JPWO2016002714A1 - Semiconductor porcelain composition and PTC element - Google Patents

Abstract

An object of the present invention is to provide a semiconductor ceramic composition having a high temperature coefficient of resistance α. It is another object of the present invention to provide a PTC element in which an electrode is formed on the semiconductor ceramic composition. A lead-free semiconductor ceramic composition in which a part of Ba in a BaTiO3-based oxide is replaced with Bi and A (A is at least one element of an alkali metal and Na is essential), The amount of Na at the grain boundary is 3 mol% or more. The temperature coefficient of resistance is preferably 4.5% / ° C. or higher.

Description

  The present invention relates to a semiconductor ceramic composition and a PTC element used for a PTC heater, a PTC thermistor, a PTC switch, a temperature detector, and the like.

Conventionally, as a material exhibiting PTC (Positive Temperature Coefficient of Reactive) characteristics, semiconductor porcelain compositions in which various semiconducting elements are added to a BaTiO ₃ oxide have been proposed. This semiconductor ceramic composition provided with electrodes can be used as a PTC element.

Most BaTiO ₃ -based semiconductor ceramic compositions have a Curie temperature of around 120 ° C. These semiconductor porcelain compositions need to shift the Curie temperature depending on the application. For example, it has been proposed to shift the Curie temperature by adding SrTiO ₃ oxide to BaTiO ₃ oxide, but in this case, the Curie temperature is shifted only in the negative direction and in the positive direction. Do not shift. PbTiO ₃ is a material that is currently in practical use and is known as an additive that shifts the Curie temperature in the positive direction. However, since lead is an element that causes environmental pollution, a lead-free semiconductor ceramic composition containing no lead is desired.

As a semiconductor porcelain composition that is lead-free and has a high Curie temperature, a part of Ba in the BaTiO ₃ oxide is substituted with Bi—Na.
Patent Document 1, at least one of the composition formula _{[(BiA) x (Ba 1} -y R y) 1-x] [Ti 1-z M z] O 3 (A is Na, Li, K, R Is at least one of rare earth elements including Y, M is at least one of Nb, Ta, and Sb), and x, y, and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, and 0 ≦ z A semiconductor ceramic composition having crystal grains satisfying ≦ 0.01 (where y + z> 0) is described.
In addition, Patent Document 1 describes, as a manufacturing method thereof, (BiA) TiO ₃ -based first raw material and (BaR) [TiM] O ₃ (R is at least one of rare earth elements including Y, M is Nb, Ta, A second raw material of each system is prepared, and the first raw material is calcined at 700 ° C. or higher and 950 ° C. or lower; The raw material of 2 is calcined at 900 ° C or higher and 1300 ° C or lower, and the calcined materials are mixed to form a third raw material. The third raw material is heat treated at 900 ° C or higher and 1250 ° C or lower, and then sintered. It is described to do.

International Publication No. 2013/157649

A semiconductor ceramic composition in which part of Ba in the BaTiO ₃ oxide is substituted with Bi—Na is effective for shifting the Curie temperature in the positive direction. However, the temperature coefficient of resistance α may not be sufficiently high.

  Therefore, an object of the present invention is to provide a semiconductor ceramic composition having a high resistance temperature coefficient α. Another object of the present invention is to provide a PTC element in which an electrode is formed on the semiconductor ceramic composition.

The present invention is a lead-free semiconductor ceramic composition in which a part of Ba in a BaTiO ₃ -based oxide is replaced with Bi and A (A is at least one element of an alkali metal and contains Na as an essential element). The amount of Na at the grain boundaries of the crystal grains is 3 mol% or more.
The semiconductor ceramic composition of the present invention can have a temperature coefficient of resistance of 4.5% / ° C. or higher.
The semiconductor ceramic composition of the present invention, at least one composition formula of the crystal grains is _{[(BiA) x (Ba 1} -y R y) 1-x] [Ti 1-z M z] O 3 (A is an alkali metal Wherein R is at least one of rare earth elements including Y, M is at least one of Nb, Ta, and Sb), and x, y, and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, and 0 ≦ z ≦ 0.01 may be satisfied.
Electrodes can be formed on these semiconductor ceramic compositions to form PTC elements.

  Even if the composition is the same, the semiconductor ceramic composition of the present invention can obtain a high resistance temperature coefficient α when the amount of Na at the grain boundaries of the crystal grains is 3 mol% or more. Therefore, when an electrode is formed on this semiconductor ceramic composition, a PTC element having an excellent resistance temperature coefficient α can be obtained.

It is a figure which shows the relationship between the amount of Na in the crystal grain boundary of the semiconductor ceramic composition of this invention, and resistance temperature coefficient (alpha). It is a figure which shows the relationship between the amount of Na in the crystal grain boundary of another semiconductor ceramic composition of this invention, and resistance temperature coefficient (alpha). It is a figure which shows the relationship between the amount of Na in the crystal grain boundary of another semiconductor ceramic composition of this invention, and resistance temperature coefficient (alpha). It is a STEM image in the crystal grain boundary of the semiconductor ceramic composition of this invention. It is a figure which shows an example of the manufacturing method for obtaining the semiconductor ceramic composition of this invention. It is a figure for demonstrating resistance temperature coefficient (alpha). It is the figure which showed typically the measurement location at the time of carrying out line analysis of sample No.2-12 by STEM-EDX. It shows the Na concentration and Bi concentration when sample No. 2-12 was line analyzed. This shows the Na concentration and Bi concentration when Comparative Example * No. 1-1 was line analyzed.

The present invention is a lead-free semiconductor ceramic composition in which a part of Ba in a BaTiO ₃ -based oxide is replaced with Bi and A (A is at least one element of an alkali metal and contains Na as an essential element). In addition, as shown in FIG. 1, it has been found that the resistance temperature coefficient α can be increased by increasing the amount of Na at the grain boundary of the crystal grains (hereinafter referred to as grain boundary Na amount). The reason why the temperature coefficient of resistance α increases is presumed to be that the presence of Na at the grain boundary increases the grain boundary level and increases the grain boundary double Schottky barrier.

In the present invention, the crystal grain boundary refers to a boundary surface between two different tetragonal crystal grains (BaTiO ₃ -based oxides) 1a and 1b as shown in FIG. The amount of grain boundary Na was measured at the center of the cross section of the boundary surface with a scanning transmission electron microscope (STEM) at a field of view of 100,000 times. Details of the measurement method will be described later.

