JP6970702B2 - Method for manufacturing ferroelectric ceramics - Google Patents

Description

The present invention relates to a method for manufacturing a ferroelectric ceramic used for a capacitor which is supposed to be used in a harsh environment such as an in-vehicle use or an aerospace use.

Conventionally, as this kind of strong dielectric ceramics, as shown in FIGS. 7 and 8, in a strong dielectric ceramic having a core-shell structure in which a shell material is added to a core material and fired, BaTIO ₃ (barium titanate) is used as the core material. ), For example, ZrO ₂ (zirconium dioxide) is used as the shell material, and those produced by adding a small amount of ZrO _{2 to this BaTiO 3} powder and firing it are known (Non-Patent Document 1). ..

That is, by adding a small amount of the above ZrO _{2 to the BaTiO 3} powder and firing it, the zirconium component diffuses from the periphery of the _{BaTiO 3} , and the phase given by _{BaTi 1-x} Zr _x O ₃ is formed around the _{BaTiO 3 particles.} Then, as shown in FIG. 7, a ferroelectric ceramic G having a core-shell structure _{having BaTiO 3} particles as a core and BaTi _1-x Zr _x O _{3 as a shell is produced.}

Here, in the chemical composition of the ferroelectric ceramics, the closer to the surface, the _{higher the variable x in BaTi 1-x} Zr _x O ₃ , that is, the higher the concentration of the Zr component, and the closer to the center, the more pure BaTIO ₃ . It will be in a close state.

On the other hand, _{a strong dielectric ceramic having a core-shell structure having BaTiO 3} particles as a core and BaTi _1-x Zr _x O ₃ as a shell is also known as a relaxer dielectric, and such a relaxer dielectric has. , together show a having a broad peak dielectric constant-temperature characteristics, has characteristics that change continuously peak position in accordance with changes in the chemical composition BaTi _1-x Zr _x O ₃ in variable x, relative dielectric constant Since the maximum temperature in the temperature characteristics is determined by the curry temperature of the core material, the relative permittivity fluctuation is 25 ° C in the temperature range from a low temperature of about -55 ° C to about 125 ° C, which is slightly higher than the curry temperature of the core material. dielectric constant stable high temperature range characteristics are known to be obtained can be maintained within 15% ± to as reference, also additional oxide also by various oxides not limited to ZrO ₂ and combining them, the Relative permittivity temperature characteristics have been established as the EIA X7R standard and have been commercialized.

After that, with the aim of further expanding the stable high-temperature region characteristics, as shown in FIGS. 7 and 8, in the ferroelectric ceramics having a core-shell structure obtained by adding a shell material to the core material and firing it, as described in Patent Document 1. In addition, we invented a ferroelectric ceramic composed of _{KSr 2} Nb ₅ O ₁₅ (potassium niobate), which has a higher Curie temperature than _{BaTiO 3,} as the core material, and _{ZrO 2 (zirconium dioxide) as the shell material.}

That is, by adding a small amount of ZrO _{2 to the KSr 2} Nb ₅ O ₁₅ powder and firing, the zirconium component diffuses from the periphery of _{KSr 2} Nb ₅ O _{15 and K 1-x} Sr _{2 + x} Nb _5-x Zr. given phase _x O ₁₅ is formed around the _KSr 2 _Nb 5 _{O 15} particles, as shown in FIG. _7, the core KSr ₂ Nb _{5 O 15 particles, K 1-x Sr 2 +} x Nb 5-x Zr x O A strong dielectric ceramics G having a core-shell structure having _{15 as a shell will be manufactured.}

Here, in the chemical composition of the ferroelectric ceramics G, the closer to the surface, the _{higher the variable x in K1-X} Sr _{2 + X} Nb _5-X Zr _x O ₁₅ , that is, the higher the concentration of the Zr component, and the center. The closer it is, the closer it becomes to _{pure KSr 2} Nb ₅ O _15.

The ferroelectric ceramics G having a core-shell structure having a core of _{KSr 2} Nb ₅ O ₁₅ particles _{and a shell of K 1-X} Sr _{2 + X} Nb _5-X Zr _x O _{15 is also known as a relaxer dielectric.} Such a relaxor dielectric exhibits a relative permittivity temperature characteristic having a wide peak, and peaks according to a change in the variable x in the _{chemical composition K 1-X} Sr _{2 + X} Nb _5-X Zr _x O _15. The position also has the characteristic of continuously changing, and the maximum temperature in the relative permittivity temperature characteristics is determined by the Curie temperature of the core material of 156 ° C. Flat temperature characteristics have been obtained in the temperature range up to 195 ° C.

