GB2193204A

GB2193204A - Method of producing PLZT ceramic composition

Info

Publication number: GB2193204A
Application number: GB08705883A
Authority: GB
Inventors: Hidetsugu Ono; Yasuyuki Ogata; Seiji Yamanaka
Original assignee: Mitsubishi Mining and Cement Co Ltd
Current assignee: Mitsubishi Mining and Cement Co Ltd
Priority date: 1986-07-30
Filing date: 1987-03-12
Publication date: 1988-02-03
Anticipated expiration: 2007-03-12
Also published as: GB8705883D0; DE3710975C2; DE3710975A1; JPS6335449A; FR2602225A1; GB2193204B; BE1000125A4; FR2602225B1; NL8701520A

Description

(12) UK Patent Application g) GB 1) 2 193 204(13A (43) Application

published 3 Feb 1988 (21) Application No 8705883 (5 1) INT CL4 C04B 35/49 (22) Date of filing 12 Mar 1987 (52) Domestic classification (Edition J):

(30) Priority data CIIJ 17 19 21 2 33 A (31) 61/179639 (32) 30 Jul 1986 (33) JP UlS 1422 C1J (56) Documents cited GB 1347188 US 3917780 US 3718723 (71) Applicant Mitsubishi Mining and Cement Co. Ltd. (58) Field of search

Cli (incorporated in Japan) Selected US specifications from IPC sub-class C04B

5-1 Marunouchi 1 -chome, Chiyoda-ku, Tokyo, Japan (72) Inventors Hicletsugu Ono Yasuyuki Ogata Seiji Yamanaka (74) Agent and/or Address for Service Page White & Farrer, 5 Plough Place, New Fetter Lane, London EC4A 1 HY (54) Method of producing PUT ceramic composition PATENTS ACT 1977 SPECIFICATION NO.2197204A

The rollowing corrections were allowed under Section 117 on 22 August 1988 Front page Heading (72) Inventor for Ronald James Furlong read Ronald John Furlong THE PATENT OFFICE 12 September 1988 0 _Plk GB2193204A 1 SPECIFICATION

Method of producing ceramic composition This invention relates to a method of producing a ceramic composition and, more particularly, it 5 relates to a method of producing starting ceramic powder represented by the following general formula fl):

Pb,La,,(ZrYTil -Y) 1-14'3 (1) 10 (wherein 0<x<l, 0<y<1) which is useful as dielectric material, transparent ceramic material and electro-optically functional material.

In recent years, reduction in the size and higher accuracy, as well as higher reliability have been demanded for the functional ceramic such as for ceramic capacitors and ceramic optical materials. 15 In putting such ceramics to practical use, baking cost is increased as the sintering temperature rises. Particularly, when the ceramics are utilized as multi-layered capacitors, they require such expensive high melting noble metals as I'd and Pt to be used as inner electrodes, which results in a remarkable problem for the reduction of manufacturing cost of the capacitors. In view of the above, it has highly been demanded for the functional ceramics that they can be sintered at low 20 temperature by the use of inner electrodes mainly composed of inexpensive silver for the multi layered capaciators.

As for such fucntional ceramics, those compounds represented by the abovementioned gen eral formula (1) (hereinafter simply referred to as---PLZ7) have been attracting attention as polyfunctional material having dielectric characteristics, transparency, electro-optical characteristics, etc.

Heretofore, PLZT ceramic compositions have been generally prepared by using oxides and carbonates of various metallic components as starting materials, mixing and pulverizing them in a mortar or a ball mill followed by firing. However, it is extremely difficult in such a conventional method of manufacturing PLZT to attain uniform composition, high purity and sufficient microni- 30 zation of starting material powder, because it is difficult to mix the powder thoroughly and impurities are readily incorporated during mixing and, moreover, there is a certain limit to the extent of the pulverization.