When the grain boundary Na content is less than 3 mol%, the resistance temperature coefficient α does not exceed 4.5% / ° C. The grain boundary Na amount is preferably 5 mol% or more, more preferably 7 mol% or more.
On the other hand, the upper limit of the amount of grain boundary Na is not particularly limited, but if it exceeds 20 mol%, it becomes a shape of a fired body different from that during molding due to melting or softening, or the processing object in the furnace is installed. There is a problem that it reacts with a table or a container. Therefore, the grain boundary Na content is preferably 20 mol% or less.

The semiconductor ceramic composition of the present invention has crystal grains in which a part of Ba in a BaTiO ₃ oxide is substituted with Bi and A.
Among them, the composition formula is [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ (A is at least one element of an alkali metal and Na is essential. And R is represented by at least one of rare earth elements including Y, M is represented by at least one of Nb, Ta, and Sb), and x, y, and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, Those having crystal grains satisfying 0 ≦ z ≦ 0.01 are preferable.

  Curie temperature can be 130 degreeC-200 degreeC by making the range of x exceed 0 and 0.2 or less. If x exceeds 0.2, it is not preferable because a different phase is easily formed. x is more preferably 0.03 or more and 0.1 or less.

  A composition in which neither R nor M is added may be used (y = z = 0). In this case, however, the efficiency decreases when the heater element is used for low voltage applications with a room temperature resistivity exceeding 200 Ωcm. Therefore, it is preferable to satisfy y + z> 0. However, both R and M are not necessarily required, and at least one of them may be used.

The value of y in R may be in the range of 0 ≦ y ≦ 0.02, but 0 <y ≦ 0.02 is a preferable range. When y is 0, the composition is not sufficiently semiconducting, and when it exceeds 0.02, the room temperature resistivity tends to increase. The valence can be controlled by changing the value of y. However, when the valence control of the composition is performed in a system in which a part of Ba in the BaTiO ₃ oxide is substituted with Bi and A, the addition of a trivalent cation as a semiconducting element results in a monovalent effect. There is a problem that the room temperature resistivity increases due to the presence of A ions. Therefore, a more preferable range is 0.002 ≦ y ≦ 0.02. R is at least one element selected from rare earths (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Tb, Tm, Yb, Lu), particularly La and Y are preferable because excellent PTC characteristics can be obtained.

  Z indicating the amount of M may be in a range of 0 ≦ z ≦ 0.01, but 0 <z ≦ 0.01 is a preferable range. When z is 0, the valence cannot be controlled and the composition is not sufficiently semiconducting. When z is more than 0.01, the room temperature resistivity increases or the Curie temperature tends to decrease. A more preferable range is 0.001 ≦ z ≦ 0.005. M is preferable because Nb can obtain particularly excellent PTC characteristics among Nb, Ta, and Sb.

  A good ratio of Bi and A is 1: 1. However, even when this ratio is 1: 1 when blending the materials, Bi is volatilized by the calcination or sintering process, and the ratio of Bi and A is shifted, resulting in a 1: 1 ratio in the sintered body. This is also included in the present invention. Bi: A = 0.78 to 1.55: 1 is acceptable, and if it is within this range, the increase in heterogeneous phase can be suppressed, so that the increase in room temperature resistivity and change with time can be suppressed. A more preferable range is Bi: A = 0.90 to 1.2: 1.

In the above composition formula, the ratio of the A site on the [(BiA) _x (Ba _1-y R _y ) _1-x ] side and the B site on the [Ti _1-z M _z ] side is A site: B site = 0.9 It may deviate in the range of -1.1: 1. Preferably, A site: B site = 0.9 to 1.0: 1, more preferably 0.990 to 1.000: 1. The effect of reducing the change with time and the effect of improving the resistance temperature coefficient α can be expected.

  In addition to these, Si raw materials and Ca raw materials can be used as sintering aids. When these sintering aids are used, Si and Ca may be included in the above composition formula.

Below, the preferable manufacturing method for obtaining the semiconductor ceramic composition of this invention is demonstrated.
A raw material for producing a lead-free semiconductor ceramic composition in which a part of Ba in a BaTiO ₃ oxide is substituted with Bi and A (A is an element of at least one alkali metal and contains Na as an essential element). As described above, the semiconductor ceramic composition can be obtained by using a Na compound having a melting point of 865 ° C. or higher. When a Na compound having a melting point of less than 865 ° C. is used, Na cannot be precipitated at 3 mol% or more at the grain boundary. The Na compound preferably has a melting point of 1000 ° C. or higher, more preferably 1100 ° C. or higher. For example, Na ₂ Ti ₃ O ₇ (melting point: about 1130 ° C), Na ₂ Ti ₆ O ₁₃ (melting point: about 1300 ° C), or Na _0.5 Bi _4.5 Ti ₄ O ₁₅ (melting point: 1300 ° C or higher) should be used. Can do.
By using a Na compound with a high melting point, when NaTiO ₃ -based oxide crystal grains are formed, some of the Na in the Na compound is not taken into the crystal grains and remains at the crystal grain boundaries. Na can be segregated at grain boundaries. As a result, the semiconductor ceramic composition having a large resistance temperature coefficient α according to the present invention is obtained.

As a manufacturing method for obtaining the semiconductor ceramic composition of the present invention, a manufacturing method having steps (Step 1) to (Step 7) shown in FIG. 5 below can be adopted.
(Step 1) (BiA) TiO ₃ system (A is at least one element of alkali metal and contains Na essential) and (BaR) [TiM] O ₃ (R is a rare earth element containing Y) At least one of them, M is at least one of Nb, Ta, and Sb, and at least one of R and M is essential).
(Step 2) The first raw material is calcined at 700 ° C. or higher and 950 ° C. or lower, the second raw material is calcined at 900 ° C. or higher and 1300 ° C. or lower,
(Step3) Mix each calcined material to make the third raw material,
(Step 4) The third raw material is heat-treated at 900 ° C. or higher and 1250 ° C. or lower, and then
(Step 5) To the heat-treated third raw material, a Na compound having a melting point of 865 ° C. or higher is added,
(Step6) Molding,
(Step 7) Sinter at 1200 ° C or higher and 1500 ° C or lower.

