JPH0253397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a single crystal of yttrium aluminum garnet (Y ₃ Al ₅ O ₁₂ ) or a solid solution thereof.

Conventionally, single crystals of Y ₃ Al ₅ O ₁₂ have been produced by the following four methods.

(1) The so-called pulling method that pulls a single crystal from a melt.

(2) A method using a flux mainly composed of PbO-PbF ₂ system.

(3) Floating zone method.

(4) Heat exchange method.

The pulling method described in (1) above is a method in which the raw material is melted in an iridium crucible, a seed crystal is inserted from above, the tip is brought into contact with the melt, and the melt is gradually solidified to obtain a single crystal. be. Although this method yields large single crystals, it has drawbacks such as the iridium crucible being expensive and easily worn out, the components of the crucible being easily incorporated, and an undesirable part called the core appearing in the center of the crystal.

The above flux method uses a flux with a low melting point.
This is a method in which Y ₃ Al ₅ O ₁₂ is dissolved and a single crystal is precipitated using slow cooling or a temperature gradient. This method has the disadvantage that flux is incorporated into the crystal as inclusions or impurities, and that it takes time to grow the crystal, and that the yield is low, resulting in high cost.

The floating zone method uses, for example, a movie projector to collect the light from a lamp and use it as a heating source (condensing type) or a hollow cathode as a heating source to create a floating zone.
This is a method of growing a single crystal on a seed crystal. This method has the disadvantage that it is difficult to obtain high-quality and homogeneous products because temperature control immediately after growth is insufficient. In addition,
In this method, a crystal growth method using an after-heater to suppress crystal defects was also attempted, but it was not possible to satisfactorily resolve the crystal non-uniformity affected by the shape of the solid-liquid interface.

The heat exchange method is a method in which a raw material melted in a large high-melting point metal container is slowly cooled from one end to form a single crystal as a whole. This method has drawbacks such as slow cooling is technically difficult, it is difficult to grow a single crystal uniformly, and there is contamination from the container.

An object of the present invention is to provide a method for producing a highly pure and homogeneous yttrium aluminum garnet or a solid solution single crystal thereof using a floating zone method.

The floating zone method referred to in the present invention refers to a raw material rod being rotated from above and sent into a part (melting zone) that is kept at a temperature slightly higher than the melting temperature, while a seed crystal is introduced from below in the opposite direction to the raw material rod. The raw material rod and the seed crystal are fed in while rotating, and the two are brought into contact with each other through the molten part to obtain a state in which there is no support to the molten part other than the raw material rod and the seed crystal, that is, a floating zone is formed, and then the raw material rod and A method in which seed crystals are simultaneously sent downward at the same constant speed, and a single crystal is deposited on the seed crystal during this time.

When producing Y ₃ Al ₅ O ₁₂ or its solid solution single crystal using the floating zone method, the present inventor installed a heat insulating device around the seed crystal on the crystal side and the grown crystal part to control the temperature distribution. When I do it,
It was discovered that a highly pure and highly homogeneous yttrium aluminum garnet single crystal can be easily obtained, and the present invention was completed based on this knowledge.

The raw material rod used in the method of the present invention is a mixture of components and component ratios that give yttrium aluminum garnet or its solid solution single crystal, that is, yttrium oxide (Y ₂ O ₅ ) and aluminum oxide (Al ₂ O ₃ ). The molar ratio is preferably 3
or a mixture of yttrium oxide (Y ₂ O ₃ ) as a main component and a rare earth element oxide mixed with aluminum oxide (Al ₂ O ₃ ) in a molar ratio of preferably 3:5. This is a rod-shaped product made by press-molding and sintering the mixture. The melting zone is a liquid saturated with the same composition as above, and the seed crystals are solid solution crystals having the same composition as above.

As the yttrium oxide used in the present invention, commercially available yttrium oxide may be used as is without any chemical treatment, but in order to allow the reaction with aluminum oxide to proceed quickly, the smaller the particle size, the more It is preferably 1 mm or less, particularly preferably 10 μm or less. The purity may be at the level of a conventional reagent grade, but when Y ₃ Al ₅ C ₁₂ is used as an optical material, contamination with impurities is discouraged, so the higher the purity of the starting material, the better. Furthermore, if a sample obtained by calcining in air at 1000° C. for one day is used as a starting material, it is more preferable to proceed with the desired chemical reaction.

The aluminum oxide used in the present invention may be of ordinary reagent grade, but the higher the purity, the more preferable it is. The particle size is preferably as small as possible in order to allow the chemical reaction with yttrium oxide to proceed quickly, and is preferably 1 mm or less, particularly preferably 10 μm or less.

