JPH0782087A - Production of oxide single crystal - Google Patents

Abstract

PURPOSE:To control the growing shape of a perovskite-type oxide single crystal for elements such as optical wavelength conversion element and to improve the processing yield of the element. CONSTITUTION:A perovskite-type oxide single crystal having a general formula ABO3 (A is Li, K or Na and B is Nb or Ta or A is Ba and B is Ti) is produced by TSSG process by growing the crystal in a specific direction, pulling up the most part of the grown crystal until the crystal is brought into contact with the hot solution at a part of the bottom of the crystal, and continuing the growth of new crystal from the contacting part of the crystal and the solution.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a perovskite type oxide single crystal represented by the general formula ABO ₃ .

[0002]

2. Description of the Related Art In recent years, perovskite type oxide single crystals such as KNbO ₃ crystals and BaTiO ₃ crystals have been attracting attention as nonlinear optical crystals for wavelength conversion or photorefractive crystals. These crystals are TSSG (Top Seeded Solution Grow).
It is cultivated by a method called “th method”. T
The SSG method is one of solution growth in which the melt temperature is gradually lowered while the seed crystal is kept in a high temperature solution, and the crystal is precipitated around the seed crystal. When the seed crystal is pulled up at about 0.2 mm / h In some cases, the seed crystal may not be pulled up.

In general, as in the case of solution-grown crystals, according to the TSSG method, crystals often grow in a form surrounded by a specific crystal plane called a crystal habit. This is because the crystal growth mechanism takes a mechanism called creeping growth in which atoms are arranged along a specific crystal plane. In particular, those having a cubic perovskite structure at the growth temperature have a cubic or rectangular parallelepiped shape surrounded by {100} _pc ((100) plane in the cubic perovskite structure and a plane equivalent thereto). grow up.

The crystal produced by this method has the following features. (1) It is difficult to freely control the shape at the time of growth, and the shape is restricted by the crystal habit. (2) Always grow in a form surrounded by a specific crystal plane, and a junction of different growth planes is called a sector boundary, and has different optical properties from other portions. Therefore, in manufacturing an actual optical element, there are problems such as difficulty in manufacturing a large-sized element, reduction in yield, and deterioration in element performance.

The above (1) and (2) will be described more specifically by taking the growth of a KNbO ₃ crystal as an example. TS
The difficulty and problems of growing a KNbO ₃ single crystal by the SG method are described in the article “Progress in
KNbO ₃ Growth ”, Journal of
Crystal Growth, Vol. 78 (198
6) Details on pp 431-437 and the like.

KNbO ₃ crystal has a crystal growth temperature of 1050
The above-mentioned cubic perovskite structure is formed at around ° C. Therefore, the KNbO ₃ crystal is basically {10
0} It grows in the form surrounded by _pc faces. In the case of the TSSG method, the seed crystal orientations [100], [110], and [111]
As a result, the crystal grows into the shape shown in FIG.
It is difficult to control the crystal shape.

In addition, since the sector boundary has a non-uniform refractive index, a good quality optical element cannot be cut out.
For example, the crystal grown by the conventional method with the seed crystal oriented in the [110] _pc direction has a complicated sector boundary 6 as shown in FIG. 9, and if the sector boundary 6 is avoided, the processing steps become complicated. However, there are problems such as that, it becomes wasteful during processing, and it is difficult to manufacture a large element.

Here, in all the drawings shown in FIGS. 1 to 10 below, the same parts and portions are designated by the same reference numerals,
The description in each figure is omitted. In FIGS. 1 to 9, 1 is a seed crystal, 2 is a neck-like portion formed by slightly growing crystals from the seed crystal 1, 3 is a first stage grown crystal,
Reference numeral 4 is a second stage grown crystal, 5 is a crystal defect, 6 is a sector boundary, and 7 is a solution surface. Further, in FIG. 10, 8 is an alumina ceramic tube as a holder for the seed crystal 1, 9 is a platinum crucible for containing the crystal raw material,
10 is a ceramic refractory on which the platinum crucible 9 is mounted.
Reference numeral 1 is a resistance heater for heating and melting the crystal raw material.
Reference numeral 2 is a raw material solution, and 13 is a crystal.