The core-shell structure has typically meant a non-uniform structure in composition such that one core is wrapped in a shell in a single particle, but in recent years, other than such a structure has been used. For example, a structure in which one shell contains multiple cores in a single particle, a structure in which a shell having multiple layers wraps one core like an onion, or a shell in which a rod-shaped or wire-shaped core is not granular. The existence of various core-shell structures such as the one-dimensional structure surrounded by is summarized in Non-Patent Document 2, and the core-shell structure dealt with in the text also includes ceramics having nano-sized composition inhomogeneities of such components. It shall include.

Separately from the above, the relative permittivity temperature characteristics of the tungsten bronze ceramics of _{Sr 2} NaNb _5-x Ta _x O ₁₅ having a composition in which a part of Nb in _{Sr 2} NaNb ₅ O _{15 was replaced with Ta were examined, and the details are not described.} It is shown in Patent Document 3.

The raw material oxides SrCO ₃ , Na ₂ CO ₃ , Nb ₂ O ₅ and Ta ₂ O ₅ were weighed to a chemical quantitative ratio, sufficiently mixed using a planetary ball mill, and calcined at 1,150 ° C. for 7 hours. After confirming by X-ray diffraction that the obtained calcined product had no different phases other than the same window in the tungsten bronze single phase, the calcined product was again pulverized using a planetary ball mill. The obtained powder was pressure-molded into a disk shape and charged into an electric furnace in an oxygen atmosphere and fired at a temperature of 1,250 ° C to 1,350 ° C for 8 hours to prepare a ceramic sample.

By X-ray diffraction, the ceramic is a tungsten bronze single phase with good crystallinity, and its lattice constant changes almost linearly depending on the value of x of _{Sr 2} NaNb _5-x Ta _x O _{15 tungsten bronze.} Since it was found that the value of x was determined in a primary manner, it was shown that the obtained ceramics are uniform ceramics having no nano-sized composition non-uniformity such as core-shell structure.

Gold electrodes were formed on both sides of the ceramics by sputtering, connected to an LCR meter, and the relative permittivity at each frequency from 1 kHz to 1 MHz was evaluated in the temperature range of up to 400 ° C from the boiling point of liquid nitrogen. As described in Non-Patent Document 3, a wide relative permittivity peak that appears in a temperature range of approximately -100 ° C to 0 ° C and a wide relative permittivity that appears in a temperature range of approximately −150 ° C to 300 ° C. A generally flat relative permittivity temperature characteristic consisting of two peaks of rate peak was obtained.

The peak position of the relative permittivity peak _{has the characteristic of continuously transitioning to the low temperature side as the value of x in the chemical composition Sr 2} NaNb _5-x Ta _x O ₁₅ increases, and is characterized by a high temperature at, for example, composition x = 0. The highest point of the peak position appearing on the side is at _{273 ° C, which is considered to correspond to the Curie temperature of Sr 2} NaNb ₅ O ₁₅ , and at the composition x = 0.2, the peak position appearing on the low temperature side is approximately -150 ° C. Although it covers a wide temperature range such as some, the relative permittivity fluctuation is still large for each composition ceramic, and the relative permittivity is realized in the temperature range wider than -55 ° C to 195 ° C realized by _{KSr 2} Nb ₅ O _15. The rate fluctuation could not be suppressed within ± 15% on the basis of 25 ° C.

Patent No. 6267673

T. Armstrong, et al. "Dielectric Properties of Luxed Barium Titanate Ceramics with Zirconia Additions" Journal of the American Ceramic Society Vol. 73 pp. 700-706 (1990) Matias Acosta, et al. , "Core-Shell Lead-Free Piezoelectric Ceramics: Currant Status and Advanced characterization of the Bi1 / 2Na1 / 2TIO3-SrTIO3 System" 98 pp. 3405-3422 (2015) Hiroshi Iwai, Sakura Miyajima, Sasuke Ishimaru: "Relative Permittivity Temperature Characteristics of Sr2NaNb5-xTaxO15 Ceramics" 64th JSAP Spring Meeting (2017) 15p-P4-6 Lecture Proposal and Poster F. Lin, et al. "Microstructure Refinement of Sintered Alumina by a Two-Step Sintering Technology" Journal of the American Ceramic Society, Vol. 80 pp. 2269-2277 (1997)

