JPH085670B2 - Barium titanate-based composition - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to barium titanate-based dielectric compositions and more particularly to stoichiometric, dispersible submicron particles having a very narrow particle size distribution. It relates to barium titanate or coforms.

Technical Background Barium titanate's high dielectric constant and dielectric strength make barium titanate a particularly desirable material from which capacitors and other electrical components can be constructed. Of particular interest is that the electrical properties of barium titanate can be adjusted over a wide range by the formation and doping of mixed crystals.

Very simple cubic perovskite structure represented by barium titanate
Is a high temperature crystalline form for many ABO ₃ type mixed oxides. This crystal structure consists of a regular array of corner-shared oxygen octahedra with small Ti (IV) cations occupying the B position of the central octahedron, and Ba (II) cations with a larger 12-coordinate A Fills the gap between the octahedra in position. This crystal structure is particularly important because it allows for excessive multication substitution in both the A and B positions to readily produce a large number of more complex ferroelectric compounds.

The relatively simple lattice structure of barium titanate is characterized by a TiO ₆ octahedron which, due to its high polarizability, substantially determines the dielectric properties of the structure. This high polarizability is small Ti
(IV) due to the fact that the ions have relatively more voids in the oxygen octahedron. However,
This cubic unit cell is only stable above the Curie point temperature of about 130 ° C. Ti (IV) below 130 ℃
Ions occupy off-center positions. This transition to the off-center position causes the crystal structure to change from cubic to tetragonal at temperatures between 5 ° C and 130 ° C, orthorhombic at temperatures between -90 ° C and 5 ° C, and It will eventually change to a rhombohedral system at temperatures below -90 ° C. Of course, the dielectric constant and dielectric strength also decrease in proportion to these changes in temperature and crystal structure.

The dielectric constant of barium titanate ceramics has a strong temperature dependence and exhibits a clear maximum dielectric constant at or near the Curie point. Due to the temperature dependence of the permittivity and its relatively low value at room temperature, pure BaTiO ₃ is rarely used in the production of industrial dielectric compositions. Therefore, in practice, additives are used to improve the dielectric properties of barium titanate. For example, partial substitution of strontium and / or calcium for barium and zirconium and / or tin for titanium can be used to move and broaden the Crieury temperature to a lower temperature, thereby increasing room temperature to 10,000- 1
It is known in the art to obtain materials with a maximum dielectric constant of 5,000. Alternatively, partial substitution of lead (II) for barium can increase the Curie temperature. In addition, 1971, published by Academic Press, Inc., New York City, USA. B.Jaffee, double. R. Cook,
Junia (WRCook, Jr) and H. Jiatsuhue (H.
Jaffe), as summarized in "Piezoelectric Ceramics," small amounts of other metal ions of appropriate size, but different valences than barium and titanium, can cause large changes in dielectric properties. it can.

In industrial practice, barium titanate-based dielectric powders can be mixed with the necessary pure titanates, zirconates, stannates and dopants, or oxidized barium, calcium, titanium, etc. By directly forming the desired dielectric powder by high temperature solid state reaction of an intimate mixture of a suitable stoichiometric amount of a compound or an oxide precursor (eg carbonate, hydroxide or nitrate). Is generated. Pure titanates, zirconates, stannates, etc. are also typically produced by the high temperature solid state reaction method. In such a calcination process, the necessary reactants are wet milled to form an intimate mixture. Dry the resulting slurry, then about 700 ° C
Calcination at elevated temperatures ranging from 1 to 1200 ° C. to achieve the desired solid state reaction. Thereafter, the calcined product is re-ground to produce a dispersible powder for producing a green body.

Although barium titanate-based dielectric formulations produced by solid state reactions are satisfactory for many electrical applications, they have some disadvantages.
First, the milling process acts as a source of impurities that can adversely affect the electrical properties. Microscale
Structural inhomogeneities in e) can lead to the formation of undesirable phases such as barium orthotitanate that can increase moisture sensitivity. Furthermore, substantial grain growth and intergranular sintering can occur during calcination. The resulting milled product consists of irregularly shaped, crushed aggregates with a broad particle size distribution ranging from about 0.2 microns to 10 microns. Published studies have shown that green bodies formed from such aggregate powders having a wide aggregate particle size distribution require elevated sintering temperatures and yet provide a sintered body with a wide particle size distribution. Shows.
However, in manufacturing composite dielectrics such as monolithic multilayer capacitors, it is substantially economically advantageous to employ lower sintering temperatures than higher sintering temperatures. This is because the percentage of low cost silver at the silver-palladium electrode can increase as the sintering temperature decreases.