When mixing the samples of the present invention, it is preferable to mix them as uniformly as possible, and it is preferable to mix them thoroughly in a milk drum with organic reagents such as alcohols and acetone, or by using a mixer such as a ball mill. There is a method, and the average particle size after sample mixing is 1 mm.
The thickness is preferably adjusted to 10 μm or less.

In the present invention, the blending of yttrium oxide and aluminum oxide to make the mixed powder that is the raw material for Y ₃ Al ₅ O ₁₂ is carried out in order to avoid mixing as inclusions of different phases during crystal growth. Molar ratio of aluminum oxide to 3.5:5.0 to 2.5:
It is preferable to keep the ratio within the range of 5.0, particularly preferably 3.0 to 5.0.

Commercially available rare earth element oxides used in the present invention may be used as they are without any chemical treatment, but the particle size must be adjusted to allow the reaction with aluminum oxide to proceed quickly. The smaller the diameter, the more preferable it is, 1 mm or less, particularly preferably 10 μm or less. The purity may be at the conventional reagent grade level, but when using R ₃ Al ₅ O ₁₂ (R represents a rare earth element) as an optical material, contamination with impurities is avoided, so the higher the purity of the starting material, the higher the purity. The more preferable. In addition, as a starting material,
It is more preferable to use a sample obtained by calcining in air at 1000° C. for one day in order to allow the desired chemical reaction to proceed.

The acid combination of aluminum oxide and rare earth element oxide to make the mixed powder that is the raw material for the molten part is as follows:
The molar ratio of aluminum oxide to rare earth element oxide must be in the range 4:1 to 3:2, particularly preferably 4:2 to 3:2. If the composition of the melted zone is outside the range, crystal phases other than R ₃ Al ₅ O ₁₂ may also become saturated, leading to the contamination of different phases, making it unsuitable.

In the method of the present invention, when pressing the mixed powder of the raw material rod, a molding method using one-way or two-way compression using a mold may be used, but in order to prevent bending during heating, etc. It is preferable to use a rubber press method in which pressure is applied unidirectionally.

The rubber press method is a method in which sample powder is placed in a rubber tube, both ends are sealed, and the tube is pressurized with high oil pressure in a closed hydraulic pressure vessel. The hydraulic pressure may be as high as 500 kg/cm ² or higher, but it is preferably 1 to 2 ton/cm ² because it is inexpensive and can be obtained manually. Pressure time is 5
The duration is at least 1 second, preferably 1 minute. Molded products that are not sufficiently pressurized are likely to break.

The shape of the press-formed product in the present invention may be any thin and long shape in order to be applied to the floating zone method, but a cylindrical shape with a certain thickness is particularly preferable, for example, a diameter of 1 mm to 10 cm and a length of 1 mm to 5
m, preferably a diameter of 3 mm to 1 cm and a length of 5 mm to 30 cm.

During the calcination of the pressure-formed product in the present invention, nitrogen and Preferably, the coexistence of an inert gas such as argon is avoided. The bubbles of an inert gas such as nitrogen or argon are taken into the melting zone during the crystal growth operation described below, and some of them accumulate to form large bubbles, which eventually burst and interfere with the smooth growth of the crystal.

At the beginning and after the completion of calcination in the present invention, it is preferable to slowly heat and cool slowly at a rate of 30 degrees per minute or less in order to avoid thermal destruction of the molded product.

The heating temperature of the press-molded product is preferably 1300 to 1800°C, particularly preferably 1500 to 1800°C.

The heating time of the press-molded product is set to such a length that the bulk density of the press-molded product after calcination becomes 50 to 80% of the true density. More preferably, the length is such that the bulk density is 70 to 75%.

The part of the floating zone method crystal growth apparatus used in the present invention that maintains a temperature slightly higher than the melting temperature, that is, the melting part, is the material rod.
Depending on the diameter of the Y ₃ Al ₅ O ₁₂ raw material molded sintered body, it must be maintained at 2000° C. or higher, which is the melting temperature of the Y ₃ Al ₅ O ₁₂ raw material, over 3 to 15 mm above and below.
It is not preferable for the part above 2000°C to be too long or too short vertically. There are no restrictions on the temperature distribution other than above and below near the high temperature portion.

The apparatus for the crystal growth method used in the present invention must have equipment that allows the crystal growth section to be disconnected from the outside air and to change the atmosphere depending on the purpose.

The heat retaining device in the present invention is, for example, a cylinder having an inner diameter larger than the outer diameter of the growing crystal, and is provided so as to cover the seed crystal and the part of the grown crystal close to the melting part.The simplest example is a cylinder made of alumina. It is a ceramic cylinder.