The production method for obtaining the semiconductor ceramic composition of the present invention particularly has (Step 5) “step of adding a Na compound having a melting point of 865 ° C. or higher to the heat-treated third raw material”. . By this step, a semiconductor ceramic composition having an excellent resistance temperature coefficient α is obtained.
In other words, by mixing the calcined powder of the first and second raw materials into the third raw material, the third raw material is heat-treated at 900 ° C. or higher and 1250 ° C. or lower, so that the semiconductor ceramic composition to be finally obtained [(BiA) (BaR)] [TiM] O ₃ system ((specifically, [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ (x, y, z is 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.01)) or a compound having a composition close thereto, and then the melting point is 865. Add an Na compound at a temperature not lower than ° C. Since the [(BiA) (BaR)] [TiM] O ₃ compound has a composition that is stable to some extent even at high temperatures, fluctuations in the composition are suppressed even in subsequent sintering. Since the added Na compound has a high melting point, the time for Na to volatilize can be shortened, and the time during which the Na component is in a liquid phase during sintering can be shortened. It is suppressed that Na is contained in the grains. By this mechanism, Na is likely to segregate at the grain boundaries of the crystal, and the Schottky barrier at the grain boundaries increases, so it is assumed that the temperature coefficient of resistance increases.

The steps (Step 1) to (Step 7) will be described below.
First, (Step 1) will be described in detail. The (BiA) TiO ₃ -based first raw material is prepared by mixing A ₂ CO ₃ , Bi ₂ O ₃ , and TiO ₂ as raw material powders. Note that the (BiA) TiO ₃ -based first raw material refers to a raw material for forming the (BiA) TiO ₃ oxide.
The (BaR) [TiM] O ₃ -based second raw material is a raw material powder of BaCO ₃ , TiO ₂ , R, M, for example, an R element oxide such as La ₂ O ₃ , Nb ₂ O _5, etc. It is made by mixing the M element oxide. R and M are used as semiconducting elements. Note that the (BaR) [TiM] O ₃ -based second raw material refers to a raw material for forming the (BaR) [TiM] O ₃ oxide.

In the step (Step 1), both the first raw material and the second raw material may be pulverized according to the particle size of the raw material powder when the raw material powder is mixed. The raw material powder may be mixed by either wet mixing using pure water or ethanol or dry mixing. However, when dry mixing is performed, compositional deviation is more easily prevented. In addition to A ₂ CO ₃ , Bi ₂ O ₃ , TiO _2, etc., another A compound, Bi compound, or Ti compound may be used as the first raw material. Similarly, other Ba compounds and Ti compounds may be used for the second raw material in addition to BaCO ₃ , TiO ₂ and the like.

The calcination of the (BiA) TiO ₃ -based first raw material in (Step 2) will be described in detail.
The calcining temperature of the first raw material is 700 ° C. or higher and 950 ° C. or lower. When the calcining temperature is less than 700 ° C, unreacted A ₂ CO ₃ and Bi or Ti and unreacted A ₂ O react with the solvent in the case of moisture in the furnace atmosphere or wet mixing, and generate heat, The composition tends to deviate from the desired value and PTC characteristics tend to become unstable. On the other hand, when the calcining temperature exceeds 950 ° C., the volatilization of Bi proceeds, causing a composition shift and promoting the generation of a different phase. In addition, there is a problem that the reaction with the mortar used for calcination increases and the deterioration is accelerated, which is not preferable.
The calcination time is preferably 0.5 hours or more and 10 hours or less. When the calcination time is less than 0.5 hours, the obtained PTC characteristics are likely to be unstable for the same reason as when the calcination temperature is less than 700 ° C. When the calcining time exceeds 10 hours, the generation of a heterogeneous phase is easily promoted for the same reason as when the calcining temperature exceeds 950 ° C. The calcination time is preferably 1 hour or more and 8 hours or less.
The calcination of the first raw material is preferably performed in the air.
In order to suppress the volatilization of Bi, the calcining temperature of the first raw material is preferably lower than the calcining temperature of the second raw material.

  When the composition of the second raw material is a composition in which neither R nor M is added, the room temperature specific resistance is increased. Therefore, at least one of R and M is preferably essential.

The calcination of the (BaR) [TiM] O ₃ -based second raw material in (Step 2) will be described in detail.
The calcining temperature of the second raw material is 900 ° C. or higher and 1300 ° C. or lower. When the calcining temperature is less than 900 ° C., (BaR) [TiM] O ₃ is not completely formed, and some BaO decomposed from BaCO ₃ reacts with water, or a part of the remaining BaCO ₃ is water. Or the like, it may cause a compositional deviation and the characteristics may vary.
On the other hand, when the calcining temperature exceeds 1300 ° C., a part of the calcined powder is sintered together, which is not preferable because it prevents solid solution with the (BiA) TiO ₃ calcined powder to be mixed later. In addition, since it sticks to the mortar used for calcination, it is difficult to handle the calcined powder, and the problem of accelerating the deterioration of the mortar is not preferable.
The calcining time is preferably 0.5 hours or more. If the calcining time is less than 0.5 hours, it causes a composition shift. The upper limit is not particularly limited, but it is preferable that the upper limit is 100 hours or less because solid solution with the (BiA) TiO ₃ calcined powder to be mixed later can be promoted.
The calcination of the second raw material is preferably performed in the air.

  By the steps of (Step 1) and (Step 2), the volatilization of Bi is suppressed, the composition deviation of Bi-A is prevented, the generation of heterogeneous phase containing A is suppressed, the room temperature resistivity is lowered, and the Curie is reduced. Variation in temperature can be suppressed.

(Step 3) will be described in detail.
Each calcined powder is blended in a predetermined amount and then mixed to obtain a third raw material.
Mixing may be either wet mixing using pure water or ethanol or dry mixing. Further, depending on the particle size of the calcined powder, pulverization may be performed after mixing, or mixing and pulverization may be performed simultaneously. The average particle size of the calcined powder after mixing and pulverization is preferably 0.5 μm to 7.0 μm. Furthermore, 0.8 μm to 5.0 μm is preferable, and 1.0 μm to 4.0 μm is more preferable.