As known in the art, the capacitance of a dielectric layer is inversely proportional to its thickness. In the currently used multilayer capacitors, the thickness of the dielectric layer is about 25 microns. Although highly desirable, this value cannot be substantially reduced. This is because the number of defects such as pinholes in the dielectric film increases as the layer thickness decreases. This defect adversely affects the performance of the capacitor. One of the major causes of such defects is the presence of non-dispersive aggregates with sizes comparable to the thickness of the dielectric film. Because of the existence of such aggregates,
Non-uniform shrinkage occurs during calcination, forming pinholes.
Therefore, the use of barium titanate-based dielectric formulations formed by solid state reactions significantly increases the overall manufacturing cost of monolithic multilayer capacitors.

The prior art has developed several other barium titanate production processes in view of the limited product due to conventional solid state reaction processes. These methods involve the thermal decomposition of barium titanyl oxalate and barium titanyl citrate and the high temperature of a spray solution of either barium alcoholate and titanium alcoholate dissolved in alcohol or barium lactate and titanium lactate dissolved in water. And oxidation. In addition, barium titanate can be used as a molten salt, by hydrolyzing barium alkoxide and titanium alkoxide dissolved in alcohol, and by hydrothermally reacting barium hydroxide and titania, and reacting in an aqueous medium. It has been manufactured by both. Since the morphology of the products derived from some of these processes approximates the morphology desired here, the prior art describes barium titanate-based compositions by the same methods used to produce pure barium titanate. Attempted to manufacture. For example, bee. Jay. Mulder (BJ
Mulder is a Ceramic Bulleti
n), 49, No. 11, 1970, pp. 990-993, "Preparation of BaTiO ₃ and Other Ceramic Powders by Cop Recipe of Citrate in an Alcohol (Preparation of BaT
iO ₃ and Other Ceramic Powders by Coprecipitation o
f Citrates in an Alcohol) ”
Composition or Kofuomu a TiO ₃ based is disclosed that can by connexion produced coprecipitation. In this way Ti
(IV), Zr (IV) and / or Sn (IV) citrate and Ba (II), Mg (II), Ca (II), Sr (II) and / or
An aqueous solution of each Pb (II) formate is sprayed in alcohol to coprecipitate. The precipitate is decomposed by calcination at 700-800 ° C. in a stream of air diluted with N ₂ into spherical and rod-shaped particles with an average particle size of 3-10 microns.

Coffome based on barium titanate is the Journal of the American Ceramics Society (J.Amer.Ceramics Soc.) Vol. 46, No. 8, 1963.
Year pp. 359-365, "Preparation of Semi-Conducting Titana.
tes By Chemical Methods), as disclosed by Gallagher et al. in a paper entitled "Tes By Chemical Methods", upon precipitation and subsequent calcination of a mixture of alkali metal and / or Pb (II) titanyl and / or zirconyl oxalate. It was manufactured. These researchers
A BaTiO ₃ -based composition in which is replaced by Sr or Pb in the range 0-50 mol% or Ti (IV) is replaced by Zr (IV) in the range 0-20 mol%. Proved that it can be generated.

Faxon et al. In U.S. Pat. No. 3,637,531 have a titanium chelate or titanium alkoxide,
It has been disclosed that a BaTiO ₃ -based coform can be synthesized by heating a solution of an alkaline earth salt and a lanthanide salt to form a semi-solid mass. The semi-solid mass is then calcined to produce the desired titanate coform.

However, in each of the prior art references cited above, calcination is employed to synthesize barium titanate-based coform particles. For the reasons already indicated, this high-temperature operation produces an aggregate product which, after grinding, gives rise to smaller aggregate fragments with a broad particle size distribution.

In the prior art, titanates mixed alkaline earth - Yotsute to be synthesized by a molten salt reaction zirconate compositions, also to avoid the drawbacks of the conventionally produced BaTiO ₃ powder I tried. Such a method is disclosed in US Pat. No. 4,293,534 to Arendt. In practicing this method, titania or zirconia or a mixture thereof and barium oxide, strontium oxide or a mixture thereof and an alkali metal hydroxide are mixed and then to a temperature sufficient to melt the hydroxide solvent. To heat. The reactants are dissolved in a melting solvent and then alkaline earth titanate, zirconate,
Alternatively, it is precipitated as a solid solution having the general formula Ba _x Sr _(1-x) Ti _y Zr _(1-y) O ₃ . The product is characterized as chemically homogeneous, relatively monodisperse, submicron (<1 μm) crystallites. However, this method is limited in the drawback that it only produces coforms containing Sr and / or Zr.

