JPH06116010A - Production of bismuth laminar compound - Google Patents

Abstract

PURPOSE:To enhance the orientation property of easily polarizable axes of a bismuth laminar compd. by a simpler method than hot pressing. CONSTITUTION:A compact formed from powdery starting materials mixed in such a compsn. ratio as to give the objective bismuth laminar compd. is preliminarily sintered under uniaxial pressurization and then subjected to normal sintering under uniaxial pressurization from a direction perpendicular to the direction of this pressurization. Since the grains of the compact are made linear and orient even in a one-dimensional direction, the orientation property of the easily polarizable axes 10 is further enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bismuth layered compound having piezoelectricity, which can be used as a pressure sensor, a high frequency filter and the like.

[0002]

2. Description of the Related Art As ceramics having piezoelectricity,
Barium titanate (BaTiO _3), lead titanate (Pb
TiO ₃ ), lead zirconate titanate solid solution (PZT),
Bismuth layered compounds (SrBi ₄ Ti ₄ O ₁₅ ) and the like are known. For example, PZT is used as a piezoelectric actuator because it has a particularly high sensitivity. Further, the bismuth layered compound is not as high in sensitivity as PZT, but has a high strength and a high Curie temperature of 500 to 800 ° C. and can be used in a wide temperature range. Therefore, it is expected to be used as a pressure sensor.

A pressure sensor made of a bismuth layered compound includes bismuth oxide (Bi ₂ O ₃ ) and titanium oxide (Ti).
O ₂ ), raw material powders such as strontium carbonate (SrCO ₃ ) are mixed at a predetermined ratio to prepare a powder raw material, and a compact having a predetermined shape is formed from the powder raw material and then sintered to obtain a sintered body. Is manufactured by polarization processing. By the way, a bismuth layer compound is a piezoelectric element excellent in high-temperature characteristics at a high Curie temperature, but has a large crystal anisotropy, but since the crystals are sintered in a randomly oriented state, the piezoelectric sensitivity is low. There are drawbacks. Therefore, JP-A-52-86
Japanese Unexamined Patent Publication No. 198 discloses a manufacturing method in which the crystal axes of plate-like crystals are aligned in one direction by applying pressure in one direction during sintering using a hot press or the like, thereby improving the sensitivity. . According to this manufacturing method, the plate crystals of the bismuth layered compound are sintered in a state of being oriented in the direction perpendicular to the pressing direction, and the axes of easy polarization are aligned in the direction perpendicular to the pressing direction, improving the piezoelectric sensitivity. To do.

[0004]

However, in the hot pressing method disclosed in the above publication, not only the apparatus itself is expensive, but a sintered body that can be pressed at one time is usually 1
Since it is an individual piece and the productivity is low, the manufacturing cost is also high. The present invention has been made in view of such circumstances, and an object thereof is to enhance the orientation of the easy axis of polarization of the bismuth layered compound by a method simpler than the above hot pressing method.

[0005]

[Means for Solving the Problems] First to solve the above problems
The method for producing a bismuth layered compound of the invention comprises a mixing step of mixing a plurality of raw materials at a composition ratio to form a bismuth layered compound into a powder raw material, a molding step of forming a molded body from the powder raw material, and a uniaxial addition of the molded body. From the temporary sintering step of temporarily sintering while pressing to form a temporary sintered body, and the main sintering step of sintering the temporary sintered body while uniaxially pressing in a direction perpendicular to the pressing direction of the temporary sintering step. It is characterized by

The mixing step and the molding step can be performed in the same manner as the conventional manufacturing method. As the bismuth layer compound, a general compound represented by the general formula (Mx Biy) Ti ₄ O ₁₅ can be used. Here, M is a metal element having a valence of 1 to 5, and Sr, Be, Mg, Ca, Ba, R
Alkaline earth metal such as a, Li, Na, K, Rb, C
Various kinds can be selected from alkali metals such as s and Pb. In addition, Mn, Ni, Cr within the range that does not impair the performance
Metal elements such as

It is desirable that the pre-sintering step be performed at a temperature of 900 to 1050 ° C. If this temperature is lower than 900 ° C., the formation of the bismuth layer compound in the pre-sintering step becomes insufficient, and it is difficult to obtain the desired effect. On the other hand, if the temperature is higher than 1050 ° C., the sintering proceeds too much, and the orientation of the crystals in the main sintering step becomes insufficient, so that it is difficult to obtain the desired effect. In addition, sintering may be insufficient, and problems may occur in the strength of the sintered body.

[0008]

The bismuth layered compound is a material having extremely strong anisotropy due to its crystal structure, and the easy polarization direction is limited to a specific direction. Moreover, the crystal is also plate-shaped, and is easily oriented in one direction. However, in the molding / sintering by the usual manufacturing method, the axis of easy polarization becomes random, and improvement in piezoelectric characteristics cannot be expected.

Therefore, in the manufacturing method of the present invention, as shown in FIG. 1, the compact is pre-sintered while being uniaxially pressed from the P ₁ direction. Thereby, the plate crystal of the bismuth layered compound is
The flat surface grows while being oriented in a direction perpendicular to the pressing direction. In the obtained pre-sintered body, the crystals are layered as shown in FIG. 2, and the easy axis of polarization 10 is in the same plane in one layer, but has a two-dimensional random orientation. .

Further, in the present invention, the main sintering step is performed while pressing the temporary sintered body from the direction P ₂ perpendicular to the pressing direction P ₁ of the temporary sintering step. As a result, the crystal becomes a needle-like crystal as shown in FIG. 2 and is also oriented one-dimensionally. Therefore, the orientation of the easy polarization axis of the crystal of the present sintered body is significantly improved, and the piezoelectric characteristics are improved.

