JPS62275097A - Macro single crystal of barium tetratitanate and its production - Google Patents

Abstract

PURPOSE:To easily produce a macro single crystal of barium tetratitanate by growing a crystal by a floating zone melting method under specified growth conditions with a bar-shaped sintered body consisting of barium oxide and titanium oxide in a specified ratio. CONSTITUTION:A round bar-shaped sintered body consisting of 1mol equiv. barium oxide and 3.8-4.2mol equiv, titanium oxide is formed as starting material. A crystal is grown on a seed crystal by a floating zone melting method at 0.5-4.0mm/hr growth rate with the bar-syhaped starting material. By this method, a macro single crystal of barium tetratitanate having a composition represented by a formula BaxTiOy (where x=0.97-1.04 and y=8.97-9.04) is obtd. The diameter of the single crystal is regulated to the desired value of about 3-8mm or above according to the size of a heating furnace and the output of light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a giant single crystal of barium tetratitanate and its 91
6 Regarding Manufacturing Method Barium tetratitanate (hereinafter sometimes abbreviated as BT4) has excellent dielectric properties in the microwave region, and is expected to be used as a microwave resonator.

Conventionally, Br3 has been synthesized by a sintering method or a hot pressing method, but when Br3 is synthesized by such a method, the dielectric properties of Br3 determined by the grain size, sinterability, sintered density, etc. of the raw materials are The disadvantage is that there are variations in the data, and there are also considerable variations in the data reported so far [for example, D, J, Masse
etat,, Proc, IEEE, 5
9 (11) 1628 (1971) and H, M, O'br.
yan et al., + J. Aller.

Ceram, Soc., 57(10)450(1
974)]. It is thought that such variations are related to the grain boundaries of the sintered body. Therefore, if Br3 can be synthesized as a single crystal, the influence of such grain boundaries can be eliminated, and high-quality Br3 with consistent properties can be obtained, with anisotropy in the crystal axis direction. It is expected that this method will be used to miniaturize microwave resonators and improve their performance.

However, Br3 is a decomposed molten compound with a melting point of 1432°C, and it has been reported that it decomposes into T i O2+ liquid at temperatures above the melting point [H, M, O'bryan
et at+, J, Amer, Ceram, So
c, *57 (12) 522 (1974)], therefore, it was thought that it was impossible to create a giant single crystal of Br3 by the melting method. In fact, to the best of the present inventors' knowledge, there has been no report on the production of giant (large) single crystals of Br3 by any method (a general method for producing giant single crystals of 1° decomposed molten compounds). , (a) 7 lux method and (b) hydrothermal method, etc.
The present inventors attempted to grow a giant single crystal of Br3 using these methods, but no satisfactory results were obtained. For example, in the case of the Brax method, a giant single crystal of barium titanate (BaT io 3) has been successfully created for BaOTi0z 0z using potassium heptadide (KF) as a solvent, but It is not possible to dissolve titanium oxide in an amount necessary for the synthesis of Br3 in potassium heptadide, and it is extremely difficult to synthesize Br3 by this method. In addition, although the hydrothermal method uses an aqueous solution, it is practically impossible to create a soluble ion complex of barium.
Even by this method, synthesis of Br3 is considered to be extremely difficult.

Therefore, the present inventors developed a giant single crystal of Br3! ! As a result of intensive research on the original method, we have now used the condensed floating zone melting method (concentrated FZ method) to develop specific growth conditions from a raw material rod made of a sintered body with a specific ratio of barium oxide and titanium oxide. By growing a single crystal underneath, they succeeded in creating a giant single crystal of Br3.

As mentioned above, a giant single crystal of Br3 has never been produced by any method and is a novel substance. Here, "giant single crystal" refers to a particularly large single crystal, and generally the weight of one single crystal is 0.1
g or more, preferably 0.5 g or more, more preferably 1.
0g or more, and the maximum diameter of the single crystal is preferably 3
Al is 111 or more, more preferably 5ma1 or more.

The stoichiometric composition of barium tetratitanate is BaTi.

However, the composition of the giant single crystal of Pariwaum titanate provided by the present invention may slightly deviate from the stoichiometric composition depending on the manufacturing conditions. The crystal has the following composition formula: % Formula % Here, X is a number from 0.97 to 1.04, and y is 8.
It has a composition in the range shown by, which is a number from 97 to 9.04.

The BT4 giant single crystal of the present invention is produced by a floating zone melting method using a rod-shaped raw material made of a sintered body of barium oxide and titanium oxide! ! It is possible to build. In the floating zone melting method, infrared rays emitted from an infrared rice generation source such as a halogen lamp or xenon lamp are focused on a rod-shaped sintered raw material using a spheroidal mirror to form a molten zone at the tip of the raw material rod. By bringing a seed crystal into contact with this melted zone and gradually moving the melted zone along the raw material rod, crystallization is performed at the interface on the seed crystal side, and the raw material rod is melted at the other interface to form a crystal on the seed crystal. This is a single-crystal growth method that continuously performs operations to compensate for the decrease in the melting method due to crystal growth.

