FR2619370A1 - COMPOSITIONS BASED ON BARIUM TITANATE DOPE - Google Patents

Abstract

The present invention relates to doped and dispersible barium titanate coforms that are substantially spherical, intimately mixed on a particle size and submicron size scale with narrow particle size distributions. According to the invention, the size of a primary particle of the doped coforms is between 0.05 and 0.4 microns. The amount of the oxide or doping oxides contained in the coform is between more than zero and 10%. Regardless of the dopant or dopants chosen, all coforms are identified by the same unique morphological characteristics shown in the figure. The invention applies in particular to compositions based on barium titanate for the electronics industry.

Description

1. 26 193 70

  The present invention relates to composi-

  based on barium titanate and, more particularly,

  refers to submicron, dispersible, doped barium titanate coforms with narrow particle size distributions. Barium titanate compositions are extensively used in the electronics industry for the production of capacitors, condensers and

  PTCR devices (temperature coefficient resistance)

  positive). Barium titanate is particularly useful and versatile in electronic applications because its electrical properties can be substantially

  modified by the incorporation of additives and / or dopants.

  The additives that are frequently used are MAO3 compounds, where M is a divalent cation and A is a tetravalent cation having the perovskite BaTiO3 structure. Typical additives include titanates, zirconates and stannates of calcium, strontium, barium and lead. Since the additive or additives have the same crystal structure as BaTiO3, they easily form

  a solid solution during calcination or sintering.

  In general, the additives represent more than 3 mole% of the BaTiO3 based formula. Dopants cover a wide range of metal oxides. These, in general, represent less than 5 mole% of the total formula based on BaTiO3. The dopant or dopants employed may be completely or partially miscible in the perovskite network or may be immiscible in this network. Examples of dopants employed include La, lanthanide, Y, Nb, Ta, Cu, Mo, W, Mn oxides.

Fe, Co, Ni, Zn, Al, Si, Sb and Bi.

  In commercial practice, barium titanate formulas are produced either by mixing the required titanates, zirconates, pure stannates and dopants or directly producing the desired powder by a solid state reaction at a high temperature of a mixture. intimate appropriate stoichiometric amounts of the oxide or oxide precursors (such as carbonates, hydroxides or nitrates) of barium, calcium, titanium, etc. Titanates, zirconates, pure stannates, etc. are also typically produced by a high temperature solid phase reaction process. The prior art processes for the production of barium titanate and barium titanate compositions by solid phase reactions are

  relatively simple; nevertheless, they suffer from

  its disadvantages. First, grinding stages serve as a source of contaminants that can adversely affect electrical properties. Secondly, lack of compositional homogeneity, resulting from incomplete mixing on a microscopic scale, can lead to the formation of undesirable phases such as the barium orthotitanate, Ba2TiO4, which can give rise to properties sensitive to humidity. Thirdly, during calcination, a significant growth of

  particles and sintering between particles occur.

  As a result, crushed products consist of aggregates

  fractures of irregular shape which have a wide distribution

  size ranging from about 0.2 to about one micron. In addition, it has been established that green bodies

  formed of such aggregated powders with broad

  aggregates, required high sintering temperatures and

  sintered with wide grain size distributions.

  Many attempts have been made to attempt to overcome the limitations of conventional solid state reaction processes. Precipitation of doped barium titanyl oxalate or doped barium titanate oxalate with partial substitution of strontium or barium lead and titanium zirconium is taught by Gallagher et al., "Preparation of Semiconducting Titanates by Chemical Methods", 46, J. Amer. Chem. Soc., 359 (1963); Schrey, "Effect of pH on the Chemical

  Preparation of Barium-Strontium Titanate, 48, J. Amer.

3 26937 0

  Cer. Soc., 401 (1965) and Vincenzini, "Chemical Preparation of Doped BaTiO3," Proceedings of the Twelfth Int. 1 Conf., Science of Ceramics, Volume 12, page 151 (1983). The oxalates decompose at elevated temperature to form the doped barium titanate compositions. U.S. Patent No. 3,637,531 teaches heating of a simple solution of the dopant, the titanium compound and alkaline earth salts to form a semi-solid mass which is converted to the desired titanate product by calcination. U.S. Patent No. 4,537,865 discloses the combination of Ti, Zr, Sn or Pb hydric oxide precipitates and hydrous oxides of dopants with aqueous slurries of Ba, Sr, Ca or Mg precipitated carbonates. The solids are calcined to give the required product. Kakegawa and

  other, "Synthesis of Nb-doped Barium Titanate Semi-

  conductor by a Wet-Dry Combination Technique, 4, J. Mat.