The heat retaining cylinder in the present invention is preferably made of a material with high thermal conductivity in order to make the temperature gradient in the grown crystal gentle. For the same reason, it is preferable that the heat insulating cylinder has a small thickness and a small heat capacity. However, it is not limited to this.

The heat retaining device is for controlling the temperature distribution in the growing crystal. These change the path of the heat flow near the molten part in the crystal, which in turn changes the shape of the crystal growth interface. In the present invention, it is possible to maintain the crystal growth interface in a shape suitable for the growth of high quality crystals by delicately controlling the heat retaining device.

In the present invention, by utilizing the floating zone method, the crystal growth rate using the R ₃ Al ₅ O ₁₂ raw material molded sintered body, the molten zone, and the seed crystal is determined by using the raw material rod and the seed crystal. equal to the downward feed rate, the invention maintains the feed rate at least 0.1 mm per hour;
It is characterized by growing R ₃ Al ₅ O ₁₂ single crystal.
The feeding speed is preferably high, but in order to prevent the properties of the obtained crystals from being impaired, the feeding speed should be increased every hour.
It is preferably 10 cm or less, usually 8 mm or less, particularly preferably 1 to 4 mm/hour. Too slow feed rate
It reduces the efficiency of R ₃ Al ₅ O ₁₂ single crystal production and increases costs.

In the method for producing R ₃ Al ₅ O ₁₂ or its solid solution single crystal of the present invention, if a single crystallized material is used as a raw material instead of a sintered raw material rod, the melting of the raw material into the molten zone will be reduced. The crystallization becomes uniform and therefore crystallization on the seed crystal becomes stable, making it possible to obtain a high-quality single crystal.

According to the method of the present invention, compared to Y ₃ Al ₅ O ₁₂ single crystals produced by conventional methods, Y ₃ Al ₅ O ₁₂ or its solid solution single crystals are produced which have higher purity and homogeneity and are much cheaper. There is a potential effect.

Y ₃ Al ₅ O ₁₂ or its solid solution single crystal obtained by the method of the present invention can be obtained by conventional methods.
It will be used as a substrate for laser materials or microwave magnetic materials as an inexpensive and high-quality alternative to Y ₃ Al ₅ O ₁₂ single crystals.

Example 1 Yttrium oxide (Y ₂ O ₃ ) with a purity of 99.9% or more
Weighing the powder and aluminum oxide (Al ₂ O ₃ ) powder with a purity of 99.9% or more to a molar ratio of 3.0 to 5.0,
Acetone was added and thoroughly mixed in a milk drum to obtain a fine powder mixture with an average particle size of 1 μm.

Approximately 12 g of the mixture was put into a thin rubber tube with an inner diameter of 11 mm, both ends were sealed, the mixture was inserted into a metal ring with an inner diameter of 11.5 mm, and the mixture was heated at a pressure of 1 ton/cm ² in a hydraulic hydrostatic pressure generator at a pressure of about 1 ton/cm 2 . It was pressed and molded for a minute.

Outer diameter approximately 8mm and length approximately 80mm obtained by the above operation
A round rod-shaped sample with a diameter of 2 mm was inserted into a rigid electric furnace maintained at 1700°C and fed with 1 atm of oxygen gas, and calcined. Inserting the sample into the furnace and removing it from the furnace took 1 hour each to prevent destruction of the sample due to rapid heating and cooling.

The Y ₃ Al ₅ O ₁₂ raw material rod with an outer diameter of about 6.5 mm and a length of about 60 mm obtained by the above operation was placed on the upper side of a concentrating heating type floating zone method single crystal production device using a xenon arc lamp as a heating source. Fixed to the sample rotation axis,
Y ₃ Al ₅ O ₁₂ with an outer diameter of about 7 mm prepared separately in the same way
Cut a single crystal to a length of about 30 mm, use this as a seed crystal,
It was fixed to the lower seed crystal rotating shaft of the device. An alumina tube with an inner diameter of 22 mm was fixed in advance to the device so as to cover the entire seed crystal and lower shaft, and its tip was placed at a position expected to be the boundary between the crystal and the molten zone. Nitrogen gas at 1 atm was introduced as an atmosphere into the crystal growth chamber, which was fused with outside air using a fused silica tube, and heating was started after the atmosphere was sufficiently replaced with air. The atmosphere was supplied near the floating zone at a rate of 2.0 cm/sec. The tip of the Y ₃ Al ₅ O ₁₂ seed crystal is adjusted to be at the highest temperature point in the single crystal production equipment, and as soon as the tip is melted by heating, the temperature is fixed by constant heating, and the upper The Y ₃ Al ₃ O ₁₂ raw material rod was moved downward to combine with the seed crystal through the molten zone, and both were rotated in opposite directions at a speed of 30 revolutions per minute. Rotation was continued until the end of crystal growth. After finely adjusting the temperature and the distance between the raw material rod and the seed crystal so that the melted zone is neither too large nor too small, the raw material rod and the seed crystal are moved downward at the same speed at 1.0 per hour. It was moved at a speed of mm to deposit Y ₃ Al ₅ O ₁₂ crystals on the seed crystal. The precipitated crystal was a single crystal with the same orientation as the seed crystal.