(Step 4) will be described in detail.
The third raw material is heat-treated at 900 ° C. to 1250 ° C. With this heat treatment, the composition of the first calcined powder and the second calcined powder can be made uniform, and the homogenized state is close to the state immediately before the crystal grains are grown. However, although this composition does not change greatly, crystal grains are formed, but there is an effect that the raw material composition added after this step is easily retained outside the crystal grains.
The temperature of the heat treatment is preferably set to a temperature at which the diffraction line peaks of the X-ray diffraction of both compositions are in the same position, that is, a solid solution state by this step. Below 900 ° C, Bi is not sufficiently diffused. If it exceeds 1250 ° C, the melting point of the (BiA) TiO ₃ system is around 1250 ° C, so Bi evaporates into the furnace atmosphere. In order to prevent the evaporation of Bi, it is desirable to perform heat treatment at a low temperature, but if it is too low, it is necessary to perform the heat treatment for a long time. A more preferable heat treatment temperature is 1000 ° C. or higher and 1200 ° C. or lower.

The heat treatment time is preferably 0.5 hours or more and 20 hours or less. When the time is shorter than 0.5 hours, the solid solution of the (BaR) [TiM] O ₃ type calcined powder and the (BiA) TiO ₃ type calcined powder is not stable, and the obtained PTC characteristics are not stable. On the other hand, when it exceeds 20 hours, the volatilization of Bi increases and the composition shift tends to occur. The heat treatment time is preferably 1 hour or more and 12 hours or less, more preferably 1.5 hours or more and 6 hours or less. The heat treatment of the third raw material is preferably performed in the atmosphere.

(Step 5) will be described in detail.
A Na compound having a melting point of 865 ° C. or higher is added to the heat-treated third raw material.
For example, Na ₂ Ti ₃ O ₇ (melting point: about 1130 ° C), Na ₂ Ti ₆ O ₁₃ (melting point: about 1300 ° C), or Na _0.5 Bi _4.5 Ti ₄ O ₁₅ (melting point: 1300 ° C or higher) should be used as the Na compound. Can do. By adding a Na compound after the heat treatment of (Step 4) above, it is possible to suppress the inclusion of Na in the crystal grains, compared with a case where a Na compound having a melting point of less than 865 ° C. (for example, Na ₂ CO ₃ ) is used. And the amount of grain boundary Na can be increased.

When Na ₂ Ti ₃ O ₇ or Na ₂ Ti ₆ O ₁₃ is used as the Na compound, it is preferable to add 0.005 mol% or more with the third raw material as 100 mol%.
If it is less than 0.005 mol%, the amount of grain boundary Na generated at the crystal grain boundary does not exceed 3 mol%, and as a result, the effect of increasing the resistance temperature coefficient α cannot be obtained. The upper limit is not particularly limited, but if it exceeds 5 mol%, there is a problem that the material melts or softens during firing to form a fired body different from that during molding or reacts with the container of the firing furnace. is there. Therefore, the upper limit is preferably 5 mol% or less. A more preferable amount of Na compound added is 0.5 mol% or more and 3 mol% or less.
When Na _0.5 Bi _4.5 Ti ₄ O ₁₅ is used, it is preferably added in a range of 0.1 mol% or more. The upper limit is not particularly limited, but is preferably 5 mol% or less. The reason for limiting the upper limit and the lower limit is the same as that when Na ₂ Ti ₃ O ₇ or Na ₂ Ti ₆ O ₁₃ is used. A preferable addition amount of Na _0.5 Bi _4.5 Ti ₄ O ₁₅ is 0.5 mol% or more and _3.5 mol% or less.

  Known means can be employed to mix the third raw material and the Na compound. For example, the organic solvent and the third raw material are mixed to form a slurry having a solid solution concentration of 30 to 60%, and a Na compound is added to this slurry until the center particle diameter becomes 1.0 to 5.0 μm by a ball mill or a pot mill. A means for mixing while pulverizing can be used.

In order to reduce the change over time of the PTC characteristics of the semiconductor ceramic composition, it is preferable to add a Y raw material such as Y ₂ O ₃ . Y material is preferably added in the third Y ₂ 0 ₃ 4.0 mol% or less of the range of 0.5 mol% in terms of the raw material.

Further, in any of the steps (Step 1) to (Step 5), an oxide containing Ba and Ti that becomes a liquid phase at a temperature of more than 1250 ° C. and 1500 ° C. or less (hereinafter referred to as BaTi oxide) may be mixed. it can. By adding BaTi oxide, even if the sintering temperature varies, the resistance temperature coefficient α can be suppressed from decreasing, and the obtained characteristics are stabilized. Further, the addition of BaTi oxide can reduce the change with time in the PTC characteristics.
BaTi oxide is represented by the composition formula Ba ₆ Ti ₁₇ O ₄₀ , BaTi ₂ O ₅ , Ba ₄ Ti ₁₃ O ₃₀ , BaTi ₃ O ₇ , BaTi ₄ O ₉ , Ba ₂ Ti ₉ O ₂₀ , Ba ₂ TiO _5. Can be applied. Even if the sintering temperature is low, the resistance temperature coefficient α can be suppressed from decreasing. It is particularly preferable to use Ba ₆ Ti ₁₇ O ₄₀ as the BaTi oxide.
The BaTi oxide is preferably added in an amount of 0.1 mol% or more and 1.0 mol% or less in terms of the above composition formula with respect to the third raw material.

(Step 6) will be described in detail.
A mixture of the third raw material and the Na compound is formed. You may granulate a mixture with a granulator as needed before shaping | molding. Compact density after the forming is preferably ^{2.5~4.2g / cm 3, 2.5~3.5g / cm} 3 is more preferable.

(Step 7) will be described in detail.
Sintering can be performed at a sintering temperature of 1200 ° C to 1500 ° C. If the sintering temperature is less than 1200 ° C., the sintering tends to be insufficient. If the sintering temperature exceeds 1500 ° C., it becomes soft during sintering and does not become a desired shape, and the temperature coefficient of resistance α tends to decrease.

For example, when Na ₂ Ti ₃ O ₇ is used as the Na compound in (Step 5), the sintering temperature is more preferably 1250 ° C. or higher and 1460 ° C. or lower. When Na ₂ Ti ₆ O ₁₃ is used as the Na compound, the sintering temperature is more preferably 1200 ° C. or higher and 1380 ° C. or lower. When Na _0.5 Bi _4.5 Ti ₄ O ₁₅ is used as the Na compound, the sintering temperature is more preferably 1200 ° C. or higher and 1500 ° C. or lower.