  Sci. Lets., 1266 (1985) describe a similar synthesis process. Mulder, "Preparation of BaTiO3 and Other Ceramics Powders by Coprecipitation of Citrates in an Alcohol", 49, Ceramic Bulletin, 990-993 (1970), prepares doped BaTiO3 and BaTiO3 products by spraying an aqueous solution of citrates or formates. constituents in a

  alcohol for dehydration and coprecipitation

  tion. The products obtained by calcination of coprecipitated citrate or formate powders consist mainly of compact globules having sizes in the range of 3 to 10 microns. U.S. Patent No. 4,061,583 discloses doped BaTiO3 compositions prepared by addition.

  a solution of the nitrates or chlorides of the constituents

  required solutions to an aqueous alkaline solution containing hydrogen peroxide. Decomposition of the peroxide-containing precipitate to about 100 ° C results in the

  formation of an amorphous BaTiO3 composition.

  Calcination of the amorphous product at about 600 ° C gives crystalline powders. Unfortunately, the sizes of

  Primary particles of the products are not characterized.

  A reproduction of some of the examples given in the patent indicated that the amorphous powders had primary particle sizes that were substantially

  smaller than 0.05 micron. Electron micrographs

  -nique transmission of products have shown that the primary particles of the products calcined at 600 C

had aggregated.

  In the above examples of the typical processes of the prior art, calcination is employed to accomplish the synthesis of particles of the desired compositions. For reasons already noted, this operation at high temperature is harmful because it gives aggregated products which, after grinding, give smaller fragments of aggregate having broad distributions of

cut.

  US Pat. Nos. 4,233,282, 4,293,534 and 4,487,755 describe the synthesis of BaTiO 3 and BaTiO 3 compositions by a molten salt reaction where Ba is partially replaced by Sr and Ti is partially replaced by Zr. The products are characterized as being chemically homogeneous and consisting of relatively monodisperse crystallites of sub-micron size. Products based on doped BaTiO3 have not been synthesized. Yoon et al., "Influence of the PTCR Effect in Semiconductor BaTiO3," 21, Mat. Res. Bul., 1429 (1986), teach the use of a molten salt process for the synthesis of products having the composition Ba (o, 900xSro, 100ooSbxTi03, oxa values of 0.001, 0.002, 0.003 and 0.004. from the molten salt process showed greater effects on PTCR in their resistivity-temperature characteristics and higher resistivities at room temperature and

  greater variations of current in the characteristics

  current-time ticks that comparable specimens formed from powders obtained by calcining a mixture of oxides and oxide precursors. The differences were attributed to the use of KCl in the molten salt synthesis process and the smaller size and grain size distribution in the derived samples. Although the molten salt synthesis process can be used to produce sub-micron sized doped products having narrow size distributions, the powders are inevitably contaminated with alkali metals because the molten salts consist of alkali metals. Of course, in most electronic applications, metals

  alkalis are harmful contaminants.

  Several aqueous base processes have been described for the production of BaTiO3 as well as compositions based on BaTiO3 where Ba is partially replaced by Sr and Ti is partially replaced by Sn or, optionally, by Zr. In the process taught in US Pat. No. 3,577,487, alkaline earth-doped multicomponent titanates, stannates, zirconates and / or hafnates and / or Pb (II) are prepared. In these cases, either the coprecipitated hydrogels are treated with alkaline earth hydroxides and subjected to the same treatment steps as those used for the production of BaTiO 3 or the required gels and alkaline earth hydroxides are added to a preformed slurry of BaTiO 3 which is then subject to

  fluid energy grinding and calcination. Wrong-

  fortunately, the products before grinding by fluid energy were not characterized. However, experience would indicate that doped multicomponent products, before grinding, must have specific surface areas in excess of 20 m 2 / g, indicating that the primary particle sizes of the powder are smaller than about 0.05 micron. Even after grinding with fluid energy at outlet temperatures above 427 ° C., the multicomponent products mentioned in the examples had

  specific surface areas in excess of 18 m2 / g.

  The calcination results in a further decrease in the specific surface area. This, for the reasons

  already described, will lead to the formation of aggregated products.

