JPH0338802A - Manufacture of positive temperature coefficient semiconductor porcelain - Google Patents

Abstract

PURPOSE:To lower a resistivity by a method wherein a composition of a specific barium titanate-based semiconductor is baked in a neutral atmosphere and/or a reducing atmosphere of N2, Ar, H2 or the like, or the composition is baked in the air and, after that, is heat-treated in the neutral atmosphere and/or the reducing atmosphere and, after that, a heating and oxidation treatment is executed. CONSTITUTION:A composition of a barium titanate-based semiconductor containing an element to form a semiconductor such as Y, La, Nb or the like is baked in a neural atmosphere and/or a reducing atmosphere of N2, Ar, H2 or the like; or the composition is baked in the air and, after that, it heat-treated in the neutral atmosphere and/or the reducing atmosphere; after that, a heating and oxidation treatment is executed at 800 deg.C or higher. When an oxidation treatment temperature is less than 800 deg.C, a positive temperature coefficient semiconductor porcelain provided with a resitivity and a resistance ratio is difficult to obtain; on the other hand, even when the temperature exceeds 1200 deg.C, an effect corresponding to the temperature is difficult to obtain. Thereby, it is possible to obtain the positive temperature coefficient semiconductor porcelain whose resistivity at room temperature is low and which is provided with an excellent PTC characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing positive characteristic semiconductor ceramics with low resistivity using barium titanate-based semiconductors.

[Prior art]

Barium titanate-based semiconductor porcelain has barium titanate as its main component, and is mixed with semiconducting elements such as rare earth elements such as Y, La, 5eCe, and Ga, or transition elements such as Nb and Ta, and heated to high temperatures. It is known that the material is heated and sintered. This barium titanate-based semiconductor porcelain is 5 kg,
-The electrical resistance value changes rapidly at one point. It has so-called positive characteristics (PTC characteristics).

However, semiconductor porcelain with the positive characteristics described in item 2 is generally manufactured by solid phase reaction. That is, 1, for example, raw material powder 13 a CO2, T i O□, Y203S i
02, AN20. , MnO2 is mixed and calcined,
Grinding, 1 granulation, forming a precept, and burning a precept. Further, production methods using a coprecipitation method and an alkoxide method have also been attempted. However, no matter which method is used, the limit of the specific resistance is 5Ω·Cl11.

As will be described later, positive characteristic semiconductor ceramics are required to have as low a resistivity as possible.

Furthermore, according to Japanese Patent Publication No. 4, H134, for barium titanate-based compositions to which no semiconductor element is added, the above-mentioned calcination is performed in a neutral atmosphere such as Nz or Ar, and then the temperature is slightly lower than the calcination temperature. A manufacturing method is disclosed that involves aging in an oxidizing atmosphere. However, this one is also 25°
The specific resistance at C is about 100 Ω·cm even if it is low.

On the other hand, as a method for manufacturing positive characteristic semiconductor porcelain with low specific resistance, firing is performed in the atmosphere after the above-mentioned molding, and Nz, A
There is also a method in which reduction treatment is performed in a neutral or reducing atmosphere such as r, Hz, etc., and then reoxidation treatment is performed in the atmosphere. There is also a method in which after the above molding, reduction firing is performed in the reducing atmosphere and then reoxidation is performed in the atmosphere.

However, as shown in FIG. 4, there is a correlation between specific resistance and PTC characteristics [resistance ratio (digits)].

When trying to obtain positive characteristic semiconductor porcelain with low resistivity, PTC
The characteristics deteriorate, and on the other hand, if one attempts to obtain high PTC characteristics, the specific resistance increases.

As shown in the figure, the normal positive characteristic semiconductor porcelain has a specific resistance of about 10 Ω·Cll1 and a resistance ratio of 4 to 5 digits that exhibits PTC characteristics. When this is subjected to reduction firing treatment, the specific resistance becomes 0.1 to 1 Ω·cm, but the resistance ratio decreases to about 0 to 1 digit. Furthermore, if this material is reoxidized in the atmosphere, the resistance ratio will increase, but the negative force specific resistance will also increase.

In addition, there are various theories regarding the conduction mechanism of positive characteristic semiconductor ceramics (PTC thermistors), including the 3D electron hopping conduction theory. ) is common. Incidentally, the resistance of positive characteristic semiconductor porcelain is expressed by the sum of the bulk and grain boundaries, but generally, at temperatures below the Curie temperature (Tc), the resistance of the bulk increases, and at temperatures above Tc, the resistance of the grain boundaries increases. It is known that each resistance is dominant. In order to lower the resistivity of today's positive characteristic semiconductor ceramics, it is important to control the bulk that governs the resistivity at room temperature.

Now, the room temperature resistivity of positive characteristic semiconductor porcelain is generally expressed as follows.

ρPTc′, ρbulk−1/ [ND′ e・
u) (ND: donor density, e: electron charge.

μ2 mobility) Therefore, the resistance of positive characteristic semiconductor ceramics depends on the donor density, that is, the concentration of oxygen vacancies in the bulk, and in order to obtain a low resistivity, the concentration of oxygen vacancies must be increased. There is a need.

Therefore, by firing or heat-treating the positive characteristic semiconductor porcelain in a neutral/reducing atmosphere, it is possible to increase the oxygen defect concentration and lower the resistivity. is reduced, and the PTC properties disappear.
Or new problems arise.

[Problem to be solved] As described above, as shown in the above-mentioned patent publication and Figure 4, an attempt was made to oxidize the grain boundaries by reoxidizing and selectively reduce only the bulk to achieve a low resistivity. It is being

However, there is a correlation between PTC characteristics and resistivity, and lowering the resistivity worsens the PTC characteristics, resulting in low resistivity.
It is difficult to obtain positive characteristic semiconductor porcelain with excellent C characteristics.

In addition, as mentioned above, it is difficult to obtain positive characteristic semiconductor porcelain that has low resistivity and excellent PTC characteristics. A method has also been adopted in which two are connected in parallel. but.

This method of use is applicable when applying positive characteristic semiconductor porcelain to overcurrent protection devices and motor starting elements.

There are restrictions on the usage environment and placement space, and it also causes a significant increase in cost.

In view of these problems, the present invention seeks to provide a method for manufacturing positive characteristic semiconductor ceramics having low specific resistance at room temperature and excellent PTC characteristics.

[Means for solving problems]

The present invention provides a barium titanate semiconductor composition containing semiconductor elements such as Y, La, and Nb.

After firing in a neutral and/or reducing atmosphere such as N2, Ar, Hz, etc., or after firing the above composition in the air and heat-treating it in a neutral and/or reducing atmosphere,
A method for producing characteristic semiconductor porcelain characterized by carrying out a heating oxidation treatment at a temperature of 0.degree. C. or higher.

What should be noted in the present invention is that the fired body is subjected to heat oxidation treatment at a high temperature of 800° C. or higher. By performing this thermal oxidation treatment, it is possible to obtain a positive characteristic semiconductor ceramic having a low specific resistance without deteriorating the PTC characteristics.

Therefore, such thermal oxidation treatment is performed by heating to a high temperature in an oxygen atmosphere such as in the air. This oxygen atmosphere is formed by a combination gas of oxygen gas and a neutral gas such as Ar or Nz using an oxygen atmosphere furnace or an oxygen atmosphere furnace, in addition to the atmosphere [1]. These pressurized gas atmospheres can also be used.

Further, the oxidation treatment temperature described in "2" shall be 800°C or higher.

If it is less than a o o 'c, it is difficult to obtain a positive characteristic semiconductor porcelain having a resistance ratio of 1 (double ratio).On the other hand, 1200
Even if it exceeds 'c, it is difficult to obtain a commensurate effect.

Further, the treatment time is preferably 0.5 to 8 hours. If it is less than 0.5 hours, it is difficult to obtain the above specific resistance and resistance ratio,
On the other hand, even if it exceeds 8 hours, it is difficult to obtain a commensurate effect.

Next, as the barium titanate-based semiconductor composition, a barium titanate-based semiconductor is used, and the above-mentioned Y, La, Ce
, Nb, Ta, and other semiconductor-forming elements are preferably contained.
It is usually added as an oxide such as Y2O3. But Y
(1° Y (NO3), l-a C (! or more (for example, simultaneous addition of Y-Nb Y-La La-Ta).

Further, as for the sintering aid such as S i 02 ANz 03, it is better to use as little as possible, and it is preferable that no additive is added. This is because reduction and reoxidation may be hindered by liquid phase components precipitated at grain boundaries due to the addition of the sintering aid. In addition, Curie temperature (Tc) and PTC
To control properties Pb, Sr, Ca, Zn Sn
, Mn, Fe, Cu, etc. may also be added.

Further, it is preferable that the positive characteristic semiconductor porcelain used in the present invention is porous and has a uniform grain size.

This is because when the grains are porous and have a uniform particle size, reduction and heating/oxidation treatments proceed smoothly and variations among crystals are reduced.

Further, the laminated body is fired in a neutral and/or reducing atmosphere. Such atmospheres include N2Ar, N2. There is a mixture of these gases. Also, the firing temperature is 1250~1
The temperature is preferably 350°C. If the temperature is lower than 1250°C, firing is difficult, while if the temperature exceeds 1350°C, the resistivity may increase. In addition, the stratified body is B a C
For example, raw material powder such as Ch T i 02 is mixed, calcined, crushed, and granulated, and then molded into a desired shape.

Next, the above method has been described in which firing is performed in a neutral and/or reducing atmosphere, but the firing is performed in the air, and then heat treatment (reduction treatment) is performed in a neutral and/or reducing atmosphere. It is also possible to adopt a method in which a heating oxidation treatment is then carried out as described above.

In this case, the above-mentioned atmospheric firing is performed at 1280 to 14 oo'c.
Let's do it. Further, the heat treatment in a neutral and/or reducing atmosphere is carried out at 1900 to 1300'C using the same atmosphere as above. Note that the heating oxidation treatment is the same as the method described above.

In addition, in the third invention, barium titanate-based porcelain sintered body (B a Ti
03-X) preferably has a relative density of 80 to 97%.

Even if the m-dense sintered body having a relative density of more than 97% is subjected to a heating oxidation treatment in the next step, oxygen diffusion is slow and the treatment requires a long time. Therefore, the oxidation of the surface of the fired body may progress too much, and the room temperature resistance of the PTC may increase.

On the other hand, if the 1 relative density is less than 80%, the PTC properties will improve, but the strength of the 1 sintered body will be low, and the specific resistance may increase.

The above relative density can be adjusted by adding combustible material such as carbon to make one granule after the above-mentioned calcination and pulverization in the manufacturing process, burning it during pre-firing after molding, and then firing one granule. To do something, such as by doing something.

As mentioned above, by setting the relative density within the above range,
The thermal oxidation treatment can be performed quickly and uniformly, and positive characteristic semiconductor porcelain having low resistivity and excellent PTC characteristics can be obtained.

In addition, in the present invention, the barium titanate ceramic obtained by firing or heat treatment in the above atmosphere has its B site atoms (Ti) and A site atoms (e.g. Ba, Pb, S
molar ratio B/A (1' i / B a ) with r) is 1
．． The range is preferably from 00 to 1.08. This makes it possible to obtain positive characteristic semiconductor porcelain with low resistivity and excellent PTC characteristics.

That is, when B/A (Ti/Ba) is less than 1.00,
Or, if it exceeds 1.08, the specific resistance may become large. Here, the above B/A ('"i/Ba)" is
It is the molar ratio of B-site atoms, ie, TI compound (eg, TiO□), to A-side atoms, ie, Ba compound (eg, BaC05).

Furthermore, in the present invention, it is preferable that the semiconductor element is added to 100 moles of barium titanate (BaTi03) in the following range.

Outside this range, the specific resistance may increase due to heat oxidation treatment.

Y: 0.02 to 1.2 mol La: 0.02 to 1.0 mol Ce: 0.02 to 0.8 mol Nb: 0.02 to 1.0 mol Ta: 0.02 to 1.0 mol One or more of these semiconductor-forming elements are added.

[Action and effect]

In the present invention, as described above, a final thermal oxidation treatment is performed to obtain a positive characteristic semiconductor ceramic product.

Therefore, a positive characteristic semiconductor ceramic having excellent PTC characteristics and low resistivity can be obtained.