The atmosphere during sintering is preferably the air, a reducing atmosphere, or an inert gas atmosphere having a low oxygen concentration.
The sintering time is preferably 1 hour or more and 10 hours or less. If the sintering time is less than 1 hour, sintering is insufficient. When the sintering time exceeds 10 hours, Na precipitated at the grain boundary diffuses from the grain boundary and forms another phase that is not tetragonal between the crystals, resulting in a low resistance temperature coefficient α. There is a possibility of becoming. A more preferable sintering time is 2 hours or more and 6 hours or less.

In the present invention, the amount of Na at the crystal grain boundary, the temperature coefficient of resistance α, the evaluation method of the room temperature specific resistance R ₂₅ , and the composition analysis of the crystal grains were performed as follows.

(Na amount at grain boundaries)
First, using a JEOL atomic resolution analytical electron microscope (model number JEM-ARM200F), a field of view where the cross-sections (grain boundaries) of two crystal grains are adjacent to each other is defined. Since possibly a BaTiO ₃ other than based crystal, confirms that these grains is tetragonal in BaTiO ₃ system. After that, the interface between these two crystals is subjected to elemental analysis with STEM-EDX. The magnification is 100,000 times. The acceleration voltage is 200 kV and the beam diameter is 0.2 nm. Measure five points on an arbitrary boundary surface, and take the average value as the Na amount at the grain boundary.

(Resistance temperature coefficient α)
The temperature coefficient of resistance α was calculated by measuring resistance-temperature characteristics while raising the temperature of the semiconductor ceramic composition to 260 ° C.
The resistance temperature coefficient α is defined by the following equation.
α = (lnR _L -lnR _C ) × 100 / (T _L -T _C )
As shown in FIG. 6 (horizontal axis: temperature, vertical axis (logarithmic notation): specific resistance), R _L is the specific resistance at 260 ° C, T _L is 260 ° C, T _C is the Curie temperature, and R _C is T _C The specific resistance at. Here, the Curie temperature T _C was set to a temperature at which the non-resistance is twice the room temperature specific resistance R ₂₅ .

(Room temperature resistivity R ₂₅ )
The room temperature resistivity R ₂₅ (Ωcm) of the semiconductor ceramic composition was measured at 25 ° C. by a four-terminal method.

(Composition analysis of crystal grains)
Using an atomic resolution analytical electron microscope (model number JEM-ARM200F) manufactured by JEOL, the inside of the crystal grains was subjected to elemental analysis by STEM-EDX. The measurement conditions were the same as the measurement of the grain boundary Na amount.

(Example 1)
By changing the amount of Na compound added, the relationship between the change in grain boundary Na amount and the accompanying temperature coefficient of resistance α was investigated.
As shown in FIG. 5, a (BiA) TiO ₃ -based first material and a (BaR) [TiM] O ₃ -based second material were prepared as raw materials (Step 1). In this example, raw material powder of Na ₂ CO ₃ , Bi ₂ O ₃ , TiO ₂ was prepared as the first raw material of (BiA) TiO ₃ system, and the molar ratio Bi / Na Bi / Na of 1.05 ( Bi _0.525 Na _0.500 ) TiO ₃ was blended and dry mixed. In addition, a raw material powder of BaCO ₃ , TiO ₂ , and La ₂ O ₃ was prepared as the second raw material of the (BaR) [TiM] O ₃ system, blended so as to be (Ba _0.994 La _0.006 ) TiO _3, and pure Mixed with water.
The first raw material was calcined at 700 to 950 ° C., and the second raw material was calcined at 900 to 1300 ° C. (Step 2). In this example, the obtained first raw material was calcined in the air at 800 ° C. for 2 hours to prepare a (BiA) TiO ₃ -based calcined powder. The second raw material was calcined at 1200 ° C. for 4 hours in the air to prepare a (BaR) [TiM] O ₃ -based calcined powder.
The calcined materials were mixed to obtain a third raw material (Step 3). In this example, (BiA) TiO ₃ -based calcined powder and (BaR) [TiM] O ₃ -based calcined powder were converted into [(Bi _0.5 Na _0.5 ) _0.085 (Ba _0.994 La _0.006 ) _0.915 ] TiO ₃ It mixed so that it might become. This material was mixed and pulverized with a pot mill using pure water as a medium until the average particle size became 2.0 μm to 3.0 μm, and then dried to obtain a third raw material.
The third raw material was heat-treated at 900 ° C. to 1250 ° C. (Step 4). In this embodiment, the heat treatment (BIA) and calcined powder of TiO ₃ system (BaR) [TiM] for reacting O ₃ based calcined powder at 1150 ° C. The third raw material, with 4 hours in the air went. The third raw material heat-treated at this temperature has one diffraction line for each of the (BaR) [TiM] O ₃ type calcined powder and the (BiA) TiO ₃ type calcined powder as measured by X-ray diffraction. It was.

Thereafter, a Na compound having a melting point of 865 ° C. or higher was added to the heat-treated third raw material (Step 5). In this example, a Na ₂ Ti ₃ O ₇ compound was used as the Na compound, and 0.01 mol%, 0.5 mol%, 2.0 mol%, 4.0 mol%, and 5.0 mol% were added with the third raw material as 100 mol%.
Thereafter, in this example, BaTi oxide represented by Ba ₆ Ti ₁₇ O ₄₀ , Y ₂ O ₃ and CaCO ₃ were added. The addition amount of Ba ₆ Ti ₁₇ O ₄₀ , Y ₂ O ₃ and CaCO ₃ is that the third raw material is 100 mol%, Ba ₆ Ti ₁₇ O ₄₀ is 0.6 mol%, Y ₂ O ₃ is 1.0 mol%, CaCO ₃ Was 2 mol%.
In addition, as a comparative example, a product without addition of Na compound (0 mol%) was also produced. In Comparative Example 1, a semiconductor ceramic composition was produced in the same manner as in Example 1 except that no Na compound was added. The same applies to the following steps.
Thereafter, molding was performed (Step 6). In this example, PVA was added, mixed, and granulated. The obtained granulated powder was molded with a single screw press machine and subjected to binder removal treatment by heating at 700 ° C. for 10 hours.
Thereafter, sintering was performed (Step 7). In this example, sintering was performed in nitrogen at an oxygen concentration of 0.007 vol% (70 ppm) by holding at 1420 ° C. for 4 hours to obtain a sintered body.
The obtained sintered body is processed into a plate of 10 mm × 10 mm × 1.0 mm to produce a test piece, a base metal ohmic electrode is applied, and a cover electrode mainly composed of Ag is further applied to 180 ° C. After drying, the electrode was formed by baking at 600 ° C. for 10 minutes to form a PTC element.

