JP6267673B2 - Method for producing ferroelectric ceramics - Google Patents

Description

  The present invention relates to a ferroelectric ceramic used for a capacitor assumed to be used in a harsh environment such as in-vehicle or aerospace, and a method for manufacturing the same.

Conventionally, as this kind of ferroelectric ceramic, in a core-shell structure ceramic obtained by adding a shell material to a core material and firing, the core material is BaTiO ₃ (barium titanate), and the shell material is ZrO ₂ (zirconium dioxide). ) Are used, and those prepared by adding a small amount of ZrO ₂ to this BaTiO ₃ powder and baking it are known.

That is, by adding a small amount of ZrO ₂ to the BaTiO ₃ powder and firing, the zirconium component diffuses from the surroundings of BaTiO ₃ , and the phase given by BaZr _X Ti _1-X O ₃ is present around the BaTiO ₃ particles. As shown in FIG. 4, a core-shell ferroelectric ceramic having BaTiO ₃ particles as a core and BaZr _X Ti _1-X O ₃ as a shell is produced.

Here, the chemical composition of the ferroelectric ceramic is such that the closer to the surface, the higher the variable _X in BaZr _X Ti _1-X O ₃ (the higher the Zr component concentration), and the closer to the center, the closer to pure BaTiO ₃ . It becomes a state.

On the other hand, in the ceramic of the core-shell structure having the BaTiO ₃ particles as a core and the BaZr _X Ti _1-X O ₃ as a shell, it is also known as a relaxor dielectric, and in such a relaxor dielectric, In addition to exhibiting a relative dielectric constant temperature characteristic having a wide peak, the peak position also changes continuously according to the change of the variable _{X in} the chemical composition (BaZr _X Ti _1-X O ₃ ), and the dielectric constant temperature Since the maximum temperature in the characteristics is determined by the Curie temperature of the core material, it is known that a flat temperature characteristic can be obtained in a temperature range from a low temperature of about −55 ° C. to about 150 ° C. which is the Curie temperature of the core material. Yes.

T.A. R. Armstrong et al. J. et al. Am. Ceram. Soc. 72 (1989) 605

However, in the case of the conventional ferroelectric ceramics produced by adding a small amount of ZrO ₂ to the BaTiO ₃ powder and firing, the temperature becomes 150 ° C. or more as shown in the relative dielectric constant temperature characteristic shown in FIG. As a result, the stability of the dielectric constant is significantly reduced, and in such a capacitor material for in-vehicle or aerospace use of such conventional ferroelectric ceramics, EIA standard X8R characteristics, that is, −55 ° C. to 150 ° C. Ferroelectric ceramics with high-temperature characteristics that have a variation in relative dielectric constant within ± 15% in the temperature range are currently available, but when the temperature exceeds 150 ° C, the stability of the dielectric constant decreases significantly. Therefore, there is a disadvantage that it may not be possible to meet more stringent requirements.

SUMMARY OF THE INVENTION The present invention has been made to solve the above disadvantages. Among the present inventions, the invention according to claim 1 is a method for producing a ceramic having a core-shell structure in which a shell material is added to a core material and fired. a is, the core material is Ri tungsten bronze-type oxide der, the tungsten bronze-type oxide is KSr ₂ Nb ₅ O _15, ferroelectric ceramics, wherein said shell material is ZrO ₂ It is in the manufacturing method .

Further, a second aspect of the present invention, a method for manufacturing a ceramic core-shell structure formed by the addition of shell material to the core material firing, the core material is Ri tungsten bronze-type oxide der, the tungsten bronze-type oxide is _KBa 2 _Nb 5 _{O 15,} the shell material is in the strong manufacturing method of a dielectric ceramic, which is a ZrO _2.

Also, third aspect of the present invention, a method for manufacturing a ceramic core-shell structure formed by the addition of shell material to the core material firing, the core material is Ri tungsten bronze-type oxide der, the tungsten bronze-type oxide is NaBa ₂ Nb ₅ O _15, the shell material is in the strong manufacturing method of a dielectric ceramic, which is a ZrO _2.

As described above, the present invention provides a method for producing a ceramic having a core-shell structure in which a shell material is added to a core material and fired. The core material is a tungsten bronze oxide. Therefore, it is possible to obtain a ferroelectric ceramic with stable high temperature characteristics that can maintain a variation in relative permittivity within ± 15% even under temperature conditions of 150 ° C. or higher, and high temperature characteristics are required. The tungsten bronze type oxide is KSr ₂ Nb ₅ O ₁₅ , so that it can be used in a wide temperature range up to 195 ° C. Ferroelectric ceramics with stable high temperature characteristics that can maintain a variation in rate within ± 15% can be obtained, and ZrO ₂ is used as the shell material. Therefore, a ferroelectric ceramic having a core-shell structure in which the core material is a tungsten bronze type oxide can be obtained at low cost.

