JP2002193657A - Polycrystal and its manufacturing method, and method for manufacturing single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a high performance single crystalline polycrystal and single crystal, which is preferably used for optical part, electronic part, structural part or the like, without through a liquid phase, in a relatively short time, easily and at a low cost. SOLUTION: The single crystalline polycrystal in which the particle size of the central part is larger in comparison with the particle size of the surface and the single crystal which is cut off from the central part of the single crystalline polycrystal are used. The single crystalline polycrystal is obtained by disposing a formed body containing a ceramic powder and a single crystal particle in a cavity resonator and growing the single crystal particle by heating through applying a micro wave to the formed body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in various characteristics such as optical characteristics, thermal characteristics, electric characteristics, and mechanical characteristics. In particular, optical parts such as optical isolators, laser oscillators, dielectrics, piezoelectrics, and translucent materials. The present invention relates to a polycrystal that can be suitably used for electronic components such as conductive parts and superconductors, functional components, and structural materials, a method for producing the same, and a method for producing a single crystal.

[0002]

2. Description of the Related Art Conventionally, a material utilizing light characteristics such as a laser, an electron emitting material utilizing a specific crystal plane, or a filter utilizing surface acoustic waves (SAW) has a light transmitting property or a piezoelectric property. Polycrystals and single crystals are used. Examples of the method for producing these materials include the Czochralski method (CZ method), the Bernoulli method, the zone melting method, the floating zone melting method (FZ method), and the Bridgman method.

Each of these methods is a single crystal growth method from a liquid phase, and requires special equipment. The composition and shape are varied, impurities are mixed, and it is difficult to obtain a large single crystal. Alternatively, there is a problem that the crystallinity is low.

Further, in such a method for producing a single crystal,
In order to obtain a single crystal with high reactivity in the liquid phase and high uniformity, it is necessary to optimize many crystal growth conditions such as seed crystal movement speed, rotation speed, temperature gradient, etc. And there is a problem that the cost increases.

Therefore, the single crystal garnet is bonded to the polycrystalline garnet and sintered to selectively grow the single crystal garnet. Thereafter, the single crystal garnet is subjected to a pressure treatment by a hot isostatic press to reduce the cost of the single crystal garnet. A method for producing crystals has been proposed in Japanese Patent Publication No. 63-35496.

[0006]

However, the above method for producing a single crystal requires a relatively large seed crystal.
In addition, the obtained single crystal is likely to contain many bubbles, a special high-pressure generator is required to remove the mixed bubbles, and the performance and cost are not sufficient as compared with the conventional single crystal manufacturing method. There was no problem.

Therefore, according to the present invention, the mixing of air bubbles is small,
The present invention relates to a polycrystal excellent in various properties, a method for producing the same at low cost and excellent in mass productivity, and a method for producing a single crystal produced from the polycrystal.

[0008]

SUMMARY OF THE INVENTION The present invention selectively heats a single crystal inside a compact formed of ceramic particles and single crystal particles to selectively grow the internal single crystal. It is based on the finding that a defect in an internal crystal gradually diffuses to a grain boundary, a polycrystal containing a single crystal having high crystallinity can be obtained, and characteristics comparable to a single crystal can be realized by a polycrystal.

That is, the polycrystal of the present invention is characterized in that it contains single crystal particles having a maximum particle diameter of at least five times the maximum particle diameter of the outermost surface portion. It is preferable that the maximum particle diameter of the contained single crystal particles is 100 μm or more.

In a normal polycrystalline material having a uniform particle size, other elements diffuse in the grain boundaries, and a compound is formed inside the polycrystalline material, thereby deteriorating characteristics and shortening the life. Therefore, a single crystal is sometimes desired, but many single crystals have a tendency to open,
The workability is a problem. Therefore, by including a single crystal particle having a maximum particle diameter that is five times or more the maximum particle diameter of the outermost surface portion and having few defects therein, characteristics including mechanical characteristics such as workability can be reduced. It can be close to a crystal.

In particular, by setting the maximum particle diameter of the single crystal particles contained therein to 100 μm or more and the relative density to 98% or more, diffusion of impurities can be suppressed only at the surface portion, and electrical and optical characteristics can be suppressed. Can be made into a polycrystal which is comparable to a single crystal and has excellent strength.