Table 1 shows the results of the amount of Na compound added, the amount of grain boundary Na, the resistance temperature coefficient α, the room temperature resistivity R ₂₅ , and the Curie temperature Tc. In Table 1, the comparative examples are marked with *.

When the composition of the crystal grains of each semiconductor ceramic composition of Table 1 was examined, the composition formula was [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ (A Is at least one of Na, Li and K, R is at least one of rare earth elements including Y, M is at least one of Nb, Ta and Sb), and x, y and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, and 0 ≦ z ≦ 0.01 were satisfied.

No. 1-1 is a comparative semiconductor porcelain composition prepared without adding a Na compound, but the amount of grain boundary Na was less than 3 mol%. The temperature coefficient of resistance α was as low as 4.4% / ° C.
On the other hand, in the semiconductor ceramic compositions of the present invention of No. 1-2 to 1-6, the grain boundary Na amount was all 3 mol% or more, and the resistance temperature coefficient α was 4.5% / ° C. or more.

  FIG. 4 is a result of observing the grain boundary of No. 1-3 with STEM. There are crystal grains 1a and 1b on the left and right, and the grain boundary 2 of the crystal grains can be confirmed. When the amount of Na in the grain boundary 2 was measured in the same field of view, it was confirmed that the amount of Na in the grain boundary was larger than that in the crystal grains.

(Example 2)
The relationship between the change in the grain boundary Na amount and the accompanying resistance temperature coefficient α was investigated by changing the sintering temperature.
(Step 1) to (Step 4) were performed under the same conditions as in the production methods of No. 1-3 and No. 1-4 of Example 1 (the addition amounts of Na compound were 0.5 mol% and 2.0 mol%).
Thereafter, a Na compound having a melting point of 865 ° C. or higher was added to the third raw material heat-treated in (Step 4) (Step 5). In this example, a Na ₂ Ti ₃ O ₇ compound was used as the Na compound, and the third raw material was added at 0.5 mol% with 100 mol% and 2.0 mol% added.
Thereafter, in this example, BaTi oxide represented by Ba ₆ Ti ₁₇ O ₄₀ , Y ₂ O ₃ and CaCO ₃ were added. The amount of addition was 100 mol% for the third raw material, 0.6 mol% for Ba ₆ Ti ₁₇ O ₄₀ , 1.0 mol% for Y ₂ O _{3 and 2} mol% for CaCO ₃ .
Thereafter, molding was performed (Step 6). In this example, PVA was added, mixed, and granulated. The obtained granulated powder was molded with a single screw press machine and subjected to binder removal treatment by heating at 700 ° C. for 10 hours.
Thereafter, sintering was performed (Step 7). In this embodiment, those of Na ₂ Ti ₃ O ₇ was added 0.5 mol% in (Step5) alters the sintering temperature in the range of 1300 ℃ ~1460 ℃, nitrogen at 4 hour hold, the oxygen concentration 0.007Vol% Sintering was performed under the condition of (70 ppm) to obtain respective sintered bodies (2-1 to 2-7). In (Step 5), 2.0 mol% of Na ₂ Ti ₃ O ₇ was added. The sintering temperature was changed in the range of 1340 to 1460 ° C, and the oxygen concentration was 0.007vol% (70ppm) in nitrogen after holding for 4 hours. Sintering was performed under the conditions to obtain respective sintered bodies (2-8 to 2-13).
Subsequent processing, electrode formation, and evaluation were performed in the same manner as in Example 1.
Table 2 shows the results of the Na compound addition amount, sintering temperature, grain boundary Na amount, resistance temperature coefficient α, room temperature resistivity R ₂₅ , and Curie temperature Tc.

Examination of the crystal grains of the composition of the semiconductor ceramic composition shown in Table 2, the composition formula _{[(BiA) x (Ba 1} -y R y) 1-x] [Ti 1-z M z] O 3 (A Is at least one of Na, Li and K, R is at least one of rare earth elements including Y, M is at least one of Nb, Ta and Sb), and x, y and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, and 0 ≦ z ≦ 0.01 were satisfied.

  As shown in Table 2, the semiconductor ceramic composition of the present invention having a grain boundary Na amount of 3.0 mol% or more had a high resistance temperature coefficient α, and in this example, all were 4.5% / ° C. or more. The resistance temperature coefficient α is more preferably 5.0% / ° C. or more.

(Comparative Example 1)
A Na compound having a melting point of less than 865 ° C. was used, and the relationship between the change in grain boundary Na amount and the accompanying temperature coefficient of resistance α was investigated.
(Step 1) to (Step 4) were performed under the same conditions as in No. 2-3 of Example 2 (the amount of Na compound added was 0.5 mol%).
Thereafter, Na ₂ CO ₃ having a melting point of 851 ° C. was added to the heat-treated third raw material at 0.4 mol% with the third raw material as 100 mol% (corresponding to Step 5).
Further, the BaTi oxide and Y ₂ O ₃ and CaCO ₃ represented by Ba ₆ Ti ₁₇ O _40, with respect to the third material, BaTi oxide 0.6 mol%, Y ₂ O ₃ is 1.0 mol%, CaCO ₃ was added at 2 mol%.
Thereafter, a PTC element was manufactured through the same process as the manufacturing method of Example 1 and evaluated.
Table 3 shows the results of the amount of Na compound added, the amount of grain boundary Na, the resistance temperature coefficient α, the room temperature specific resistance R ₂₅ , and the Curie temperature Tc.

  As shown in Table 3, the amount of grain boundary Na was less than 3.0 mol%. Further, the temperature coefficient of resistance α was low, which was 2.3% / ° C. in this comparative example.

