CA1278183C

CA1278183C - Dielectric compositions

Info

Publication number: CA1278183C
Application number: CA000508122A
Authority: CA
Inventors: Ian Burn
Original assignee: EI Du Pont de Nemours and Co
Current assignee: Tam Ceramics LLC; EIDP Inc
Priority date: 1985-05-01
Filing date: 1986-05-01
Publication date: 1990-12-27
Anticipated expiration: 2007-12-27
Also published as: EP0200200B1; DK198286A; GR861168B; EP0200200A2; US4640905A; JPH0316961A; DE3688098T2; JPH0653606B2; DK198286D0; DE3688098D1; EP0200200A3

Abstract

DIELECTRIC COMPOSITIONS
ABSTRACT
The invention is directed to barium titanate-based densified dielectric bodies corresponding to the formula (1-X)[(Ba1-xPbx)(Ti1-(u+v)ZruSnv)O3] +
X[A(Zn1/3Nb2/3)O3] + Y[F], wherein A is selected from Pb, Ba and mixtures thereof.
X = 2.5 to 11.5% by weight, = 1.0 to 5.0% by weight, u = 0 to 0.125, v = 0 to 0.125, x = 0 to 0.125, u+v = 0.015 to 0.125, and F is a manganese-doped zinc borate flux.

Description

S~L~3 TlT~E EL-0195A
DI~LECTRIC COMPOSITIONS

Field of InYention ThQ ~nvention relate~ to dielectric compo~itions and parti~ularly to low-fi~ing temperature dielect~ic composition6.

Backqround of the Invent~on Because o~ their high volumetric efficiency and thus their 8mall size, multilayer ceramic capacitors (~LC's) a~e the most widely used orm o~
ceEam1c capacitors. These capac~to~ are fabricatea by stackin~ aad co~ic~ng thi~ ~heets of ceramlc dielectLic on which an appropriate electrode patte is printed. Each patterned layel i~ of~set ~rom the ad30ining layer~ in 8uch manner that the electlode layers are expo~Qd alternately at each end o~ th~
a~se~blage. The e~po~ed edges of the elect~ode pattern ars eoated with a conducti~e ~aterial which 2$ electrlcally connect8 all the layer~ of the structure, thu~ forming a group of parallel connect~d capacitor~ w~thin the laminated structure.
Capacitor~ of th~ type are feequently re~erred to a~
monolithic caeaci~or6.
The thin sheets of cer~mic dielectric used fo~ ~he fabLicat1on of MLC'~ are compri~ed o~ a layer of inely divided dlelectric particle~ which are bound together by an organic poly~eric matecial. The un~i~ed ceramic can be p~epared by 81ip casting a ~lurry o~ the dielectric part~cles di~per~ea in a ~olutio~ o~ polyme~, pla~ticizer and ~olvent onto a ., ~,~,~ .

, .

~2~ 33 carrier ~uch as polypropylene, Mylar~ polyester film or stainless steel and then adju~ting the thickne~ of the cas~ film by passing the ca~t ~lurry under a doctor blade to form a thin "green tape".
Metallization6 u6eful in producing conductor6 for multilayer capacitor~ normally comprise finely divided metal particles applied to green tape in the form of a di6persion of such particles in an inert liquid vehicle. ~lthough the above-described "green tape" proce66 i6 more widely u6ed, thece are neverthele6s other procedure6 with which dielectric composition6 of the invention can be u6ed to make MLC's. One technique is the so-called "wet proce66". In one aspect, this may involve passing a flat ubstrate through a falling sheet of dielectric 81ip one or more time6 to build up a dielectric layer (see Hurley et al., U S. Pat. No.

3,717,487).
Another method of making MLC's involveE
forming a paste of the dielectric material and then alternately Bcreen printing the dielec~ric and metal layers with intervening drying step6 until the de6igned 6tructure i8 compleee. A ~econd electrode layer i6 then printed atop the dielectric layert and the entire as6emblage i8 cofired.
~ nolithic multilayer capacitors are typically manufactured by cofiring barium titanate based formulations and conductive electrode material6 in oxidizing atmospheres at temperature6 of lZ00-1400~C. Thi6 process yields durable, well sintered capacitors with high dielectric constant, e.g., greater than 1000. However, firing under these conditions requires an elect~ode material with high melting point, good oxidation resis~ance at elevated temperatures, sinterability at the maturing temperature of the dielectric, and minimal tendency ~78~

