JP2000335999A - Production of barium titanate single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a barium titanate single crystal, which enables high-purity and high-quality tetragonal barium titanate single crystal to stably be obtained. SOLUTION: This method for producing a barium titanate single crystal comprises the following processes: sandwiching a Ba-Ti-O composition between the seed crystal of a barium titanate single crystal and a barium titanate polycrystalline substance; melting the Ba-Ti-O composition by heatup to bond it to the seed crystal; and transferring a melting zone formed by melting the Ba-Ti-O composition by heatup to the side of the barium titanate polycrystalline substance to obtain a barium titanate single crystal. The molar ratio [Ti/(Ti+ Ba)] and the aspect ratio of the Ba-Ti-O composition exist in the range of the tetragon (including its apices and sides) connecting points A, B, C and D in the Figure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a traveling solvent floating zone method (TSFZ).
Method) for producing a high-quality tetragonal barium titanate single crystal by the method.

[0002]

2. Description of the Related Art Conventionally, the photorefractive (PR) effect has attracted attention in the application field of nonlinear optics, and a tetragonal barium titanate (BaTiO ₃ ) single crystal as a ferroelectric has a large PR effect with a small laser output. As shown, it is one of the most promising materials. FIG. 2 is a two-dimensional BaO-TiO ₂ system diagram in which the abscissa indicates the mole percentage of TiO ₂ and the ordinate indicates the temperature (° C.). As can be seen from FIG. 2, barium titanate shows a consistent melting composition, but undergoes a cubic-hexagonal phase transition at 1460 ° C., and attempts to grow a single crystal from a stoichiometric melt. Barium titanate is grown. The hexagonal barium titanate does not undergo phase transition to a tetragonal system exhibiting the PR effect even when cooled to room temperature. Therefore, it is necessary to grow at a temperature of 1460 ° C. or less that does not cause phase transition to hexagonal crystal. Therefore, conventionally, the Remeika method using KF flux (JP Remeika; J. Am. Ceram. Soc., 76 (1954) p940),
TS that slowly raises TiO ₂ excess raw material solution while pulling it down
SG method (Akiharu Amimura et al .; Journal of Japanese Society for Crystal Growth _, 17 (1990)
Barium titanate single crystals have been grown for example in p110). In FIG. 2, cub indicates a cubic crystal and hex
Indicates a hexagonal crystal.

[0003] Here, TSSG, which is currently performed in the mainstream, is used.
An outline of a method for producing a barium titanate single crystal by the method will be described. The raw material powders of BaCO ₃ and TiO ₂ (both having a purity of 99.99% or more) are each 35 mol%, 6
Mix at a rate of 5 mol%, and in air at 1000 ° C for 10
After calcining for a time, the mixture is filled in a platinum crucible. This is 150
After the temperature was raised to 0 ° C. and melted, and cooled to the melting point (about 1430 ° C.), a seed crystal barium titanate single crystal was seed-touched. Thereafter, while cooling the temperature at a rate of 0.1 ° C./hour, the seed crystal is pulled up at a rate of 0.1 mm / hour to grow the crystal. The diameter of the single crystal to be grown is about 20 mm. In this method, as the barium titanate single crystal grows, the composition of the raw material melt shifts to a composition rich in Ti (see FIG. 2), and the temperature of 1322 ° C.
To reach the peritectic point, and the precipitation of barium titanate ends.
For this reason, the crystal size that can be grown is limited. Also,
Since the growth rate is slow, it takes much time to grow a single crystal. These have caused the cost of the barium titanate single crystal to be high. In addition, the influence of crystal contamination by the crucible material cannot be avoided. In general, when a certain element such as Fe or Ce is added to barium titanate, the PR effect increases, but for other elements, the PR effect decreases or the Curie temperature, which is a tetragonal-cubic phase transition temperature, is lowered. Sometimes. Therefore, the mixing of elements other than the target must be avoided as much as possible. Further, in the TSSG method, a growing technique is difficult, and unless the growing conditions such as uniform temperature distribution and cooling of a seed crystal are strictly controlled, a high-quality barium titanate single crystal that can withstand optical use cannot be obtained.

