JPH01157500A - Production of barium titanate single crystal - Google Patents

Abstract

PURPOSE:To efficiently produce the title large cubic system single crystal having high purity, by equipping solvent consisting of sintered compact of BaO, TiO2 and B2O3, and seed crystal under a specified raw material rod, and by melting the solvent to deposit the single crystal. CONSTITUTION:The raw material rod 1 consisting of sintered compact of a mixture of (4.7/5.3)-(5.5) BaO/TiO2 mol ratio is attached to a clasp 8 of a sample rotating shaft 3 equipped at the upper part of a chamber, and the solvent 2 consisting of sintered compact of a mixture of 30-60mol% BaO, 20-60mol% TiO2 and 10-50mol% B2O3 is attached on the terminal surface of the BaTiO3 seed crystal 5 attached on a sample rotating shaft 4 equipped at the under part of the chamber. Then, the seed crystal 5 and solvent 2 are surrounded with a heat insulating tube 6, the shafts 3 and 4 are surrounded with a quartz tube 7, and O2 is introduced after excluding the external atmosphere. The terminal surfaces of material rod 1 and solvent 2 are touched and as the terminal surfaces are melted by heating, the raw material rod 1 and the seed crystal 5 are joined through the solvent 2 and the shafts 3 and 4 are rotated in opposite direction with each other to deposit BaTiO3 single crystal.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for producing a barium titanate single crystal, and particularly to a method for producing a cubic barium titanate single crystal used as a photorefractive crystal for optical 10 processing or a nonlinear optical crystal. This invention relates to a method for producing crystals.

[Conventional technology and its problems] Barium titanate single crystal is conventionally fluxed (FIUX)
method, Top 5eed method (also known as Chiroporous method) and Floating zone method (Floating zone method).
manufacturing method.

Flux methods include the method of Remeika [Journal of American Chemical Society (J, Am, Chem, Soc, ), p940 (1954>]) using potassium fluoride as a flux, and the method of Remeika using potassium fluoride as a flux, and the method of Remeika using potassium fluoride as a flux. The method of Blattner et al. using barium [
11elv, Phys, Acta, 20 p2
25 (1947)], and the former, in particular, is also called the Shimaica method, and uses as a raw material an equimolar mixture of high-purity barium carbonate and titanium oxide, to which iron oxide is added if necessary. A barium titanate single crystal is obtained by the following treatment. That is, the raw material mixture was calcined for 2 hours, pulverized, and sieved, divided into a fine powder that passed through 100 meshes and an O powder that passed through 40 meshes but not 60 meshes, and these were mixed appropriately. A predetermined amount of potassium fluoride is placed in the bottom of a platinum crucible, and a predetermined amount of potassium fluoride is placed on top of it as a flux so that the raw material mixture is covered.Then, this is placed in a furnace to melt and slowly cool, and the flux is poured out. It is then cooled and the crystals are extracted. However, this method has the disadvantage that it is difficult to obtain large, high-quality crystals, and impurities caused by the flux and the crucible are mixed in.

The top seed method is a method that combines the flux method and the crystal pulling method, and was developed by Lintz et al. [Material Research Printing ) fa
terial Research Bulletin)
6 p899 (1971)], which is Ba0-
In the TiO system, crystals are grown from a TiO2-rich solution using the same method as the crystal pulling method (Czochralski method). The temperature for growth is 13
At 90 DEG C., the temperature is lowered at a rate of several tenths of DEG C. per hour, and at the same time the crystal is pulled up at a rate of 0.5 to 1.0 mm per hour. This top seed method is a general method for obtaining barium titanate single crystals, but the maximum size of the crystals obtained by this method is currently 15x15X.
101! The crystal size was about 111, and no larger crystals were obtained. Furthermore, although high-quality crystals can be obtained, the growth technique is difficult, and the cost of reagents, crucibles, etc. is higher than the floating zone method described below.

Floating zone method is Brown
[Journal of Applied Physics (Journal of 8 pages)]
Lied Physics ) 35 (5)
p1954 (1964)], Buplau et al. found that when crystallized using a raw material with a B a T i O3 composition, only hexagonal barium titanate, which does not exhibit ferroelectricity, was obtained; BaTiO3-8rT containing a few percent of Sr'l'i03
When using the iO3 system, barium titanate crystallizes directly as a cubic crystal that exhibits ferroelectricity, and crystallization is performed using the floating zone method.
, a cubic crystal with a diameter of 3.2 m was obtained. S r Ti O 3 used in this method is an essential component to maintain the crystal structure of BaTiO 3 as a cubic crystal exhibiting ferroelectricity, but 5rTi 0 3 remains as a solid solution in the obtained crystal and is not pure. Barium titanate has not been obtained.

Therefore, an object of the present invention is to provide a novel method capable of efficiently producing high-purity, large-sized cubic barium titanate single crystals by solving the problems and drawbacks of the above-mentioned conventional techniques, particularly the floating zone crystallization method. Our goal is to provide the following.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and the method for producing a barium titanate single crystal of the present invention includes a barium oxide (BaO) component/titanium oxide (TiO2> Under the raw material rod consisting of a sintered body of a mixture with a molar ratio of components in the range of 4.715.3 or more and less than 515, 30 to 60 mol
A solvent consisting of a sintered body of a mixture of % barium oxide (BaO), 20 to 60 mol% titanium oxide (T i 02 ), and 10 to 50 mol% boron oxide (B2' 03 ) is provided, and under the solvent The method is characterized in that a seed crystal made of barium titanate is provided and heated so that the solvent portion is melted to precipitate a barium titanate single crystal.

In the method for producing barium titanate single crystal of the present invention, the raw material rods used are BaQ component and T i O2.
It is a sintered body of a mixture having a molar ratio of 4.715.3 or more to less than 515. Naturally, the raw material rod has a B a T i 03 composition (BaO component/T i O
Ideally, the molar ratio of the two components is 515). However, according to the inventor's study, pure B a T i 03
In contrast, if the raw material rod composition is rich in T i 02 components, melting will occur smoothly and crystal growth will be interrupted. It was found that the process progressed easily. However, if the T i O2 component is increased too much, Ba
Since it will deviate from the TiO3 composition, T i O
A composition slightly enriched in two components is desirable. From this point of view, the molar ratio of BaO component/T i O2 of the raw material rod is limited to a range of <4.715.3 or more and less than 515 as described above, and is particularly preferably 4.915°1 or more and 5/5. The range is less than 5.

In addition, the solvents used in the method of the present invention include 30 to 60 mol% barium oxide (BaO) and 2
0 to 60 mol% titanium oxide (T i 02 ) and 1
It is a sintered body of a mixture consisting of 0 to 50 mol% of boron oxide (B203).

Add barium oxide (BaO) here to 30 to 60 IlNot.
The reason for limiting it to % is less than 30 mol% or 60 mol%
This is because, if it exceeds this, crystals other than B a T i O3 will precipitate, which is not preferable. Also, titanium oxide (T i
The reason why 02) was limited to 20 to 60 mol% is 20
Similarly, if less than mol% or more than 60 mol%, B a
This is because crystals other than T i O3 are precipitated, which is not preferable. Furthermore, 10 to 5 boron oxide (B203)
The reason why it is limited to 0 mol% is that 10 mol% ungrooved is undesirable because hexagonal (high-temperature type) BaTiO3 will precipitate, and exceeding 50 mol% is undesirable because crystals other than BaTiO3 will precipitate.

[Function] According to the present invention, by using a raw material rod with a predetermined chemical composition and a solvent with a predetermined chemical composition in crystal growth by the floating zone method, it becomes possible to grow a barium titanate single crystal at a low temperature, Highly pure cubic crystals can be obtained.

[Examples] Hereinafter, the present invention will be further explained with reference to Examples, but the present invention is not limited to these Examples.

[Example-1] Barium carbonate (99.99% purity) was used as the raw material for the raw material rod.
B a C03> and rutile-type titanium oxide (T i 02 ) powder with a purity of 99.99% were used, and these were combined with BaO
The molar ratio of component/T i O2 component is 4.9515.0
They were weighed and mixed so that the total amount was 5. In addition, as a raw material for the solvent, barium titanate (BaTiO
3> and 99.99% purity barium carbonate (B a CO
3> and boron oxide (B203) with a purity of 99.99% as BaT i 03 component/BaB4 o7 (BaO
+2B203>The molar ratio of the components is 6.5/3.5, that is, barium oxide (BaO): 42.5 mol%, titanium oxide (TiO2): 27.5 mol%, boron oxide (B203): 30. They were weighed and mixed to make Omol M.