to interact with the dielectric at the sintering temperatuce. The6e requirements normally limit the choice of electrode mate~ial6 to the noble metal~
platinum and palladium, or to alloys of platinum, palladium and gold. See also U.S. 3,872,360 to J. L.
Sheard which i6 directed to the preparation of monolithic multilayer capacitors.
Several attempt6 have been made to reduce the maturing temperature of dielectric~ by the use of "6intering aids". Addition6 of bismuth oxide or bentonite to barium titanate lowers the maturing temperatu~e to about 1200C. (Nel60n et al. U. S.
Pat. No. 2,908,579). Maturing temperature6 of 1200-1290C may be attained by addition of phogphate~ to titanates as de6cribed in Thurnauer et al. U.S. Pat. No. 2,626,220. However, in each of these cases, the decrease in maturing tempera~ure is not ~ufficient to permit the use of cofired silvel electrode~, and dielectric properties are often 29 degraded.
Another technique for lowsring the ~inteeing temperature of titanate-ba~ed dielectric~ is by mixing high temperature ferroelectric phase6 (titanates~ zirconate6, etc.) with glasse6 which mature at relatively low tempera~ures. Examples of this approach are given in Maher U.S. Pat. No.
3,619,220, Burn U.S. Pat. No. 3,638,084, Maher U.S.
Pat. No. 3,682,766, and Maher U.S. Pat. No.
3,811,937. The drawback of this technique is that the dilution effect of the glass often cause6 the dielectric constant of the mixture to be relatively low.
Bouchard has very succe6sfully approached ~he problem of dielectric compositions having low firing temperature6 and dielectric constant6 a6 high a6 6000 for use in Z5U-type capacitors by the use of %~
lead-ba~ed diele~tri~s in~tead of barium titanate.
~hese sub~tituted lead tlt~nate ~ompo~itlon~
coere~pond to the ~ollowing formula:
x l-XTi3)a(PbMg~E3o3)b~ whe~eiD, x n 0-0 ~ r ~ O . 4~-Q ~ 55 ~1 0.35-0.5 ~ ~1 0~55-O~
b . 0.5~0.65 ~(r~) .. 1, and ~(a~b) ~ 1.
Such ~ate~ials are disclosed in U.S. Patents 40048,546, ~,063,341, and 4,228.482, all to Bouchard More recently, ~homa~ in U.S. Patent 4,582,812, has improved upon the .
Bouchard dielectric composit~on~ to make the~ mo~e guitable for Z5U-type servic~. In ~hese, ~e Bouch~rd compo~itions a~e doped with small amounts of trans~ion metal oxide~ and zlrcona~e~ and ~tannates o ~adm~u~ and zin~.
Notwith~ta~ding the substantial p~ogress ~oward ~t~aini~ hig~er di~lectri~ co~ant8, th~
electronics industry foregees the ~eed for dielect composit~on~ with lo~ PbO conte~t~ (i,e. <10% w~.~
b~i~q ~111 highe~ ~ielect~ie c~ta~s ~X~ ~ the 25 order 9~ 8000 and even blgher, ~hi~ ~evert~e~e~ ca~
still be u~ed ~ith ~o~Yen~cional ~ilver-contaitliag electrode~ such a~ 30/70 palladium/~ilver ele~trodes.

Br~e~ Descr~ption of the~ vention The invention i~ therefore direc~Qd in its primary aspect to a composit~on for ~orming a den~i~ied dlelectric body at low ~iring temperature~
comprisi~g a mixture o ~inely d~vided pa~ticles o~:
BaTiO3, ~b) ~Znl/3Nb2/3)o3~

~ J

~78~3 lc) A Curië point 6hiPter 6elected from BaZrO3, PbZrO3, BaSnO3, PbSnO~ and mixtures thereof, (d) a manganese-doped zinc borate flux (F) and/or oxide precursors thereof, the proportion~ of (a) - (d) being ~ub6tan~ially equivalent 6toichiometrically to the formula:
(l-X)~(Bal_xPbx)(Til (u v)Zr Sn )O3] f ~ ( 1/3 2/3)3] ~ Y~F], wherein A i~
selected from Pb, Ba and mixtures thereof.
X = 2.5 to 11.5% by weight, Y = 1.0 to 5.0% by weight, u = O to 0.125, ~ = O to 0.125, x = 0 to 0.125, and u~ = 0.015 to 0.125.