On the other hand, the Remeika method has a disadvantage that it is difficult to obtain a large single crystal, and the crucible material and flux components are easily taken in as impurities.

[0005]

SUMMARY OF THE INVENTION In order to avoid the above-mentioned problems, the present inventors have proposed a traveling solvent melting method.
t Floating Zone Method (TSFZ method) was considered. Since the crucible is not used in the TSFZ method, contamination of impurities from the crucible material can be avoided, and single crystal growth of a material having a nonconformal melting composition can be realized. In addition, since barium titanate is always supplied from the raw material rod due to composition fluctuation in the solvent due to precipitation of barium titanate on the seed crystal, theoretically,
The growth can be continued as long as the raw materials continue. For this reason,
High purity and low cost tetragonal barium titanate single crystal can be expected to grow. The growth of tetragonal barium titanate single crystals by the FZ method was first attempted by Brown et al. (J. Appl. Phys., 35 (1964) p1954), and several mol% of strontium titanate was fixed on barium titanate. It has been found that upon dissolution, tetragonal barium titanate is obtained directly. By this method, a diameter of 3.2 mm and a length of 25 m
m has been successfully grown. However, the crystal obtained by this method is a solid solution of barium titanate and strontium titanate. There is a problem that the strontium solid solution lowers the Curie temperature (tetragonal-cubic phase transition temperature) of barium titanate. Was. On the other hand, Turn
er et al. use the TSFZ method using TiO ₂ as a solvent (CETurner
According to et.al .; J. Cryst. Growth, 56 (1982) p137), a pure tetragonal barium titanate single crystal that is not a solid solution and has a diameter of about 5 mm and a length of about 10 mm is obtained. But,
The growth of long crystals has not been successful yet, and a Pt-Rh wire heater is used to form the molten zone, and since this heater is in contact with the melt, Pt and Rh are mixed as impurities. There was a problem.

[0006] Therefore, a main object of the present invention is to provide a method for producing a barium titanate single crystal capable of stably obtaining a high purity and high quality tetragonal barium titanate single crystal.

[0007]

SUMMARY OF THE INVENTION The present invention comprises a step of sandwiching a Ba-Ti-O composition between a seed crystal of barium titanate single crystal and a polycrystalline barium titanate;
a step of heating and melting the i-O composition to bond to the seed crystal; and moving a melt zone formed by heating and melting the Ba-Ti-O composition to the barium titanate polycrystal side to thereby form a barium titanate. A step of obtaining a single crystal, comprising the steps of:
Assuming that the composition has a Ti / (Ti + Ba) molar ratio and an aspect ratio of points A (0.68, 2.2) and B (0.8
1,2.1), C (0.85, 0.1), D (0.7
This is a method for producing a barium titanate single crystal that belongs to the range of a square having a vertex of (2, 0.2) (including the vertex and on the side). Here, FIG. 1 is a graph in which the horizontal axis represents Ti / (Ti + Ba) [molar ratio] in the Ba—Ti—O composition and the vertical axis represents the aspect ratio. The aspect ratio refers to the ratio of the height of the cylindrical sample to the diameter.

According to the TSFZ method, a barium titanate single crystal having a Ti / Ba ratio of 1 is used as a seed crystal, a barium titanate polycrystal is used as a raw material rod, and a solvent between the seed crystal and the raw material rod is used as a solvent. A barium titanate single crystal can be obtained by sandwiching the Ba-Ti-O composition and moving the molten zone formed by heating and melting the solvent to the raw material rod side. Usually, the composition of the Ba—Ti—O composition is selected from the liquidus PQ shown in FIG. 2, and a molten zone is formed by heating and melting the composition. Liquidus line PQ
Is relatively narrow. However, since barium titanate dissolves from the seed crystal and the raw material rod in the melt zone, the composition of the melt zone shifts toward the barium titanate having a Ti / Ba ratio of 1. In addition, during the growth of the single crystal, the precipitation of the barium titanate single crystal on the seed crystal and the dissolution of barium titanate from the raw material rod into the fusion zone occur repeatedly, so that the composition of the fusion zone changes periodically. Therefore, during the growth of the single crystal, the composition of the melt zone may come into contact with the precipitation region or peritectic point (Q in FIG. 2) of hexagonal barium titanate. In this case, a tetragonal barium titanate single crystal cannot be stably obtained. However, in the present invention,
By making the Ti / (Ti + Ba) molar ratio and the aspect ratio of the Ba—Ti—O composition fall within the range (including the vertices and sides) of the square having the point ABCD as the vertex in FIG. A high-quality tetragonal barium titanate single crystal can be stably grown. Further, according to the present invention, a long single crystal can be obtained.