Y ₃ Al ₅ O ₁₂ When the raw material rods are almost completely consumed,
The grown single crystal and the raw material rod were separated, and after cooling, a Y ₃ Al ₅ O ₁₂ single crystal in the shape of a round rod with a diameter of 6 mm and a length of 50 mm was obtained.

The obtained single crystal was determined by powder X-ray method as Y ₃ Al ₅ O ₁₂
It was confirmed that Also, using an optical microscope,
It became clear that this was a high quality crystal with few light scattering sources.

Example 2 A high quality Y ₃ Al ₅ O ₁₂ single crystal was grown.

The single crystal obtained by the method of Example 1 and the raw material were recrystallized in the same manner as in Example 1 to obtain high quality Y ₃ Al ₅ O ₁₂ with a diameter of 6 mm and a length of 40 mm.
A single crystal was obtained.

A part of the obtained single crystal was cut out into a cylindrical shape with both ends mirror-polished, and examined using a polarizing microscope, and it was confirmed that the magnitude of the fluctuation in the refractive index was 10 ^-5 or less.

Example 3 A single crystal was grown with a composition of Y _2.97 Nd _0.03 Al ₅ O ₁₂ .

Yttrium oxide (Y ₂ O ₃ ) with purity of 99.9% or more
Neodymium oxide (Nd ₂ O ₃ ) with powder and purity over 99.9%
powder and aluminium oxide ₍ Al ₂ O ₃ ) powder with a purity _{of 99.9} % or _more .
They were weighed to a molar ratio of 2.85:0.15:5.0, and acetone was added in a mortar and thoroughly mixed to obtain a mixture of two types of fine powder with an average particle size of 1 μm.

Approximately 12 g of the two kinds of mixtures were put into a thin-walled rubber tube with a content of 11 mm, and both ends were sealed, and the inner diameter was 11.5.
It was inserted into a metal frame of 1.0 mm in diameter, and pressed and molded in a hydraulic hydrostatic pressure generator for about 1 minute at a pressure of 1 ton/cm ² .

Outer diameter approximately 8mm and length approximately 80mm obtained by the above operation
A round rod-shaped sample of 2.97 mm in diameter was inserted into a vertical electric furnace maintained at 1700°C for the Y _2.97 Nd _0.03 Al ₅ O ₁₂ raw material, and 1600°C for the solvent raw material, and calcined. Inserting into the furnace and pulling out from the furnace each took one hour.
Prevented sample destruction due to rapid heating and cooling.

Approximately 6.5 mm in outer diameter and approximately 6.5 mm in length obtained by the above operation
A 60 mm Y _2.97 Nd _0.03 Al ₅ O ₁₂ raw material rod was fixed to the upper sample rotating shaft of a floating zone method single crystal production device that adopted an infrared concentrated heating method, and a molten part with an outer diameter of approximately 7 mm was obtained in the same manner. The raw material rod was cut to a length of approximately 20 mm, fixed to the lower seed crystal rotation shaft of the device, and 1 atm nitrogen gas was introduced as an atmosphere into the crystal growth chamber, which was isolated from the outside air with a fused quartz tube, to ensure sufficient air. After the replacement, heating was started. The atmosphere was supplied near the floating zone at a linear velocity of 0.6 cm/sec.
Adjust the tip of the raw material rod in the melting zone to be at the highest temperature point in the single crystal production equipment, and as soon as the tip melts due to heating, the heating is kept constant to fix the temperature, and Y _0.97 Nd is heated from above. _{The 0.03} Al ₅ O ₁₂ raw material rod was moved downward, and the molten part and the raw material rod were combined using the molten portion as an intermediary. Next, the melting zone raw material rod was separated so that an appropriate amount of the Y _2.97 Nd _0.03 Al ₅ O ₁₂ raw material rod remained at the lower end, heating was interrupted, and it was removed from the apparatus. Thereafter, a separately prepared Y _2.97 Nd _0.03 Al ₅ O ₁₂ sintered rod having a diameter of 6.5 mm and a length of 20 mm was attached as a seed crystal to the lower shaft in place of the molten zone raw material rod, and was installed in the apparatus. The device is pre-installed with an inner diameter that covers the seed crystal and the lower shaft.
A 22 mm alumina tube was fixed, and its tip was placed at a position that was assumed to be the boundary between the crystal and the molten zone. Heating is performed again to melt the molten zone raw material attached to the lower end of the Y _2.97 Nd _0.03 Al ₅ O ₁₂ raw material rod, and the seed crystal is adjusted appropriately to contact the molten zone, and the raw material is transferred through the molten zone as an intermediary. It was connected to a rod and both were rotated in opposite directions at a speed of 30 revolutions per minute. The rotation is
This continued until the end of crystal growth. After finely adjusting the temperature and the distance between the raw material rod and the seed crystal to obtain a state in which the molten zone is neither too large nor too small, both were moved downward at the same speed at a rate of 1.0 mm per hour. ,
Crystals of Y _2.97 Nd _0.03 Al ₅ O ₁₂ were deposited on the seed crystal. The precipitated crystals were initially polycrystalline, but the size of the crystals was 3 to 5 mm.
After growth, it had a single crystal cross section.