[0009]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned drawbacks of the prior art, and in the oxide single crystal manufacturing technique by the TSSG method, the crystal is controlled and grown in a desired shape. Provide a new method,
Further, the present invention newly provides a technology for producing an oxide single crystal that minimizes the sector boundary in the crystal and enables the production of a large element and the improvement of the yield.

Further, according to the present invention, cracks of crystals during slow cooling which have occurred in crystals such as KNbO ₃ crystals and BaTiO ₃ crystals whose structure changes from the crystal growth temperature to the room temperature, It is possible to solve the problems such as twin formation.

[0011]

The present invention has been made to solve the above-mentioned problems, and has the general formula ABO ₃ (A =
Li, K, Na, B = Nb, Ta, or A = Ba,
A method for producing a perovskite type oxide single crystal represented by B = Ti) by bringing a seed crystal into contact with a high temperature solution of a raw material, and gradually growing the crystal while rotating the seed crystal. After growing in the direction, most of the crystal is pulled up from the hot solution until the grown crystal comes into contact with the hot solution at a part of the bottom, and then crystal growth is newly started from the contact portion between the crystal and the hot solution. The present invention provides a method for producing an oxide single crystal characterized by the above.

In a preferred embodiment of the present invention, the general formula ABO ₃ is KTa _x Nb _1-x O ₃ (0 ≦
It is characterized in that it is a perovskite type oxide single crystal represented by x ≦ 1).

Further, as a preferred embodiment of the present invention, the orientation of the seed crystal is [110] _pc which is the [110] orientation in the cubic perovskite type structure. Further, the specific direction is characterized by [001] _pc orientation and [00-1] _pc orientation which are [001] orientation and [00-1] orientation in the cubic perovskite structure. Here, in the present invention, [00-1]
The azimuth means an azimuth opposite to the [001] azimuth.

As another preferred embodiment of the present invention,
After contacting the seed crystal with the high temperature solution of the raw material, 0.06 ~
The seed crystal is pulled up at a speed of 0.10 mm / h to form a crystal part thinner than the seed crystal in a thickness of 1 to 3 mm. Further, the crystals may be grown in a specific direction while the pulling of the seed crystal raw material from the high temperature solution is stopped. Furthermore, after growing a crystal of a predetermined length in a specific direction, most of the crystal is pulled out of the solution at a rate of 1 to 20 mm / h until a part of the bottom of the crystal and the high temperature solution come into contact with each other. It is also possible to grow a crystal newly from the contact portion of the solution to grow a crystal having a thickness of a predetermined length in the specific direction.

The above rate of 0.06 to 0.10 mm / h reduces the supersaturation degree of the solution so that the crystal growth rate becomes slow, that is, the slow cooling rate of the solution is kept at 0.1 ° C./h or less. Even at the growth rate, the seed crystal is preferable in the sense that it is a low speed at which crystal growth can be maintained without leaving the solution. 1 to 3
A crystal part with a thickness of mm is preferable as a length long enough to prevent defects propagated from the seed crystal to reach the crystal to be grown. The speed of 1 to 20 mm / h is preferable in the sense that the growth rate of the crystal cannot catch up with the pulling rate, and the crystal is not subjected to thermal strain due to rapid withdrawal from the solution or rapid cooling.

[0016]

Function: As is the case with solution-grown crystals, T
According to the SSG method, crystals often grow in a form surrounded by a specific crystal plane called a crystal habit. This is because the crystal growth mechanism takes a mechanism called creeping growth in which atoms are arranged along a specific crystal plane. In particular, those having a cubic perovskite structure at the growth temperature grow into a cubic or rectangular parallelepiped shape surrounded by {100} _pc .

According to the experiments by the present inventors, it was found that the average linear growth rate of each growth surface is influenced by the temperature distribution in the furnace, the orientation of the growth surface, and the pulling rate.

In particular, according to the experiments by the present inventors, when the seed crystal is [110] _pc , when the solution temperature is lowered without pulling up, the four planes are equivalent planes. As shown in FIG. 5, it was found that crystals were likely to grow in two directions of [001] and [00-1]. On the contrary, it has been found that when the pulling speed is increased to some extent, the growth in the two directions is suppressed and the growth of the two surfaces of [100] and [010] is promoted.

