JPH06211600A - Production of oxide single crystal - Google Patents

Abstract

PURPOSE:To mass-produce an oxide single crystal having a desired composition in a short time at the time of VTE-treating a material by reducing the heat- treating time. CONSTITUTION:A material 7 consisting of an oxide single crystal and an oxide powder 6 having a different composition from that of the oxide is heat-treated to change the composition of the single crystal of the material 7. While the single crystal is heated above the Curie temp., a voltage is impressed on the single crystal, and the single crystal is formed into a single domain. The oxide is preferably lithium niobate and lithium tantalate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an oxide single crystal such as a lithium niobate single crystal.

[0002]

2. Description of the Related Art Lithium niobate is a single crystal oxide material necessary and important for optical devices.
It is written as bO ₃ . Currently, almost all commercially available lithium niobate single crystals are produced by the so-called Czochralski method. In this method, the so-called congruent composition (Li is 48.6 mol%)
A single crystal can be pulled in the vicinity. However, pulling a single crystal having a composition deviating from the congruent composition is not possible at present because not only is it difficult to control the composition but also problems such as cracks.

Lithium niobate is widely used especially as an optical material. However, due to the above manufacturing restrictions, much research has been conducted on the optical characteristics of lithium niobate having a congruent composition, but optical studies have not been made on those having a composition other than the congruent composition. Therefore, it is expected that lithium niobate having a congruent composition will be mass-produced and used as an optical device.

As a method for producing lithium niobate having a congruent composition, VTE (Vapor Transport) is currently used.
Equilibration) method is known. This method will be briefly described. First, the columnar lithium niobate single crystal is pulled by the Czochralski method. This single crystal has a congruent composition. Next, the single crystal is annealed, and a voltage is applied at 1175 ° C. to perform a single domain treatment, and then the columnar body is cut to obtain a thin plate. On the other hand, a powder composed of lithium niobate having a desired composition, for example, Li ₂ O of 50 mol% is prepared, and the thin plate and the powder are enclosed in a closed container.
When heat treatment is performed in the closed container at a sufficiently high temperature for a sufficiently long time, the composition in the thin plate and the composition in the powder reach an equilibrium state due to transport in the gas phase and solid phase diffusion.

[0005]

Lithium niobate having a congruent composition has a Curie temperature of 1146 ° C.
Then, even if the single crystal is subjected to the single-domain processing, if the heat treatment is performed at a temperature higher than the Curie temperature of the single crystal, the domain of the single crystal returns to the multi-domain state again. Therefore, the heat treatment temperature must not exceed the Curie temperature of the single crystal.

With the composition containing 50 mol% of Li ₂ O, the Curie temperature of the single crystal is 1190 ° C. And as the above powder
When Li niobate having a composition of 50 mol% Li ₂ O is used, the Curie temperature of the single crystal is 1146 ° C to 1190 ° C.
Rise toward. For this reason, conventionally, the heat treatment was performed at about 1100 ° C, but it took about 500 hours until the Curie temperature of the single crystal reached 1190 ° C.

On the other hand, in the composition containing 47.2 mol% of Li ₂ O,
The Curie temperature of the single crystal is 1090 ° C. Then, the case using lithium niobate composition Li ₂ O is 47.2Mol% as the powder, the Curie temperature of the single crystal 1146 ° C.
To 1090 ° C. Therefore, in the past,
Although heat treatment was performed at about 50 ° C, it took about 800 hours until the Curie temperature of the single crystal reached 1090 ° C.

Moreover, in the above example, the thickness of the thin plate is
It is about 0.5 mm, and if it is made thicker, it will take a much longer time to reach the equilibrium state in the system. As described above, in order to synthesize lithium niobate having a composition other than the congruent composition, an extremely enormous amount of time and a large amount of heat are required, resulting in a high manufacturing cost and hindering full-scale research and commercialization. It was

An object of the present invention is to make it possible to shorten the heat treatment time when VTE-treating a material composed of an oxide single crystal, and to mass-produce an oxide single crystal having a desired composition in a short time. That is.

[0010]

According to the present invention, the composition of a single crystal is changed by heat-treating a material composed of an oxide single crystal and an oxide powder having a predetermined composition different from the composition of the oxide. And a step of subjecting the single crystal to a single domainization treatment by applying a voltage to the single crystal while heating the single crystal above its Curie temperature. is there.

As the above-mentioned oxide, various complex oxides can be exemplified. Examples of such complex oxides include:
Examples _include LiNbO _{3 and} LiTaO ₃ .

[0012]

As described above, in the present invention, the material of the oxide single crystal is first subjected to the VTE treatment to change its composition, and then this single crystal is subjected to the single-domain treatment. Therefore, in the stage of the first VTE treatment, the single crystal domain may be in a multi-domain state, and thus the single crystal can be VTE-treated at a temperature higher than the Curie temperature. Therefore, it is possible to manufacture an oxide single crystal having a desired composition in a heat treatment time that is extremely shorter than in the past.

Moreover, in the present invention, after the above VTE treatment, the single crystal is subjected to the single-domain treatment. This single-domain processing can be performed in a short time.

[0014]

EXAMPLES Examples of the present invention will be described below. First, in the following examples, an example in which the present invention is mainly applied to the production of a lithium niobate single crystal will be described.

First, a lithium compound and a niobium compound are mixed, calcined at 950 ° C., and calcined at 1050 ° C., for example. Using this baked product, the Czochralski method is used to pull it up at 1252 ° C. to pull up the columnar substance having a congruent composition.
Next, this columnar material is annealed at 1170 ° C. to remove the strain in the crystal. Next, this columnar product is cut to obtain a thin plate having a predetermined thickness.

Next, a lithium niobate powder having a predetermined composition different from the congruent composition and the thin plate are housed in a container and the container is heat-treated to change the composition of the lithium niobate single crystal forming the thin plate. . 1 (a) and 1 (b) are sectional views schematically showing a heat treatment apparatus suitable for this VTE treatment.

The container 8 is composed of a main body 2 and a lid 1. The upper opening of the main body 2 is covered with the lid 1. The outer shape of the main body 2 is substantially cylindrical, and the upper end surface 2a of the main body 2 has a lid 1
The edge 1d is placed. A step 1a is formed inside the edge 1d of the lid 1, and the step 1a projects into the inner space of the container 2. The planar shape of the step portion 1a is substantially circular, and the side peripheral surface 1c is provided around the step portion 1a.

Both the upper end surface 2a and the edge portion 1d are accurately ground and the parallelism between them is increased. This increases the airtightness of the inner space and prevents the volatile components from being contained in the container 20.
I didn't run away from him. As a result, it became easy to maintain the equilibrium state of lithium in the gas phase in the container 8. In addition, since the step portion 1a is projected into the inner space, the side peripheral surface 1c
The distance between the inner wall surface 2b and the inner wall surface 2b has become smaller. As a result, the lithium component was less likely to escape from the portion where the main body 2 and the lid 1 were rubbed together.

A lithium niobate powder 6 having a predetermined composition is contained in the main body 2. A pair of flat plate-shaped electrodes 5 is placed in this powder 6.
A and 5B are embedded, and the plate electrodes 5A and 5B are substantially parallel to each other and perpendicular to the bottom surface 2c. Lead wires 3A and 3 are provided on the upper ends of the flat plate-shaped electrodes 5A and 5B, respectively.
B is connected, and each lead wire 3A, 3B is a through hole of the lid 1.
Each of them is inserted into 1e and pulled out of the container 8. The lead wires 3A and 3B are connected to a power source (not shown). Alumina cement 4 seals around the lead-out ports of the lead wires 3A and 3B.

A predetermined number of thin plates 7 made of a single crystal of lithium niobate having a congruent composition are embedded in the powder 6. Each thin plate 7 is arranged between the pair of flat plate-shaped electrodes 5A and 5B so as to be parallel to them.

In this embodiment, the present invention is carried out by using the heat treatment apparatus shown in FIGS. 1 (a) and 1 (b). That is, the composition of the single crystal is changed by heat-treating the inside of the container 8.
Then, a voltage is applied to the single crystal while heating the inside of the container 8 to the Curie temperature of the single crystal or higher, thereby forming a single domain domain in the single crystal. In this case, the VTE treatment and the single domainization treatment are successively performed by the same heat treatment apparatus.

There is also a method in which the above-mentioned VTE processing and single-domain processing are performed by separate heat treatment apparatuses. In this case, it is preferable to perform the VTE process by the device shown in FIG.

The container 18 comprises a main body 12 and a lid 11. The upper opening of the main body 12 is covered with a lid 11. Body
The outer shape of 12 is, for example, a substantially cylindrical shape, and the upper end surface 12 of the main body 12 is
The edge 11d of the lid 11 is placed on a. Edge 11 of lid 11
The step 11a is formed inside the d, and the step 11a
Project into the inner space of the container 12. The planar shape of the step portion 11a is substantially circular, and the side peripheral surface 11 is formed around the step portion 11a.
c is provided.

Both the upper end surface 12a and the edge portion 11d are ground with high precision and their parallelism is increased. As a result, the airtightness in the inner space is improved, and the volatile components are prevented from escaping out of the container 18. A lithium niobate powder 6 having a predetermined composition is contained in the main body 12.

A predetermined number of thin plates 7 made of a single crystal of lithium niobate having a congruent composition are embedded in the powder 6. Each thin plate 7 is substantially parallel to the side wall surface 12b,
It is substantially perpendicular to the bottom wall surface 12c.

In this embodiment, the VTE treatment is performed by changing the composition of the thin plate 7 using the heat treatment apparatus shown in FIG. Then
The temperature in the container 18 is lowered, the lid 11 is removed, and the thin plate 7 is taken out of the powder 6. Next, as shown in FIGS. 1 (a) and 1 (b), the thin plate 7 is set in the container 8 and the above-described single-domain division processing is performed.

