阅读说明：本技术 铁酸铋-钛酸钡基压电陶瓷的制备方法 (Preparation method of bismuth ferrite-barium titanate-based piezoelectric ceramic ) 是由 黄荣厦 张艺 杜祖超 戴叶婧 林华泰 于 2021-08-27 设计创作，主要内容包括：本发明公开了一种铁酸铋-钛酸钡基压电陶瓷的制备方法,其包括：(1)将氧化铋、氧化铁、钛酸钡、掺杂剂按照(0.3～0.4)：(0.3～0.37)：(0.2～0.35)：(0.002～0.003)的摩尔比混合,得到混合物；(2)将所述混合物球磨,得到浆料；(3)将所述浆料造粒,得到第一粉料；(4)将所述第一粉料成型,得到生坯；(5)将所述生坯埋入第二粉料,然后烧制,得到铁酸铋-钛酸钡基压电陶瓷成品；其中,所述第二粉料选用氧化锆和/或氧化铌,所述第二粉料的粒径为0.001～2mm。实施本发明,可有效提升铁酸铋-钛酸钡基压电陶瓷的压电性能。(The invention discloses a preparation method of bismuth ferrite-barium titanate-based piezoelectric ceramic, which comprises the following steps: (1) mixing bismuth oxide, ferric oxide, barium titanate and a dopant according to the ratio of (0.3-0.4): (0.3-0.37): (0.2-0.35): (0.002-0.003) to obtain a mixture; (2) ball-milling the mixture to obtain slurry; (3) granulating the slurry to obtain a first powder material; (4) molding the first powder to obtain a green body; (5) embedding the green body into second powder, and then firing to obtain a bismuth ferrite-barium titanate-based piezoelectric ceramic finished product; wherein the second powder material is selected from zirconium oxide and/or niobium oxide, and the particle size of the second powder material is 0.001-2 mm. By implementing the invention, the piezoelectric performance of the bismuth ferrite-barium titanate-based piezoelectric ceramic can be effectively improved.)

1. A preparation method of bismuth ferrite-barium titanate-based piezoelectric ceramic is characterized by comprising the following steps:

(1) mixing bismuth oxide, ferric oxide, barium titanate and a dopant according to the ratio of (0.3-0.4): (0.3-0.37): (0.2-0.35): (0.002-0.003) to obtain a mixture;

(2) ball-milling the mixture to obtain slurry;

(3) granulating the slurry to obtain a first powder material;

(4) molding the first powder to obtain a green body;

(5) embedding the green body into second powder, and then firing to obtain a bismuth ferrite-barium titanate-based piezoelectric ceramic finished product;

wherein the second powder material is selected from zirconium oxide and/or niobium oxide, and the particle size of the second powder material is 0.001-2 mm.

2. The method of preparing a bismuth ferrite-barium titanate-based piezoelectric ceramic according to claim 1, wherein said second powder material is zirconia.

3. The method of preparing a bismuth ferrite-barium titanate-based piezoelectric ceramic according to claim 2, wherein the particle size of the zirconia is 0.4 to 1 mm.

4. The method for preparing a bismuth ferrite-barium titanate-based piezoelectric ceramic according to claim 1, wherein the molar ratio of bismuth oxide to iron oxide is (1.01 to 1.05): 1.

5. the method of claim 1, wherein the dopant is MnO₂、La₂O₃、Li₂O、Ga₂O₃One or more of (a).

6. The method for preparing a bismuth ferrite-barium titanate-based piezoelectric ceramic according to claim 1 or 5, wherein MnO is selected as the dopant₂。

7. The method for preparing a bismuth ferrite-barium titanate-based piezoelectric ceramic according to claim 1, wherein in the step (2), the mixture is mixed with a dispersant and ball-milled using zirconia balls as a milling medium;

wherein the dispersant is water and/or ethanol, and the weight ratio of the mixture to the dispersant is 1: (1.2-1.5).

8. The method of preparing a bismuth ferrite-barium titanate-based piezoelectric ceramic according to claim 7, wherein in the step (3), the slurry is heated, and the dispersant is removed by evaporation to obtain a third powder; then adding a binder for granulation;

wherein, the binder is PVA and/or PVB, and the weight ratio of the third powder to the binder is 1: (0.01-0.05).

9. The method of preparing a bismuth ferrite-barium titanate-based piezoelectric ceramic according to claim 1, wherein the step (5) comprises:

(5.1) placing the green body into a crucible and burying the green body with a second powder material;

(5.2) heating the crucible filled with the green body and the second powder to 950-1100 ℃ at the heating rate of 3-10 ℃/min, then preserving the heat at 950-1100 ℃ for 1-3 h, and cooling to obtain the finished product of the bismuth ferrite-barium titanate-based piezoelectric ceramic.

10. A bismuth ferrite-barium titanate-based piezoelectric ceramic, characterized by being prepared by the preparation method according to any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of piezoelectric ceramics, in particular to a preparation method of bismuth ferrite-barium titanate-based piezoelectric ceramics.

Background

With the rapid development of economy and science and technology, people have higher and higher requirements on materials applied to electronic components, and piezoelectric ceramics are widely applied to the fields of mobile communication, aerospace and the like due to the characteristics of high power density, long service life, wide use temperature range, good safety performance and the like. At present, Pb (Zr, Ti) O₃(PZT) -based ceramics having higher Curie temperature (T) due to their excellent dielectric and piezoelectric properties_cApproximately 360 ℃) occupies the main market of high-temperature piezoelectric ceramics for a long time, but with the concept of green development and environmental protection, and the traditional PZT-based piezoelectric ceramics can not work safely in high-temperature environment, the lead-free piezoelectric ceramics get more and more extensive attention and research in the field of piezoelectric ceramics, wherein the bismuth ferrite-barium titanate-based piezoelectric ceramics become one of the lead-free piezoelectric ceramics with the most potential in the future due to the high Curie temperature and excellent piezoelectric performance.

Bi also exists in the common bismuth ferrite-barium titanate-based piezoelectric ceramics³⁺The ions are volatile, and Fe ions are easily valence-changed (Fe)³⁺→Fe²⁺) The piezoelectric performance is still different from that of lead-containing piezoelectric ceramics, so that the main research direction at present is to improve the piezoelectric performance, reduce the loss, improve the stability and the like on the basis of keeping the performance advantage of the bismuth ferrite-barium titanate-based piezoelectric ceramics that can work in a high-temperature environment.

In addition, the bismuth ferrite-barium titanate based piezoelectric ceramics are all prepared by antimony oxide, bismuth oxide, barium carbonate and titanium oxide, and the barium carbonate is decomposed at high temperature to influence the yield, so the bismuth ferrite-barium titanate based piezoelectric ceramics are often prepared by adopting the processes of two-step roasting and two-time ball milling. However, two-step firing tends to easily cause Bi³⁺The loss is increased. Researchers also adopt a process of ball milling once and roasting once to prepare the bismuth ferrite-barium titanate-based piezoelectric ceramic, but the bismuth ferrite-barium titanate-based piezoelectric ceramic can face the problems of greatly reduced yield and lower piezoelectric performance.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a preparation method of bismuth ferrite-barium titanate-based piezoelectric ceramic, which can effectively shorten the process flow, improve the production efficiency and simultaneously ensure the yield and the piezoelectric performance of the finished product.

The invention also aims to solve the technical problem of providing the bismuth ferrite-barium titanate-based piezoelectric ceramic.

In order to solve the technical problem, the invention provides a preparation method of bismuth ferrite-barium titanate-based piezoelectric ceramic, which comprises the following steps:

(1) mixing bismuth oxide, ferric oxide, barium titanate and a dopant according to the ratio of (0.3-0.4): (0.3-0.37): (0.2-0.35): (0.002-0.003) to obtain a mixture;

(2) ball-milling the mixture to obtain slurry;

(3) granulating the slurry to obtain a first powder material;

(4) molding the first powder to obtain a green body;

(5) embedding the green body into second powder, and then firing to obtain a bismuth ferrite-barium titanate-based piezoelectric ceramic finished product;

wherein the second powder material is selected from zirconium oxide and/or niobium oxide, and the particle size of the second powder material is 0.001-2 mm.

As an improvement of the technical scheme, the second powder is zirconia.

As an improvement of the technical scheme, the particle size of the zirconia is 0.4-1 mm.

As an improvement of the technical scheme, the molar ratio of the bismuth oxide to the ferric oxide is (1.01-1.05): 1.

as an improvement of the technical proposal, MnO is selected as the dopant₂、La₂O₃、Li₂O、Ga₂O₃One or more of (a).

As an improvement of the technical scheme, MnO is selected as the dopant₂。

As an improvement of the above technical scheme, in the step (2), the mixture is mixed with a dispersant, and zirconia balls are used as grinding media for ball milling;

wherein the dispersant is water and/or ethanol, and the weight ratio of the mixture to the dispersant is 1: (1.2-1.5).

As an improvement of the technical scheme, in the step (3), the slurry is heated, and the dispersant is removed by evaporation to obtain a third powder material; then adding a binder for granulation;

wherein, the binder is PVA and/or PVB, and the weight ratio of the third powder to the binder is 1: (0.01-0.05).

As an improvement of the technical scheme, the step (5) comprises the following steps:

(5.1) placing the green body into a crucible and burying the green body with a second powder material;

(5.2) heating the crucible filled with the green body and the second powder to 950-1100 ℃ at the heating rate of 3-10 ℃/min, then preserving the heat at 950-1100 ℃ for 1-3 h, and cooling to obtain the finished product of the bismuth ferrite-barium titanate-based piezoelectric ceramic.

Correspondingly, the invention also discloses bismuth ferrite-barium titanate-based piezoelectric ceramic which is prepared by adopting the preparation method.

The implementation of the invention has the following beneficial effects:

(1) the bismuth ferrite-barium titanate-based piezoelectric ceramic is prepared by taking bismuth oxide, iron oxide, barium titanate and a doping agent as raw materials, and only one-time ball milling and one-time firing are carried out, so that the process flow is greatly shortened, and the production efficiency is improved.

(2) The preparation method of the bismuth ferrite-barium titanate-based piezoelectric ceramic adopts a powder embedding sintering process to embed the green body into the zirconia and/or niobium oxide powder for firing, and the process not only greatly improves the yield, but also ensures that the finished piezoelectric ceramic has excellent piezoelectric performance.

Drawings

FIG. 1 is a graph showing dielectric constants of samples of bismuth ferrite-barium titanate-based piezoelectric ceramics according to examples 1 to 3 and comparative examples 1 to 3 of the present invention;

FIG. 2 is a graph showing dielectric loss of samples of bismuth ferrite-barium titanate-based piezoelectric ceramics according to examples 1 to 3 of the present invention and comparative examples 1 to 3.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and detailed description.

The invention provides a preparation method of bismuth ferrite-barium titanate-based piezoelectric ceramic, which comprises the following steps:

s1: mixing bismuth oxide, ferric oxide, barium titanate and a dopant according to the ratio of (0.3-0.4): (0.3-0.37): (0.2-0.35): (0.002-0.003) to obtain a mixture;

the bismuth ferrite-barium titanate-based piezoelectric ceramic is prepared by taking bismuth oxide, ferric oxide and barium titanate as main raw materials, and the raw materials do not generate a large amount of gas in the high-temperature firing process, so that a good foundation is laid for adopting a one-step sintering process, and the firing yield is effectively improved.

Wherein the molar ratio of bismuth oxide to ferric oxide is (0.3-0.4): (0.3-0.37), exemplary is 0.31: 0.3,0.32:0.31,0.35:0.35,0.36: 0.352 or 0.37:0.365, but is not limited thereto. Preferably, the molar ratio of bismuth oxide to iron oxide is (1.01-1.05): 1, Bi can be reduced by maintaining a slight excess of bismuth oxide³⁺The piezoelectric performance is adversely affected by the loss of the firing process. More preferably, the molar ratio of bismuth oxide to iron oxide is (1.015 to 1.025): 1.

wherein the molar ratio of bismuth oxide to ferric oxide to barium titanate is (0.3-0.4): (0.3-0.37): (0.2-0.35). Further, (bismuth oxide + iron oxide): barium titanate ═ (0.65 to 0.72): (0.28 to 0.32) (molar ratio). By controlling the ratio of the three, a piezoelectric ceramic with sufficient solid solution can be formed.

The doping agent is a metal oxide which can be dissolved in the bismuth ferrite-barium titanate-based piezoelectric ceramic structure after sintering, and can improve the piezoelectric performance. Specifically, in the present invention, MnO may be used as the dopant₂、La₂O₃、Li₂O、Ga₂O₃But is not limited thereto. Preferably, the dopant is MnO₂It can inhibit valence change of Fe by reducing generation of oxygen vacancy, thereby effectively improving ferroelectric and piezoelectric properties.

