Method for producing barium titanate-based powder, and multilayer ceramic capacitor

Abstract

A method for producing a barium titanate-based powder that includes mixing a titanium compound and a barium compound together with water and chlorine to prepare a slurry, and temporarily firing the mixture of the titanium compound and the barium compound which is contained in the slurry to provide a barium titanate-based powder. The chlorine in the slurry is in the form of chlorine ions in a ratio of 230 to 1100 wt ppm based on the amount of the barium titanate-based powder to be synthesized.

Claims

1. A method for producing a barium titanate-based powder, the method comprising: mixing a titanium compound and a barium compound together with water and chlorine to prepare a first slurry, the chlorine being in the form of chlorine ions in a ratio of 230 to 1100 wt ppm based on an amount of the barium titanate-based powder to be produced; firing the mixture of the titanium compound and the barium compound contained in the first slurry to produce the barium titanate-based powder; dispersing the produced barium titanate-based powder in a second slurry; and removing chlorine contained in or on the barium titanate-based powder obtained after the firing of the mixture of the titanium compound and the barium compound contained in the first slurry and after dispersing the produced barium titanate-based powder in the second slurry.

2. The method for producing a barium titanate-based powder according to claim 1, wherein the chlorine is added as ammonium chloride to form the first slurry.

3. The method for producing a barium titanate-based powder according to claim 1, wherein the titanium compound is titanium dioxide.

4. The method for producing a barium titanate-based powder according to claim 3, wherein the titanium dioxide comprises grains having a specific surface area of 30 to 50 m.sup.2/g.

5. The method for producing a barium titanate-based powder according to claim 1, wherein the barium compound is barium carbonate.

6. The method for producing a barium titanate-based powder according to claim 5, wherein the barium carbonate comprises grains having a specific surface area of 10 to 30 m.sup.2/g.

7. The method for producing a barium titanate-based powder according to claim 1, further comprising drying the first slurry before the firing is carried out.

8. The method for producing a barium titanate-based powder according to claim 7, wherein the drying is carried out at 100 to 200 C. for 12 to 36 hours.

9. The method for producing a barium titanate-based powder according to claim 1, wherein the firing is carried out at 800 to 1100 C. for 1 to 5 hours.

10. The method for producing a barium titanate-based powder according to claim 1, wherein the chlorine contained in or on the barium titanate-based powder is removed until a content of the chlorine contained in or on the barium titanate-based powder is reduced to 100 wt ppm or less.

11. The method for producing a barium titanate-based powder according to claim 1, wherein the chlorine is removed by passing the second slurry in which the produced barium titanate-based powder is dispersed through an ion exchange resin.

12. The method for producing a barium titanate-based powder according to claim 1, wherein the chlorine is removed with the use of an ion exchange resin.

13. A multilayer ceramic capacitor which is produced using the barium titanate-based powder obtained by the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a view schematically showing one example of a chlorine removing step using an ion exchange resin;

(2) FIG. 2 is a sectional view schematically showing an example of a multilayer ceramic capacitor according to the present invention; and

(3) FIG. 3 is a graph showing a relationship between the content of chlorine ions in a slurry and the integral breadth of a (222) plane diffraction peak of a barium titanate-based powder.

DETAILED DESCRIPTION OF THE INVENTION

(4) Hereinafter, a method for producing a barium titanate-based powder according to an aspect of the present invention and a multilayer ceramic capacitor according to another aspect of the present invention will be described with reference to the drawings.

(5) However, the present invention is not limited to the following constitutions, and may be applied while a change is appropriately made as long as the gist of the present invention is not changed. The present invention also includes combinations of two or more individual preferred constitutions of the present invention as described below.

(6) First, the method for producing a barium titanate-based powder according to the present invention will be described.

(7) (1) Mixing Step

(8) First, a mixing step of mixing a titanium compound and a barium compound together with water to prepare a slurry is carried out.

(9) Titanium dioxide can be used as the titanium compound.