In the conventional heat treatment schedule 21 shown in FIG. 3, the heat treatment is continued at a temperature of 1100.degree. Also in this case, the Curie temperature T _c of the thin plate 7 is, for example, 1146 ° C. to 11 ° C.
It goes up to 90 ° C and rises over time. However, in this method, it takes a long time for the Curie temperature to reach 1190 ° C. For example, if the thickness of the thin plate is 0.5 mm, it takes about 500 hours.

Next, in the case of producing a lithium niobate single crystal having a Li ₂ O content of 47.2 mol%, in the conventional heat treatment schedule 22 shown in FIG. 4, the heat treatment was performed at 1070 ° C., for example. The Curie temperature T _c of the single crystal of the thin plate 7 is 1090 ℃
It took about 800 hours of heat treatment to reach (when the sheet thickness is 0.5 mm).

On the other hand, according to the present invention, a lithium niobate single crystal having a composition other than the congruent composition can be produced with an extremely short heat treatment time. For example, it was found that when a thin plate 7 made of a lithium niobate single crystal having a congruent composition was heated at 1175 ° C. and subjected to VTE treatment, the composition of the single crystal became 50 mol% of Li ₂ O within 54 hours. Moreover, these results were obtained even when the thin plate had a thickness of 3 mm. In this way, the VTE treatment can be accelerated at a temperature above the Curie temperature (1146 ° C) corresponding to the congruent composition,
This is because heat treatment can be performed.

Moreover, in the present invention, after the above VTE treatment, the thin plate 7 is heated while applying a voltage,
Single domain domains can be formed in the single crystal that constitutes this.

As a result, the heat treatment time of lithium niobate by the VTE method was remarkably shortened, the production amount thereof was remarkably increased, and the production cost was greatly reduced. Moreover, a single crystal in which the domains of the single crystal are single-domained can be obtained.

Further, for example, a thin plate 7 made of a lithium niobate single crystal having a congruent composition is heated at 1175 ° C.,
After VTE treatment, the composition of the single crystal was changed to Li within 36 hours.
_It was found that ₂ O was 47.2 mol%.

In the above VTE treatment and single domainization treatment, the heat treatment temperature of the single crystal must be lower than the melting temperature of the single crystal, and the difference between the heat treatment temperature and the melting temperature is 10%.
It is preferable that the temperature is not lower than ° C. When a pair of plate-like electrodes are embedded in oxide powder and a material such as a thin plate is embedded between the pair of plate-like electrodes, the voltage magnitude (V) is determined by the distance between the pair of plate-like electrodes ( If the value divided by (cm) is 1 V / cm or more,
The material can be reliably divided into domains.

Further, in the present invention, the VTE process and the single domainization process can be sequentially carried out by an apparatus as shown in FIG. 5, for example. Further, the VTE process can be performed by the device as shown in FIG. 2 and then the single domain processing can be performed by the device as shown in FIG. Of the constituent parts shown in FIG. 5, the same parts as those shown in FIG. 1 are designated by the same reference numerals.

In the heat treatment apparatus shown in FIG. 5, each thin plate 7 is embedded so as to be substantially perpendicular to the bottom surface 2c. The flat electrode 5C is connected to the lead wire 3A, and the flat electrode 5D is connected to the lead wire 3B. The flat plate-shaped electrodes 5C and 5D are both embedded substantially parallel to the bottom surface 2C.

In order to divide the lithium niobate single crystal into single domains, it is necessary to apply a voltage in the Z-axis direction. Therefore, when the positional relationship between the flat plate-shaped electrodes 5A and 5B and the thin plate 7 is in the state shown in FIG. 1, it is easy to process the Z plate. On the other hand, when the X plate having the X axis that is perpendicular to the main surface and suitable for optical waveguide use is subjected to the single domain processing, the Z axis exists in the thin plate 7. Therefore, as shown in FIG. 5, the thin plate 7 is arranged vertically to the flat plate-shaped electrodes 5C and 5D, and the Z axis of the thin plate 7 is arranged so as to substantially coincide with the voltage application direction. Also for the Y plate, it is preferable to arrange the thin plate 7 and the flat plate-shaped electrodes 5C and 5D similarly to this.

In the case of a 128 ° Y plate suitable for a surface acoustic wave (SAW) substrate, 128 ° perpendicular to the main surface of the thin plate 7.
The Y axis appears. Therefore, even if the thin plate 7 is installed as shown in FIG. 1, a considerable part of the magnitude of the voltage is applied in the Z-axis direction and a small amount is applied in the Y-axis direction. Therefore, if a slightly larger voltage is applied as compared with the case where the Z plate is subjected to the single-domain processing, and the decrease of the applied voltage in the Z-axis direction is compensated, the single-domain processing can be performed without any problem.

(Experiment 1) Hereinafter, more specific experimental results will be described. Using the heat treatment apparatus shown in FIG. 1, a single crystal of lithium niobate having a congruent composition was subjected to VTE treatment, and then subjected to single-domain treatment. A 3-inch diameter columnar body made of a lithium niobate single crystal having a Li ₂ O content of 48.6 mol% was pulled up from the Czochralski furnace to obtain a columnar body having a length of 100 mm. This was annealed and cut with an inner peripheral blade to obtain a thin plate having a predetermined thickness.

The thin plate was subjected to optical polishing on the Z surface to obtain a rectangular sample having a length of 20 mm and a width of 10 mm. The plate electrodes 5A and 5B were made of platinum having a thickness of 1 mm. Li ₂ O
A 50 mol% lithium niobate powder was used as powder 6.

The powder 6 in the container 8 was compression-molded so that the height of the powder 6 was adjusted to 30 mm, the gap between the samples 7 was filled, and cracking due to pyroelectricity was prevented. Then, the flat plate-shaped electrodes 5A, 5
Platinum lead wires 3A and 3B having a diameter of 0.5 mm were connected to B, and the gap between the lid 1 and the platinum lead wires 3A and 3B was sealed with alumina cement 4.

In this way, the experiment numbers 1 to 1 shown in Table 1 were obtained.
VTE treatment was performed under each condition of 10 and then single domainization treatment was performed. However, the thickness of the thin plate 7 and the heat treatment conditions during the VTE treatment were changed as shown in Table 1. Then, the Curie temperature of the single crystal after the VTE treatment and the single-domain treatment was measured, and the single-domain determination was performed.

The heat treatment conditions and the like in Experiment Nos. 1 to 10 will be further described with reference to FIG. However, in FIG. 6, graph 26 shows the heat treatment schedule,
27 shows the schedule of the applied voltage.

The container 8 was placed in an electric furnace and heated at a rate of 100 ° C./hour to reach a desired heat treatment temperature T ₁ at time t ₁ . This T1 is the heat treatment temperature shown in Table 1.
However, in Experiment Nos. 1 to 3, two-step heat treatment was performed.

Then, the VTE treatment is performed at the heat treatment temperature and time shown in Table 1. That, t ₂ -t shown in FIG. 6
₁ is the heat treatment time shown in Table 1. And the above V
After the TE treatment was completed, the temperature was raised and the heat treatment temperature was set to 1195 ° C. at time t ₄ . Application of voltage was started 6 hours after the heat treatment temperature reached 1195 ° C., the applied voltage was gradually increased, and a predetermined applied voltage was obtained 6 hours later.

The heat treatment temperature was kept at 1195 ° C. for 20 hours,
It was cooled to room temperature at a temperature decrease rate of 50 ° C./hour. The time when the temperature reaches room temperature is t ₅ . Then, the applied voltage was set to OV for 3 hours after reaching room temperature.

The magnitude of the applied voltage depends on the pair of flat plate-shaped electrodes 5.
It was set to 1V per 1 cm of the powder interposed between A and 5B. However, the distance between the flat plate-shaped electrodes 5A and 5B is as shown in FIG.
It is m shown in (a).

When the magnitude of the applied voltage is less than 1 V / cm, even if the thin plate 7 is heated above its Curie temperature,
Not all single crystal domains are aligned.

In Experiment Nos. 11 and 12 shown in Table 1, the thin plate 7 was subjected to the single-domain processing, and then the VTE treatment was performed by the conventional VTE apparatus according to the conventional heat treatment schedule shown in FIG. The Curie temperature T _C of the single crystal was measured using a DTA device. In addition, when the domain of the single crystal had a single domain, the item of “single domain determination” was displayed as “◯”.

In Experiment Nos. 1 to 10, time t.
_At the time point of ₂ , it was separately confirmed that the Curie temperature reached 1190 ° C. and the single domainization treatment was completed.

[0050]

[Table 1]

Further, a phase diagram of lithium niobate is schematically shown in FIG. As can be seen from this phase diagram, there is a relationship shown in Table 2 between the ratio of Li ₂ O and the Curie temperature T _C and the melting temperature.

[0052]

[Table 2]

As can be seen by comparing Experiment Nos. 1 to 10 and 11, 12, according to the present invention, a lithium niobate single crystal having a Curie temperature of 1190 ° C. can be produced in an extremely short time as compared with the conventional method. be able to. This is because the VTE reaction is basically temperature-controlled. Moreover, the single crystal domain was also well divided into single domains.

Even under the same heat treatment conditions, the thin plate 7 has a thickness of 3
mm, the heat treatment time became slightly longer. Further, it was found that when the thickness of the thin plate 7 exceeds 5 mm, it is difficult to make the composition uniform inside.

As can be seen from the phase diagram of FIG. 10, in the congruent composition, the melting temperature is 1252 ° C., and at least at this point, heat treatment at 1150 to 1242 ° C. can accelerate the VTE reaction, and The higher the temperature, the better. However, when Li ₂ O reaches 50 mol%, the melting temperature becomes 1
Since the temperature drops to 200 ° C, the heat treatment temperature should be adjusted at this point.
It is recommended to carry out at 1190 to 1150 ° C.