(Example 3)
The composition formula changes the amount of R (La amount) in [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ and changes the amount of grain boundary Na and accompanying it The relationship of the resistance temperature coefficient α was examined.
As shown in FIG. 5, a (BiA) TiO ₃ -based first material and a (BaR) [TiM] O ₃ -based second material were prepared as raw materials (Step 1). In this example, raw material powder of Na ₂ CO ₃ , Bi ₂ O ₃ , TiO ₂ was prepared as the first raw material of (BiA) TiO ₃ system, and the molar ratio Bi / Na Bi / Na of 1.05 ( Bi _0.525 Na _0.500 ) TiO ₃ was blended and dry mixed. In addition, raw material powders of BaCO ₃ , TiO ₂ , and La ₂ O ₃ are prepared as (BaR) [TiM] O ₃ -based second raw materials, and (Ba _0.999 La _0.001 ) TiO ₃ , (Ba _0.998 La _0.002 ) TiO ₃ and (Ba _0.997 La _0.003 ) TiO ₃ , respectively, and mixed with pure water (Step 1).
(Step 2) and subsequent steps were manufactured under the same conditions as in the manufacturing method of Example 1, then processed, formed electrodes, manufactured PTC elements, and evaluated.
Table 4 shows the results of the Na compound addition amount, R amount y, grain boundary Na amount, resistance temperature coefficient α, room temperature resistivity R ₂₅ , and Curie temperature Tc.

When the composition of the crystal grains of each semiconductor ceramic composition in Table 4 was examined, the composition formula was [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ (A Is at least one of Na, Li and K, R is at least one of rare earth elements including Y, M is at least one of Nb, Ta and Sb), and x, y and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, and 0 ≦ z ≦ 0.01 were satisfied.

  As shown in Table 4, the semiconductor ceramic composition of the present invention having a grain boundary Na amount of 3.0 mol% or more has a higher resistance temperature coefficient α than that of the comparative example (No. 1-1). All were above 4.5% / ° C.

FIG. 1 shows the relationship between the amount of grain boundary Na and the temperature coefficient of resistance α of the semiconductor ceramic composition of the present invention.
The grain boundary Na amount and the resistance temperature coefficient α used in FIG. 1 are the values in Tables 1, 2, and 4 of Examples 1 to 3. The black points are the comparative example (No. 1-1).
In the semiconductor ceramic composition of this example, the temperature coefficient of resistance α tends to increase as the grain boundary Na amount increases. No. 1-1 having a grain boundary Na amount of less than 3 mol% has a small grain temperature Na amount of 2.7 mol% and a small temperature coefficient of resistance α, specifically less than 4.5% / ° C.
In the range where the grain boundary Na amount is 3 mol% or more, the resistance temperature coefficient α is 4.5% / ° C. or more, and the resistance temperature coefficient α tends to increase as the grain boundary Na amount increases. In particular, when the grain boundary Na amount is 5 mol% or more, the grain boundary Na amount and the resistance temperature coefficient α are proportionally improved, and the resistance temperature coefficient α is further increased.

FIG. 7 is a diagram schematically showing measurement locations when sample No. 2-12 is subjected to line analysis by STEM-EDX. Each measurement point is the position of a round point on a line drawn in the center lateral direction. The magnification is 100,000 times.
FIG. 8 shows the Na concentration and Bi concentration when Sample No. 2-12 was subjected to line analysis. The Na concentration tends to increase from the inside of the grain toward the interface. On the other hand, such a tendency was not seen in the Bi concentration.
Although not shown in the figure, Ti also tends to have a higher concentration at the interface than in the grains. However, the concentration of Ba tended to decrease as the concentration of Ti increased. The temperature coefficient of resistance α of Sample No. 2-12 is 6.0% / ° C.
FIG. 9 shows the Na concentration and Bi concentration when the sample * No. 1-1, which is a comparative example, was similarly subjected to line analysis. As in FIG. 8, the Na concentration tends to increase from the inside of the grain toward the interface, but the maximum value of Na concentration is 2.8 at%, and the resistance temperature coefficient α is 4.4% / ° C. The value is lower than that of

(Example 4)
The type of Na compound was changed, and the relationship between the change in grain boundary Na content and the accompanying temperature coefficient of resistance α was investigated.
(Step 1) to (Step 4) were performed under the same conditions as in the manufacturing method of Example 1.
Thereafter, a Na compound having a melting point of 865 ° C. or higher was added to the heat-treated third raw material (Step 5). Na ₂ Ti ₆ O ₁₃ was used as the Na compound. A material obtained by adding 0.5 mol% the Na ₂ Ti ₆ O ₁₃ a third raw material as 100 mol%, was prepared which was added 2.0 mol%.
Thereafter, in this example, BaTi oxide represented by Ba ₆ Ti ₁₇ O ₄₀ , Y ₂ O ₃ and CaCO ₃ were added. The addition amount of Ba ₆ Ti ₁₇ O ₄₀ , Y ₂ O ₃ and CaCO ₃ is that the third raw material is 100 mol%, Ba ₆ Ti ₁₇ O ₄₀ is 0.6 mol%, Y ₂ O ₃ is 1.0 mol%, CaCO ₃ Was 2 mol%.
Thereafter, molding was performed (Step 6). In this example, PVA was added, mixed, and granulated. The obtained granulated powder was molded with a uniaxial press machine and subjected to binder removal treatment at 700 ° C. for 10 hours.
Thereafter, sintering was performed (Step 7). In this example, in the case where 0.5 mol% of Na ₂ Ti ₆ O ₁₃ was added in (Step 5), the sintering temperature was changed in the range of 1200 to 1420 ° C., and the oxygen concentration was 0.007 vol% (in nitrogen with holding for 4 hours). Sintering was performed under the condition of 70 ppm) to obtain respective sintered bodies (5-1 to 5-7). In (Step 5), 2.0 mol% of Na ₂ Ti ₆ O ₁₃ was added. The sintering temperature was changed to 1200 ° C and 1260 ° C, and the oxygen concentration was 0.007vol% (70ppm) in nitrogen after holding for 4 hours. Were sintered to obtain respective sintered bodies (5-8 to 5-9).
Subsequent processing, electrode formation, and evaluation were performed in the same manner as in Example 1.
Table 5 shows the results of the Na compound addition amount, sintering temperature, grain boundary Na amount, resistance temperature coefficient α, room temperature resistivity R ₂₅ , and Curie temperature Tc.

When the composition of the crystal grains of the semiconductor ceramic composition of Table 5 was examined, the composition formula was [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ (A is At least one of Na, Li, and K, R is at least one of rare earth elements including Y, M is at least one of Nb, Ta, and Sb), and x, y, and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, and 0 ≦ z ≦ 0.01 were satisfied.