A hydrothermal method in which coforms are produced is also described. In British Patent No. 715,762 Bardaza (B
ulduzzi) and Steinemann are hydrated TiO ₂
Was heated to a temperature between 200 ° C. and 400 ° C. with a stoichiometric amount of alkaline earth hydroxide to form a mixed alkaline earth titanate. Although it was stated that it was possible to produce products of any desired size up to about 10 μm, a product having the morphological characteristics of the invention was obtained, except in the case of Sr-containing coforms. Is doubtful. This claim is contrary to that Ba (OH) ₂ is soluble in the aqueous medium Ca (OH) ₂ , whereas Mg (OH) ₂ is relatively insoluble, especially in the presence of Ba (OH) _2. Based on. Therefore, in the case of calcium-containing coforms, BaTiO ₃ is first produced and then Ca (OH) ₂ is unreacted titania during the heating operation to 200-400 ° C under the experimental conditions of Bardage and Steinmann. It was found that CaTiO ₃ was produced by reacting with the remainder of.

Matsushita et al. European Patent Application No. 34
In the specification of 306926.1, the dilute slurry of hydrous titania is
It has been demonstrated that heating to temperatures up to 110 ° C. can react with Ba (OH) ₂ and / or Sr (OH) ₂ to produce either BaTiO ₃ or Sr-containing coforms. The morphological features of these coforms appear to be comparable to that of the present invention. However, this method also
It is limited to the manufacture of containing Coffome only.

"Easy Jin Tallable B" by Abe et al.
aTiO ₃ Powder (Easily Sinterable BaTiO ₃ Powder)
The Sakai Chemical Industry Company publication entitled, Formula B
aTi _(1-x) discloses a hydrothermal synthesis method Kofuomu based on barium titanate having a Sn _x O _3. In this method, 0.6 M Ti _(1-x) Sn _x O ₂ slurry prepared by neutralizing an aqueous solution of SnOCl ₂ and TiCl ₄ was added to 0.9 M Ba.
(OH) ₂ and then at 200 ° C. for at least 5
Subject to hydrothermal treatment over time. Abe et al., Although not explicitly mentioned, implied heating the slurry to high temperatures. The BaTiO ₃ product produced by the same method, although no description of coform morphology is given, had a surface area of 11 m ² / g and a particle size of 0.1 μm and appeared to be dispersible . Possibly the Sn-containing coform has a morphological structure comparable to the Sn-containing coform of the invention,
Therefore, it is comparable to the Sn-containing Coffome of the present invention. However, Abe et al. Is limited in that it only teaches that Sn (IV) can be synthesized into a barium titanate coform. By analogy, maybe Abe et al. Sr (OH) ₂ is Ba
It is completely soluble in aqueous media like (OH) ₂
Use of other tetravalent cations such as (IV) and possibly divalent Sr
It may have suggested the use of (II). However, the method of Abe et al. Cannot be used for substituting divalent Curie point transfer agents such as Pb and Ca for divalent Ba.

Therefore, in the prior art, barium titanate containing calcium and / or lead, or composite divalent and tetravalent compounds having a narrow particle size distribution, stoichiometric, dispersible, spherical and submicron. There is no coform of the cation substitute.

SUMMARY OF THE INVENTION The present invention includes a wide variety of dispersible barium titanate coforms having a narrow particle size distribution, being substantially spherical, stoichiometric and submicron. Most importantly, the barium titanate-based dielectric composition according to the present invention comprises a coform having partial substitution with divalent lead and / or calcium instead of divalent barium, and divalent barium with lead. , Cofome, which is partially replaced by calcium and strontium, and tetravalent titanium is partially replaced by tin, zirconium and hafnium.

Kofuomu based on barium titanate in one important embodiment of the present invention have the general _{formula: Ba (1-x-x'} -x ") Pb x Ca x 'Sr x" Ti
Range _{'in "Hf y} O _{3 (wherein, x, x (1-y} -y'-y) Sn y Zr y"' and x "represents the mole fraction of the divalent cation, and from 0 to 0.3 , And the sum of x + x ′ + x ″ has values ranging from 0 to 0.4, while y, y ′ and y ″ are 4
It represents the molar fraction of valent cations and has independent values ranging from 0 to 0.3, and the sum of y + y ′ + y ″ is 0.
With a value ranging from 0.4 to 0.4).

Barium titanate Kofuomu In another important embodiment of the present invention have the general _{formula, Ba (1-x ')} Ca x' Ti (1-y-y'-y ") Sn y Zr
_{y ′} Hf _{y ″} O ₃ (wherein calcium is partially replaced in place of the divalent barium cation), and in yet another important embodiment of the present invention, a barium titanate dielectric. body composition _{formula, Ba (1-x) Pb} x Ti (1-y-y'-y ") Sn y Zr y 'Hf y" O
₃ (in this case, lead has been replaced by divalent barium). Mole fraction x in each of the latter embodiment, x ', x "and y, y', y" independent value for the general formula _{Ba (1-x-x'-} x ") Pb x Ca x 'Sr x _″ Ti
Having _(1-y-y'-y ") Sn y Zr y 'Hf y" O 3, matches already cited independent values for more complex Kofuomu.

