NL8701007A - CO FORMS OF BARIUM TITANATE. - Google Patents

Description

N034451 1

Co-forms of barium titanate.

FIELD OF TECHNOLOGY.

The present invention relates to dielectric compositions based on barium titanate and more particularly relates to stoichiometric, dispersible barium titanate or submicrometer size co-shapes with very narrow particle size distributions.

STATE OF THE ART.

The high dielectric constant and high strength of barium titanate makes it a particularly desirable material from which capacitors and other electronic components can be made. Particularly attractive is the fact that the electrical properties of barium titanate can be controlled within a wide range by means of mixed crystal formation and doping.

The very simple cubic perovsket structure exhibited by barium titanate is the high temperature crystal form for many mixed oxides of the AB03 type. This crystal structure consists of a regular sequence of angle-dividing oxygen octahedra with smaller titanium (IY) cations occupying the central octahedron B site and barium (II) cations filling the gaps between octahedra in the larger 12 coordinated A sites. This crystal structure is of particular significance since it is susceptible to supersaturation of multiple cation substitutions at both the A and B sites so that much more complex ferroelectric compounds can be easily generated.

The relatively simple lattice structure of barium titanate is characterized by the TiOg octahedra which, due to their high polarizability, mainly determine the dielectric properties of the structure. The high polarizability is due to the fact that the small Ti (IV) ions have relatively more space within the oxygen octahedron. However, this cubic unit cell is only stable above the Curie point temperature of approximately 13 ° C. Below 130 ° C, the Ti (IV) ions occupy eccentric positions. This transition to the eccentric position results in a change in crystal structure from cubic to tetragonal between temperatures of 5 ° C and 130 ° C, to orthorombic between -90eC and 5 * C and finally to rhomboedrian at temperatures less than -9Q * C. Needless to say, the dielectric constant and strength also decrease with respect to these temperature and crystal structure changes.

8701007 «5409 ^ V« fi 2

The dielectric constant of barium titanate ceramics has a strong temperature dependence and shows a pronounced maximum dielectric constant at or around the Curie point. In view of the temperature dependence of the dielectric constant and its relatively low value at room temperature, pure BaTiO 3 is rarely used for the manufacture of commercial dielectric parts. Consequently, additives are used in practice to improve the dielectric properties of barium titanate. For example, it is known in the art that the Curie temperature can be shifted and broadened to lower temperatures by partial substitution by strontium and / or calcium for barium and by performing zirconium and / or tin for titanium, thereby resulting in materials with a maximum dielectric constant of 10,000 to 15,000 at room temperature. Also, the Curie temperature can be increased by partial substitution of lead (II) for barium. Also, the substitution of small amounts of other metal ions of suitable size, but with valences different from that of barium and titanium, as summarized in B. Jaffee, W.R. Cook, Jr. and H. Jaffe, "Piezoelectric Ceramics", Academy Press, N.Y. 1971, cause profound changes in the nature of the dielectric properties.

In commercial practice, barium titanate-based dielectric powders are prepared by mixing the required pure titanates, zirconates, stannates and dopants or by directly manufacturing the desired dielectric powder by a high-temperature solid-state reaction of a thorough mixture of the appropriate stoichiometric amounts of the oxides or oxide precursors (e.g. carbonates, hydroxides or nitrates) of barium, calcium, titanium, etc. The pure titanates, zirconates, stannates, etc. are usually also prepared by a solid phase reaction process 30 at high temperature. In such calcination processes, the required reagents are wet milled to effect the formation of a thorough mixture. The resulting suspension is dried and calcined at elevated temperatures ranging from about 700 to 1200 ° C to achieve the desired solid state reactions. Thereafter, the calcined product is reground to produce a dispersible powder for use in making initial objects.

Although the barium titanate dielectric formulations produced by solid phase reactions are acceptable for many electrical applications, they suffer from various drawbacks. First, the milling stage acts as a source of contamination, which can adversely affect electrical properties. Inhomogeneities in the composition on a micro scale can lead to the formation of undesirable phases, such as barium orthotitanate, which can give rise to moisture sensitive properties. In addition, during the calcination, significant particle growth and particle caking may occur. As a result, the ground product consists of irregularly shaped, broken aggregates, which have a wide particle size distribution ranging from about 0.2 to 10 microns. Published studies have shown that initial objects formed from such aggregated powders with wide distributions of the aggregate size require elevated firing temperatures and give sintered objects with wide grain size distributions. However, in the manufacture of complex dielectric objects, such as multilayer monolytic capacitors, there is a significant economic advantage of using lower firing temperatures than higher firing temperatures, since the percentage of less costing silver in the silver-palladium electrode can be increased as the firing temperature 20 is lowered.