Therefore, the PLZT obtained is not quite satisfactory in their characteristics and the low temperature sintering property. Accordingly, it has been impossible so far to produce functional 35 ceramics having enhanced accuracy and improved reliability at reduced cost.

The present invention provides a method of producing ceramic composition represented by the following general formula (I):

Pb,-,La,(ZryTi,-y) 1-,4 3 40 (wherein 0<x<l, 0<y<l), wherein the method comprises mixing an aqueous solution contain ing lanthanum nitrate and/or lanthanum acetate and a mixed solution of lead alkoxide, zirconium alkoxide and titanium alkoxide thereby causing hydrolysis of the alkoxides and coprecipitation of the lanthanum components and heating the thus obtained precipitates thereby obtaining a cera- 45 mic composition of the above-mentioned composition.

Preferred embodiments of the present invention will now be described by way of example only.

In this invention, an aqueous solution containing lanthanum nitrate and/or lanthanum acetate is at first mixed with a mixed solution of lead alkoxide, zirconium alkoxide and titanium alkoxide, to 50 induce hydrolysis of lead alkoxide, zirconium alkoxide and titanium alkoxide under the effect of water in the aqueous solution containing lanthanum nitrate and/or lanthanum acetate and, at the same time, coprecipitate the lanthanum component.

That is, in this invention, lanthanum nitrate and/or lanthanum acetate are used as the starting material for the lanthanum component of P1-ZT. These starting materials can be easily purified to 55 a high extent by recrystallizing commercially available products.

An aqueous solution containing lanthanum nitrate and/or lanthanum acetate may be prepared by dissolving these starting materials each by a predetermined amount into water so as to obtain a desired PLZT composition ratio. In this case, the amount of water is desirably as low as possible for the sake of easy handling and it is generally preferred that the water is used in 60 such an amount as to give an aqueous solution containing from 5 to 40 % by weight of the starting material component. Further, dissolution is preferably conducted at a temperature from to 800C.

While on the other hand, as the starting materials for lead, titanium and zirconium compo nents, lead alkoxide, titanium alkoxide and zirconium alkoxide represented respectively by the 65 2 GB2193204A 2 following chemical formulas (a), (b) and (c) are used:

Pb(OR)2 Ti(OR)4 (b) Zr(OR). (c) 5 (wherein R represents an alkyl group).

The specific kind of the alkyl group R in these alkoxides is not substantially important. For the convenience of handling, etc, it is generally desirable to use alkoxides of lower alkyl group such as methyl group, ethyl group, iso-propyl group or butyl group.

The titanium alkoxide and zirconium alkoxide can be obtained by a conventional method, for 10 example, by the introduction of ammonia gas into an alcohol solution of titanium (or zirconium) chloride, in accordance with the following chemical formula (d).

TiC'4+4ROH+4NH3Ti(OR)4+4NH,CI (d) 15 These alkoxides are also commercially available at a sufficient purity. Examples of the commercially available alkoxides include titanium propoxide (Ti(OC3H7)4), titanium butoxide (Ti(OC,H,)4), zirconium propoxide (Zr(OC,H7)4), and zirconium butoxide (Zr(C04H,Q.

The lead alkoxide can easily be prepared at a high purity by the method as disclosed in Japanese Patent Application No. Sho 60-52332 filed previously by the present applicant, that 20 is, a method which comprises forming an alcohol solution of lead alkoxide by the addition of lead acetate in a theoretically excess amount to a sodium alkoxide according to the following chemical formula (e):

Pb(CH3C00)2+2NaOR-Pb(OR)2+2CH3COONa (e) 25 removing the alcohol by distillation from the alcohol solution of the lead alkoxide obtained and then adding an aromatic hydrocarbon compound to the residue as a solvent for dissolving the lead alkoxide extracting and then filtering the lead alkoxide to obtain a solution of the lead alkoxide in an aromatic hydrocarbon solution at high purity. 30 It is preferable, for maintaining the homogeniety of the composition, that the mixed solution of these metal alkoxides is prepared by dissolving necessary metal alkoxides in an organic solvent so as to obtain a desired PLZT composition ratio and prepared by applying sufficient mixing by mechanical stirring or the like.

