JPH075434B2 - Single crystal manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for efficiently producing an oxide single crystal containing B as one of constituent elements by a pulling method.

(Problems to be Solved by Prior Art and Invention) β-BaB ₂ O ₄ is a nonlinear optical crystal that has been receiving attention in recent years. The compound represented by the stoichiometric composition BaB ₂ O ₄ is 925 ° C.
The crystallographic atomic structure changes at the boundary temperature (so-called phase transformation). In this case, the high temperature phase crystal of 925 ℃ or higher is called α type (α-BaB ₂ O ₄ ) and the low temperature phase crystal of 925 ℃ or lower is β type (β-BaB ₂ O ₄ ). Of these, the β type is regarded as a promising crystal. Because α-BaB ₂ O ₄ in the high temperature phase has a center of symmetry,
This is because the center of symmetry disappears in β-BaB ₂ O ₄ due to the displacement of the atoms, and thus the nonlinear characteristic occurs.

In order to obtain BaB ₂ O ₄ crystals, BaCO ₃ which is a mother material is generally used.
1 and B ₂ O ₃ molar ratio: in proportions of 1, the _{BaCO 3 + B 2 O 3 →} BaB 2 O 4 + CO 2 ↑ reaction when heated to melt to obtain a BaB ₂ O ₄ melt. Next, the melt is crystallized by a pulling method or the like to obtain a BaB ₂ O ₄ single crystal.

By the way, when the ratio of BaCO ₃ and B ₂ O ₃ is set to 1: 1 as described above, 1095 ° C. becomes the melting temperature of the base material, and conversely, when the melt heated above this temperature is cooled to 1095 ° C. Crystallization begins at ° C. However, since the crystal in this case is crystallized at 925 ° C or higher, it is always crystallized as α-BaB ₂ O ₄ .

Further, the solidified crystal is cooled, and the crystal temperature is 925.
When the temperature falls below ℃, β-BaB ₂ O ₄ undergoes a phase transformation, but as described above, the changing directions of the constituent atoms vary depending on the location. In other words, since “domains” are formed, it is difficult to transform into uniform β-BaB ₂ O ₄ with atoms displaced in one direction throughout the crystal, and even if transformed, the uniformity is poor and a high-quality single crystal is formed. I can't get crystals.

A good single crystal in this case is "domain-free" β-BaB ₂
It is an O ₄ crystal. Avoiding this problem, good quality β-BaB ₂ O ₄
In order to obtain a single crystal, a method in which a melt at 925 ° C or lower is prepared and cooled to directly crystallize a β-BaB ₂ O ₄ single crystal can be considered. This is because it is very easy to obtain a β-BaB ₂ O ₄ single crystal with a uniform atomic structure due to the change from liquid to solidification.

By the way, the method of lowering the melt temperature of the mother raw material (melt temperature at the time of crystal production) in this way is (a) shifting the compounding ratio of the mother raw material, so-called self-flux method (self-flux), B) There is a flux method in which a completely different flux is added in addition to the mother raw material.

In the case of BaB ₂ O ₄ , to realize the self-flux method,
The blending ratio of B ₂ O ₃ may be increased, and the flux method may be realized by adding Na ₂ CO ₃ , for example. In any case, a molten state can be realized at a temperature of 925 ° C or lower.

However, whichever method is used, lowering the temperature of the melt causes a new serious problem.

That is, the viscosity of B ₂ O ₃ , which is the mother material of the melt from which crystals are crystallized, becomes higher at lower temperatures and is as large as 230 poise at 900 ° C.
Since the viscosity of the melt is high and the heat conduction is poor, a large single crystal cannot be obtained efficiently. Specifically, when the pulling method (Czochralski or cairoporous method) is performed from such a melt, the growth rate becomes extremely slow at 0.1 to 0.5 mm per hour, which leads to an increase in crystal size and inclusion in B ₂ O _3. The problem is that it is difficult to obtain a good quality crystal free from inclusions such as bubbles caused by the water content.

Further, as another B-containing compound, Li ₂ B ₄ O having piezoelectricity
There is ₇ . In this case, it is not necessary to lower the melt temperature in relation to the phase transformation, but a large amount of B ₂ O ₃ is needed from another viewpoint. That is, the mother material Li ₂ CO ₃ and B ₂ O ₃ have a molar ratio of 1:
Were mixed with _{2, Li 2 CO 3 + 2B} 2 O 3 → Li 2 B 4 O 7 + CO 2 ↑ reaction with the form of Li ₂ B ₄ O ₇ melt by heating at 917 ° C. or higher, with pull-up method or the like Single crystallize.

In this case, B ₂ O ₃ requires twice as much amount as other mother raw material (Li ₂ CO ₃ ), and since the temperature during crystal pulling is just above 917 ° C, the viscosity of the melt is 200-230. Poise and expensive. According to the experiment, in order to obtain a large crystal that does not include inclusions such as bubbles,
A viscous melt of this degree required a very slow pulling rate of about 0.3 to 1.0 mm per hour, resulting in extremely poor production efficiency.

As can be seen from the various examples above, the viscosity of B ₂ O ₃ changes greatly with temperature, so other conditions such as the crystal pulling temperature and pulling rate are specified, and optimum conditions including production efficiency are determined. There was a problem that it would be a limiting factor in realizing.

(Object of the invention) The present invention was proposed in order to improve the above-mentioned drawbacks, and its object is to improve the high viscosity of the melt when growing an oxide single crystal containing B as one of the constituent elements. It is to realize a low-viscosity raw material melt that solves a certain point and to produce a B oxide single crystal with high efficiency.

(Means for Solving the Problems) In order to achieve the above object, the present invention, in the case of producing a composite oxide single crystal containing boron as one of the constituent elements, at the temperature for producing the oxide single crystal. As impurities that reduce the viscosity of the complex oxide melt containing boron, P
The gist of the invention is a method for producing a single crystal, which is characterized by mixing any one or two or more of b, Bi, As, Ga and oxides thereof.

The present invention reduces the viscosity at the liquidus temperature Tg at the time of producing a crystal of a melt containing B ₂ O ₃ as a main component in the production of the single crystal by adding a specific impurity (conventional 1 / 2 to 1/1
There is no known method for reducing the viscosity of the melt at the liquidus temperature Tg, which is the most important feature.

If further added, it is conventionally necessary to add a specific impurity element in order to change the characteristics of the obtained single crystal, but to add a specific impurity in order to reduce the viscosity of the melt in which the crystal grows. Has no report.

Next, examples of the present invention will be described. Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

[Example 1] BaB ₂ O ₄ was prepared by blending BaCO ₃ and B ₂ O ₃ in a molar ratio of 1: 1 and when heated, it melted at 1095 ° C. to form a α-BaB ₂ O ₄ and crystallized to about 925 ° C. In the following, the crystal structure does not have centrosymmetry and undergoes a phase transformation into β-BaB ₂ O ₄ belonging to the practically meaningful space group R ₃ . Since there is a problem described in the section of the prior art here, in order to efficiently produce a high quality β-BaB ₂ O ₄ crystal,
The melt temperature must be below 925 ° C. For this purpose, B ₂ O ₃
And the melt temperature can be lowered.
However, the viscosity of B ₂ O ₃ is ~ 100 poise, 900 at 1000 ° C.
Since it is as high as ~ 230 poise at ℃, the viscosity of the low temperature melt with increased B ₂ O ₃ becomes extremely large, which is not suitable for crystal growth. Accordingly, B ₂ were mixed PbO 5 mole percent B ₂ O ₃ used O
_{Using 3} (Pb) as the starting material, BaCO _{3 and} this B ₂ O ₃ (Pb)
The liquidus temperature Tg by increasing B ₂ O ₃ (Pb) from 1: 1
Was lowered to ~ 920 ° C. As a result, the viscosity of the melt in this case was 20 to 25 poises, which was about 1/10 of the viscosity without PbO addition, and the heat conduction became large, resulting in the extremely easy production of single crystals.

Example 2 In Example 1, which is a so-called self-flux method in which one compounding ratio of the mother raw material is shifted to obtain a desired crystal in a melt, a crystal after phase transformation is used. As a method for obtaining it, there is a method of lowering the liquidus temperature by using a flux. Several fluxes can be considered for the production of β-BaB ₂ O ₄ , but here we use Na ₂ CO ₃ to mix xBaCO ₃ + yNa ₂ CO ₃ + zB ₂ O ₃ (Pb) as a raw material. , z = 50 in a molar ratio, a mixture of PbO 5 mol% B ₂ O ₃ B ₂ O ₃
(Pb) to form β-
It was possible to grow a BaB ₂ O ₄ single crystal. The fertility of the solution at this time was about 1/2 to 1/10 smaller than that of the additive-free B ₂ O ₃ , and therefore large single crystals were easily obtained.

In the above embodiments, the case of the self-flux method has been described, but it can be easily understood that the low temperature and low viscosity can also be achieved by the flux method. In this way, B ₂ O ₃ used as a mother material is mixed with another element that lowers the viscosity (such B ₂ O _{3 is referred} to as B ₂ O ₃ (X). = Pb)), a low-viscosity melt can be realized even at low temperatures regardless of the self-flux method or the flux method, and therefore a high-quality β-BaB ₂ O ₄ single crystal can be easily and efficiently produced. Obtainable.

Example 3 cold by mixing Pb in Examples 1 and 2 in B ₂ O ₃ (added in the form of PbO), has been realized a solution of low viscosity, Bi instead of Pb
(Or Bi ₂ O ₃ ) mixed with 2.5 mol% B ₂ O ₃ 92
Viscosity is about 100 poise in the temperature range of 0 ~ 850 ℃, additive-free B ₂ O
_When using B ₂ O _{3 in} which As (or As ₂ O ₃ ) was mixed at 0.8 mol% to about 1/2 of the viscosity of _3, the viscosity was ˜130 poise, and the viscosity was reduced to about 60%. Β-BaB ₂ O in the same way as 1,2
₄ single crystals could be obtained efficiently.

Similar effects were obtained when Ga and its oxide were added to B ₂ O ₃ .

In addition, it is also possible to use two or more of Pb, Bi, As, Ga or an oxide thereof together as an additive.

(Effect of the Invention) As described above, in order to produce a β-BaB ₂ O ₄ single crystal
A melt below 925 ° C is required, and it is essential for crystal growth to minimize the viscosity of this melt. This is because the higher the viscosity, the worse the heat conduction and the slower the crystal growth rate, and in order to solve this point, lowering the viscosity of the melt is important for efficient production of crystals. According to the present invention, there is an advantage that the viscosity of the liquid can be reduced by 1/2 to 1/10 as compared with the case of no addition by mixing a specific additive element with B ₂ O ₃ which is the main raw material. .

In the examples, Pb (PbO), Bi (Bi
₂ O ₃ ), As (As ₂ O ₃ ) are set to mol% as described, but the present invention does not prescribe this mixing ratio. The point is to add a specific element to reduce the viscosity of the melt. Therefore, as can be seen from the examples, instead of using premixed B ₂ O ₃ (X), a specific element in the form of metal or oxide is added to a melt capable of producing a β-BaB ₂ O ₄ single crystal. Even if added, the effect is the same. If you add more,
Although the optical refractive index of β-BaB ₂ O ₄ thus obtained was slightly increased, other properties were not changed.

It can be easily inferred that the present invention can be applied to B oxide crystals other than β-BaB ₂ O ₄ (for example, Li ₂ B ₄ O ₇ shown as a conventional example). That is, when a large amount of B ₂ O ₃ is used as a base material such as Li ₂ B ₄ O ₇ , the viscosity of the melt can be reduced at low temperature, which increases the degree of freedom in optimizing the manufacturing conditions. Needless to say, it is more effective in practical use.

Claims (2)

[Claims] 1. When producing a composite oxide single crystal containing boron as one of its constituent elements, as an impurity for reducing the viscosity of a boron-containing composite oxide melt at a temperature for producing the oxide single crystal. , Pb, Bi, As, Ga or any one of oxides thereof, or a mixture of two or more thereof, for producing a single crystal _2. Pb, Bi, As, Ga, PbO, Bi as impurities in B ₂ O _3.
The single crystal is produced using B ₂ O ₃ as a raw material, which is one of ₂ O ₃ , As ₂ O ₃ and Ga ₂ O ₃ or a mixture of two or more thereof. Item 6. A method for producing a single crystal according to item.