As known in the art, the capacity of a dielectric layer is inversely proportional to its thickness. In current multilayer capacitors, the thickness of the dielectric layer is of the order of 25 microns. Although highly desirable, this value cannot be substantially reduced, because as the layer thickness is decreased, the number of defects in the dielectric film, such as holes, increases.

The defects adversely affect the behavior of the capacitor. A main source of such defects is the presence of undispersed aggregates with dimensions comparable to the film thickness. Due to the presence of such aggregates, shrinkage does not occur uniformly during firing. holes formed. Thus, the use of barium titanate-based dielectric formulations formed by solid state reactions significantly increases the total manufacturing cost of multilayer monolytic capacitors.

In view of the limitations of the product posed by conventional solid state reaction processes, the prior art has developed several other methods for the preparation of barium titanate. These methods include the thermal decomposition of barium titanyl oxalate and barium titanyl citrate and the high temperature oxidation of atomized solutions of both barium and titanium alkanoate solutions dissolved in alcohol or barium and titanium actives dissolved in water. . In addition, barium titanate has been prepared from molten salts, dissolved in alcohol by hydrolysis of barium and titanium alkanoates and by the reaction of barium hydroxide with titanium oxide both hydrothermally and in an aqueous medium. Because the product morphologies from some of these methods approach those desired herein, the prior art has attempted to produce barium titanate-based compositions by the same methods used to prepare pure barium titanate. For example, B.J. Mulder in an article entitled "Preparation of BaTi03 and Other Ceramic Powders at Coprecipitation of Citrates in a Alcohol", Ceramic Bulletin, 49, no. 11, 1970, biz. 990-993, that compositions or co-forms based on BaTiO3 can be prepared by a co-precipitation process. In this process, 15 aqueous solutions of Ti (IV), Zr (IV) and / or Sn (IV) citrates and formates of Ba (II), Mg (II), Ca (II), Sr (II) and / or Pb (II) sprayed in alcohol to effect co-precipitation. The precipitates are decomposed by calcination in a stream of air with N 2 at 700-800 ° C decomposed to form spherical and rod-shaped particles having an average size of 3 to 10 microns.

Barium titanate co-forms have been prepared by precipitation and subsequent calcination of mixed alkali metal and / or PbdDtitanyl and / or zircon oxalates as described by Callagher et al. In an article entitled "Preparation of Semi-Conducting Tita-25 nates by Chemical Methods ", J. Amer. Ceramics Soc., 46, No. 8, 1963 pp. 359-365. These investigators showed that compositions based on BaTiO 3 in which Ba was replaced by Sr or Pb in the range of 0 to 50 mol% or in which Ti (IV) was replaced by Zr (IV) in the range of 0 to 20 mol. % has been replaced, can be prepared.

Faxon et al. Describe in U.S. Pat. No. 3,637,531 that co-forms based on BaTiO 3 can be synthesized by heating a solution of a titanium chelate or a titanium alkanoate, an alkaline earth metal salt and a lanthanide salt to form a semi-solid mass. The mass is then calcined to produce the desired titanate coform.

However, in each of the prior art references cited above, calcination is used to synthesize the particles of the co-forms based on barium titanate. For reasons already mentioned, this operation produces aggregated products 40 at elevated temperature which, after comminution, yield smaller aggregate fragments with wide size distributions.

The prior art has also attempted to overcome the drawbacks of conventionally prepared BaTiOj powders by synthesizing a mixed composition of alkaline earth metal titanate zirconate by a reaction as molten salt. Such a method is described in Arendt's U.S. Patent 4,293,534. In the practice of this process, titanium oxides or zirconia oxides or mixtures thereof and barium oxide, strontium oxide or mixtures thereof are mixed with alkali metal hydroxides and heated to temperatures sufficient to melt the hydroxide solvent. The reagents dissolve in the molten solvent and precipitate as an alkaline earth metal titanate, zirconate or a solid solution of the general formula BaxSr (i_x) TiyZr (i_y) 03. The products are characterized as chemically homogeneous, relatively monodisperse crystals of sub-micrometer size. However, this method is limited in that it can produce only Sr and / or Zr containing co-forms.

Hydrothermal processes have also been described, producing co-forms. Balduzzi and Steinemann of British Patent 715,762 heat aqueous suspensions of hydrated TiO2 with stoichiometric amounts of an alkaline earth metal hydroxide to temperatures between 200 and 400 ° C to form mixed alkaline earth metal titanates. Although it is claimed that products of any desired size can be produced up to about 100 µm, it is doubtful that, unlike in the case of Sr 25 containing co-forms, products having the morphological characteristics of the present invention can be obtained. This claim is based on the fact that while Ba (0H) 2 is soluble in aqueous mediums, Ca {0H) 2 and Mg (0H) 2, especially in the presence of Ba (0H) 2, are relatively insoluble. Accordingly, in the case of Ca-containing co-forms, it has been found that under the experimental conditions of Balduzzi and Steinemann BaTiO 3 is first deformed and then Ca (0H) 2 reacts with the rest of the unreacted titanium oxide to form CaTiO 3 during the heating process at 200 to 400 ° C.