Any of organic solvents may be used so long as they can dissolve the metal alkoxides, and 35 aromatic hydrocarbons such as benzene, toluene and xylene, alcohols such as ethanol and propanol or the mixed solutions of them are appropriate in view of the solubility. The starting material components are desirably dissolved into the solution of the organic solvent such that they are contained in about from 5 to 40 % by weight therein.

The mixing metal alkoxide solution thus prepared and the aqueous solution containing lan- 40 thanurn ions are mixed either by dropping an aqueous solution containing lanthanum ions under stirring to the mixed solution of metal alkoxides, or by dropping the mixed solution of the metal alkoxides under stirring to the aqueous solution containing lanthanum ions. In both of the cases, the dropping rate is, preferably, about from 1 to 40 mi/min.

Hydrolysis of the alkoxides and the coprecipitation of the lanthanum component are effected 45 by mixing both of the solutions. In this case, for the convenience of handling, the reaction temperature is desirably within a range higher than the melting point of the components and not higher than 20WC, preferably, from 0 to 1OWC and, particularly preferably, from 10 to 7WC.

Although the reaction is usually carried out under atmospheric pressure, it may be carried out under an increased pressure of not higher than 250 atm or under a reduced pressure of not 50 lower than 0 1 atm.

PLZT crystals can be obtained by filtering the resultant precipitates, separating to remove the filtrate, drying and then heating the residue.

As apparent also from the analysis for the filtrate obtained by the separation of the precipi- tate, lead, lanthanum, titanium and zirconium components can be coprecipitated substantially 55 completely to a desired composition with little leaching and remaining of these components in the filtrate according to this invention.

The PLZT powder obtained by the method of this invention as described above has an extremely-small and uniform grain size from 0.008 to 0.01 lim when observed under an electron microscope in a case where the precipitate is fired at 40WC for 2 hours. Since the method of 60 this invention is basically a liquid phase reaction, it can produce the PLZT at high purity and in homogeneous composition as compared with the conventional method. Further, the PLZT ob tained by heating is extremely homogeneous and fine powder.

As has been described above, according to the method of producing ceramic composition according to this invention, it-is possible to easily and reliably produce homogeneous and fine 65 3 GB2193204A 3 PLZ-r powder at high purity and having homogeneous composition.

Tfie thus obtained ceramic composition is extremely excellent in the characteristics, i.e., showing high dielectric constant, insulation resistance and volume resistance and a small dielectric loss. By the use of the ceramic composition obtained by this invention, compact largecapacity capacitors of high reliability can be produced. 5 Moreover, since the ceramic composition obtained by this invention possesses excellent low temperature sintering property and can be fired at a low temperature, the cost of burning is inexpensive. When this is used in a multi-iayered capacitor, inner electrodes such as made of relatively inexpensive silver type material can be used. Accordingly, it is possible to reduce the production cost of the multi-layered capacitor and greatly decrease the price of the capacitor. 10 For the purpose of this invention, x and y in the general formula (1) lie within the range: 0<x<'I and 0<y<1 and, preferably, 0.02<x:50.25 and 0.10- :!5y-:50.90, because the PLZT with the highest possible characteristics can be obtained when the composition lie within the range.

Now, working examples and comparative examples will be cited below for the illustration of the low temperature sintering property of the PLZT powder produced according to this invention, 15 as well as for the dielectric property as one of the functions of P1-ZT. It should be noted that this invention is not limited to the following examples unless it departs the spirit of the invention.

