) and silica (SiO ₂ )
Was made by ball milling using isopropyl alcohol wetting agent and high density yttria stabilized zirconia balls in polyethylene bottles. The ground powder was then dried and calcined at about 950 ° C. The resulting fired product is ground again,
A mixture of calcined powders having an average particle size of less than 1 micron was obtained.

Mixing of the starting powder in the organic vehicle was accomplished by grinding in a 200 cc polyethylene container for 12 hours using barium titanate balls.

The resulting slip was poured after drying using a standard doctor blade technique on a glass plate. The castings were each cut into small squares of approximately 1 x 1 cm. The square was then sintered, and after cooling, a silver electrode paste was applied to the opposing surfaces of the sintered chip heated to substantially 800 ° C. and solidified to form the electrode.

In the first case, ie in Example 1 (a) of Tables 1 and 2, the barium titanate used was:
It has an average particle size of 0 microns (micrometers) and the flux is as described in the aforementioned US Pat. No. 4,266,265.
Cadmium silicate (5CdO.SiO
₂ ). It has been found to be the only effective sintering aid in barium lead titanate ceramics. This is unlike other sintering aids that melt at temperatures below the sintering temperature and initiate "liquid phase sintering"
This results in a melting point above the sintering temperature of 0 ° C. This flux melts and begins liquid phase sintering only after using a small amount of barium from the ceramic instead of a small amount of cadmium in the flux that lowers the melting point. This substitution is made first by solid state diffusion.

When this flux is baked at 1100 ° C., 2% by weight is insufficient to bring about densification by sintering. As shown in Example 1 (b) of Table 1, a green chip of the same composition was fired at 1120 ° C. and the body would not yet be sintered or densified. In Example 2, the total amount of cadmium silicate was increased to 3% by weight and baked at 1100 ° C. successfully. The temperature coefficient (TCC) of the capacitor was outside the ± 15% X7R limit over the range of -55 to + 125 ° C, but very high dielectric constant (K) at room temperature was obtained. However, when cadmium silicate was added at 4%, K was considerably lowered, and at the same time, TCC was deteriorated. Although a decrease in K was expected, the TCC with substantially less smoothness when using increased amounts of flux is in direct contrast to what the prior art taught.

In the next four examples, 4 (a) to 6, the same 1 micron barium titanate used in Examples 1 (a) to 3 was used, but was used. The flux was cadmium boride. Boride fluxes are known to have good large flux effectiveness compared to silicate fluxes of the same relative weight.

Since spherical barium titanate particles are used, the relationship between the surface area (SA) of the powder and the diameter (D) of the powder particles in microns is the theoretical SA (gm / gm / barium titanate). m ³ ) = 1 / D very close,
And a powder of 1 micron particles has a surface area of 1 m ² / g.

In Examples 1 (a) to 6 the barium titanate powder is produced by a method utilizing hot water, and the powder particles are substantially spherical. However, an average diameter of 1 micron is typical of the finest titanium particles with irregular, elongated shapes created by calcination, crushing and large-scale milling, for example by milling or jet milling. It is the diameter of barium acid. Spherical particle powder will sinter without flux at lower temperatures than regular crushed particle powder of the same size. However, all the examples presented here use the spherical particle powder produced, and therefore the use of such produced spherical particle powder with an average size of 1 micron This is considered more meaningful control. That is, in view of the control, a ceramic was produced using the preferred finer spherical particles detailed below.

Referring to Example 4 (a) in Tables 1 and 2, the 1.5% (CdO.2ZnO.B ₂ O ₃ ) flux is sufficient to sinter barium titanate at 1100 ° C. However, as shown in Example 4 (b),
The composition is sintered at 1120 ° C. and has a high K of 2650.
Yields a useful X7R dielectric ceramic having This one
For micron BaTiO ₃ powder, 3% cadmium silicate gives an equivalent weight of 5.4 mg glass forming oxide (SiO ₂ ) per square meter of BaTiO ₃ powder surface, while 1.5% cadmium borate , BaTiO
Per square meter of ₃ powder surface was given just boride oxide 4.3mg of (B ₂ O _3). Thus, the molar amount of glass forming silicon per square meter of the surface of the barium titanate powder is 1.5 times the molar amount of boron per square meter of boron.
It is twice.

Furthermore, increasing the amount of cadmium borate has almost no effect on the dielectric properties, as shown by the data in Examples 5 and 6.