35 Matsushita et al. In European patent application no.

34,306,926.1 show that dilute aqueous titanium oxide suspensions can be reacted with Ba (0H) 2 and / or Sr (0H) 2 by heating to temperatures up to 110 ° C to produce BaO 3 or Sr containing co-forms. The morphological properties of these co-40 forms appear similar to that of the present invention. The 8701007 k. 7-.? However, the process is again limited to producing only Sr-containing co-forms.

A publication of Sakai Chemical Industry Company entitled "Easily Sinterable BaTiO 3 Powder" by Abe et al. Describes a hydrothermal process for synthesizing a co-form based on barium titanate of the formula BaTi (i x) SnxO 3. In this method, a 0.6 molar suspension of Tl (1x) Snx ° 2> is prepared by neutralizing aqueous solution of SnOCl2 and TiCl4 3 with 0.9 molar Ba (0H) 2 and mixing 10 on a hydrothermal treatment at 200 ° C for at least 5 hours. Although not explicitly outlined, Abe et al. Imply that the suspension was heated to temperature. Although no description of the morphology of the coform was given, the BaO3O product produced by the same method had a specific surface area of 11 ml / g, a particle size of 0.1 / un and was found to be dispersible. Likely, the Sn containing coforms have similar morphologies and are thus similar to those of the present invention. However, Abe et al. Is limited in that it is only taught that Sn (IV) can be synthesized into a co-form of barium titanate. The use of other tetravalent cations, such as Zr (IV) and possibly the use of divalent Sr (II), may be suggested by analogy, since Sr (0H) 2 such as Ba (OH) 2 ta-. is sparingly soluble in aqueous mediums. However, the method of Abe et al. Cannot be used for substitution of divalent Cu-25 call point shearing agents such as Pb and Ca for the divalent Ba.

Thus, in the prior art, any co-form of barium titanate containing calcium and / or lead or multiple bivalent and tetravalent cation substitutions which are stoichiometric, dispersible, spherical and sub-micrometer in size with narrow distributions of the size of the particles, absent.

SUMMARY OF THE INVENTION.

The present invention encompasses a wide variety of dispersible barium titanate coforms which are substantially spherical, stoichiometric, and sub-micrometer in size with narrow particle size distributions. Most importantly, the dielectric compositions based on barium titanate of the present invention comprising co-forms with a partial substitution by divalent lead and / or calcium for the divalent barium, as well as co-forms in which the divalent barium is partially replaced by 40 lead, calcium and strontium and the tetravalent titanium partly 8701007

V

7 capture is by tin, zirconium and hafnium.

In an important embodiment of the present invention, the barium titanate-based co-form is represented by the general formula 5 Ba (ixx | _x ") PbxCax, Srx" Ti (1-y-y'-y ") SnyZry'Hfy ' O3 where x, x 'and x "represent the mole fractions of the divalent cat ions and have independent values ranging from 0 to 0.3 and the sum x + x1 + x" has a value ranging from 0 to 0.4, while y, y 'and y "have the mole fractions of the tetravalent cations and have independent values ranging from 0 to 0.3 and the sum of y + y' + y" has a value, it ranges from 0 to 0.4.

In another important embodiment of the present invention, the co-form of barium titanate is represented by the general formula 15 Ba JX * J Cax 'Ti (yy_y * .yn SSfyZry * Hfy1103), wherein calcium is partially substituted for the divalent barium cation and in another important embodiment of the invention, the dielectric composition of barium titanate is represented by the general formula 20 Ba {1.x) PbxTi (i_y-y'.y »} SnyZry * Hfy..03, wherein lead for the divalent barium is substituted In each of the latter embodiments, the independent values for the mole fractions x, x ", x" and y, y ', y "are compatible with those already quoted for the more complex co-form of the general formula 25 Ba (ixx «_x“) PbxCax »Srx« Ti (i.y_y «.y ^ jSny Zry'Hfy *« 03.