The two types of mixtures obtained were thoroughly mixed in a mortar to form a fine powder mixture with an average particle size of 10 μm or less in order to accelerate the subsequent reaction. In addition, barium carbonate (B
a CO3) and rutile-type titanium oxide (T i 02 ) having a purity of 99°99% may be used.

Approximately 15 g of each of the two types of mixtures obtained in this way was taken, each sealed in a rubber tube with a diameter of 5 m, and then pressurized for approximately 15 seconds at a pressure of 500 kg/- using a hydrostatic pressure device. By molding, press molded bodies for raw material rods and solvents were obtained. By press-forming using such a rubber press method, a press-molded product without bending can be obtained.

The press-molded body for the raw material rod obtained in the above process is attached to a soaking section in a heating device (vertical siliconite furnace) and heated at 1250 to 1350°C for about 1 hour in the second sintering process. did. At this time, the oxygen flow rate in the furnace was 1°01/min.
I made it. The thus sintered press-molded body was taken out and crushed using a mortar, finely divided into particles having an average particle size of about 10 μm in the same manner as in the above-mentioned process, and then press-molded again. This pressure molding is carried out by maintaining a pressure of 1000 kg/- for 5 minutes. Then, the obtained press-molded body was heated and sintered again in the above-mentioned furnace in a secondary sintering step. At this time, the oxygen flow rate in the furnace was set to 1. O1/min, the temperature was set at 1560°C, and the press-formed body was raised and lowered at a lifting speed of 5 cm/min in such an atmosphere to perform secondary sintering. A raw material sintered rod having an outer diameter of about 70 nm and a density of 90% or more was obtained. On the other hand, the press-formed body for the solvent is heated for about 1 hour in a furnace with an internal temperature of about 800°C, an oxygen flow rate of 1, and O1/min, similar to the press-formed body for the raw material rod described above. Obtain a solvent sintered rod of 400-500 mm.

Next, a single crystal of barium titanate was grown using the raw material sintered rod and solvent sintered rod prepared in this way, and a floating zone method single crystal growth device using infrared concentrated heating as a single crystal growth device. was manufactured. As shown in FIG. 1, which shows the layout of the chamber inside the apparatus used, the prepared raw material sintered rod 1 was attached via a hook 8 to a sample rotating shaft 3 disposed above the chamber. On the other hand, the solvent raw material rod 2 was attached to the end face of a seed crystal 5 (barium titanate single crystal) that was attached via a holder (not shown) to a sample rotating shaft 4 disposed at the lower side of the chamber. Next, the seed crystal 5 and the solvent raw material rod 2 were surrounded by an alumina heat-retaining tube 6 so that the temperature gradient of the precipitated crystal part and solid-liquid interface part was gentle. Then, a quartz tube 7 is encircled from the upper sample rotation shaft 3 to the lower sample rotation shaft 4 to block outside air, and a flow rate of 1. O1/
m! Oxygen was pumped in using n.

Next, the positions of the raw material sintered rod 1 and the solvent sintered rod 2 are adjusted vertically so that the opposing end surfaces of the raw material sintered rod 1 and the solvent sintered rod 2 are located in the area where the infrared light is focused and reaches the highest temperature in the device. At the same time, the heating temperature is held constant, and the raw material sintered rod 1 is moved downward to join the raw material sintered rod 1 and the seed crystal 5 via the molten solvent sintered body 2. Sazena. At this time, the axis misalignment was suppressed to about 0.5 points at most.

In this way, a 70-ting zone (floating zone) was formed, but during the above joining, the sample rotation shafts 3.4 were rotated at 20 to 30 r, p, m in opposite directions to ensure that the molten part was stabilized. The temperature was raised by increasing the voltage of a light source lamp (not shown) until the Next, the sample rotation shaft 3
．． 4 were moved downward at a speed of 0°3 mm/h. In this manner, by stably maintaining the molten zone in a constant shape, the raw material was melted from the raw material rod into the molten zone, and single crystals were precipitated from the molten zone into seed crystals. At this time, if the temperature is raised too much, the barium titanate formed changes into a high-temperature hexagonal crystal (transition point 1460°C), so stabilization does not cause a phase transition.
It is necessary to carry out the process at a low temperature below ℃.