Now, referring to Tables 3 and 4, similar tests were performed in the same manner, except that barium titanate powder having an average particle diameter of 0.5 micron was used. Example 1 (a), which used 1 micron barium titanate with cadmium silicate, was not possible, whereas Example 7 resulted in a 2% cadmium silicate flux sintering at 1100 ° C. Excellent X7R materials with high dielectric constants have been produced. Example 8
In, slightly more flux slightly reduces the dielectric properties. For this finer (0.5 micron) barium titanate powder, the use of a cadmium borate flux was compared to the cadmium silicate flux in Examples 7 and 8 with 0.5 micron barium titanate. Examples 9 and 10 are much less effective.

In the ninth and tenth embodiments, the finer.
Cadmium borate with 5 micron barium titanate is also less effective than in Examples 4 (b), 5 and 6 using 1.0 micron barium titanate. Surprisingly, however, the exact opposite is true with the fine 0.5 micron barium titanate of Examples 7 and 8 compared to the cadmium silicate with 1.0 micron barium titanate of Examples 2 and 3. Applies to cadmium silicate combinations.

In Examples 11, 12, 13 and 14, zinc silicate was used as the flux. Example 1
The degree of densification achieved at 1100 ° C. in 1 and 12 was inferior to that using cadmium containing flux used in Examples 7-10. Therefore, the combustion temperature was 1125 in Examples 13 and 14.
C. and abandoned some of the advantages obtained when using lower sintering temperatures. For example, a small amount of palladium required for a palladium-silver alloy embedded electrode in a monolithic capacitor was abandoned. Although the dielectric density and permittivity are slightly improved, the TCC is well outside the standard range of X7R.

However, for future applications where the use of cadmium will be banned, these compositions with zinc silicate as flux may be useful, especially if they contain less than 1.5% zinc silicate. It would be particularly useful if sintered at a temperature close to 1200 ° C. that is,
The X7R portion can be produced at the same time as the desired high density and high dielectric constant. However, using such high firing temperatures for monolithic ceramic capacitors,
It would require the use of expensive electrodes of over 50% palladium. The composition of the powder from 9 to 14 is
It is not included in the scope of the present invention.

The density of pure barium titanate is 6.02
gm / cc and the examples in the table where a cadmium silicate flux was used show that at least up to 94% of theoretical density.

In Examples 15 to 18 whose data are shown in Tables 5 and 6, the cadmium silicate flux was combined with barium titanate powders of various average particle sizes of 0.3 to 1 micron. You. Everything is 110
Sintered at 0 ° C., 3% by weight flux is required for 1 micron barium titanate to sinter,
The rest used 2% by weight of flux. Only when 0.7 micron and 0.4 micron barium titanate was used did the X7R dielectric material result. Maximum BaTiO
_{Both the three} particle powder (Example 15) and the minimum BaTiO ₃ particle powder (Example 18) produced a less smooth TCC ceramic as required by the X7R standard.

All the fine BaTiO ₃ of Example 18
Glass-forming oxide (Si) in cadmium silicate flux
O ₂ ) is sintered, taking into account anyway in the range of 1 mg / m ² , while in Example 15 the cadmium silicate flux was sintered at just 1100 ° C. and 2.5
It appears to be remarkable that it is somehow sufficient to give mg / m ² particle-surface-area coverage.

Referring to similar Examples 19 to 22 in Tables 7 and 8, 2% by weight of cadmium borate is used in place of the cadmium silicate of Examples 16 to 18. In Examples 16 to 18, the glass-forming silicon BaTiO 3 combined with the fine barium titanate powder was used.
The molar amount per surface area of ₃ is essentially the same as the molar amount of boron per surface area in Examples 20 to 22 using the same fine powder of barium titanate.
Cadmium silicate gave a uniformly higher dielectric constant than cadmium borate using fine BaTiO ₃ .

Realized by combining the high melting point cadmium silicate powder described above and in US Pat. No. 4,266,265 with conventional ground 1 micron barium titanate or barium lead titanate. The description of the unique advantages provided is also largely applicable to partially describing the efficacy of barium silicate combined with the finer barium titanate powder disclosed herein. However, why cadmium borate, which melts well below the sintering temperature used herein, achieves excellent results when combined with 1 micron barium titanate, but with smaller particle sizes, It is not described whether the results obtained when combined with barium titanate powder are clearly inferior to cadmium silicate.

This can be considered as follows. That is, it can be explained in part by the fact that the wettability of the borate flux on the surface of the barium titanate particles during sintering is much greater for cadmium silicate. With the use of fine barium titanate powder, where the amount of glass former is very small compared to the large surface area of barium titanate, the skin of the borate flux covers most of the surface of the titanate, As a result, the overall dielectric constant of the ceramic is reduced. Cadmium silicate, on the other hand, spheres in larger pockets at grain boundaries, leaving less direct contact between adjacent particles, and consequently has a higher dielectric constant.

