JPH03119608A - Nonreducing dielectric ceramic - Google Patents

Abstract

PURPOSE:To reduce variation ratio of electrostatic capacity to DC electric field in nonreducing dielectric ceramic by setting an oxygen defective quantity of the ceramic in the specific range. CONSTITUTION:In nonreducing dielectric ceramic composed of barium titanic acid as the principal ingredient and the other metallic oxide, to reduce variation ratio (DC bias characteristics) of electrostatic capacity to DC electric field can be realized by setting the oxygen defective quantity in the ceramic which is calculated on the basis of weight difference between before and after heat treatment at 1000 deg.C in the air, for a range from 10<17> to 10<19>pcs/cm<3>. As a result, a lamination layer type ceramic condenser of which inner electrode is made of a base metal such as nickel can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a non-reducible dielectric ceramic suitable for a ceramic capacitor, particularly a laminated ceramic capacitor having an internal electrode made of a base metal such as nickel.

(Prior Art) Conventionally, multilayer ceramic capacitors generally consist of sheet-like BaTi0. It is formed by laminating a plurality of sheets of dielectric material whose main component is, connecting the internal electrodes of each sheet alternately and in parallel to a pair of external connection electrodes, and sintering and integrating them. Such laminated ceramic capacitors have come to be used in a wide range of electronic circuits as electronic components have rapidly become smaller with the recent advances in electronics.

However, ordinary dielectric materials mainly composed of BaTiOs need to be fired at a high temperature of 1250°C to 1350°C, and when this material is used as the dielectric of a multilayer ceramic capacitor, the internal electrodes are Palladium (melting point: 1555° C.), which is an expensive noble metal that does not melt or oxidize at the firing temperature, or an alloy thereof is used. Conventional multilayer ceramic capacitors have excellent dielectric properties, but their price has been a major impediment to their progress, especially for those with large capacitances, which increase the number of internal electrodes, resulting in higher costs.

Therefore, attempts have been made to use inexpensive base metals, such as nickel, as the internal electrodes in order to overcome the drawback of the conventional multilayer ceramic capacitors being expensive. However, when a base metal such as nickel is used as an internal electrode, when simultaneously sintering a dielectric material such as barylum titanate (BaTiOs) and a base metal internal electrode, the conditions are such that the base metal can be sintered as a metal film without being oxidized. is Ni/
The equilibrium oxygen partial pressure of NiO is approximately 3X10 at 1300℃
-ate, the oxygen partial pressure must be lower than that, and in this case, the dielectric material made of barium titanate or its solid solution is generally reduced and loses its insulating properties under the above oxygen partial pressure. This has the disadvantage that practical dielectric properties for a multilayer ceramic capacitor cannot be obtained.

Therefore, various compositions have been proposed as non-reducible dielectric ceramic compositions. For example, BaT to.

Japanese Patent Publication No. 57-425 reported that reduction resistance can be improved by incorporating A ions in excess of the stoichiometric ratio in the ABOs-type perot-type lobskite structure represented by
No. 88, Ca is added as an additive to BaTiO3.
Ti0. ．． 5rTiO, etc., BaZr0.
In addition to zirconate salts such as , CaZr01, MgZrOs, Bit's and their compounds, Yz(h, Lag'
s, rare earth oxides such as Nd2O2, nino, MgO
, AI! It has been proposed to combine various metal oxides such as 03.

(Problems to be Solved by the Invention) Up until now, non-reducible dielectric ceramic compositions have been improved by improving the composition through combinations of additives, etc., as described above, to achieve the required main properties, namely, high dielectric constant and high dielectric constant. Insulation resistance, low dielectric loss,
Regarding characteristics such as reduction of temperature change rate of dielectric constant,
I was able to get something that was satisfying to a certain extent.

However, in addition to the above characteristics, temperature-stable multilayer ceramic capacitors are required to have a small rate of change in capacitance with respect to a DC electric field (hereinafter referred to as DC bias characteristics). This DC bias characteristic depends not only on the applied DC electric field (but also on the measurement temperature and the application time of the DC electric field).

