JPH11106256A - Production of barium titanate-based semiconductor material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a material, having a region for forming a semiconductor of a low resistance within a wide temperature range and stable in characteristics by irradiating a formed compact formed of a semiconductor-forming agent selected from a raw material powder containing a rare earth element, Nb, Ta, W and Sb in a barium titanate-based magnetic composition with microwaves, heating and sintering the formed compact. SOLUTION: A formed compact formed of a semiconductor-forming agent selected from a raw material powder containing a rare earth element, Nb, Ta, W and Sb in a barium titanate-based magnetic composition is irradiated with microwaves used at preferably >=5 GHz, more preferably >=6 GHz frequency, heated and sintered at preferably 1,150-1,450 deg.C sintering temperature for preferably about 5-30 min sintering time. In the raw material formed compact at a low concentration of <0.2 mol.% of the added semiconductor-forming agent, the sintering is advanced at a low temperature in a short time by the microwave sintering and the abnormal grain growth is suppressed to provide a uniform granular structure. In the raw material formed compact at a high concentration of >=0.2 mol.% of the added semiconductor-forming agent, the diffusion of substances is more activated as compared with that of baking in an electric furnace and sintering reaction is promoted to achieve grain growth. Thereby, the sufficient semiconductor formation is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor ceramic (hereinafter abbreviated as a PTC element) having a positive temperature coefficient of electrical resistance. The present invention relates to a method for producing a barium titanate-based semiconductor material that provides a material.

[0002]

2. Description of the Related Art A barium titanate-based semiconductor material contains barium titanate as a main component and contains a trace amount of one or more rare earth elements such as Bi, Sb, Ta and La, and has a specific resistance at room temperature. Is low, and when the resistance exceeds a sudden change point (Curie temperature), a significant positive change in resistance temperature is exhibited. Utilizing this characteristic, it is used as a temperature sensing element, a current limiting element, or the like. Generally, such a semiconducting mechanism is widely understood by valence control theory. However, when the amount of the semiconducting agent added to barium titanate exceeds 0.2 mol%, the specific resistance at room temperature increases again, and at 0.8 mol%, it becomes an insulator again. This phenomenon is accompanied by rapid miniaturization of the sintered body particles, and it is clear that the growth of the particles is deeply related to the conversion to a semiconductor. However, the mechanism of the transition from the semiconductor to the insulator has been variously discussed and has not been clarified yet. Therefore, in the conventional manufacturing method, in order to obtain a barium titanate-based semiconductor porcelain, the upper limit of the amount of the semiconducting agent is limited to 0.6 mol%. In addition, since a semiconductor region showing low resistance is narrow, it has been a cause of variation in commercialization. Also, a method of adding Mn is known in order to widen the range of semiconductor conversion.

For example, Japanese Patent Application Laid-Open No. 50-76112 discloses a barium titanate-based porcelain composition as a basic composition,
In this basic composition, 1.5 to 15 mol% of Ba is C
e, a rare earth element such as Y, La or the like, Bi is substituted with at least one of Bi, and Mn is added to 0.1 mol per 100 mol of the basic composition.
A barium titanate-based semiconductor ceramic composition containing 0 to 0.30 mol% is disclosed.

[0004]

However, the effect of the method described in Japanese Patent Application Laid-Open No. 50-76112 is as follows.
This property can be obtained only with a material in which the Ba site is replaced with Y or the like, and is not applied to a material in which the Ti site is replaced with Nb, Ta, or the like. Further, it is necessary to control a very small amount of Mn in a narrow range, and it is essential to minimize the contamination of impurities such as Mn and Fe from the raw materials used and the external environment. From these, the above-mentioned JP-A-50-76112
The method described in Japanese Patent Application Laid-Open Publication No. H10-15064 cannot be said to be an essential solution for expanding the semiconductor region. To date, many proposals have been made on the material composition and manufacturing method for further lowering the resistance, but none have been satisfactory.

An object of the present invention is to solve the above problems,
An object of the present invention is to provide a method for manufacturing a barium titanate-based semiconductor material having a low-resistance semiconductor region over a wide range and having stable characteristics.

[0006]

By heating and sintering by microwaves, the present inventors have realized that the range of addition of the semiconducting agent, which has conventionally been an insulator, does not depend on additives such as Mn. It has been found that barium titanate-based semiconductor porcelain with low resistance can be obtained. That is, the present invention provides a barium titanate-based porcelain composition comprising a rare earth element, N
The present invention relates to a method for producing a barium titanate-based semiconductor material, which comprises irradiating a microwave to a compact of a raw material powder containing at least one of b, Ta, W and Sb and heating and sintering the compact.

[0007]

According to the method of the present invention for producing a barium titanate-based semiconductor material having a positive temperature coefficient of resistance, its formation mechanism is not yet clear, but barium titanate having a wide range of semiconducting regions and excellent PTCR characteristics is provided. A series semiconductor material is obtained.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the production method of the present invention, first, a raw material powder produced by a general method is prepared. Next, the raw material powder is formed into a desired shape to obtain a formed body of the raw material.
Then, the raw material compact is irradiated with microwaves under optimum conditions to sinter the compact. At this time, when the compact is irradiated with microwaves, it is rapidly heated from the inside of the compact and sintering proceeds. As the microwave used in the present invention, if the frequency is excessively low, the sinterability may be deteriorated and the resistance may be increased. Therefore, a microwave having a frequency of 5 GHz or more, particularly 6 GHz or more is preferable. The frequency on the high frequency side is not particularly limited, and a commercially available microwave generator can be suitably used.

