JP2000302545A - Bi4Ti3O12 FERROELECTRIC AND ITS PRODUCTION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a Bi4Ti3O12 ferroelectric for a dense sintered compact by a simple process. SOLUTION: The designated amounts of TiO2 powder and Bi2O3 powder as raw materials are weighed, blended to obtain calcined powder, which is then compacted. The compacted body is filled in a carbon die together with reduction preventing powder, which is then sintered while plasma is discharged by a constant heating speed sintering method to sinter a sample by heating to 800-1,000 deg.C at a constant speed under pressure and holding for a prescribed time or a constant electric current sintering method to sinter a sample while supplying a constant electric current under pressure until 800-900 deg.C to produce the sintered compact having 95% relative density with good reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a Bi ₄ Ti ₃ O ₁₂ ferroelectric used in electronic ceramics, using the spark plasma sintering method, there is no composition change in a short time heating, low dielectric loss Bi ₄ Ti ₃ O ₁₂ to obtain a dense Bi ₄ Ti ₃ O ₁₂ ferroelectric
The present invention relates to a ferroelectric and a method for manufacturing the same.

[0002]

In general, electronic ceramics, functional ceramics Bi ₄ Ti is used as component ₃ O ₁₂ ferroelectric,
As raw materials, after weighing a predetermined amount of TiO ₂ fine powder and Bi ₂ O ₃ fine powder, wet mixing, drying, firing at 700 ° C to 900 ° C, obtaining calcined powder, pulverizing and molding, 2 at 1150 ° C in air
It has been obtained by the ordinary sintering method in which sintering is performed for a long time.

[0003]

However, the ferroelectric obtained by the ordinary sintering method is densified, but it is not always easy in the manufacturing process.

[0004] The present invention provides a Bi ₄ Ti ₃ O ₁₂ ferroelectric and a method for producing a dense sintered body having excellent dielectric properties by a simple process for obtaining a Bi ₄ Ti ₃ O ₁₂ ferroelectric. It is intended to provide a method.

[0005]

Means for Solving the Problems The inventor has studied various methods for producing a dense sintered body having excellent dielectric properties by a simple process, and has recently developed a spark plasma sintering method used for producing cermet materials. I paid attention.

[0006] The spark plasma sintering method is a sintering method in which a powder sample is filled in a carbon die, the temperature is rapidly increased by applying electricity under pressure, and the sample is densified in a short time. However, with respect to the application of this sintering method, few studies have been made on the production of oxides, particularly electronic materials.

[0007] The inventors have found that a lead-free compound ferroelectric, Bi ₄ Ti ₃
O ₁₂ discharge plasma sintering method is applied to, and examined the manufacturing conditions. As a result, a predetermined amount of the raw material TiO ₂ powder and Bi ₂ O ₃ powder were weighed to obtain a calcined powder, which was formed into a columnar shape, and the formed body was filled into a carbon die together with a reduction preventing powder, Constant temperature ramp-up sintering method in which the temperature is raised to 800 ° C to 1000 ° C at constant speed (50 ° C / min) under pressure and held for various hours, and 800 ° C to 900 ° C at constant current under pressure The constant current sintering method of conducting and sintering was tested.

As a result, the inventors have obtained the former constant-speed temperature-increased sintering method with the fluctuation of the current value flowing during sintering.
Although the density of the Bi ₄ Ti ₃ O ₁₂ sintered body fluctuates, the relative density is 9
It was found that a Bi ₄ Ti ₃ O ₁₂ single phase ferroelectric substance was obtained at 0% or more.

[0009] In addition, in the latter constant-current sintering method, densification occurs at 850 ° C without depending on the current value, and the relative density is about 9%.
It was found that a 5% sintered body could be produced with good reproducibility, and the resulting phase of the obtained sintered body was composed of a single phase of Bi ₄ Ti ₃ O ₁₂ and had a uniform microstructure.

[0010] That is, the present invention is to form a calcined powder obtained by firing a mixed powder of the required raw material powder, and then sinter the molded article together with a desirably reduced powder by a discharge plasma sintering method. a relative density of 90% or more, Bi ₄ the production phase is characterized by obtaining a Bi ₄ Ti ₃ O ₁₂ ferroelectric composed of a single phase of Bi ₄ Ti ₃ O ₁₂
This is a Ti ₃ O ₁₂ ferroelectric and its manufacturing method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a calcined powder is prepared by weighing raw materials of TiO ₂ powder and Bi ₂ O ₃ powder so as to have a Bi ₄ Ti ₃ O ₁₂ composition, wet-mixing and drying, and then heating at 700 ° C. Any known calcined powder manufacturing method such as a method of calcining to obtain a calcined powder can be adopted.

In the present invention, any known molding method can be employed as a method for molding the calcined powder, in addition to the uniaxial pressing and cold isostatic pressing (CIP) method described in the embodiments.

[0013] In the present invention, the discharge plasma sintering method is compared with the conventional sintering method by directly applying pulsed electric energy to the compact and applying the generated discharge plasma to thermal diffusion and electric field diffusion. The method is for producing a dense sintered body in a short time at a low temperature, and here, a constant-speed sintering method and a constant-current sintering method can be adopted.

As shown in the examples, the constant-speed temperature-increased sintering method involves filling a compact together with a reduction-preventing powder in a die, and sintering under pressure to a sintering temperature of 800 ° C. to 1000 ° C. at a constant speed, for example, 50 ° C. The temperature is raised at a rate of ° C./min, and then the temperature is held for 0 to 30 minutes. The current value, the rate of temperature rise, and the holding time may be appropriately selected according to the target density, the type of the anti-reduction powder described below, and the like.

[0015] In the constant current sintering method, as shown in the examples, the compact is filled in a die together with the anti-reduction powder, and a current is applied under pressure, for example, at 450A, 700A until the temperature reaches 800 ° C to 900 ° C, and the sintering is performed. The current value and the like may be appropriately selected according to the target density, the type of the anti-reduction powder described below, and the like.

[0016] In the present invention, it is desirable to adopt a carbon die in consideration of heat resistance and conductivity.
Further, the pressing force may be appropriately selected according to the shape of the molded body, the target density, and the like.

[0017] In the present invention, as the anti-reduction powder, Al
₂ O ₃ powder, ZrO ₂ powder, Sb-doped SnO ₂ powder, SnO ₂ -ZrO ₂ mixed powder can be considered, but with Al ₂ O ₃ powder, the relative density of the sintered body is 65% and densification is not enough, ZrO ₂ powder has a relative density of 75% and is not sufficiently densified, while Sb-doped SnO ₂ powder has
Since the nO ₂ powder itself sinters and strongly bonds to the sintered body, it is not preferable.If the SnO ₂ -ZrO ₂ mixed powder is used, the sintering temperature is 850 ° C. or higher regardless of the current amount, and the relative density is It is preferable because 95% or more can be obtained.

[0018] The sintered body obtained by the manufacturing method according to the present invention is:
It becomes a dense ceramic without composition fluctuation.

[0019]

Example 1 TiO ₂ powder and Bi ₂ O ₃ powder were weighed so as to have a Bi ₄ Ti ₃ O ₁₂ composition, wet-mixed, dried, and fired at 700 ° C. to obtain a calcined powder. This calcined powder was formed into an outer diameter of 10 mm and a thickness of 2 mm by uniaxial pressing (50MP) and CIP (100MP).

[0020] The resulting molded _{article, Al 2 0 3, ZrO 2} , SnO 2, SnO 2 /
Filled together with ZrO ₂ anti-reduction powder in a carbon die and pressurized at 39MPa, sintering temperature 800 ℃ as shown in Table 1.
Up to 1000 ° C at a constant rate of 50 ° C / min.
Spark plasma sintering was performed by a constant-speed temperature-rising sintering method for 0 minutes, and the densification was examined.

In the case of Al ₂ O ₃ powder, Bi ₄
Although a single phase of Ti ₃ O ₁₂ was obtained, there was no difference in relative density, and it was about 65%. Then, sintering at a higher temperature of 1000 ° C. was attempted, but metal Bi was generated by reduction.

In the case of ZrO ₂ powder, sintering was performed at 900 ° C. for 0 to 30 minutes. As a result, the relative density did not change after sintering time of 5 minutes, and was about 75%. Sb Dove SnO ₂ is a conductive oxide
When trying to make a dense sintered body using powder, Sn
The O ₂ powder itself sintered and a strong bond with the sample occurred.

The sintering in the case of using a mixed powder of SnO ₂ powder and ZrO ₂ powder was examined. Table 2 shows the results. The effect of using the conductive powder on sintering was great, and a remarkable increase in density was observed.

