JPS61261263A - Manufacture of dielectric ceramic - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application: The present invention relates to a method for producing a bismuth-doped low-temperature fired barium neodymium titanate dielectric, and more particularly to the minimum sintering temperature for obtaining a dense aged ceramic dielectric. It relates to a method in which a very small amount of bismuth is included in the starting material in order to significantly reduce the

BACKGROUND OF THE INVENTION: Many manufacturers of ceramic capacitors use barium neodymium titanate with various additives to produce bodies with a low temperature coefficient of dielectric constant, for example ±50 ppm/'O. Additives used in the prior art include alkaline earth metal zirconates, stanniates and titanates. Bismuth titanate is also added. The amount of bismuth is typically 1.8 to 4.7 moles of oxide of all cations in the body, calculated as oxides. Other manufacturers added bismuth, lead, and silicon oxides to precalcined or calcined barium neodymium titanate powder before sintering to obtain lower sintering temperatures.

However, low temperature coefficient regions containing significant numbers and amounts of additives are difficult to control in composition and dielectric properties during manufacture.

Problem to be Solved by the Invention: The purpose of the present invention is to provide a process for producing bismuth-doped titanate, licumneodymium, which significantly reduces the minimum sintering temperature of the ceramic with a particularly small amount of bismuth doping agent. . Another objective is to use the actual oxides of cations in ceramics as starting materials and to obtain a method that more reliably achieves the left-side reactivity of the starting components.

Means for solving the problem: According to the present invention, barium neodymium titanate having a low calcination temperature is prepared by preparing a mixture of powder precursors of barium neodymium titanate doped with bismuth, and calcining the precursors to react. It is manufactured by pulverizing the calcined precursor, forming the pulverized precursor into a body, and sintering the 1TE at less than 1200° C. to form a dense aged ceramic body. All of the micronized precursors or starting materials are oxides or oxide equivalents such as carbonates, hydroxides, hydrates and oxalates. The amount of bismuth-containing precursors, calculated as oxides, is 0.25 to 1.5 molar of the molar sum of all precursors calculated as oxides.

Operation: Overall, the invention is based on the recognition that the presence of particularly small amounts of bismuth in the paraelectric crystals of barium neodymium titanate material dramatically reduces the sintering temperature of this material. It is further recognized by the present invention that when a mixture of calcined barium neodymium titanate and bismuth-containing compounds such as bismuth oxide and bismuth titanate is sintered, no or little reaction occurs. Thus, in the method of the present invention, it is important to include bismuth in the starting materials for forming barium neodymium titanate, since bismuth enables the desired male doping.

EXAMPLE: A large number of experimental Queno-type capacitors as shown in FIG. 1 were assembled. The wafer body is first combined with ceramic precursor powder, wet j-ring for 2 hours, drying, granulation and 1
It is formed by the usual left side of power firing at 200°C for 2 hours. This is followed by milling and jet milling to an average particle size of about 1-1.5 microns.

Combine fine powders in organic vehicle, approximately 0.625 m thick
Pour into a (25 mil) square. This square or wafer has a minimum sintering temperature of 1100-1350°C. Apply silver electrode paste to two wide sides of each aged ceramic wafer.

The wafers with electrodes were baked at 800°C, and the first
A wafer-shaped capacitor was formed having a podium 10 and electrodes 11, 12 as shown in the figure.

The nine lowest sintering temperatures, indicated at 50° C. intervals for densification of each ceramic, are shown in Table 3 along with the corresponding composition of the ceramic for a series of experimental wafer capacitors. No sintering flux was used and all starting products reacted simultaneously on the left.

The starting products were inter alia neodymium carbonate, barium carbonate, titania, bismuth hexaoxide, lead oxide and zinc oxide. However, whether these materials are carbonates, hydroxides, hydrates, succinates or oxides, they all effectively become a group of reacted oxides after sintering. The particular shape selected from these starting materials does not affect the composition and properties of the sintered ceramic. In Table I, the ceramic compositions are conveniently given in molar amounts in the oxide form of the starting materials.