In the working examples and comparative examples shown below, after applying compression molding to a given powder fired at 700'C for 5 hours under the pressure of 3,000 kgf/cM2 into 20 disks 16 mm in diameter and 1 mm in thickness, further firing for 1 hour in air at each of the temperature of 1,050'C, 1,100'C, 1,150'C and 1,200'C, a silver electrode was baked to both of the surfaces of the disks for each of the obtained sintering products. Then, the dielectric property of the PLZT powder was examined by measuring the dielectric constant, dielectric loss and electrical resistance at 25'C. Besides, the variation coefficients of static capacity (TC) at 25 -55'C and 125'C were measured based on the static capacity of 25'C as a reference. The dielectric constant and the dielectric loss were determined by the use of a digital LCR meter at 1 kHz. The insulation resistance was determined by an insulation resistance meter after 5 seconds application of a 10OV of voltage.

30 Example 1

To a mixed solution comprising 1,310 mi of a benzene solution containing lead butoxide (0.672 mol/f), 82.7 9 of titanium iso-propoxide (commercial product at 99. 99 % purity) and 261 g of zirconium butoxide (commercial product at 99.99 % purity), 173 mi of an aqueous solution of lanthanum nitrate (0.694 mol/l) were added slowly -dropwise while stirring at a rate of 30 35 mi/min. The temperature during reaction was maintained at 30'C.

After filtering the thus obtained precipitate by using filter paper, the precipitate was dried at 80'C for 10 hours and then heated at 700'C for 5 hours, to obtain a PLZT powder of the following composition:

40 Pb La(, 12(Zr.,,,Ti,,30)09703 The Oelectric characteristics of thus obtained ceramic composition were measured and the result is shown in Tqble 1.

45 Example 2

A PLZT powder of the aimed composition was obtained in the same procedures as in Example,l excepting that an aqueous solution of lanthanum acetate was used instead of the aqueous solution of lanthanum nitrate at the same concentration.

The results of the measurement for the dielectric characteristics of the thus obtained ceramic 50 composition were identical with those in Example 1 within the range of measuring error.

Example 3

A PLZT powder of an aimed composition was obtained in the same procedures as in Example 1 excepting for using titanium butoxide instead of titanium iso-propoxide in Example 1. 55 The results for the measurement of dielectric characteristics of thus obtained ceramic compo- sition were equal to those in Example 1 within the range of measuring error.

Example 4

A PLZT powder of an aimed composition was obtained in the same procedures as in Example 60 1 excepting for using zirconium iso-propoxide instead of zirconium butoxide in Example 1.

The results for the measurement of dielectric characteristics of thus obtained ceramic composition were equal to those in Example 1 within the range of measuring error.

Example 5 65

4 - GB2193204A 4 A PLZT powder of an aimed composition was obtained in the same procedures as in Example 1 excepting for using lead isopropoxide instead of lead butoxide in Example 1.

The results for the measurement of dielectric characteristics of thus obtained ceramic compo sition were equal to those in Example 1 within the range of measuring error.

5 Example 6

A PLZT powder of an aimed composition was obtained in the same procedures as in Example 1 excepting that the temperature upon reaction was changed from WC to WC in Example 1.

The result for the measurement of dielectric characteristcs of thus obtained ceramic compo- sition were equal to those in Example 1 within the range of measuring error. 10 Example 7

A PLZT powder of an aimed composition was obtained in the same procedures as in Example 1 except that a xylene solution of lead iso-propoxide was used instead of lead butoxide in benzene solution. 15 The results for the measurement of dielectric characteristics of thus obtained ceramic compo sition were equal to those in Example 1 within the range of measuring error.

Example 8

A PLZT powder of an aimed composition was obtained in the same procedures as in Example 20 1 excepting that a toluene solution of lead iso-propoxide was used instead of the benzene solution of lead butoxide in Example 1.

25 Comparative Example 1 After mixing and pulverizing each of metal oxides; PbO, M02, La20. and Zr02 in a ball mill so as to obtain the same composition ratio as in Example 1, they were calcined at 70WC for 5 hours, pulverized again in a ball mill to prepare PLZT powder with the same composition as that in Example 1. 30 The results for the measurement of dielectric characteristics of the thus obtained ceramic composition are shown in Table 1.

Example 9

A PLZT powder of the following composition: 35 Pb,,Lao 1AZrO 6J'0 J0 9703 was obtained in the same procedures as in Example 1 excepting for varying blending ratio for each of the starting materials in Example 1. 40 Results for the measurement of dielectric characteristics of the thus obtained ceramic compo sition are shown in Table 2.

Comparative Example 2 A PLZT powder of the same composition as that in Example 9 was prepared in the same 45 procedures as in Corpparative Example 1 excepting for varying the blending ratio of the starting materials.

The results for the measurement of the dielectric characteristics of thus obtained ceramic composition are shown in Table 2.

50 Examples 10-15 Composition powders each with the value as shown in Table 3 for x and y in the above mentioned general formula (1) were obtained by varying the mixing ratio for each of the starting materials in Example 1. The results for the measurement of dielectric characteristic of thus obtained powder are shown in Table 3. 55 It is apparent from Tables 1 through 3 that PLZT ceramic compositions having extremely low sintering temperatures and exhibiting excellent electrical properties can be obtained with PLZT powder according to this invention.

The preferred embodiments of the present invention can provide a method capable of produc ing PLZT ceramic starting material powder represented by the above- mentioned general formula 60 (I):

(1) at a high purity; (2) with a favorable homogeneous composition; and (3) in a highly pulverized form, without entailing the aforementioned drawbacks of the conven tional method. 65 GB2193204A 5 The preferred embodiments of the present invention can enhance the function and characteristics, as well as improve the low temperature sintering property of the ceramics produced from the powder represented by the above-mentioned general formula (1).

(3) Table 1

Dielectric characteristics of Pb 0.88 La 0.12 (Zr 0.70 Ti 0.30)037 0 3 F1ring in t Dieledtric Dielectric RejAstivity TC(%)(-55%l25% temp. In ering 3 density constant (c) loss (%) (X10 2 - cm) (glem) (OC) Example 1 Comparative Example 1 Comparative Example 1 Comparative Example 1 Comparative Example 1 Comparative X Exampel 1 Example 1 Example Example 1 Example 1 1050 7.53 6.77 2560 1750 1.0 5.9 1.0 0.2 -35, -14 -39, -18 1100 7.51 7.10 2400 2110 1.1 2.4 M 0.8 -34, -12 r35, -14 1150 7.46 7.21 2270 2180 1.0 1.7 1.7 0.8 -26, -8 ?-29, "12 7.44 7.29 2260 2220 1.2 1.5 1.9 0.7 22, -10 -24, -12 Table 2

Dielectric characteristics of Pbo.88La 0.12 (Zr 0.65 Ti 0.35)037 0 3 Firing Sinterin83 density Dielectric Dielectric Refistivity. TC(X)(-55'C, 125"C) temp. (g/cm) constant (e) loss (%) (Xio Q. cm) (1,C) Example I Comparative Example 1 Comparative Example I Comparative Example I Example 1 Example I Comparative Example I Example I Example 1 1 Comparatiqve Example 1 1050 7.51 6.78 2500 1700 0.9 8.0 1.1 0.5 -38, -15 -40, -20 1100 7.51 7.05 2390 2060 1.0 2.4 1.5 0. 7 -32, -16 -37, -17 11200 7.49 7.19 2320 2130 1.1 1.9 0.9 0.8 -32, -13 -35, -13 1150 7.45 7.25 2310 2170 1.0 1.9 1.1 0.8 -37, -15 a) co 1 '. k -j 1 Table 3