Further, since the positive characteristic semiconductor ceramic has a low specific resistance, a desired resistance value can be obtained even in a small size, and self-heating (voltage drop) can be reduced. Therefore, 1. For example, creating an overcurrent protection device that can be used even in windless conditions.
Greater freedom in design. Furthermore, it is possible to downsize the applied product and reduce costs.

〔Example〕

1st Example A barium titanate-based semiconductor composition was reduced and fired in a neutral, reducing atmosphere, or fired in the air and then subjected to reduction treatment in the above atmosphere to produce 9 sintered bodies with various relative densities. Had made. Then, the roasted sweetfish body is subjected to heat oxidation treatment,
Positive characteristic semiconductor porcelain was manufactured. Then, the characteristics of the porcelain were evaluated.

The above composition, the relative density of the reduction treatment after reduction firing or atmospheric firing, the conditions of the heating oxidation treatment, the specific resistance (ρ2゜Ω・cm) at 20°C of the obtained positive characteristic semiconductor porcelain, and the PTC
The characteristics (resistance ratio ΔR 1 digit) and the quality judgment are shown in Table 1.

The pass/fail judgment was based on 3 passes (○ mark in the same table), which satisfied both of the specific resistance at 20'C of 5 Ω·Cm or less and the PTC characteristic ΔR of 3 digits or more.

However, in manufacturing the above porcelain, first of all, BaCO
5100 mol, 101 mol of Ti01, YzO
0.2 mol of 's was added, pure water was added in a ball mill using ZrO and cobblestones, and the mixture was mixed for 20 hours.

After that, it was dried at 150°C for 524 hours, and then calcined in the air at 1000°C for 4 hours.

A calcined powder of barium titanate-based semiconductor was obtained. This calcined powder was wet-pulverized using a conventional method.

Add carbon powder, granulate and mold to form a compact.

Heating was performed in the air. Thereafter, the compact was subjected to reduction firing for 1 hour at high temperature in a neutral and/or reducing atmosphere shown in Table 1 to obtain a reduced sintered compact (Nα1-11
).

Alternatively, the above molded body was fired in the atmosphere and then subjected to a reduction treatment in the atmosphere shown in Table 1 to obtain a reduced sintered body (N
[L12-14).

The reduced sintered bodies thus obtained have various relative densities as shown in Table 2. This relative density is O to 20wL% of the pulverized product (in terms of dry matter) after the above wet pulverization.
Carbon powder was added thereto, granulated and shaped, and then pre-fired at 1100°C in the atmosphere to remove carbon. After heating in the atmosphere, reduction firing, firing in the atmosphere, and reduction treatment were performed.

Next, this reduced sintered body was processed under the conditions shown in Table 1.
Heat oxidation treatment was performed. As a result, semiconductor porcelain was obtained.

2. Polish the end face of this semiconductor porcelain to create an ohmic A
After applying g electrode and cover Ag electrode, 525'C, 1
Baking was performed for 0 minutes. Then, the specific resistance (ρ2o) and PTC characteristics [ΔR (=log Rm
ax/Rmin)) was evaluated.

In addition, for comparison, as shown in Table 1, a product that was neither fired in a neutral/reducing atmosphere nor heated and oxidized (No, CI)
, those without heat oxidation treatment (No, C2), comparative examples with low or high relative density (N).

Similar measurements were also carried out for C3, C4, C5, C6). Note that the reduction firing or reduction heat treatment time was 1 hour as described above.

As can be seen from Table 1, the specific resistance of the 9th invention product is 4.6Ω.
・It has excellent performance with a PTC characteristic of 3 digits or more and less than cm.

On the other hand, as is known from Table 1, those that were not subjected to reduction firing or heat oxidation treatment (No, C1,) had a high specific resistance. In addition, those that were subjected to reduction firing but not heat oxidation treatment (No. C2) had very low resistivity but extremely poor PTC characteristics.

Furthermore, although C3 has been subjected to heat oxidation treatment, its relative density is low, so its specific resistance is high. In addition, comparative example No. C
4, C5, and C6 have a large or small relative density, and therefore have a small PTC characteristic or a large specific resistance.

Further, the PTC characteristics of the semiconductor ceramics according to the present invention shown in No. 4 in Table 1 are shown in FIG. 1 by curve N04. Also, for comparison, conventional products shown in No., C1, N
The comparative height measurement shown in C4 is indicated by curve No., CI or C4 in the figure.

As can be seen from the figure, the product of the present invention has low resistivity and excellent PTC characteristics.

Second Example As shown in Table 2, <, B site atom/A site atom (T
Positive characteristic semiconductor ceramics were manufactured in the same manner as in the first embodiment with various ratios of i/Ba, Pb, Sr) and their characteristics were evaluated. The above B/A (Ti/Ba, Pb, Sr) ratio is the molar ratio of Tt○2 to BaC0:+.

In this example, addition of carbon to the pulverized material and preliminary firing to remove the carbon as shown in the first example were not performed.

Table 2 shows the molar amount of each component of the porcelain composition, the manufacturing method (reduction firing, reduction treatment after atmospheric firing, and heating oxidation treatment), the characteristics 1 judgment of the obtained semiconductor porcelain, etc., as in Table 1. It was shown to.

As is known from Table 2, N (L21
~38 semiconductor porcelains all have a low specific resistance of 4.9Ωan or less, and an excellent PTC of 3.1 orders of magnitude or more.
It shows the characteristics.

In contrast, regarding conventional examples, NoC21 has a high resistivity because it is only fired in the atmosphere, and No. C22 has extremely poor PTC46 properties because it has not been subjected to heat oxidation treatment. Regarding Comparative Example G, C2324 is B/A (
Since T i /B a ) is less than 1.00, the specific resistance is very high. C25 is B/A (Ti/B
a) is 11, so the specific resistance is high.

In addition, the PTC characteristics of the semiconductor porcelain according to the present invention shown in No. 23 of Table 2 are shown in FIG.
, 23. In addition, the conventional product shown as No. C21 is shown as a curve No. C21 in the same figure.

From the figure, it can be seen that the product of the present invention has low resistivity and excellent PTC characteristics.

Third Example As shown in Table 3, various semiconductor elements were added in various ratios (moles) to 100 moles of barium titanate, and positive characteristic semiconductor porcelain was produced in the same manner as in the first example. manufactured and characterized. still.

In this example, the addition of carbon to the pulverized material and the preliminary firing for removing the carbon shown in the first example were not performed.

Table 3 shows the molar amount of each component of the porcelain composition, the manufacturing method (reduction firing, reduction treatment after atmospheric firing, and heating oxidation treatment), the characteristics 1 judgment of the obtained semiconductor porcelain, etc., as in Table 1. It was shown to.

As can be seen from Table 3, N according to the present invention.

Semiconductor ceramics Nos. 51 to 78 all have a low resistivity of 4.9 Ωcm or less and an excellent P of 3.1 digits or more.
It shows TC characteristics.

In comparison, C51 and C52 of the conventional examples have high specific resistance or extremely poor PTC characteristics because they are only fired in the atmosphere or are not subjected to heat oxidation treatment.

Further, regarding the comparative example, C53 has a high specific resistance because it has a small amount of Y2O. Also, C54 has a lot of Y2O3, and C55
is La20. Or less, C56? ; Since there is a large amount of tLaz03, each has a high specific resistance. Similarly below, C58 to C62
Because the amounts of Cez Oi, Nb2O5, and Ta2o are small or large, the resistivity is high.

In addition, the PTC characteristics of the semiconductor porcelain according to the present invention shown in No. 53 in Table 3 are shown in curve No. 5 in FIG.
3. In addition, for comparison, the conventional product shown as No. C51 is shown as a curve No. C51 in the same figure.

As can be seen from the figure, the product of the present invention has low resistivity and excellent PTC characteristics.

[Brief explanation of drawings]

1, 2, and 3 are diagrams showing the relationship between temperature and specific resistance of the positive characteristic semiconductor porcelain shown in the first, second, and third examples; is the specific resistance and resistance ratio (PT
It is a figure showing the relationship with C characteristic).

Claims (1)

[Claims] After firing a barium titanate-based semiconductor composition containing semiconducting elements such as Y, La, and Nb in a neutral and/or reducing atmosphere such as N_2, Ar, and H_2, the composition is 1. A method for producing positive characteristic semiconductor porcelain, which comprises firing in the air, heat-treating in a neutral and/or reducing atmosphere, and then performing a heating oxidation treatment at 800° C. or higher.