JPS59152285A - Preparation of single crystal - Google Patents

Abstract

PURPOSE:To obtain a large amount of a uniform single crystal having a controlled crystal direction and low segregation of composition in high productivity, by using a single crystal of thin film as a seed crystal, forming the single crystal of thin film on the surface of polycrystal line material to be processed into a single crystal, heat-treating the resultant composite material. CONSTITUTION:A single crystal of thin film is formed on the surface of polycrystalline material to be processed into a single crystal, and the resultant composite material is heat-treated at a temperature not exceeding the melting point of the single crystal of thin film and that of the polycrystalline material. The single crystal of thin film on the surface of the polycrystalline material is used as a seed crystal, and the polycrystalline material is processed into a single crystal by a solid-phase reaction. The single crystal on the surface of the polycrystalline material, for example, is formed by irradiating it only in the vicinity of the surface layer of the polycrystalline material with laser, so that it is melted, precipitated in a solid phase and processed into a single crystal. A thin film-forming substance is partially supplied from the outside, reacted with the polycrystalline material in a proper atmosphere, and the single crystal of thin film is formed on the surface of the polycrystalline material.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for producing a single crystal.

Structures of conventional examples and their problems Currently, inorganic compound single crystals are used in ferrite single crystals for magnetic head materials for magnetic recording, quartz single crystals for 9-wave elements, YAG single crystals for lasers, and YAG single crystals for sensors and surface wave devices. LiN
Many materials are used, including bO2 and L t Ta O3 single crystals. Conventional single crystal manufacturing methods include various methods such as the Czochralski method, Bridgman 21'' method, Bernoulli method, flux method, hydrothermal synthesis method, and high temperature reaction method. Examples include CVD (chemical reaction method), liquid phase epitaxy method, and sputtering method.

These methods have advantages and disadvantages, such as difficulty in controlling crystal orientation, non-uniform composition, low mass productivity, or difficulty in producing homogeneous ingots.

Purpose of the Invention The present invention provides a method for producing a single crystal with less compositional segregation and a homogeneous and controlled crystal orientation compared to the conventional methods as described above.
The purpose is to provide a method that can be manufactured in large quantities with good mass productivity.

Structure of the Invention The present invention uses a thin film single crystal as a seed crystal, forms this thin film single crystal on the surface of a polycrystalline body to be single crystallized, and then heat-treats it, thereby making it possible to control the crystal orientation. , which enables homogeneous single crystals to be produced in large quantities with good mass productivity. According to this method, a 3ba-3 single crystal of any composition can be produced.

In the method of the present invention, a thin film of small crystals preferably having a thickness of 0.5 mm or less is formed on the surface of a polycrystalline material as a starting material to be single-crystallized, and then the thin film single crystal and the polycrystalline material are separated from each other. It is characterized by heat treatment at a temperature that does not exceed the melting point, and by using a thin film of small crystals on the surface of the polycrystal as a seed crystal, the polycrystal is turned into a single crystal by an in-phase reaction. In this method, the polycrystalline material used as the starting material reaches a certain temperature Tc when heated.
A polycrystalline material in which some of the crystal grains of the polycrystalline material undergo rapid grain growth may be used, and heat treatment may be performed at a temperature higher than Tc and lower than the melting point.

The inventors investigated a method for converting a bulk single crystal into a polycrystal by bonding a single crystal and a polycrystal and heat-treating the same to form a single crystal through a solid phase reaction. It has been found that the desired single crystal can be obtained by bonding and heat treatment.

The present invention further improves this method so that on the surface of the polycrystalline material,
We discovered that once a thin single crystal film is formed, polycrystals can be made into single crystals by in-phase reactions using it as a seed crystal. For example, the crystal in the R film on the surface of the polycrystalline body may be a single crystal formed by irradiating only the vicinity of the surface layer of the polycrystalline body with a laser beam to melt and precipitate the same phase, or a single crystal of the thin film forming material. By supplying a substance from the outside and reacting with the polycrystal in an appropriate atmosphere, the material formed on the surface of the polycrystal, and furthermore, the thin film-forming substance is transported from the outside to the surface of the polycrystal and precipitated. It may be formed by

