JP3364269B2 - PTC thermistor material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PTC thermistor material used for temperature control elements and the like.

[0002]

2. Description of the Related Art A thermistor is one of the functional materials that have been actively studied in recent years. The thermistor is a circuit element that utilizes the property that the specific resistance greatly changes with temperature.

The thermistor has an NTC due to its temperature coefficient.
There are thermistors and PTC thermistors. NTC thermistor has a negative temperature coefficient
It is a material that has a specific resistance that decreases with increasing temperature.
It is used as a temperature sensor in temperature compensation circuits.
On the other hand, the PTC thermistor has a positive temperature coefficient (Positive Temp
It is a material that has a specific coefficient of temperature, and its specific resistance sharply increases at a certain temperature.By utilizing its properties, it is widely applied as a temperature control element, an overcurrent control element, a motor starting element, and a constant temperature heating element. ing.

A typical example of such a PTC thermistor is BaTiO ₃ ceramics. BaTi
O ₃ is a ferroelectric substance having a perovskite structure, and its PT
CR (Positive Temperature Co
The efficient of Resistivity) characteristic appears near the phase transition temperature. Therefore, the PTCR characteristics are considered to be based on the phase transition. Regarding the mechanism of expressing the PTCR characteristics, an interface acceptor level is formed by oxygen and impurities excessively present on the surface of the crystal grain, whereby electrons in the crystal are trapped and a depletion layer is formed. A Schottky type potential barrier is generated at the grain boundary. This barrier is PTC
It is considered to be the cause of high specific resistance at a temperature equal to or higher than the temperature showing the R characteristic (Curie temperature: Tc). On the other hand, Tc
In the following region, the spontaneous polarization causes a negative charge at the grain boundary with a probability of 50%, so that the acceptor is compensated and the height of the barrier is lowered. There is. Furthermore, it is presumed that, above Tc, the barrier height returns to its original level due to the disappearance of spontaneous polarization, and the resistivity increases.

As a material showing PTCR characteristics, BaTi
In addition to O ₃ -based ceramics, PbTiO ₃ —TiO ₂ -based ceramics are also known, and the common point of these materials exhibiting the PTCR characteristics is a ferroelectric having a perovskite structure. In addition, it is important that this ferroelectric substance is made into a semiconductor by a valence control method.

[0006] The present inventors have also proposed Japanese Patent Application No. 4-3310.
No. 75, among the bismuth layer structure oxides having a quasi-perovskite type sublattice, most of which are ferroelectrics, have a composition of Bi ₄ Ti ₃ O ₁₂ and part of Ti is Nb.
It has been proposed to obtain a semiconducting bismuth layered structure oxide which is substituted with, and to have PTCR characteristics by substituting a part of Bi of this oxide with Sr.

This bismuth layer structure oxide has a temperature of 200.degree.
It exhibits excellent PTCR characteristics in a temperature range exceeding 40 ° C. and has a sharp change in resistance. However, it is difficult to control the content of the components because the composition range showing the PTCR characteristics is limited. Therefore, there is a problem in yield in manufacturing, and further improvement is desired.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a PTC thermistor material having excellent PTCR characteristics in a wide composition range.

[0009]

These objects are achieved by the present invention described in (1) to (5) below. (1) An oxide containing bismuth oxide and titanium oxide, containing the Bi ₂ Ti ₄ O ₁₁ phase alone as a main phase, or separating the Bi ₂ Ti ₄ O ₁₁ phase and the TiO ₂ phase from each other. Contained as a main phase, or Bi ₂ Ti ₄ O ₁₁ phase and Bi
₄ Ti ₃ O ₁₂ phase is a semiconducting oxide which is phase-separated from each other and contains as a main phase.
₂ O ₃ , when the titanium oxide is converted to TiO ₂ , B
i ₂ O ₃ / (Bi ₂ O ₃ + TiO ₂ ) is 0.1 mol% or more and less than 40 mol%, and a part of the titanium oxide is replaced with one or more of niobium oxide, tantalum oxide and antimony oxide. PTC thermistor material. (2) Bi ₂ O ₃ / (Bi ₂ O ₃ + TiO ₂ ) is 0.
The PTC thermistor material according to (1) above, which is 1 to 39.5 mol%. (3) The above niobium oxide, tantalum oxide, antimony oxide, and titanium oxide are added to Nb ₂ O ₅ and Ta ₂ O, respectively.
When converted to ₅ , Sb ₂ O ₅ and TiO ₂ , (Nb
₂ O ₅ + Ta ₂ O ₅ + Sb ₂ O ₅ ) / (Nb ₂ O ₅ + T
_{a 2 O 5 + Sb 2 O} 5 + TiO 2) is from 0.05 to 7.5
The PTC thermistor material according to the above (1) or (2), which is a mol%. (4) The PTC thermistor material according to any one of the above (1) to (3), wherein a part of the bismuth oxide is replaced with one or more of strontium oxide, calcium oxide and barium oxide. (5) The strontium oxide, calcium oxide, barium oxide and bismuth oxide are added to SrO and C, respectively.
When converted to aO, BaO and Bi ₂ O ₃ , (Sr
O + CaO + BaO) / (SrO + CaO + BaO + B
i ₂ O ₃ ) is 40 mol% or less, the PTC of the above (4)
Thermistor material.