In the method for producing a barium titanate single crystal according to the present invention, a Ba—Ti—O composition is disposed on a seed crystal in a vertical direction, and a barium titanate polycrystal is formed thereon. Arrangement is preferable to prevent the effect of dripping of the melt.

Further, in the method for producing barium titanate according to the present invention, the barium titanate polycrystal and the Ba—TiO composition are each formed of a single crystal that is desired to be a columnar shape having a diameter of 20 mm or less. Preferred to obtain.

In the method for producing barium titanate according to the present invention, Ba-Ti-
It is preferable to heat and melt the O composition in order to prevent impurities from being mixed.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the drawings.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is an illustrative view showing one example of a single crystal growing apparatus used for a method for producing a single crystal according to the present invention. This single crystal growing apparatus 10 includes a housing 12. The housing 12 accommodates therein a bi-elliptical mirror 14 having a bi-elliptical rotation surface obtained by rotating a bi-ellipse around its long axis.
A bi-ellipse refers to a shape in which two ellipses are combined while sharing one focus. Halogen lamps 16 and 16 are arranged in the bi-elliptical mirror 14 at positions corresponding to the opposite focal points with the shared focal point of the bi-ellipse therebetween.
The halogen lamps 16 and 16 are light sources as heat sources,
The irradiated light is reflected by the inner surface of the bi-elliptical mirror 14 and is concentrated on the common focus. Thus, the sample held in advance at the shared focal point can be heated and melted to form a fusion zone. That is, in this embodiment, the halogen lamp 1
The light heating device is composed of 6, 16 and the bi-elliptical mirror 14. A quartz tube 22 is accommodated in the bi-elliptical mirror 14, and an upper shaft 18 and a lower shaft 20 for holding the raw material rod and the seed crystal and vertically moving the same in the quartz tube 22 are provided. , Are arranged to face each other vertically in the vertical direction with a common focus interposed therebetween. By moving the upper and lower shafts 18, 20 in synchronization with each other in the vertical direction, the melt zone can be moved in the longitudinal direction of the raw material rod and the seed crystal. The upper shaft 18 holds a raw material rod 24 obtained by processing a barium titanate polycrystal into a cylindrical shape. A seed crystal 26 obtained by processing a barium titanate single crystal into a cylindrical shape is held on the lower shaft 20. At the end of the seed crystal 26 facing the raw material rod 24, a Ba-Ti-O composition 28 processed into a cylindrical shape is attached. Examples and comparative examples using the device 10 will be described below.

(Example 1) Barium carbonate (purity 9) as a starting material for a raw material bar made of polycrystalline barium titanate
9.99%) and titanium oxide (purity 99.99%),
It was weighed so that Ba / Ti (molar ratio) became 50/50, and mixed with a cobblestone and pure water in a pot mill. Further, barium carbonate (purity 99.99%) and titanium oxide (purity 99.99%) as starting materials for producing a Ba-Ti-O composition were mixed with Ti in the Ba-Ti-O composition.
/ (Ti + Ba) [molar ratio] are points A, B, C,
The sample was weighed so as to belong to the range of the quadrangle having D as a vertex (including the vertex and on the side), and mixed with a cobblestone and pure water in a pot mill. Each mixture was dehydrated and dried, and then passed through a mesh to adjust the particle size. The two types of mixtures thus obtained were each filled in an alumina crucible and calcined in a resistance heating type firing furnace. This calcining,
The test was performed at 1200 ° C. for 2 hours in an air atmosphere. The obtained calcined powder was pulverized in a mortar, filled in rubber tubes each having an inner diameter of 10 mm, and then 2 t / cm in a hydrostatic press.
^By pressing under a pressure of ² , a cylindrical molded body was obtained.
The diameter of the obtained cylindrical molded body was 8 mm. Each of the columnar shaped bodies was fired again in a resistance heating type firing furnace. This calcination was performed in a temperature range of 1300 to 1460 ° C. for 2 hours in an air atmosphere. The diameter of the sintered cylinder after sintering was 7.5 mm. The sintered Ba-Ti-O composition was cut into a height having an aspect ratio within the range of a rectangle (including the vertices and the sides) having the vertices of points A, B, C, and D in FIG.