Conventionally, regarding this DC bias characteristic, Pd or Ag-P
This did not pose any particular problem in a multilayer ceramic capacitor manufactured by using d as an internal electrode and firing in the atmosphere. However, in multilayer ceramic capacitors manufactured by firing in a reducing atmosphere using base metals such as Ni as internal electrodes, although the initial characteristics are met, the DC bias characteristics described above, especially the change in capacitance with respect to the application time of the DC electric field, are It had the fatal drawback of being large.

Although additives have been investigated for the above characteristics, non-reducible dielectric ceramics with good and stable characteristics have not yet been obtained, and therefore this type of multilayer ceramic capacitor The current situation is that the practical application of the technology has been delayed.

(Means for Solving the Problems) As a result of repeated research into the relationship between this non-reducible dielectric ceramic and the above DC bias characteristics, the inventors have found that the above characteristics are highly dependent on the amount of oxygen defects in the porcelain. find something to do,
After further consideration of the preferable amount of defects, we found that the amount of oxygen defects in porcelain calculated from the weight difference before and after the treatment when porcelain obtained by firing in a reducing atmosphere was heat treated in air at 1000'C. 10'7~1019 pieces/d
It has been found that excellent DC bias characteristics can be obtained by setting the value within the range of .

The present invention will be explained in detail below.

Non-reducible dielectrics, such as barium titanate (BaTi), are commonly used in multilayer ceramic capacitors with Ni internal electrodes.
When porcelain whose main component is Os) is fired in a reducing atmosphere, free electrons (e') and oxygen defects (vO) are generated by the reducing action of the atmosphere according to the following formula (1). Insulation resistance tends to decrease. Therefore, in order to suppress this decrease in insulation resistance, low valence elements called acceptor type elements such as MnO are used for BaTi0+.
By the following formula (2), a large amount of oxygen defects (■6) and Via % M
Cation site defects such as nTi are generated. Since insulation resistance increases as the amount of solid solution of Mn in Ti sites and the concentration of oxygen vacancies increase, attempts have been made to increase the amount of oxygen vacancies by adding a large amount of acceptor type additives such as MnO. According to measurements made by the present inventor, the number of defects was approximately 1020/C-.

On the other hand, the present invention is completely contrary to the conventional concept as described above, and aims to improve the DC bias characteristics by reducing the amount of oxygen defects in the porcelain. This is due to the large amount of oxygen defects formed by formula (2) or cation site defects such as V□ and Mn71, which have polarizability in pairs, and the polarization acts as a local bias, resulting in the dielectric It is based on the idea that the voltage characteristics are susceptible to deterioration.

This is made clear from FIG. 1, which shows the relationship between the amount of oxygen defects in porcelain and the rate of change in capacitance over time.

That is, it is understood from FIG. 1 that as the amount of oxygen vacancies decreases, the rate of change decreases, that is, the voltage characteristics are significantly improved.

Based on the relationship between the above characteristics and the amount of oxygen defects, it is important that the non-reducible dielectric ceramic of the present invention has an amount of oxygen defects of 10'7 to 1019/c+4, particularly 1017 to 10111/ld. Therefore, if the amount of oxygen defects is more than 1019/d, the effect of improving the DC bias characteristics cannot be obtained, and for porcelain with the amount of oxygen defects less than 1017/cd, the oxygen concentration in the atmosphere during firing must be considerably high. This is undesirable because the Ni internal electrodes may be oxidized.

In addition, the amount of oxygen defects in the present invention is based on the thermogravimetric method. Porcelain fired in a reducing atmosphere is heat-treated in the atmosphere at 1000°C, and the porcelain is sufficiently supplied with oxygen to reach a saturated state (this (assuming that the oxygen defect concentration at (!=i6g/d) NA: Avogadro's number (#6.022 x 1023/mol) River 0:
It was calculated based on the atomic weight of oxygen (15,999 g/mol).