In the latter half of the description, it is further explained that NbO ₅ , Ta ₂
The use of reactive inhibitors such as O ₅ , Bi ₂ O ₃ , TiO ₂ and titanates of Nb, Ta and Bi is also conditioned. Only when such inhibitors are used are the particles kept small during sintering and the surface area of barium titanate kept large. From Curve (30), the Curie temperature is about 125 ° C.,
It can also be noted that this is the same as the starting BaTiO ₃ powder.

By the way, referring to Tables 9 and 10, similar disk test capacitors were made. Additional cadmium silicate flux compositions were prepared according to Examples 23 and 2,
4 and 25 and Example 26. Here, the 5CdO used in Example 26 was used except that the cadmium silicate flux used in all Examples in Tables 9 and 10 had an average particle size of 0.5 microns.
The composition of the 2SiO ₂ flux is the same as that used in Example 7. Therefore, the twenty-sixth embodiment acts as a controller here.

A number of experimental monolithic condensers, group A, were made by the following conventional procedure, but using an unusual composition. Barium titanate powder with an average particle size of 0.5 micron, 2% by weight of 5CdO.
The 2SiO ₂ flux and 1 wt% Nb ₂ O ₅ were mixed in a binder medium of organic vehicle and turpentine. The organic vehicle consisted of a 70/30 weight ratio of xylene and amyl alcohol, respectively. The binder is
Polyvinyl buterol. This mixture or slurry contained 50% by weight of solvent, 9% of binder, small amounts of organic dispersant and plasticizer, the balance being the composition of the starting powder. The slurry was milled for about 6 hours.

A sequential coating of the milled slurry was applied on a glass support, followed by drying of each layer and 7
An electrode paste consisting of 0% silver and 30% palladium was injected and screen printed on the dried layer. Prior to applying the next continuous dielectric layer, the interrupted pattern under the electrode paste was dried. As shown in FIG. 2, the ceramic (20) with the buried electrodes (21) and (22) is cut from the stack and fired at 1100 ° C. for 2.5 hours until fully sintered. Was cut. The distance between adjacent buried electrodes in this example is 0.4 mil (10.2 microns), but in other tests using the same materials and methods, the distance between adjacent electrodes was 0.1 mil. An excellent X7R monolith capacitor of 2 mils (5.1 microns) was made. Silver paste was then applied to one end of the body (20) where the edge of the buried electrode was exposed. The body was baked at 750 ° C. for several minutes to form silver ends.

These capacitors exhibit a dielectric constant (K) of 3460, a dielectric loss tangent (DF) of 2.3, and an unusually gentle TCC as represented by curve (32) in FIG.

Another group of experimental monolithic capacitors, ie, group B, was manufactured by the same conventional process for manufacturing the group A monolithic capacitors described above, but in Example 23. The same composition of the same starting powder as used to make the disk capacitors was used. There were a total of nine active dielectric layers in each of the group of B capacitors, and each active dielectric layer was 9 microns thick. These capacitors exhibit a dielectric constant (K) of 3900 and a gradual TCC as represented by curve (32) in FIG.

However, in the process where a small amount of ceramic powder was used to make the test capacitor described above, the starting powder was simply mixed in an organic vehicle (eg, ground in a ball mill). This mixing step achieved homogenization and, consequently, the making of a slurry or slip that was used to form the dielectric layer of the trial capacitor.

Large-scale production of the capacitors of the present invention requires a large mixture of ceramic powders that has not yet reacted, or at least reacts only on the outer surface. Such large powder mixtures are prone to segregation and non-uniformity in transportation and transport.

Commercially useful amounts of the ceramic powders of the present invention can be prepared to maintain powder homogeneity.

For example, the starting barium titanate, cadmium silicate and particle growth inhibitor powders are first
Surfactants such as DARVAN (RTVanderbi)
ltCompany, Norwalk, Connecticut) in a 1% (volume) deionized water containing surfactant.
Further reduction in particle size is not necessary at this stage. The purpose of mixing is to create a homogeneous mixture of all starting powders.

