JPH07113177A - Production of ceramics for dielectric - Google Patents

Abstract

PURPOSE:To obtain a thick ceramic film for a dielectric free from cracking applying a soln. of metal alkoxides in alkyl alcohol to the surface of a body to be treated and burning the resultant film after drying in a supercritical state. CONSTITUTION:Metal alkoxides including lead alkoxide such as Pb(O-iso-C3H7)2 or Pb(OC4H9)2 are mixed with alkyl alcohol to prepare a sol contg. no water. This sol is applied to the surface of a body to be treated such as a substrate and the resultant film is dried in an autoclave and fired at 400-1,200 deg.C, preferably 550-750 deg.C. The alcohol used as a solvent is preferably methanol, ethanol or isopropanol and the drying is carried out in a supercritical state at 220-350 deg.C under 4-10MPa pressure.

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 ceramic for a dielectric material using a metal alkoxide as a raw material. Ceramics for dielectrics have been researched and put to practical use in various fields such as capacitors, thermistors, and optical modulators by utilizing their dielectric properties, pyroelectricity, and piezoelectricity. In particular, lead zirconate titanate (PZT) is excellent in piezoelectricity, so it is applied to piezoelectric ignition elements, bimorph oscillators, piezoelectric ceramic oscillators, piezoelectric buzzers, piezoelectric filters, etc. by taking advantage of this characteristic. . The advent of these elements has enabled the development of new devices, such as ultrasonic processing machines, ultrasonic cleaners and other actuators, accelerometers and vibration shock sensors, as well as home appliances, audio products, communication devices, and other advanced devices. Contribute to Also, this P
Lead lanthanum zirconate titanate (PLZT), which is made by adding lanthanum oxide to ZT, has transparency even though it is a ferroelectric substance, and it has new properties such as optical shutters, light valves, filters, and optical memories. Development as an information processing engineering material is expected.

[0002]

2. Description of the Related Art In ceramics for dielectrics, PZT is a solid solution of lead titanate and lead zirconate, and its manufacturing method is roughly classified into an oxide sintering method and a sol-gel method.
The former is made by repeating the steps of sintering titanium oxide, zirconium oxide, and lead oxide at 1200 to 1300 ° C., crushing and pulverizing the sintered body, and firing again. This method requires firing in a lead atmosphere, and there is a wide range of particle shapes and distributions, making it difficult to use a one-pass process, but it is possible to lower the sintering temperature by making the raw material oxide ultrafine, and , One-pass process has become possible. In the latter case, titanium alkoxide, zirconium alkoxide, and lead acetate are mixed with alkyl alcohol together with a small amount of water and a stabilizer (chelating agent), and hydrolysis and polycondensation reaction are sufficiently performed to form a sol. It is prepared by volatilizing and drying the alcohol content of the sol and then firing it. Since this method uses a simple one-pass process of drying from the liquid phase and firing, there are few spatial restrictions (shape of sintered body, shape of object to be treated), and large and complicated shapes can be easily formed. The sintering temperature is 600 to 700 ° C., which is relatively low, and has many advantages over the former. However, the gel contracts when the alcohol content is volatilized and dried, so that the gel is easily broken, which is a problem particularly when a thick film is formed on the substrate.

[0003]

When the gel of the ceramics for dielectrics prepared by the sol-gel method is dried with alcohol in the air, the gel shrinks and cracks as the drying progresses. This is because the boundary between the gel skeleton (solid), the solvent (liquid) and the air (gas) is generated in the surface layer in the stage where the drying progresses, so that a capillary force pulling the gel skeleton toward the pores is generated. On the other hand, since the inside of the gel tries to keep the volume as it is, it is said that when the tensile force of the surface layer is larger than the strength of the gel skeleton, the surface layer is cracked, and when it is violent, the whole is broken. The magnitude of the capillary force is generally represented by ΔP = 2γ · cos θ / r (1) r: capillary radius θ: wetting angle γ: surface tension. The present invention makes a solvent into a supercritical state (a fluid state in which gas and liquid cannot be distinguished at high temperature and high pressure), and thus, a capillary force defined by the formula (1) is not generated at all. By gradually reducing the pressure and releasing the solvent, the solvent is dried without cracking.
However, the supercritical point of the water added for the hydrolysis and polycondensation reaction of the sol is 374.4 ° C and 23.0 MPa, which cannot be realized by a normal autoclave. If no water is added to the solvent, the supercritical point of alcohol (eg, isopropyl alcohol 235.3 ° C, 4.8 MPa) may be used, which is a practical condition. However, when water is not added to the solution at all, lead acetate, which is a feed material for the lead component, is not dissolved and a uniform sol cannot be formed. Such a problem is P
In many cases, not only ZT but also other ceramics for dielectrics can be mentioned. Therefore, in the present invention, a lead alkoxide is used as a lead feed material to prepare a water-free sol solution, and supercritical drying is performed under practical conditions.

