JPH08319157A - Barium titanate ceramic and its production - Google Patents

Abstract

PURPOSE: To obtain a barium titanate ceramic which is suitable for a high- function varistor, high-capacity condenser or the like. CONSTITUTION: This barium titanate ceramic has an atomic ratio (x) of >=0.5, a basic composition of (Ba1-x Srx )TiO3 , in addition, contains 0.1-0.3 mole %, based on Ba, of at least one selected from La, Sb and Y and 0.025-0.1 mole % of Mn, shows a resistivity of >=10<9> Ωcm and a current-voltage non-linear coefficient α(=dlnI/dlnV) of >=7. The ceramic is fired in an air atmosphere or an oxidative atmosphere at 1350-1500 deg.C in one stage. On the firing, 0.2-2.0 mole % of TiO2 or SiO2 may be added as a sintering aid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanate-based ceramics suitable for a varistor having a high relative dielectric constant and a high current-voltage non-linearity index, a high-capacity capacitor and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Barium titanate to which a donor is added is
Abnormal positive temperature coefficient of resistance (PT
(CR characteristic) is shown. Heywang, J. Am. Ce
ram. Soc. , 47, 484-490 (1964)
Therefore, if a double Schottky barrier layer is formed at the grain boundary due to the presence of the acceptor level, and the potential barrier height rises sharply above the Curie point due to the phenomenon of the dielectric constant, the PTCR characteristics can be obtained by the grain boundary barrier layer model. Explaining. Barium titanate utilizes high dielectric constant or varistor characteristics,
It is used as a material for grain boundary barrier capacitors and varistor materials. In the conventional manufacturing method, barium titanate is manufactured by a two-step firing process. That is, in order to sufficiently lower the resistivity in the crystal grains of barium titanate, first firing in a reducing atmosphere and then Pb, B on the surface of the material.
After the low melting point oxide such as i is applied, it is heated. By heating, the low melting point oxide diffuses to the surface of the material, and only the grain boundaries are selectively made into an insulator.

[0003]

In the production method by two-step firing, the production process becomes complicated and the production cost of the obtained barium titanate increases. Moreover, during the first-stage reduction firing, ceramic particles may grow abnormally locally. The abnormal grain growth makes it difficult to uniformly re-insulate the grain boundary portion in the subsequent insulation firing process. as a result,
The characteristics deteriorate due to the non-uniform structure, and the yield decreases. Further, the reduction firing uses a reducing atmosphere shielded from the atmosphere, and thus requires complicated operations and equipment. Incidentally, a strontium titanate material exhibiting similar PTCR characteristics needs to be fired in a reducing atmosphere which is stronger than the barium titanate-based material. In the reduction firing under such conditions, the drawbacks such as the danger and the high cost associated with the use of the reducing gas become more remarkable. The present invention has been devised to solve such a problem, and to improve the component design of barium titanate to produce a barium titanate-based varistor by a single firing in an air atmosphere. And the resistivity at room temperature is 10 ⁹ Ωcm
Thus, it is an object of the present invention to obtain a barium titanate-based ceramic exhibiting a high relative dielectric constant of 10 ⁴ or more and a current-voltage nonlinear index of 7 or more, and having both high capacity capacitor characteristics and varistor characteristics.

[0004]

In order to achieve the object, the barium titanate-based ceramics of the present invention has an atomic ratio x of 0.5 to 0.8 and is a basic material of (Ba _1-x Sr _x ) TiO ₃ . It has a composition, and the ratio to Ba is 0.1 to 0.3.
One or more selected from La, Sb and Y of mol% and 0.025 to 0.1 mol% of Mn are contained, and the composition is baked in an air atmosphere or an oxidizing atmosphere. . The barium titanate-based ceramics has a resistivity at room temperature of 10 ⁹ Ωcm or more, a relative dielectric constant of 10 ⁴ or more, and a current-voltage nonlinear index α (= d ln I / d ln V) of 7
That is all. The barium titanate-based ceramics of the present invention have an atomic ratio x of 0.5 to 0.8 and have a composition of (Ba _1-x Sr _x ) T.
BaTiO ₃ powder and S so that the basic composition of io ₃
The rTiO ₃ powder is mixed, and the ratio to Ba is 0.1 to 0.1.
After thoroughly mixing one or more selected from 0.3 mol% of La, Sb and Y and 0.025 to 0.1 mol% of Mn, the mixed powder is molded into a product shape, It is manufactured by firing at a temperature of 1350 to 1500 ° C. for 1 to 7 hours in the air atmosphere. Add 0.2 to the mixed powder.
It is preferable to add ˜2.0 mol% of TiO ₂ or SiO ₂ as a sintering aid.

