JP6212821B2 - Method for producing hexagonal barium titanate dielectric material - Google Patents

Description

  The present invention relates to a method for producing a hexagonal barium titanate crystal obtained at a low firing temperature.

  In recent years, the miniaturization and performance of electrical and electronic devices have rapidly progressed, and electronic components used in such devices have various characteristics such as relative permittivity and temperature characteristics while ensuring sufficient reliability. It is demanded to improve. This is no exception for ceramic capacitors which are examples of electronic components.

  As a dielectric material of such a capacitor, particularly a dielectric material having a high relative dielectric constant, a material mainly composed of cubic barium titanate is used. On the other hand, in recent years, a reduction in the thickness of the dielectric layer has been studied in order to improve the capacitance. In order to reduce the thickness of the dielectric layer, the smaller the particle size of the dielectric particles, the better. However, when cubic barium titanate is atomized, there is a problem in that the dielectric constant decreases.

  Further, hexagonal barium titanate has been studied as a material having a high relative dielectric constant. Although hexagonal barium titanate is inherently lower in dielectric constant than cubic crystals, it has been suggested that the introduction of oxygen vacancies significantly improves the relative dielectric constant (Patent Document 1).

  Moreover, in the crystal structure of barium titanate, the hexagonal crystal structure is a metastable phase and can usually exist only at 1460 ° C. or higher. For this reason, in order to obtain hexagonal crystals at room temperature, it is necessary to rapidly cool from a high temperature of 1460 ° C. or higher. However, due to rapid cooling, the particle size becomes 1 μm or more, and there is a problem that when applied to an electronic component, it cannot cope with thinning and sufficient reliability cannot be secured.

In view of such circumstances, a technology that has hexagonal barium titanate as the main phase and exhibits an extremely high relative dielectric constant, excellent insulation resistance, and sufficient reliability has been developed (Patent Literature). 2). That is, a substance represented by the following formula in which Ti is replaced with Mn and Ba is replaced with a rare earth element M.
(Ba _1−α M _α ) _A (Ti _1−β Mn _β ) BO ₃ (where 0.900 ≦ (A / B) ≦ 1.040, 0.003 ≦ α ≦ 0.05, 0.03 ≦ β ≦ 0.2))
The firing temperature of this barium titanate-based material can be actually reduced to 1150 ° C., and it is possible to produce fine particles with suppressed grain growth.
Patent document 6 is also mentioned as a similar technique.

  However, from the viewpoint of manufacturing, further reduction in the firing temperature is desired from the viewpoint of reducing power consumption and making the electrode base metal.

JP 2005-213083 A JP 2011-116629 A JP 2007-326768 A JP 2010-215450 A JP 2011-184289 A JP 2011-116628 A

  That is, the problem to be solved is to provide a method for producing a hexagonal barium titanate-based dielectric material that can further reduce the firing temperature.

According to the first aspect of the present invention, a precursor gel is prepared by a sol-gel method from a sol solution in which Ba alkoxide, Ti alkoxide, and KF are mixed, and is baked at 600 ° C. or higher to obtain Ba _1-x K _x. It is a dielectric material manufacturing method characterized by obtaining a hexagonal barium titanate-based dielectric material having a composition of TiO _3−x F _x (where 0.5 ≧ x ≧ 0.4).

  The upper limit of the firing temperature is not particularly limited, but a hexagonal crystal can be obtained at 600 ° C. or higher. Therefore, it is preferably 1000 ° C. or lower, more preferably 800 ° C. or lower from the viewpoint of production energy. . In addition, when x = 0.4 and the firing temperature is 600 ° C., nearly 90% is hexagonal and the remainder is cubic, which can be said to be substantially hexagonal. Even when (less than 20% as a guide) is included, it is assumed to be hexagonal or hexagonal (when x = 0.4, all are hexagonal if the firing temperature is 650 ° C.).

According to the second aspect of the present invention, a precursor gel is prepared by a sol-gel method from a sol solution in which Ba alkoxide, Ti alkoxide, and KF are mixed, and is baked at 600 ° C. or higher, whereby Ba _1-x K _x A barium titanate-based dielectric material having a composition of TiO _3−x F _x (where 0.4> x ≧ 0.2) and a mixed crystal of hexagonal type and cubic type is obtained. It is a dielectric material manufacturing method.

  Grain growth based on the fact that it is a mixed crystal and has a high relative dielectric constant inherent to cubic crystals, while obtaining a high relative dielectric constant derived from hexagonal crystals by introducing oxygen vacancies and firing at a relatively low temperature. It is possible to obtain a material having new characteristics that can be expected to maintain a high relative dielectric constant derived from the suppression of.

