JPH06151106A - Semiconductor porcelain composition for positive temperature coefficient thermistor - Google Patents

Abstract

PURPOSE:To increase withstand voltage per grain in a grain boundary layer by standardization to the withstand voltage per fixed resistance as a withstand voltage evaluation method for optimizing the amount of a rare earth element to be added and the amount of a Mn compourld to be added. CONSTITUTION:For a barium titanate composition expressed by (Ba1-x-ySrxCay) TiO3 (where 0<=X<=0.15, 0.13<=Y<=0.17), 0.5 to 1.5mol% of TiO2, 1.0 to 2.5mol% of SiO2 and a rare earth element and a Mn compound are contained so that the relationship b=0.2a-0.006+ or -0.01 is formulated when the rare earth element is less than 0.26 atomic % and the relationship b=0.715a-0.143+ or -0.02 is formulated when the rare earth element is equal to or more than 0.26 atomic %, where the rare earth element is (a) atomic % and Mn is(b)atomic %. By this, the grain diameter in a barium titanate sintered body is made fine and the withstand voltage per grain in a grain boundary layer is increased, which can result in a high withstand voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor ceramic composition for a positive temperature coefficient thermistor, and more particularly to a positive temperature coefficient thermistor used as an overcurrent protection element or a switching element having an improved withstand voltage per unit resistance. The present invention relates to a semiconductor porcelain composition.

[0002]

2. Description of the Related Art Generally, for example, barium titanate, strontium titanate, lead titanate, calcium titanate, etc., or Nb, Dy which is a rare earth element in a solid solution thereof,
When a small amount of La or the like is added and fired, a semiconductor ceramic material having a positive resistance coefficient (material for positive temperature coefficient thermistor) can be obtained.

Today, these materials are used for overcurrent protection elements and the like, but as a characteristic thereof, they must have sufficiently low resistance to a load, and at the same time, they must have sufficiently high breakdown voltage. .

However, since the low resistance characteristic and the high withstand voltage characteristic are contradictory characteristics, it is difficult to satisfy both characteristics at the same time, and various studies have been made so far to make both characteristics as excellent as possible. . The following two methods can be given as specific methods for simultaneously improving the low resistance characteristic and the high breakdown voltage characteristic. The first method is to reduce the grain size in the sintered body and further suppress abnormal grain growth to prevent the voltage from being concentrated in one place. It is a method of improving the withstand voltage in the grain boundary layer per grain.

When manufacturing a positive temperature coefficient thermistor (hereinafter referred to as PTC thermistor), a method of adding a sintering aid such as SiO ₂ or TiO ₂ and performing liquid phase sintering can be adopted. It is relatively easy to control the diameter, and there are many reports using the first method. In addition to the sintering aid, Ca
There is also known a method of making the particle size finer by adding a compound such as JP-B No. 54-10110 and JP-A No.
No. 192456, etc., discloses that Ba of barium titanate is Ba.
Atoms are replaced by Ca, and in addition, SiO ₂ , TiO ₂ , M
A method for obtaining a semiconductor porcelain by adding n and the like and sintering is described.

However, it has been reported that in the above method for making the particles fine, the PTC thermistor becomes insulated when the particle size is reduced to about 3 μm, and there is a limit to this method. Conceivable.

[0007]

On the other hand, regarding the second method, the evaluation method for the effect itself has not been established, and its study itself is not easy. The reason is that when the withstand voltage in the grain boundary layer per one particle is changed, the PTC effect itself also changes, and it is difficult to evaluate the withstand voltage.

As an additive that affects the PTC effect,
For example, a rare earth element such as Nb, which is a semiconducting agent, or Mn that affects the resistance change width can be used. As seen in the above-mentioned known example, it has been a known fact from the past to add rare earth elements and Mn for semiconductorization of PTC thermistors, but for both, only a rough range is defined, The relationship between the amounts of rare earth elements and Mn added for increasing the withstand voltage has not been studied so far.

In reality, it is known that both of them dissolve in the main component at the same time, and at the same time, they also cause valence compensation, which greatly influence each other. Since these relationships also greatly affect the withstand voltage, it is necessary to study the relationship between the two with respect to the withstand voltage. However, since an appropriate evaluation method has not been conventionally used, there remains a problem that the amount added is not set in the optimum range.

