JPH02221152A - Production of dielectric porcelain - Google Patents

Abstract

PURPOSE:To obtain dielectric porcelain having high permittivity regardless of small grain size by adding both at least one or more kinds of the compd. of element selected from La, Ce, Nd, Pr and Sm and Zr compd. to barium titanate of a raw material and molding the mixture and calcining the molded body in the oxygen atmosphere. CONSTITUTION:Dielectric porcelain is obtained by adding both at least one or more kinds selected from among La compd., Ce compd., Nd compd., Pr compd., Sm compd. and Zr compd. to BaTiO3 of a raw material and molding this composition and calcining the molded body in the atmosphere contg. >=60% e.g. 95% O2 concn. The contents of respective components contained in this porcelain are regulated to 2.5-5.0mol% oxide of La-series elements and 0.5-5mol ZrO2 for 100 mol% BaTiO3. When this dielectric porcelain is utilized, a miniaturized laminated porcelain capacitor having large capacity is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to a dielectric material mainly made of barium titanate, which has a high dielectric constant, a small change in capacitance due to temperature, and a dense dielectric ceramic. This invention relates to a method for manufacturing porcelain.

(Prior Art) Many ceramic capacitor compositions based on barium titanate have been known. Barium titanate has a Curie point around 120°C, 10,000°C.
Although it shows a similar dielectric constant, barium titanate alone cannot achieve a high dielectric constant at room temperature.

For this reason, a so-called shifter material is added to move the Curie point to room temperature and provide a high dielectric constant at room temperature. Tin oxide, zircon oxide, and rare earth metals are well known as this shifter material.

By the way, the recent trend of miniaturization of ceramic capacitors, especially in multilayer ceramic capacitors, is that the thickness of the ceramic dielectric is 1
There is a tendency for the layer to become thinner, with a thickness of 0 μm to 20 μm. In addition, it is desired that the grain of porcelain be small from the viewpoint of reliability, and porcelain compositions based on barium titanate with small grains are proposed in Japanese Patent Application No. 56-18059 and Japanese Patent Application No. 57.
-16809, patent application No. 57-105919. Special request 1977
No. 7-196469 has been proposed. These barium titanate-based porcelain compositions are made by adding cerium oxide to barium titanate, adding cerium oxide and barium zirconate, or adding neodymium oxide, and creating them in an atmosphere with air circulation. By firing, barium titanate with small grain size was obtained.

(Problems with the prior art) However, in the method for manufacturing dielectric ceramic described above, the dielectric constant is around 10,000 at room temperature, which is lower than that of barium titanate with large grains, making it difficult to use multilayer ceramic capacitors. When miniaturized, it has been difficult to obtain large capacitance.

In addition, since changes in grain boundaries are thought to be largely influenced by properties, barium titanate with a small grain size has a larger grain boundary area than barium titanate with a large grain size and high dielectric constant. , the dielectric constant inevitably decreased.

Therefore, the present invention is an attempt to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing dielectric ceramic that can have a high dielectric constant despite having a small grain size. It is.

(Means for Solving the Problems) The method for manufacturing dielectric porcelain of the present invention includes barium titanate 1
Lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide relative to 00 mol%.

Obtain dielectric ceramic containing 2.5 mol% to 5.0 mol% of at least one oxide selected from samarium oxide and 0.5 mol% to 5.0 mol% of zirconium oxide. In this case, lanthanum compound is used for barium titanate raw material.

It is characterized by firing a molded body made of a composition to which at least one selected from cerium compounds, neodymium compounds, praseodymium compounds, and samarium compounds and a zirconium compound are added in an atmosphere with an oxygen concentration of 60% or more. be.

(Example) First, barium carbonate and titanium oxide were mixed in a molar ratio of 1:
1, and mixed for 16 hours in a ball mill using zirconia cobblestones to obtain a mixture. After evaporating the water in the obtained mixture, 1150
The mixture was calcined by being held at ℃ for 2 hours, and then ground again in a ball mill until the average particle size became 2 μm or less to obtain a fine powder of barium titanate.

Next, for the obtained barium titanate fine powder,
Lanthanum oxide in the proportions shown in Table 1.

Cerium oxide, praseodymium oxide, neodymium oxide,
Samarium oxide, zirconia oxide, and barium zirconate were selectively added and weighed, and a vinyl acetate binder was added and mixed for 16 hours. At this time, titanium oxide, silicon oxide, aluminum oxide, and manganese carbonate were selectively added as mineralizing agents.