[0011]

〔Example〕

(1) Mixing process As a starting material, strontium oxide (SrCO ₃ ),
Bismuth oxide (Bi ₂ O ₃ ), titanium oxide (TiO ₂ )
And manganese oxide (MnO) were used to weigh the respective raw material powders so that the composition ratio was SrBi ₄ Ti ₄ O ₁₅ and MnO was contained in an amount of 0.1 wt% in terms of Mn weight. Wet mix in a pot mill for 48 hours.

The mixed powder is dehydrated with ethanol and dried at 800 ° C.
It was calcined for 2 hours. The calcined powder was wet-mixed again in the pot mill for 48 hours, and dried with ethanol to obtain a powder raw material. (2) Molding process Polyvinyl alcohol (PVA) was added to the powder raw material in about 3 parts.
The mixture was added by weight% and granulated, and the granules were fed into a mold having a cubic cavity of 10 mm square and molded at a pressure of 1 t / cm ² . (3) Temporary Sintering Step The obtained compact was heated at a temperature rising / falling rate of 200 ° C./h, and
Preliminary sintering was performed by holding at 00 ° C to 1050 ° C for 2 hours. When the holding temperature is reached, the pressure of 10 MPa is applied in the uniaxial direction P
_It was applied to the molded body from ₁ and the pressure application was maintained while maintaining the temperature. (4) Main Sintering Step The obtained temporary sintered body 1 is placed on a ZrO ₂ pad material,
It was placed in an alumina container, covered with an alumina lid, and placed in the furnace.
Sintering was performed by heating and holding at 100 to 1300 ° C. for 2 hours in the atmosphere. Further, when the holding temperature was reached, a pressure of P ₂ = 10 MPa was applied to the pre-sintered body 1 from the direction P ₂ perpendicular to the P _1, and the pressure application was maintained during the temperature holding. (5) Polarization step The obtained main sintered body 2 was cut into a plate shape having a thickness of 1 mm in parallel with the pressure axes P ₁ and P ₂ as shown in FIG. 3, and silver paste was applied to both surfaces of the square shape. It was applied and baked to form a silver electrode. Then, in silicon oil heated to 200 ° C., a voltage of 8 kV / mm was applied for 10 minutes to perform polarization treatment.

In the sintered body 2, since the easy polarization axis 10 is oriented perpendicular to the pressing directions P ₁ and P ₂ , the easy polarization axis 10 is parallel to the thickness direction in the cut bismuth layer compound. It will be oriented. [Comparative Example 1] A molded body formed in the same manner as in the example was processed with ZrO.
Place it on the pad material made of ₂ and store it in an alumina container, cover it with an alumina lid and place it in the furnace.
The temperature was maintained at 00 ° C./h and the temperature was maintained at 1100 to 1300 ° C. for 2 hours in the air while being heated and sintered. No pressure was applied during the pre-sintering step and during sintering. Then, the sintered body was polished to a thickness of 1 mm, and the same was subjected to the polarization step as in the example. [Comparative Example 2] In the method of Comparative Example 1, a pressure of 10 MPa was applied to the molded body when the holding temperature was reached, and the pressure application was maintained while the temperature was maintained. Then, the obtained sintered body was cut out into a plate shape having a thickness of 1 mm in parallel with the pressing direction, and the polarization step was performed on it in the same manner as in the example. (Evaluation) The piezoelectric sensitivity of each of the obtained devices was measured. The results are shown in Table 1. Here, the piezoelectric sensitivity means the charge per unit force (E / F, unit pC / when the amount of charge generated when a force F is applied to the sample is E, as shown in FIG. N).

[0014]

[Table 1] From Table 1, the piezoelectric element obtained by the manufacturing method of the present invention has a sensitivity improved by 60 to 100% as compared with the piezoelectric element obtained by the comparative example which is a conventional manufacturing method. It is clear that this is the effect of applying pressure in different directions during the pre-sintering and the main-sintering and sintering.

[0015]

According to the manufacturing method of the present invention, it is possible to easily manufacture a bismuth layered compound in which the easy polarization axis is oriented in one direction as in the hot pressing method. Since it is only necessary to uniaxially pressurize in the two sintering steps, a large number of compacts can be processed at one time and the productivity is excellent, so that the production cost can be reduced as compared with the hot pressing method. it can.

In the bismuth layered compound produced by the present invention, since the easy axis of polarization is perfectly oriented in one direction, it does not receive a vibration mode from the other direction, and has a high precision filter and a high precision acceleration. It can be used as a sensor.

[Brief description of drawings]

FIG. 1 is an explanatory view of a temporary sintered body obtained in an example of the present invention.

FIG. 2 is an explanatory diagram of a main sintered body obtained in an example of the present invention.

FIG. 3 is an explanatory view showing a cutout position of a test piece from the present sintered body in an example of the present invention.

FIG. 4 is an explanatory diagram showing the relationship between force and charge output and showing the definition of piezoelectric sensitivity.

[Explanation of Codes] 1: Temporary Sintered Body 2: Main Sintered Body 10:
Polarization easy axis

Claims (1)

[Claims] 1. A mixing step of mixing a plurality of raw materials at a composition ratio of a bismuth layered compound to obtain a powder raw material, a molding step of forming a molded body from the powder raw material, and a tentatively uniaxially pressing the molded body. It comprises a temporary sintering step of sintering into a temporary sintered body, and a main sintering step of sintering the temporary sintered body while uniaxially pressing it in a direction perpendicular to the pressing direction of the temporary sintering step. A method for producing a bismuth layered compound, comprising: