JPH0311082B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a barium titanate semiconductor having excellent positive temperature coefficient (PTC) characteristics. [Conventional technology] Barium titanate (BaTiO ₃ ) with Y, La, and Sb
Barium titanate-based semiconductors containing trace amounts of trivalent metals such as Nb, Ta, etc., exhibit a rapid increase in resistivity (ρ) at temperatures above the Curie point (Tc). Positive temperature coefficient (PTC)
Show characteristics. Utilizing this characteristic, the semiconductor is used in current control devices, heaters with self-control functions, and the like. Recently, in order to further improve the response and miniaturize the above-mentioned devices, the room temperature resistivity (ρr.t) is small, and in order to limit or substantially cut off overcurrent or overtemperature rise, Semiconductors with high resistivity at temperature are desired. In other words, ρr.t is as small as possible, and the ratio of ρmax/ρr.t (ρmax is the maximum value of resistivity at temperatures above Tc) is as large as possible.
Products with PTC characteristics are required. Conventionally, attempts have been made to obtain semiconductors with excellent PTC characteristics by adjusting the amount of the semiconducting agent containing the trivalent or pentavalent metal, or by adjusting the firing temperature. With this method, it is difficult to obtain a sufficiently low ρr.t. Additionally, in order to reduce ρr.t, there is a method of firing semiconductor raw material components in a neutral or reducing atmosphere, but although this method reduces ρr.t,
At the same time, the resistivity at high temperatures also decreases, and the PTC characteristics disappear. Furthermore, there is a method of adding a substance that forms ions such as Mn ² + to the semiconductor raw material components to obtain a large ρmax, but a very small change in the amount added can greatly increase the ρr.t. This makes it extremely difficult to adjust the amount added. [Problems to be solved by the invention] The present invention overcomes the above conventional problems, and
The present invention aims to provide a method for easily manufacturing barium titanate-based semiconductors with excellent PTC characteristics. [Means for Solving the Problems] The method for manufacturing a barium titanate-based semiconductor of the present invention comprises adding nylon to raw materials consisting of barium titanate and a semiconducting agent in the form of a powder, a thin film, or a solution in which the semiconductor is dissolved in a solvent. It is characterized in that it is added in the form of at least one of the above and then fired. In the present invention, barium titanate is
It is represented by the structural formula BaTiO ₃ and forms the main body of the semiconductor. Further, a semiconducting agent is added in a small amount to this barium titanate to lower the resistance of barium titanate, which is normally an insulator, and to make it a semiconductor. As the semiconductor agent, yttrium (Y),
It is a commonly used semiconductor converting agent for compounds containing trivalent metals such as lanthanum (La) and antimony (Sb) or pentavalent metals such as niobium (Nb) and tantalum (Ta). For example, those containing trivalent metals include Y ₂ O ₃ , La ₂ O ₃ , Sb ₂ O ₃ and the like. As it has,
Examples include Nb ₂ O ₅ , Ta ₂ O ₅ , etc., and one of these
Use one or more species. The amount of the above-mentioned semiconducting agent may be within the range of the amount generally used when forming a semiconductor, but it is preferable to mix 0.2 to 0.4 atomic percent of the semiconducting agent to barium titanate at room temperature. Good for obtaining semiconductors with low resistivity. The raw material component may be formed by simply mixing barium titanate and a semiconducting agent, or barium titanate may be formed by forming a carbonate containing Ba, Ti,
oxides or organic compounds, e.g. BaCO ₃ and
It is obtained by heating TiO ₂ , BaTiO(C ₂ O ₄ ) _{2.4H 2} O, etc. as a starting material, and by mixing the starting material and a semiconducting agent, and then applying calcination, etc. A raw material component according to the present invention in which BaTiO ₃ and a semiconducting agent are mixed may be formed by performing the following steps. The raw material component consisting of barium titanate and the semiconducting agent may be in powder form or may be previously formed into a desired shape. In the present invention, nylon is added to the above raw material components. The nylon to be added is generally referred to as polyamide, such as 6-nylon, 6-nylon,
These include 6-nylon and 12-nylon, and any of these may be used alone, as a copolymer, or as a modified version thereof. The form thereof may be fine powder, film, or solution dissolved in a solvent, but fine powder or solution is preferable from the viewpoint of ease of operation. The step of adding nylon to the raw material components may be any method as long as the nylon is mixed uniformly. For example, when the raw material is in powder form, a solution of a predetermined amount of nylon dissolved in a solvent that dissolves nylon, such as alcohol, formic acid, or metacresol, is sprinkled onto the raw material or kneaded with the raw material, and then dried. There is also a method in which nylon is made into a fine powder or thin film, water or a suitable mixed solvent is added to the raw material, and then the water or mixed medium is removed. There is. Alternatively, there is a method in which the raw material components are preformed, the molded body is impregnated with an organic solution in which nylon is dissolved, and then the organic solvent is removed. In addition, in the above-mentioned impregnation method, the shaping of the raw material components in advance is carried out by pressing,
The sintering may be carried out by slip casting or the like, and preliminary sintering may be carried out at a lower temperature than the main sintering temperature in order to prevent deformation of the compact during impregnation. The proportion of nylon added to the raw material components is preferably within the range of 0.2 to 8% by weight based on the raw material components.
If the addition ratio is less than 0.2% by weight or more than 8% by weight, it is difficult to obtain a sufficiently low room temperature resistivity (ρr.t) as a semiconductor. Next, press the raw materials to which nylon has been added,
After being formed by slip casting or the like, the final firing is performed in an oxidizing atmosphere. Note that when nylon is added by the impregnation method, the raw material components have already been shaped, so the main firing is performed as they are. Through this main firing, a barium titanate-based semiconductor is obtained. The firing atmosphere is an oxidizing atmosphere such as oxygen or air. In a neutral or reducing atmosphere,
It degrades the PTC characteristics of semiconductors. Also,
The firing temperature is preferably within the range of 1250 to 1400°C.
If the temperature is less than 1250°C, no semiconductor formation occurs, and if the temperature exceeds 1400°C, the resistivity (ρr.t) at room temperature may increase. Moreover, the firing time may be within the range of 1 to 2 hours. It should be noted that almost all of the nylon added by this firing is removed from the semiconductor by evaporation or thermal decomposition. [Effects of the Invention] According to the present invention, the room temperature resistivity (ρr.t) is small and ρmax/ρr.t is large, that is, PTC
A barium titanate-based semiconductor with excellent properties can be manufactured. Although the mechanism of action by which the above effects are obtained is not clear, it can be inferred as follows. In the present invention, the added nylon causes thermal decomposition during firing of the semiconductor, and active gases such as nascent nitrogen (N ₂ ) and carbon monoxide (CO) are generated. This active gas acts on BaTiO ₃ and introduces oxygen defects into it, reducing the overall resistance value, ie, the room temperature resistivity. Furthermore, this active gas is
It is thought that it reacts with BaTiO ₃ and contributes to the formation of an intermediate phase. This intermediate phase promotes the formation of a barrier by diffusion of impurities or oxygen to grain boundaries,
It is thought that this improves the PTC characteristics. Further, according to the present invention, a barium titanate-based semiconductor having excellent PTC characteristics can be easily manufactured without requiring complicated operations. [Examples] Examples of the present invention will be described below. Example 1 BaTiO ₃ as starting material and semiconducting agent
BaCO ₃ , TiO ₂ , and Y ₂ O ₃ were mixed at a composition ratio of Ba _0.997 Y _0.003 TiO ₃ , and the mixture was heated in the air at 1100°C.
It was calcined for 2 hours and then ground to form a powdered raw material component. An ethanol solution in which soluble nylon (manufactured by Toray Industries, Ltd., CM4000) was dissolved was added to the above raw material components and mixed in a ball mill. The amount added is within the range of 0 to 10% by weight (hereinafter referred to as ωt%) of nylon based on the raw material components (for comparison, a product without nylon was also prepared). Dry the thing to evaporate the solvent ethanol and use a mold to make a diameter 20
The molded body was molded into a disk shape with a thickness of about 3 mm, and the molded body was heated in the atmosphere at two temperatures of 1300℃ and 1350℃ for 1 hour.
Fired. The obtained sintered body was electrolessly plated with Ni as an electrode, and the electrical resistance of the sintered body was measured.The electrical resistance was measured in the air at a temperature ranging from room temperature to 400°C. The results are shown in FIGS. 1 and 2. Here, FIG. 1 shows the relationship between the amount of nylon added and the room temperature resistivity (ρr.t), and curves A and B in the figure are for firing temperatures of 1300°C and 1350°C, respectively. As is clear from Figure 1, by adding nylon, the room temperature resistivity decreases, especially from 0.2 to
It can be seen that by adding 8ωt% nylon, a material with extremely low room temperature resistivity can be obtained. Figure 2 shows PTC with a firing temperature of 1350℃.
It is a characteristic curve. Note that the curves M, N, and O are those in which the amount of nylon added is 0, 0.4, and 8 ωt%, respectively. Table 1 shows ρmax/ρr.t at a sintering temperature of 1350°C and with nylon addition amounts of 0, 0.4, 4, and 8ωt%, respectively. As is clear from FIG. 2 and Table 1, the ratio of ρmax/ρr.t increases by adding nylon.

[Table] As described above, it can be seen that the barium titanate-based semiconductor manufactured according to the present invention has excellent PTC characteristics. Example 2 This example shows an example in which nylon was added in the form of a thin film or fine powder. Ion-exchanged water was injected into the same ethanol solution of soluble nylon as in Example 1 to form nylon in the form of a thin film or fine powder. This was mixed into powdered raw material components similar to those in Example 1.
Added under similar conditions. The amount of nylon added is
It was set to 0.4ωt%. This nylon-added product was molded in the same manner as in Example 1 and fired in the atmosphere at 1350°C for 1 hour. When we measured the resistance of the formed barium titanate semiconductor, we found that ρr.t was a low value of 3Ω・cm.
The ratio of ρmax/ρr.t is a high value of 1.8×10 ³ (ρmax/ρr.t is 1.6×10 ¹ when nylon is not added), indicating that it has excellent PTC characteristics. . Example 3 This example shows an example using 6-nylon or 6,6-nylon. Pellets of 6-nylon or 6,6-nylon were immersed in liquid nitrogen and then ground in a hammer mill to form a fine powder with a particle size of about 30 μm. This was mixed into powdered raw material components similar to those in Example 1.
It was added under the same conditions. In addition, the amount of nylon added is
It was set to 1ωt%. This nylon-added product was molded in the same manner as in Example 1 and fired in the atmosphere at 1350°C for 1 hour. When the resistance of the formed barium titanate semiconductor was measured, the one with 6-nylon added had ρr.t=4.2Ω・cm, ρmax/ρr.t=2×10 ³ , 6,6
−For those with nylon added, ρr.t=4.8Ω・cm,
ρmax/ρr.t= ^2.103 , indicating that the PTC characteristics are excellent. Example 4 This example shows an example in which the raw material components were molded before adding nylon, and then nylon was added by an impregnation method. The same raw material components as in Example 1 were press-molded into the same disc shape as in Example 1, and pre-sintered at 1100°C in the atmosphere. Further, soluble nylon was weighed and dissolved in ethanol so that the amount added to the temporary sintered body was 1 ωt%. Next, the temporary sintered body was immersed in this solution to impregnate it with the solution. After drying this pre-sintered body and evaporating the ethanol, it was fired at 1300° C. for 1 hour in the air. When the resistance of the formed barium titanate semiconductor was measured, ρr.t=4Ω・cm, ρmax/ρr.t=
1.5×10 ³ , which shows that it has excellent PTC characteristics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of nylon added and the room temperature resistivity of the barium titanate-based semiconductor in Example 1, and FIG. 2 is a diagram showing the PTC characteristic curve of the barium titanate-based semiconductor in Example 1. It is.

Claims (1)

[Claims] 1. Adding nylon in the form of at least one of a powder, a thin film, or a solution dissolved in a solvent to a raw material component consisting of barium titanate and a semiconducting agent, and firing this. A method for manufacturing a barium titanate semiconductor, characterized by: 2 The above nylon has a ratio of 0.2 to 8 based on the raw material components.
A method for producing a barium titanate-based semiconductor according to claim 1, in which the amount by weight is added. 3. The method for producing a barium titanate semiconductor according to claim 1, wherein the semiconductor agent is a compound containing a trivalent metal such as yttrium, lanthanum, and antimony, or a pentavalent metal such as niobium and tantalum. .