In the case of conventional ferroelectric ceramics produced by adding a small amount of ZrO ₂ to the above KSr ₂ Nb ₅ O ₁₅ powder and firing, the temperature is 195 ° C. or higher as shown in the relative permittivity temperature characteristic shown in FIG. In this case, the relative permittivity is significantly reduced, and such conventional ferroelectric ceramics are used as a capacitor material for automobiles and aerospace at a temperature wider than the temperature range of -55 ° C to 195 ° C. It has the inconvenience that it may not be possible to meet stricter requirements, which require characteristics in the high temperature range where the fluctuation of the relative permittivity is within ± 15% in the range.

The present invention aims to solve such inconveniences, and the invention according to claim 1 is a method for producing a ferroelectric ceramic having a core-shell structure, which is obtained by adding a shell material to a core material and firing it in two steps. The core material is a tungsten bronze oxide, the tungsten bronze oxide is Sr ₂ NaNb ₅ O ₁₅ (strontium sodium niobate), and the shell material is Ta ₂ O ₅ (dipentoxide). Tantalum), _{KSr 2} Nb ₅ O _{15 core-shell structural ceramics to which ZrO 2} has been added, and barium titanate _{to which ZrO 2 and} others have already been put into practical use, an example of which is shown in Non-Patent Document 1. Similar to the development of the relative permittivity temperature characteristics of barium core-shell structure ceramics, the relative permittivity temperature characteristics _{that change depending on the composition x of Sr 2} NaNb _5-x Ta _x O ₁₅ composition x are summed up in the ceramics. In a wide temperature range slightly above 273 ° C, which is considered to correspond to the curry _{temperature of Sr 2 NaNb 5} O ₁₅ from −150 ° C in principle, for example, the flatness that can suppress the relative permittivity fluctuation within ± 15% based on 25 ° C. This is a method for manufacturing a ferroelectric ceramic that can have a relative permittivity temperature characteristic.

As described above, in the invention according to claim 1, the present invention is a method for producing a ferroelectric ceramic having a core-shell structure, which is obtained by adding a shell material to a core material and firing in two steps, wherein the shell material M is used. By solidly dissolving in the core material S by diffusion of ions, a ferroelectric ceramic having a core shell structure using the core material as a tungsten bronze type oxide can be obtained at low cost, and the core material is a tungsten bronze type oxide Sr. _{Since it is 2} NaNb ₅ O ₁₅ and the shell material is Ta ₂ O ₅ , its function is a temperature condition slightly higher than 273 ° C, which is considered to correspond to the curry _{temperature of Sr 2 NaNb 5} O _{15 from −150 ° C.} In this case, it is possible to obtain ferroelectric ceramics with stable high temperature range characteristics that can maintain the fluctuation of the relative permittivity within ± 15%, and it is a capacitor material for automobiles and aerospace that requires high temperature range characteristics. Etc. can be used.

It is a manufacturing process diagram of the embodiment of the present invention. It is an explanatory front sectional view of the embodiment of the present invention. It is a scanning electron micrograph of the embodiment of the present invention. The relative dielectric constant temperature characteristic diagram of the embodiment of the present invention. It is a scanning electron microscope image of the reference embodiment of the embodiment of the present invention. It is a relative permittivity temperature characteristic figure of the reference embodiment of the embodiment of this invention. It is explanatory drawing of the embodiment of the conventional product. It is a relative permittivity temperature characteristic diagram of the embodiment of the conventional product.

1 to 4 show examples of embodiments of the present invention, and FIGS. 5 and 6 are reference examples.

In the examples of the embodiments of FIGS. 1 to 4, a ferroelectric ceramic G having a core-shell structure is produced by adding a small amount of the shell material M to the core material S made of a tungsten bronze oxide and firing it.

_{In this case, Sr 2 NaNb 5} O ₁₅ (sodium niobate strontium) is used as the tungsten bronze type oxide, and _{Ta 2} O ₅ (ditantalum pentoxide) is used as the shell material M.