Further, the polycrystalline material is Al_TwoO_Three, Y_ThreeA
l_FiveO₁₂(YAG), TiO_Two, Y_TwoO _Three, Pb (Zr, T
i) O_Three(PZT), (Pb, La) (Zr, Ti) O_Three
(PLZT), BaTiO_Three, Y_ThreeFe_FiveO₁₂(YI
G), YVO_Four, LiNbO_Three, LiTaO_Three, KNb
O_Three, Si_ThreeN_Four, AlN, GaN, REBa_TwoCu_ThreeO_7-x
(RE: rare earth element) at least one single crystal particle
It is preferred to include. In addition, in each element of the above polycrystal,
May be a solid solution of another element.

With the above-described structure, an optical component such as an optical isolator or the like, which usually requires a complicated process and a long time through a liquid phase for producing a single crystal, and it is difficult to produce a high-quality single crystal, It is possible to easily realize a polycrystal having characteristics comparable to those of a single crystal such as an electronic component such as an oscillator, a dielectric, a piezoelectric material, a translucent component, and a superconductor, a functional component, and a structural material.

The method for producing a polycrystalline body according to the present invention is characterized in that a molded body containing ceramic powder and single crystal particles is placed in a cavity resonator, and the molded body is irradiated with microwaves and heated. It is a feature. As a result, the single crystal inside the compact can be selectively heated, and the single crystal inside grows selectively, and the defects in the inside crystal gradually diffuse to the grain boundaries, and the crystallinity increases. High single crystal can be realized.

In particular, it is preferable that the ceramic powder contains at least a constituent element of a single crystal particle. Thereby, impurity contamination can be avoided, and a high-purity, high-quality single crystal that does not contain impurities during grain growth can be realized.

Further, it is preferable that the dielectric loss factor of the single crystal particles during the heating is larger than that of the ceramic powder, whereby a single crystal having a large dielectric loss can selectively absorb microwaves. The grain growth of crystal grains can be remarkable, and a larger single crystal can be realized.

Furthermore, it is preferable to remove the surface portion to obtain a polycrystal containing single crystal particles having a maximum particle diameter of 100 μm or more. As a result, a crystal having very high crystallinity and few defects can be obtained, and the above-described characteristics are improved, and a single crystal can be extracted from the polycrystal.

Further, the method for producing a single crystal of the present invention is characterized in that the polycrystalline body produced by the above method is cut and single crystal particles are taken out. In addition, a high-performance single crystal can be easily and inexpensively manufactured.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a polycrystal, in which a large number of crystal grains having a large particle diameter are present, and their properties, such as optical properties, thermal properties, electrical properties or dielectric properties, are single crystal. This is related to a so-called pseudo-single crystal having characteristics close to the above.

According to the present invention, although it is a polycrystalline body made of ceramics, a large number of crystal grains having a large particle diameter exist inside, and crystal grains having a relatively small particle diameter exist on the surface portion. And it is important to have a single crystal particle having a maximum particle diameter five times or more the outermost surface portion inside.
Thereby, since the inside is a coarse crystal and the surface portion is a fine crystal, a polycrystal having better electrical and optical properties than a normal polycrystal can be obtained, and a polycrystal having excellent strength can be obtained. realizable.

Here, the maximum particle diameter refers to the maximum particle diameter of each particle measured, and the maximum maximum particle diameter is referred to as the maximum particle diameter. The term “inside” refers to a portion that is 0.1 mm or more inside from the surface.

Further, as will be described in detail later, in order to selectively grow single crystal particles inside the compact, various defects are eliminated by making the inside grain size 5 times or more larger than the surface portion. It has high quality crystals.

In particular, it is preferable to have single crystal particles having a maximum particle diameter of 100 μm or more, particularly 200 μm or more, and more preferably 500 μm or more inside. Thus, when the crystal grain size is 100 μm or more, the amount of the grain boundary decreases,
And high purity prevents grain boundary segregation of impurities, etc.
The characteristics can be further improved.

The polycrystal of the present invention has a relative density of 9%.
It is preferably at least 8%, particularly preferably at least 99%, further preferably at least 99.5%. By reducing the number of pores and increasing the relative density to 98% or more, characteristic deterioration due to pores can be suppressed.

Further, by removing the surface portion of the above-mentioned polycrystal, a polycrystal (pseudo single crystal) composed of a crystal having a large particle diameter is obtained, and the maximum particle diameter on the surface after the removal is set to 100 μm or more. By doing so, it is possible to realize characteristics almost equal to those of a single crystal.