[0004]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is provided with the following structure to achieve the above object. As the metal alkoxide material, Zr (OCH ₃ ) ₄ , Zr (OC ₂ H ₅ ) ₄ ,
Zr (OC ₃ H ₇ ) ₄ , Zr (0-iso-C ₃ H ₇ ) ₄ , Zr (OC ₄
H ₉ ) ₄ or the like can be used, and Ti (OCH ₃ ) ₄ , Ti (OC ₂ H ₅ ) ₄ , Ti (OC ₃ ) can be used as a titanium supply source.
Etc. _{H 7) 4, Ti (0} -iso-C 3 H 7) 4, Ti (OC 4 H 9) 4,
As a lead source, Pb (O-iso-C ₃ H ₇ ) ₂ and Pb (OC ₄
H ₉ ) ₂ or the like can be used. The alcohol used as a solvent should have a practical supercritical point, such as methyl alcohol (240.5 ° C, 8.0 MPa), ethyl alcohol (243.4 ° C, 6.3 MPa), isopropyl alcohol (235.3 ° C, 4.8 MPa). Is desirable. It is desirable that all mixing processes of these materials be performed in an atmosphere of dry nitrogen and dry argon, and it is particularly desirable that the water content is 300 ppm or less. When performed in the air, a stabilizer (chelating agent) may be mixed, and diethanolamine, acetylacetone, or the like can be used. Depending on the purpose, a polymeric viscosity modifier, an acid, an alkali or the like may be added to the sol, or a soluble metal compound such as La (OC ₃ H ₇ ) ₃ may be added. The method of applying it to the surface to be treated such as the substrate is not particularly limited, and examples thereof include a dip coating method, a spin coating method, and a spray coating method. The surface to be treated preferably has high wettability with the sol, and when it has low wettability, surface treatment may be performed. Supercritical drying can be easily realized by using an autoclave. Both the temperature and the pressure may be set slightly higher than the supercritical point of the alcohol used as the solvent, and from that state, only the pressure may be gradually decreased while keeping the temperature constant. Firing is in the air, nitrogen atmosphere,
Alternatively, it can be performed in a vacuum or the like, and it is desirable that the temperature raising / lowering process is controlled by a programming temperature controller or the like. The firing temperature is 400 to 1200 ° C, preferably 550 to 750 ° C. Firing temperature is 1
If the temperature is higher than 200 ° C., lead volatilizes violently and it becomes difficult to keep the stoichiometric ratio constant, which is not preferable, and if it is lower than 400 ° C., crystallization does not sufficiently occur, which is not preferable.
The dielectric ceramics according to the present invention include BaTiO ₃ , (Ba, Sr) TiO ₃ , and Sr in addition to the above-mentioned PZT.
TiO ₃ , PbTiO ₃ (PT), Pb (Mg _1/3 , Nb _2/3 )
O ₃ (PMN), PMN-PT, LiNbO ₃ (LN), Li
TiO ₃ (LT), K (Ta, Nb) O ₃ (KTN), ZnO,
AlN, (Sr, Ba) Nb ₂ O ₆ , (Sr, Ba) _0.8 (C
r, Zn, Y) _X Na _0.4 Nb ₂ O ₆ , (Pb, Ba) NbO ₆
(PBN), (K, Sr) NbO ₆ (KSN), (Pb, K) N
b ₂ O ₆ (PKN), Ba ₂ NaNb ₅ O ₁₅ (BNN), BaT
i ₅ O ₁₁ , Al-added BaTiO ₃ , 2MgO · 2Al ₂ O ₃
・ 5SiO ₂ + ZrO ₂ , Pb (Sn _1/2 Sb _1/2 ) _{0, 1} (Zr
_0.63 Ti _0.27 ) O ₃ , Bi ₄ Ti ₃ O ₁₂ , SrTiO ₃ , S
r _X B _1-X Nb ₂ O ₆ (SBN), Pb (Zn _1/3 Nb _2/3 ) O
₃ (PZN), lead germanate, Pb (Ni _1/2 Nb _2/3 ) O
₃ (PNN), Ba (Mg _1/3 Ta _2/3 ) O _{3 and the} like.

[0005]

According to the method for producing a dielectric ceramics of the present invention, a thick film of the dielectric ceramics can be easily produced on the surface of the object to be treated without cracking.

Claims (4)

[Claims] 1. A thick film of dielectric ceramics is formed on the surface of an object to be processed by applying an alkyl alcohol solution of a metal alkoxide to the surface of the object to be processed, drying the alkyl alcohol in a supercritical state, and then firing. A method for producing a dielectric ceramics, comprising: 2. The method for producing a dielectric ceramics according to claim 1, wherein the solution does not contain water. 3. The method for producing a ceramic for a dielectric according to claim 1, wherein the metal alkoxide contains at least lead alkoxide. 4. Supercritical drying 4 to 10 MPa, 220
C. to 350.degree. C., Claims 1, 2, 3
A method for producing the ceramics for a dielectric as described.