As shown in Table 5, the semiconductor ceramic composition of the present invention having a grain boundary Na amount of 3.0 mol% or more had a high resistance temperature coefficient α, and in this example, it was all 4.5% / ° C. or more.
These semiconductor porcelain compositions having a large room temperature specific resistance can be used for PTC elements that require withstand voltage, such as electric vehicles.

  FIG. 2 is a graph showing the relationship between the grain boundary Na amount and the resistance temperature coefficient α in the semiconductor ceramic composition of Table 5. As in FIG. 1, it was found that the temperature coefficient of resistance α tends to increase as the grain boundary Na amount increases in the semiconductor ceramic composition of this example.

(Example 5)
By further changing the kind of Na compound, the relationship between the change in grain boundary Na amount and the accompanying temperature coefficient of resistance α was investigated.
As in Example 1, (Step 1) to (Step 4) were performed.
Thereafter, a Na compound having a melting point of 865 ° C. or higher was added to the heat-treated third raw material (Step 5). Na _0.5 Bi _4.5 Ti ₄ O ₁₅ was used as the Na compound. As a Na _0.5 Bi _4.5 Ti ₄ O ₁₅ was added 0.5 mol% of a third material as 100 mol%, and those obtained by adding 2.0 mol%, was prepared which was added 5.0 mol%. In addition, for comparison, a sample without Na compound (0 mol%) was also prepared.
Thereafter, in this example, BaTi oxide represented by Ba ₆ Ti ₁₇ O ₄₀ , Y ₂ O ₃ and CaCO ₃ were added. The third raw material was 100 mol%, the addition amount of Ba ₆ Ti ₁₇ O ₄₀ was 0.6 mol%, the addition amount of Y ₂ O ₃ was 1.0 mol%, and the addition amount of CaCO ₃ was 2 mol%.
Thereafter, molding was performed (Step 6). In this example, PVA was added, mixed, and granulated. The obtained granulated powder was molded with a uniaxial press machine and subjected to binder removal treatment at 700 ° C. for 10 hours.
Thereafter, sintering was performed (Step 7). In this example, in the case of adding 0.5 mol% of Na _0.5 Bi _4.5 Ti ₄ O ₁₅ in (Step ₅ ), the sintering temperature was changed in the range of 1250 to 1460 ° C., and the oxygen concentration was 0.007 vol. % (70 ppm) was sintered to obtain respective sintered bodies (6-2 to 6-10). In (Step ₅ ), 2.0 mol% of Na _0.5 Bi _4.5 Ti ₄ O ₁₅ was added. The sintering temperature was changed in the range of 1340 to 1420 ° C, and the oxygen concentration was 0.007 vol% (70 ppm) in nitrogen after holding for 4 hours. ) To obtain respective sintered bodies (6-11 to 6-14).
In addition, in (Step ₅ ), Na _0.5 Bi _4.5 Ti ₄ O ₁₅ with 5.0 mol% was added at a sintering temperature of 1420 ° C. and maintained for 4 hours under nitrogen at an oxygen concentration of 0.007 vol% (70 ppm). Sintered to obtain a sintered body (6-15).
Subsequent processing, electrode formation, and evaluation were performed in the same manner as in Example 1.
Table 6 shows the results of the Na compound addition amount, sintering temperature, grain boundary Na amount, resistance temperature coefficient α, room temperature resistivity R ₂₅ , and Curie temperature Tc. Comparative examples are marked with *.

When the composition of the crystal grains of the semiconductor ceramic composition of Table 6 was examined, the composition formula was [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ (A is At least one of Na, Li, and K, R is at least one of rare earth elements including Y, M is at least one of Nb, Ta, and Sb), and x, y, and z are 0 <x ≦ 0.2, 0 ≦ y ≦ 0.02, and 0 ≦ z ≦ 0.01 were satisfied.

No. 6-1 is a comparative semiconductor porcelain composition prepared without adding a Na compound, but the grain boundary Na content was less than 3 mol%. The temperature coefficient of resistance α was 4.1% / ° C.
On the other hand, in the semiconductor ceramic compositions of the present invention Nos. 6-2 to 6-15, the grain boundary Na amount was all 3 mol% or more, and the resistance temperature coefficient α was all 4.5% / ° C. or more.

  FIG. 3 is a graph showing the relationship between the amount of grain boundary Na and the temperature coefficient of resistance α in the semiconductor ceramic composition shown in Table 6. Similar to FIG. 2, it was found that the temperature coefficient of resistance α tends to increase as the grain boundary Na amount increases in the semiconductor ceramic composition of this example.

  A PTC element can be formed by processing the semiconductor ceramic composition of the present invention into a plate shape and forming electrodes on both sides of the plate. As a method for forming the electrode, a known means can be adopted, but a means for baking after applying the electrode paste is low in cost, and this means is adopted in this embodiment.

  The semiconductor ceramic composition obtained by the present invention is optimal as a material for PTC heaters, PTC thermistors, PTC switches, temperature detectors, and the like.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on July 2, 2014 (Japanese Patent Application No. 2014-136708), the contents of which are incorporated herein by reference.

  1a, 1b: Grain, 2: Grain boundary

Claims (4)

A lead-free semiconductor ceramic composition in which a part of Ba in a BaTiO ₃ -based oxide is substituted with Bi and A (A is an element of at least one alkali metal and contains Na as an essential element),
A semiconductor ceramic composition characterized in that the amount of Na at grain boundaries of crystal grains is 3 mol% or more.   The semiconductor ceramic composition according to claim 1, wherein the temperature coefficient of resistance is 4.5% / ° C or more. The composition formula of the crystal grain is [(BiA) _x (Ba _1-y R _y ) _1-x ] [Ti _1-z M _z ] O ₃ (A is at least one element of an alkali metal and Na is essential. Wherein R is at least one of rare earth elements including Y, M is at least one of Nb, Ta, and Sb), and x, y, and z are 0 <x ≦ 0.2 and 0 ≦ y ≦ 0.02. The semiconductor porcelain composition according to claim 1, wherein 0 ≦ z ≦ 0.01 is satisfied.   A PTC element, wherein an electrode is formed on the semiconductor ceramic composition according to claim 1.

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