The present invention has been made in view of the above problems. By adopting a method of normalizing the withstand voltage per constant resistance as a method of evaluating withstand voltage, the amount of rare earth element added and the amount of Mn compound are determined. It is an object of the present invention to provide a semiconductor ceramic composition for a positive temperature coefficient thermistor in which the withstand voltage in a grain boundary layer per one particle is improved by optimizing the addition amount and the withstand voltage is further increased.

[0011]

In order to achieve the above object, a semiconductor ceramic composition for a positive temperature coefficient thermistor according to the present invention comprises (Ba _1-XY Sr _X Ca _Y ) TiO ₃ (where 0 ≦
X is less than 0.15 and 0.13 is less than Y ≦ 0.17).
O ₂ is 0.5 to 1.5 mol%, and SiO ₂ is 1.0 to ₂ .
5 mol% and the rare earth element and the Mn compound, when the rare earth element is a atom% and the Mn is b atom% and the rare earth element is less than 0.26 atom%, b = 0.2a−0.006 ± 0.01 When the rare earth element is 0.26 atomic% or more, it is contained so that the relationship of b = 0.715a−0.143 ± 0.02 is established.

[0012]

According to the semiconductor ceramic composition for a positive temperature coefficient thermistor according to the present invention, (Ba _1-XY Sr _X Ca _Y ) TiO ₃
(However, in the range of 0 ≦ X ≦ 0.15 and 0.13 ≦ Y ≦ 0.17), 0.5 to 1.5 mol of TiO ₂ is added to the barium titanate-based composition. %, SiO ₂ is 1.0 to 2.5 mol%, the rare earth element and Mn compound are less than 0.26 atomic% when the rare earth element is a atomic% and the Mn is b atomic%. , B = 0.2a-0.006 ± 0.01 When the rare earth element is 0.26 atomic% or more, it is contained so that the relationship of b = 0.715a-0.143 ± 0.02 is established. The grain size in the barium titanate sintered body was made finer, and the withstand voltage in the grain boundary layer per grain was increased, resulting in a high withstand voltage of 30V or more per 0.5Ω. To be done.

First, the Ba atom of barium titanate is replaced with Ca.
The relationship between the effect of reducing the grain size in the sintered body and the withstand voltage in the case of substituting by is explained. FIG. 1 is a graph showing the influence of the average particle size and particle size distribution of the sintered body on the withstand voltage when Ba atoms of barium titanate containing 5 mol% of Sr were replaced by Ca. It is a thing. As can be seen from Fig. 1, the average particle size of the sintered body is 10 mol% of the addition amount of Ca.
The minimum value is in the vicinity, and the average particle size is large before and after the addition amount of about 10 mol% as a boundary. In Fig. 1, the width of the particle size distribution is also shown. The width of the particle size distribution is the smallest when the amount of Ca added is around 15 mol%, and the withstand voltage is the highest around that. There is. The fact that the width of the particle size distribution is wide indicates that non-uniform grain growth occurs in the sintering process, and as described above, when there are particles larger than the surrounding particles in the sintered body, the particles are It is considered that the withstand voltage is low as a whole because the voltage is concentrated. Therefore, the condition in which the average particle size is relatively small, the width of the particle size distribution is narrow, and the voltage is not concentrated on the specific particles, that is, the range in which the amount of Ca added is 13 to 17 mol% is the high withstand voltage range.

Next, the amount of SiO ₂ added will be described. Although grain growth is suppressed by adding SiO ₂ , the addition range is preferably 1.0 to 2.5 mol%. SiO
_If the addition amount of ₂ is less than 1.0 mol%, the grain growth suppressing effect is not exhibited, and if the addition amount exceeds 2.5 mol%, segregation at grain boundaries increases the specific resistance. Not preferable.

Next, the amount of TiO ₂ added will be described. Similarly, grain growth can be suppressed by adding TiO ₂ , but the addition amount is preferably 0.5 to 1.5 mol%. If the addition amount of TiO ₂ is less than 0.5 mol%, the grain growth suppressing effect is not exhibited, and the addition amount is 1.5
If it exceeds mol%, abnormal grain growth occurs and the withstand voltage is lowered, which is not preferable.

Further, the added amounts of rare earth element and Mn will be described. Within the range of the addition amount of each additive described above, the relation between the addition amounts of rare earth element and Mn is
When mol% and MnCO ₃ are b mol%, when the rare earth element is less than 0.13 mol%, b = 0.4a−0.006 ± 0.01 When the rare earth element is 0.13 mol% or more, The composition is added so that the relationship of b = 0.15-0.143 ± 0.02 is established, and the withstand voltage thereof is high, and one of the reasons is considered that they are valence-compensated with each other. To be The atomization compensation means, for example, Nb ₂ O ₅ as a rare earth element and MnC as a Mn compound.
When O ₃ is used, both are solid-solved in the main component, but a part of them does not bond and does not serve as an electron acceptor or a donor.
It means being offset. Therefore, when the rare earth is in excess of the range of the above formula, Mn is compensated by valence compensation.
Becomes insufficient, the PTC effect becomes small, and the withstand voltage decreases. On the other hand, if Mn is excessive from the range of the above formula, the rare earth element becomes insufficient, semiconductor formation is hindered, and the withstand voltage decreases.

The rare earth element used in the present invention includes:
For example, Nb, Dy, La and the like can be mentioned. The rare earth element is preferably added as an oxide. The Mn compound used in the present invention is preferably MnCO ₃ , for example.

[0018]

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples of the porcelain composition for a positive temperature coefficient thermistor according to the present invention will be described below.

As starting materials, commercially available raw materials with a purity of 99% or more, such as BaCO ₃ , SrCO ₃ , CaCO ₃ , TiO ₂ ,
Nb ₂ O ₅ , SiO ₂ and MnCO ₃ were used.

First, the starting materials having the compositions shown in Table 1 were weighed so that the total weight of the starting materials was 100 g, 100 g of pure water was added, and the mixture was mixed and ground in a ball mill for 24 hours. The container used for mixing was made of polyethylene having a diameter of 90 mm and a height of 110 mm, and as the cobble stones, stainless steel balls having a diameter of 15 mm coated with polyethylene were used, and the balls were laid up to one third of the height of the container. After the mixing and pulverization, this was dried, put into an alumina crucible, and calcined at 1100 ° C. for 2 hours. Next, the calcined powder was crushed in an alumina mortar, and 100 g of pure water was added to 80 g of the crushed powder.
Was added, and the mixture was crushed by a ball mill for 14 hours and then dried. Further, to 50 g of the dried powder, 8 g of a 10% by weight aqueous solution of polyvinyl alcohol was added, kneaded in an alumina mortar, passed through a 250-mesh sieve and sized, and a pressure of 1 ton / cm ² was applied. To produce a disk-shaped molded body.

The disc-shaped compact thus obtained was heated at a rate of 200 ° C./hour and held at 1350 ° C. for 2 hours, and then at 100 ° C.
It was gradually cooled at a speed of / hour to obtain a disk-shaped sintered body of 10.5 mmφ. Diameter 9.5m on both sides of the obtained sintered body
m ohmic silver electrode is applied and this is applied at 580 ° C for 1
Bake for 0 minutes. The lead terminals were attached by soldering an annealed copper wire having a diameter of 0.5 mm on both surfaces of the electrode using silver-containing solder having a melting point of 300 ° C.

Table 1 shows the results of examining the withstand voltage of each of the specimens thus obtained. The term "withstand voltage" as used herein refers to a voltage that gives a minimum current value when the current-voltage characteristic curve of the PTC thermistor shown in FIG. 2 is measured. Further, in the present invention, the thickness of the molded product before firing is adjusted so that the room temperature resistance of each element is 0.5Ω, so that it is convenient to examine the withstand voltage per resistance of a constant value of each element. There is.

Regarding the withstand voltage value of each element, those having a value of 30 V or more were considered to have a sufficiently high withstand voltage in view of known examples, and were set within the scope of the present invention. The data obtained by correcting the withstand voltage of the sintered body obtained by the conventional method to a value with which the withstand voltage of the present invention can be compared is shown in Table 3 below as a comparative example.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

Examples 1 to 3 and Comparative Examples 1 to 4 shown in Table 1 above.
Shows the value of withstand voltage when the substitution amount of Ca with respect to Ba is changed, and the substitution amount of Ca is 13 to 17 mol.
In the range of%, a high withstand voltage of 30 V or higher is shown. In addition, Examples 4 to 5 and Comparative Examples 5 to 6 show withstand voltage values when the addition amount of TiO ₂ added excessively is changed, but the addition amount of TiO ₂ is 0.5 to 1.5 mol
High withstand voltage is shown in the range of%. Moreover, Example 6-
7, Comparative Example 7-8, while indicating the withstand voltage in the case of changing the added amount of SiO _2, the added amount of SiO ₂ is 1.0
High withstand voltage is shown in the range of up to 2.5 mol%.

[0028] Example 8-24 in the above Tables 1-2, Comparative Examples 9 to 17 shows a withstand voltage when changing each combination of Nb ₂ 0 ₅ and MnCO ₃ added amount. Using this result, it is summarized in Figure 3 the relationship between the withstand voltage relative to the addition amount of MnCO ₃ in the case of taking the amount of Nb ₂ 0 ₅ at a constant value. Than 3, less the amount of MnCO ₃ showing a high withstand voltage is added a small amount of area of the Nb ₂ 0 _5, 3
It can be seen that the range of the addition amount of MnCO ₃ showing a high withstand voltage of 0 V or more is narrow, about 0.02 mol%. The Nb ₂ 0 ₅
MnCO showing high withstand voltage as the amount of added MnCO increases
The amount of ₃ added increases, and M showing a high withstand voltage of 30 V or higher
It can be seen that the range of the amount of nCO ₃ added gradually widens. 0.0 actually added amount of Nb ₂ 0 ₅ as the Nb
Mn showing a high withstand voltage of 30 V or more at 65 mol% or more
The range of the amount of CO ₃ added is about 0.04 mol%.

[0029] Nb ₂ the withstand voltage indicates higher 30 V 0 ₅ and M
FIG. 4 shows the relationship between the amounts of nCO ₃ added. From this, Nb
₂ 0 a atomic% of addition amount of the rare earth element in the _5, MnCO ₃
When the amount of Mn added is b atomic%, when the rare earth element is less than 0.26 atomic%, b = 0.2a−0.006 ± 0.01 When the rare earth element is 0.26 atomic% or more , B = 0.715a−0.143 ± 0.02.

In this embodiment, the specific resistance value is 5 to
It was 15 Ω · cm.

From the data of the conventional example, it is understood that the porcelain composition for positive temperature coefficient thermistor according to the example has a withstand voltage higher by 50% or more as compared with the conventional composition.

[0032]

As described above in detail, in the semiconductor ceramic composition for a positive temperature coefficient thermistor according to the present invention, (Ba
_1-XY Sr _X Ca _Y ) TiO ₃ (however, 0 ≦ X ≦ 0.1
To 5,0.13 ≦ Y ≦ 0.17 barium titanate-based composition represented by the value) in the range of the TiO ₂ 0.5
˜1.5 mol%, SiO ₂ 1.0 to 2.5 mol%, rare earth element and Mn compound, rare earth element a atom%,
When Mn is b atomic%, when the rare earth element is less than 0.26 atomic%, b = 0.2a−0.006 ± 0.01 When the rare earth element is 0.26 atomic% or more, b = 0. 715a-0.143 ± 0.02, so that the grain size of the barium titanate sintered body can be reduced, and the grain boundary layer resistance per grain can be further improved. Voltage can be increased, resulting in a withstand voltage of 30V per 0.5Ω
As described above, the withstand voltage can be increased.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average particle size of a sintered body and the withstand voltage with respect to the amount of Ca substitution when Ba atoms are substituted with Ca in an example of the present invention.

FIG. 2 is a graph showing a current-voltage characteristic (logarithmic value) of a PTC thermistor.

FIG. 3 shows the amount of Nb ₂ O ₅ added and MnC in Examples.
Regarding the relationship between the withstand voltage value and the added amount of O ₃ , each N
the amount of b ₂ O ₅ is a graph showing a parameter.

FIG. 4 is a graph showing the relationship between the added amount of MnCO _{3 and} the added amount of Nb ₂ O ₅ when the withstand voltage value of the example is 30 V or more.

Claims (1)

[Claims] 1. (Ba _1-XY Sr _X Ca _Y ) TiO ₃
(However, in the range of 0 ≦ X ≦ 0.15 and 0.13 ≦ Y ≦ 0.17), 0.5 to 1.5 mol of TiO ₂ is added to the barium titanate-based composition. %, SiO ₂ is 1.0 to 2.5 mol%, the rare earth element and the Mn compound are a rare earth element a atom% and Mn b atom%, and the rare earth element is less than 0.26 atom%. , B = 0.2a-0.006 ± 0.01 When the rare earth element is 0.26 atomic% or more, it is contained so that the relationship of b = 0.715a-0.143 ± 0.02 is established. A semiconductor porcelain composition for a positive temperature coefficient thermistor, which is characterized in that