  In the current application, US Pat. No. 859,577, multicomponent powders having the general formula Ba (1-x-x'-X "MxMIxM x" Ti (, yy, _y |) AyA 'y Il n3 are disclosed. M indicates Pb (II), M 'indicates Ca (II), M "indicates Sr (II), A denotes Sn (IV), A' denotes Zr (IV) and A" denotes Hf (IV), x, x , xx "and y, y ', y" represent the atomic fractions of the divalent and tetravalent cations, respectively, each having independent values between 0 and 0.3 as long as the sum of (x + x' + x ') or (y + y '+ y ") does not exceed 0.4.The products having the above nominal stoichiometries were produced in a general hydrothermal process and were called coforms.Each of the coforms was characterized as

  being stoichiometric, dispersible, of less than

  below the micron and having a narrow particle size distribution. The doping of the barium titanate coforms has not been examined in the current application N 859 577. Therefore, barium titanate doped coforms containing calcium and / or lead or multiple substitutions of divalent and tetravalent cations , which are dispersible, spherical and sub-micron in size with narrow particle size distributions,

are absent from the prior art.

  Accordingly, the present invention has as its main object a sub-micron sized, dispersible doped titanate coform with

  a narrow particle size distribution.

  Another object of the present invention is to produce a wide variety of BaTiO3-doped compositions, BaTiO3 having particle sizes.

  in the range of 0.05 to 0.4 micron.

  Another subject of the present invention is a composition based on doped barium titanate having

equiaxed primary particles.

  Another subject of the present invention is compositions based on doped barium titanate which are

  substantially free of grinding agents.

  Another subject of the present invention is compositions based on doped barium titanate where all the constituents are in an intimate mixture on the

the particle size.

  The present invention relates to a wide variety of barium titanate dispersible, spherical coforms that are substantially spherical, intimately admixed with sub-micron particle size, and narrow particle size distributions. In an important embodiment of the present invention, the doped barium titanate-based coform is represented by the general formula XBa (lx) Cax, O.YTi (1yy, y,) SnyZyHfy ,, O2.zD o X, Y and Z are coefficients, where X and Y have a value between 0.9 and 1.1 and Z has a value greater than zero and smaller than 0.1, y, y 'and y "have independent values included between zero and 0.3, the sum of y + y '+ y "is smaller than 0.4, x' is greater than zero and smaller than 0.4 and D is one or more

doping oxides.

  In another important embodiment of the present invention, the doped barium titanate coform is represented by the general formula XBa (1-x) PbxO.YTi (1-yy, _y, ") SnyZry, Hfy, O2. ZD o X, Y and Z are coefficients, X and Y having a value between 0.9 and 1.1 and Z having a value greater than zero and smaller than 0.1, y, y 'and y "have independent values between zero and 0.3, the sum of y + y '+ y "is smaller than 0.4, x is greater than zero and smaller than 0.4 and D is

or more doping oxides.

  In another important embodiment of the present invention, the barium titanate coform is represented by the general formula XBa (1xx, _x,) PbxCa Srx, YTi (1-yy 'y ") SnyZrHf y, O 2. ZD o X, Y and Z are coefficients, X and Y having a value between 0.9 and 1, 1Aand Z has a value greater than zero and smaller than 0.1, X, x ', x ", y, y 'and y "each have independent values greater than zero and smaller than 0.3, the sum of x + x' + x" is smaller than 0.4, the sum of y + y '+ y "is smaller

  that 0.4 and D represents one or more doping oxides.

  Each of the doped barium titanate-based coforms of the present invention has the same unique physical properties. The average primary particle size of the barium titanate doped coforms is between 0.05 and 0.4 microns. On the other hand, the average particle size determined by image analysis is comparable to the average particle size determined by sedimentation, demonstrating that the coforms are dispersible. The size distribution curve of the doped coform particles has a quartile ratio smaller than or equal to 2.0, which establishes that the doped titanate coform coforms have a fairly narrow particle size distribution. In addition, the fact that all submicron-sized and dispersible doped barium titanate dielectric compositions of the present invention can be produced by a single general hydrothermal process is important. The invention will be better understood, and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory which will follow made with reference to the accompanying schematic drawings given solely by way of example

9 26 193 7

  illustrating several embodiments of the invention and in which: FIG. 1 is an electron micrograph of transmission at a magnification of 50,000 of a multi-dopant complex coform of submicron size and dispersible according to the present invention having for the general formula 1.02Ba 0.811Pb 0.105Ca 0.8081Sro 00.30 Tio 832 Sn 0.074Zr 0.09402 0.012CoO.0.0009MnO.0.005Nb205; and FIG. 2 is a transmission electron micrograph at a magnification of 50,000 of a single dopant complex barium titanate coform having the general formula 0.998Ba, 792Pb 104Ca 0.98Sr 0.006. Ti 0.831Sn 0.070Zr 0.09902 '0.03Co0 which has a morphology substantially similar to the

  morphology of the doped complex coform of FIG.