Notwithstanding the chemical composition of the coform, each of the barium titanate coforms of the present invention has the same unique chemical and physical properties. The dielectric formulations based on barium titanate are stoichi-metric, so that the molar ratio divalent to tetravalent of the varying co-forms is 1,000 + 0.015, regardless of the number and mole percent of all divalent and tetravalent cation substitutions. Non-stoichiometric compositions, wherein the molar ratio of divalent to tetravalent cation of the varying composition is the co-forms in the range of from 0.9 to 1.1, can also be prepared. The average primary particle size of the barium titanate based coforms is in the range of 0.05 to 0.4 micrometers. In addition, the average particle size determined by image analysis is comparable to the average particle size determined by sedimentation, showing that the co-shapes are dispersible 8701007 •> · '^ \ m «8. The curve of the size distribution of the co-shaped particles has a quartile ratio of less than or equal to 1.5, confirming that the barium titanate co-shapes have a narrow size distribution of the particles. Also significant is the fact that any of the sub-micrometer sized dispersible dielectric compositions based on barium titanate of the present invention can be prepared by a simple, generally hydrothermal process.

Consequently, it is a primary object of the present invention to provide a dispersible co-form of barium titanate of sub-micrometer size with a narrow particle size distribution.

It is another object of the present invention to provide a number of different compositions of such BaTiO 3 based co-shapes with primary particle sizes which can be controlled within the size range of 0.05 to about 0.4 µm.

Another object of the present invention is to provide a number of different co-forms which can be synthesized by a simple generally hydrothermal process.

It is yet another object of the present invention to provide a stoichiometric co-shape based on barium titanate which is substantially free from milling medium.

A further object of the present invention is to provide a co-form of barium titanate containing a number of different additives which shift and / or broaden the Curie point to the desired temperature ranges and the temperature dependence of the thus formed dielectric decreases.

Yet a further object of the present invention is to provide dispersible dielectric compositions based on BaTiO3 which can be used to form dielectric layers of reduced thickness, which are substantially free of disadvantages.

Yet another object of the present invention is to provide a dielectric formulation based on barium titanate which uniformly bakes to a high density at significantly lower temperatures than conventional temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS.

These and other details and advantages of the invention will be described in connection with the accompanying drawings, in which: 40-FIG. 1 a transmission electron micrograph at a magnification of 87.0 1 00 7 9 50,000 of a stoichiometric, dispersible complex sub-micrometer sized co-shape of the present invention of the general formula

BaO, 856Pb0.097Ca0.074Ti0.830Zr0, O99SnQ, 07103 1s and 5 Figs. 2 is a transmission electron micrograph at a magnification of 50,000 of pure barium titanate powder showing a morphology substantially similar to the morphology of the complex co-shape of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

Initially, the invention has been described in its broadest overall aspects, followed by a more detailed description. The preferred embodiment of the present invention is a co-form of the general type

Ba (lxx, -x ") PbxCax * Srx« Ti (iy.y 'y »} Sny Zry' Hfy» 03, 15 where x, x 'and x "represent the mole fractions of the divalent cat ions and independent values which range from 0 to 0.3 and more preferably from 0 to 0.2 and the sum x + x '+ x "may have values ranging from 0 to 0.4 and more preferably from 0 to 0 , 3, y »y 'and y“ represent the mole fractions of the tetravalent cations and 20 independent values ranging from 0 to 0.3 and more preferably from 0 to 0.25 and the sum of y + y' + y Has values ranging from 0 to 0.4 and again preferably from 0 to 0.3.

When the sums of {x + x '+ x ") and (y + y1 + y") are both equal to 0, the co-form simply consists of barium titanate powder. When x = x "= y = y '= y" * 0 and x' is greater than 0, the resulting product is a co-form based on barium titanate, in which x 'mole fractions of Ba (II ) in BaTiO3 have been replaced by Ca (II) to form a product of the nominal formula Ba (ix) Cax-TiO3.

Conversely, when x "= x" = y = y '= y "= 0 and x is greater than 0, the co-form has the composition Ba {i_x) PbxTi03.

Since the values of x, x ', x ", y, y * and y" each can take a wide range of values {within the quoted limits), many combinations of co-forms with a wide range of compositions can be prepared. Regardless of which composition is formed, however, each of the barium titanate coforms is uniquely characterized by its high purity, fine submicrometer size and narrow particle size distribution.

Preferably, the sub-micrometer sized fine dispersible powder of the present invention consists of a co-form of barium titanate with both a substitution of a tetravalent and a divalent metal ion between 0 and 30 mole%. The divalent barium ion may be partially replaced by lead, calcium, strontium or mixtures thereof. Conversely, the tetravalent titanium ion may be partially replaced by tin, zirconium, hafnium or mixtures thereof. Thus, the barium titanate dielectric compositions of the present invention contain simple co-forms of barium lead titanate or barium strontium titanate as well as more complex co-forms comprising barium lead stannate tritanate and barium lead strontium stannate. contain ronate tietanate. Obviously, the choice of replacing the divalent and / or tetravalent cation and the mole percentage of the substitution depends on whether it is desired to increase or decrease the Curie temperature and whether it is desired to broaden or increase the Curie peak. shift. However, regardless of which of a wide variety of barium titanate-based compositions are formed, the barium titanate co-forms of the present invention are still uniquely identified by the aforementioned morphological and chemical characteristics. Thus, both the simple and complex co-forms of barium titanate consist of substantially spherical dispersible particles with a primary particle size in the range of 0.05 to 0.4 micrometers with narrow size distributions and a mole ratio of divalent to tetravalent of 1,000 + 0.015, even when both the divalent and tetravalent ions have been replaced by one or more other ions.