Despite the chemical composition of the coforms, each of the barium titanate-based coforms of the present invention possess the same unique chemical and physical properties. Dielectric formulations based on barium titanate have different divalent to tetravalent molar ratios of covalently constructed coforms.
1.000 irrespective of the number and mol% of valent cation substitutes
Stoichiometric to be ± 0.015. The molar ratio of divalent cations to tetravalent cations of variously constructed coforms
Non-stoichiometric compositions in the range 0.9-1.1 can also be produced. Barium titanate-based coforms (mean primary particle siz)
e) is in the range of 0.05 to 0.4 micron. Furthermore, the average primary particle size measured by image analysis is comparable to the average particle size measured by the sedimentation sedimentation method which proves that the coforms are dispersible. The size distribution curve of the coform particles is less than or equal to 1.5 which establishes that the barium titanate-based coform has a narrow size distribution.
atile) ratio. Also important is the fact that any of the dispersible submicron barium titanate-based dielectric compositions of the present invention can be produced by a single conventional hydrothermal method.

It is therefore a first object of the invention to provide a dispersible, submicron barium titanate coform having a narrow particle size distribution.

It is another object of the present invention to provide a wide variety of different compositions of BaTiO ₃ -based coforms having a primary particle size that can be adjusted to a particle size range of 0.05 to about 0.4 μm. Is.

It is another object of the present invention to provide a wide variety of coforms that can be synthesized by a single general hydrothermal operation.

It is another object of the present invention to provide a stoichiometric barium titanate-based coform that is substantially free of mill media.

It is a further object of the present invention to provide a barium titanate coform that contains various additives that move and / or extend the Curie point to a desired temperature range and reduce the temperature dependence of the resulting dielectric. It is one purpose.

It is yet another object of the invention to provide a dispersible BaTiO ₃ -based dielectric composition that can be used to provide a substantially defect-free reduced thickness dielectric layer. Is the purpose.

It is yet another object of the present invention to provide a barium titanate-based dielectric formulation that sinters densely and uniformly at temperatures well below conventional temperatures.

Description of the Preferred Embodiments At the outset, the invention will be described in greater detail below in its broadest general aspect. A preferred embodiment of the present invention is generally _{type, Ba (1-x-x'} -x ") Pb x Ca x 'Sr x" Ti
_{'During "Hf y} O _{3 (wherein, x, x (1-y} -y'-y) Sn y Zr y"' and x "represents the mole fraction of the divalent cation, and from 0 to 0.3, further Preferably 0 to 0.2
Have independent values ranging up to x + x '+
The sum of x "can have values ranging from 0 to 0.4, more particularly 0 to 0.3, wherein y, y'and y" represent the molar fraction of tetravalent cations and 0 to 0.
Have independent values ranging up to 3, more preferably 0 to 0.25, and the sum of y + y ′ + y ″ is 0 to 0.4
, And more preferably having a value ranging from 0 to 0.3). More preferred embodiment, the _{formula, Ba (1-x-x'} -x ") Pb x Ca x 'Sr x" Ti
_(1-y-y'-y ") Sn y Zr y 'Hf y" O 3 ( in the formula,
x, x ′, x ″ y, y ′ and y ″ are independent values in the range of greater than 0 and less than 0.3, and x + x ′ + x ″.
In the barium titanate-based coform (composition) comprising substantially spherical particles, the sum of y + y ′ + y ″ is greater than 0 and less than 0.4, and the sum of y + y ′ + y ″ is greater than 0 and less than 0.4. The average primary particle size of the composition determined by image analysis is in the range of 0.05-0.4 μm,
The composition has a narrow particle size distribution, the primary particle size distribution curve of the composition determined by image analysis has a quartile of 1.5 or less, and the particle size measured by image analysis and primary sedimentation. Is the barium titanate-based coform (composition) that matches within a correction factor of 2.

If the sums of (x + x '+ x ") and (y + y' + y") are both equal to zero, the coform is simply composed of barium titanate powder. x = x ″ = y = y ′ = y ″
= 0 and x ′ is greater than zero, the product obtained is a barium titanate-based coform, in which case x ′ of Ba (II) in BaTiO ₃
The mole fraction is replaced by Ca (II) and each eye equation (nomi
_{nal formula) Ba (1-x} ') Ca x' products having a TiO ₃ is obtained. Conversely x '= x "= y = y' = y" = 0 and the Kofuomu when x is greater than zero having the composition _{Ba (1-x) Pb x} TiO 3.