(Experiment 2) Heat treatment cycle 23 shown in FIG.
24. According to the voltage application cycle 25, the VTE process and the single domainization process were sequentially performed. This treatment method was the same as in Experiment 1.

The heat treatment cycle and the voltage application cycle will be described. First, as shown in FIG. 2, the groove plate 7 was embedded in the powder 6 and set. Then, according to the heat treatment cycle 23, VTE treatment was performed. Specifically, the container 18 was placed in an electric furnace and heated at a rate of 100 ° C./hour to reach a desired heat treatment temperature T2 at time t ₁ .

Then, the VTE treatment is performed at the heat treatment temperature and time shown in Table 3. That, t ₂ -t shown in FIG. 7
₁ is the heat treatment time shown in Table 1. Next, the inside of the container 18 was cooled and returned to room temperature at time t ₃ . Then, the thin plate 7
Was removed from container 18 and set again as shown in FIG.

Then, the temperature was raised and the heat treatment temperature was set to 1195 ° C. at time t ₄ . Application of voltage was started 6 hours after the heat treatment temperature reached 1195 ° C., the applied voltage was gradually increased, and a predetermined applied voltage was obtained 6 hours later.

The heat treatment temperature was kept at 1195 ° C. for 20 hours,
It was cooled to room temperature at a temperature decrease rate of 50 ° C./hour. The time when the temperature reaches room temperature is t ₅ . Then, the applied voltage was set to OV for 3 hours after reaching room temperature.

When VTE treatment and single-domain processing were performed under the same conditions as in Experiment 1 except for the above, a single-domain single crystal having the same Curie temperature as in Experiment 1 was obtained.

(Experiment 3) In the same manner as in Experiment 1, Table 3
Experiment Nos. 21 to 29 shown in FIG. For each example, Table 3 shows the thickness of the thin plate 7, the heat treatment conditions during the VTE treatment, the Curie temperature after the heat treatment, and the single domain determination.

However, unlike Experiment 1, as the powder, a lithium niobate powder containing 47.2 mol% of Li ₂ O was used. The heat treatment conditions and the like in this experiment will be further described with reference to FIG. However, in FIG. 8, a graph 31 shows a heat treatment schedule, and a graph 32 shows an applied voltage schedule.

The container 8 was placed in an electric furnace and heated at a rate of 100 ° C./hour to reach a desired heat treatment temperature T2 at time t ₁ . This T2 is the heat treatment temperature shown in Table 3.
Then, the heat treatment was performed at the heat treatment temperature and time shown in Table 3. Then, after the heat treatment time shown in Table 3 had elapsed, a voltage was applied according to Schedule 32.

That is, "t ₆ -t ₁ " shown in FIG.
The heat treatment time shown in FIG. At time t ₆ or later,
The Curie temperature of lithium niobate single crystal is 10
It was confirmed that the temperature reached 90 ° C. The application of voltage was started at time t ₆ , 6 hours later, the voltage was increased to 1 V / cm, and further 8 hours later, the temperature was started to drop. The temperature decreasing rate was 50 ° C./hour. The time when the temperature reaches room temperature is t ₅ . The applied voltage was set to OV for 3 hours after reaching room temperature.

In Experiment Nos. 30 and 31 shown in Table 3, the thin plate was first subjected to the single-domain treatment, and then the VTE treatment was performed according to the heat treatment conditions shown in Table 3 in the heat treatment schedule shown in FIG.

[0067]

[Table 3]

As can be seen from the above results, according to the present invention, the single crystal can be VTE-treated in a short time. Also within the scope of the present invention, when the heat treatment temperature is high, the Curie temperature reaches 1090 ° C in a shorter time.

As can be seen from FIG. 10, Li ₂ O is 47.2 m.
When it is ol%, the melting temperature of the single crystal becomes 1230 ° C., so that the heat treatment can be performed at a heat treatment temperature of 1220 ° C. or lower. Also, as in this experiment, to obtain a Li ₂ O composition of 47.2 mol%, the Curie temperature of 1090 ° C.
In the following, for example, heat treatment was conventionally performed at 1050 ° C. Further, since the VTE process is almost rate-controlled by temperature, conventionally, it took a very long time as shown in Experiment No. 30. In this respect, the effect of the present invention is even greater.

(Experiment 4) Heat treatment cycle 28 shown in FIG.
29. According to the voltage application cycle 30, the VTE process and the single domainization process were sequentially performed. This treatment method was the same as in Experiment 1. Further, as the powder, a lithium niobate powder containing 47.2 mol% of Li ₂ O was used.

Specifically, first, as shown in FIG. 2, the thin plate 7 was embedded in the powder 6 and set. Then, according to the heat treatment cycle 28, VTE treatment was performed. VTE treatment was performed at the heat treatment temperature and time shown in Table 3. That is, FIG.
T ₂ -t ₁ shown in is the heat treatment time shown in Table 3. Next, the inside of the container 18 was cooled and returned to room temperature at time t ₃ .
The plate 7 was removed from the container 18 and set again as shown in FIG.