[0005]

In the barium titanate-based ceramics of the present invention, the Curie point is lowered to −80 ° C. or lower by adding Sr, and the appropriate amounts of La and Mn are added to improve the resistivity and PTCR characteristics at room temperature. ing. Mn
The increase in resistivity due to the addition is due to the increase in grain boundary resistivity, and it is speculated that Mn is directly involved in the formation of the interface state at the grain boundary. Specifically, the intragranular resistance changed from 0.3 Ωcm to 6 Ωcm as the Mn content increased to 0.075 mol% from the addition of no Mn, and the grain boundary resistance component was divided by the sample thickness. The resistivity changes from about 20 Ωcm to 1680 Ωcm. Similarly, for ceramics with a Mn content of 0.075 mol% or more, 10 ¹⁰ Ωc
It exhibited a room temperature resistivity of m or more and a PTCR characteristic of about 8 digits. As a result of research conducted by the present inventors, it has been found that such an action due to the addition of Mn becomes remarkable when Mn is added in an amount of 0.025 to 0.1 mol% with respect to Ba.

In (Ba _1-x Sr _x ) TiO ₃ , x <
With a composition of 0.5 or x> 0.8, the Curie point does not sufficiently lower to the low temperature region, and therefore the maximum temperature of the resistivity in the PTCR characteristic becomes a temperature of room temperature or higher, and the resistivity is sufficiently high at room temperature. The material is difficult to manufacture. In order to obtain a high relative dielectric constant and good varistor characteristics, it is essential to form a well-developed barrier layer at the grain boundaries of ceramics, but a sufficiently high resistivity (specifically 10 ⁹
It is necessary and sufficient condition in this case to obtain a material having Ωcm or more). La and Sb used as semiconductor elements
For Y and Y, the concentration range of 0.1 to 0.3 mol% is optimum. Below this concentration range, a ceramic material having a sufficiently low intragranular resistivity cannot be obtained. On the contrary, at a high concentration exceeding this concentration range, grain growth is remarkably suppressed by the addition of these elements, and it is difficult to manufacture a material having good semiconductivity. However, because some effects of the semiconducting element are diminished by the combined addition with Mn, or when the addition amount of the sintering aid is increased, the semiconducting element or Mn is added to the liquid phase formed in the firing process. Since it dissolves, it is possible to extend the allowable addition amount of the semiconducting element and Mn to the high concentration region side up to about 1.5 times at maximum.

The mixed powder containing the respective components is thoroughly mixed by a kneading machine such as a wet ball mill and then molded or compacted into a target shape. The obtained powder compact is 1350
It is fired at a temperature of 1500 ° C. for 1 to 7 hours. At this time,
Since an air atmosphere or an oxidizing atmosphere can be used, the manufacturing process is greatly simplified. In addition, Mn is preferentially oxidized by firing in an air atmosphere or an oxidizing atmosphere, and Mn-based oxide effective for improving room temperature resistivity, relative dielectric constant and current-voltage nonlinear index is a grain boundary of the surface layer portion. Is formed.
The firing conditions are preferably a firing temperature of 1350 to 1500 ° C. and a firing time of 1 to 7 hours from the viewpoint of improving the PTCR characteristics. If the firing temperature does not reach 1350 ° C., the sintering becomes insufficient, and it becomes difficult to obtain a material having a required sintering density of 93% or more. On the other hand, if the firing temperature is higher than 1500 ° C., the energy consumption increases, which is not preferable from the viewpoint of manufacturing cost, and the particles grow too much to make it difficult to obtain a material having good characteristics. Further, if the firing time is less than 1 hour, the firing reaction does not proceed sufficiently, the firing reaction does not proceed sufficiently, and it becomes difficult to obtain a material that is dense and exhibits good semiconductivity. On the contrary, long-time firing for more than 7 hours is not preferable because it causes a multi-phase formation reaction due to excessive grain growth and component evaporation. Further, the rate of temperature increase and the rate of temperature decrease during firing are preferably 10 ° C./min or less in order to deoxidize the binder and selectively oxidize the grain boundaries after sintering.

[0008]

Example: BaTiO ₃ powder having a purity of 99.98% and S
Using rTiO ₃ powder as the main raw material and a semiconducting element of 0.
30 mol% of La, 0 to 0.0 as an acceptor element
75 mol% Mn and 0.5 mol% T as a sintering aid
Ba _0.5 Sr at a Curie point of -65 ° C using iO _2.
A mixed powder having a basic composition of _0.5 TiO ₃ was obtained. This mixed powder was subjected to ZrO 2 in ethanol by a wet ball mill.
₂ was used for kneading and crushing for 24 hours. 44 μm after drying
The powder sized below was molded into pellets at an axial pressure of 60 MPa and heated in the atmosphere at 1450 ° C. for 5 hours at a heating rate of 5 ° C. /
Sintering was performed for 5 minutes at a temperature decrease rate of 5 ° C / minute. A test piece was cut out from the obtained sintered body, and the resistivity and the apparent dielectric constant were investigated. The resistivity is measured by a digital electrometer (TR8
It was measured by a direct current two-terminal method using 652). The current-voltage characteristic is a programmable pA meter (HP-4140).
It was measured at room temperature using B). The apparent dielectric constant was measured by changing the frequency with an impedance analyzer (YHP-4192A).