[0010]

Specific Structure The specific structure of the present invention will be described in detail below.

The PTC thermistor material of the present invention is an oxide containing bismuth oxide and titanium oxide, and the bismuth oxide is contained in an amount of 0.1 mol% or more and less than 40 mol% in terms of Bi ₂ O ₃ . Then, a part of titanium oxide is replaced with one or more of niobium oxide, tantalum oxide and antimony oxide.

Further, preferably by substituting a part of the bismuth oxide with one or more of calcium oxide, strontium oxide and barium oxide, a PTC thermistor material having more excellent properties can be obtained.

The sintered body obtained by firing the composition within such a range under the following conditions substantially has a Bi ₂ Ti ₄ O ₁₁ phase as a main phase, or further substantially has a Bi ₄ Ti ₃ phase. An O ₁₂ phase, substantially a TiO ₂ phase is contained as a main phase depending on the content ratio of bismuth oxide and titanium oxide. At that time, when the bismuth oxide is 20 mol% in terms of Bi ₂ O ₃ , it is usually the Bi ₂ Ti ₄ O ₁₁ phase alone, and when it is less than 20 mol%, it is usually the Bi ₂ Ti ₄ O ₁₁ phase and Ti.
O ₂ phase is phase-separated from each other and contained as a main phase, and Bi ₂ Ti ₄ O ₁₁ phase and Bi ₄ Ti ₃ O ₁₂ phase are mutually separated in the range where bismuth oxide is more than 20 mol% in terms of Bi ₂ O _3. Contains as the main phase separated. In this way, Bi ₂ Ti
PTCR characteristics are exhibited in the range including the ₄ O ₁₁ phase. In addition,
The Bi ₂ Ti ₄ O ₁₁ phase has a monoclinic structure, and
_{The 4} Ti ₃ O ₁₂ phase has a bismuth layer structure, and TiO ₂ is usually a rutile type structure. Such a phase can be confirmed by X-ray diffraction (XRD).

Further, each of the phases existing in a separated state from each other has a grain size of usually about 0.1 to 100 μm and can be observed by a scanning electron microscope.

In the sintered body having the composition range of the present invention, a peak showing a phase transition is recognized in the vicinity of the temperature showing the PTCR characteristic on the differential thermal analysis (DTA) curve. That is, Bi ₂ Ti ₄
The O ₁₁ phase exhibits a phase transition in which the lattice constant changes near 250 ° C.

The content ratio of bismuth oxide is 0.1 mol% or more and less than 40 mol% in terms of Bi ₂ O ₃ , preferably 0.1 to 39.5 mol%, more preferably 2 to 39.
Mol%. If the amount of bismuth oxide is too small, PTCR characteristics cannot be obtained.

The Bi ₂ O ₃ content is Bi ₂ O ₃ /
[Bi ₂ O ₃ + TiO ₂ (calculated as non-substitution)]
Calculate as

By substituting a part of titanium oxide with 1 to 3 of niobium oxide, tantalum oxide and antimony oxide, the oxide of the present invention is made into a semiconductor and has PTCR characteristics.

The substitution amounts of niobium oxide, tantalum oxide, antimony oxide and titanium oxide are Nb ₂ O, respectively.
When converted into ₅ , Ta ₂ O ₅ , Sb ₂ O ₅ and TiO ₂ , (Nb ₂ O ₅ + Ta ₂ O ₅ + Sb ₂ O ₅ ) / (N
b ₂ O ₅ + Ta ₂ O ₅ + Sb ₂ O ₅ + TiO ₂ ) is 0.
It is in the range of 05 to 7.5 mol%, preferably 0.5 to 5 mol%. At this time, the specific resistance value is reduced, the semiconductor is formed, and good PTCR characteristics are exhibited.