Example Composition Firing Sintering Dielectric Dielectric Resistivity TC No. Temperature density constant loss X Y (OC) (g/cm3) (xl013(1.cm) (-5511C, 125C) 0.10 0.7 1050 7.64 2340 0.9 1.3 -45, -4 11 0.11 0.7 1050 7.63 2500 0.9 1.5 -40, -11 12 0.11 0.75 1050 7.70 2700 0.9 1.6 -39, -18 13 0.12 0.6 1050 7.59 2440 1.0 1.7 -38, -15 14 0.12 0.75 1050 7.65 2620 1.5 1.6 -37, -18 0.14 0.7 1050 7.61 2740 1.0 1.4 -25, -20 G) 8 GB2193204A 8

Claims

1. A method of producing a ceramic composition having a chemical composition represented by the following general formula:

Pb,,La,,(ZryTi,,),-,,,, 5 (wherein 0<x<l, 0<y<l), wherein the method comprises mixing an aqueous solution containing lanthanum nitrate and/or lanthanum acetate with a mixed solution prepared by mixing lead alkoxide, zirconium alkoxide and titanium alkoxide thereby effecting hydrolysis of said alkoxides and coprecipitation of the lanthanum components, and heating the thus obtained precipitates. 10

2. A method of producing a ceramic composition as defined in Claim 1, wherein the mixing of lead alkoxide, zirconium alkoxide and titanium alkoxide is conducted in a state where the alkoxides are dissolved in an organic solvent.

3. A method of producing a ceramic composition as defined in Claim 1, wherein the heating of said precipitate is carried out at a temperature of not lower than 200T and not higher than 15 the decomposing temperature of the ceramic composition.

4. A method of producing a ceramic composition as defined in Claim 1, wherein x and y in the general formula lie with -in the range: 0.02--,5x---50.25 and 0.10-- "5y---50.90.

5. A method of producing a ceramic composition as defined in Claim 1, wherein the lead alkoxide is a lower alcohol alkoxide of lead. 20

6. A method of producing a ceramic composition as defined in Claim 5, wherein the lead alkoxide is lead methoxide, lead ethoxide, lead iso-propoxide or lead butoxide.

7. A method of producing a ceramic composition as defined in Claim 1, wherein the titanium alkoxide is a lower alcohol alkoxide of titanium.

8. A method of producing a ceramic composition as defined in Claim 7, wherein the titanium 25 alkoxide is titanium methoxide, titanium ethoxide, titanium iso-propoxide or titanium butoxide.

9. A method of producing a ceramic composition as defined in Claim 1, wherein the zirconium alkoxide is a lower alcohol alkoxide of zirconium.

10. A method of producing a ceramic composition as defined in Claim 9, wherein the zirconium alkoxide is zirconium methoxide, zirconium ethoxide, zirconium iso-propoxide or zircon- 30 ium butoxide.

11. A method of producing a ceramic composition as defined in Claim 1, wherein the aqueous solution containing lanthanum nitrate and/or lanthanum acetate is an aqueous solution containing lanthanum nitrate and/or acetate in an amount. of from 5 to 40 % by weight.

12. A method of producing-a ceramic composition as defined in Claim 1, wherein the mixed 35 solution obtained by mixing the lead alkoxide, zirconium alkoxide and the titanium alkoxide is a mixed solution prepared by dissolving said metal alkoxides in an organic solvent

13. A method of producing a ceramic composition as defined in Claim 12, wherein the organic solvent is an aromatic hydrocarbon or an alcohol.

14. A method of producing a ceramic composition as defined in Claim 13, wherein the 40 organic solvent is benzene, toluene, xylene, ethanol or propanol.

15. A method of producing a ceramic composition as defined in Claim 1, wherein the hydrolysis of the alkoxides and the coprecipitation of the lanthanum component are carried out at a temperature within the range from 0 to 100T.

16. A method of producing a ceramic composition as claimed in Claim 1 substantially as 45 hereinbefore described.

17. A method of producing a ceramic composition substantially as hereinbefore described in any one of Examples 1 to 15.

18. A ceramic composition whenever produced by the method of any foregoing claim.

Published 1988 at The Patent Office, State House, 66/7 T High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.