  The preferred embodiment of the present invention is a doped coform of the general type XBa (1-x-x'-x ") PbxCax, Sr xO.YTi ly-yy,") SnyZryHfy. 02-ZD o X, Y and Z are coefficients for the divalent, tetravalent and dopant cations, X and Y having a value of between 0.9 and 1.1, and better still between 0.95 and 1.05 and Z has a value of value from more than zero to 0.1 and better from more than zero to 0.05, x, x ', x "represent the fractions

  of divalent cation atoms and have independent values

  dantes between more than zero and 0.3 and more preferably between more than zero and 0.2 and the sum x + x '+ x "has a value between more than zero and 0, 4 and better between zero and 0 , 3, y, y 'and y "represent the fractions

2619370

  atoms of tetravalent cations and have independent values

  between more than zero and 0.3 and more preferably between more than zero and 0.25 and the sum of y + y '+ y "has a value between more than zero and 0, 4 and better between more than zero and 0.3 represents the doping oxides different from

the barium titanate coform.

  Preferably, the fine, dispersible, sub-micron size powder of the present invention is a doped barium titanate coform having a tetravalent metal ion substitution and divalent between more than zero and 30 mole percent. The divalent barium ion may be partially replaced by lead, calcium, strontium or mixtures thereof. In addition, the tetravalent titanium ion can be partially replaced by tin,

  zirconium, hafnium or mixtures thereof.

  The barium titanate compositions are doped with small amounts of one or more of a variety of dopants including oxides of lanthanides, cobalt, manganese, magnesium, scandium, yttrium, antimony, bismuth, zinc, cadmium, aluminum , boron, tungsten, chromium, nickel, molybdenum, iron, niobium, vanadium, tantalum, copper, silicon and their mixtures. The amount of the doping oxide or oxides contained in the coform is between more than zero and 10 mole% and preferably between more than zero and 5 mole%. Regardless of the dopant or combination of dopants used in the barium titanate coform, the barium titanate compositions are uniquely identified by the above morphological characteristics. Therefore, both the single-dopant coforms and the multi-dopant barium titanate complex coforms consist of substantially spherical and dispersible particles having a particle size.

  between 0.05 and 0.4 micron with a distribution

narrow size.

  The preferred attempt to produce doped barium titanate coforms is to intimately mix the dopant or dopants with the tetravalent hydric oxide or oxides. Intimate mixing can be accomplished by any of a wide variety of methods. Dopants can be coprecipitated with tetravalent hydric oxides. Alternatively, the dopants can be precipitated as hydric oxides of high surface area, washed and then combined with tetravalent hydric oxides. Finally, since the dopants can be precipitated in alkaline media containing Ba (II), their solutions, preferably either in the form of acetate salts, formates or nitrates or ammonium salts

  can be added to tetravalent hydric oxides.

  The slurry of the hydric oxides and dopants is hydrothermally treated with oxides or hydroxides of lead and / or calcium at temperatures up to 200 C. Then, the slurry is cooled to a temperature between 60 and 150 C. A solution of barium hydroxide or hydroxide hydroxide partially replaced by strontium hydroxide, heated to a temperature between 70 C and 100 C is added at a constant rate, in a period of time of 0.1 to 12 minutes, at the porridge

  of the divalent insoluble cation, of the tetrahydric

  are worth and doping. The slurry is maintained at the addition temperature for 10 to 30 minutes and then is heated to a temperature between 120 and 225 C to ensure that the required degree of reaction of the water oxide with

  the soluble divalent cation hydroxide will occur.