In these compo6itions, the metal zinc niobate acts both a~ a fluxing additive and as a Curie point depre~sant for the BaTiO3. This latter behavior is quite unexpected since lead zinc niobate, for example, has a Curie temperature of 140C which i~ higher than the Curie temperature of BaTiO3.
In a secondary aspect, the invention i~
directed to a method for forming a monolithic capacitor comprising the 6equential step6 of (1) applying a layer of conductive electrode material dispersed in organic medium to each of a plurality of layers of the green tape made from the above-described composition; t2) laminating a plurality of the electrode-layered green tape~ to Porm an assemblage of alternating layer~ of green tape and electrode material: and (3) firing the a~emblage of step (2) at 1000-1150~C to remove the ~7~ 3 organic medium and organic binder therefrom and to sinter the conductive electrode material and the dielectric material.
In a ~hird aspect, the inven~ion i~ directed to a ceramic capacitor compri6ing a dielectric ceramic body having a dielectric constant of at least 8,000 and at least two spaced metal electrode~ in contact with the ceramic body which consi~t6 essentially of the above-described composition which has been fired at 1000-1150C to effect densification of the dielectric solids and sintering of the metal electrode~.
In a fourth aspect, the invention is directed to a tape ca~ting composition comprising the above-described dielectric composition disper~ed in a 601ution of binder polymer in a volatile nonaqueous 6 olvent.
In a f ifth a~pect, the invention i6 directed to a method of ~orming green tape by ca6ting a thin layer of ~he above-described dispersion onto a flexible subs~rate, ~uch a~ a ~eel belt or polymeric film. and heating the cast layer to remove the volatile solvent ~herefrom.
In a sixth aspect, the invention i~ directed to screen-printable thick film compo~itions compri~ing the above-de~cribed dielectric compo6ition di6persed in organic medium.

Prior Art ~.S. 4,266,265 to Maher is directed to a method o~ making ceramic capacitor6 in which the precur~or dielectric powders are mixtures of alkaline eaeth metal titanates and cadmium silicate6. The alkaline earth metal titanates include barium-lead-titanate and barium-lead-titanate-zirconate which can be dop0d with donor atom~ such a~ Bi, Nb, Ta, Sb, W, La and U. The materials are fired at 1100~C.
U.S. ~,283,753 to Burn i8 directed to ceramic capacitor~ having dielectric constant~ of at lea6t 5,000 which are compri6ed of BaTiO3 doped with (a) large divalent ion~ selected from Ba, Pb, Sr and Ca; (b) 6mall tetravalent ions ~elected from Ti, Zr, Sn and Mn; (c) donor ions capable of having greater than ~4 valence selected from Bi, Nb, Sb, Ta, W and Mo; (d) charge compensating acceptor ions selected from Cd, Zn, Cu, Li and Na; and (e) glas6-forming ion6 6elected from B, Si, Ge, P and V. The6ematerials, which are 6aid to have dielectric con6tants of over 5,000, are fired at about 1100C to effect densification.
U.S. 4,335,216 to Hodgkins et al. is directed to dielectric ceramic compo6ition6 which are fired at 1000-1150C in which the precur~r dielec~ric pOWder~ are a mixture of BaTiO3, SrTiO3, BaZrO3, Tioz and MnO2 mixed with a gla~ frlt com~rising ZnO, SiO2, ~23~ PbO, Bi2o3 and CdO. The compo~ition6 aLe used to make multilayer ceramic capacit4rs.
U.S. ~,379,854 ~o Soong i6 directed to a dielectric compo6ition compri~ing finely divided par~icles of BaTiO3, SrZrO3, which function a~ a Curie point shifter, and Zno and B2O3 which are flux powders. The material~ are fired at 1000-1150C.
~.K. 2125028A to Ni6hioka et al. i6 directed to dielectric ceramic compositions sinterable at 1050-1200C compri6ing (a) 100 pbw of a main component corresponding to the formula (Bal xMex) (Til yMex,)O3 in which Me i~ Ca and/or Sr and Me' is Zc and/or Sn, and 5-~5 pbw, basis ta) of a secondary component (b) which is a mi~ture of 65-90%

PbTiO3, 1-10~ Pb5Ge3Oll and 1-30%
BiTi2o7. The materials are Pired at 1050-1360C.

Detailed Description of the Invention A. Dielectric Uaterials The BaTiO3 component of the composition of the invention i6 commercially available in appropriate particle 6izes. For the purpose of the invention, it is e~ential that the BaTiO3, a~ well as the other dielectric material~, have an average particle size of no more than 2.0 ~m and preferably no more than 1.5 ~m. An average particle ~ize of 0.4-1.1 i~ still further prefelred. On the other hand, when the average particle ~ize of the solids is below about 0.1 ~m, the particles become difficult ~o handle and are therefore less suitable.
The other oxide component~, i.e., the metal zinc niobate, the Curie point shifter and the flux, can be readily made by admixing finely divided palticles of the appropriate oxide~ or their precurfior~ and firing them in air. In the case of the metal zinc niobate and the Curie poin~ 6hifter, ~he compound6 are formed by firing at 800-1000C for about 5 hours which i8 BUf ficien~ time and temperature to get complete reaction oP the component oxide~, yet avoid exces~ive fiintering and too large particle 6ize. By the term "precursor" i6 meant compound6 which upon firing in air are converted to metal oxides. These include hydrate6, carbonates, hydroxides, nitrates, oxalates and alkoxide6.
Suitable fluxes are zinc borate6 in which the ratio of ZnO to B2O3 i~ 2-4 and mixture6 and precur60r6 thereo~.
In accordance with well-known gla6~-making practice, it will be understood that up to 50 mole %

~2~78~33 of the B203 can be replaced by SiO2, GeO2, A1203 or mix~ure6 thereof.
The fluxes used in ~he examples were prepared by calcining a mixture of ZnO, boric acid and ~nC03 at 700C for 18 hours and then milling.