The narrow particle size distribution and sub-micro-meter size of the dielectric compositions based on barium titanate make the co-forms of the present invention particularly attractive for further use in the manufacture of complex dielectric objects. Previous investigations have determined that initial objects formed from non-aggregated powders with narrow size distributions will bake at reduced temperatures and yield baked objects with a narrow grain size distribution. The economic advantage of using a dielectric formulation with a lower firing temperature is obvious since the percentage of cheaper silver in the silver palladium alloy can be increased as the firing temperature is lowered. In addition, since these BaTiO 3 dielectric compositions are all dispersible and have few aggregates exceeding 1 micron in size, they can be used in the formation of dielectric films of reduced thickness. Therefore, the hollow-shaped, non-aggregated, highly distributed 87 0 1 00 7 ................................... ........... “...............

11 sub-micrometer sized dielectric co-form powder of barium titanate of the present invention are particularly well suited for use in complex dielectric applications requiring firing.

In most dielectric applications, the preferred products are those in which the variability in primary particle composition is relatively narrow. In some circumstances, however, inhomogeneities in the composition are an advantage. In these cases, the availability of products of varying primary particle size can be used to produce a dispersion of two or more powders of different compositions with comparable numbers of primary particles or significantly different numbers of primary particles. Such dispersions yield initial objects and consequently baked objects with controlled degrees of microinhomogeneities. In such applications, the inhomogeneity in the composition may be inherent in the selected barurotitanate co-form or may instead result from a small amount of barium titanate co-form of a selected composition, which is added to a dispersion of barium titanate added to achieve the desired inhomogeneity in the composition. Since incomplete co-forms of divalent barium and / or tetravalent titanium can be formed in accordance with the present invention, the barium titanate based compositions of the present invention are also well suited for applications where inhomogeneities in the composition are advantageous.

The preferred approach for preparing co-forms based on barium titanate is to heat suspensions containing the aqueous tetravalent oxides with selected divalent oxides or hydroxides. After the formation of the divalent titanates, the suspension still contains considerable amounts of water-containing TiO2 and / or water-containing SnOg, ZrOg or HfCl2. The temperature and concentration of the suspension are then adjusted and a stoichiometric excess of a Ba (0H) 2 solution is then added under isothermal conditions. In order to ensure the complete conversion of the tetravalent oxides to their corresponding oxyan ions, the suspension is preferably brought to a final higher heat treatment.

The primary particle size and size distribution of the present invention are achieved whether the co-form of barium titanate 40 is simply BaTiO 3 or instead the more complex co-form with 8701007 12 the formula

Bal-x-x'-x "PbxCax'Srx''Tii_y_y '_y« ZrySriy · Hfy ** O0 is *

This is readily apparent from the transmission electron micrograph of the complex co-form 5 880 ^ 56 ^ 0.097 ^ 0.074 ^ 0.830 ^ 0.099 ^ 0.07 ^ 3 in fl * 9 · 1> which shows the presence of predominantly single, substantially spherical shapes primary particles, although a few tightly bound doublets and triplets are also present. The primary particle size of this co-shape is 0.18 micrometers with a narrow distribution of the size. A comparison of the complex co-form based on barium titanate of Fig. 1 with the transmission electron micrograph of pure barium titanate in Fig. 2 indicates that the morphologies of the barium titanate-based compositions are very similar. Note that in both micrographs the particles are substantially spherical, unaggregated, of sub-micrometer size and uniformly sized. It should also be noted that the mole ratio of divalent to tetravalent cation in this product, 1.027, is slightly greater than the values of 1,000 + 0.015 specified for stoichiometric products. This ratio can easily be reduced to the specified range by minor variations in the synthesis conditions without affecting the morphology.

In order to appreciate the physical and chemical properties of the barium titanate co-forms of the present invention, a number of different laboratory tests have been performed.

Image analysis was used to determine the primary particle size and the distribution of the primary particle size of the product. 500 to 1000 particles were sized in a plurality of TEM fields to determine the equivalent sphere diameters of the primary particles. Two or more tangent particles were visually disaggregated and the dimensions of the individual primary particles were measured.