The crystal grown after about 45 hours through the above process has facets on its surface, and finally has a length of 30 mm and a diameter of 6 mm.
We were able to obtain a large cubic barium titanate single crystal with high purity.

[Example-2] Using the same material as Example-1 as the raw material for the raw material rod,
The molar ratio of BaO component/T i 02 component is 4°951
5.05, and as a raw material for the solvent.
Bad using the same as 1.

The ratio of TiO2 and B203 is Bad: 58.3 mol%
, TiO2:' 30.1 mol%, B2O3: 11
．． They were weighed and mixed to a concentration of 6m0I%. Examples below-
The crystal grown after about 40 hours after going through the same process as 1 has facets on its surface, and finally has a length of 28 mm and a diameter of 6 mm.
We were able to obtain a large single crystal of cubic barium titanate with high purity.

[Example-3] Using the same material as in Example-1 as the raw material for the raw material rod,
The molar ratio of BaO component/T i O2 component is 4°851
5.15, and using the same solvent raw material as in Example-1, Bad.

The ratio of TlO2 and B2O2 is Bad: 42.5m.

1%, TiO2: 27.5mol%, B203
: 30. They were weighed and mixed to give Omol%. The crystal grown after about 50 hours through the same process as in Example 1 has facets on its surface and finally has a length of 35 W.
II. A large single crystal of cubic barium titanate with a diameter of 6 mm could be obtained with high purity.

[Example-4] Using the same material as in Example-1 as the raw material for the raw material rod,
The molar ratio of BaO component/T i O2 component is 47515
．． 25, and Example-1 as a raw material for the solvent.
Using something similar to Bad.

The ratio of TiO2 and B203 is BaO:40.01tlO
I%, TiO: 25. omol%, B203:
They were weighed and mixed to a concentration of 35.0 mol%. The crystal grown after about 55 hours after undergoing the same steps as in Example 1 had facets on its surface, and the final length was 38.5 m.
A large single crystal of cubic barium titanate with a diameter of 6 m and a diameter of 6 crystals was obtained with high purity.

[Examples 5 to 32] Examples 5 to 32 except that the component ratio of the raw material rod and the component ratio of the solvent were varied as shown in Table 1 within the limited range of the present invention.
By carrying out the same procedure as in Example 1, it was possible to obtain a large cubic barium titanate single crystal with high purity.

In the above embodiment, a barium titanate single crystal was used as the seed crystal, but similar results can be obtained using a barium titanate sintered body.

In addition, in Example 1, the crystal growth rate was set to 0°3 mm.
/h, but 0.1~0,5 mm/
A high quality single crystal can be obtained within a range of about h.

Further, in Example 1, 1.0. g/min of oxygen was flowed, but if the flow rate is about 0.5 to 1.51/min, 4
Since valent titanium can be prevented from becoming trivalent, the stoichiometry of the crystal can be stabilized.

[Effects of the Invention] As described above, according to the method for producing a barium titanate single crystal by the floating zone method of the present invention, by using a raw material rod with a predetermined composition ratio and a solvent with a predetermined composition ratio, the conventional floating Compared to the zone method, this method has the advantage that large and highly pure cubic barium titanate can be easily grown in a short period of time. Furthermore, compared to the conventional floating zone method, it can be grown using a minimum amount of raw material reagents, which has the advantage of significantly reducing manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a layout diagram of the interior of a crystal chamber of a single crystal manufacturing device used to carry out the method for manufacturing a barium titanate single crystal of the present invention. 1... Raw material sintered rod, 2... Solvent sintered rod, 5... Seed crystal.

Claims (1)

[Claims] (1) Barium oxide (BaO) component/titanium oxide (Ti
O_2) Under the raw material rod consisting of a sintered body of a mixture with a molar ratio of components in the range of 4.7/5.3 or more and less than 5/5, 30
~60 mol% barium oxide (BaO) and 20-60
mol% titanium oxide (TiO_2) and 10-50 mo
A solvent consisting of a sintered body of a mixture consisting of 1% boron oxide (B_2O_3) is provided, a seed crystal made of barium titanate is provided under the solvent, and titanate is heated to melt the solvent portion. A method for producing a barium titanate single crystal, which comprises precipitating a barium single crystal.