Y _2.97 Nd _0.03 When the Al ₅ O ₁₂ raw material rod is almost completely consumed, the grown single crystal is separated from the raw material rod, and after cooling, Y _2.97 Nd _0.03 is made into a round rod with a diameter of 6 mm and a length of 50 mm.
An Al ₅ O ₁₂ single crystal was obtained.

The resulting cylindrical single crystal was cut parallel to the growth direction, polished to a mirror surface, and observed under a microscope. As a result, it was found that there was no sign of non-uniformity.

Example 4 A single crystal was grown with a composition of Y ₂ YbAl ₅ O ₁₂ .

Yttrium oxide (Y ₂ O ₃ ) with purity of 99.9% or more
Powder, ytterbium oxide (Yb ₂ O ₃ ) powder with a purity of 99.9% or more, and aluminum oxide (Al ₂ O ₃ ) powder with a purity of 99.9% or more in a ratio of 2.0 to 1.0 for the Y ₂ YbAl ₅ O ₁₂ raw material. 5.0, 2.5 for melt material
0.5 to 5.0 molar ratio, acetone was added in a milk drum, and the mixture was thoroughly mixed to obtain a mixture of two types of fine powder with an average particle size of 1 μm.

The two types of mixtures were subjected to the same procedure as in Example 1 to obtain a Y ₂ YbAl ₅ O ₁₂ single crystal in the form of a round rod with a diameter of 6 mm and a length of 40 mm.

The resulting cylindrical single crystal was cut parallel to the growth direction, mirror-polished, and observed under a microscope. As a result, it was found that there was no sign of non-uniformity.

Example 5 High quality Y _2.97 Nd _0.03 Al ₅ O ₁₂ single crystal was grown.

Using the single crystal obtained by the method of Example 1 as a raw material, recrystallization was performed in the same manner as in Example 1 to obtain a high quality Y _2.97 Nd _0.03 with a diameter of 6 mm and a length of 40 mm.
An Al ₅ O ₁₂ single crystal was obtained.

A part of the obtained single crystal was cut out into a cylindrical shape with both ends mirror-polished, and examined using a polarizing microscope, and it was confirmed that the magnitude of the fluctuation in the refractive index was 10 ^-5 or less.

Claims (1)

[Claims] 1. A heating melting section is provided below the raw material rod, a seed crystal is provided below the melting section, and the raw material melts into the melting section,
In a single crystal manufacturing method using a floating zone method in which a crystal component is precipitated on a seed crystal to grow a single crystal, the raw material rod is melted into the molten zone and precipitated from it to produce yttrium aluminum garnet, or a mixture having components and component ratios that give a solid solution crystal thereof, the molten part is a high temperature liquid saturated with solid solution components of the same composition, and the seed crystal is yttrium aluminum garnet or a solid solution crystal thereof. When growing a single crystal, by insulating the area around the seed crystal and the part of the grown crystal close to the melting part, the temperature distribution of the seed crystal and the part of the grown crystal close to the melting part is adjusted to the crystal growth interface. 1. A method for producing a single crystal of yttrium aluminum garnet or a solid solution thereof, characterized in that the yttrium aluminum garnet or its solid solution single crystal is adjusted to be convex from a seed crystal toward a molten zone. 2. The method according to claim 1, wherein the raw material rod is a single crystal rod of yttrium aluminum garnet or a solid solution thereof, and the raw material rod is recrystallized.