The homogenized powder mixture is then dried by heating, for example at 300 ° C. The dried powder is then heated to a temperature of 600-800C, and the outer surfaces of the powder particles are fired. This firing is performed to make a cake that can be crushed to make a fired powder or a fired powder consisting essentially of agglomerates of a mixture of homogeneous powders. These aggregates
All are compositions consisting essentially of the same barium titanate, cadmium silicate and inhibitor as the composition of the starting powder mixture. The size of the agglomerates can be reduced to a desired size, for example, to about 1 micron by subsequent milling such as jet milling.

The resulting agglomerated powder can then be used by the capacitor manufacturer. The powder is ground, or extruded separately from the agglomerated powder,
It can be used in admixture with an organic solution containing binders, solvents and dispersants that form a paste, slurry or slip that is poured or applied to the thin layer by flow coating. The capacitor is completed through a process of drying and baking the agglomerated ceramic powder to form a dielectric layer of the capacitor.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Brief description of the drawings]

FIG. 1 is a side sectional view of a wafer or disk type ceramic capacitor of the present invention.

FIG. 2 is a side cross-sectional view of a monolithic or multilayer ceramic capacitor (MLC) of the present invention.

FIG. 3 is a plot of dielectric constant (K) as a function of capacitor usable temperature for two groups of monolithic ceramic capacitors of the present invention.

[Explanation of symbols]

 10: Ceramic 21: Electrode 22: Electrode 30: Curve 32: Curve

(56) References JP-A-2-283664 (JP, A) US Patent 4,266,265 (US, A) US Patent 4,799,127 (US, A) US Patent 4,706,163 (US, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/42-35/49 C04B 35/50 CA (STN) JICST file (JOIS) REGISTRY (STN) WPI (DIALOG)

Claims (13)

(57) [Claims] 1. a) 95 to 98% by weight of barium titanate powder having an average particle size of 0.2 to 0.7 micrometer, 1.5 to 3.5% by weight of cadmium silicate powder and 0.5 to 98% by weight of cadmium silicate powder; Combining the 1.5% by weight powdered particle growth inhibitor powder; b) mixing the combined powder to form a homogeneous powder mixture; and c) bringing the homogeneous mixture to a temperature of 600 ° C. Baking lightly at 800 ° C. to obtain a powder consisting of agglomerates of said homogeneous powder mixture; each of said agglomerates having the composition of barium titanate, cadmium silicate and particle growth inhibitor in said combined powder; A method for producing a mixture of ceramic powders, comprising the steps, having the same composition. 2. The method of claim 1, wherein the average particle size of each of the cadmium silicate and the particle growth inhibitor powder is less than 1.5 micrometers. 3. The method of claim 2, wherein the particle growth inhibitor comprises niobium;
The method of claim 1, wherein the method is selected from oxides of tantalum, bismuth and titanium, and bismuth titanate. 4. The method of claim 1, wherein the calcined powder is additionally comminuted to produce a free flowing powder having an average size of agglomerates of less than 1.5 micrometers. 5. The cadmium silicate according to claim 5, wherein the cadmium silicate is 5CdO.2S.
iO ₂ , 3CdO.SiO ₂ , 2CdO.ZnO.SiO
_2. The method according to claim 1, wherein the method is selected from ₂ and CdO.2ZnO.SiO2. 6. The method of claim 1, wherein said silicate is 3CdO.SiO ₂ . 7. The method of claim 1, wherein the particles of the barium titanate powder are spherical. 8. A mixture of ceramic powders consisting of agglomerates, a) each said agglomerate consisting of particles of a group of three powders being lightly calcined and co-reacting on the outer surface to form said group of said powders. B) combining the particles of powder together to form said individual agglomerates; b) said three types of powder particles in said individual agglomerates;
95-98% by weight of barium titanate powder having an average particle size of 0.2-0.7 micrometers, 1.5-3.
A mixture of said ceramic powders consisting of 5% by weight of cadmium silicate powder and 0.5-1.5% by weight of a particle growth inhibitor powder. 9. The method of claim 9, wherein the particle growth inhibitor comprises niobium;
9. The mixture of ceramic powders according to claim 8 , wherein the mixture is selected from oxides of tantalum, bismuth and titanium and bismuth titanate. 10. The mixture of claim 8 , wherein the average size of the agglomerates is less than 1.5 micrometers. 11. The cadmium silicate comprises 5CdO · 2
SiO ₂ , 3CdO.SiO ₂ , 2CdO.ZnO.Si
O ₂ is selected from CdO · 2ZnO · SiO _2, claim 8 mixture of ceramic powder according. 12. The ceramic powder mixture according to claim 8 , wherein the particles of the barium titanate powder are spherical. 13. The ceramic powder mixture of claim 8 , wherein said barium titanate is pure barium titanate.