[0072] Then, the temperature is raised, the heat treatment temperature at the time t ₄ was to T2. 6 after heat treatment temperature reaches T2
The application of voltage was started after a lapse of time, the applied voltage was gradually increased, and a predetermined applied voltage was obtained after 6 hours.

The heat treatment temperature was kept at T2 for 20 hours, and
The temperature was decreased to room temperature at a temperature decrease rate of ° C / hour. The applied voltage was set to OV over 3 hours after reaching room temperature.

VTE treatment and single-domain treatment were carried out as described above in the same manner as in Experiment 3, and the same single-domain single crystal as in Experiment 3 was obtained.

In the same manner as above, Li ₂ O was 47.6 mol.
%, 48.0mol%, 49.0mol%, 49.4mol%, 49.8mol%
Using lithium niobate powder 6 having the following composition, a single crystal of each composition was manufactured according to the present invention. Then, it was confirmed that single crystals of each composition could be mass-produced.

(Experiment 5) Lithium tantalate single crystal was
Made according to the present invention. This manufacturing process is based on Experiment 1.
Obeyed. However, the material of the thin plate 7 was a lithium tantalate single crystal having a congruent composition (Li ₂ O was 48.3 mol%). As the powder 6, a lithium tantalate powder containing 50.0 mol% of Li ₂ O was used.

Specifically, in the VTE processing step,
The heat treatment temperature was set to 1480 ° C and the Curie temperature was set to 64 after 30 hours.
It was confirmed that the temperature reached 6 ° C. In the subsequent single-domain processing, the heat treatment temperature was 1480 ° C., the applied voltage was 2 V / cm, and the voltage was applied in the Z-axis direction of the single crystal. Table 4
Shows the relationship between the Li ₂ O ratio and the melting temperature and Curie temperature of the single crystal.

[0078]

[Table 4]

FIG. 11 shows a phase diagram of lithium tantalate. In this phase diagram, the horizontal axis shows the mol% of tantalum. The Curie temperature Tc of the lithium tantalate single crystal is considerably lower than its melting temperature.

In the case of lithium tantalate, heat treatment at a melting temperature of −20 ° C. to a melting temperature of −100 ° C. has a great effect of promoting the VTE treatment. Further, in the case of a lithium tantalate single crystal, the Curie temperature is extremely lower than the melting temperature, and thus it has been almost impossible in the past to change the composition by performing VTE treatment without multidomaining the domain. Met.

(Experiment 6) Lithium tantalate single crystal was
Made according to the present invention. This manufacturing process is based on Experiment 1.
Obeyed. However, the material of the thin plate 7 was a lithium tantalate single crystal having a congruent composition. As powder 6,
Lithium tantalate powder containing 47.0 mol% of Li ₂ O was used.

Specifically, in the VTE processing step,
The heat treatment temperature was set to 1480 ° C, and the Curie temperature was 57 after 30 hours.
It was confirmed that the temperature reached 4 ° C. In the subsequent single-domain processing, the heat treatment temperature was 1480 ° C., the applied voltage was 2 V / cm, and the voltage was applied in the Z-axis direction of the single crystal.

When the samples manufactured by the above Experiments 1 to 6 were used as a substrate and an optical waveguide was formed on this substrate, a suitable optical waveguide substrate, voltage sensor, focus An electric sensor was obtained. Also,
There is no particular limitation on the size of the sample, for example, a diameter of 1
It can process ~ 4 inch wafers, and several at a time.

Next, still another aspect of the present invention will be described. FIG. 12 is a cross-sectional view schematically showing a heat treatment structure suitable for carrying out the VTE treatment step of the present invention.

For example, at the upper opening of the main body 42 of the rectangular parallelepiped, a lid is
41 is covered. The edge 42a of the main body 42, the edge of the lid 41
41c is placed. A step 41a is formed inside the edge 41c, and the step 41a projects into the inner space of the container 48. The planar shape of the step portion 41a is rectangular, and the side peripheral surface 41b is provided on the four circumferences of the difference portion 41a. The edge 42a of the main body and the edge 41c of the lid 41 are in contact with each other.

An inner container 43, preferably made of platinum, is housed in the inner space of the container 48. The inner container 43 is the main body
It consists of 45 and lid 44. The main body 45 is placed on the bottom surface 42c, and the lid 44 is placed on the edge of the main body 45. A cap portion 44a extending downward substantially parallel to the side wall surface 42b is provided on the peripheral edge of the lid 44.

A lithium niobate powder 47 having a predetermined composition is contained in the inner space of the main body 45, and a support frame 46 made of a platinum wire is fixed to the powder 47. That is, the end 46 of the support frame 46
a is stabbed in the powder 47 and fixed, and the protrusion 46b,
Two housing recesses 46d, for example, are formed between 46c. The thin plates 7 are stacked in the respective accommodation recesses 46d, and the platinum wire 49 is interposed between the thin plates 7 that are vertically adjacent to each other.

