JPS6046078B2 - Single crystal growth method of solid solution composition of inorganic composite oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for growing a single crystal of a solid solution composition of an inorganic composite oxide.

Single crystals of solid solution compositions of inorganic composite oxides are attracting attention as piezoelectric elements and electro-optic crystals. Conventional methods for growing a single crystal of an inorganic composite oxide include (1) a method of attaching a seed crystal to a melt of an inorganic composite oxide and pulling it up;

However, if the composition of the pulled single crystal differs from the composition of the remaining residual melt (when pulling a single crystal from an incongruent melt), the so-called top seeding method is used.

(2) A method of enlarging the seed crystal by placing a seed crystal in the melt and cooling the melt, the so-called chiroporous method.

(3) A method in which melt is generated in a cylinder with a four-walled wall at the bottom and is lowered into a furnace with a temperature gradient, the so-called Bridzman method. (4) Or a method using a crucible of the same shape as (3) to lower the overall temperature while maintaining a temperature difference between the top and bottom of the outside of the cylinder, the so-called furnace temperature reduction method.

(5) Bring the ends of two sintered bodies into contact, set one sintered body to the desired composition, attach a seed crystal to the end of the other sintered body, and create a molten body in the contact area (this part heating), a method of growing crystals, the so-called floating zone method.

Methods such as I are known.

In the method (1) above, cell closure occurs within the crystal, making it difficult to obtain a large, high-quality single crystal.

Although method (2) above can produce a fairly large and high-quality single crystal, it has the disadvantage that the furnace temperature must be gradually lowered and that it requires a particularly long time to grow.

In methods (3) and (4) above, many seeds with different growth directions are formed on the sloped wall of the filter, making it difficult to grow one seed into a large single crystal. Since the method (5) involves rapid cooling, it is difficult to obtain a high quality single crystal.

The present invention aims to improve the shortcomings of these conventional methods, the Bridgeman method and the furnace temperature reduction method, and to provide a method for easily growing large single crystals.

As a result of research on the properties of the residual melt during the sub-liquid growth of single crystals by the Bridgmann method and the furnace temperature reduction method, the present inventors found that, for example, as shown in the phase diagram of KTaO3-KNbO3-based inorganic composite oxide in Figure 1. From the melt having the composition A, A
A crystal with a composition of B with more Ta and less Nb than the composition of is formed.

As a result, the residual melt contains more Nb ions. However, the Nb ions expelled as a result of crystal growth are not uniformly diffused into the remaining melt, and the lighter Nb ions rise to the top of the melt without sinking to the bottom. There is no accumulation of melt at the melting point, and cell growth does not occur in the crystal. However, as the growth of the crystal progresses, the composition of the melt becomes one in which the proportion of Ta ions becomes smaller, and the composition of the obtained single crystal changes. Therefore, a sintered body having the desired single crystal composition should be placed in the lower part of the crucible, and a sintered body having a composition containing a higher specific gravity inorganic oxide in the solid solution composition than the desired single crystal composition should be stacked thereon. It was found that the composition of the melt could be kept constant by using the method. In addition, as mentioned above, in the conventional Bridgman method and furnace temperature reduction method, the lower part of the crucible used is funnel-shaped, so crystals are grown on the inclined surface, resulting in crystals with many different growth directions. Seeds are large. It is difficult to grow it into a single crystal.

In the present invention, by forming the crucible into a flat-bottomed cylindrical shape, even if multiple nuclei are produced in the case of growing rectangular crystals, the direction of production is the same, so that the final product can be obtained. The crystal becomes one large crystal. Crystals are obtained. Also, when the diameter of the crucible becomes larger (~207T1m
φ or more), nuclei with different growth directions may be formed on the bottom surface of the crucible. In order to improve this point, blowing a gas such as nitrogen or air into the center of the bottom of the crucible lowers the center of the temperature/degrees at the bottom and creates a high temperature gradient in the periphery. It turns out that it is possible to grow only the nucleus formed in the . This method is effective not only for growing rectangular single crystals but also for growing single crystals of all shapes. The present invention was completed based on these findings. The gist of the present invention is to provide a method for growing a single crystal by storing a sintered body of a solid solution composition of an inorganic composite oxide in a crucible and heating and melting the crucible. A sintered body having a crystalline composition is superimposed thereon, and a crude sintered body containing an inorganic oxide having a high specific gravity in a solid solution composition component in an amount higher than the target single crystal composition is superimposed thereon, and A method for growing a single crystal of a solid solution composition of an inorganic composite oxide, which is characterized by growing a crystal by heating and melting a sintered body with a temperature gradient in which the lower part temperature is lower and the upper part temperature is higher.

Examples of the inorganic composite oxide in the present invention include KTa
Examples include l-XNbxO3 and LiTal-XNbx03, which can be obtained by growing single crystals of solid solutions of these.

However, it is not limited to the above-mentioned inorganic composite oxide. Furthermore, the composition of the sintered body placed in the crucible needs to have at least two steps, but it is optional to make it more than that.