  Primary particle size and distribution

  the size of the coforms produced by the hydro-

  are the same, that the doped titanate coform coforms simply contain a single dopant or on the contrary several dopants. This becomes easily apparent from the transmission electron micrograph of the complex multi-dopant coform

  1.02Bao 811Pbo 10, 15Cao 0.81Sro0.0030.TiO, 832Sno0.074Zr 0.94202-

  0.012CoO.0.009MnO.0.005Nb205, of Figure 1 which shows

  the presence of substantially spherical primary particles

  predominantly simple, with a

12 2 6 1937 0

  primary particle size of 0.20 microns with a quartile ratio of 1.29, indicating that the product has a narrow primary particle size distribution. A comparison of the barium complexed complex barium titanate coform with FIG. 1 with an electron micrograph of transmission of a coform of barium titanate with a single dopant 0.998Ba0.792Pb o0.10io4Cao0.098Sro, 0060. Tio, 831Sno, 070Zr 0.09902 0.03Co0, of Figure 2, indicates that the morphologies of each of the barium titanate compositions are very similar. This is best highlighted by the image analysis results which show that the product of Figure 2 has a primary particle size of

  0.18 microns and a quartile ratio of 1.26.

EXPERIMENTAL PROCESS

  To evaluate the physical and chemical properties of doped barium titanate-based coforms for

  the present invention, a wide variety of laboratory tests

  This has been accomplished. Reagent grade chemicals or their equivalents have been used all the time. The Ba (OH) 28H 2 O products used contained either about 1.0 mole or 0.3 mole% Sr. tends to focus in the product. All Ba (OH) 2 solutions, maintained between 70 and 90 C, were filtered

  before use to remove any carbonate present.

  CaCO3 was calcined at 800 ° C to give CaO. The latter compound was contacted with water to give Ca (OH) 2. Tungsten was introduced as an ammonium tungstate solution. It was prepared by dissolving tungstic acid, WO 3 H 2 O in a solution heated to 2 moles of ammonia with stirring. The formed solution was metastable and was used little

after its preparation.

  Hydrogen oxides of TiO2, SnO2 and ZrO2 were prepared by neutralizing aqueous solutions of the respective chlorides with aqueous ammonia at ambient temperatures. The products were filtered and washed until chloride-free filtrates were obtained, determined by AgNO 3. Hydrogen Nb (V) oxide was likewise prepared by neutralizing a solution of Nb (V) fluoride. Mixed water oxides of TiO 2 and SnO 2, and TiO 2 and Sb 2 O 3, were likewise prepared by neutralizing solutions containing Ti (IV) and Sn (IV) and Ti (IV) and Sb (III) chlorides, respectively. A coprecipitate of water-soluble TiO2 and Bi203 was prepared by neutralizing an aqueous solution containing

  Ti (IV) chloride and Bi (III) nitrate. The

  centage of solids present in the washed wet loaves

  was determined after calcination for one hour at 900 C.

  Several wet loaves of each product were used

during the course of work.

  All the synthesis experiments have been completed

  in a 2 liter autoclave. To prevent contamination

  nation, all wet parts of the autoclave were either made of titanium metal or were coated with Teflon (trademark). All the synthesis experiments were performed in the absence of CO 2. of the

  filtered solutions of Ba (OH) 2, maintained at a temperature of

  About 80.degree. C. were introduced into the autoclave either by means of a high-pressure pump, or, for rapid addition, by discharging a solution of Ba (OH) 2, contained in a heated bomb, in 10 seconds in the autoclave using N2 at high pressure. The contents of the autoclave were agitated by a 25.4 mm diameter turbine-type stirrer operating at 1,000 to 1,500 rpm during the synthesis process. After synthesis, the resulting slurries were transferred to a pressurized filter without exposure to the atmosphere (to prevent formation

  BaCO3 insoluble), filtered and dried under vacuum at 100 C.

  Image analysis was used to determine the

  primary particle size of the product and the distribution

  primary size. They were determined in

  500 to 1,000 particles in a number of TEM (transmission electron microscopy) fields to obtain the equivalent spherical diameters of the primary particles. Two or more touching particles were visually disaggregated and individual primary particle sizes were measured. Equivalent spherical diameters were used to calculate the cumulative mass percentage distribution as a function of primary particle size. The average particle size, by weight, was taken as the size of the primary particles of the sample. The ratio of quartiles, OR, defined as the diameter of the top quartile (in weight) divided by the diameter of the bottom quartile, was taken as a measure of the width of the distribution. Monodisperse products have a RQ value of 1.0. Products with QR values between 1.0 and 1.5 were classified as having narrow size distributions; those with RQ values between 1.5 and about 2.0 were classified as having moderately narrow size distributions while those with RQ values larger than about 2.0 were classified as

  having large size distributions.