The niobium oxide, tantalum oxide, or antimony oxide may be present as a compound other than titanium oxide, which is not substituted with titanium oxide. .

If the amount of substitution is too large, the specific resistance value at room temperature becomes too high, which is unsuitable for practical use. On the other hand, if the amount is too small, it does not become a semiconductor and does not show PTCR characteristics. When substituting two or more of these, the substitution ratio is arbitrary.

Further, in the above composition, preferably, when a part of bismuth oxide is replaced with 1 to 3 kinds of strontium oxide, calcium oxide and barium oxide, PTCR is obtained.
The characteristics are further improved. The substitution amount of one or more of these strontium oxide, calcium oxide and barium oxide is
Strontium oxide, calcium oxide, barium oxide and bismuth oxide were added to SrO, CaO and BaO, respectively.
And when converted to Bi ₂ O ₃ , (SrO + CaO +
BaO) / (SrO + CaO + BaO + Bi 2 O 3) is 40 mol% or less, preferably 2 to 30 mol%. If the amount of substitution is too large, the range of change in specific resistance described below becomes small,
It is inappropriate for practical use.

In the case of such substitution, strontium oxide is used as an essential component and the substitution amount is 0.10 in terms of SrO.
PTCR when 5 mol% or more and 1 to 3 kinds of the above are used
The properties give even more favorable results.

The strontium oxide, calcium oxide and barium oxide 1 to 3 may be present as a compound other than bismuth oxide and not substituted with bismuth oxide.

The sintered body is substantially composed of each of the above oxides.

For the production of the PTC thermistor material of the present invention, any of generally used solid-phase reaction method, wet method of coprecipitating oxalate or the like, and alkoxide method of hydrolyzing metal alkoxide can be used. You can

The raw materials used are not particularly limited, but in the solid phase reaction method, the raw material powders of the respective elements are usually mixed and used. At this time, the raw material powder is an oxide or an oxide by subsequent firing. That is, normally, an oxide containing the above-mentioned element may be used, but other carbonates, hydroxides and the like may also be used.

Mixing is performed using such raw materials. The mixing method is not particularly limited, but wet mixing with a ball mill or the like together with ethanol, water, hexane or the like is preferable.

Then, calcination is performed in air at a temperature of about 600 to 900 ° C. for about 30 minutes to 5 hours. After calcination, it is preferably wet-milled using a ball mill or the like. After drying the obtained powder, it is molded under a molding pressure of about 500 kg / cm ^{2 to 2} t / cm ² , and the temperature rising rate is about 50 to 500 ° C./h and the temperature lowering rate is about 50 to 500 ° C./h. ~ 1300 ° C
About 30 minutes to 10 hours, the firing is performed in a reducing atmosphere to obtain a sintered body.

The PTC thermistor material of the present invention is used for, for example, a self-controlled heating element, a degaussing element for a color television, a starting element for a motor, an overcurrent limiting element and the like.

[0031]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

The raw material powder is Bi ₂ O having an average particle size of 0.5 μm.
₃ , TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , Sb ₂ O ₅ ,
SrO, CaO and BaO were used. After mixing, calcining, pulverizing, and mixing by the above-mentioned method, about 1
It was formed into a cylindrical shape of 0 mmφ × 5 mm. This molded body is 105
A sintered body was obtained by firing in an Ar atmosphere at 0 ° C. for 4 hours.

Example 1 Samples 1 to 9 were obtained by changing the composition ratio of Bi ₂ O ₃ , TiO ₂ and Nb ₂ O ₅ as shown in Table 1. Then, the PTCR characteristics of the obtained sintered body were measured by the following specific resistance temperature characteristic measuring method, and from the obtained measured values, the specific resistance change width (Δ) and the specific resistance change rate (α) were calculated using the following formulas. Was calculated and evaluated.

<Specific Resistance Temperature Characteristic Measurement Method> The specific resistance temperature characteristic of the sintered body was measured by using the DC two-terminal method. First, I
An n-Ga electrode was applied on the surface of the sintered body to obtain ohmic contact. Furthermore, the sample was sandwiched with a stainless steel plate to prevent oxidation and evaporation of the electrode due to temperature rise. The measurement was performed by raising and lowering the temperature of the sintered body sample in the air and recording the change in the current value flowing through the sample. The temperature rising rate was 5 ° C./min, and the temperature was raised to 800 ° C., and the temperature was lowered by the furnace cooling rate. Constant voltage power supply / monitor (Advantest; TR
-6143), an electric field of 5 mV / cm 2 was applied to the sample, the current value was measured, and the specific resistance (ρ) was calculated by the following formula.