The values of x, x ', x ", y, y'and y" can each be in a wide range of values (within specified limits), so that many cofoam combinations with a wide range of compositions can be manufactured. You can However, each of the barium titanate-based coforms, regardless of their composition, is uniquely characterized by their high purity, fine submicron size and narrow particle size distribution.

Preferably, the finely dispersible submicron powder of the present invention comprises between 0 and 30 mol% tetravalent metal ions and 2
It consists of a barium titanate coform with both substitutions of valent metal ions. The divalent barium ion can be partially replaced by either lead, calcium, strontium, or a mixture thereof. Conversely, the tetravalent titanium ion can be partially replaced by tin, zirconium, hafnium or mixtures thereof. Thus, the barium titanate-based dielectric composition of the present invention comprises a single coform of barium lead titanate or barium strontium titanate and lead barium titanate stannate and barium lead strontium zirconate titanate strontium zirconate. Includes more complex coforms. Of course, the choice of divalent and / or tetravalent cation substitution and the mole% substitution is related to whether it is desired to raise or lower the Curie temperature, and the Curie peak broadens. It depends on whether it is desired or if it is desired to move. However, whether formed by a wide variety of different compositions based on barium titanate, the barium titanate coforms according to the present invention are still uniquely identified by the morphological and chemical properties described above. To be done. Therefore, both the simple and complex cofoams of barium titanate have a primary particle size in the range of 0.05 micron to 0.4 micron with both divalent and tetravalent ions being 1
It consists of substantially spherical dispersible particles having a narrow particle size distribution and a divalent to tetravalent molar ratio of 1.000 ± 0.015 even when replaced by one or more other ions.

The narrow particle size distribution and submicron size of the barium titanate-based dielectric compositions make the coforms of the present invention particularly attractive for complex dielectric fabrication and yet further applications. To do. Previous studies have confirmed that a green body formed from a non-aggregated powder with a narrow particle size distribution sinters at low temperatures to give a sintered body with a narrow particle size distribution. The economic benefits of using a dielectric formulation with a low sintering temperature are clear.
Because 100 of low cost silver in silver-palladium alloy
This is because the fraction may increase as the sintering temperature decreases. In addition, all of these BaTiO ₃ -based dielectric compositions are dispersible and have few aggregates above sub-micron size, so they have a reduced thickness. It can be used to form a dielectric film. For this reason, the spherical, non-aggregated, submicron, and narrowly distributed barium titanate dielectric coform powders of the present invention are particularly well suited for use in composite dielectrics requiring sintering.

The preferred products for most dielectric applications are those with relatively low variability in primary particle composition.
However, compositional heterogeneity is advantageous in some circumstances. In these cases, the utility of products with different primary particle sizes is utilized to produce two or more different compositions with either an equal number of primary particles or a substantially different number of primary particles. It is possible to produce a dispersion of a powder of Such a dispersion gives a green body and thus a sintered body with a controlled microheterogeneity.
In such applications, compositional inhomogeneity may be inherent in the selected barium titanate coforms,
Alternatively, it may result from a small amount of the barium titanate coform having the selected composition added to the barium titanate dispersion to achieve the desired compositional heterogeneity. Divalent barium and / or 4 according to the invention
The barium titanate-based compositions of the present invention are also well suited for applications where compositional inhomogeneities are advantageous, since any of the valent titanium can form insufficient coforms.

A preferred method of making barium titanate-based coforms is to heat a slurry containing hydrous tetravalent oxide with a selected divalent oxide or hydroxide. After formation of the divalent titanate, the slurry still contains a substantial amount of hydrous TiO ₂ and / or hydrous SnO ₂ , ZrO ₂ or HfO ₂ . The temperature and concentration of the slurry is then adjusted and a stoichiometric excess of Ba (OH) ₂ solution is added under isothermal conditions. It is preferred to subject the slurry to a final high temperature treatment to ensure complete conversion of the tetravalent oxides to their corresponding oxyanions.