Table I Composition (mol qb> 167.5 17.010.0 15.510.0 1
! +50℃2 ” 15.5 /1.5 15.5
, /ll・0 1250#3 N 14.0 /
3,0 15.510.0 1300 〃4 N
17.010.0 14.0 /1.5 1250 〃
5 # 17.010.0 12.515.0
#〃6 N 17.010.0 11.0
/4.5 1200 〃7 # 15.5/1.5
12.5/! 1.0 # 〃871.4414
．． 7!110.0 14.2B10.0 1250〃9
// 12.7a/1.5 14.2810.0
1150 〃10' 12.78/1.5 1
2.78/1.5 1200#BaO/ZnO 1171,4414,2a10.0 127a/1.5
1250〃12 // 14.2+310.0
11.28/3.0 〃#1!168.7515.
75/1.25 14.2510.0 1150 Example 1
The main component of the ceramic of ~7 is (17Nd203)” (
15,5BaO) ” (67,5Ti02) The compositions of examples 1.2 and 3 are Bi substituted for Nd2O3.
The amount of 2O3 gradually increases. Lower minimum sintering temperature 1250 in view of the intermediate amount of bismuth doping according to Example 2
℃ is obtained.

Example 4. 5. Although the composition of 6 does not contain bismuth,
Lead is added to replace barium. Increasing the amount of lead doping also reduces the minimum sintering temperature, but the optimal amount of lead is not clear.

Although the reduction in sintering temperature due to the addition of lead is small, the addition of lead is useful because it has the effect of increasing the temperature coefficient of capacity. Adding more bismuth as in Example 7 to the lead P-ping material of Example 5 has a small effect compared to the lowest sintering temperature shown in Example 2 without lead.

Example 8 barium neodymium titanate (Nd203・BaO
・5 TiO2 composition) is bismuth or lead P
- Has a relatively low sintering temperature even without a pinging agent. However, the addition of 1.5 molar amounts of B12o3 according to Example 9 lowers this sintering temperature by 100"O.

When lead is further added as in Example 10, the sintering temperature unexpectedly increases. Substituting barium and adding zinc instead of lead, as shown in Examples 11 and 12, has no apparent effect on the sintering temperature.

Due to all the above compositions of barium neodymium titanate, N
Ceramics showing an X-ray diffraction image of d2O3"BaO' 4 TlO2 are obtained. This observation shows that 1.1.4 ceramic containing bismuth oxide with a portion of neodymium substituted, that is, 14.4 Nd2O3.16. 67BaO・66
．． 67 This leads to an experiment to produce T1o2. This material has an expected low sintering temperature and differs from all other secondary phase-based compositions by showing almost no titanium-rich second phase in scanning electron microscopy examination. This nearly single-phase composition has particular advantages over other compositions, although confirmatory studies are still needed.

In the above experiment, 1.0% of B1-3 was added to barium neodymium titanate.
In the case of 25 moltizo, the above example suggests that there is some abnormal process that has not yet been fully elucidated.

A graph of the minimum sintering temperature as a function of the amount of Bi2O3 contained in the ceramic composition is shown in FIG. 2 by curve 13. This graph shows Examples 1-7.13 and 8-12 respectively.
The lowest sintering temperatures of the three basic compositions of barium neodymium titanate indicated by the 0 group are considered. This ordered group has a minimum sintering temperature that decreases with a given type and amount of doping agent. In this way, 5ao
The phenomenon in the graph of Figure 2 for the lowest sintering temperature that occurs with the addition of s 1-25% Ti
The basic composition of all barium neodymium titanates of the general titanium-rich class contains at least 25 tS each. The special vertical scale used in the graph of FIG. 2 takes into account the base materials of Examples 1-70.

These experiments necessitate another series of experiments to precisely determine the effect that bismuth doping of barium neodymium titanate has on sintering temperature.

Using the method described for the fabrication of the queha bodies of Examples 1-13, the materials of Examples 14-22, whose material compositions are shown in Table 1, were made.

Table ■ 14 68.75 17.0Q10.0 14.251
5 〃16.2510.85 ”16 〃15.
75/1.25 〃17 〃15.25/1
．． 75 〃18 〃14.75/2.25
#19 〃14.25/2.75 〃20 1/
15.7515.25 /121 〃15.2
515.75 〃22 〃12.75/4.25
As mentioned above, the bismuth is advantageously reacted initially with a precursor of the basic barium neodymium titanate. However, sintering was carried out one at a time for each day, increasing the temperature by 6.7°C/min, holding at 1200°C for 60 minutes, and then heating to 1300°C at the same rate. The thickness of the opened can body was continuously measured with an inflatable needle. The sintering curves thus obtained are shown in FIG. 6 for each side. Here, the number of each curve corresponds to the example number. Curve 23 shows the furnace temperature.

Sintered meso from each formulation is examined by scanning electron microscopy. When the bismuth oxide doping amount is greater than 3.25 moles, a second phase of bismuth titanate begins to appear, indicating a very limited solubility and affinity of barium neodymium titanate for bismuth.

Data points from the experimental information shown in FIG. 6 were plotted in the graphs of FIGS. 4 and 5. In the graph of Fig. 4, curve 25 indicates the sintering temperature at which 6.5 inches of shrinkage occurred.
Shown as a function of pinging agent content. Song W in the graph of Figure 5
s27 is fitted to a data point plotting shrinkage at 6.5 hours of sintering. These curves show the unusually large advantage of Bia03 of about 1.2s*tp-zo in this ceramic system.

Furthermore, the valley centered at about 1.25 mmol of Bi2O3 in song #I25 is deep and very narrow. In fact, the best performance is 1.
This is achieved with a doping amount of less than 5 molar amounts, especially less than 1.4 molar amounts. Bi2O3 doping agent 1.25 molar is B12o,,y
- corresponding to lower sintering temperatures obtained using other amounts of pinging agent.

Electron microscopy and micro-Rozorode analysis of some of the sintered samples of Examples 1 to 16 show that the main base of barium neodymium titanate is Small spots of high titanate second phase were observed. The number N of cations in the basic barium neodymium titanate is very approximately represented by 3(NNd + NB&) = 2NT□, whereby each Nd cation removed in the crystal replaces a portion of the Nd cations. The use of a c11 phase formation (avoidance of a second phase) which still gives a one-phase crystalline composition instead of a large number of Ba cations provides a simple system that is easily understood and therefore provides better manufacturing control and is advantageous. It is. Maintaining one molar deviation of the six major cations within 5 or 6 inches of the amount indicated by the one-phase relationship is considered sufficient to obtain the control benefits.

In order to use the optimally bismuth-doped barium neodymium titanate composition in the production of monolithic ceramic capacitors with low cost silver-palladium electrodes, flux is added to the raw ceramic slurry to further reduce the sintering temperature. It is hoped that Commonly used alloy 70A
g/60pa (jusagi part) has a melting point of 1160℃, and the capacitor sintering temperature is 115℃ to avoid melting of the buried electrode.
Must be below 0°C. Electrodes with higher silver content melt at lower temperatures, but are of course more expensive.

Each of the various experimental monolithic capacitors was manufactured using the following conventional process. Ceramic with high sintering temperature (i.e. 68.75'I'102-15-75 NdaO
s ・1-25 Bi25s ・14-25 Bad)
The calcined and ground fine powder of
To and lecithin 5% were mixed in vehicle and binder medium. This slurry containing about 70% solids by weight was milled for about 6 hours.

The ground slurry was sequentially cast onto a glass substrate, each layer was dried in turn, and an electrode paste of 70% silver and 30% palladium was screen printed onto the cast and dried layers. The screen printed pattern of electrode paste was dried before casting the subsequent dielectric layer. As shown in FIG. 6, a body 30 having embedded electrodes 31 and 32 was cut out from the laminate and fired at 1100° C. for 21/2 hours until ripening.

Next, silver paste was applied to both ends of the podium 30 where the edges of the buried electrodes were exposed. The pode was fired at 750° C. for several minutes to form silver terminals 35 and 36.

The compositions of examples 26-29 of these experimental monolithic capacitor ceramic bodies are shown in Table 2 along with TCC and DF data.

Table ■ 2597 5 Cd()2ZnO・B2O3N650
．． 012495 5 CdO'2ZnO"B2O3N
500.0122 Bi2Ti20fu2595 3 Cd0・2ZnO・B2O3P7 0
．． 0074 PbTiO3 26923Cd0・2ZnO-B203 N4 (L
O153PbTiO3 2BaTi03 2792 3 Cd0・2ZnOB203 N270
．． 0095 BaTiO3 2898,5L5 BaO・2B2C)s N47
CLOO32997-752,25BaO*B2O3N
540.0073068 29 8rTi03 5 Cd0-2ZnO-8203N7500.01 All these capacitor bodies are sintered at 1100°C and are nearly non-porous and dense. The dielectric constants of all bodies were 75-90.

Dissipation factor (DF) was measured at 1 KHz. Small amounts of lead and/or barium titanate have a temperature coefficient of capacity (
It is considered an effective means for adjusting TCC).

The high-fired additives lead titanate, barium titanate, bismuth titanate, and strontium titanate appear to have little, if any, reactivity with neodymium titanate, which is calcined during sintering. Other additives including alkaline metal zirconates and stannate have been used with similar effect. As mentioned above, these are useful for adjusting the temperature coefficient of the body, but have relatively little effect on other properties. For example, the dielectric constant of the ceramic pods of Examples 23 to 29 ranges from 60 to 80, and that of Example 60 is about 9.
It is 0.

The effect of these additives on the minimum sintering temperature is almost zero.

Example 2 except that in another experiment (Example 26A) bismuth is not used to form calcined barium neodymium titanate.
One material was made in the same way as in step 6. Bi2O34 instead
, 25% by weight in combination with 3% by weight of zinc borate PR Tam flux, so the ingredients of this Example 23 were as follows: Example 26
(For example, bismuth oxide is 1.25 mole of barium neodymium titanate). 10 raw pods of two examples 26 and 23A
Sintered at 50° C. for 21 hours. Although the pode of Example 23A was porous and not well densified and had poor electrical properties (e.g. DF=o, 14ts), the pode of Example 23 was dense and otherwise sintered at 1100°C. It cannot be distinguished from that of this same group.

The barium borate fluxes of Examples 28 and 29 were found to be very effective in reducing sintering temperatures and obtaining low DF. Other fluxes tested were magnesium borate and cadmium silicate. Silicates were found to be less effective at lowering the sintering temperature, and borate fluxes were found to be advantageous9.

In another experiment, calcined and ground bismuth-doped barium neodymium titanate or 17Nd2 (C
O3)・16.75BaC03・1.25Bi203
・68 TiO2 with 34% by weight of pb'rio and powder flux or sintering aid Cd0.2 ZnO.B, 0
33% by weight. A slurry of this mixture was used to form the galvanic portion of a group of monolithic ceramic capacitors. The buried electrode is 70Ag:/50P(
Consists of 1 alloy. The organic binder is removed at about 700°C,
The ceramic capacitor was placed in an aluminum crucible with an airtight cover and sintered at 11,100° C. for 21/2 hours.

The capacitance of each capacitor is 1000 pF.

DF is 0.01% with lKH2! low, 10MHz
The DF is approximately 0.051. The induction factor is 80±2. The insulation resistance is greater than 106 megohms and the temperature coefficient of capacitance is 0±10 ppm/°C from -55°C to +125°C. Dielectric thickness mil (0,0251111) at 150℃
No deterioration of these properties was observed after 200 hours of stress in this D1604e bolt. This barium neodymium titanate meets the above criterion of 6 times the sum of neodymium and barium atoms being within 6% of twice the number of titanium atoms, and the titanate component is a substantially one-phase material.

The experiment compared the properties of various ceramic materials in which various amounts of bismuth oxide were incorporated into the starting components by substituting one mole of bismuth oxide per mole of neodymium oxide. By introducing an equal amount of bismuth oxide in place of the titanium oxide, this same bismuth addition was found to be even more effective in lowering the minimum sintering temperature. When bismuth replaces titanium in this way, stoichiometry is clearly maintained approximately and sintering is more easily achieved. For the above 1:1:4 phase, the composition is (1-X')Nd2O・lB1203・BaO11
It is represented by 4T102.

Examples 1-1 except that bismuth is introduced instead of titanium.
Examples 61 to 6 having the ceramic composition shown in Table 1 using the same method as described for preparing the ceramics of Example 6
Five groups of ceramic wafers corresponding to No. 5 were prepared.

Table■ 31 14.25 17.00 68.7510.00
62 ・II # 68.0Q10.7555
〃” 67.50/1.2534 # 〃
67, OG/1.7565 “ 66.50/2
．． The wafers from each sample were sintered in separate crucibles at 1250° C. to ensure densification of all wafers. Representative wafers from Examples 14-18 in which bismuth additive replaced neodymium were similarly sintered. The degree of shrinkage was measured for each sintered wafer, and the value for each theoretical density was 5.67 for 100 inches of theoretical density for these materials.
Calculations were made based on this measurement in g/cIcj.

In FIG. 7, a curve 29 is plotted showing the curve 29 for the theoretical density of the wafers of Examples 14 to 18 (Table 2). Examples 31-6
A similar 7° lot for the wafer No. 5 (Table ■) is shown by curve 30 in FIG. These curves show that bismuth substitution of titanium (track 11iI30) is more effective and results in less doping of bismuth than that shown by the neodymium substitution example shown by curve 29.
It is clear that the Ik low sintering temperature significantly lowers the sintering temperature. Actually Bi2O at about 85% of the theoretical density.

requires rounding 0.5 inch to replace neodymium, but
To obtain the same density considered suitable for sintering, approximately 0.2
Titanium may be replaced with 5 moles of Bi2O3. Thus, the large reduction in sintering temperature, which is a feature of the present invention, can be achieved with an amount of 0.25 mmol of bismuth oxide.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a wafer-type capacitor having the body of the present invention, Figure 2 is a diagram showing the relationship between bismuth doping amount and minimum sintering temperature, and Figures II and 5 are diagrams showing the relationship between sintering time and temperature and shrinkage. Figure 4 shows the relationship between the bismuth doping amount and sintering temperature taken from Figure 3, and Figure 5 shows the relationship between the amount of bismuth doping and shrinkage taken from Figure 6. 6 is a cross-sectional view of a multilayer capacitor, and FIG. 7 is a diagram showing the relationship between the bismuth doping amount and the theoretical density. 10.30...Body, 11, 12, 31° 32・・・
・Electrode, 35.36...Terminal sintering time (h)

Claims (1)

[Claims] 1. Prepare a mixture of powder precursors each of which is an oxide or an oxide equivalent of barium neodymium titanate doped with bismuth, and calculate the amount of bismuth as Bi_2O_3 to form the precursor oxide. 0.25 to 1.5 of the molar sum of
mol%, and the relative number N of cations in barium neodymium titanate is 3 (N_N_d + N_B_a) = 2N_
T_i, and the number N of each of these three cations is actually 4% of the number represented by this formula.
Calcining this mixture to react the precursors to produce bismuth-doped barium neodymium titanate; Grinding and pulverizing the calcined titanate; Calcined and pulverized titanate 1. A method for producing a dielectric ceramic, comprising forming a salt body and sintering the body at a temperature below 1250° C. to form a dense aged ceramic body. 2. The method according to claim 1, wherein the amount of Bi_2O_3 is lower than 1.4 mol% of the molar sum. 3. Claim 1 in which the oxide equivalent is selected from carbonates, hydroxides, hydrates, oxalates and combinations thereof
The method described in section. 4. To further reduce the sintering temperature to below 1160°C, the crushed sintering flux is mixed with the pulverized and calcined titanate, and the palladium is not more than 30% by weight of silver and palladium. A body is formed containing a buried layer of electrode paste made of palladium, and this body is sintered at a temperature below 1160° C. in order to form the buried electrode so that it does not melt during sintering and does not flow out of the body. A method according to claim 1. 5. The method of claim 4, wherein the flux comprises a glass-forming element selected from boron, silicon, and combinations thereof. 6. The method of claim 5, wherein the amount of flux is less than 3% by weight of the micronized and calcined titanate. 7. Selected from titanate, zirconate, stannate and combinations thereof, as the micronized and calcined titanate improves the temperature coefficient of dielectric constant without significantly changing the minimum sintering temperature of the body. 5. A method according to claim 4, comprising a ground and calcined compound. 8. The method of claim 7, wherein the ground and calcined titanate, zirconate and stannate are selected from barium, calcium, strontium, bismuth and lead salts. 9. The molar composition given as a precursor oxide of barium neodymium titanate doped with bismuth is 17.0Nd_2O_3・13.75BaO・68.
0TiO_2.1.25Bi_2O_3 The method according to claim 1. 10. Barium neodymium titanate doped with bismuth shown as a precursor oxide is (1-x)Nd_2O_3・xBi_2O_3・BaO
- The method according to claim 1, which is 4TiO_2.