(10) The titanium dioxide may be either titanium dioxide produced by a chlorine method or titanium dioxide produced by a sulfuric acid method. When titanium oxide produced by a chlorine method is used, surface chlorine may exist on the surfaces of titanium dioxide grains, and therefore it is preferable that the surface chlorine content is measured, and the amount of a chlorine ion source to be added later is adjusted.

(11) The surface chlorine content can be measured in the following manner: a titanium dioxide powder is put in pure water, the mixture is stirred, ultrasonically dispersed, and then centrifugally separated to collect a supernatant liquid, and the supernatant liquid is diluted, and then filtered with a 0.2 m filter, and quantitative determination is performed by ion chromatography.

(12) The total chlorine content: a surface chlorine content and an internal chlorine content of titanium dioxide grains can be measured in the following manner: 1000 mg of a sample is distilled with water vapor at 1400 C., a decomposed product is collected in 50 ml of ultrapure water, and quantitative determination is performed by ion chromatography.

(13) Measurement conditions of ion chromatography for measuring the surface chlorine content or the total chlorine content: a surface chlorine content and an internal chlorine content may include such conditions that the chlorine content is measured at a flow rate of 1 ml/min using Dionex AS17-C as a column and 5-40 mM KOH as an eluant. DXi-500 manufactured by Nippon Dionex K.K. can be used as an ion chromatography apparatus.

(14) When titanium dioxide grains are used as the titanium compound, the specific surface area of the titanium dioxide grains is preferably 30 to 50 m.sup.2/g.

(15) The barium compound is not particularly limited, and for example, barium carbonate can be used.

(16) When barium carbonate grains are used as the barium compound, the specific surface area of the barium carbonate grains is preferably 10 to 30 m.sup.2/g.

(17) The ratio of the barium compound to the titanium compound is not required to meet a stoichiometric composition as long as it is in a range ensuring that the effect of the invention of the present application is exhibited, but it is preferable that the ratio is defined so as to fall within a range of 0.980 to 1.020 in terms of a molar ratio (Ba/Ti).

(18) It is preferable to use distilled water, ion-exchanged water, pure water, ultrapure water or the like as water.

(19) In the mixing step, the slurry is made to contain chlorine as chlorine ions in a ratio of 230 to 1100 wt ppm based on the amount of the barium titanate-based powder to be synthesized.

(20) For adjusting the amount of chlorine ions, it is preferable to add a compound serving as a chlorine source, and it is preferable to add ammonium chloride as the chlorine source.

(21) When the surface chlorine content of titanium dioxide is measured as described above, it is preferable that the added amount of the compound serving as chlorine source is defined on the assumption that all surface chlorine of titanium dioxide is ionized in the slurry.

(22) Other components may be added in addition to the titanium compound, the barium compound, water and the compound serving as a chlorine source.

(23) As other components, compounds serving as a Sr source, a Ca source or a Zr source may be added.

(24) When these compounds are added, a barium titanate-based powder of a Perovskite type compound represented by the general formula ABO.sub.3 (the site A is Ba, the site B is Ti and O is oxygen) where the site A is substituted with Sr or Ca, and the site B is replaced with Zr is obtained.

(25) A dispersant may be added as other components.

(26) As the dispersant, a polycarboxylic acid type polymer dispersant, a polycarboxylic acid ammonia salt, a maleic anhydride-based comb type polymer or the like can be used.

(27) For mixing in the mixing step, a known method such as a wet-mixing method using a ball mill can be employed.

(28) The mixing order of the titanium compound, the barium compound, water, the compound serving as a chlorine source and other components is not particularly limited.

(29) (2) Drying Step and Temporary Firing Step

(30) The slurry obtained in the mixing step is dried in a dryer, and subsequently, the dried mixture is fired in a fired furnace to obtain a barium titanate-based powder.

(31) Preferably, the drying step is carried out at 100 to 200 C. for 12 to 36 hours.

(32) Preferably, the temporary firing step is carried out at 800 to 1100 C. for 1 to 5 hours. Preferably, firing is performed in the air.

(33) The obtained barium titanate-based powder may be directly used as a raw material for a multilayer ceramic capacitor, or may be further subjected to a chlorine removing step to reduce the chlorine content.

(34) (3) Chlorine Removing Step

(35) In the chlorine removing step, chlorine deposited on the surface of the barium titanate-based powder obtained in the temporary firing step.

(36) The method for removing chlorine is not particularly limited, but it is preferable to remove chlorine using an ion exchange resin. Mention is made of a method including using water-washing in addition to the method including using an ion exchange resin.

(37) As the ion exchange resin, a known anion exchange resin to be used for removing chlorine ions can be used, and an anion ion exchange resin having an amino group and an imino group (e.g. DIAION (registered trademark) SA10A-OH model manufactured by Mitsubishi Chemical Corporation) can be used.

(38) FIG. 1 is a view schematically showing one example of a chlorine removing step using an ion exchange resin.

(39) In the chlorine removing step using an ion exchange resin, a chlorine removing apparatus 20 can be used in which a plastic tube 30 is filled with an ion exchange resin 40, the tip of the tube 30 is covered with a filter cloth 50 as shown in FIG. 1.

(40) In the chlorine removing step, the barium titanate-based powder is mixed with water (preferably pure water), and dispersed to prepare a slurry 70, and the slurry 70 is put in the chlorine removing apparatus 20. The slurry 70 is caused to pass through the ion exchange resin 40, and subjected to ion exchange to remove chlorine ions, and a slurry 80 after removal of chlorine is discharged from a filter cloth 50, and collected on a receptacle table 60.

(41) Thereafter, the slurry is dried to obtain a barium titanate-based powder with the chlorine content reduced to 100 wt ppm or less.

(42) The chlorine content of the barium titanate-based powder after the chlorine removing step can be measured by ion chromatography. The method for measuring the chlorine content can also be applied to the barium titanate-based powder before the chlorine removing step.

(43) Subsequently, the multilayer ceramic capacitor according to the present invention will be described.

(44) The barium titanate-based powder obtained by the method for producing a barium titanate-based powder according to the present invention is suitable as a raw material powder for a multilayer ceramic capacitor.

(45) The multilayer ceramic capacitor according to the present invention is a multilayer ceramic capacitor produced using a barium titanate-based powder obtained by the method for producing a barium titanate-based powder according to the present invention.

(46) FIG. 2 is a sectional view schematically showing an example of a multilayer ceramic capacitor according to the present invention.

(47) In a multilayer ceramic capacitor 1, a plurality of dielectric ceramic layers 11 and internal electrode layers 12 are laminated to form a laminated body 10.

(48) The internal electrode layers 12 are alternately exposed to the surface of the laminated body 10 at both opposite end surfaces 14a and 14b of the laminated body 10.

(49) At both end surfaces 14a and 14b of the laminated body 10, a pair of external electrodes 13a and 13b are formed so as to electrically connect the internal electrode layers 12.

(50) In the multilayer ceramic capacitor 1, the dielectric ceramic layer 11 is a sintered body having a barium titanate-based grains as main phase grains, and is represented by the general formula ABO.sub.3 (the site A is Ba, and may contain at least one selected from the group consisting of Sr and Ca in addition to Ba; the site B is Ti, and may contain at least one selected from the group consisting of Zr and Hf in addition to Ti; and O is oxygen).

(51) The dielectric ceramic layer 11 is preferably a ceramic layer further containing other accessory components.

(52) Accessory components that may be contained in the dielectric ceramic layer 11 include elements such as Mg, Dy, Si and Mn. The existence form of the accessory component is not limited, and for example, the accessory component may exist at crystal grains of barium titanate-based grains. Specifically, a grain including a core part composed of a barium titanate-based grain, and a shell part formed by solid solution of an element as an accessory component in the periphery of the barium titanate-based grain as a core part is preferable.

(53) The accessory component may exist at a crystal grain boundary or a triple point in the form of an oxide etc.

(54) The internal electrode layer 12 is preferably an electrode layer containing Ni, specifically an electrode layer containing metal nickel, an electrode layer containing a nickel alloy, or the like.

(55) The external electrodes 13a and 13b are, for example, electrodes containing Ag or Cu as a main component.

(56) Specifically, mention is made of an electrode including a thick film formed by baking a conductive paste containing copper; a nickel-plated film formed on the thick layer; and a tin-plated film formed on the nickel-plated film. An electrode having a known configuration can be used.

(57) The multilayer ceramic capacitor 1 may be either a two-terminal type capacitor including two external electrodes 13a and 13b or a multi-terminal type capacitor including multiple external electrodes.

(58) Hereinafter, one example of a method for producing the multilayer ceramic capacitor according to the present invention will be described.

(59) First, a barium titanate-based powder obtained by the method for producing a barium titanate-based powder according to the present invention is provided.

(60) Next, a compound as an accessory component is mixed with the barium titanate-based powder as necessary to obtain a ceramic raw material.

(61) The form of the compound as an accessory component is not particularly limited, and various forms such as oxide powders, carbonate powders, chloride powders, sols and metal organic compounds can be used.

(62) The mixing form of the compound as an accessory component is not particularly limited. For example, a plurality of accessory components may be mixed beforehand, or heat-treated and synthesized. A specific accessory component may be mixed in two stages.

(63) As necessary, an organic binder, a plasticizer and an organic solvent are added to the ceramic raw material obtained in the manner described above, and the mixture is stirred using a ball mill etc. to prepare a ceramic slurry.

(64) Thereafter, a ceramic green sheet is prepared using the ceramic slurry, a conductive paste film to form an internal electrode is formed, and the ceramic green sheet provided with the conductive paste film is laminated and fired to obtain a laminated body including a dielectric ceramic layer and a plurality of internal electrode layers.

(65) Finally, an external electrode is formed at each of both end surfaces of the laminated body to produce a multilayer ceramic capacitor.

(66) In each of these steps, a known technique and process conditions can be used.

(67) Preferably, firing after laminating the ceramic green sheet is performed in a reducing atmosphere of a H.sub.2N.sub.2H.sub.2O gas with an oxygen partial pressure of 10.sup.9 to 10.sup.12 MPa at 1150 to 1250 C.

(68) The method for forming the external electrode may also be a method in which a conductive paste layer to form an external electrode is applied and formed before firing of the ceramic green sheet, and the conductive paste layer is baked in synchronization with firing of the laminated body.

EXAMPLES

(69) Hereinafter, examples disclosing a method for producing the multilayer ceramic capacitor according to the present invention more in detail will be shown. The present invention is not limited to these examples.

Examples 1 to 5 and Comparative Examples 1 to 3

(70) A) Production of Barium Titanate-Based Powder

(71) A BaCO.sub.3 powder, and a TiO.sub.2 powder having a specific surface area of 30 m.sup.2/g were provided, weighed to a molar ratio (Ba/Ti) of 1.0, and put in a 1 L vinyl chloride pot together with a medium (2 mm) made of partially stabilized zirconia, a predetermined amount of pure water was added, and a special polycarboxylic acid type polymer surfactant as a dispersant was further added in a ratio of 3.2 wt % based on the total amount of BaCO.sub.3 and TiO.sub.2 powders.

(72) Eight such samples were provided, and a predetermined amount of ammonium chloride (NH.sub.4Cl) was added in each of the pots to obtain slurries adjusted so as to have chlorine contents of 40, 70, 230, 410, 600, 850, 1100 and 2000 wt ppm, respectively, based on the amount of barium titanate to be synthesized.

(73) Table 1 shows the content of chlorine ions in the slurry in each of examples and comparative examples.

(74) Each of these pots was placed on a pot stand, and rotated at 150 rpm for 72 hours to perform mixing. The obtained slurry was put in a dryer at 100 C., and dried.

(75) Next, the dried mixture was put in a zirconia sagger, heated to a temperature of 950 to 1000 C. at a temperature rise rate of 5 C./minute in a firing furnace, held in the air for 1 hour, and temporarily fired to produce a barium titanate-based powder.

(76) The surface chlorine content of the TiO.sub.2 powder used was measured using ion chromatography, and found to be 35 ppm based on the amount of barium titanate to be synthesized. Therefore, in consideration of the surface chlorine content, ammonium chloride was added so as to obtain a predetermined chlorine ion content.

(77) B) Evaluation of Specific Surface Area and Crystallinity

(78) For the barium titanate-based powders obtained by performing temporary firing in Examples and comparative examples, the specific surface area was measured using a specific surface area measurement apparatus: Macsorb (registered trademark) manufactured by Mountech Co., Ltd. The integral breadth of a (222) plane diffraction peak was measured (X ray source: CuK) using an X-ray diffractometer (X'Pert PRO MPD manufactured by PANalytical B.V.). The results are shown in Table 1. Table 1 shows the integral breadth under the condition of performing temporary firing at 1000 to 1060 C. (temporary firing temperature) to obtain a specific surface are of 3.3 m.sup.2/g.

(79) FIG. 3 illustrates a relationship between the content of chlorine ions in a slurry and the integral breadth of a (222) plane diffraction peak of a barium titanate-based powder.

(80) TABLE-US-00001 TABLE 1 Content of chlorine ions in Integral breadth of slurry (222) plane (wt ppm) diffraction peak () Comparative 40 0.265 Example 1 Comparative 70 0.263 Example 2 Example 1 230 0.244 Example 2 410 0.238 Example 3 600 0.235 Example 4 850 0.240 Example 5 1100 0.249 Comparative 2000 0.269 Example 3

(81) In Comparative Examples 1 and 2, the content of chlorine ions in the slurry was as low as 40 or 70 wt ppm, so that the firing temperature was high, resulting in occurrence of coagulation, and the integral breadth was as large as 0.265 or 0.263, so that crystallinity was reduced.

(82) In Comparative Example 3, the content of chlorine ions in the slurry was as high as 2000 wt ppm, and thus the amount of chlorine as an impurity increased, so that crystallinity was rather reduced. Accordingly, the integral breadth was 0.269.

(83) On the other hand, in Examples 1 to 5, the content of chlorine ions in the slurry fell within a preferred range, and thus the integral breadth was as 0.25 or less, so that a barium titanate-based powder having high crystallinity was obtained.

(84) This may be because during firing, Ba.sup.2+ ions originating from the barium compound and chlorine ions existing in the slurry react with each other at around 900 C. to form BaCl.sub.2, and the resulting compound acts as a reaction accelerator and a sintering additive in the form of a liquid phase, so that grain growth of BaTiO.sub.3 is promoted to increase crystallinity.

(85) Since a part of chlorine is eliminated as a gas during firing, the amount of chlorine contained in the barium titanate-based powder produced in each of Examples 1 to 5 is about 150 to 600 wt ppm.

(86) C) Chlorine Removing Step

(87) The barium titanate-based powder prepared in any one of Examples 1 to 5 and Comparative Examples 1 to 3 was put in a 1 L vinyl chloride pot together with a medium (2 mm) made of partially stabilized zirconia, a predetermined amount of pure water was added, and the pot was placed on a pot stand, and rotated at 150 rpm for 24 hours to perform mixing, thereby obtaining a slurry.

(88) A chlorine removing apparatus 20 as shown in FIG. 1 was provided.

(89) An ion exchange resin 40 (DIAION (registered trademark) SA10A-OH model manufactured by Mitsubishi Chemical Corporation) was packed at one end of a plastic tube 30 so as to have a thickness of 30 mm, further covered with a filter cloth 50, and fixed.

(90) A slurry 70 was injected from the other end, and caused to pass through the ion exchange resin 40, and a slurry 80 passing therethrough was collected.