In this example, the container 43, which is in direct contact with the lithium niobate powder 47, is made of platinum which is non-reactive with this.
However, since the container 43 is formed of a thin platinum plate, steam leaks from the gap between the lid 44 and the main body 45. Therefore, by providing the cap portion 44a, the flow path of steam is lengthened, and the inner container 43 is housed in the container 48.

In the VTE treatment method of this embodiment, even if the powder 47 is thermally contracted during the heat treatment, there is no risk of cracks in the thin plate 7. Further, if the powder adheres to the thin plate 7, it is necessary to remove the powder by polishing, but there is no such possibility. However, when the thin plate 7 is subjected to the VTE process in the state as shown in FIGS. 1, 2 and 5, since the diffusion isotropically proceeds from the entire surface of the thin plate 7, it takes time to complete the VTE process. The length of the thin plate 7 is shorter than that of the example shown in FIG. 12, and the composition change can be surely completed up to the inside of the thin plate 7 having a large thickness.

13 to 15 are cross-sectional views schematically showing the structure in the state of being subjected to the single-domain processing according to the present invention.

In FIG. 13, the container 58 is composed of a main body 52 and a lid 51. The upper opening of the main body 52 is covered with a lid 51. An edge portion 51d of the lid 51 is placed on the upper end surface 52a of the main body 52. A step 51a is formed inside the edge 51d of the lid 51, and the step 51a projects into the inner space of the container 58. A side peripheral surface 51c is provided around the step portion 51a.

A predetermined number of thin plates 7 which have been subjected to the VTE process are prepared, stacked vertically and brought into contact with each other to form a columnar array 57. This VTE process is preferably performed by the method described above. The flat electrode 5D is brought into contact with the lower end surface of the array 57, and the flat electrode 5C is placed on the upper end surface of the array 57. These are housed in the inner space of the main body 52.
A refractory material 53 is placed on the flat plate-shaped electrode 5C.

Lead wires 3 are respectively attached to the flat plate-shaped electrodes 5C and 5D.
A and 3B are contacted, and the lead wires 3A and 3B are connected to the through hole 5 of the lid 51.
Each of them is inserted into 1e and pulled out of the container 58. The lead wires 3A and 3B are connected to a power source (not shown). Alumina cement 4 is used to seal the peripheries of the lead wires 3A and 3B. Then, while heating the inside of the container 58 to the Curie temperature of the single crystal or higher, a voltage is applied to the array 57,
Form single domain domains in a single crystal.

By adopting such a single-domain processing method, a large number of thin plates 7 can be single-domain processed at one time in one heat treatment container. In addition, refractory materials are arranged above the array 57.
By placing 53 as a weight, it is possible to prevent gaps from being generated between the thin plates 7 and between the thin plates 7 and the flat plate-shaped electrodes 5C and 5D. This is because such minute gaps cause cracks due to the occurrence of pyroelectricity.

In the structure of FIG. 13, the gap between the outer peripheral surface of the array 57 and the inner surface of the main body 52 is made as small as possible,
It prevents the thin plate 7 and the flat plate-shaped electrodes 5C, 5D from being laterally displaced and causing pyroelectricity.

The material of the flat electrodes 5C and 5D is preferably a soft metal which is non-reactive with the single crystal 7, and an unused platinum plate is particularly preferable. This is because the unused platinum plate had particularly good adhesion to the thin plate 7. Also, preferably, the lead wire is placed in an insulating tube made of a substance that is non-reactive with the oxide single crystal.
It is preferable to insert 3A and 3B to prevent mispolarization.

Materials for the main body 52 and the lid 51 are selected to be insulating and non-reactive with the oxide single crystal. When subjecting the lithium niobate single crystal and the lithium tantalate single crystal to single-domain treatment, magnesia ceramics in which magnesium accounts for 98 mol% or more of the contained metal atoms is particularly preferable.

The structures for single domainization processing shown in FIGS. 14 and 15 are basically the same as those shown in FIG. However, in FIGS. 14 and 15, the container is larger than that in FIG.
The horizontal dimension of 58 is large, and there is a gap between the outer peripheral surface of the array 57 and the inner side surface 52b of the main body 52.

In FIG. 14, the dummy member 54 is housed in this gap. The height of the dummy material 54 is preferably at least higher than that of the flat plate-shaped electrode 5C. Dummy material 54
Must be formed of an insulating material that does not react with the oxide single crystal when heated. The planar shape of the main body 52 is an annular shape,
When the thin plate 7 has a substantially circular shape, it is preferable that the planar shape of the dummy material 54 is semicircular or arcuate. When the planar shape of the main body 52 is a square, it is preferable that the dummy material 54 has a prismatic shape and that a large number of the dummy materials 54 are arranged in the gap.