In this case, in the production of the ferroelectric ceramics G, as shown in FIG. 1, first, as the raw material of the tungsten bronze type oxide, the raw material oxides Na ₂ CO ₃ , SrCO ₃ and Nb ₂ O ₅ are weighed by the chemical quantitative ratio. Then, these raw materials are mixed for 24 hours using a planetary ball mill and calcined at 1,150 ° C. for 8 hours to prepare a tungsten bronze type oxide as the core material S.

Then, it is confirmed by the X-ray diffraction method that the prepared calcined powder of the tungsten bronze type oxide is Sr ₂ NaNb ₅ O _{15 single phase.}

_{Next, Ta 2} O ₅ as the shell material M was directly added to the calcined powder of the tungsten bronze type oxide as the core material S, and the mixture was sufficiently stirred using, for example, a planetary ball mill, and the resulting mixture was obtained. The powder is pressurized at a pressure of about 196 MPa to form pellets, and the pellets are put into a heating furnace and held at a temperature of 1,300 ° C. for about 1 to 3 minutes in an oxygen atmosphere in the heating furnace. , Cooled to 200 ° C. and fired at the same temperature for 8 hours by a two-step firing method, which causes _{ion diffusion from Ta 2} O ₅ , and as shown in FIG. 2, the above tungsten bronze type oxide is used as a core. Then, a strong dielectric ceramic G having a core-shell structure having _{Sr 2} NaNb _{5-x T x} O _{15 as a shell will be produced.}

As described in Non-Patent Document 4, for example, the two-step firing method can produce dense ceramics even under conditions of a lower firing temperature than a normal firing method, and at the same time, grains produced in the final stage of sintering. It is also known to be able to curb growth.

When the grain growth in the final stage of sintering is remarkable, as shown in Non-Patent Document 1, the diffusion of the components between the core and the shell accompanying the grain growth is promoted, and as a result, the core-shell structure is lost and uniform chemistry. becomes the ceramic composition, core-shell structure specific dielectric constant temperature characteristic is lost, the ceramics, for example, _{Sr 2 NaNb 5-x Ta x} O 15 Sr 2 NaNb 5-x Ta x O 15 rather than that of when the core-shell structure of the composition Relative permittivity temperature characteristics of uniform composition are exhibited, and as mentioned above, the relative permittivity fluctuation is ± 15% based on 25 ° C. in the temperature range from -55 ° C to 195 ° C realized by _{KSr 2} Nb ₅ O _15. Although it cannot be suppressed to the inside, this problem can be easily solved by performing two-step firing as compared with normal one-step firing.

In the ferroelectric ceramics G thus produced, the surface thereof was a scanning electron microscope image shown in FIG.

Gold electrodes are formed on both sides of the ceramics by sputtering, and the relative permittivity at a frequency of 1 kHz is fixed in a sample table with a heating device in the temperature range from the liquid nitrogen temperature to a maximum of 250 ° C using an LCR meter, and liquid nitrogen is used. Relative permittivity was measured while cooling, and in the temperature range from room temperature to a maximum of 450 ° C., the sample was fixed on a sample fixing table installed in a heating furnace in the atmosphere, and the relative permittivity was measured for each.

As a result, the horizontal axis shown in FIG. 4 is the temperature (° C), the vertical axis is the relative permittivity, and the relative permittivity shows a maximum of about 1,578 as shown in the relative permittivity temperature characteristic diagram shown under the condition of a frequency of 1 kHz. The relative permittivity becomes about 1,531 at a temperature of 25 ° C, and after showing a minimum of 1,316 at a temperature of 150 ° C, the value of the relative permittivity stabilizes up to a temperature of about 200 ° C, and from the time when the temperature exceeds 230 ° C. The relative permittivity showed a slight increase again and then showed a decreasing tendency.

Below the freezing point, the relative permittivity rises with increasing temperature, reaching 1,301 at about -70 ° C, which corresponds to a 15% decrease in the relative permittivity of 1,531 at a temperature of 25 ° C, and at a temperature of 252 ° C, the temperature is also 25 ° C. After showing 1,301, which corresponds to a 15% decrease in the relative permittivity of 1,531, it shows a decrease in the relative permittivity as the temperature rises, while conversely, it increases by 15% in the relative permittivity of 1,531 at a temperature of 25 ° C. The corresponding 1,760 did not reach the entire temperature range of -70 ° C to 252 ° C, and as a result, this dielectric has a relative permittivity reference with a relative permittivity variation of + 25 ° C over a wide temperature range of -70 ° C to 252 ° C. It was confirmed that it was within ± 15%.