  Experience has indicated that doped coforms can be classified as having narrow, moderately narrow and broad size distributions by visual examination of TEM. Based on this experience, visual examination was used to classify the particle size distribution of the products of this work. Since the vast majority of the doped coforms produced had narrow size distributions, in this work the average size of the primary particle was reliably determined by sizing 20 to 30 particles in the micrographs. Quantitative and semi-quantitative

  Quantitative size measurements indicated that doped titanate-based coforms had primary particle sizes between 0.05

and 0.4 micron.

  Particle size was also calculated from surface areas determined by nitrogen uptake. In these calculations, the densities of the products were calculated from the composition of the powders and the densities, found in the literature, of the pure component perovskites. As the quantities of dopants in the samples are small, and as the dopants, typically, have densities that are not very different from those of the perovskites of interest, the effect of the dopant on the

  product density was intentionally ignored.

  The error introduced by this approximation is small.

  It should be mentioned that an exact match between the particle size determined by microscopy and surface area can only be expected for monodisperse spherical powders. As the distribution expands, the degree of sphericity decreases and

  the surface roughness of the particles increases, the difference

  The difference between the particle sizes determined by the two techniques increases. Thus, in real systems, the particle size determined by microscopy is typically larger than the size calculated from the surface area. In this work, agreement with a factor of two between the two size measurements was taken as evidence that the amounts of the fine size precipitates associated with the particles were small. Dispersibility of the product was determined by comparing the primary particle sizes and size distributions determined by the image analyzes with comparable values determined by sedimentation processes. The sedimentation process

  gives the Stokes diameter of a particle which

  closely corresponds to the spherical equivalent diameter

  undermined by image analysis. In this work, a Sedigraph Micromeritics (Norcross, Georgia, USA) was used to determine cumulative mass percentage distributions in terms of Stokes diameters from which

16 26 1937 0

  calculated the mean diameters of Stokes and the values

from QR.

  Before sedimentation, the powders were dispersed by a 15 to 30 minute sonification in isopropanol containing 0.12% by weight of Emphos PS-21A (Witco Organics Division, 520 Madison Avenue, New York, USA) as a dispersant.

  The particle sizes determined by sedimentation

  image analysis depend on different principles.

  For this reason, an exact match of size by these two methods is not always obtained. Moreover, as already noted, in image analysis, the touching particles, some of which can be glued together, are visually disintegrated. In the sedimentation process, both touching and bound particles act as simple entities. These entities occur both because of the existence of binding (i.e. clamping) between some of the primary particles forming cemented aggregates which can not be easily broken during the sonication process and because of the stability of the dispersion which is far from optimal, which leads to some flocculation. In this work, agreement with a factor of two between mean weight sizes, determined by image analysis and sedimentation, was taken as an indication that the product was dispersible. Similarly, it can be expected (and found) that the QR values determined by sedimentation are larger than those found by image analysis. It is reasonable to assume that at optimal dispersion conditions, the value of QR will be between the values determined by image analysis.

  and by sedimentation. In this work, the additional criterion

  used to determine dispersibility was that the QR values of the sedimentation powders

are smaller than 2.0.

  A qualitative process was also used to determine dispersibility. Experience from this work has shown that products can be classified as dispersible if the mass of primary particles in TEM is present as single particles. This qualitative determination of dispersibility will satisfy the quantitative criteria described above to characterize

dispersibility.

  The uniformity of the sample was determined by scanning electron microscopy having

  an X-ray analysis capability dispersing energy.

  The composition of several primary particles has been determined. the product was judged to be uniform, on a particle size scale, if at least% of the particles contained all the constituents of the powder. In practice, when scanning electron microscopy was performed, the criterion was always met. On the other hand, the quantities of the various constituents, although not quantified, appeared, by the peak intensities, to be reasonably comparable (within the limit).

  80%) on a particle-by-particle basis.

  The composition of the product was determined by elemental analysis using inductively coupled plasma spectroscopy, IPC, after dissolution of

  the sample. The precision of the analyzes for the constitutions

  Major killers were about + 2%. The accuracy of the results for the minor items was smaller than this figure. Atomic relationships. Ba (II) / Ti (IV) samples that predominantly included BaTiO3 were also determined by X-ray fluorescence. These ratios are somewhat more accurate than those determined by solution analysis and were used.

where possible.