Be filed in primary particle size and the primary particle size distribution is simply BaTiO ₃ barium titanate Kofuomu of the present invention, or Formula _{Instead, Ba 1-x-x'-} x "Pb x Ca x 'Sr x" Ti
Having _{1-y-y'-y "} Zr y Sn y 'Hf y" O 3, is achieved shall apply in more complex Kofuomu. This will be readily apparent from the transmission electron micrograph of the complex co-form Ba _0.856 Pb _0.097 Ca _0.074 Ti _0.830 Zr _0.099 Sn _0.071 O ₃ in FIG. First
The figure shows that although there are also a few tightly bound doublets and triplets, there is primarily a single substantially spherical primary particle. The primary particle size of this coform is 0.18 micron and has a narrow particle size distribution. Comparison of the composite barium titanate-based coforms of FIG. 1 with the transmission electron micrographs of pure barium titanate in FIG. 2 shows that the morphologies of barium titanate-based compositions are very similar. Is shown. It should be noted that the particles in both micrographs were substantially spherical, non-aggregated, submicron, and non-uniformly sized. It is also noted that the molar ratio of divalent cations to tetravalent cations 1.027 in this product is slightly higher than the value 1.000 ± 0.015 specified for stoichiometric products. This ratio can be easily reduced to a specific range without affecting the morphology due to small variations in synthesis conditions.

Various laboratory tests were carried out in order to evaluate the physical and chemical properties of the barium titanate-based coforms according to the invention. 1 of products using image analysis
The secondary particle size and primary particle size distribution were measured. In order to measure the equivalent spherical diameter of the primary particles, 500 to 1000 particles were sized for many TEM fields. Two or more contact particles were visually disaggregated and individual primary particle size was measured. The equivalent spherical diameter was used to calculate the cumulative mass% distribution as a function of primary particle size. The median particle size by weight was taken as the primary particle size of the sample. The quartile ratio QR, defined as the upper quartile diameter (weight) divided by the lower quartile diameter, was used as a measure of the width of the distribution. The monodisperse product has a QR value of 1,
For the purposes of the present test, products having a QR value ranging from 1.0 to about 1.5 were classified as having a narrow particle size distribution, 1.
Those with QR values ranging from 5 to about 2.0 were classified as having a fairly narrow distribution, while those with values substantially greater than 2.0 were classified as having a broad particle size distribution. Barium titanate of the present invention
The cohorm quartiles were measured to be between 1.0 and 1.5, indicating that the primary particles have a narrow size distribution.

The surface area was calculated from the primary particles of coform and found to be in agreement with the surface area measured by nitrogen adsorption.
The secondary particles were shown to be substantially non-porous. When the N ₂ surface area substantially exceeded the TEM surface area, the difference could be easily explained as due to the presence of unreacted high surface area hydrous oxide.

The coforms of the present invention have a narrow particle size distribution, so
The average primary particle size was easily determined by classifying 30 particles in size order. D = 6 / ρS, where D is the particle size (microns), ρ is the density (g / cc), and S is the N ₂ surface area (m ² / g) It has been found that a good measurement of the primary particle size of cofoam can be made. According to this formula, it has been found that barium titanate based coforms have a primary particle size in the range between 0.05 and 0.4 microns regardless of which coform composition is tested. The product dispersibility of coforms was evaluated by comparing the primary particle size and particle size distribution measured by image analysis with comparable values measured by the sedimentation procedure. The sedimentation method gave the equivalent spherical diameter a particle Stokes diameter roughly corresponding. Two sedimentation methods, the Joyce Loeble Disc Centrifuge (Vitzkers Instrument, London, England) and the Micromeritics Sedigraph.
graph) (Norcross, GA, USA) was used to measure the cumulative mass% distribution with respect to Stokes diameter. From the Stokes diameter, the median Stokes diameter and
The QR value was calculated.

0.08 at pH 10 when measuring particle size by sedimentation
Water containing g / L sodium tripolyphosphate or Emphos PS-21A [Madison Avenyu 520, New York City, USA, Witco Organic Division] 0.08 wt% or 0.12 wt% isopropanol 15-30 minutes of sonication (sonificatio)
The powder was dispersed according to n).

Since the particle sizes measured by image analysis and by sedimentation are based on different principles, it is not always possible to obtain a particle size agreement between these two methods. Moreover, the contact particles are visually disaggregated in the image analysis as described above. In the sedimentation method, bound particles or agglomerated particles act as a single substance. These products have some bonds [eg necking] between the primary particles, giving tightly bound aggregates that cannot be easily destroyed during the sony calcination operation, and some It occurs because of sub-optimal dispersion stability resulting in flocculation. That is,
As expected, the QR values measured by the sedimentation method are slightly higher than the QR values found by image analysis.

The primary particles measured by image analysis in the barium titanate-based coforms of the present invention are reasonably consistent with the primary particle sizes measured by sedimentation. The median value of the measured particle size is the correction factor (factor, factor, conversion factor)
It fluctuated below 2. This proves that Cofohm is dispersive.