  The invention according to claim 3 is a dielectric ceramic manufacturing method, characterized in that a dielectric ceramic is obtained by spark plasma firing of the crystal powder obtained by the dielectric material manufacturing method according to claim 1 or 2. is there.

  In the case of producing ceramics in which oxygen or deficiency is positively introduced by volatilizing K or F in the crystal, whether it is normal sintering or spark plasma, high-temperature annealing (for example, 900 ° C. or more, In some cases, the temperature may be 1000 ° C. or higher. The same can be said for sol-gel firing.

According to a fourth aspect of the invention, the general formula _{Ba 1-x K x TiO 3} -x F x ( however, 0.5 ≧ x ≧ 0.4) hexagonal having a composition represented as a dielectric material It is.

  According to the present invention, the firing temperature can be lowered to obtain a hexagonal barium titanate dielectric material or a cubic crystal mixed barium titanate dielectric material. By using the obtained dielectric material as a raw material, it becomes possible to achieve a high relative dielectric constant and atomization.

It is an XRD plot by each calcination temperature in case of x = 0.10 and 0.20. It is an XRD plot by each calcination temperature in case of x = 0.30 and 0.40. It is an XRD plot by each calcination temperature in case of x = 0.50 and 1.00. It is the figure which showed the relationship between a KF substitution rate, a calcination temperature, and an integral intensity ratio. It is the figure which showed the relationship between a calcination temperature and integral intensity ratio, and the relationship between the substitution rate x and integral intensity ratio. It is the figure which showed the relationship between KF substitution rate, the calcination temperature T, and a crystal form. It is the figure which showed the temperature dependence of the dielectric constant of the dielectric ceramic which solidified the sample of the hexagonal crystal obtained by x = 0.4 and the calcination temperature of 650 degreeC with SPS at 1000 degreeC, and annealed at 1000 degreeC in oxygen. .

Hereinafter, a method for producing the barium titanate of the present invention by a sol-gel method will be described in detail.
<Reagents used>
The reagents used are as follows.
・ Methanol (dehydration): Kanto Chemical Co., Inc., purity 99% / GC
・ 2-Methoxyethanol: Kishida Chemical Co., Ltd. purity 99% or higher / Special grade ・ 2-Ethoxybarium: High purity chemical laboratory, purity 99.0% / Special grade ・ Titanium (IV) isopropoxide: Kishida Chemical Co., Ltd. 99.0% or higher / Grade 1 / Potassium fluoride: Kishida Chemical Co. 99% / Special grade

<Determination of amount of raw material reagent>
The calculation method of the amount of raw material reagent was as follows.

In the experiment, x = 0.10, 0.20, 0.30, 0.40, 0.50, and 1.00 were weighed. The reagent amount is shown below.

<Experimental procedure>
1.
First, methanol (dehydrated) and 2-methoxyethanol were weighed and mixed in a tall beaker. Next, potassium fluoride, 2-ethoxybarium, and titanium (VI) isopropoxide were weighed and mixed in the glow box. After mixing, the precursor solution was stirred with a magnetic stirrer for 1 hour. Since titanium (IV) isopropoxide easily reacts with moisture in the air, it was weighed in a glow box filled with nitrogen gas. Further, since potassium fluoride is a deliquescent substance, it was dried at 200 ° C. for 48 hours.

2.
The precursor solution after completion of stirring was placed in a stirrer and cooled at 0 ° C. for 1 hour. Then, distilled water was sprayed while stirring the solution with a glass rod to gel the entire solution. After this hydrolysis, the solution was aged at 50 ° C. for 24 hours to cause liquid separation.

3.
The precursor gel was loosened and dried in a dryer at 90 ° C. for 24 hours. The dried precursor gel was crushed in a mortar. Thereafter, half of the precursor gel was placed in a zirconia container and ground with a planetary ball mill (GokinPlanetaring Planet M2-3F). In a planetary ball mill, zirconia balls (10 pieces of φ = 5 mm, 20 pieces of φ2 mm) were put and pulverized for 8 minutes at a rotational speed of 300 rpm.

4).
The pulverized powder is put into an alumina crucible (45 mm × 55 mm), and the temperature is set to 400 ° C., 500 ° C., 600 ° C., 650 ° C., 700 ° C., 800 ° C., 900 ° C., 1000 ° C., and 1050 ° C. in an electric furnace. Baked for hours. The temperature was raised from room temperature to the set temperature over 3.75 hours, then the set temperature was maintained for 12 hours, and finally returned to room temperature over 3.75 hours from the set temperature.