  The doped barium titanate coforms according to the present invention comprise coforms having a partial substitution of the bivalent divalent lead or calcium. Doped coforms also include coforms where divalent barium is partially replaced by mixtures of lead and calcium or mixtures of lead, calcium or strontium. Partial replacement of the tetravalent titanium cation with tin, zirconium and hafnium is also within the scope of the invention. As shown by our request for

  N 859 577, irrespective of the particular substitution

  divalent or tetravalent cation, the characteristics

  Morphological ticks of barium titanate coforms are the same. Consequently, the nonlimiting examples which follow only comprise more complex barium titanate coforms and are intended to give teachings equally representative of the morphological characteristics of the doped barium titanate coforms.

  lead and calcium barium titanate and their modifications

  cations with tetravalent cations.

EXAMPLE 1

  A series of coforms containing a single dopant was prepared by heating, from room temperature to 200 ° C, in about 70 minutes, 0.64 liters of a vigorously stirred slurry containing 0.167 moles of TiO 2, 0.066 moles of Sn, 0. , 02 moles of ZrO 2, 0.022 moles of PbO, 0.022 moles of CaO and 0.006 moles of added doping salt in the form of a nitrate. The slurry was cooled to 120 ° C. and 0.46 l of a solution of Ba (OH) 2 heated between 70 ° and 90 ° C., containing about 40 ° C., was added to the slurry in 3.0 + 0.2 minutes. 0.21 moles of Ba (OH) 2. The temperature of the resulting slurry was maintained at 120 ° C for about 30 minutes and then heated to 200 ° C in about 30 minutes. The slurry samples were filtered and dried and then the surface area, the

  chemistry and morphological characteristics.

26193 7

  Atomic ratio in solids Dopant Ba Pb Ca Sr Ti Sn Zr Dopant Co (II) 0.790 0.104 0.098 0.006 0.831 0.070 0.099 0.030 Mn (II) 0.819 0.107 0.105 0.006 0.828 0.072 0.100 0.030 The (III) 0.802 0.100 0.085 0.006 0.841 0.080 0.087 0.027 Cr (III) 0.792 0.102 0.098 0.006 0.830 0.072 0.098 0.032 Ratio Area Particle Size Dopant Distribution X / Y (m 2 / g) TEM Size Area Co (II) 0.998 10.8 0.09 0.18 Narrow Mn (II) 1.037 12, 4 0.08 0.15 Narrow (III) 0.993 10.9 0.09 0.19 Narrow Cr (III) 0.998 10.9 0.09 0.19 Narrow Concentrations of dopants and Tetravalent hydric oxides in the filtrates were all below the detection limits of the equipment (minus -4 of 1 x 10 4 mol / l). It can therefore be assumed that these metals were almost quantitatively incorporated into the solid phase. The micrographs showed that the particles of the product were substantially spherical and submicron in size. The particle size determined from the surface area was in agreement, within a factor of two, with the particle size determined by microscopy, indicating that little

  Fine-sized matter was associated with particles.

  All doped coforms are classified as dispersible. Visual TEM examination of the cobalt-doped product indicated a quartile ratio of 1.26. The TEMs of the other products were determined by eye and

  are shown to have similar size distributions.

  A quantitative determination of dispersibility, using the sedimentation process, was obtained from the manganese doped product. This process shows that the product has a particle size of 0.21 micron, a value that is well in agreement with the particle size obtained from TEM, and a quartile ratio of 1.69. These quantitative data confirm that the product is dispersible.

EXAMPLE 2

  Complex coforms containing three dopants were prepared by hydrothermal treatment using comparable amounts and sources of the tetravalent hydric oxides and alkaline earth cations and Pb (II) used in Example 1. 0.002 moles of each dopant were added as nitrate salts or, in the case of niobium, in the form of wet Nb (OH) 5 bread, in the tetravalent hydric oxide slurry before addition of the barium hydroxide. After the hydrothermal treatment process, it was found that the ratios of tetravalent and divalent atoms in the solid phase were comparable to those of Example 1 and are not reported here. Mole ratio Ratio Area Particle size doping oxides 2 (microns) Perovskite dopant X / Y (m / 9) TEM range Co (II) Nb (V) 0.031 1.035 10.0 0.10 0.20 Mn (II) Cr (III) Co (II) 0.024 1.034 12.6 0.08 0.15 Al (III) About 50 to 60% of Al (III) related to the filtrate, and accordingly, the molar ratio of these oxidation oxides to perovskite, that is, the value of the

  coefficient Z, for the chromium-cobalt doped coform

  aluminum, was smaller than for the cobalt-niobiummanganese doped coform. All products seemed to be

  substantially spherical, dispersible and had.