The equivalent sphere diameters were used to calculate the percentage distribution of the cumulative mass as a function of the primary particle size. The average particle size, by weight, was taken as the primary particle size of the sample. The quartile ratio, QR, defined as the top quartile diameter (by weight) divided by the bottom quartile diameter, was taken as the measure of the width of the distribution. Monodisperse products with a QR value of 1 and, for our research purposes, products with QR values ranging from 1.0 to about 1.5 were classified (T classified as having narrow size distributions, 10 0 7 13 those with QR values ranging from 1.5 to about 2.0 were classified as having a fairly narrow distribution, while those with values significantly above 2.0 were classified as having be in possession of wide distributions of size.

The quartile ratio of the barium titanate coforms of the present invention was determined to be between 1.0 and 1.5, indicating that the primary particles have a narrow size distribution.

Specific surfaces were calculated from the primary particles of the co-shapes and found to be consistent with the specific surfaces determined by nitrogen adsorption, indicating that the primary particles are substantially non-porous. In cases where the N specific surface area significantly exceeded the TEM specific surface area, it was found that the difference is easily explained by the presence of unreacted water oxides having a large specific surface area. .

Since the co-shapes of the present invention have a narrow size distribution, the average primary particle size was easily determined by sorting 20 to 30 particles by size. It has been found that the relationship D = 6 / fS, where D is the particle diameter 20 meters (micrometers), ^ is the density (g / cm3) and S is the Ng specific surface area (m2 / g), can be used to obtain a good measure of the primary particle size of the co-shape. According to this formula, it has been found that the barium titanate coforms have a primary particle size in the range between 0.05 and 0.4 micrometers regardless of which coform composition has been tested.

The product dispersibility of the coforms was determined by comparing the primary particle sizes and size distributions determined by image analyzes with the comparable values determined by sedimentation methods. The sedimentation process gives the Stokes diameter of the particle, which roughly corresponds to the equivalent sphere diameter. Two sedimentation methods, Joyce Loebl Disc Centrifuge (Vickers Instruments, Ltd., London, Ü.K.) and the Micromeritics Sedigraph (Norcross, Georgia) were used to determine the percent distributions of the cumulative mass in terms of Stokes diameters, from which the median Stokes diameter and QR values were calculated.

In determining the particle size by sedimentation, the powders were dispersed in water containing 0.08 g / l sodium tripolyphosphate at pH 10 40 or in isopropanal containing 0.08 or 0 by sound wave treatment for 15 to 30 min. 12 wt% Emphos PS-12A (Vlitco 8701007 ♦ 'wl 14

Organics Division, 520 Madison Ave., New York).

Since the particle size determined by image analysis and by sedimentation depends on different principles, an exact size match was not always obtained by these two methods. In addition, as already mentioned, particles hitting the image analysis are visually disaggregated. In the sedimentation process, bound or flocculated particles act as single units. These units arise due to the existence of some bonding (e.g., constriction) between the primary particles to form cemented aggregates, which cannot easily degrade with sound waves during the process and due to less than the optimum dispersibility, which leads to some flocculation . Therefore, as expected, QR values determined by sedimentation were slightly greater than those found by image analysis.

In the barium titanate co-forms of the present invention, the primary particle size determined by image analysis was in reasonable agreement with the primary particle size determined by sedimentation. The determined median particle size varied by no more than a factor of 2. This shows that the coforms are dispersible.

Two additional measurements were used to determine dispersibility. In the first method, the mass fraction of the product with a Stokes diameter greater than 1 micron was used as a measure of the amount of hard to disperse aggregates. In the second method, a product was classified as dispersible when the mass of the primary particles in the TEMs were present as single particles. When a significant constriction was observed, the product was classified as aggregated. In each of these experiments, the barium titanate coforms were reclassified as dispersible.

The composition of the product and the stoichiometry of the co-shapes were determined by elemental analysis using inductively coupled plasma spectroscopy after sample dissolution. The accuracy of the analyzes was approximately + 1%. The molar ratio of divalent cation to tetravalent cations of the co-forms, regardless of the number or molecular weight of the divalent and tetravalent cation substitutions, was 1,000 + 0.015. This ratio indicates that the barium titanate coforms of the present invention are stoichiometric.

40 The unique properties of the co-forms based on barium titan- 8701007

dC34CStC

4 * - *% 15 are further illustrated by the following nonlimiting examples.

Reagent grade chemicals or their equivalents were used in all examples. The reagent grade 5 Ba {0H) 2.8H 2 O used contained 1 mole% Sr. Experiments have shown that Sr (II) is more easily incorporated into the co-form than Baill). For this reason, all co-forms described herein contain Sr (II). This cation represents about 1 mol% of the total divalent cation content of the co-form. For simplification, the mole fraction Sr (II) is included in the mole-10 fraction Ba (II). Ba (0H> 2 and / or Sr (0H) 2 solutions, maintained at 70-100 "C, were filtered prior to use to remove any carbonates present. CaCO3 was calcined at 800" C to form CaO. last compound, when contacted with water, gave CaiOHJg * Pb (0H) 2 prepared by neutralizing a solution of PbiNO2) with aqueous NH3. The hydroxide-washed wet cake was used in subsequent experiments.