The amount of oxygen defects in porcelain mainly depends on the oxygen partial pressure during firing of the porcelain and the oxygen annealing conditions during cooling, and as is clear from the above explanation, it also greatly depends on the amount of acceptor type additives added. do. In addition, since it changes depending on the powder physical properties of the BaTiO3 raw material powder, it is necessary to comprehensively control these. For example, the amount of oxygen vacancies in the porcelain tends to decrease as raw material powder whose sphericity is closer to 1 is used.

In addition, although the non-reducible dielectric ceramic of the present invention is mainly made of BaTiOs, other dielectric properties such as dielectric constant and temperature characteristics are improved, except for setting the amount of oxygen vacancies within the above-mentioned range. There is no problem in adding the above-mentioned known additives for the purpose of BaTi0. If used alone, the insulation resistance will deteriorate significantly, which is undesirable. Therefore, it is preferable to use MnO in a proportion of 0.1 to 10 mol% based on the total amount.
MgO, MgO-Zr0t, CaZrO3, CaTiO
In addition to s, it is preferable to add a rare earth oxide or the like as appropriate.

The invention will now be explained with the following examples.

(Example) BaTiO, a powder with excellent crystallinity with a sphericity of about 1 and an average size of 1μ, was used as a raw material, and MgO1M was added as an additive.
n01 Furthermore, MgO-ZrO was weighed in the proportions shown in Table 1, wet-pulverized and mixed in a ball mill, dried and granulated, and the granules were press-molded at a pressure of 1 ton/cm2 to form 12 mmφ A doublet for evaluating characteristics and a tablet for measuring the amount of oxygen vacancies were prepared.

After depyrining these tablets at 400° C., they were fired by setting the firing temperature and oxygen partial pressure in the firing atmosphere to the conditions shown in Table 1.

The amount of oxygen defects in the obtained porcelain was measured as follows.

First, the cylindrical part of the obtained porcelain is polished, ultrasonically cleaned in acetone, and dried at 150° C. for 1 hour.

The weight of the porcelain is then measured using a microbalance.

After the measurement, the porcelain was heat-treated in air at 1000° C. for an hour, then weighed again using a microbalance, the weight difference (Δm) before and after the heat treatment was calculated, and the amount of oxygen defects was calculated using the above-mentioned formula (3).

On the other hand, the dielectric constant and insulation resistance of the porcelain for characteristic evaluation were determined after being left at room temperature for 24 hours, at a frequency of 1.0 KHz, and an input signal level of 1. OVr+++s, under the condition of applying a DC voltage of 50 V, and further voltage characteristics, the change in capacitance due to the application time with a voltage of 1.3 KV per 1 m+a applied to the porcelain, AC = IKHz, 2 V/mm for 10,000 seconds The rate of change in capacity from 1000 seconds to too many seconds was calculated. The results are shown in Table 1.

(Left below) In Table 1, the relationship between the amount of oxygen vacancies and voltage characteristics is shown in Table 1.
Shown in the figure.

According to Table 1, it can be seen that the rate of change in voltage characteristics is large for all samples with Nα2, 3.7, in which the amount of oxygen vacancies exceeds 10'9/cyh. Although it is within the scope of the present invention, other insulation resistances are low, so it is necessary to improve it by adding other oxides.

On the other hand, samples Nα1.4 and Nα5.6 of the present invention both showed excellent DC bias characteristics, and at the same time obtained satisfactory results in both dielectric constant and insulation resistance, and sample Nα6 in particular was the most excellent. .

(Effects of the Invention) As detailed above, the non-reducible dielectric ceramic of the present invention can improve voltage characteristics while having high insulation resistance by setting the amount of oxygen defects within a specific range. As a result, the practical application of multilayer capacitors using temperature-stable base metals such as nickel as internal electrodes can be greatly promoted.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of oxygen vacancies and voltage characteristics.

Claims (1)

[Claims] (1) In non-reducible dielectric porcelain whose main component is barium titanate and which also contains metal oxides,
Non-reducible dielectric porcelain, characterized in that the amount of oxygen defects in the porcelain calculated based on the weight difference before and after heat treatment at °C is 10^7 to 10^1^9/cm^3.