Next, after drying and granulating this, 2000Kg/cm2
Press molding was carried out at a pressure of 10 mm to obtain a disc-shaped molded body with a diameter of 10 mm and a thickness of 1 mm. Then, the obtained molded body was fired under the firing conditions shown in Table 1 to obtain dielectric porcelain. Note that the firing patterns A, B, and C of the firing conditions are as follows. Firing pattern A is as shown in Figure 1 (A>).
The temperature is raised at a rate of 200° C./hour, held at that firing temperature for 2 hours, and then cooled to room temperature at a rate of 200° C./hour. Firing pattern B is as shown in Figure 2 (B), in which the temperature is raised to the firing temperature shown in Table 1 at a rate of 200°C/1 hour in an oxygen atmosphere with the oxygen concentration shown in Table 1. After holding the firing temperature for 2 hours, it is cooled to room temperature at a rate of 200° C./hour. Firing pattern C is as shown in Figure 1 (C).
The temperature was raised at a rate of °C/1 hour, and the firing atmosphere was changed from air to an oxygen atmosphere with an oxygen concentration shown in Table 1.
The temperature is increased from 800° C. to the firing temperature shown in Table 1 at the same rate. Then, under the oxygen atmosphere, at the same firing temperature,
After being maintained for a certain period of time, it is cooled down to 800° C. at a rate of 200° C./hour, and the firing atmosphere is returned to the atmosphere and cooled down to room temperature at the same rate.

Next, a silver electrode was formed on the amphiboid surface of the obtained disc-shaped dielectric ceramic by baking to obtain a sample of a ceramic capacitor. Then, the dielectric constant, dielectric loss, and rate of change of capacitance with temperature at room temperature were measured for the obtained ceramic capacitor, and the results are shown in Table 2. Note that the dielectric constant and dielectric loss were measured at a frequency of IKHz, and
Regarding the rate of change in capacity with temperature, the capacity at 85°C was measured based on the capacity at 20°C.

In the above-described embodiments, an oxide was used as a compound added to barium titanate, but the compound is not limited to an oxide, and the following compounds may also be used.

Lanthanum compound - La2CO3, La ([03) 2.
La (C204) 3 cerium compound・CeCO3,
Ce(803)3. Ce(OH)4 neodymium compound/
・・Nd (DH) 3td(NO3) 3°Nd2(
CO3)syNd2(C20a)3Praseodymium compound-Pr2((:03)3tPr(NO3)3Semarium compound-Sm2(C20a)3tsm(NO3)3Zirconium compound-=-BaZr03.(:aZr0
3. ZrCl4゜ZrO(NO3)2. Zr0(CH
3COO) 2 (hereinafter referred to as blank space Table 1); beating is outside the scope of the author's work.As is clear from Tables 1 and 2, the sample (sample number 4
-13), the grains of the sintered bodies were as small as 1 to 31 tm, and they exhibited high dielectric constants of 13,000 or more. In addition, the temperature change rate of capacity at 85°C is within -80%,
It satisfied the F characteristic, which is the temperature characteristic of the JIS standard (the rate of change in capacitance from -25°C to +85°C does not exceed 180% to +30%, based on the capacitance at 20°C).

Furthermore, regarding Sample N (sample numbers 1 to 3 and sample numbers 14 to 18), which are outside the scope of the present invention, the following can be understood.

(b) In sample numbers 1 and 2, added lanthanum oxide,
Since the amount of cerium oxide, neodymium oxide, and samarium oxide added is small, the dielectric constant at room temperature is low.

(b) In sample No. 3, the amount of zirconia oxide added is small and the rate of change in capacity with temperature exceeds 180%, making it impossible to satisfy the F characteristic, which is the temperature characteristic of the JIS standard.

(c) For sample numbers 14 and 15, cerium oxide.

Because the amount of neodymium oxide and samarium oxide added is large, the Curie point moves to a lower temperature and the dielectric constant at room temperature becomes lower.

(d) In sample numbers 16 to 18, the oxygen concentration during firing was low and the dielectric constant was low.

(Effects of the Invention) As explained above, according to the method for manufacturing dielectric ceramic of the present invention, dielectric ceramic having a high dielectric constant can be obtained despite having a small grain size.

Further, by using such dielectric ceramic, it is possible to obtain a multilayer ceramic capacitor that is smaller and has a larger capacity than conventional multilayer ceramic capacitors.

[Brief explanation of the drawing]

FIGS. 1A to 1C are explanatory diagrams showing firing patterns (the relationship between firing atmosphere, temperature, and time). No. (△) (已) Mouth

Claims (1)

[Claims] Based on 100 mol% of barium titanate, 2.5 mol% to 5.0 mol% of at least one oxide selected from lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide, and cemarium oxide, and zirconium oxide When obtaining dielectric ceramic containing 0.5 mol% to 5.0 mol% of barium titanate, at least one compound selected from lanthanum compounds, cerium compounds, neodymium compounds, praseodymium compounds, and samarium compounds is added to the barium titanate raw material. A method for producing dielectric porcelain, which comprises firing a molded body made of a composition containing a zirconium compound or more and a zirconium compound in an atmosphere with an oxygen concentration of 60% or more.