Aqueous oxides of TiO2, SnO2 and ZrOg were prepared by neutralizing aqueous solutions of their respective chlorides with water containing NH3 at ambient temperatures. The products were filtered off and washed until chloride-free filtrates (determined as with AgNO3) were obtained. The specific surfaces of the hydrous oxides determined after drying at 110 ° C were 380, 290 and 150 m2 / g for HO2, Sn02 and Zr02 * 25, respectively. In addition, coprecipitates of hydrous HO2 and Zr02 or hydrous HO2 and Sn02 prepared by neutralizing aqueous solutions of the chlorides of Ti (IV) and Sn (IV) or Ti (IV) and Zr (IV).

All experiments were performed in a 2 liter autoclave.

To prevent product contamination, all wetted parts of the autoclave were coated with Teflon and every attempt was made to exclude CO2 from all parts of the system. Ba (0H) 2 or Ba (QH2 and Sr (0H) 2 solutions were introduced into the autoclave by means of a high pressure pump or by rapid release of a solution of the hydroxide or hydroxides contained in a heated bomb in the autoclave by nitrogen or high pressure The contents of the autoclave were stirred at 1500 rpm throughout the synthesis process.

Example I.

A calcium-containing co-form was prepared by hydrothermal treatment of 0.64 L of a slurry containing 0.20 mole of water 8701007

X

1 ^ ιό> - 16

TiOg and 0.04 mole Ca (0H) 2, up to 200eC. The suspension was cooled and 0.46 L of 0.41 mol air Ba (0H) 2 was added to the suspension at 120 ° C. The temperature of the resulting suspension was raised to 150 ° C and held there for 60 min. The sample was filtered and the concentrations of divalent cation in the filtrates were determined. The filter cake was dried and its surface area, nominal stoichiometry and morphological properties were determined.

10 filtrate mole ratio cation mole ratio specific g / 1 in solids divalent / surface _ ______ tetravalent

Ba Ca Ca: Ba: Sr: Ti cation m2 / g 2.62 0.446 0.127: 0.842: 0.019: 1.00 0.988 12.0 Primary Particle Size Distribution (TEM) Size 0.15 micrometer narrow Example 2.

A lead-containing co-form was prepared by hydrothermal treatment of 0.64 L of a slurry containing 0.2 mole aqueous TiO 2 and 0.04 moT PbO. 0.46 1 Ba (OH) 2 were added to the suspension at 150 ° C. The suspension was brought to 150 ° C for 60 min and then elevated to complete conversion of the tetravalent oxides to the perovskite structures. The suspension was sampled and characterized. The results obtained are as follows: filtrate molar ratio cation moT ratio specific 30 g / l in solids divalent / surface area.

Ba Ca Ca: Ba: Sr: Ti cation_ m2 / g 10.6 2.74 0.810: 0.173: 0.024: 1,000 1.007 11.5 35 primary particle size distribution (TEM) size 0.07 μm narrow

Example III.

Complex co-forms are formed in which the Ba (11) and Ti (IV) in 8701007 17 the BaTiO 3 are partly replaced by one or more divalent and tetravalent cations. A preheated Ba (OH 2 solution was introduced into the suspensions heated to 150 ° C or 120 ° C containing the tetravalent aqueous oxides and pre-synthesized perovskites of 5 Pb (II) and / or Ca {II). After the suspensions were kept at temperature for 20 to 30 minutes, the suspensions were brought to a final temperature to ensure that the tetravalent aqueous oxides were converted to stoichiometric perovskites. The resulting suspension was characterized with the following results: 10 mole ratio mole ratio cation in solid divalent / spec, tetravalent surfactant.

Ba: Pb: Ca: Ti: Zr: Sn cation_ m ^ / g 15 sample 1 0.908: 0.090: 0.000: 0.904-: 0.096: 0.000 0.988 8.0 sample 2 0.881: 0.000: 0.123: 0.881: 0.119: 0.000 1.004 12 , 2 sample 3 0.856: 0.097: 0.074: 0.830: 0.099: 0.071 1.028 9.8 20 primary particles size distribution (TEM) size sample 1 0.14 μm very narrow sample 2 0.2 μm narrow sample 3 0.2 micrometer narrow 25 _image danalyse_ sedimentation___ size (micrometer) QR size (micrometer) QR sample 1 0.12 1.33 0.24 2.2 30 sample 2 0.19 1.31 0.24 1.6 sample 3 0.18 1.25 0.24 1.5

The quantitative data for Examples II and III agree well with the estimated particle size, size distribution and dispersibility data from the transmission electron micrographs. Sample 1, however, as determined by the QR value, is only moderately dispersible. Nevertheless, the sedimentation data indicate that less than 5% by weight of the material are present as aggregates of size greater than 1 micron.