Therefore, [001] and [00-
After the crystal is grown in the two directions [1], the crystal thickness can be made the length between the two surfaces by starting the pulling of the crystal.

Further, as shown in FIG. 6, most of the crystals grown in the [001] and [00-1] 2 directions are pulled out from the solution so that the solution and a part of the crystal bottom are in contact with each other. Then, as shown in FIG. 7, when crystal pulling growth is newly started from the contact portion between the crystal and the solution, a crystal having a shape as shown in FIG. 1 is obtained. That is, as shown in FIG. 2, the crystal defects generated at the junction with the seed crystal are prevented from propagating to the crystal grown in the next stage.

As shown in FIG. 4, if the neck portion 2 thinner than the seed crystal 1 is formed before growing the first-stage crystal, the effect of preventing the propagation of crystal defects can be further enhanced. Further, since the crystal growth planes can be limited to two planes in the second-stage crystal growth, the sector boundary sandwiched between the growth planes as shown in FIG. Become.

[0022]

【Example】

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described in detail by taking growth of a KNbO ₃ crystal as an example.

FIG. 10 is a side sectional view showing the basic structure of a crystal production apparatus by the TSSG method. Resistance heater 11
The internal furnace has an inner diameter of about 10 cm and can heat up to 1500 ° C. Platinum crucible 9 has an inner diameter of 6 cm and a depth of 7 c
Ceramic refractory 10 with a volume of about 150 cm ³ in m
Placed on top.

The starting material is anhydrous K ₂ CO with a purity of 99.5%.
195.51 g of ₃ and anhydrous Nb ₂ O having a purity of 99.99%
340.25 g of ₅ is mixed. This mixing ratio is K ₂ CO
The molar ratio of ₃ and Nb ₂ O ₅ is 52.5 mol% to 47.5.
Mol%.

A 150 cm ³ platinum crucible 9 was added to the mixed raw material.
Put in. As the seed crystal 1, KNbO ₃ having a columnar [110] _pc orientation of 3 mm × 3 mm × 16 mm is used. It is fixed in a seed crystal holder made of alumina ceramic tube 8 and positioned on a platinum crucible 9.

The temperature of the electric furnace is raised to melt the raw material, and 1060
Adjust seeding temperature from 0 ° C to 1065 ° C. When the solution temperature reaches an appropriate temperature for seeding, add 10 rp of seed crystal 1
While rotating at m, it is gradually lowered and brought into contact with the surface of the raw material solution 12. After seeding, the KNbO ₃ seed crystal 1 contacted is adjusted to a temperature at which the KNbO ₃ seed crystal 1 melts, does not separate from the solution, and does not grow obviously, and is held for 6 hours.

0.08 mm while cooling at 0.1 ° C./h
/ H, and a neck-shaped part having a length of 2 mm is grown. After making the neck, stop pulling up with the cooling rate kept constant,
Begin the first stage of training. By keeping it for a long time without pulling it up, it is possible to preferentially grow the [001] and [00-1] directions. [001], [00
After growing to about 20 mm (crystal thickness) in the −1] direction, the solution 12 is pulled up at a rate of 9 mm / h with the temperature kept constant. At this time, the contact area between the crystal 13 and the solution 12 is minimized while maintaining the contact between the crystal 13 and the solution 12.

After the contact area between the crystal 13 and the solution 12 is minimized, the second stage growth is started. While keeping the same cooling rate and rotation speed as in the growth in the first stage, the pulling rate was set to 0.
14 mm / h. As a result, the crystals are [001],
While suppressing the growth in the [00-1] direction, [100],
Crystal growth only in the [010] direction is possible. When the second stage growth reached 30 mm in the [100] and [010] directions, crystals 1 were obtained from solution 12 at the same 9 mm / h as in the first stage
3 is completely drawn out, and the crystal growth is completed.

The crystal is gradually cooled from the crystal growth temperature to 550 ° C.
Up to 15 ° C / h, from 550 ° C to room temperature at 8 ° C / h. After cooling, the size of the 2nd stage crystal part is 20mm × 30m
Crystals of m × 30 mm and about 80 g were obtained. From this crystal, it was possible to process into a crystal for an optical element having a maximum size of 12 mm × 12 mm × 20 mm, which could not be cut out due to the existence of a sector boundary.