The invention according to claim 2 is a method for producing a ceramic having a core-shell structure in which a shell material is added to a core material and fired, and the core material is made of a tungsten bronze type oxide. Ferroelectric ceramics with stable high temperature characteristics that can maintain a variation in relative permittivity within ± 15% even under temperature conditions of ℃ or higher can be obtained. It can be used for aerospace capacitor materials and the like, and by using the tungsten bronze type oxide as KBa ₂ Nb ₅ O ₁₅ , a temperature condition of 150 ° C. or higher reaching the Curie temperature of KBa ₂ Nb ₅ O ₁₅ even under, it is the variation of the dielectric constant to obtain a ferroelectric ceramic having a stable high temperature range characteristics can be maintained within 15% ±, further, the Since made using ZrO ₂ as the E sealing material, it is possible to obtain a ferroelectric ceramics of the core-shell structure that a core material with tungsten bronze-type oxide at low cost.

In the invention according to claim 3, since the core material is made of a tungsten bronze type oxide, it is a method for producing a ceramic of a core shell structure in which a shell material is added to the core material and fired. Ferroelectric ceramics with stable high temperature characteristics that can maintain a variation in relative permittivity within ± 15% even under temperature conditions of ℃ or higher can be obtained. It can be used for aerospace capacitor materials and the like, and the tungsten bronze type oxide is NaBa ₂ Nb ₅ O ₁₅ , so that the temperature condition is 150 ° C. or higher to reach the Curie temperature of NaBa ₂ Nb ₅ O ₁₅ even under, it is the variation of the dielectric constant to obtain a ferroelectric ceramic having a stable high temperature range characteristics can be maintained within 15% ±, further, Since made using ZrO ₂ as the serial shell material, it is possible to obtain a ferroelectric ceramics of the core-shell structure that a core material with tungsten bronze-type oxide at low cost.

It is a manufacturing-process figure of the example of embodiment of this invention. It is an explanation front sectional view of an example of an embodiment of the invention. It is a dielectric constant temperature characteristic figure of the example of an embodiment of the invention. It is an explanatory front sectional view of an embodiment of a conventional product. It is a dielectric constant temperature characteristic figure of the example of an embodiment of the conventional product.

  FIG. 1 to FIG. 3 show an embodiment of the present invention. A small amount of shell material M is added to core material S and fired to produce a core-shell structure ferroelectric ceramic G. As core material S, tungsten is used. Bronze type oxide is used.

In this case, KSr ₂ Nb ₅ O ₁₅ is used as the tungsten bronze oxide, and ZrO ₂ is used as the shell material M.

In this case, when producing the ferroelectric ceramic G, as shown in FIG. 1, first, a high-purity oxide K ₂ CO ₃ , SrCO ₃ , Nb ₅ O ₁₅ is used as a raw material for the tungsten bronze type oxide. The raw materials are mixed for 24 hours using a planetary ball mill and calcined at 1,150 ° C. for 8 hours to produce a tungsten bronze type oxide as the core material S.

The produced tungsten bronze oxide calcined powder is confirmed to be a KSr ₂ Nb ₅ O ₁₅ single phase by an X-ray diffraction method.

Next, ZrO ₂ (zirconium dioxide) as the shell material M is added to the calcined powder of tungsten bronze type oxide as the core material S. In this case, zirconium tetrapropoxide and other zirconium compounds are added. For example, it is dissolved in a solvent such as ethanol or propyl alcohol, and KSr ₂ Nb ₅ O ₁₅ calcined powder as a tungsten bronze type oxide is put into the solution, and is sufficiently stirred using, for example, a planetary ball mill. Thus, a ZrO ₂ (zirconium dioxide) layer as the shell material M is formed on the surface of the KSr ₂ Nb ₅ O ₁₅ powder as the tungsten bronze type oxide, and the shell material M is formed on the surface of the tungsten bronze type oxide Pressed the powder at a pressure of about 196 MPa to make pellets, Pellets were charged into the furnace temperature 1250 ° C. to 1300 ° C. in a heating furnace as baking temperature, and calcined for 4 hours in an oxygen atmosphere in the heating furnace, thereby ion exchange from ZrO ₂ occurs, FIG. 2 As shown in FIG. _{5, a} ferroelectric ceramic G having a core-shell structure using the tungsten bronze oxide as a core and K _1-X Sr _{2 + X} Nb _{5 -X} Zr _X O ₁₅ as a shell is manufactured.

In place of the step of dissolving zirconium tetrapropoxide and other zirconium compounds in the above-described production process, ZrO ₂ as the shell material M is not dissolved in the calcined powder of tungsten bronze type oxide with the solvent. In addition, since the ceramic G can be sufficiently dense under a temperature condition lower than the above firing temperature by stirring with a planetary ball mill, it may be fired at a low firing temperature. .