Such a dummy material 54 has an effect of suppressing pyroelectricity due to lateral displacement of the thin plate 7 and the flat plate-shaped electrodes 5C, 5D. Further, by reducing the gap between the dummy materials 54, the resistance against the flow of the vapor evaporated from the thin plate 7 increases, and the composition fluctuation of the single crystal due to evaporation can be prevented.

In the example of FIG. 15, the oxide powder 55 is contained below the dummy material 54. The composition of the oxide powder 55 is preferably substantially the same as the composition of the single crystal of the thin plate 7. When the oxide powder 55 is arranged below the dummy material 54 in this way, the components also evaporate from the oxide powder 55 during heating, so the vapor in the vicinity of the array 57 is kept substantially constant, and the vaporized components from the thin plate 7 are removed. It becomes difficult to come off.

[0102]

As described above, according to the present invention, it is possible to produce a single-domain oxide single crystal having a desired composition in a heat treatment time which is extremely shorter than that of the prior art.

[Brief description of drawings]

1A is a cross-sectional view showing a state where a thin plate 7 is being processed in a container 8, and FIG. 1B is a cross-sectional view taken along line Ib-Ib of FIG.

FIG. 2 is a cross-sectional view showing a state in which a thin plate 7 is subjected to VTE processing inside a container 18.

FIG. 3 is a graph showing a conventional heat treatment schedule.

FIG. 4 is a graph showing a conventional heat treatment schedule.

5 is a cross-sectional view showing a state where the thin plate 7 is being processed in the container 8. FIG.

FIG. 6 is a graph showing a heat treatment schedule and a voltage application schedule according to an embodiment of the present invention.

FIG. 7 is a graph showing a heat treatment schedule and a voltage application schedule according to an embodiment of the present invention.

FIG. 8 is a graph showing a heat treatment schedule and a voltage application schedule according to an embodiment of the present invention.

FIG. 9 is a graph showing a heat treatment schedule and a voltage application schedule according to an example of the present invention.

FIG. 10 is a phase diagram of lithium niobate.

FIG. 11 is a phase diagram of lithium tantalate.

FIG. 12 is a sectional view schematically showing a state where the thin plate 7 is subjected to VTE processing.

FIG. 13 is a cross-sectional view that schematically shows a state in which the array body 57 formed by stacking the thin plates 7 is subjected to the single-domain processing.

FIG. 14 is a cross-sectional view schematically showing a state where the arrayed body 57 formed by stacking the thin plates 7 is subjected to the single-domain processing.

FIG. 15 is a cross-sectional view that schematically shows a state in which the arrayed body 57 formed by stacking the thin plates 7 is subjected to the single domain processing.

[Explanation of symbols]

1, 11, 41, 51 Lid 2, 12, 42, 52 Main body 3A, 3B Power supply lead wires 5A, 5B, 5C, 5D A pair of flat plate electrodes 6,47, 55 Oxide powder having a predetermined composition 7 oxides of single crystal thin 8,18, 43, 48, 58 container 21, 22, 23, 24, 26, 28, 29, 31 heat treatment schedules 25, 27, 30, 32 voltage application schedule T _C Curie temperature T1, T2 heat treatment temperature

Claims (7)

[Claims] 1. A step of changing the composition of the single crystal by heat-treating a material composed of an oxide single crystal and an oxide powder having a predetermined composition different from the composition of the oxide; A method for producing an oxide single crystal, comprising the step of applying a voltage to the single crystal while heating the crystal to its Curie temperature or higher to subject the single crystal to single-domain processing. 2. The method for producing an oxide single crystal according to claim 1, wherein the heat treatment is performed while the material is embedded in the oxide powder. 3. Embedding the material in the oxide powder,
The method for producing an oxide single crystal according to claim 1, wherein the single domainization treatment is performed with a pair of plate-shaped electrodes embedded in the oxide powder at positions sandwiching the material. 4. A support frame made of a wire made of a substance that is non-reactive with the single crystal is fixed on the upper side of the oxide powder, and a plurality of the materials are vertically arranged in the recesses of the support frame, and adjacent to each other. The method for producing an oxide single crystal according to claim 1, wherein the heat treatment is performed in a state where a wire rod of a substance that is non-reactive with the single crystal is interposed between the matching materials. 5. An array is formed by stacking the materials in a vertical direction while making contact with each other, and plate electrodes are respectively brought into contact with an upper end and a lower end of the array, and fireproof is provided on the upper plate electrode. Performing the single domainization process with the object placed,
The method for producing an oxide single crystal according to claim 1. 6. A dummy material made of a substance that is non-reactive with the single crystal is arranged in a gap between the array and the refractory and an inner surface of a container that houses them.
A method for producing the oxide single crystal described. 7. A dummy material made of a substance non-reactive with the single crystal and the powder are arranged in a gap between the array and the refractory and an inner side surface of a container containing the array and the dummy. The method for producing an oxide single crystal according to claim 5, wherein the powder is arranged below the material.