(Example 2) K using the same furnace as in Example 1
The growth of the Ta _x Nb _1-x O ₃ crystal will be described below.

The starting material is anhydrous K ₂ CO with a purity of 99.5%.
195.51 g of ₃ and anhydrous Ta ₂ having a purity of 99.99%
282.83 g of O ₅ and anhydrous Nb having a purity of 99.99%
170.13 g of ₂ O ₅ is mixed. This mixing ratio is K ₂
The molar ratio of CO ₃ , Ta ₂ O ₅ and Nb ₂ O ₅ is 52.5.
Mol% to 27.75 mol% to 27.75 mol%.
This means that 5 mol% of K ₂ O was added as a flux to KTa _0.5 Nb _0.5 O ₃ (x = 0.5).

The mixed raw materials are put into a 150 cm ³ platinum crucible. As the seed crystal, 3 mm × 3 mm × 16 mm prismatic [110] _pc oriented KTaO ₃ is used. It is fixed in a seed crystal holder made of alumina ceramic tube and placed on the crucible. The electric furnace is heated to 1400 ° C. to melt the raw materials, and the seeding temperature is adjusted from 1250 ° C. to 1255 ° C. When the solution temperature reaches an appropriate temperature for seeding, the seed crystal is gradually lowered while rotating at 10 rpm to bring it into contact with the solution surface.

Since KTaO ₃ used for the seed crystal has a higher melting temperature than the crystal composition to be grown, unlike the case of using KNbO ₃ as the seed crystal for growing the KNbO ₃ crystal of Example 1, after seeding, Crystals rarely dissolve and leave the solution. In this case, the temperature is adjusted so that the KTaO ₃ crystal that becomes the seed after seeding does not grow, and the temperature is maintained for 2 hours.

While the seed crystal is not pulled up, it is cooled at 0.2 ° C./h while waiting for the crystal to start growing. When the crystals start to grow from the seed crystals, while cooling at 0.1 ° C./h, the crystals are pulled up at 0.08 mm / h to grow a neck portion having a length of 2 mm.

After the neck-shaped portion has been grown, the pulling is stopped and the first-stage growing is started with the cooling rate kept constant. By putting it for a long time without pulling it up, [001]
And the [00-1] direction can be preferentially grown. After growing to about 10 mm (crystal thickness) in the [001] and [00-1] directions, the temperature was kept constant at 9 m from the solution.
Pull up at a speed of m / h. At this time, the contact area between the crystal and the solution is minimized while maintaining the contact between the crystal and the solution.

After the contact area between the crystal and the solution is minimized, the second stage growth is started. The pulling speed is 0.14 m while maintaining the same cooling speed and rotation speed as in the first stage growth.
m / h As a result, the crystals are [001], [00-
[100], [01] while suppressing the growth in the 1] direction.
Crystal growth only in the [0] direction becomes possible. In the second stage growth, when it became 25 mm in the [100] and [010] directions,
The crystal is completely pulled out from the solution at 9 mm / h, which is the same as in the first step, and the crystal growth is completed.

The gradual cooling of the crystal is performed from the crystal growth temperature to room temperature at 10 ° C./h. As a result, a crystal having a size of the second stage crystal portion of 10 mm × 25 mm × 25 mm and about 70 g was obtained. The crystal composition is approximately KTa _0.8 Nb _0.2 O ₃
(X = 0.2). From this crystal, up to 5 mm ×
A 5 mm × 10 mm optical element could be processed.

[0038]

In the crystal production according to the present invention, after the crystal is grown in two directions as described above, the crystal pulling can be started and the crystal thickness, length and other shapes can be controlled, so that the crystal raw material is wasted. Less is.

Since the contact area between the first growing portion and the second growing portion is small, it is not necessary to stop the crystal defect generated from the seed crystal at the first crystal and propagate it to the crystal grown at the second step. Good quality crystals can be obtained. Therefore, even if the crystal cracks due to a crystal defect introduced at the time of seeding the crystal, the crack is stopped by the first-stage crystal and does not propagate to the second-stage crystal. In addition, twins are difficult to propagate.

If a neck-like portion thinner than the seed crystal is formed before growing the first-stage crystal, the effect of preventing the propagation of the crystal result can be further enhanced.