  In this embodiment, since the core shell S is a ceramic G having a core-shell structure formed by adding the shell material M to the core material S and firing, the tungsten bronze type oxide is used as the core material S. A core-shell structure ceramic G in which the concentration of the component of the shell material M increases from the center of the core material S made of oxide toward the surface portion, and the variation in the relative dielectric constant even under a temperature condition of 150 ° C. or higher. Ferroelectric ceramics G having stable high-temperature characteristics that can be maintained within ± 15% can be obtained, and can be used for on-vehicle and aerospace capacitor materials that require high-temperature characteristics.

In this case, since the tungsten bronze type oxide is KSr ₂ Nb ₅ O ₁₅ , stable high-temperature characteristics capable of maintaining variation in relative dielectric constant within ± 15% even in a wide temperature range up to 195 ° C. Can be obtained.

Further, in this case, since the shell material M is ZrO ₂ , the shell material M is dissolved in the core material S by diffusion of ions so that the shell material M is relaxed, and the core material S is made of tungsten bronze oxide. The core-shell structure ferroelectric ceramic G can be obtained at low cost.

That is, the relative permittivity is the maximum as shown in the relative permittivity temperature characteristic diagram shown by KSr ₂ Nb ₅ O ₁₅ under the condition of frequency 10 kHz, where the horizontal axis shown in FIG. 3 is temperature (° C.) and the vertical axis is the relative permittivity. The relative dielectric constant increases with increasing temperature at a temperature below freezing point. The relative dielectric constant reaches about 1,500-15% at about -55 ° C, and the relative dielectric constant is about 0 ° C. The value of the dielectric constant does not change stably until the temperature reaches about 150 ° C., and the relative dielectric constant tends to decrease from the time when the temperature exceeds 150 ° C., and the relative dielectric constant becomes about 195 ° C. Below 1,500-15%.

  3 to obtain a ferroelectric ceramic G having a stable high temperature range characteristic in which variation in relative permittivity can be maintained within ± 15% even under a temperature condition of 150 ° C. or higher. Was confirmed.

In this case, as a form other exemplary, instead of the _KSr 2 _Nb 5 _{O 15} as the tungsten bronze-type oxide in the form the _examples, or using KBa ₂ Nb _{5 O 15,} or, NABA ₂ or with Nb ₅ O _{15, or} sometimes or using _{NaSr 2-X Ca X Nb 5} O 15.

In these three other embodiments, the tungsten bronze type oxide is KBa ₂ Nb ₅ O ₁₅ , so that even under a temperature condition of 150 ° C. or higher up to the Curie temperature of KBa ₂ Nb ₅ O ₁₅ , Ferroelectric ceramics G having stable high-temperature characteristics that can maintain a variation in relative dielectric constant within ± 15% can be obtained, and the tungsten bronze oxide is NaBa ₂ Nb ₅ O _15. Thus, a ferroelectric ceramic G having a stable high temperature characteristic that can maintain a variation in relative dielectric constant within ± 15% even under a temperature condition of 150 ° C. or higher up to the Curie temperature of NaBa ₂ Nb ₅ O ₁₅ is obtained. In addition, when the tungsten bronze type oxide is NaSr _2-X Ca _X Nb ₅ O ₁₅ , Na Ferroelectric ceramics with stable high temperature characteristics that can maintain a variation in relative dielectric constant within ± 15% even under temperature conditions of 150 ° C. or higher up to the Curie temperature of Sr _{2 -X} Ca _X Nb ₅ O ₁₅ G can be obtained.

  Note that the present invention is not limited to the above-described embodiment, and the production conditions are appropriately changed depending on the contents of the core material S and the shell material M.

  As described above, the intended purpose can be sufficiently achieved.

S Core material G Ceramics M Shell material

Claims (3)

A was added to the shell material in the core substrate fabrication method of ceramics fired to become core-shell structure, the core material is Ri tungsten bronze-type oxide der, the tungsten bronze-type oxide in KSr ₂ Nb ₅ O ₁₅ There, a method for manufacturing a ferroelectric ceramic, wherein said shell material is ZrO _2. A was added to the shell material in the core substrate fabrication method of ceramics fired to become core-shell structure, the core material is Ri tungsten bronze-type oxide der, the tungsten bronze-type oxide in KBa ₂ Nb ₅ O ₁₅ There, a method for manufacturing a ferroelectric ceramic, wherein said shell material is ZrO _2. A was added to the shell material in the core substrate fabrication method of ceramics fired to become core-shell structure, the core material is Ri tungsten bronze-type oxide der, the tungsten bronze-type oxide in NaBa ₂ Nb ₅ O ₁₅ There, a method for manufacturing a ferroelectric ceramic, wherein said shell material is ZrO _2.