(91) The collected slurry was put in a dryer at 100 C., and dried to obtain a barium titanate-based powder passing through the chlorine removing step.

(92) In addition, the slurry was discharged from the pot without passing through the ion exchange resin, and dried in the same manner as described above to prepare a barium titanate-based powder.

(93) D) Evaluation of Chlorine Content

(94) The chlorine content of each of the barium titanate-based powder passing through the chlorine removing step and the barium titanate-based powder not passing through the chlorine removing step in each of examples and comparative examples was measured by an ion chromatography method. The measurement results are shown in Table 2.

(95) TABLE-US-00002 TABLE 2 Chlorine content Chlorine content of barium of barium Content of titanate-based titanate-based chlorine powder not passing powder passing ions in through chlorine through chlorine slurry removing step removing step (wt ppm) (wt ppm) (wt ppm) Comparative 40 30 11 Example 1 Comparative 70 58 13 Example 2 Example 1 230 154 8 Example 2 410 310 9 Example 3 600 500 10 Example 4 850 530 12 Example 5 1100 600 20 Comparative 2000 1200 110 Example 3

(96) As described above, a part of chlorine is eliminated as a gas during firing, and therefore the amount of chlorine contained in the barium titanium-based powder produced in each of examples and comparative examples is smaller than the content of chlorine ions in the slurry as shown in the results of measurement of the amount of chlorine in the barium titanate-based powder not passing through the chlorine removing step.

(97) By causing the slurry to pass through the ion exchange resin, the amount of chlorine contained in the barium titanate-based powder is reduced.

(98) In Comparative Example 3, the amount of chlorine contained in the barium titanate-based powder not passing through the chlorine removing step is very large, and therefore the chlorine content is as high as more than 100 wt ppm even after the barium titanate-based powder passes through the chlorine removing step.

(99) E) Production of Multilayer Ceramic Capacitor

(100) A predetermined amount of each of MgO, Dy.sub.2O.sub.3, SiO.sub.2, MnCO.sub.3 and BaCO.sub.3 as an additive was added to the barium titanate-based powder (passing or not passing through the chlorine removing step) produced in each of examples and comparative examples, the mixture was put in a vinyl chloride pot together with a polyvinyl butyral as an organic binder, ethanol as an organic solvent, and a medium (2 mm) made of partially stabilized zirconia, and the mixture was stirred, pulverized, and formed into a slurry.

(101) The slurry was molded into a sheet using a doctor blade method in such a manner that the sheet thickness would be 0.8 m after firing, and the sheet was cut to a predetermined size to obtain a rectangular green sheet.

(102) Next, the green sheet was screen-printed with a conductive paste containing a nickel powder as a conductive component, thereby forming a conductive paste layer (internal electrode pattern) that would form an internal electrode layer after firing.

(103) The green sheet provided with the internal electrode pattern was laminated, a green sheet which was not provided with an internal electrode pattern was laminated as an outer layer, and pressure bonding was performed to prepare a laminated block. An unfired laminated body obtained by cutting the laminated block to a predetermined size was heat-treated in the air (at 350 C. for 3 hours) to remove the binder, and then fired for 2 hours in a reducing atmosphere of a H.sub.2N.sub.2H.sub.2O gas with a pressure of 10.sup.10 MPa at 1200 C. to obtain a fired laminated body (ceramic laminated body).

(104) A conductive paste for formation of an external electrode was applied to both end surfaces of the fired laminated body, and baked, and Ni and Sn were electrolytic-plated to form external electrodes electrically connected to the internal electrode.

(105) In this way, a multilayer ceramic capacitor as shown in FIG. 2 was prepared. The prepared multilayer ceramic capacitor has a size with a length (L) of 1.6 mm, a width (W) of 0.8 mm and a thickness (T) of 0.8 mm, the element thickness (thickness of the dielectric ceramic layer) is 1.5 m, and the number of dielectric ceramic layers laminated is 320.