In the polycrystal of the present invention, Al ₂ O ₃ , Y ₃
Al ₅ O ₁₂ (YAG), TiO ₂ , Y ₂ O ₃ , Pb (Zr,
Ti) O ₃ (PZT), (Pb, La) (Zr, Ti)
O ₃ (PLZT), BaTiO ₃ , Y ₃ Fe ₅ O ₁₂ (YI
G), YVO ₄ , LiNbO ₃ , LiTaO ₃ , KNb
O ₃ , Si ₃ N ₄ , AlN, GaN, REBa ₂ Cu ₃ O _7-x
It is preferable to include at least one single crystal particle of (RE: rare earth element). In addition, in each element of the above-mentioned polycrystal, other elements may be a solid solution, for example,
Bi or the like may be dissolved in Y of YIG.

Next, a method for producing the polycrystal of the present invention will be described below. First, ceramic powder and single crystal particles are prepared as raw material powders. The ceramic powder has a purity of 99.9% or more and an average particle diameter of 0.1 to 10%.
μm ceramic powder, and as single crystal particles,
Single crystal particles having a purity of 99.9% or more are desirable. here,
The size of the single crystal particles is not particularly limited, but is preferably 1
000 μm or less, desirably 500 μm or less, especially 1 μm
It is desirably not more than 00 μm. When single crystal particles having a size of more than 1000 μm are added, the dispersibility of the single crystal itself is poor, and the moldability at the time of forming a molded body is poor. Further, the ratio of the single crystal particles is 0.01 vol% or more, preferably 1 vol% or more,
In particular, 5 vol% or more is desirable. This single crystal particle
Either one or many may be used.

The obtained mixed powder raw material is molded by a known method. For example, a uniaxial pressing method and a CIP (cold isostatic pressing) method can be mentioned, and it is also possible to form a tape by using a doctor blade method, and to form a molded article by laminating the molded articles. In addition, cold isostatic pressing (CIP) after press molding to increase the green density of the molded body
May be performed.

According to the present invention, it is desirable that the ceramic powder in the compact be smaller than single crystal particles. This is because the driving force of the grain growth on the surface of the single crystal particles during sintering is caused by the difference in the particle diameter, and the grain growth rate of the single crystal particles can be increased by using a smaller ceramic powder.

Next, it is necessary to place the obtained compact in a cavity resonator, irradiate the compact with microwaves and heat it to selectively grow the single crystal particles. The compact is placed in a resonator of a microwave heating device, and is oscillated by an oscillation tube such as a magnetron, klystron, or gyrotron, and irradiates the compact with microwaves guided into the cavity resonator through the waveguide.

The frequency of the microwave used here may be in the microwave band (300 MHz to 300 GHz), but is preferably 1 GHz or more for heating the single crystal particles. From the viewpoint of heating uniformity, it is 10 GHz or more, especially 20 GHz.
GHz or more is desirable. By surrounding the molded body with a heat insulating material made of alumina fiber or the like, heat radiation from the sample surface can be suppressed, and heating can be performed effectively. Also,
The sample temperature can be measured by a known measuring method, for example, a thermocouple such as tungsten-rhenium or a non-contact method such as a two-color thermometer.

By irradiating a microwave to the compact containing the single crystal particles in the ceramic powder and heating the same, the diffusion of the single crystal particles is promoted by the non-thermal effect of the microwave, so that the single crystal particles grow in a solid phase. The ceramic single crystal can be obtained in a relatively short time, and a single crystal can be produced without melting the powder. A uniform and high-quality single crystal can be produced at low cost without fluctuation during growth. Further, defects inside the particles during heating can be reduced.

Further, the ceramic powder in the compact is
It is desirable to include at least the elements constituting the single crystal particles. If the ceramic powder does not contain the elements constituting the single crystal particles, it may remain as impurities in the single crystal,
Different compounds may form and inhibit grain growth. Further, the produced single crystal cannot be made uniform and high quality. Therefore, it is desirable that the ceramic powder contains at least an element constituting the single crystal particles, particularly the same compound as the compound of the single crystal, and particularly preferably contains a compound constituting the single crystal particle as a main component. Further, homogeneous polyimage materials having the same compound but different crystal structures may be used. For example, in the case of titanium oxide, anatase type and rutile type, and in the case of Si ₃ N ₄ , β type and α type are exemplified.