The thin film single crystal may have the same or similar composition and crystal structure as the polycrystalline body, or may have a different composition and structure from the polycrystalline body. In any case, the subsequent single crystallization of the polycrystalline body is influenced by the method of combination, the conditions for forming the thin film single crystal formed on the surface of the polycrystalline body, and the like. Therefore, the inventors investigated the combination of thin film single crystal and polycrystal. A typical example of a combination of thin film single crystal and polycrystal is “0.5Z”.
n FeO-Mno, 5zn0.6 e24.0.5
24 MnznFeO-Nio, 5Zno, 5Fe2o40.
6 0.5 24 YIG-GGG, Mn. , 5Zn0.5Fe204-Y
IG5B S゛Mn Zno,es O,5Fe204- CoF OMn
Zn. , 6 Fe2O2-NiFe2o4, and these thin film single crystals were formed on the polycrystalline surface to a thickness of 1 μm to 1 tone by CVD or sputtering. Each of these combinations of composites was heat-treated at an appropriate temperature and atmosphere.

As a result, it was confirmed by X-ray diffraction and observation of etch pits that the thin film single crystal was formed from the polycrystalline surface over a range of several tens of μm to 2 to 3 square meters. We also investigated the combination of thin film single crystals and polycrystals of other inorganic compounds, and found that if a thin film single crystal can be formed on the surface of a polycrystalline material, the composite can be made into a single crystal by heat treatment. Served.

The feature of the single crystal manufacturing method of the present invention is that a thin film single crystal is used as a seed crystal, and the thin film single crystal is directly applied to the polycrystalline body to be single crystallized by CVD method, sputtering method, substrate reaction, etc. By using the process of precipitation or adhesion, the polycrystalline material is converted into a single crystal by a solid-phase reaction by an appropriate heat treatment, and becomes a 6-layer polycrystalline material. Conventionally, compared to other single crystal growth methods, such as the method of using a single crystal produced by the Bridgman method as a seed crystal, joining it to a polycrystal, and heat-treating the polycrystal, the polycrystal is made into a single crystal. The manufacturing method of the present invention does not use expensive seed single crystals, and also eliminates the need for a polishing step for finishing the bonding surfaces to a mirror finish and a heat treatment step for bonding. In addition, in order to prevent cracks in the bonded body, it takes a lot of effort to match the thermal expansion coefficients of the seed single crystal and polycrystal (composition check, measurement of the thermal expansion coefficient, sorting and combination of samples with the same thermal expansion coefficient, etc.) becomes unnecessary. This is because the single crystal formed on the surface of the polycrystalline body is a thin film, so the thermal stress is small and cracks and fractures are less likely to occur.

According to the present invention, the thin film single crystal is formed using the CVD method.

Regardless of the substrate reaction method, sputtering method, vapor deposition method, etc., a large amount can be processed at once, so mass production is easy. It has also been found that when the polycrystalline material used in the present invention is an oxide, single crystallization is promoted by 7 pages by heat treatment in a slightly reducing atmosphere. The heat treatment temperature at this time needs to be lower than the melting point temperature of the polycrystalline body and lower than the melting point temperature of the thin film single crystal in order to convert the polycrystalline body into a single crystal by an in-phase reaction. This is because at temperatures above the melting point, the thin film crystal melts or evaporates and ceases to function as a seed crystal.

As a result of repeated experimental research, the inventors further determined that in order to further promote the single crystallization of a polycrystalline body, the shape, grain size, and grain size distribution of the crystal grains constituting the polycrystalline body, porosity, and pore size were changed. The shape, the shape of the pore distribution, the shape of the two grain boundaries, the thickness of the grain boundary layer, the state of grain growth, etc. were investigated, and the relationship with the single crystallization rate was determined. As a result, compared to polycrystalline materials in which the crystal grains exhibit normal grain growth,
It has been found that, at a certain temperature Tc, in a polycrystalline body in which some crystal grains suddenly increase in size, the single crystallization rate is 2 to 6 times higher. In particular, it has been found that the single crystallization rate increases when the heat treatment is performed at a temperature higher than Tc and lower than the melting point, preferably at a temperature below T2 defined below. T2 is the temperature at which the entire polycrystal becomes an aggregate of giant crystals, or in other words, the temperature at which all the crystal seeds start grain growth at once. That is,
It has been found that the single crystallization rate increases when heat treatment is performed in a temperature range expressed by T<T2, where T is the heat treatment temperature.