In this embodiment , as shown in FIGS. 1 and 2, a method for producing a ferroelectric ceramic G having a core-shell structure, which is obtained by adding a shell material M to a core material S and firing in two stages, is a method of producing a shell. By dissolving the material M in the core material S by diffusion of ions, a ferroelectric ceramic G having a core shell structure in which the core material S is a tungsten bronze type oxide can be obtained at low cost, and the core material S can be obtained at low cost. Is a tungsten bronze type oxide Sr ₂ NaNb ₅ O ₁₅ , and the shell material M is Ta ₂ O ₅ , so that the component concentration of the shell material M increases from the center to the surface of the core material S. As a result of producing the ferroelectric ceramics G having a structure, the tungsten bronze type oxide is Sr ₂ NaNb ₅ O ₁₅ as its function. Therefore, in principle, even in a wide temperature range slightly higher than −150 ° C. to 273 ° C. It is possible to obtain the ferroelectric ceramics G having stable high temperature region characteristics in which the fluctuation of the relative permittivity can be maintained within ± 15%.

In the actually obtained embodiment , even under the temperature condition from −70 ° C. to 254 ° C., the variation with respect to the relative permittivity of 25 ° C. can be maintained within ± 15%. Dielectric ceramics G can be obtained, and as a result, the relative permittivity fluctuates even in a temperature range wider than the temperature range from -55 ° C to 195 ° C realized by the _{ZrO 2} added KSr ₂ Nb ₅ O _{15 core shell structure.} It is possible to obtain a ferroelectric ceramic G having stable high temperature region characteristics that can be maintained within ± 15%, and it can be used as a capacitor material for automobiles and aerospace where high temperature region characteristics are required.

5, FIG. 6 is a reference embodiment, similarly to the embodiment of the above embodiment, FIG. 1, as shown in FIG. 2, a tungsten bronze-type oxide as the core material S _Sr 2 NaNb ₅ O _15, the The shell material M is Ta ₂ O ₅ , and the shell material M is added to the core material S, put into a heating furnace at 1,250 ° C., and fired in an oxygen atmosphere in the heating furnace for 8 hours. As shown in FIG. 2, the one-step firing method produces a ferroelectric ceramic G having a core-shell structure in which the component concentration of the shell material M increases from the center to the surface of the core material S made of a tungsten bronze-type oxide. It will be.

In the ferroelectric ceramics G thus prepared, the surface thereof was a scanning electron microscope image shown in FIG.

Gold electrodes are formed on both sides of the ceramics by sputtering, and the relative permittivity at a frequency of 1 kHz is fixed in a sample table with a heating device in the temperature range from the liquid nitrogen temperature to a maximum of 250 ° C using an LCR meter, and liquid nitrogen is used. Relative permittivity was measured while cooling, and in the temperature range from room temperature to a maximum of 450 ° C., the sample was fixed on a sample fixing table installed in a heating furnace in the atmosphere, and the relative permittivity was measured for each.

As a result, the horizontal axis shown in FIG. 6 is the temperature (° C.) and the vertical axis is the relative permittivity. The relative permittivity becomes 1,216 at a temperature of 25 ° C, and after showing a minimum of 1,041 at a temperature of 130 ° C, the value of the relative permittivity does not change stably until the temperature is about 200 ° C, and exceeds the temperature of 220 ° C. From around that time, the relative permittivity rose a little and then showed a downward trend.

Below the freezing point, the relative permittivity rises as the temperature rises, reaching about 1,034, which corresponds to a 15% decrease in the relative permittivity of 1,216 at a temperature of 25 ° C at about -65 ° C, and the same temperature 25 at a temperature of 263 ° C. After showing 1,034, which corresponds to a 15% decrease in the relative permittivity of 1,216 at ° C, the relative permittivity decreases as the temperature rises, while conversely, 15% of the relative permittivity 1,216 at a temperature of 25 ° C. The increase of 1,398 was not reached over the entire temperature range of -65 ° C to 263 ° C, resulting in a relative permittivity variation of +25 over a wide temperature range of -65 ° C to 263 ° C. It was confirmed that it was within ± 15% based on the relative permittivity at ° C.

In the relative permittivity temperature characteristic diagram of FIG. 6, a discontinuous change in the relative permittivity is observed at about 50 ° C., which means that the sample is fixed on a sample table with a heating device from the liquid nitrogen temperature to 50 ° C. Relative permittivity was measured while cooling with liquid nitrogen, whereas in the temperature range of 50 ° C or higher, the sample was fixed on a sample fixing table installed in a heating furnace and the relative permittivity was measured. It was caused as an error due to a change in the floating permittivity, etc. Without this error, the fluctuation in the relative permittivity would be rather small, but it would not affect the overall conclusion.

The reference embodiment is a method for producing a ferroelectric ceramic G having a core-shell structure, which is obtained by adding a shell material M to a core material S and firing it in one step, as in the above-described embodiment. Since the core material S is a tungsten bronze type oxide Sr ₂ NaNb ₅ O ₁₅ and the shell material M is Ta ₂ O ₅ , the shell material M dissolves in the core material S by the diffusion of ions to form a core. A ferroelectric ceramic G having a core-shell structure using the material S as a tungsten bronze-type oxide can be obtained at low cost, and as its function, the tungsten bronze-type oxide is Sr ₂ NaNb ₅ O ₁₅ , in principle. Can obtain ferroelectric ceramics G having stable high temperature range characteristics in which the fluctuation of the relative permittivity can be maintained within ± 15% even in a wide temperature range slightly higher than −150 ° C. to 273 ° C.

As shown in FIG. 6, even in the actually obtained reference embodiment , the fluctuation with respect to the relative permittivity of 25 ° C. can be maintained within ± 15% under the temperature conditions from −65 ° C. to 263 ° C. and is stable. it is possible to obtain a ferroelectric ceramics G having a high temperature region characteristics, it can be used for a capacitor material or the like for automotive and aerospace high-temperature zone properties are required, ZrO ₂ added KSr a conventional example of FIG. 8 Strong with stable high temperature characteristics that the fluctuation of the relative permittivity can be maintained within ± 15% even in a temperature range wider than the temperature range from -55 ° C to 195 ° C realized by the ₂ Nb ₅ O _{15 core shell structure.} Dielectric ceramics G can be obtained, and can be used as a capacitor material for automobiles and aerospace where high temperature region characteristics are required.

The one-step firing method as the heat treatment form adopted in the reference form example has fewer firing parameters and is easier to operate than the two-step firing method, but the continuous firing temperature is relatively high, so that the grains are grains. Although it has the drawback of being prone to growth and leading to the destruction of the core-shell structure, sufficiently stable relative permittivity temperature characteristics can be obtained as shown in this example if the firing parameters are properly selected.

_{When adding Ta 2} O ₅ as the shell material M to the tantalum bronze-type oxide calcined powder as the core material S, Ta ₂ O ₅ powder was added to both the above-described embodiment and the reference embodiment. The liquid phase method described below, that is, tantalum pentapropoxide and other soluble compounds of tantalum, are dissolved in a solvent such as ethanol or isopropyl alcohol, and tungsten bronze is contained in the solution. _{A calcined powder of Sr 2} NaNb ₅ O ₁₅ as a mold oxide is added, the above tantalum compound is applied to the surface of the powder particles, and then the tantalum compound is heated in the air at 600 ° C. or higher for about 10 to 30 minutes. _May form a layer _{of Ta 2} O 5 as the shell material M on the surface of the particles.

This powder is pressurized at a pressure of about 196 MPa to make pellets, and the pellets are put into a heating furnace having a furnace temperature of 1,200 ° C to 1,300 ° C as the firing temperature, and in an oxygen atmosphere in the heating furnace 7 It is kept for a long time or fired according to other predetermined heat treatment conditions, which causes _{ion diffusion from Ta 2} O ₅ , and as shown in FIG. 2, the above tungsten bronze type oxide is used as a core, and Sr ₂ NaNb _5-X Ta. A strong dielectric ceramic G having a core-shell structure having _x O _{15 as a shell can be obtained.}

The present invention is not limited to the above embodiment, and is designed by appropriately changing the manufacturing conditions of the ferroelectric ceramics G 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 ferroelectric ceramics M shell material

Claims (1)

A method for producing a ferroelectric ceramic having a core-shell structure in which a shell material is added to a core material and fired in two stages . The core material is a tungsten bronze-type oxide, and the tungsten bronze-type oxide is Sr ₂ NaNb. _A method for producing a ferroelectric ceramic, which is 5 O ₁₅ and the shell material is Ta ₂ O _5.

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