[0009] In a low-concentration raw material compact having an addition amount of the semiconducting agent of less than 0.2 mol%, sintering proceeds at a low temperature and in a short time by microwave sintering, so that abnormal grain growth is suppressed. , Resulting in a uniform particle structure. In particular, when a microwave having a frequency of 6 GHz or more is used, a barium titanate-based semiconductor material having low resistance can be manufactured. On the other hand, in a raw material compact having a high concentration of the semiconducting agent of 0.2 mol% or more, the diffusion of the substance is more activated and the sintering reaction is promoted as compared with the firing in a conventional electric furnace. Grain growth is achieved. Therefore, even when the concentration of the semiconducting agent is high, it is possible to sufficiently realize semiconversion. Especially,
When a microwave having a frequency of 6 GHz or more is used, the addition amount of the semiconducting agent, which cannot be obtained by a conventionally known method, is 1 mol% to 7 mol%, and the raw material compact having a high concentration is low in a wide range. A barium titanate-based semiconductor material having a semiconductor region with resistance and stable characteristics can be manufactured.

In the present invention, the microwave sintering is preferably carried out at a sintering temperature of 1150 to 1450 ° C. If the temperature is lower than 1150 ° C., sintering becomes insufficient and the semiconductor is not sufficiently converted into a semiconductor.
When the temperature is higher than 50 ° C., the surface of the element is melted, and a good sintered body cannot be produced.

The sintering time is preferably about 5 to 30 minutes. If the sintering time is less than 5 minutes, the sintering reaction is not sufficient, while if it exceeds 30 minutes, a good sintered body cannot be obtained.

Further, the magnitude of the resistance change at the Curie temperature can be improved by subjecting the sintered body obtained by microwave irradiation to heat treatment again under appropriate conditions, if necessary.

[0013]

The present invention will be specifically described below with reference to examples and comparative examples. Example 1 As starting materials, BaCO ₃ , TiO ₂ , Nb ₂ O ₅ ,
La ₂ O ₃ was prepared so as to have a predetermined ratio, and wet ball mill mixing was performed for 18 hours using zirconia balls.
After drying, it was calcined at 1150 ° C. for 2 hours. The calcined powder was pulverized, and 2% by weight of polyvinyl alcohol was further added to form a disc having a diameter of 8.73 mm and a thickness of 2.7 mm at a pressure of 1000 kg / cm ² .

Next, this was irradiated with microwave under the following conditions to sinter the compact. 6 GHz resonance frequency,
The microwave output is set to 600 W and 145
It was kept at 0 ° C. for about 10 minutes. The heating and cooling rates were all 30 ° C./min. 1 for the microwave sintered body
Heat treatment was performed at 050 ° C. in the air to obtain PTC ceramics. An Ag electrode having good ohmic contact was baked on this ceramic to obtain a PTC element. This P
For the TC element, the specific resistance at room temperature (25 ° C.) and the resistance-temperature characteristics were measured. Also, there was hardly any variation in characteristics among the obtained products.

Comparative Example 1 For comparison, the same measurement was performed on a PTC element obtained by heating a molded body produced under the above conditions in an electric furnace according to a conventional method at 1450 ° C. for 20 hours. In the above embodiment, a carbonate or an oxide is used as a starting material. However, this is not particularly important, and a material giving a predetermined component ratio by thermal decomposition or the like may be used.

In the above embodiment, Mn for improving the PTCR characteristic and SiO ₂ as a sintering aid were not added. However, the same applies to the raw material compact containing them as in the present invention. The effect is obtained.

Further, part of the Ba site of barium titanate is simultaneously replaced with Pb, Sr and Ca, and M is added as an additive.
n and SiO ₂ may be contained.

FIG. 1 shows the dependence of the specific resistance at room temperature on the semiconducting agent in each PTC element.

FIG. 2 shows the temperature dependence of the specific resistance in a PTC element to which 1.0 mol% of a semiconducting agent is added.

As is clear from FIGS. 1 and 2, the PTC element of each embodiment has a greatly increased concentration range for semiconductor conversion as compared with that of the comparative example. On the other hand, in the comparative example,
If the addition amount of the semiconducting agent is out of the range of 0.02 to 0.6%, the resistance increases sharply and a semiconductor material cannot be obtained. As described above, the present invention can remarkably improve the semiconductor region of the PTC element to ten times that of the conventional one, and its academic and industrial effects are remarkable.

[0021]

According to the present invention, a barium titanate-based semiconductor material having a low-resistance semiconducting region in a wider range than before can be manufactured by heating and sintering by microwave irradiation. . Moreover, since the dependence on the material composition is small, management in the manufacturing process is easy,
The industrial utility value is extremely high.

[Brief description of the drawings]

FIG. 1 is a diagram showing the dependence of the room temperature resistivity on the semiconducting agent in each PTC element.

FIG. 2 is a diagram showing temperature dependence of specific resistance in a PTC element to which a semiconductor agent is added at 1.0 mol%.

Claims (1)

[Claims] In a barium titanate-based porcelain composition, heating and sintering is performed by irradiating a microwave to a compact of a raw material powder containing at least one of rare earth elements, Nb, Ta, W and Sb. A method for producing a barium titanate-based semiconductor material.