Description of examples Examples of the present invention will be described in detail below.

Example 1 Fe20353mol% MnO28mol/l/% and Z
High-purity raw materials with a purity of 99.9% or more were blended and mixed to give nO19 morch, and then dried, granulated, and molded. The molded body was hot pressed (temperature 13oO℃, holding time 3 hours, pressure 3ooKtp). /c/l) L, density 9
Dense Mn-Zn ferrite polycrystal of 9.9% or more (average grain size 10 μm/porosity 0.01 inch or less)
was created. This polycrystalline body is 1o x 20mm x 30
The starting polycrystal is cut into nano-sized pieces and the surface is washed to form a single crystal. The surface of this polycrystal was annealed using a carbon dioxide laser to form a single crystal over a thickness of about 1 μm from the surface. With this sea 9 page annealing, it was not possible to form a single crystal deeper than this. On the other hand, this polycrystalline body was heated in N2 for 2 hours to a temperature Tc at which some crystal seeds suddenly started grain growth.
It has been confirmed that the temperature T2 at which grain growth occurs on the whole is 1360°C. Therefore, a polycrystal with a single crystal surface was placed in N2 at 1
Heat treatment was performed at 330° C. for 2 hours. After the heat treatment, the central part of the sample was cut, the cut surface was lapped to a mirror finish, and then etched with concentrated hydrochloric acid, and the distance @It at which single crystallization had progressed was measured. As a result, the temperature was 3 to 5 tpan. For comparison, when the same heat treatment was applied to a polycrystalline material whose surface layer was not made into a single crystal, the single crystallization did not proceed and giant crystals (grain size 2 to 3 mm) were formed from the surface part of the polycrystalline material. It was growing towards the center. In addition, a polycrystalline body with the same composition sintering conditions and normal grain growth was processed into the same shape as in Example 2 and Example 1. 1 ot''
YIG (yttrium iron garnet) polycrystal with rapid grain growth (average grain size 5 μm, porosity 0.0
5% impurities include SiO2 of 0.01% by weight or less, Ca
0.005 wt.
A thin film single crystal was formed. Its crystal orientation is perpendicular to the surface <
110> direction. On the other hand, the N of this YIG polycrystal
When examining the grain growth start temperature Tc of some crystal grains in two gases, 'rc = 1320°C, and T2 is 1380°C.
It was ℃. Therefore, the above composite was heat-treated at 1350° C. for 3 hours in N 2 in an attempt to single-crystallize the YIG polycrystal. As a result, single crystallization occurs from the surface toward the center of the polycrystalline body, and the crystal orientation becomes perpendicular to the surface111
The length a of the single crystallized portion was 2 to 3 yas. As in Example 1, for comparison, we used the same polycrystalline material with no MqO single crystal thin film formed on its surface, and one using YIG polycrystalline material with normal grain growth points that do not show rapid grain growth. A thin MqO film single crystal was formed on the surface under the same conditions.
1 bacon was heat-treated under the same conditions. After heat treatment,
The central portion was cut and the single crystallization length 2 was measured. As a result, single crystallization did not occur in the case where MqO single crystals were not formed on the surface, and when polycrystals showing normal grain growth were used, single crystallization progressed only to about 10 to 20 μm. Ta.

Furthermore, when comparing the heat treatment temperatures, when the composite of the present invention is heat treated at 1300C and 1400C, 100
For those heat-treated at 0°C, ρ was about 0.5 mm, and for those heat-treated at 1400°C, l was about 0.5 fin. This is because the heat treatment temperature was too high, so crystal grain growth occurred within the polycrystalline body faster than single crystallization, and single crystallization was inhibited. The single crystal manufacturing method of the present invention can also be applied to homozygotes and peterozygotes of other inorganic compounds.

can be manufactured.

410-

Claims (1)

[Claims] A thin single crystal is formed on the surface of a polycrystalline material to form a composite.
This composite is heat-treated at a temperature that does not exceed the melting points of the thin film single crystal and the polycrystalline body, and the polycrystalline body is transformed into a single crystal by using the thin film single crystal on the surface of the polycrystalline body as a seed crystal. A method for producing a single crystal characterized by: