JPS6215519B2 - - Google Patents

Description

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

Conventional configurations and their problems Currently, oxide single crystals are used in ferrite single crystals for magnetic head materials for magnetic recording, crystal oscillation elements, YAG single crystals for lasers, sensors, and surface wave devices.
LiNbO ₃ , LiTaO ₃ single crystals, etc. are widely used in the fields of electronic and mechanical industries. For example, among single-crystal ferrites, Mn-Zn-ferrite has mechanical properties (wear resistance,
It is widely used as a magnetic head material for audio/video tape recorders, magnetic disks for computers, etc. by effectively utilizing its surface roughness (surface roughness, etc.) and magnetic properties. In particular, single-crystal ferrite produces fewer chips, chips, etc. that occur during magnetic head processing than polycrystalline ferrite, and is produced at a higher yield.

Conventional methods for producing single crystals include various methods such as the Czyochralski method, the Bridgeman method, the Beinoulli method, the flux method, the hydrothermal synthesis method, and the high temperature and high pressure reaction method. By the way, conventionally, single crystal ferrite was generally produced by the Bridgeman method.
In this Bridgeman method, the raw material ferrite is heated once to a temperature above its melting point to melt it, and then gradually passed through a low-temperature section to perform solid phase precipitation from the liquid phase to obtain a single crystal. Therefore, a crucible for melting raw materials that can withstand high temperatures is required, and in the case of producing ferrite single crystals, platinum crucibles are used. Because of the use of this platinum crucible,
Single crystal ferrite has become expensive. Furthermore, in the ordinary Bridgeman method, it is quite difficult to control the crystal orientation, and when processing a single crystal, the usable area decreases, causing a decrease in yield.

Purpose of the Invention The present invention is intended to solve the above-mentioned drawbacks of the conventional Bridgeman method. The object of the present invention is to provide a method for producing large quantities of single crystals with a high yield and low compositional segregation and uniformly controlled crystal orientation.

Composition of the Invention In order to achieve the above object, the method for producing an oxide single crystal of the present invention includes an oxide single crystal, a crystal having the same composition as this oxide single crystal or a composition close to it, and a crystal having the same composition as this oxide single crystal. An oxide polycrystal which has a structure and exhibits grain growth in which giant crystal grains are gradually generated from a part of the polycrystal when heated at a certain temperature T _c is bonded, and at least either argon gas or nitrogen gas is used. The oxide polycrystal is made into a single crystal by subjecting the bonded body to a heat treatment in an atmosphere containing one of the two as a main component at a temperature higher than the temperature at which giant crystal grains begin to form.

The manufacturing method of the present invention will be explained in more detail. FIG. 1 shows one of the outlines of the conjugate used in the present invention. Fig. 1a shows the external appearance, and b schematically shows the central cut section of the joined body after heat treatment for single crystallization, in which 1 is a pair of thin plate-like single crystals, 2
is a polycrystal sandwiched between both single crystals 1 and subjected to single crystallization heat treatment, 3 is a single crystallized portion from polycrystal 2, and L is a single crystallized portion measured from the junction boundary between single crystal 1 and polycrystal 2. The length of the part 3, 4 is the polycrystalline 2
They are giant crystal grains that grow from the surface.

In Fig. 2, curve B shows the average crystal grain size of the polycrystal as a function of the heating temperature when the polycrystal used in the present invention is heated for 3 hours in an atmosphere mainly composed of Ar gas or N ₂ gas. This is what is shown. Curve A shows the growth of polycrystalline grains in ferrite, for example, due to "abnormal grain growth" as referred to in Japanese Patent Application Laid-Open No. 162496/1983. Curve C shows the growth of polycrystalline grains by "continuous grain growth" as described in JP-A-55-162496. Note that the heating time of 3 hours is the heat treatment time during actual manufacturing.

FIG. 3 shows the grain growth of polycrystalline grains shown by curve B in FIG. 2. At each temperature T ₁ , T _c , T ₂ , T ₃ shown in FIG. The internal cut planes of the polycrystal are schematically shown in order from a to d. Here, T _c is the temperature at which the polycrystal used in the present invention starts grain growth of giant crystals,
T ₁ is a temperature 20 to 50° C. lower than T _c , and T ₂ is a temperature approximately between T _c and T ₃ , which is a temperature at which the entire surface of the polycrystal is covered with giant crystal grains. However, T ₃
is the temperature at which the entire polycrystal is composed of giant grains. The appearance of polycrystals at these temperatures can be easily understood by referring to FIG.

The abnormal grain growth polycrystal of curve A in FIG.
Grain growth hardly occurs until T _c is reached, and some _giant crystals suddenly eat surrounding microcrystals and suddenly become very large. These giant crystals are not limited to being generated from the surface of the polycrystal as shown in FIG. 3, but are uniformly generated from the inside as well.

The present invention does not use abnormally grown polycrystals as shown in curve A of FIG. 2, but uses polycrystals with so-called duplex structure grain growth as shown in curve B. This paper proposes a method for manufacturing monocrystalline monocrystals.

In addition to using polycrystals exhibiting grain growth as shown in curve _{B in} FIG _.
The heat treatment is carried out in a temperature range from ₃ to T3, and the heat treatment atmosphere is appropriately controlled.

By the way, when manufacturing a bonded single crystal in which a single crystal and a polycrystal are bonded and heat-treated to form a single crystal,
When using an abnormally grown polycrystal as shown by curve A in Fig. 2, heat treatment at a temperature lower than _Tc allows the single crystal to move from the bonding interface between the single crystal and the polycrystal toward the polycrystal side. is becoming more and more popular. On the other hand, if heat treatment is performed at a temperature higher than T _c , giant crystal grains will eventually occur inside the polycrystal and grow throughout the polycrystal, inhibiting single crystallization or even after single crystallization.
Island-like crystal grains may remain inside the crystal, making it impossible to obtain a homogeneous single crystal. Normally, when manufacturing bonded single crystals, the smaller the polycrystal grain size, the greater the driving force received when the single crystallization interface moves from the bonding interface toward the center of the polycrystal. Polycrystals are required to have a small and constant grain size during heat treatment. Therefore, it is necessary to perform the heat treatment at a temperature lower than T _c .

Since the polycrystal used in the present invention is a polycrystal in which giant crystal grains are generated from a part of the polycrystal and undergo grain growth as shown by curve B in Fig. 2, the heat treatment temperature is performed at a temperature lower than T _c . It is not necessary, and the single crystallization rate (single crystal-polycrystal interface movement rate) increases when the heat treatment is performed at a temperature higher than _Tc . However, if the heat treatment temperature is raised too much and the temperature exceeds T ₃ , crystal grains will grow inside the polycrystal, and for the reasons mentioned earlier, single crystallization will be inhibited or island-shaped crystals will form. Since the grains are left behind in the single crystallized area, it becomes difficult to obtain a homogeneous single crystal. Therefore, in the present invention, T _c or more, preferably,
Heat treatment is performed in a temperature range from T _c to T ₃ . At this temperature, giant crystal grains that appear on the surface do not occur at the junction interface between single crystal and polycrystal;
This occurs only at end faces other than the bonding interface. However, in the production method of the present invention, the single crystallization rate is significantly higher than the growth rate of giant crystal grains, so single crystallization as seen in FIG. 1b progresses.

When the polycrystal used in the present invention is heat-treated in an atmosphere of at least one of Ar gas and N ₂ gas, the single crystallization rate increases. When this polycrystal is heat-treated in other atmospheres, such as air, single crystallization from the bonding interface toward the center of the polycrystal does not occur, or even if single crystallization progresses, it is significantly reduced (1/50 to 1/100 ) The growth rate decreases. However, _some (0.001
For some polycrystals, the rate of single crystallization increases when _H2 gas (~1.0% by volume) is mixed.

As mentioned above, in the present invention, within a certain heating time (within a heating treatment time of 1 to 12 hours), as shown by curve B in FIG.
A polycrystalline material having a region in which giant crystal grains are generated and grows within a temperature range of In such a case,
If the heat treatment temperature is set to a temperature at which giant crystal grains are generated on the polycrystalline surface, crystallization will proceed in a shorter time.
By removing the giant crystal portion at the periphery, the single crystal portion at the center can be effectively utilized.

Prior to setting the heat treatment temperature, the present inventors
Experiments were conducted at each temperature of T ₁ , T _c , T ₂ , and T ₃ under the same conditions including atmosphere, type of polycrystal, heat treatment time, etc., and the single crystallization length L shown in Figure 1 b was measured. did. The length L was measured by cutting the heat-treated joined body at the center, mirror-polishing the cut surface, etching it with strong acid, and observing the surface. The ratio of length L values when heat treated at each temperature T ₁ , T _c , T ₂ , T ₃ was 1:3:10:4. However, T ₁ , T _c , T ₂ , and T ₃ are each 30°C apart, and in the polycrystalline used in this experiment, T _c = 1300°C.
It was hot. At T ₁ , the polycrystal after heat treatment consisted of a single crystallized portion and a portion consisting of microcrystalline particles, and no giant crystals were found. At T _c , as shown in FIG. 1b, some giant crystal particles 4 were generated in the peripheral area, but no giant crystal particles 4 were found in the single crystallized portion 3.
For confirmation, the bonded body was cut into thin strips at several locations and the single crystallized portions were observed using the same method, but no giant crystal particles 4 were found. The case of T ₂ was similar to the case of T _c . In T ₃ , a giant crystal existed in front of the interface of the single-crystalline part, blocking movement of the interface. The maximum length of the four portions of giant crystal grains at the periphery at T _c and T ₂ is 1/10 to 1/20 of the single crystallization length L, and by cutting and removing them, the subsequent single crystal grains can be There was no problem in using the crystal, and therefore it was found that heat treatment at a temperature near T ₂ was most efficient.

When the single crystal produced by the present invention is compared with that produced by the ordinary Bridgeman method, there is no difference in magnetic properties (magnetic permeability, saturation magnetic flux density, coercive force, etc.), electrical properties (electrical resistance), etc. Even when mass-produced, there was little variation in properties, and in terms of yield, it was superior to the Bridgeman method. Thus, it is clear that the manufacturing method of the present invention is extremely valuable as a method for manufacturing oxide single crystals.

Description of Examples Example 1 Composition ratio: 52 mol% Fe ₂ O ₃ , 32 mol% MnO, 16
A general method for making ceramics from crystalline Mn-Zn-ferrite with mol% ZnO and grain growth as shown in curve B in Figure 2 (raw material formulation → mixing → calcination →
It was created by crushing → molding → final firing). In this example, the hot press method (1270℃-
300Kg/cm ² -3 hours). The obtained polycrystal had a porosity of 0.01% and an average grain size of 20 μm. Cut this into a rectangular parallelepiped of 30 x 20 x 15 ^mm2 ,
Two sides of 30 x 20 mm ² , #2000 mesh and #4000
Polished with mesh SiC abrasive grains and diamond abrasive grains with a grain size of 3 μm to give a mirror finish. On the other hand, a single crystal with the same composition ratio and created by the Bridgeman method,
The thickness is 1.0 to 1.5 mm, and the 30 x 20 mm ² surface is the [100] surface,
It was cut into thin plates so that each side was a [110] plane. This single-crystal thin plate was also polished to a mirror finish using SiC abrasive grains and 3 μm diamond abrasive grains, just like the polycrystalline one.

After cleaning both the polycrystalline rectangular parallelepiped and the single crystal thin plate, dilute nitric acid was applied to the joint surfaces of 30 x 20 mm ² , and they were bonded together to form a joint, which was then wrapped in alumina powder and placed in a mold. , hot pressing (1250° C., 30 Kg/cm ² , 30 minutes) was carried out by applying pressure perpendicular to the joint surfaces in an atmosphere in which N ₂ gas was flowed. By this hot pressing, the single crystal and polycrystal were completely fixed at the joint surface by solid phase reaction. In this hot press heat treatment, single crystallization did not occur, and no polycrystalline grain growth occurred.

Previously, we heat-treated this polycrystal in N ₂ gas for 3 hours, checked the temperature at which giant crystals were generated on the surface, and confirmed that T _c = 1300°C and T ₂ = 1360°C. After that, the bonded body was heat-treated at 1320° C. for 3 hours in an N ₂ gas atmosphere. After heat treatment, the center of the bonded body is cut with a diamond cutter, the cut surface is mirror-polished, and
Etching was performed for 2 to 3 minutes with 8N hydrochloric acid at a temperature of 0.degree. C., and the cut surface was observed. The single crystallized length L is 3~
4 mm, and the length of the giant crystals at the periphery extending toward the center of the polycrystal was 0.2 to 0.3 mm.

For comparison, for the joined body after hot pressing,
Similar heat treatments were carried out except that the heat treatment temperature was changed to 1270°C and 1360°C. As a result, in the case of a heat treatment temperature of 1270°C, the single crystallization length L is 0.2 to 0.3
mm, and was hardly single crystallized. On the other hand, in the case of the heat treatment temperature of 1360° C., the single crystallization length L was about 1 mm, and the inside of the polycrystal had grown into giant crystal grains with a grain size of about 0.1 to 1.0 mm. Next, heat treatment was performed at a constant heat treatment temperature of 1320° C., and only the heat treatment atmosphere was changed to Ar gas, CO ₂ gas, or air. As a result, in Ar gas, a single crystal was obtained to the same extent as in N ₂ gas, but in CO ₂ gas and air, the reduction was too strong, or the single crystallization did not progress at all. All I could get was that.

Furthermore, the single crystal Mn-
Zn-ferrite was cut out and its magnetic properties were measured. The magnetic permeability is approximately 8000 at a frequency of 1KHz, and the coercive force is
It was 0.05 Oe and was the same as the single crystal of the seed.

Example 2 Composition ratio: 51 mol% Fe ₂ O ₃ , 25 mol% MnO, 24
mol% ZnO with grain growth as shown in curve B in Figure 2 (hereinafter referred to as ``B polycrystals''), and those with the same composition that exhibit abnormal grain growth as shown in curve A (hereinafter referred to as ``B polycrystals''). Two types of polycrystals (referred to as "polycrystal A") were prepared in the same manner as in Example 1. Single crystals having the same composition ratio as these were prepared, and a bonded body was obtained by hot pressing in the same manner as in Example 1.
These B polycrystals and A polycrystals both have a porosity of 0.01%, an average crystal grain size of 15 μm, and the temperature T _c at which each giant crystal grain starts to generate and grow is the same.
It was 1310℃. In the B polycrystal, the temperature T ₃ when the whole was composed of giant crystal grains was 1360°C.

Prepare multiple pieces of these two types of zygotes,
Under Ar gas atmosphere, 1280℃, 1310℃,
After heat treatment at 1340° C. for 3 hours, the joined body was cut at the center and taken out, mirror polished and etched, and the state of single crystallization was observed. In the case of using A polycrystal, the single crystallization length L when heat-treated at 1280° C. was 2.0 mm, and the same was 2.0 mm when B polycrystal was used. At this time, the average crystal grain size of the polycrystals was almost the same, 15 μm.
However, when heat treated at 1310℃, 1.0 to 2.0 mm of
A giant crystal with a diameter of 1.0 mm is generated, and the single crystal length L is 1.0 mm.
It stayed there. On the other hand, in the case using B polycrystal, giant crystals were observed in the peripheral area other than the bonding interface, but the size was about 0.2 mm, and the single crystallization length L was 2.5 to 3.0 mm. . When heat-treated at 1340°C, almost no single crystallization was observed in the A crystal, and the average crystal grain size was 0.5 mm.
It was made up only of giant crystals. On the other hand, in the case of using B polycrystal, the single crystallization length L is 3.5 to 4.0 mm, and the size of the surrounding giant crystal grains is about 0.3 to 0.4 mm.
It was hot. For comparison, we used a sample with grain growth as shown in curve C in Figure 2, and similarly
Single crystallization experiments were carried out in the temperature range of , but the polycrystalline material did not become single crystallized.

Effects of the Invention As described above, according to the present invention, since the reaction occurs from a solid phase to a solid phase without going through the process of precipitation from a liquid phase to a solid phase, there is little compositional segregation and uniform control is achieved. It is possible to obtain a single crystal with a specific crystal orientation, increase the growth rate of this single crystal, and produce this single crystal in large quantities with a high yield. Since high temperatures (1600 to 1750°C) are not required, there is no need to use an expensive container such as a platinum crucible, and a firing furnace for ordinary ceramics can be used.

[Brief explanation of the drawing]

Figure 1a is a diagram showing the appearance of an example of a single-crystal-polycrystalline bonded body used in the present invention, Figure 1b is a schematic cross-sectional view of the central part of the bonded body after heat treatment, and Figure 2 is a diagram showing the heat treatment temperature. FIG. 3 is a diagram showing the grain growth of polycrystals used in the present invention. 1...Single crystal, 2...Polycrystal, 3...Single crystallized portion, 4...Giant crystal particle.

Claims (1)

[Scope of Claims] 1. An oxide single crystal, which has the same composition as this oxide single crystal or a composition close to it, has the same crystal structure as this oxide single crystal, and has a temperature of a certain temperature (T _c ) and an oxide polycrystal exhibiting grain growth in which giant crystal grains are gradually generated from a part of the polycrystal, and the bonded body is A method for producing an oxide single crystal, characterized in that the oxide polycrystal is converted into a single crystal by subjecting the oxide polycrystal to a heat treatment at a temperature higher than the temperature (T _c ) at which giant crystal grains start to form. 2. The method for producing an oxide single crystal according to claim 1, characterized in that a ferrite magnetic material is used as the oxide single crystal and the oxide polycrystal.