[Specific Resistance (ρ) Calculation Formula] ρ = (E / I) × (S / h) However, E: Applied voltage I: Current flowing through the sample S: Cross-sectional area of sample h: Thickness of sample

The width of change in specific resistance (Δ) was obtained by the following formula.

[Calculation formula for specific resistance change width (Δ)] Δ = log (ρ _max / ρ _min ) where, ρ _max : maximum specific resistance in the temperature rising process ρ _min : minimum specific resistance in the temperature rising process

The specific resistance change rate (α) was calculated by the following equation.

[Calculation Formula for Rate of Change in Specific Resistance (α)] α = ln10 {log (ρ ₂ / ρ ₁ ) / (T ₂ / T ₁ )} × 100, where ρ ₁ : specific resistance ρ _{2 at} temperature T ₁ : Specific resistance at temperature T ₂

T ₁ and T ₂ are intermediate specific resistance (ρ _M )
The temperature is within ± 5 ℃ and the intermediate resistivity (ρ _M )
Was calculated by the following formula. log ρ _M = (log ρ _max + log ρ _min ) / 2

The composition ratio and the obtained results are shown in Table 1.
The composition of Table 1 is shown by composition ratio (molar ratio).
The total composition ratio of each sample is shown to be 1. Sample 1 containing no bismuth oxide did not have PTCR characteristics.

[0042]

[Table 1]

Example 2 Bi ₂ O ₃ , TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and Sb
Samples 11 to 17 were obtained by changing the composition ratio of ₂ O ₅ , SrO, CaO, and BaO as shown in Table 2. The PTCR characteristics of the obtained sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 2.

The compositional representation of Table 2 is the same as that of Table 1.

[0045]

[Table 2]

From the results shown in Tables 1 and 2, it is clear that excellent characteristics can be obtained in the composition range of the present invention.

[0047]

The composition of the present invention makes it possible to obtain a PTC thermistor material having excellent PTCR characteristics in a wide composition range, and contributes to improvement in product yield in manufacturing.

Claims (5)

(57) [Claims] 1. An oxide containing bismuth oxide and titanium oxide, which contains Bi ₂ Ti ₄ O ₁₁ phase alone as a main phase,
Alternatively, a Bi ₂ Ti ₄ O ₁₁ phase and a TiO ₂ phase are separated from each other and contained as a main phase, or a Bi ₂ Ti ₄ O ₁₁ phase and a Bi ₄ Ti ₃ O ₁₂ phase are separated from each other. When the bismuth oxide is converted into Bi ₂ O ₃ and the titanium oxide is converted into TiO ₂ , the oxide is a semiconducting oxide contained as a main phase, and Bi ₂ O ₃ / (Bi ₂ O ₃ + TiO ₂ ) is 0. A PTC thermistor material which is 1 mol% or more and less than 40 mol% and in which a part of the titanium oxide is replaced with one or more of niobium oxide, tantalum oxide and antimony oxide. 2. Bi ₂ O ₃ / (Bi ₂ O ₃ + TiO ₂ ).
Is 0.1 to 39.5 mol%, and the PTC thermistor material according to claim 1. 3. The niobium oxide, tantalum oxide, antimony oxide and titanium oxide are added to Nb ₂ O ₅ and T, respectively.
When converted into a ₂ O ₅ , Sb ₂ O ₅ and TiO ₂ ,
(Nb ₂ O ₅ + Ta ₂ O ₅ + Sb ₂ O ₅ ) / (Nb ₂ O
₅ + Ta ₂ O ₅ + Sb ₂ O ₅ + TiO ₂ ) is 0.05 to
7. The PTC thermistor material according to claim 1, which is 7.5 mol%. 4. The PTC thermistor material according to claim 1, wherein a part of the bismuth oxide is replaced with one or more of strontium oxide, calcium oxide and barium oxide. 5. The strontium oxide, calcium oxide, barium oxide and bismuth oxide are added to Sr, respectively.
When converted to O, CaO, BaO and Bi ₂ O ₃ ,
(SrO + CaO + BaO) / (SrO + CaO + Ba
O + Bi ₂ O ₃ ) is 40 mol% or less, P of claim 4.
TC thermistor material.