A single crystal growing apparatus shown in FIG. 3 is used for the raw material rod of the barium titanate polycrystal obtained in the above-described steps, the Ba—Ti—O composition, and the barium titanate single crystal used as a seed crystal. It was set to 10. B on the seed crystal 26
The a-Ti-O composition 28 was placed, and the Ba-Ti-O composition 28 was heated and melted by the light heating devices 14 and 16. The raw material rod 24 was brought into contact with the molten Ba-Ti-O composition 28, and the upper shaft 18 and the lower shaft 20 were rotated for about one hour while rotating about the same axis in opposite directions. Thereafter, the upper shaft 18 and the lower shaft 20 are driven synchronously to be pulled down vertically at a rate of 1 mm / hour, so that the raw material rods 24 which are relatively vertically upper while maintaining the fusion zone in a constant shape and stable. Moved to the side. Thus,
Dissolution of the raw material from the raw material rod 24 to the melt zone and precipitation of a single crystal from the melt zone to the seed crystal 26 side were continuously performed.

Table 1 shows the results of growing barium titanate single crystals using Ba—Ti—O compositions having variously changed Ti / (Ti + Ba) molar ratios and aspect ratios. Table 1 also shows the product phases confirmed by X-ray structural analysis. Here, BaTiO ₃ (tet.) Indicates tetragonal barium titanate, and BaTiO ₃ (hex.)
Indicates hexagonal barium titanate. In Table 1, *
Those marked are outside the scope of the present invention.

[0017]

[Table 1]

Sample No. shown in Table 1 1 to No. The 21 experimental results are described below.

(Sample 1) Ti / (Ti + Ba) (molar ratio) is 0.68, and Ba-T having a diameter of 7.5 mm is cut to a height of 16.5 mm so as to have an aspect ratio of 2.2.
A barium titanate single crystal was grown using the i-O composition. The obtained crystal was confirmed by X-ray structural analysis to be a tetragonal single phase. Further, after the obtained single crystal was divided into single domains by poling, a two-wave mixing experiment was performed using two argon lasers (wavelength: 514.5 nm). As a result, amplification of signal light intensity was confirmed.

(Sample 2) Ti / (Ti + Ba) (mol
Ratio) is 0.68 and the aspect ratio is 2.3.
Ba- of 7.5 mm in diameter cut out to 17.25 mm
Growth of barium titanate single crystal using Ti-O composition
Was done. In the obtained crystal, a different phase is visually observed in the crystal.
X-ray structural analysis shows that tetragonal barium titanate and B
aTi_TwoO _FiveWas confirmed to be a mixed phase.

(Sample 3) Ba− of 7.5 mm in diameter cut out to a height of 15.75 mm so that Ti / (Ti + Ba) (molar ratio) is 0.68 and the aspect ratio is 2.1.
A barium titanate single crystal was grown using the Ti—O composition. In the obtained crystal, a different phase was visually observed in the crystal, and X-ray structure analysis confirmed that it was a mixed phase of tetragonal and hexagonal barium titanate.

(Sample 4) Barium titanate was prepared using a Ba—Ti—O composition cut to a height of 9 mm so that Ti / (Ti + Ba) (molar ratio) was 0.70 and the aspect ratio was 1.2. A single crystal was grown. The obtained crystal was confirmed to be a tetragonal single phase by X-ray structural analysis. The obtained single crystal is divided into single domains by poling, and then two argon lasers (wavelength: 514.5 nm)
As a result of the two-wave mixing experiment, amplification of the signal light intensity was confirmed.

(Sample 5) Using a Ba—Ti—O composition cut to a height of 15.75 mm so that Ti / (Ti + Ba) (molar ratio) is 0.70 and the aspect ratio is 2.1, titanium A barium acid single crystal was grown. The obtained crystal was confirmed to be a tetragonal single phase by X-ray structural analysis. After the obtained single crystal is divided into single domains by poling, two argon lasers (wavelength 514.5) are used.
nm), the amplification of the signal light intensity was confirmed.

(Sample 6) Using a Ba—Ti—O composition cut to a height of 8.25 mm so that Ti / (Ti + Ba) (molar ratio) is 0.70 and the aspect ratio is 1.1, titanium A barium acid single crystal was grown. In the obtained crystal, a heterogeneous phase was visually observed in the crystal, and X-ray structure analysis confirmed that it was a mixed phase of tetragonal and hexagonal barium titanate.

(Sample 7) Ti / (Ti + Ba) (molar ratio) is 0.70, and a Ba—Ti—O composition cut to a height of 16.5 mm so as to have an aspect ratio of 2.2. A barium acid single crystal was grown. In the obtained crystal, a foreign phase was visually observed in the crystal, and it was confirmed by X-ray structure analysis that it was a mixed phase of tetragonal barium titanate and BaTi ₂ O ₅ .

(Sample 8) Ti / (Ti + Ba) (molar ratio) was 0.72, and an aspect ratio of 0.2 was used to cut titanium to a height of 1.5 mm using a Ba—Ti—O composition. A barium acid single crystal was grown. X-ray structural analysis confirmed that the obtained crystal was a tetragonal single phase. After the obtained single crystal was divided into single domains by poling, a two-wave mixing experiment was performed using two argon lasers (wavelength: 514.5 nm). As a result, amplification of signal light intensity was confirmed.

(Sample 9) Using a Ba—Ti—O composition cut to a height of 15.75 mm so that Ti / (Ti + Ba) (molar ratio) is 0.80 and the aspect ratio is 2.1, titanium A barium acid single crystal was grown. The obtained crystal was confirmed by X-ray structural analysis to be a tetragonal single phase. After the obtained single crystal is divided into single domains by poling, two argon lasers (wavelength 514.
5 nm), the amplification of the signal light intensity was confirmed.

(Sample 10) Using a Ba—Ti—O composition cut to a height of 1.5 mm so that Ti / (Ti + Ba) (molar ratio) is 0.80 and the aspect ratio becomes 0.2, titanium A barium acid single crystal was grown. X-ray structural analysis confirmed that the obtained crystal was a tetragonal single phase. After the obtained single crystal was divided into single domains by poling, a two-wave mixing experiment was performed using two argon lasers (wavelength: 514.5 nm). As a result, amplification of signal light intensity was confirmed.

(Sample 11) Using a Ba—Ti—O composition cut to a height of 0.75 mm so that Ti / (Ti + Ba) (molar ratio) is 0.80 and the aspect ratio is 0.1, titanium A barium acid single crystal was grown. In the obtained crystal, a heterogeneous phase was visually observed in the crystal, and X-ray structure analysis confirmed that it was a mixed phase of tetragonal and hexagonal barium titanate.

(Sample 12) Ti / (Ti + Ba) (molar ratio) was 0.80, and the titanium was obtained by using a Ba—Ti—O composition cut to a height of 16.5 mm so as to have an aspect ratio of 2.2. A barium acid single crystal was grown. In the obtained crystal, a foreign phase was visually observed in the crystal, and it was confirmed by X-ray structure analysis that it was a mixed phase of tetragonal barium titanate and BaTi ₂ O ₅ .

(Sample 13) Using a Ba—Ti—O composition cut to a height of 15.75 mm so that Ti / (Ti + Ba) (molar ratio) is 0.81 and the aspect ratio is 2.1, titanium A barium acid single crystal was grown. The obtained crystal was confirmed by X-ray structural analysis to be a tetragonal single phase. After the obtained single crystal is divided into single domains by poling, two argon lasers (wavelength 514.
5 nm), the amplification of the signal light intensity was confirmed.

(Sample 14) Using a Ba—Ti—O composition cut to a height of 10.5 mm so that Ti / (Ti + Ba) (molar ratio) is 0.83 and the aspect ratio is 1.4, titanium A barium acid single crystal was grown. In the obtained crystal, a foreign phase was visually observed in the crystal, and it was confirmed by X-ray structure analysis that it was a mixed phase of tetragonal barium titanate and BaTi ₂ O ₅ .

(Sample 15) Using a Ba—Ti—O composition cut to a height of 6.0 mm so that Ti / (Ti + Ba) (molar ratio) is 0.83 and the aspect ratio is 0.8, titanium A barium acid single crystal was grown. The obtained crystal was confirmed by X-ray structural analysis to be a tetragonal single phase. After the obtained single crystal is divided into single domains by poling, two argon lasers (wavelength 514.5 n) are used.
As a result of the two-wave mixing experiment according to m), amplification of the signal light intensity was confirmed.

(Sample 16) Using a Ba—Ti—O composition cut to a height of 0.75 mm so that Ti / (Ti + Ba) (molar ratio) is 0.85 and the aspect ratio becomes 0.1, titanium A barium acid single crystal was grown. X-ray structural analysis confirmed that the obtained crystal was a tetragonal single phase. The obtained single crystal is divided into single domains by poling, and then two argon lasers (wavelength: 514.5 nm)
As a result of the two-wave mixing experiment, amplification of the signal light intensity was confirmed.

(Sample 17) Using a Ba—Ti—O composition cut to a height of 1.5 mm so that Ti / (Ti + Ba) (molar ratio) is 0.85 and the aspect ratio is 0.2, titanium A barium acid single crystal was grown. In the obtained crystal, a foreign phase was visually observed in the crystal, and it was confirmed by X-ray structure analysis that it was a mixed phase of tetragonal barium titanate and BaTi ₂ O ₅ .

(Sample 18) Using a Ba—Ti—O composition cut to a height of 0.375 mm so that Ti / (Ti + Ba) (molar ratio) is 0.85 and the aspect ratio becomes 0.05, titanium A barium acid single crystal was grown. In the obtained crystal, a foreign phase was visually observed in the crystal, and it was confirmed by X-ray structure analysis that it was a mixed phase of tetragonal and hexagonal barium titanate.

(Sample 19) Ti / (Ti + Ba) (molar ratio) was 0.65, and titanium was obtained by using a Ba—Ti—O composition cut to a height of 16.5 mm so as to have an aspect ratio of 2.2. A barium acid single crystal was grown. In the obtained crystal, a heterogeneous phase was visually observed in the crystal, and X-ray structure analysis confirmed that it was a mixed phase of tetragonal and hexagonal barium titanate.

(Sample 20) Using a Ba—Ti—O composition cut to a height of 0.75 mm so that Ti / (Ti + Ba) (molar ratio) is 0.86 and the aspect ratio becomes 0.1, titanium A barium acid single crystal was grown. In the obtained crystal, a foreign phase was visually observed in the crystal, and it was confirmed by X-ray structure analysis that it was a mixed phase of tetragonal barium titanate and BaTi ₂ O ₅ .

(Sample 21) Barium titanate was prepared using a Ba—Ti—O composition cut to a height of 9 mm so that Ti / (Ti + Ba) (molar ratio) was 0.75 and the aspect ratio was 1.2. A single crystal was grown. The obtained crystal was confirmed by X-ray structural analysis to be a tetragonal single phase. After the obtained single crystal is divided into single domains by poling, two argon lasers (wavelength 514.5 n) are used.
As a result of the two-wave mixing experiment according to m), amplification of the signal light intensity was confirmed.

(Comparative Example 1) Ba-
A barium titanate single crystal was grown without using the Ti-O composition. The obtained single crystal was analyzed by X-ray structural analysis.
It was confirmed that it was a single phase of hexagonal barium titanate.
After the obtained single crystal was divided into single domains by poling, a two-wave mixing experiment was performed using two argon lasers (wavelength: 514.5 nm). As a result, amplification of signal light intensity was not confirmed.

Next, examples and comparative examples in which the thickness of the raw material rod and the Ba-Ti-O composition are changed will be described below.

Example 2 Under the same conditions as in Example 1, a barium titanate single crystal was grown using a raw material rod having a diameter of 20 mm after sintering and a Ba—Ti—O composition. Ba-Ti-O composition is Ti / (Ti + Ba)
(Molar ratio) was 0.80 and the height was 4 mm so as to have an aspect ratio of 0.2. The obtained crystal was confirmed by X-ray structural analysis to be a tetragonal barium titanate single phase. After the obtained single crystal is divided into single domains by poling, two argon lasers (wavelength 514.
5 nm), the amplification of the signal light intensity was confirmed.

Example 3 Under the same conditions as in Example 1, a barium titanate single crystal was grown using a raw material rod having a diameter of 1 mm after sintering and a Ba—Ti—O composition.
The Ba—Ti—O composition was cut out to a height of 0.2 mm so that Ti / (Ti + Ba) (molar ratio) was 0.80 and the aspect ratio was 0.2. The obtained crystal was confirmed by X-ray structural analysis to be a tetragonal barium titanate single phase. After the obtained single crystal is divided into single domains by poling, two argon lasers (wavelength 514.
5 nm), the amplification of the signal light intensity was confirmed.

(Comparative Example 2) Under the same conditions as in Example 1, a barium titanate single crystal was grown using a raw material rod having a diameter of 21 mm after sintering and a Ba-Ti-O composition. Ba-Ti-O composition is Ti / (Ti + Ba)
(Molar ratio) was 0.80 and the height was 4.2 mm so that the aspect ratio was 0.2. However, a single crystal was not obtained due to insufficient melting of the crystal.

[0045]

According to the present invention, a high purity and high quality tetragonal barium titanate single crystal can be easily and stably grown. As a result, for example, a tetragonal barium titanate single crystal having suitable characteristics as an optical device material such as an optical hologram memory can be supplied at a relatively low cost.

[Brief description of the drawings]

FIG. 1 shows a method for producing a single crystal according to the present invention.
It is a graph which shows the range to which Ti / (Ti + Ba) (molar ratio) and aspect ratio in a Ba-Ti-O composition belong.

FIG. 2 is a two-dimensional phase diagram of a BaO—TiO ₂ system.

FIG. 3 is an illustrative view showing one example of an apparatus for growing a single crystal used in a method for producing a single crystal according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 single crystal growing apparatus 12 housing 14 double elliptical mirror 16 halogen lamp 18 upper shaft 20 lower shaft 22 quartz tube 24 raw material rod 26 seed crystal 28 Ba-Ti-O composition

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takashi Fujii 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Inside Murata Manufacturing Co., Ltd. (72) Kikuo Wakino 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Stock Company Murata Manufacturing Co., Ltd. (72) Inventor Masakatsu Okada 22F, Jurakumado-Higashicho, Nakagyo-ku, Kyoto-shi, Kyoto, Japan 1103 F-term (reference) 4G077 AA02 AB09 AB10 BC41 CE03 EC08 GA10 HA01

Claims (4)

[Claims] A step of sandwiching a Ba—Ti—O composition between a seed crystal of barium titanate single crystal and a polycrystalline barium titanate; and heating and melting the Ba—Ti—O composition. Joining the seed crystal and heating and melting the Ba-Ti-O composition to move the molten zone toward the barium titanate polycrystal side to obtain a barium titanate single crystal. 1. A method for producing a barium titanate single crystal comprising: a Ti— (Ti + Ba) molar ratio and an aspect ratio of the Ba—Ti—O composition, wherein a point A (0.68, 2,.
2), B (0.81, 2.1), C (0.85, 0.
1) A method for producing a barium titanate single crystal belonging to the range of a rectangle having D (0.72, 0.2) as a vertex (including the vertex and the side). 2. The titanic acid according to claim 1, wherein the Ba—Ti—O composition is disposed on the seed crystal in the vertical direction, and the barium titanate polycrystal is disposed thereon. A method for producing a barium single crystal. 3. The production of the barium titanate single crystal according to claim 1, wherein the polycrystalline barium titanate and the Ba—Ti—O composition are each a column having a diameter of 20 mm or less. Method. 4. The method of producing a barium titanate single crystal according to claim 1, wherein the Ba—Ti—O composition is heated and melted by an optical heating device.