B. Green Tape Castinn Solution As mentioned above, green ~apes of the dielectric composition of the invention are made by casting a di6persion of the dielectric material in a solution of polymeric binder and volatile organic solvent onto a flexible ~ubstrate, such as a steel belt or polymeric film, and then heating the cast layer to remove the volatile solvent therefrom.
The organic medium in which the ceramic solids are dispersed con~ists of the polymeric binder which is dis~olved in a volatile organic solvent and, optionally, other dissolved material~ 6uch a~
plasticize{s, release agent~, di&per6ing agent~, s~ripæing agents, antifouling agents and wetting agents.
To obtain better binding efficiency, it i8 preferred to use at least 5% wt. polymer binder for 95~ wt. ceramic solids. However, i~ iB fur~her preferred to use no more than 20% wt. polymer binder in 80% wt. ceramic solids. ~ithin the6e limits, it is desirable to use the least po~sible amount of binder vis-à-Yi6 fiolids in order to reduce the amount of organics which must be removed by pyrolysi6.
In the 2ast~ variou6 polymeric materials have been employed as the binder for green tape6, e.g., poly(vinyl butyral), poly(vinyl acetate), poly(vinyl alcohol), cellulo6ic polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, methylhydcoxyethyl cellulose, atactic . . .

~L27~33 1~
polypropylene, polyethylene, ~ilicon polymers su~h as poly(methyl siloxane). ~oly(methylehenyl siloxane), polystyr~ne, butadiene/styrene copolymer, poly~tyrene, poly(vinyl pyr411idon*), polyamide6, high molecular weight polyethers, copolymers of ethylene oxide and propylene oxide, polyacrylamide~, and various acrylic polyme~ such a~ sodium polyacrylate, poly(lower alkyl acrylates), poly(lower alkyl methacrylates) and various copolymers and multipolymers of lower alkyl acrylates and methacrylates. Copolymer~ of ethyl methacryla~e and methyl acrylate and terpolymers of eehyl acrylate, methyl meehacrylate and methacrylic acid have been previou~ly been used a6 binders for slip casting materials.
More recently, Usala, in Canadian Patent Application Serial No. 456,061, filed June 07, 1984, has disclosed an or~anic binder which is a mixture -of compatible multipolymers of 0-100~ wt. Cl 8 alkyl methacrylate, 100-0% wt. Cl_8 alkyl acrylate and 0-5% wt. ethylenically unsaturated carboxylic acid or amine. Because the polymers permit the use of minimum amounts of binder and maximum amounts of dielectric solids, their use is preferred with the dielectric composition of this invention.
The solvent component of the ca~ting solution iB chosen 80 a~ to obtain compleee ~olution of the polymer and sufficiently high volatility to enable the solvent to be evaporatad from the dl~persion by the applicaeion of relatively low level~ of héat at atmo~pheric pressure. In addition.
the solvent mu~t boil well below the boiling point ~27~ 33 and decompo~ition temperature of any other additive~
contained in the organic medium. Thus, solvent~
having atmospheric boiling poin~ below 150C are u~ed most frequently. Such ~ol~ents include benzene, acetone, xylene, methanol, ethanol, methyl ethyl ketone, l,l,l-trichloeoethane, tetrachloroethylene~
amyl acetate, 2,2,4-~riethyl pentanediol-l,~-monoiEo-butyrate, toluene and methylene chloride.
Frequently, the organic medium will also10 contain a small amount, relative to the binder polymer, of a plasticizer which serve6 to lower the glass transition temperature (Tg) of the binder polymer. However, the u6e of such material6 ~hould be minimized in order to reduce the amount of organic material~ which must be removed when the films ca6t therefrom are fired. The choice of plasticizers is, of course, determined primarily by the polymer ~hich must be modified. Among ~he pla6ticizers which have been u~ed in variou~ binder ~yætems are diethyl phthalate, dibutyl phthalate, octyl phthala~e, butyl benzyl phthalate, alkyl phosphate~, polyalkylene glycols, glycerol, poly(ethylene oxide6~, hydroxyethylated alkyl phenol, dialkyldithiophos-phonate and eoly(isobutylene). Of the~e, bu~yl benzyl phthalate i8 most frequently used in acrylic polymer sy6~ems because it can be u~ed effectively in rela~ively small concen~ration~.