40 It can therefore be deduced from the previous examples and the description 8701007.

It is recognized that the co-forms of barium titanate comprise by the present invention, which include dielectric compositions containing calcium and / or lead or multiple replacements for each or both of the divalent barium and tetravalent titanium cations which are uniquely characterized in that they are spherical, have a primary particle size in the range of 0.05 to 0.4 micrometers, a mole ratio of divalent to tetravalent of 1,000 + 0.015 and a narrow particle size distribution. No prior art barium titanate dielectric compositions containing calcium, lead or the complex forms described herein have these unique morphological and chemical properties.

8701007

Claims (18)

Co-form based on barium titanate base, characterized in that it contains substantially spherical particles of the formula A barium titanate coform according to claim 1, characterized in that the average primary particle size of the coform is in the range of 0.05 to 0.4 micrometers. Co-form of barium titanate according to claim 1 or 2, characterized in that the primary particle sizes determined by image analysis and by sedimentation correspond within a factor of two. Co-form of barium titanate according to claims 1 to 3, characterized in that the co-form has a narrow particle size distribution and the distribution curve of the primary particle size of the co-form has a quartile ratio of at most 1.5 has. Co-form of barium titanate according to claims 1 to 4, characterized in that the molar ratio (Ba + Ca) / (Ti + Sn + Zr + Hf) is 1,000 + 0.015. 5 Ba (2_x · jCax 'Tiy "y — y * .. y") SnyZry' Hfy'Og, where y, y 'and y "independently have values ranging from zero to 0.3, the sum of y + y '+ y "is less than 0.4 and x' is greater than zero and less than 0.4. Co-form of barium titanate according to claims 1 to 4, characterized in that the molar ratio (Ba + Ca) / (Ti + Sn + Zr + Hf) is in the range between 0.9 and 1.1. Co-form based on barium titanate, characterized in that it contains substantially spherical particles of the formula ^ (1-xl ^ x ^ dy-y'-y '^^ y ^ y' ^ y '^ S * where y 'and y "independently have values ranging from zero to 0.3, the sum of y + y' + y" is less than 0.4 and x is greater than zero and 30 is less than 0.4 . A co-form of barium titanate according to claim 7, characterized in that the average primary particle size of the co-form is in the range of 0.05 to 0.4 micrometers. 9. Co-form of barium titanate according to claim 7 or 8, characterized in that the primary particle sizes determined by image analysis and by sedimentation correspond within a factor of two. Co-form of barium titanate according to claims 7 to 9, characterized in that the co-form has a narrow particle size distribution and the distribution curve of the primary particle size of the 40 co-form has a quartile ratio of at most 1.5 has. 8701007 Co-form of barium titanate according to claims 7 to 10, characterized in that the mol ratio (Ba + Pb) / (Ti + Sn + Zr + Hf) is 1,000 + 0.015. 12. Co-form of barium titanate according to claims 7 to 10, characterized in that the mol ratio (Ba + Pb) / (Ti + Sn + Zr + Hf) is in the range between 0.9 and 1.1. 13. Co-form based on barium titanate, characterized in that it contains substantially spherical particles of the formula Ba jj * “χ11) 1 Sr ^“ Ti | '—y11) ^^ y ^^ y * ^^ y11 ®3 * 10 where x, x ', x ", y, y' and y" each have independent values greater than zero and less than 0.3, the sum of x + x '+ x "is less than 0.4 and the sum of y + y '+ y "is less than 0.4. 14. Co-form of barium titanate according to claim 13, characterized in that the average primary particle size of the co-form is in the range of 0.05 to 0.4 micrometers. Co-form of barium titanate according to claim 13 or 14, characterized in that the primary particle sizes determined by image analysis and by sedimentation correspond within a factor of two. 16. Co-form of barium titanate according to claims 13 to 15, characterized in that the co-form has a narrow particle size distribution and the distribution curve of the primary particle size for the co-form has a quartile ratio of at most 1.5 has. Co-form of barium titanate according to claims 13 to 16, characterized in that the mole ratio of (Ba + Ca + · Pb + $ r) / (Ti + Sn + Zr 25. Hf) 1,000 + 0.015. Co-form of barium titanate according to claims 13 to 16, characterized in that the mol ratio of (Ba + Ca + Pb + Sr) / (Ti + Sn + Zr + Hf) is in the range between 0.9 and 1 , 1. ______ 8701007