JPH0653011A - Barium titanate based semiconductor porcelain having negative resistance temperature characteristic - Google Patents

Abstract

PURPOSE:To obtain barium titanate based semiconductor porcelain which is excellent in temperature stability at a low temperature and has negative resistance temperature characteristics whose resistance decrease ratio is large at a high temperature, wherein the B constant at a temperature higher than or equal to the phase transition point is larger than the B constant at a temperature lower than or equal to the phase transition point. CONSTITUTION:In a barium titanate based semiconductor porcelain, the mol ratio of a Ba site and a Ti site (Ba site/Ti site) is adjusted in the range from 0.99 to 1.05, and set so as to contain Mn of 0.001-0.5mol%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a barium titanate-based semiconductor porcelain having a negative resistance temperature characteristic used for an overcurrent preventing element for preventing an overcurrent at the initial stage of power supply in a switching power supply or the like.

[0002]

2. Description of the Related Art In a switching power supply or the like, in order to prevent an overcurrent at the time of power-on, a semiconductor ceramic (negative-characteristic thermistor) having a negative temperature characteristic in which the resistance decreases as the temperature rises. ) Is used. Since this negative-characteristic thermistor has a high resistance at room temperature, it suppresses overcurrent at the initial stage of power-on of a switching power supply, etc., and then it self-heats to raise its temperature to a low resistance, so power consumption in the steady state is reduced. It has the property of decreasing and is widely used in various applications as an overcurrent preventing element.

However, a conventional negative characteristic thermistor used for a switching power supply or the like has a B constant of 2000 to 4000K, which represents the relationship between temperature and resistance, and is therefore easily affected by the ambient temperature, and changes due to changes in the outside air temperature. There is a problem that the initial resistance fluctuates greatly and the rising characteristics vary. In particular, at a low temperature of 0 ° C. or lower, there is a problem that the rise is too slow.

In order to solve the above problems,
A negative characteristic thermistor having a characteristic that the B constant is small near room temperature (-50 to 50 ° C.) and increases at a temperature higher than that is required.

As such an element, an element in which 20% by weight of Li ₂ CO ₃ is added to barium titanate (BaTiO ₃ ) has been proposed (Japanese Patent Publication No. 48-6352).

However, although this element has a characteristic that the B constant rapidly increases when it exceeds the phase transition point, the specific resistance at 140 ° C. is as large as 10 ⁵ Ω · cm or more, so that in a steady state. There is a problem that the power consumption is large.

The present invention solves the above-mentioned problems. It has a low resistance and can suppress the power loss during energization, and the B constant is negative at room temperature and large at high temperatures. An object of the present invention is to provide a barium titanate-based semiconductor ceramic having resistance temperature characteristics.

[0008]

In order to achieve the above object, a barium titanate-based semiconductor ceramic having a negative resistance temperature characteristic of the present invention has a molar ratio of Ba site and Ti site (Ba site / Ti site). Is 0.99 to 1.05, and 0.001 to 0.5 mol% of Mn is contained.

That is, the barium titanate-based semiconductor porcelain having the negative resistance-temperature characteristic of the present invention has a Ba site /
By adjusting the Ti site (molar ratio) in the range of 0.99 to 1.05 and adding Mn in the range of 0.001 to 0.5 mol%, the resistance is suppressed low and the phase from cubic to tetragonal is reduced. The B constant at a temperature above the transition point (for example, 120 ° C.) is made larger than the B constant at a temperature below the phase transition point.

[0010]

EXAMPLES The features of the present invention will be described in more detail below with reference to examples of the present invention.

First, the raw materials BaCO ₃ , La ₂ O ₃ and
Powders of TiO ₂ , MnO ₂ and SiO ₂ are weighed so as to have a composition represented by the following formula: (Ba _0.998 La _0.002 ) _m TiO ₃ + XMn + 0.01SiO ₂ . Then, each raw material powder is wet mixed with water in a ball mill for 5 hours, dried, and then calcined at 1150 ° C. for 2 hours. Next, a binder is added to the obtained powder (calcined powder), and the mixture is wet mixed in a ball mill for 5 hours, crushed, filtered, dried, and then pressure-molded into a disk having a diameter of 10 mm, and nitrogen is added to % In a mixed atmosphere of hydrogen (H ₂ / N ₂ = 3 vol%) 1350
Sintered by heating for 2 hours at ℃.

Then, on both sides of the sintered disk, In-G
The resistance-temperature characteristic was measured for the sample on which a was applied to form an electrode.