C. Thick Film Paste O~ten it may be desired to apply the compo~ition~ of the inventisn as a thick film paste by such technigues as screen printing. When the dispersion is to be applied as a thick film pa6te, conventional thick film organic media can be used 35 with appropriate rheological adjustmen~s and the u~e ~2~ 83 of lower volatility 601vent6. In this event. the composition6 must have appropriate viscosity ~o that they can be pas6ed through the s~reen readily. In addition, they should be thixotropic in order ~hat they set up rapidly after being screened, thereby giving good resolution. While the rheological properties are of primary importance, the organic medium i~ preferably formulated also to give appropriate wettability of the solids and the substrate, good drying rate, dried film 6trength sufficient to withstand rough handling and good firing properties. Satisfactory appearance of the fired composition is also important.
In view of all the~e criteria, a wide variety of inert liquids can be used a6 organic medium. The organic medium for most thick film compo~itions i6 ty~ically a ~olution o~ resin in a ~olvent and, frequently, a solvent ~olution containing both re6in and thixo~ropic agent. The solvent usually boils within the cange of 130-350C.
Es~ecially suitable re~in~ for thi~ ~urpo6e are polymethacryla~es of lswer alcohols and monobutyl ether of ethylene glycol monoacetate.
The most widely used solvents for thick film applications are tecpenes such as alpha- or beta-terpineol or mixtures thereof with other solvents such a~ kerosene, dibutylphthalate, butyl cacbitol, butyl carbitol acetate, hexylene glycol and high boiling alcohols and alcohol esters. Variou~
combinations of these and other solvents are formulated to obtain the desired visco6ity and volatility requirements for each application.
Among the thixotro~ic agents which are commonly used are hydrogenated castor oil and decivatives thereof. It is, of course, not alway~

~27~ 3 neces~aly to incorporate a thixotropic agent since the solvent~resin properties coupled ~ith the 6hear thinning inherent in any 6uspension may alone be suitable in this regard.
The ratio o~ organic medium to inorganic 601id6 in the dispersions can vary considerably and depends upon the manner in which the dis~ersion is to be applied and the kind of organic medium u6ed.
Normally, to achieve good coverage, the dispersions will contain complementally by weight 60-90% solid~
and 40-10% organic medium. Such disper6ions are usually o~ 6emifluid consi~tency and are referred to commonly as "pa6te6".
The pa~tes are conveniently prepared on a three-roll mill. The visco6ity of ~he pa6te6 i8 typically within the following ranges when mea6ured at room ~emperature on Brookfield viscometer6 at low, moderate and high shear rate~:
Shear Rate (Sec 1~ViscositY fPa.s) 0.2 100-5000 300-2000 Preferred 600-1~00 Most preferred 100-250 Preferred 2~ 140-200 Most preferred 3~4 7-40 10-25 Preferred 12-18 Most preferred l'he amount and type of organic medium (vehicle) utiliæed iB determined mainly by the final desired formulation viscosity and print thickness.

D. ~ itor Processinq As described above, many multilayer capacitors are fabricated by printing on electrode , ~2~ 33 metallization in the desired pattern upon a dielectric 6ub~trate which i6 a green tape. The printed dielectric ~ubstrate~ are 6tacked, laminated and cut to form the desired capacitor ~tructures.
The green dielectric material i6 then fired ~o effect removal o~ the organic medium from the electrode material and of the organic binder from the dielectric material. The removal of the~e materials i~ accomplished by a combination of evaporation and thermal decomposi~ion during the firing operation.
In some in6tance6 it may also be de6iLable to interpose a preliminary drying step prior to firing.
The thickness of the unfired green tape i8 typically about 1.2-1.3 mils and upon firing the thickness becomes about 0.9-1.0 mil.
~ hen firing the above-described capacitor a~8emblage~, it i8 preferred to employ a fiEst firing ~tep ;n which the a~semblage is heated 610wly ~0 100-550~C, which will be effective to remove all of the organic material without damage to the laminated a~emblage. Typically the organic burnout period i8 18-24 hour6 to a~6ure complete remoYal of organic~.
When thi6 has been completed, ~he as6emblage is then heated more rapidly to the desired 6intering temperature.
The desired sintering temperature i8 determined by the physical and chemical characteri~tic~ of the dielectric material.
Ordinarily the sintering temperature will be chosen to obtain maximum densification of the dielectric material. For the dielectric compo6itions of thi6 invention, the temperature will range from 1000 to 1150C. However, it will be recognized by tho~e ~killed in the art of fabricating capacitor~ that 35 maximum den6iEication i6 not alway6 needed.