[0024]

【table 1】

[0025]

[Table 2]

Example 2 Next, a mixed powder of SnO ₂ powder and ZrO ₂ powder (SnO ₂ / ZrO ₂ = 3 /
Fill into a carbon die together with 1), constant current 450A under the pressure of 39MPa (average heating rate 75 ° C / min above 800 ° C), or 800-900 ° C at 700A (250 ° C / min) Energize, 8
Immediately after the temperature reached 50 ° C., the power supply was stopped. The total time for heating and heating was 8 to 10 minutes.

The relative density of the manufactured Bi ₄ Ti ₃ O ₁₂ sintered body sample was
Approximately 95% above 850 ° C regardless of the amount of current.
As shown in the figure, it was a single phase of Bi ₄ Ti ₃ O ₁₂ .

Observation of the microstructure of the sintered body revealed a remarkable difference depending on the heating rate. The sintered body made with 450A
Although the whole sample had a uniform structure (Fig. 2a), the one produced by rapid heating at 700A had a mixture of a dense part (Fig. 2b) and a part where only neck formation was observed (Fig. 2c). Organization.

[0029] Therefore, the spark plasma sintering method uses SnO powder for Bi ₄ Ti ₃ O ₁₂ powder synthesized by a solid phase reaction.
₂ powder and a mixed powder of ZrO ₂ powder (SnO ₂ / ZrO ₂ = 3/1),
It became clear that heating at 450A to 850 ℃ with constant current was the optimal condition.

[0030]

According to the present invention, as is apparent from the embodiments,
Using a plasma plasma sintering method to obtain Bi ₄ Ti ₃ O ₁₂ ferroelectric material, there is no change in composition with a simple process and short-time heating,
A dense Bi ₄ Ti ₃ O ₁₂ ferroelectric material having a small dielectric loss can be obtained.

In particular, in spark plasma sintering by the constant current sintering method, densification occurs at 850 ° C. without depending on the current value, and a sintered body having a relative density of 95% can be produced with good reproducibility. But Bi ₄
A Bi ₄ Ti ₃ O ₁₂ ferroelectric having a uniform fine structure of a Ti ₃ O ₁₂ single phase is obtained.

[Brief description of the drawings]

FIG. 1 is an XRD pattern diagram of a Bi ₄ Ti ₃ O ₁₂ sintered body according to the present invention.

FIGS. 2a, 2b and 2c are photomicrographs showing the microstructure of a Bi ₄ Ti ₃ O ₁₂ sintered body according to the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G031 AA11 AA12 AA31 AA35 BA09 GA07 5G303 AA10 AB20 BA09 BA12 CA01 CB05 CB31 CB35 CB39 CC08 DA05

Claims (7)

[Claims] Claims: 1. The relative density is 90% or more, and the generated phase is Bi ₄ Ti ₃ O
Bi ₄ Ti ₃ O ₁₂ ferroelectric consisting of ₁₂ single phases. 2. Production of a Bi ₄ Ti ₃ O ₁₂ ferroelectric material in which a calcined powder obtained by firing a mixed powder of required raw material powders is molded, and the molded product is sintered by a discharge plasma sintering method. Method. 3. A Bi ₄ Ti ₃ O ₁₂ steel which is formed by calcining a calcined powder obtained by calcining a mixed powder of required raw material powders and then sintering the molded product together with a reduction preventing powder by a discharge plasma sintering method. A method for manufacturing a dielectric. 4. The method for producing a Bi ₄ Ti ₃ O ₁₂ ferroelectric according to claim 2 or 3, wherein the spark plasma sintering method is performed by a constant-speed temperature-rise sintering method. 5. The method for producing a Bi ₄ Ti ₃ O ₁₂ ferroelectric according to claim 2, wherein the spark plasma sintering method is a constant current sintering method. 6. The method according to claim 3, wherein the reduction-preventing powder comprises SnO ₂
A method for producing Bi ₄ Ti ₃ O ₁₂ ferroelectric, which is a mixed powder of powder and ZrO ₂ powder. 7. The method for producing a Bi ₄ Ti ₃ O ₁₂ ferroelectric according to claim 3, wherein a mixing ratio of the SnO ₂ powder and the ZrO ₂ powder is 3: 1 by weight.