According to the present invention, it is desirable that the dielectric loss factor (product of the dielectric constant and the dielectric loss) of the single crystal particles at the time of heating is larger than the dielectric loss ratio of the ceramic powder other than the single crystal particles. This is because in microwave heating, the energy (heat) received by the particles themselves depends on the dielectric loss factor. By using single crystal particles having a large dielectric loss factor as compared with ceramic powder, the single crystal particles are more likely to be used. Selective grain growth can be performed. At this time, an additive that generates a liquid phase during sintering may be added to the ceramic powder to promote the grain growth of the single crystal particles. Alternatively, they may be unavoidably added as impurities. The magnitude of the dielectric loss factor at a high temperature can be determined by, for example, irradiating a molded product having the same shape, volume, and porosity with a microwave having a constant output and measuring the temperature rise.

Heating and grain growth by microwave irradiation can be carried out in an atmosphere in which the oxygen partial pressure is adjusted as required, in a vacuum, or in an inert atmosphere.

The heating rate, holding temperature, and holding time when heating the compact by microwave irradiation vary depending on the material. However, the firing temperature is set to be smaller than the pore growth rate in order to reduce defects. Is determined so that the grain growth rate does not remain. Further, according to the present invention, after sintering a polycrystal having a grain size to be obtained at a certain temperature, grain growth at a temperature 5 to 20% lower than the sintering temperature is performed in order to reduce defects. It is preferable that the annealing treatment in a small temperature range is performed by the same microwave irradiation. This annealing may be performed during or after sintering.

According to the present invention, the relative density of the polycrystal obtained by the above method is 98% or more, preferably 99%.
As described above, it is more desirably 99.5% or more. If it is less than 98%, light-transmitting properties, piezoelectricity, and other necessary properties cannot be sufficiently exhibited, and there are many single crystal defects contained therein. Further, it is important that the maximum particle diameter inside the polycrystal is 5 or more as compared with the maximum particle diameter on the surface in order to enhance the above-mentioned light-transmitting properties, piezoelectric properties, and other mechanical properties. This is because ordinary polycrystals have low mechanical strength due to large grain size.

According to the present invention, single crystal particles having excellent translucency or piezoelectric characteristics can be obtained by cutting out particles having a large particle diameter from the polycrystal obtained by the above-mentioned production method. At this time, it is desirable that the single crystal portion to be cut out is formed of one particle not including a grain boundary in order to make the crystal lattice uniform.

More specifically, in the case of the TiO ₂ -based polycrystal, the anatase or rutile type TiO ₂ single crystal particles and the anatase or rutile type TiO ₂ powder are combined. Desirably, firing is performed in a carbon dioxide gas and nitrogen atmosphere in which the oxygen partial pressure is adjusted to 1400 to 1800 ° C. In the case of titanium oxide, the crystal may become dark blue due to oxygen deficiency. In such a case, it is preferable to perform an oxidation treatment after firing.

Further, the firing conditions, the polycrystalline body containing a single crystal grain of each ceramic compounds (hereinafter, referred to as ceramic polycrystalline body.) To describe, Al ₂ O ₃
In the case of a system polycrystal, it can be fired in an oxidizing atmosphere at 1400 to 1800 ° C. Y ₃ Al ₅ O ₁₂ (YA
G) In the case of a Y ₃ Fe ₅ O ₁₂ (YIG) -based polycrystal, an oxidizing atmosphere at 1300 to 1800 ° C., and in the case of a Y ₂ O ₃ -based polycrystal, an oxidation atmosphere of 1600 to 2000 ° C. Pb (Zr, Ti) O ₃ (PZT), (Pb, L
a) In the case of (Zr, Ti) O ₃ (PLZT) or BaTiO ₃ based polycrystal, in an oxidizing atmosphere at 800 to 1200 ° C., Y
The VO ₄ -based polycrystal is in an oxidizing atmosphere at 1200 to 1700 ° C., and the LiNbO ₃ -based polycrystal is 800 to 1100 ° C.
In an oxidizing atmosphere at ° C., the LiTaO ₃ based polycrystal 12
In an oxidizing atmosphere of 00 to 1500 ° C., and in an oxidizing atmosphere of 700 to 1000 ° C. for a KNbO ₃ -based polycrystal, Si ₃
For N ₄ -based polycrystals, a non-oxidizing atmosphere at 1500 to 1800 ° C., and for AlN and GaN-based polycrystals,
In a non-oxidizing atmosphere at 00 ° C., REBa ₂ Cu ₃ O _7-x (R
E: a rare earth element-based polycrystal can be produced by firing in an oxidizing atmosphere at 800 to 1200 ° C., respectively.

As described above, the present invention does not require a step of melting powder or rotating a seed crystal as in the case of the ordinary FZ method or EFG method. Can be produced at low cost by a method which is highly productive, and the obtained polycrystal or single crystal can be applied to various uses requiring optical characteristics and surface smoothness.

[0042]

EXAMPLE 1 This example relates to the case of growing a single crystal of titanium oxide (TiO ₂ ). Titanium oxide powder having a purity of 99.99% was used as a raw material. Fine ceramic powder having a mean crystal grain size of 1 μm as a fine ceramic powder, and a single crystal grain having a crystal grain size of 500 μm
A m-rutile type c-axis oriented titania powder was used. 5 vol% of single crystal particles having a particle diameter of 500 μm were mixed with powder having a particle diameter of 1 μm to obtain a mixed powder.

Thereafter, a molded body of □ 10 × 10 mm was produced by a uniaxial press at a molding pressure of 100 MPa. CIP was performed at 2000 kg / cm ² to further increase the green density.

Next, the above-mentioned molded body was fired in a microwave heating furnace. Here, a gyrotron having a frequency of 28 GHz and an output of 10 kW was used as a microwave source of the microwave heating furnace. Then, the compact was placed in the alumina heat insulating material in the cavity resonator, and the compact was irradiated with microwaves. The heating is performed at a rate of 15 ° C./min,
After holding for a time, the oscillation of the microwave was stopped and the furnace was cooled to obtain a sintered body.

The obtained sintered body was a quasi-monocrystalline polycrystalline body composed of single crystal particles having a maximum particle size of 0.5 mm at the outermost surface and a maximum particle size of 2 mm at the center of the sample. Was.
The relative density measured by the Archimedes method was 99%. It shows good translucency even when polished to a thickness of 2 mm using the center of the sample, and a single crystal of 2 mm square and 0.5 mm thick can be obtained using one particle from the center. Was. As a result of observing the state of the crystal produced by an X-ray topograph, it was confirmed that the crystal was a uniform crystal having a constant refractive index and no subgrain in the sample. Further, the deflector and analyzer parts for the optical isolator were cut out of a single crystal, and the characteristics were evaluated. As a result, the characteristics were equivalent to those of a commercially available pulled product.

Comparative Example 1 The same compact as that used in Example 1 was subjected
Heated at 700 ° C. for 100 hours. The average crystal of both the surface and the center of the sintered body was 2 mm, but the translucency was poor. As a result of taking out one crystal from the particles at the center and observing it with an X-ray topograph, a number of portions having a non-uniform refractive index possibly due to the influence of internal bubbles were found.

Comparative Example 2 A titania single crystal was produced by the Czochralski method.
High frequency power supply has oscillation frequency of about 65kHz, maximum output 50K
Using a high-frequency induction heating method for rotating W,
The crucible has a diameter of 50mm, a height of 50mm, and a thickness of 1.5m
m iridium crucible was used. Around the iridium crucible, a bubble made of zirconium oxide and a refractory crucible were installed, and the heat insulation was maintained. An iridium-iridium / rhodium thermocouple was installed at the bottom of the iridium crucible to monitor the temperature.

The raw material had a purity of 99.99 similar to that of the example.
% Titanium oxide powder was used. About 400 g of the starting powder was subjected to CIP molding at a pressure of 4000 kg / cm ² and fired at 1500 ° C. in the atmosphere for 15 hours to be used as a raw material for growing a crystal. The baked raw material for growth was filled in an iridium crucible, and after flowing an atmosphere gas, heating by a high-frequency induction method was started. As the atmosphere gas, a gas obtained by mixing 0.5% by volume of O ₂ with N ₂ was used. The raw material for growth was completely melted by the high frequency power of about 5 KW. At this time, the temperature of the thermocouple at the bottom of the iridium crucible was 1875 ° C.

After holding the melt for 5 hours, crystal growth was started. The seed crystal was 5 mm long and 5 mm wide cut out in the c-axis direction.
A crystal having a length of 40 mm and a length of 40 mm was used. The growth conditions were a crystal rotation speed of 20 rpm and a pulling speed of 3.0 mm / h. After growing the straight body for 15 hours, raise the
The crystal was cut off by increasing the pressure to 0 mm / h and gradually increasing the high frequency power. The grown crystal was held at a position of about 10 mm above the melt and cooled to room temperature in about 20 hours.

Although the obtained crystal had a diameter of about 25 mm, fluctuation was observed. This indicates that crystal growth has not been performed stably. In addition, an expensive crucible was required for producing a single crystal, and a lot of time was required for each of melting, growing, and cooling, the process was complicated, and it was difficult to perform stable crystal growth.

As a result of observing the state of the crystal by X-ray topography in the same manner as in Example 1, no subgrain was confirmed, but the crystal had a non-uniform crystal with different refractive indices at the center and the periphery of the crystal.

Example 2 The following is an example of Y ₃ Fe ₅ O ₁₂ (YIG). As raw materials, Fe ₂ O ₃ and Y ₂ having a purity of 99.9% or more and a particle size of 1 μm
O ₃ was prepared, and a commercially available YIG single crystal having a purity of 99.99% or more and a particle diameter of 500 μm was prepared as single crystal particles.
Fe ₂ O ₃ and Y ₂ O ₃ were mixed so as to have a Y ₃ Fe ₅ O ₁₂ composition, and a 20 vol% YIG single crystal was added to the powder. Molding and firing were performed in the same manner as in Example 1, and the firing conditions were 1400 ° C. for 6 hours. The relative density of the obtained sintered body was 99%, and the maximum particle size of the surface portion was 500%.
μm, and the maximum particle size at the center was 3000 μm. As a result of evaluation by the same method as in Example 1, the obtained polycrystal had excellent translucency, and there was no huge defect causing a change in the refractive index. As a result of cutting out the rotor part for the optical isolator from the particles at the center and evaluating it, it showed the same performance as a single crystal produced by a commercial pulling method.

[0053]

According to the present invention, a high-quality single crystal can be obtained without the need for a step of melting a powder, rotating a seed crystal, or the like.
Alternatively, polycrystals can be produced at low cost by a method that is highly productive, and the resulting polycrystals or single crystals can be applied to various applications that require optical properties, piezoelectric properties, and surface smoothness. It is possible.

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Claims (9)

[Claims] 1. A polycrystalline body containing therein single crystal particles having a maximum particle diameter of at least five times the maximum particle diameter of the outermost surface portion. 2. The polycrystal according to claim 1, wherein the maximum particle diameter of the single crystal particles contained therein is 100 μm or more. 3. The polycrystal according to claim 1, wherein the relative density is 98% or more. 4. Al ₂ O ₃ , Y ₃ Al ₅ O ₁₂ (YAG), Ti
O ₂ , Y ₂ O ₃ , Pb (Zr, Ti) O ₃ (PZT), (P
b, La) (Zr, Ti) O ₃ (PLZT), BaTi
O ₃ , Y ₃ Fe ₅ O ₁₂ (YIG), YVO ₄ , LiNb
O ₃ , LiTaO ₃ , KNbO ₃ , Si ₃ N ₄ , AlN, G
_{3. The} polycrystal according to claim 1, comprising at least one kind of single crystal particles of aN, REBa ₂ Cu ₃ O _7-x (RE: rare earth element). 5. A method for producing a polycrystalline body, comprising: placing a compact containing ceramic powder and single crystal particles in a cavity resonator; and irradiating the compact with microwaves and heating. 6. The method for producing a polycrystalline body according to claim 5, wherein said ceramic powder contains at least a constituent element of a single crystal particle. 7. The method for producing a polycrystalline body according to claim 5, wherein the dielectric loss factor (the product of the dielectric constant and the dielectric loss) of the single crystal particles during the heating is larger than that of the ceramic powder. . 8. The method according to claim 1, wherein the maximum particle diameter is 100 μm by removing the surface portion.
The method for producing a polycrystal according to any one of claims 5 to 7, wherein a polycrystal containing m or more single crystal particles is obtained. 9. A method for producing a single crystal, comprising cutting a polycrystal produced by the method according to claim 5 and extracting single crystal particles.