~.2~ 33 Therefore, the term "sintering temperature" refers to the temperature ~and implici~ly the amount of time as well) to obtain the desired degree of den~ificatio~
of the dielectric material for the particular capacitor application. Sintering time~ also vary with the dielectric composition but ordinarily on the order of two hours at the 6intering temeerature i~
preferred.
Upon completion of ~intering, ~he rate of cooling to ambie~t temperature i6 carefully controlled in accordance with resistance of the component6 to thermal ~hock.
The following propertie6 which are relevant to the ability oP a given capacitor to function properly are referred to in the example~.

E. Te~t Procedure6 CaPa~itance Capa~itance i6 a mea6ure of the capability ~0 of a material to store an electrical charge expres~ed mathematically, C = RAN divided by t, where K i8 dielectric con~tant, A equal~ area overlap of electrodes, N i6 number of dielectric layers, and i~ thi~kne~s of dielec~ric layer.
The units of capacitance are farads or fractions thereof ~uch a6 microfarad6 (10 6 farad), nanofarads (10 9 farad) or picrofarads (1o-12 farad).
Di~sipation Factor Di66ipation ~actor (DF) i6 a mea6ure of ~he ehase difference between voltage and current. In a perfect capacitor the phase difference would be 90.
However, in practical dielectric sy6tem6, thi~ phase dif~erence is less than 90 by an amount a because of leakage and relaxation 1066es. In particular, DF
is the tangent of the angle a.

~278~3 Insulation Re~i~tance Insula~ion ReEi~tance (IR) is a mea~ure of the ability of a charged capacitor to withstand leakage in DC cur ent. Insulation resistance ~xpres~ed a~ ohm.farad~ (nF) i~ a con~tant for any given dielectric regardless of capacitance.
The following examples and comparative ~howings are pre6ented to illustrate the advantage of the present invention. In the examples and elsewhere in the ~pecification and claims, all parts, percentages, proportions, etc., are by weiqht, unle~6 otherwi~e ~tated.

EXAMPLES
Example l - PreParation of Materials A. Barium Titanates The barium titanates were commercial materials.
Fuji HPBT-l was used mainly but good results were obtained with an alternate material ~219-6) from the Tran6elco Division of Ferro Corporation. Typical particle ~ize di~tributions a~ determined with a Leed~ and Northrup particle size analyzer (Miccotrac) are given below:
Dlo D50 Dgo tmiccometers) Fuji HPBT-l 0.31 0.53 0.93 Transelco 219-6 0.42 0.9~ 2.35 B. Lead Zinc Niobate The lead zinc niobate was prepared by first ballmilling 65.9% PbO, Z6.1% Nb205 and 8.0% ZnO
(part6 by weight) in i~opropanol or other liquid for 5 hours with ZrO2 media. When dried, the mixed powders were calcined at 800C for 5 hours, and then * denotes trade mark ' ~, ' ' ' .

~2~ 33 ballmilled 16 hour~ to give a typical particle size (D50) of 0.9 micrometer.

C. PbZrO3 or PbSnO3 These additive6 were prepared by milling and calcining 6toichiometric amountfi of PbO with ZrOz or SnO2 under the 6ame condition~ a6 tho~e u~ed for the lead zinc niobate. Particle 8ize8 (D50) were typically 0.7 to 1.0 micrometer.

These were commercial powder6. The BaSnO3 tTranselco) was used as received, whereas the BaZrO3 wa6 premilled. Typical particle size6 were 0.9 to 1.1 micrometer.

E. ~rit/Ylu~
Detail6 of the preparation of the fluxe6 used in the invention are given in the example~ which follow.
Ceramic tape ~as made by ca~ting a milled slurry con~i~ting of 66.0 g bindeE 601ution ~Du Pont 5200) to the following mixtures of powder6: BO.O
BaTiO3 (Fuji HPBT-l)o 12.50 PbSnO3, 3.82 ~5 Pb(znl/3Nb2/3)o3~ 2.50 BaSnO3, and 1.50 mangane6e-doped zinc borate frit. The zinc borate frit con6ifited of 74.83~ ZnO, 21~35% B203 and 3. 82~ MnCO3 and was ~ade by calcining a mixture of ZnO, boric acid, and MnCO3 a~ 700C for 18 hour~
and then milling to a particle 6ize le~s than 2 micrometers. The ceramic tape wa~ cut and laminated into plates approximately 0.4 x 0.4 x 0.0Z5".
Following a bakeout 6tep in air at 750C to remove the organic binder, these plates were fired in a clo~ed alumina crucible at 1100C for 2-1/2 hour~.
AEter firing, the plates were electroded with sil~er ., ' ' . -lBpaste (Du Pont 6730) before measuring dielectric ~roperties a~ 1 kHz and 1.0 volt. The Curie ~emperature wa~ 35OC and ~he dielectric con~nt was 8400~500 with DF = 1.2%.