Note that the reason why the raw material of the solid solution composition is used as a sintered body is to make it easy to store in the crucible, increase the amount of storage, and to easily maintain the composition.

In the method of the present invention, as a method for creating a temperature gradient in which the lower temperature of the sintered body of the crucible is lower and the upper temperature is higher, the outer periphery of the crucible may be heated to create such a temperature gradient; This can be done by lowering the crucible into a furnace maintained at such a temperature gradient.

According to the method of the present invention, the difference in the composition of the sintered body placed in the crucible and the temperature gradient between the upper and lower temperatures at which the sintered body in the crucible is heated and melted combine to cause the melt to melt. Since the composition can be maintained at one composition even as crystal growth progresses, the composition of the resulting single crystal can be kept constant.

In addition, according to the method of the present invention, since the bottom of the crucible is flat, even if multiple nuclei are generated when growing rectangular crystals, the direction of growth is the same, so they will ultimately become one single crystal. . Also, large crucibles (~20r1rmφ or more)
When using a crucible, it has the excellent effect of squeezing the nucleus into one and growing it into one large single crystal by blowing an air stream to the center of the lower surface of the bottom of the crucible.

Example 1 KTa0.5NYX). 503 Single Crystal Growth A furnace temperature reduction method was applied to this single crystal growth.

A cylindrical flat-bottomed platinum crucible measuring 15φ×1407rOn was used.

Using K2CO3, Ta2O5, N■05 as raw materials, CA) K2CO3 (60%), Ta2O5 (8%),
Nb2O5 (32%) (B) K2CO3 (60%), T
a2O5 (9.2%), Nb2O5 (30.8%) (C
) K2CO3 (60%), Ta2O5 (10%), Nb
Three types of compositions were prepared: 2O5 (30%) (% is mol%).

These raw material powders were calcined at 900'C and CA
), (B), and (C) were stacked in equal amounts in three layers in this order, molded to form a crucible, and sintered with C at 1050°C.

Place the obtained sintered body in a crucible with the sintered body at the bottom.
The temperature of the crucible was set to 1350°C at the top and 1300'C at the bottom.
After keeping it for 24 hours as
The temperature was lowered to 100°C.

The mixture was allowed to cool naturally from 1100°C to lower to room temperature.

The obtained crystal was a colorless and transparent single crystal having a composition of KTaO3 (50%)-KNlO3 (50%) and having a size of 14φ×100 (Tmln). Example 2 KTaO with large diameter
．． 5NbO. Growth of 5O3 single crystal The furnace temperature reduction method was also applied in this case.

A cylindrical flat-bottomed platinum crucible measuring 30φ×150w$t was used.

Using K2CO3, Ta2O5, N■03 as raw materials, CA) K2CO3 (60%), Ta2O5 (8%),
Nb2O5 (32%) (B) K2CO3 (60%), T
a2O5 (9.2%), Nb2O3 (30.8%) (C
) K2CO3 (60%), Ta2O5 (10%), Nb
Three compositions of 2O3 (30%) were prepared.

Each of these raw material powders is calcined at approximately 900°C and CA
), (B), and (C) were stacked in three layers in equal amounts in this order, molded to fill a crucible, and sintered at 1050°C.

Place the obtained sintered body so that (4) is at the bottom, and while blowing an air stream to the center of the bottom surface of the crucible, increase the temperature of the upper part of the crucible to 1350°C and the temperature of the lower part to 1350°C.
It was kept at 300°C for 24 hours. Thereafter, the temperature was lowered at a rate of 1 CC/Hr until the lower temperature reached 1100°C, and from 1100°C, the temperature was allowed to cool naturally to room temperature. The obtained crystal has a diameter of 27φ
×90w! colorless and transparent KTaO. 5NbO. 5O3
It was a single crystal.

[Brief explanation of the drawing]

The figure shows the phase diagram of the KTaO3-KNbO3 system.

Claims (1)

[Claims] 1. A method of growing a single crystal by storing a sintered body of a solid solution composition of an inorganic composite oxide in a crucible and heating and melting the crucible, in which a flat-bottomed cylindrical crucible is used as the crucible, and a lower part of the crucible is A sintered body having a target single-crystal composition is superimposed thereon, and a sintered body having a composition containing a higher specific gravity inorganic oxide in the solid solution composition component than the target single-crystal composition is stacked on top of the sintered body, and 1. A method for growing a single crystal of a solid solution composition of an inorganic composite oxide, which comprises growing a crystal by heating and melting a sintered body with a temperature gradient in which the bottom temperature is low and the top temperature is high. 2. The method for growing a single crystal according to claim 1, wherein the outer periphery of the crucible is heated with a temperature gradient in which the temperature at the bottom of the crucible is low and the temperature at the top is high. 3. The method for growing a single crystal according to claim 1, wherein the crucible is lowered into a furnace with a temperature gradient in which the lower temperature is lower and the upper temperature is higher. 4. The single crystal growth method according to claim 1, wherein an airflow is blown onto the center of the bottom outer surface of the crucible.