Utilizing two additional measurements to evaluate the dispersibility, the first method has a mass fraction of products with a Stokes diameter greater than 1 micron.
n) was used as a criterion for the quantity of hard-to-dispers aggregates. In the second method, the product was classified as dispersible if the majority of the primary particles in the TEM were present as single particles. The product was classified as agglomerated if substantial netting was observed. In each of these tests, again the barium titanate-based coform was classified as dispersible.

The product composition and stoichiometry of coforms were inductively coupled after dissolution of the sample.
d) Measured by elemental analysis using plasma spectroscopy. The accuracy of the analysis was about ± 1%. The molar ratio of divalent cations to tetravalent cations of coform is divalent and 4
1.000 regardless of the number of valency cation substitutions and% by weight
It was ± 0.015. This ratio indicates that the barium titanate coform of the present invention is stoichiometric.

The unique properties of barium titanate-based coforms are further illustrated by the following non-limiting examples.

Reagent grade chemicals or their equivalents were used throughout the examples. Reagent grade Ba using (OH) ₂ · 8H ₂ O is 1 mol%
Of Sr. Experiments have shown that Sr (II) is more easily incorporated into coforms than Ba (II). For this reason, all of the coforms described here contain Sr (II). This cation represents approximately 1 mol% of the total divalent cation content of coform. In short, the Sr (II) mole fraction is included in the Ba (II) mole fraction. Each Ba (OH) ₂ and / or Sr (OH) ₂ solution maintained at 70-100 ° C. was filtered prior to use to remove any carbonate present. CaCO ₃ was calcined at 800 ° C. to obtain CaO. The latter compound produced Ca (OH) ₂ when contacted with water. Pb (OH) ₂ was prepared by neutralizing a Pb (NO ₃ ) ₂ solution with aqueous NH ₃ . The washed hydroxide wet cake was used for subsequent experiments.

Hydrous oxides of TiO ₂ , SnO ₂ and ZrO ₂ were prepared by neutralizing aqueous solutions of their respective chlorides with aqueous NH ₃ at ambient temperature. The product was filtered, containing no chloride (measured by AgNO ₃₎ filtrate was washed until is obtained. The surface area of the hydrous oxide measured after drying at 110 ° C was approximately 380 and ₂ for TiO ₂ , SnO ₂ and ZrO ₂ , respectively.
It was 90 and 150 m ² / g. In addition, Ti (IV) and Sn (I
V), or Ti (IV) and Zr hydrous TiO ₂ and ZrO ₂ or a hydrous TiO ₂ and by neutralizing the aqueous solution of the chloride (IV)
Each coprecipitate of SnO ₂ was produced.

All experiments were conducted in a 2-litre autoclave. Every effort was made to coat all wet parts of the autoclave with Teflon to prevent product contamination and to eliminate CO ₂ from all parts of the system. Ba (OH) ₂ or Ba (OH) ₂ either by a high-pressure pump or by rapidly discharging a solution of one or more hydroxides contained in a heated cylinder into the autoclave with high-pressure nitrogen. And a solution of Sr (OH) ₂ were introduced into the autoclave. The contents of the autoclave were agitated at 1500 RPM throughout the synthetic procedure.

Example 1 A calcium-containing coform was prepared by hydrothermally treating a 0.64 slurry containing 0.20 mol of water-containing TiO ₂ and 0.04 mol of Ca (OH) ₂ at 200 ° C. Cool the slurry,
0.41 mol / liter Ba (OH) ₂ solution 0.4 at 120 ℃
6 was added to the slurry. The temperature of the obtained slurry is 1
Raised to 50 ° C and held there for 60 minutes. The sample was filtered and the concentration of divalent cation in the filtrate was measured. The filter cake was dried and its surface area, nominal stoichiometry and morphological properties were measured.

Example 2 A lead-containing coform was produced by hydrothermal treatment of a slurry 0.64 containing 0.2 mol of hydrous TiO ₂ and 0.04 mol of PbO. 0.46 liter of 0.41 mol / liter Ba (OH) ₂ solution was added to the slurry at 150 ° C. 150 ℃ slurry
For 60 minutes and then raised to elevated temperature to fully convert the tetravalent oxide to the perovskite structure. A sample of the slurry was taken and characterized. The results obtained are as follows: Example 3 A composite coform was formed in which Ba (II) and Ti (IV) in BaTiO ₃ were partially replaced by one or more divalent and tetravalent cations. Preheated Ba
(OH) ₂ solution with tetravalent hydroxide and Pb (II) and / or
Containing Ca (II) pre-synthesized perovskite, 150 ℃
Alternatively, it was introduced into a slurry heated to 120 ° C. After holding at this temperature for about 20-30 minutes, raise the slurry to the final temperature and
The valent hydrated oxides were reliably converted to stoichiometric perovskites. The resulting slurry was characterized by the following results.

Molar ratio of cation in solid Ba : Pb : Ca : Ti : Zr : Sn Sample 1 0.908: 0.090: 0.000: 0.904: 0.096: 0.000 Sample 2 0.881: 0.000: 0.123: 0.881: 0.119: 0.000 Sample 3 0.856: 0.097: 0.074 : 0.830: 0.099: 0.071 The quantitative data for samples 2 and 3 are in good agreement with the estimated particle size, particle size distribution and dispersibility data drawn from transmission electron micrographs. However, only Sample 1 is reasonably dispersible as evaluated from the QR values. Nevertheless, the sedimentation data show that no more than 5% by weight of the material is present as aggregates with a particle size greater than 1 micron.

Therefore, the barium titanate coforms included in the present invention from the foregoing examples and disclosures include calcium and / or lead or multiple substitutions for either divalent barium cations and tetravalent titanium cations, or both. Including a dielectric composition containing a compound, wherein the coforms are spherical and have a size in the range of 0.05 to 0.4 microns.
It is uniquely characterized in that it has a sub-particle size, a divalent to tetravalent molar ratio of 1.000 ± 0.015, and a narrow particle size distribution. Disclosed herein are prior art barium titanate-based dielectric compositions including calcium, lead or composite forms having the unique morphological and chemical properties described above. There is no one.

It should be understood that the above description is merely illustrative and not limiting of the present invention, and that various modifications may be made without departing from the spirit of the claimed invention.

[Brief description of drawings]

The drawings illustrate these and other details and advantages of the invention. In the drawings, FIG. 1 is at 50,000 times expansion of the stoichiometric, dispersible, submicron, composite cofoam particle structure according to the invention having the general formula Ba _0.856 Pb _0.097 Ca _0.074 Ti _0.830 Zr _0.099 Sn _0.071 O ₃ . It is a transmission electron micrograph. FIG. 2 shows the grain structure of pure barium titanate powder having a morphology substantially similar to that of the composite coform shown in FIG.
It is a transmission electron micrograph at a magnification of 0,000 times.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 54-18679 (JP, B2) JP 51-80 (JP, B2)

Claims (6)

[Claims] 1. A _{formula, Ba (1-x-x} ') Pb x Ca x' Ti
_{(1-y-y ')} Sn y Zr y' O 3 ( wherein, x, x ', y and y' are independent values ranging from greater than 0 and less than 0.3 respectively, the sum of x + x '0 Greater than 0.4 and the sum of y + y 'is greater than 0 and less than 0.4) and comprising barium titanate-based compositions comprising substantially spherical particles, the composition being determined by image analysis. Has an average primary particle size in the range of 0.05 to 0.4 μm, the composition has a narrow particle size distribution, and the primary particle size distribution curve of the composition determined by image analysis has a quartile ratio of 1.5 or less. Moreover, the barium titanate-based composition, wherein the particle sizes measured by image analysis and primary sedimentation agree within a correction factor of 2. 2. The barium titanate-based composition according to claim 1, wherein the molar ratio of (Ba + Pb + Ca) / (Ti + Sn + Zr) is within the range of 1.000 ± 0.015. 3. The barium titanate-based composition according to claim 1, wherein the molar ratio of (Ba + Pb + Ca) / (Ti + Sn + Zr) is in the range of 0.9 to 1.1. 4. The formula, Ba _{(1-x-x'-x ")} Pb _x Ca _{x 'S.}
r _{x ″} Ti _{(1-y−y′−y ″)} Sn _y Zr _{y ′} Hf _{y ″} O ₃ (where x, x ′, x ″, y, y ′ and y ″ are each greater than 0 and 0.3). An independent value in the range of less than x + x '
The sum of + x ″ is greater than 0 and less than 0.4, and y + y ′ +
The sum of y ″ is greater than 0 and less than 0.4.), and in a barium titanate-based composition comprising substantially spherical particles, the average primary particle size of the composition is from 0.05 to In the range of 0.4 μm, the composition has a narrow particle size distribution, the primary particle size distribution curve of the composition determined by image analysis has a quartile of less than or equal to 1.5, and the image analysis and primary The barium titanate-based composition, wherein the particle sizes measured by settling match within a correction factor of 2. (5) (Ba + Pb + Ca + Sr) / (Ti + Sn + Zr + Hf)
The barium titanate-based composition according to claim 4, wherein the molar ratio of is within the range of 1.000 ± 0.015. 6. (Ba + Pb + Ca + Sr) / (Ti + Sn + Zr + Hf)
The barium titanate-based composition according to claim 4, wherein the molar ratio is within the range of 0.9 to 1.1.