In Tables 1 and 2, changes in specific resistance at 25 ° C. and 150 ° C. measured for each sample in which the value of Ba site / Ti site (molar ratio) m and the value of Mn amount X were changed. The characteristics such as the rate, the B constant at 25 ° C. and 150 ° C., and the ratio thereof are shown.

[0014]

[Table 1]

[0015]

[Table 2]

In Tables 1 and 2, the sample number is *
Those marked are comparative examples that are outside the scope of the present invention, and others indicate examples of the present invention.

The Mn content X = 0.005 mol%, Ba
FIG. 1 shows the relationship between the specific resistance and the temperature (resistance temperature characteristic) of a sample (sample No. 20 in Table 1) having a molar ratio of sites to Ti sites (Ba site / Ti site) m = 1.010 (sample No. 20 in Table 1).

In the sample according to the embodiment of the present invention shown in FIG. 1, the B constant has a phase transition point (12) from cubic to tetragonal.
It has a resistance temperature characteristic of about 430K below 0 ° C) and about 2200K above the phase transition point (120 ° C).
It can be seen that the B constant has a negative resistance-temperature characteristic such that it is small at room temperature and large at high temperature.

Further, from Tables 1 and 2, Ba site / Ti
For the samples according to the examples of the present invention in which the site (molar ratio) m is in the range of 0.99 to 1.05 and the Mn amount X is in the range of 0.001 to 0.5 mol%, the phase transition point (120
It can be seen that the B constant increases at a temperature (150 ° C.) or higher.

The value of the molar ratio m is 0.99 to 1.05.
2 in the sample having the Mn amount X of less than 0.001 (for example, the sample of Sample No. 17 having the Mn amount X = 0 mol% and the molar ratio m = 1.010) even in the range of After showing a weak positive resistance temperature characteristic, it shows a negative resistance temperature characteristic. Therefore, the ratio of the specific resistance ρ at 25 ° C. to the specific resistance ρ at 150 ° C., that is, the rate of change in resistance (ρ25 ° C./ρ150° C.) becomes 2 or less, which is a practical problem.

Therefore, the Ba site / Ti site (molar ratio) m is 0.99 to 1.05, and the Mn amount X is 0.001.
By adjusting the composition so as to fall within the range of 0.5 mol%, the ratio of the B constant at 150 ° C to the B constant at 25 ° C (B150 ° C / B25 ° C) is 2 or more, and the rate of change in resistance ( A barium titanate-based semiconductor porcelain having a negative resistance temperature characteristic of ρ25 ° C./ρ150° C. of 2 or more can be obtained.

In the above embodiments, the barium titanate-based semiconductor porcelain containing a trace amount of La in the Ba site has been described, but the barium titanate-based semiconductor porcelain having the negative resistance temperature characteristic of the present invention is particularly La. Even when not containing, it is possible to obtain the same effect as in the above-mentioned embodiment, and it is also possible to coexist with a rare earth element such as Y which is a semiconducting agent and other trace components in addition to La.

[0023]

As described above, in the barium titanate-based semiconductor ceramic having the negative resistance temperature characteristic of the present invention, the Ba site / Ti site molar ratio is adjusted within the range of 0.99 to 1.05. , Mn 0.001 to 0.5 mol%
Since it is contained, it has excellent temperature stability at low temperature, low resistance, a large rate of decrease in resistance at high temperature, and a cubic to tetragonal phase transition point (for example, 120 ° C). ) It is possible to obtain a barium titanate-based semiconductor ceramic having a negative resistance-temperature characteristic in which the B constant at the above temperature is considerably larger than the B constant at the temperature below the phase transition point.

[Brief description of drawings]

FIG. 1 is a diagram showing a resistance temperature characteristic of a barium titanate-based semiconductor ceramic having a negative resistance temperature characteristic according to an embodiment of the present invention.

FIG. 2 is a diagram showing a resistance temperature characteristic of a barium titanate-based semiconductor ceramic having a negative resistance temperature characteristic of a comparative example.

Claims (1)

[Claims] 1. In a barium titanate-based semiconductor ceramic having a negative resistance temperature characteristic, the molar ratio of Ba site to Ti site (Ba site / Ti site) is 0.99 to 1.0.
5. The barium titanate-based semiconductor porcelain having negative resistance-temperature characteristics, characterized in that Mn is 5 and 0.001 to 0.5 mol% is contained.