Further, since the crystal growth planes can be limited to two in the second stage crystal growth, the sector boundary sandwiched between the growth planes and the growth planes is located in the central longitudinal direction of the crystal as shown in FIG. The number of crystals becomes one, and the process of processing the crystal can be simplified. As a result, the yield of the optical element using crystals is improved, and excellent effects such as the ability to cut out a large element are produced.

[Brief description of drawings]

FIG. 1 is a perspective view of a crystal grown according to an embodiment of the present invention.

FIG. 2 is a side sectional view for explaining the propagation of crystal defects in a grown crystal according to the embodiment of the present invention.

FIG. 3 is a perspective view showing an example of the present invention and illustrating a sector boundary formed in a grown crystal.

FIG. 4 is a front view (a) and a side view (b) of a neck-shaped crystal in a growing step, showing an embodiment of the present invention.

FIG. 5 shows an embodiment of the present invention, and is a front view (a) and a side view (b) of the crystal in the first-stage crystal growing step.

FIG. 6 shows an embodiment of the present invention, and is a front view (a) and a side view (b) of the crystal in the first-step crystal drawing step.

FIG. 7 shows an embodiment of the present invention, and is a front view (a) and a side view (b) of a crystal in a second-stage crystal growing step.

FIG. 8 is a perspective view for explaining the orientation and crystal shape of a seed crystal in growing a KNbO ₃ crystal by the TSSG method.

FIG. 9 is a perspective view for explaining a sector boundary formed in a crystal grown in a [110] _pc orientation by a conventional method.

FIG. 10 is a cross-sectional view of the basic structure of a crystal manufacturing apparatus by the TSSG method.

[Explanation of symbols]

 1: Seed crystal 2: Neck part 3: First stage grown crystal 4: Second stage grown crystal 5: Crystal defect 6: Sector boundary 7: Solution surface 8: Alumina ceramic tube 9: Platinum crucible 10: Ceramic refractory 11: Resistance heater 12: Raw material solution 13: Crystal

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hirohiko Kumagai 1150, Hazawa-machi, Kanagawa-ku, Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Laboratory (72) Masahiro Hirano 1150, Hazawa-machi, Kanagawa-ku, Yokohama Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Center

Claims (7)

[Claims] 1. The general formula ABO ₃ (A = Li, K, Na, B
= Nb, Ta, or A = Ba, B = Ti), a perovskite type oxide single crystal is brought into contact with a high temperature solution of a raw material, and the seed crystal is gradually grown while rotating the seed crystal. A method of manufacturing, after growing a crystal in a specific direction, most of the crystal is pulled up from the hot solution until the grown crystal comes into contact with the hot solution at a part of the bottom, and then the crystal and the hot solution A method for producing an oxide single crystal, characterized in that crystal growth is newly started from a contact portion. 2. The general formula ABO ₃ is KTa _x Nb _1-x O.
_The method for producing an oxide single crystal according to claim 1, which is a perovskite-type oxide single crystal represented by ₃ (0 ≦ x ≦ 1). 3. The method for producing an oxide single crystal according to claim 1, wherein the orientation of the seed crystal is [110] _pc which is the [110] orientation in the cubic perovskite structure. 4. The specific directions are [001] _pc orientation and [00-1] _pc orientation which are [001] orientation and [00-1] orientation in a cubic perovskite structure.
A method for producing the oxide single crystal described. 5. The seed crystal is brought into contact with a high temperature solution of a raw material, and then the seed crystal is pulled up at a rate of 0.06 to 0.10 mm / h to form a crystal portion 1 to 3 mm thinner than the seed crystal. A method for producing the oxide single crystal described. 6. The method for producing an oxide single crystal according to claim 5, wherein the crystal is grown in the specific direction while the pulling of the seed crystal raw material from the high temperature solution is stopped. 7. After growing a crystal having a predetermined length in the specific direction, most of the crystal is pulled out of the solution at a rate of 1 to 20 mm / h until a part of the bottom of the crystal comes into contact with the high temperature solution. The method for producing an oxide single crystal according to claim 6, wherein a crystal having a thickness of a predetermined length in the specific direction is grown by newly growing the crystal from a contact portion between the crystal and the high temperature solution.