<Experimental result>
The X-ray diffraction measurement results when x and the firing temperature are changed are shown in FIGS. In each figure, a cubic crystal has a peak at 2θ≈56.3 °, and a hexagonal crystal has two peaks close to 2θ≈55.7 °, and a partial enlarged view thereof is also shown.

  As a result of the X-ray diffraction measurement, x = 0.10, hexagonal crystals begin to appear at a firing temperature of 800 ° C. A hexagonal crystal appears at 600 ° C. to 650 ° C. at x = 0.20, 600 ° C. at x = 0.30, 0.40, and 500 ° C. at x = 0.50. It was also confirmed that when the firing temperature was increased from the hexagonal crystal appearance temperature, the hexagonal crystal strength increased and the cubic crystal strength decreased at any substitution rate.

FIG. 4 is a diagram showing the relationship among the KF substitution rate, the firing temperature, and the integrated intensity ratio. That is, when the cubic type integrated intensity is I _c and the hexagonal type integrated intensity is I _h , the integrated intensity ratio I_r is expressed as I_r = I _h / (I _c + I _h ). Note that cubic type peaks are used around 39 °, 45 °, 56 °, and 66 °, and hexagonal type peaks are used around 38 °, 44 °, 55 °, and 65 °. It was decided to take. I_r = 0 indicates that the cubic type is 100%, and I_r = 1 indicates that the hexagonal type is 100%. FIG. 5 shows the relationship between the firing temperature and the integrated intensity ratio, and the relationship between the substitution rate x and the integrated intensity ratio. FIG. 6 shows the relationship between the KF substitution rate, the firing temperature T, and the crystal type.

  From the integrated intensity ratio, when x ≧ 0.4 and the firing temperature is 600 ° C. or higher, hexagonal barium titanate is obtained, and 0.4> x ≧ 0.2, and the firing temperature is 600. It was confirmed that barium titanate in a mixed crystal of hexagonal type and cubic type can be obtained when the temperature is higher than ℃. It was also confirmed that the abundance ratio of the mixed crystal was variable by adjusting x and the firing temperature.

<Production of ceramics and evaluation of dielectric properties>
A hexagonal sample obtained at x = 0.4 and a firing temperature of 650 ° C. is solidified at 1000 ° C. by SPS (Spark Plasma Sintering), and a dielectric ceramic is produced by annealing at 1000 ° C. in oxygen. did. When the degree of sintering was calculated, it was almost 100%. The temperature dependence of the relative dielectric constant of this sample is shown in FIG. The value of the relative dielectric constant ε ′ was about 65, and the dielectric loss tan δ was less than 0.01. This is almost the same as the value of the hexagonal BaTiO ₃ ceramics shown in FIG. 7 of Document 6, and the temperature dependency is also similar to the point that the temperature decreases from low temperature to room temperature. That is, in the present invention, it was found that a ceramic having the same dielectric property as the hexagonal BaTiO ₃ ceramic was formed although it was a KF partial substitution type hexagonal BaTiO ₃ . In other words, it was confirmed that the hexagonal barium titanate obtained by the present invention or a mixed crystal of this and cubic barium titanate is a dielectric material.

According to the present invention, a hexagonal crystal cannot be obtained unless it is conventionally fired at a high temperature of 1460 ° C., but a hexagonal or cubic mixed crystal can be obtained even if the firing temperature is lowered to 800 ° C. or higher. K and F in the crystal can be oxygen deficient by high-temperature exposure, and can contribute to applications utilizing the hexagonal type, such as improvement of relative dielectric constant.

Claims (4)

From a sol solution in which Ba alkoxide, Ti alkoxide and KF are mixed, a precursor gel is prepared by a sol-gel method, and calcined at 600 ° C. or higher.
Ba _1-x K _x TiO _3−x F _x (where 0.5 ≧ x ≧ 0.4)
A method for producing a dielectric material, comprising obtaining a hexagonal barium titanate dielectric material having a composition of: From a sol solution in which Ba alkoxide, Ti alkoxide and KF are mixed, a precursor gel is prepared by a sol-gel method, and calcined at 600 ° C. or higher.
_{Ba 1-x K x TiO 3} -x F x ( however, 0.4> x ≧ 0.2)
A method for producing a dielectric material comprising obtaining a mixed crystal barium titanate-based dielectric material having a composition of:   A dielectric ceramic manufacturing method comprising: spark plasma firing the crystal powder obtained by the dielectric material manufacturing method according to claim 1 or 2 to obtain a dielectric ceramic. The general formula is Ba _1−x K _x TiO _3−x F _x (where 0.5 ≧ x ≧ 0.4)
A hexagonal dielectric material having a composition expressed as:

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