ExamPles 2, 3 and 4 Ceramic tape6 were made with the following ceramic composition (in parts by ~eight): B2.0 ~aTiO3 (HPBT-l), 6.0 Pb(Znl/3Nb2/3)O3, 5.5 PbZrO3 and 5.0 BaZrO3. to which varying amount~
of zinc borate frit were added. The 2inc borate frit wa~ made from a mixture of 45.4 wt. ~ ZnO, 23.0 wt.
boric acid, 11.7 ~t. % MnCO3 and 20.0 wt. ~ BaCO3 which was calcined 5 hour~ at 700C and ~hen milled to a particle ~ize of l.Z5 micrometer~. In the~e examples, BaCO3 was added with the MnCO3 to maintain cation ~toichiometry relative to the BaTiO3. ~ultilayer ceramic capacitors we~e made with 1.0 mil dielectric layers and 30 Pd-70 Ag electcodes for frit level~ of 1.25, 1.50 and 1.75 wt.
%. The~e capacitor~ were fired a6 in ~he previou~
example~ with the following re~ult6:
Cucie Exam- Frit Level Temp. IR
pl~ K DF(~) 1CL

2 1.25 9800 1.7010 14,000 (max3 3 1.50 8300 1.3510 9,500 ~ 1.75 8100 1.3510 ~,000 ~IR was variable, indicating marginal den~ification Example 5 Plate capacito~s were made as in Example 1 but with the following compo~ition: 87.0 BaTiO3 (HPB-T), 11.5 pb(znl~3Nb2/3~o3 and 1.5 ~inc borate frit, which was the ~ame as that u6ed in Example 2. When fired a~ in the previou6 examples, the Curie temperature ~as 35C and the dielectric con6tant at 25C wa6 as high a~ 7600, with DF =
0.8%. This compo6ition had marginal dielectric 0 constant for the application of this invention.
COMPOSITION SUMMARY
Exam- X x Y u v Mn02 Ple (wt. %) (mol) (wt. ~) (mol2 (mol) wt. %
1 3.9 0.0~7 1.52 - 0.108 0.043 2 6.1 0.041 1.270.0~8 - 0.13 3 6.1 0.041 1.520.088 - 0.16 4 6.1 ~.041 1.780.088 - 0.19 11.7 - 1.52 - - 0.1$

ExamPle MLC capacitors were made with the 6ame ba6ic ceramic compo~ition a6 Example 2 and by the 6ame method e2cept that Tcan~elco 219-6 barium titanate wa6 u6ed instead of HPBT-l and a few drop6 of acetic acid were added to the ceramic slip to improve di~per6ion. Experiment6 were carried out with 1.25 and 1.50% frit only. The capacitors were fired a6 described previously and had the following electrical re6ults.

~2~

1.25% Frit 1.50% Frit Capacitance (microfarad) 0.076 0.075 DF (1 Volt) 1.2 1.1 K 9000~500 8~00~200 Curie Temp. (C) 5 5 IR (QF) 15,000 8,500 ExamPles 7-12 Two further compo6itions were made by the procedure of Example 2 and each wa~ fired at three di~erent ~emperature~ to ob6erve the effact of sin~ering temperature on electrical propertie6. The com~o~ition and propertie~ of the6e material6 are given in Table 1 belo~.
Table 1 xam~le No. 7 8 ~9 comPosition of Ma~erials Fuji HPBT-l, % wt.~3.083.0 83.0 BaZrO3 4.0 4.0 4.0 Lead Zinc Niobate6.0 6.0 6.0 2S PbZrO3 5.5 5.5 5.5 Frit 1.5 1.5 1.5 Firin~ TemPerature, C1107 1093 1079 Electrical ProPertie~
30 K 10,000 9,200 9,100 DF, % 1.5 1.1 1.3 ~27~3~83 Table 1 (continued) ExamPle No. 10 11 12 _ Composition of Material~
Fuji HPBT-l, % wt.82.5 82.582.5 BaZrO3 4.5 4.5 ~.5 Lead Zinc Niobate6.0 6.0 6.0 PbZrO3 5.5 5.5 5.5 10 F~it 1.5 1.5 1.5 Firinq TemPerature~ C 11071093 1079 Electrical ProPerties R 10.300 9,0008.700 DF, % 1.2 1.1 1.0 The dielectric constant as well a6 the DF value of the dielectriç tended to be reduced as the ~intering temperature WaB lowered.

xample 13 The u~e of barium zinc nioba~e in the invention i~ illu~trated by the example in which 200 gram6 of BaCO3 were ballmilled for 5 hour6 in isopropanol with ga.80 gram6 of Nb2O5 and 30.24 geams ZnO. After being dried, the mixed 2owder was calcined at 1000C for 5 hours in a high purity alumina crucible. It was then milled wi~h ZrO2 balls to a particle size (D50) of 0.81 micrometer~.
Multilayer ceramic capacitors were made as in the previous exameles with electrode~ of 30%
Pd-70% Ag. The ceramic compssition was a~ follow~:
82.25 wt. % BaTiO3 (~uji HPBT-l), 11.0 wt. %
PbZrO3, 4.5 wt. % Ba(Znl/3Nbz/3)o3 and 1.25 . . .