When the measurement results are arranged in relation to the temperature, as shown in FIG. 1, all the semiconductor characteristics are exhibited at a temperature near -100 ° C., and P is 10 ⁶ to 10 ⁷ times as high as room temperature.
It exhibited a TCR effect. Further, all the test pieces containing Mn have a resistivity of 10 ⁹ Ωcm or more at room temperature,
It was found that the material has a large dielectric constant of 000 or more. Further, the barium titanate sintered body Ba _0.4 Sr _0.6 TiO ₃ containing 0.025 mol% of Mn was examined for current-voltage characteristics at room temperature, and the relationship shown in FIG. 2 was obtained. In this current-voltage characteristic, α = δ (ln
The non-linear index α represented by I) / δ (ln V) was 9.5. Other test pieces having different Mn contents also exhibited a high current-voltage nonlinearity index α of 7 or more. From this, it is confirmed that the barium titanate sintered body according to the present invention is a material exhibiting remarkable varistor characteristics in a high voltage region.

Further, a barium titanate sintered body (Ba _0.5 Sr _0.5 ) TiO ₃ containing 0.075 mol% of Mn is added.
The surge absorption characteristics were investigated using a high-current pulse generator. The surge absorption characteristic indicates the degree of decrease in applied voltage and its shape, and is used for characteristic evaluation such as power level used as an overcurrent protection element and response speed of functional characteristics. The applied voltage waveform of the investigation result is shown in Fig. 3 (a).
The diameter of the voltage after passing the varistor is shown in FIG. From FIG. 3, it can be seen that the high-capacity varistor according to the present invention sufficiently absorbs the surge when a voltage is applied and has an ideal function as a varistor material. On the other hand, in a normal ZnO diameter varistor, a large voltage peak (overshoot) appears when a voltage is applied, as shown in FIG.

[0011]

As described above, the barium titanate-based ceramics of the present invention have a sufficiently reduced Curie point due to the addition of Sr (Ba _1-x Sr _x ) TiO ₃ -based La, Sb, Y, etc. By adding Mn together with the semiconducting element, the resistivity at room temperature is improved to 10 ⁹ Ωcm or more, the relative permittivity to 10 ⁴ or more, and the current-voltage nonlinear index α to 7 or more. In addition, since it is manufactured by one-time firing in an air atmosphere or an oxidizing atmosphere, the manufacturing cost is reduced as compared with the conventional two-step firing method involving reduction firing. In this way, according to the present invention, a high-performance ceramic material having both high capacity capacitor characteristics and varistor characteristics can be obtained at low cost.

[Brief description of drawings]

FIG. 1 Mn affecting temperature dependence of permittivity and resistivity
Effect of content

FIG. 2 Ba _0.4 with 0.025 mol% Mn added
Room temperature current-voltage characteristics of Sr _0.6 TiO ₃ ceramics

FIG. 3 is an applied voltage waveform (a) showing surge absorption characteristics of barium titanate ceramics obtained according to the present invention.
And voltage waveform after passing the varistor (b)

Claims (4)

[Claims] 1. An atomic ratio x of 0.5 to 0.8 (Ba _1-x
Sr _x ) TiO _{3 having} a basic composition, and one or more selected from La, Sb and Y in a proportion of 0.1 to 0.3 mol% relative to Ba and 0.025 to 0.1 mol. % Mn, and sintered in an air atmosphere or an oxidizing atmosphere. 2. The resistivity at room temperature is 10 ⁹ Ωcm or more, the relative permittivity is 10 ⁴ or more, and the current-voltage nonlinear index α [= δ.
The barium titanate-based ceramics according to claim 1, wherein (ln I) / δ (ln V)] is 7 or more. 3. An atomic ratio x of 0.5 to 0.8 (Ba _1-x
Sr _x ) TiO _{3 so that} the basic composition of BaTiO ₃
The powder and the SrTiO ₃ powder are mixed, and one or more kinds selected from La, Sb, and Y in a proportion of 0.1 to 0.3 mol% with respect to Ba and 0.025 to 0.1 mol%. M
After thoroughly mixing the mixed powder with n added, it is molded into a product shape, and 1350 to 1 in an air atmosphere or an oxidizing atmosphere.
A method for producing barium titanate-based ceramics, which comprises firing at a temperature of 500 ° C. for 1 to 7 hours. 4. The mixed powder according to claim 3, further comprising 0.2 to
A method for producing barium titanate-based ceramics, wherein 2.0 mol% of TiO ₂ or SiO ₂ is added as a sintering aid.