Specifically, the molar ratio of the dopant to the iron oxide is (0.3-0.37): (0.002-0.003), exemplary are 0.31: 0.002, 0.33:0.0025, 0.35:0.0022, 0.36:0.0025, but not limited thereto.

S2: ball-milling the mixture to obtain slurry;

specifically, the mixture is mixed with a dispersant, and ball milling is carried out by taking zirconia balls as grinding media. Wherein, the dispersant can be selected from water or ethanol, and preferably, absolute ethanol is selected. The weight ratio of the mixture to the dispersant is 1: (1.2-1.5); illustratively, the weight ratio of the mixture to the dispersant is 1:1.2, 1:1.3, 1:1.4, or 1:1.5, but is not limited thereto.

S3: granulating the slurry to obtain a first powder material;

among them, granulation can be performed by spray drying, wheel milling after partial drying, humidification granulation after complete drying, and the like, but is not limited thereto. Preferably, in one embodiment of the present invention, the following process is used for granulation:

heating the slurry, and evaporating to remove the dispersant to obtain third powder; and then, sieving the third powder with a 60-100-mesh sieve, and then adding a binder for granulation.

Wherein the binder is PVA and/or PVB, and the dosage of the binder is 1-5% of the weight of the third powder. Furthermore, the binder is added in the form of a solution, and the concentration of the binder solution is 5-10 wt%.

S4: molding the first powder to obtain a green body;

the molding process may be, but is not limited to, dry pressing or isostatic pressing. Preferably, the biscuit is formed by dry pressing, and then isostatic pressing is carried out, wherein the pressure of the dry pressing is 20-40 MPa, and the pressure of the isostatic pressing is 100-300 MPa.

S5: embedding the green body into second powder, and then firing to obtain a bismuth ferrite-barium titanate-based piezoelectric ceramic finished product;

specifically, S5 includes:

s51: placing the green body into a crucible, and burying the green body with second powder;

specifically, the second powder material is zirconium oxide and/or niobium oxide, and the powder materials of the two materials are adopted for burning in a burying way, so that the piezoelectric property can be effectively improved, and the yield can be improved. Preferably, the second powder is made of zirconium oxide, and the zirconium oxide is buried and burned, so that the dielectric loss can be effectively reduced.

Specifically, the particle diameter (average particle diameter D50) of the second powder is 1 μm to 2mm, and exemplary ones are 5 μm, 20 μm, 100 μm, 0.4mm, 0.5mm, 0.6mm, 1.2mm or 1.8mm, but not limited thereto. Preferably, the particle size of the second powder is 0.4-0.6 mm. The second powder with the particle size is used for burning in a burying way, so that high yield, high voltage performance and low dielectric loss can be considered.

S52: and firing and cooling the crucible filled with the green body and the second powder to obtain the finished product of the bismuth ferrite-barium titanate-based piezoelectric ceramic.

Wherein, the heating rate in the firing process is 3-10 ℃/min, illustratively 4 ℃/min, 5 ℃/min, 6.5 ℃/min, 7 ℃/min or 8 ℃/min, but not limited thereto.

The firing temperature (i.e., the maximum firing temperature) is 950 to 1100 ℃, and 980 ℃, 1020 ℃, 1040 ℃, 1050 ℃, 1080 ℃, or 1090 ℃ is exemplified, but not limited thereto.

The heat preservation time at the sintering temperature is 1-3 h. And cooling along with the sintering furnace after heat preservation is finished.

Correspondingly, the invention also discloses bismuth ferrite-barium titanate-based piezoelectric ceramic which is prepared by adopting the method. Piezoelectric constant d of bismuth ferrite-barium titanate-based piezoelectric ceramic in the invention₃₃＞180pC/N。

The invention is further illustrated by the following specific examples:

example 1

17.2717g of bismuth oxide powder (D50 ═ 20 μm), 5.8031g of iron sesquioxide powder (D50 ═ 30 μm), 7.2637g of nano barium titanate powder (D50 ═ 300nm) and 0.0227g of manganese dioxide powder (D50 ═ 80 μm) were mixed, 40g of absolute ethanol was added as a solvent, and ball-milled for 4 hours. And then heating and evaporating the ball-milled slurry to remove the absolute ethyl alcohol. Sieving with 80 mesh sieve, adding 10g of mixed powder into 6ml of 8% PVB for granulation, placing the granulated powder in a mold, dry-pressing at 30MPa to form a biscuit, and then carrying out cold isostatic pressing at 200 MPa. The obtained product is used as raw materialThe blank is made of niobium oxide powder (D50 ═ 15 mu m, Nb)₂O₅) And (3) placing the wrapped and embedded powder in a muffle furnace, heating to 1030 ℃ for 4 hours, preserving heat for 2 hours, and cooling to room temperature along with the furnace to complete sintering.

Example 2

17.2717g of bismuth oxide powder (D50 ═ 20 μm), 5.8031g of iron sesquioxide powder (D50 ═ 30 μm), 7.2637g of nano barium titanate powder (D50 ═ 300nm) and 0.0227g of manganese dioxide powder (D50 ═ 80 μm) were mixed, 40g of absolute ethanol was added as a solvent, and ball-milled for 4 hours. And then heating and evaporating the ball-milled slurry to remove the absolute ethyl alcohol. Sieving with 80 mesh sieve, adding 10g of mixed powder into 6ml of 8% PVB for granulation, placing the granulated powder in a mold, dry-pressing at 30MPa to form a biscuit, and then carrying out cold isostatic pressing at 200 MPa. The obtained green body is wrapped by zirconia powder (D50 is 20 mu m) and is placed in a muffle furnace after being buried in powder, the temperature is raised to 1030 ℃ after 4 hours, the temperature is kept for 2 hours, and then the green body is cooled to room temperature along with the furnace to finish sintering.

Example 3

17.2717g of bismuth oxide powder (D50 ═ 20 μm), 5.8031g of iron sesquioxide powder (D50 ═ 30 μm), 7.2637g of nano barium titanate powder (D50 ═ 300nm) and 0.0227g of manganese dioxide powder (D50 ═ 80 μm) were mixed, 40g of absolute ethanol was added as a solvent, and ball-milled for 4 hours. And then heating and evaporating the ball-milled slurry to remove the absolute ethyl alcohol. Sieving with 80 mesh sieve, adding 10g of mixed powder into 6ml of 8% PVB for granulation, placing the granulated powder in a mold, dry-pressing at 30MPa to form a biscuit, and then carrying out cold isostatic pressing at 200 MPa. And the obtained green body is wrapped by zirconia balls with the diameter of 0.5mm and is placed in a muffle furnace after being buried with powder, the temperature is raised to 1030 ℃ after 4 hours, the temperature is kept for 2 hours, and then the green body is cooled to room temperature along with the furnace to complete sintering.

Comparative example 1

17.2717g of bismuth oxide powder (D50 ═ 20 μm), 5.8031g of iron oxide trioxide powder (D50 ═ 30 μm), 7.2637g of nano barium titanate powder (D50 ═ 300nm) and 0.0909g of manganese dioxide powder (D50 ═ 80 μm) were mixed, 40g of absolute ethanol was added as a solvent, and ball milling was carried out for 4 hours. And then heating and evaporating the ball-milled slurry to remove the absolute ethyl alcohol. Pre-sintering the obtained powder at 800 ℃, then carrying out secondary ball milling for 4 hours, heating and evaporating the ball-milled powder to remove a solvent, sieving the powder by using a 80-mesh sieve, adding 10g of mixed powder into 6ml of 8% PVB for granulation, placing the granulated powder in a mould, carrying out dry pressing at the pressure of 30MPa to form a biscuit, and then carrying out cold isostatic pressing at the pressure of 200 MPa. And the obtained green body is wrapped by zirconia balls with the diameter of 0.5mm and is placed in a muffle furnace after being buried with powder, the temperature is raised to 1030 ℃ after 4 hours, the temperature is kept for 2 hours, and then the green body is cooled to room temperature along with the furnace to complete sintering.

Comparative example 2

17.2717g of bismuth oxide powder (D50 ═ 20 μm), 5.8031g of iron sesquioxide powder (D50 ═ 30 μm), 7.2637g of nano barium titanate powder (D50 ═ 300nm) and 0.0227g of manganese dioxide powder (D50 ═ 80 μm) were mixed, 40g of absolute ethanol was added as a solvent, and ball-milled for 4 hours. And then heating and evaporating the ball-milled slurry to remove the absolute ethyl alcohol. Sieving with 80 mesh sieve, adding 10g of mixed powder into 6ml of 8% PVB for granulation, placing the granulated powder in a mold, dry-pressing at 30MPa to form a biscuit, and then carrying out cold isostatic pressing at 200 MPa. And placing the obtained green body in a muffle furnace, heating to 1030 ℃ for 4 hours, preserving heat for 2 hours, and cooling to room temperature along with the furnace to complete sintering.

Comparative example 3

17.2717g of bismuth oxide powder (D50 ═ 20 μm), 5.8031g of iron sesquioxide powder (D50 ═ 30 μm), 7.2637g of nano barium titanate powder (D50 ═ 300nm) and 0.0227g of manganese dioxide powder (D50 ═ 80 μm) were mixed, 40g of absolute ethanol was added as a solvent, and ball-milled for 4 hours. And then heating and evaporating the ball-milled slurry to remove the absolute ethyl alcohol. Sieving with 80 mesh sieve, adding 10g of mixed powder into 6ml of 8% PVB for granulation, placing the granulated powder in a mold, dry-pressing at 30MPa to form a biscuit, and then carrying out cold isostatic pressing at 200 MPa. And wrapping the obtained green body with powder (bismuth oxide-iron oxide-barium titanate-manganese oxide-PVB-water powder, D50 is 0.5mm) obtained by early-stage granulation, embedding the powder, placing the powder in a muffle furnace, heating to 1030 ℃ for 4 hours, keeping the temperature for 2 hours, and cooling to room temperature along with the furnace to finish sintering.

Comparative example 4

17.2717g of bismuth oxide powder (D50 ═ 20 μm), 5.8031g of iron sesquioxide powder (D50 ═ 30 μm), 7.2637g of nano barium titanate powder (D50 ═ 300nm) and 0.0227g of manganese dioxide powder (D50 ═ 80 μm) were mixed, 40g of absolute ethanol was added as a solvent, and ball-milled for 4 hours. And then heating and evaporating the ball-milled slurry to remove the absolute ethyl alcohol. Sieving with 80 mesh sieve, adding 10g of mixed powder into 6ml of 8% PVB for granulation, placing the granulated powder in a mold, dry-pressing at 30MPa to form a biscuit, and then carrying out cold isostatic pressing at 200 MPa. And wrapping the obtained green body with alumina powder (D50 is 100 mu m), embedding the green body in the powder, placing the powder in a muffle furnace, heating the powder to 1030 ℃ for 4 hours, preserving the temperature for 2 hours, and cooling the powder to room temperature along with the furnace to finish sintering.

The results of the tests of examples 1 to 3 and comparative examples 1 to 4 are shown in the following table:

wherein the piezoelectric constant d₃₃The measuring method comprises the following steps: quasi-static d by ZJ-3AN (Acoustic institute of Chinese academy of sciences)₃₃The measuring instrument is used for testing the piezoelectric property of a sample, the sample needs to be polarized before testing, and the polarization condition is as follows: the polarization electric field is 3-5kV/mm, the polarization temperature is 120 ℃, the polarization time is 10min, and the material is placed for 24h and then directly passes through a quasi-static state d₃₃Measuring piezoelectric constant d by measuring instrument₃₃。

The method for measuring the dielectric constant, the dielectric loss and the Curie temperature comprises the following steps: the curie temperature Tc was determined by measuring the dielectric constant and dielectric loss of the sample at 10K using an LCR precision impedance analyzer model TH2816 of yokoku electronics ltd, and observing the abnormal dielectric peak temperature of the sample.

20 samples of each preparation example and comparative example were subjected to statistics of yield.

The results are shown in the following table:

as can be seen from the above table, the notebook is adoptedThe preparation method of the invention, the piezoelectric constant d of the obtained bismuth ferrite-barium titanate-based piezoelectric ceramic₃₃Not less than 186pC/N, and is obviously improved compared with a sample prepared by a common method.

The results of the dielectric constant and dielectric loss measurements are shown in fig. 1 and 2. Specifically, it can be seen from the figure that the sample obtained in example 3, in which zirconia pellets with a diameter of 0.5mm were used for powder embedding, had a moderate dielectric constant but a significantly low dielectric loss.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.