  narrow distributions of size. Image analysis demonstrated that the cobalt-niobium-manganese doped coform had a primary particle size of 0.20 micron

  and a quartile ratio of 1.29. Sediment studies

  tation showed that the product had a particle size of 0.26 microns and a quartile ratio of 1.67. These quantitative measurements confirm the qualitative determinations that the products are dispersible and have narrow particle distributions. On the other hand, the agreement within a factor of two between particle size determined by microscopy and surface area calculations also indicates dispersibility. The coform of

  complex barium titanate doped with cobalt-niobium-

  manganese was subjected to STEM analysis. All particles were found to contain barium, lead, calcium, strontium, titanium, zirconium, tin, manganese, cobalt and niobium in roughly comparable amounts. The results from STEM show that the complex multi-core coforms of barium titanate are homogeneous on a scale of

size of the particle.

22 2619370

R E V E N D I CA T I 0 N S

  1.- Coform based on barium titanate dope,

  characterized in that it comprises particles

  spherical elements having the formula XBa (lx,) CaxO.yTi (11-y-yy ") SnyZrytHfy" O2.ZD where X and Y have values between 0.9 and 1.1, Z has a value greater than zero and smaller than 0.1, y, y 'and y "have independent values between zero and 0.3, the sum of y + y' + y" is smaller than 0.4, x 'is larger that zero and less than 0.4 and D is at least one doping oxide, where the average primary particle size of the doped coform is

between 0.05 and 0.4 micron.

  2. Co-form based on doped barium titanate, characterized in that it comprises substantially spherical particles having the formula XBa (lx) PbxO.YTi (lyy) SnyZryHFyO2.ZD, where X and Y have values between 0.9 and 1.1, Z has a value greater than zero and smaller than 0.1, y, y 'and y "have independent values between zero and 0.3, the sum of y. + Y' + y "is smaller than 0.4, x 'is greater than zero and smaller than 0.4 and D is at least one doping oxide, o the average primary particle size of the doped coform is included

between 0.05 and 0.4 micron.

  3. Coform based on doped barium titanate, characterized in that it comprises substantially spherical particles having the formula XBa (lxx-x. ") PbxCaxSrx. OYTi (lY-y'_y") SnyZry, Hfy O2.ZD o X and Y have values between 0.9 and 1.1, Z has a value greater than zero and smaller than 0.1, x, x ', x ", y, y' and y" each have independent values greater than zero and smaller than 0.3, the sum of x + x '+ x "is smaller than 0.4, the sum of y + y' + y" is smaller than 0.4 and D is at least one doping oxide, wherein the average size of a primary particle of the doped coform is between 0.05 and

0.4 micron.

  4.- Coform doped according to any one of

  preceding claims, characterized in that the at

  at least one dopant oxide D is selected from the group consisting of oxides of lathanides, cobalt, manganese, magnesium, yttrium, bismuth, aluminum, boron, tungsten, niobium, chromium, nickel, molybdenum, iron, antimony, vanadium, tantalum, copper, silver, zinc, cadmium,

silicon and their mixtures.

  5.- Coform doped according to any of the

  1, 2 or 3, characterized in that the

  Primary particle sizes, determined by image analysis and sedimentation, are in agreement in the

limits by a factor of two.

  6.- Doped form according to any of the

  Claims 1 or 2, characterized in that the coform

  doped to a narrow particle size distribution determined by image analysis and the primary particle size distribution curve of the a-doped coform

  a ratio of quartiles smaller than or equal to 2.0.

  The doped co-form according to claim 3, characterized in that it has a narrow particle size distribution determined by image analysis and the primary particle size distribution curve for the doped coform at a ratio of quartiles plus small

than or equal to 1.5.

  8.- Coform doped according to any one of

  1, 2 or 3, characterized in that the

  X / Y ratio is 1,000 + 0,015.

  9.- Coform doped according to any one of

  1, 2 or 3, characterized in that the

  X / Y ratio is between 0.95 and 1.1.