~2~ L83 wt. % of the Mn-doped zinc borate flux used i~ -Example 2. When fi~ed as in the previous example6, the Curie temperature was 25C and the dielectric constant was 9600 with DF = 3.0%. In~ulation re6istance exceeded 10,000 QF.

Claims

1. A composition for forming a densified dielectric body at low firing temperatures comprising a mixture of finely divided particles of:
a. BaTiO3, b. A(Zn1/3Nb2/3)O3, c. A Curie point shifter selected from BaZrO3, PbZrO3, BaSnO3, PbSnO3 and mixtures thereof, d. a manganese-doped metal borate flux (F) selected from zinc borates in which the ratio of ZnO to B2O3 is 2-4 and mixtures and oxide precursors thereof, the proportions of a. - d. being substantially equivalent stoichiometrically to the formula:
(1-X)[(Ba1-xPbx)(Ti1-(u+v)ZruSnv)O3] +
X[A(Zn1/3Nb2/3)O3] + Y[F]
wherein A is selected from Pb, Ba and mixtures thereof.

X = 2.5 to 11.5% by weight, Y = 1.0 to 5.0%
u = 0 to 0.125, v = 0 to 0.125, x = 0 to 0.125, and u+v = 0.015 to 0.125.

2. The composition of claim 1 which contains additionally 0.05-0.5% wt. manganese oxide added in the form of MnO2, BaMnO3 or precursors thereof.

3. The composition of claim 1 in which c. is a mixture of PbZrO3 and BaZrO3, and d. is 3ZnO.B2O3.

4. The composition of claim 3 in which up to 50 mole % of the B2O3 is replaced by SiO2, GeO2, Al203 or mixtures thereof.

5. A dielectric composition consisting essentially of the composition of claim 1 which has been fired in air at 1000-1150°C to effect sintering of the particles and densification of the mixture.

6. The composition of claim 1 in which the mixture of finely divided solids is dispersed in an organic medium comprising a polymeric binder dissolved in organic solvent.

7. The composition of claim 6 in which the organic solvent is a volatile nonaqueous solvent and the dispersion is of castable consistency.

8. The composition of claim 7 in which the polymeric binder is a mixture of compatible polymers of 0-100% wt. C1-8 alkyl methacrylate, 100-0% wt.
C1-8 alkyl acrylate and 0-5% ethylenically unsaturated carboxylic acid or amine, the multipolymer being further characterized as having a number average molecular weight (Mn) of 50,000-100,000 a weight average molecular weight (Mw) of 150,000-350,000, the ratio of Mw to Mn being no greater than 5.5, the total amount of unsaturated carboxylic acid or amine in the multipolymer mixture is 0.2-2.0% wt. and the glass transition temperature of the polymer and plasticizer therein, if any, is -30 to +45°C.

9. The composition of claim 8 in which the alkyl methacrylate is ethyl methacrylate and the alkyl acrylate is methyl acrylate.

10. The composition of claim 8 in which the ethylenically unsaturated carboxylic acid is a monocarboxylic acid selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof.

11. A dielectric green tape comprising a layer of the composition of claim 7 from which the volatile solvent has been removed.

12. A method for forming a monolithic capacitor comprising the sequential steps of (1) applying a layer of conductive electrode material dispersed in organic medium to each of a plurality of layers of the green tape of claim 11; (Z) laminating a plurality of the electrode-layered green tapes to form an assemblage of alternating layers of green tape and electrode material; and (3) firing the assemblage of step (2) at 1000-1150°C to remove the organic medium and organic binder therefrom and to sinter the conductive electrode material and the dielectric material.

13. The composition of claim 6 in which the organic solvent is a solution comprising a resin and thixotropic agent dissolved in a solvent having a boiling point of 130-350°C and the dispersion is of paste consistency suitable for screen printing.

14. A ceramic capacitor comprising a dielectric ceramic body having a dielectric constant of at least 9,000 and at least two spaced metal electrodes in contact with the ceramic body which consists essentially of the composition of claim 1 which has been fired at 1000-1150°C to effect densification of the dielectric solids and sintering of the metal electrodes.