(106) F) Evaluation of Reliability

(107) (1) Highly Accelerated Life Test (HALT)

(108) For 100 multilayer ceramic capacitors produced in each of examples and comparative examples, a direct current voltage of 16 V was applied at an ambient temperature of 150 C. to conduct a HALT test.

(109) At the time when the insulation resistance decreased to 10.sup.5 or less, a sample was judged to fail, and Weibull analysis was performed to calculate a mean time to failure (MTTF). The results are shown in Table 3.

(110) TABLE-US-00003 TABLE 3 MTTF of sample MTTF of sample Content of using barium using barium chlorine titanate-based titanate-based ions in powder not passing powder passing slurry through chlorine through chlorine (wt ppm) removing step (hr) removing step (hr) Comparative 40 13 13 Example 1 Comparative 70 13 14 Example 2 Example 1 230 20 20 Example 2 410 23 23 Example 3 600 24 24 Example 4 850 24 24 Example 5 1100 21 21 Comparative 2000 11 10 Example 3

(111) (2) Humidity Resistance Load Life Test

(112) Next, similarly for 100 multilayer ceramic capacitors produced in each of examples and comparative examples, a direct current voltage of 37.5 V was applied at an ambient temperature of 85 C. and a relative humidity of 85% RH to conduct a humidity resistance load life test. A sample short-circuited after 1000 hours of test was judged to fail, and a failure rate was determined. The results are shown in Table 4.

(113) TABLE-US-00004 TABLE 4 Failure rate of Failure rate of sample using sample using Content of barium titanate- barium titanate- chlorine based powder not based powder ions in passing through passing through slurry chlorine removing chlorine removing (wt ppm) step (hr) step (hr) Comparative 40 0 0 Example 1 Comparative 70 0 0 Example 2 Example 1 230 1 0 Example 2 410 1 0 Example 3 600 1 0 Example 4 850 1 0 Example 5 1100 2 0 Comparative 2000 2 1 Example 3

(114) From the results shown in Table 3, the multilayer ceramic capacitors of Examples 1 to 5 in which in the mixing step, the slurry contained chlorine ions in a ratio of 230 to 1100 wt ppm based on the amount of the barium titanate-based powder to be synthesized had a MTTF of 20 hours or more, so that satisfactory reliability was achieved.

(115) The barium titanate-based powder produced in each of Examples 1 to 5 is a barium titanate-based powder in which the integral breadth of a (222) plane diffraction peak is 0.25 or less as shown in Table 1, namely a barium titanate-based powder having high crystallinity. In the case of a barium titanate-based powder having high crystallinity, grain growth in firing may be suppressed, resulting in suppression of coarsening of crystal grains.

(116) The use of a barium titanate-based powder having high crystallinity is considered to lead to satisfactory reliability with the MTTF being 20 hours or more in the HALT test.

(117) Further, as shown in Table 4, reliability in the humidity resistance load life test was also improved by carrying out the chlorine removing step to reduce the chlorine content to 100 wt ppm or less.

(118) On the other hand, in Comparative Examples 1 and 2 where in the mixing step, the slurry contained 40 or 70 wt ppm of chlorine ions, the integral breadth of a (222) plane diffraction peak was 0.265 or 0.263, i.e. more than 0.25, so that only a barium titanate-based powder having low crystallinity was obtained. When such a barium titanate-based powder was used, grain growth occurred during firing, and thus reliability was deteriorated, so that the MTTF tended to decrease.

(119) In Comparative Example 3 where in the mixing step, the slurry contained 2000 wt ppm of chlorine ions, the amount of chlorine as an impurity was excessively large, and chlorine was dissolved, so that the MTTF tended to decrease.

(120) Further, the integral breadth of a (222) plane diffraction peak was 0.269, i.e. more than 0.25, so that only a barium titanate-based powder having low crystallinity was obtained. Further, even when the chlorine removing step was carried out, the chlorine content was not reduced to 100 wt ppm or less, and a failure occurred in the humidity resistance load life test.