In producing the BT4 giant single crystal, in the present invention, 1 molar equivalent of barium oxide and 3.0 molar equivalent of titanium oxide are used as raw material rods.
A rod-shaped sintered body with a molar equivalent of 8 to 4.2, preferably 3.85 to 4.0 molar equivalent is used. This rod-shaped sintered body is
Usually, a titanium oxide of high purity, preferably 99.9% or higher purity, and a barium oxide precursor compound of high purity, preferably 99.9% or higher purity (a compound that decomposes under firing conditions to give barium oxide) , for example, with barium carbonate in a proportion such that the oxide exchange chimolar ratio is within the above range, and after drying the mixture in air,
A raw material powder is prepared by firing at 0 to 1100'C for 1 to 5 hours, and then this raw material powder is molded by rubber pressing method (filling the powder into a rubber bag and rubber pressing it with hydrostatic pressure without using a binder). 0.8 to 1.5 tons/cm
It can be manufactured by molding it into a rod shape under water pressure in step 2 and sintering it. Sintering is usually done at 120°C in an oxidizing atmosphere.
This can be done by heating at 0 to 1400°C for 2 to 5 hours. The rod-shaped sintered body thus obtained can be of various sizes depending on the size of the equipment used in the floating zone melting method and its operating conditions, but generally speaking, the diameter is 5 to 15 I, preferably 1. is suitably within the range of 5 to 10 mm.

On the other hand, as a seed crystal, any BT4 crystal oriented in the a-axis direction, b-axis direction, or C-ring direction may be used, but if a crystal oriented in the C-axis direction is used, a beautiful round rod-shaped single crystal can be obtained.

BT4 by floating zone melting method using the above rod-shaped sintered body
The production of giant single crystals can usually be carried out using a single-tank circular or bielliptical infrared concentrated heating furnace. Attached 1st
The figure shows the principle of an example of a single-tank circular infrared central heating furnace.
The heating furnace is a spheroidal mirror body (1) with two focal points.
A halogen lamp or xenon lamp (2) is placed at one focus, and a rod-shaped raw material (3) is placed at the other focus.
) is located. The monolithic raw material (3) is held by the upper rotating shaft (4), and the seed crystal (5) is set on the lower rotating shaft (6). The rod-shaped raw material (3), seed crystal (5), upper and lower rotating shafts (4), (6) are enclosed in a transparent quartz tube (7), and the atmosphere inside the tube can be freely controlled. It is also possible to put it in a vacuum or pressurized state.

The output of the halogen lamp or xenon lamp (2) is not particularly limited, but is generally 0°8 to 4.5K.
A material of about W is used. When the lamp (2) is turned on, the infrared rays emitted from it are concentrated at the other focal point, and only the part of the rod-shaped raw material (3) that corresponds to that focal point is heated, and a molten zone ( 8) is formed. The molten zone (8) can be relatively moved by moving the rotating shafts (4), (6) upward or downward, thereby controlling the crystal growth rate.

To operate, first, set the rod-shaped raw material (3) and the seed crystal (5) as close as possible, turn on the lamp (2), and place the rod-shaped raw material (3) at a position (focus) close to the seed crystal (5). A molten zone (8) is formed, after which the seed crystal (5) is moved upwards into contact with the molten zone (8). After confirming that an equilibrium state has been reached, the upper and lower rotating shafts (4) and (6) are rotated and moved downward in accordance with the crystal growth speed, and the seed crystal (5) is grown. A transparent single crystal is obtained. That is, due to the movement, the raw material melts at the interface between the melting zone (8) and the unmelted portion of the rod-shaped raw material (3), while crystallization occurs at the interface between the melting zone (8) and the seed crystal (5). It will be done.

The rotation of the upper and lower rotating shafts (4), (6) takes place in mutually opposite directions, and their rotational speeds are generally 10-S each.
Orpm, preferably within the range of 2O-30rp+s. Furthermore, the moving speed of the upper and lower rotating shafts (4) and (6), that is, the growth speed of the single crystal, is 0°5-4. Om
m/h, especially in the range 1.0-2.5 mm/h.

Furthermore, the atmosphere within the quartz tube (7) may generally be air, but an inert gas atmosphere such as nitrogen may also be used; however, in this case, a dark blue single crystal is obtained due to oxygen defects. However, this single crystal is grown in air at 1000 to 130
A colorless and transparent single crystal is obtained by child-nealing for 2 to 5 hours at 0°C.

The BT4 single crystal produced as described above can have any size from about 3+am in diameter to about 8aIL11 or more depending on the size of the heating furnace and the output of the light, and can be used in microwave resonators. It is expected to be used for applications such as miniaturization, commercial performance, semiconductor production, and 11-electrode photocatalysts.

Next, the present invention will be further explained by examples.

Example 1 Titanium oxide (T +
02 > and 99.9% purity barium carbonate (B a
Using COy ), each raw material was weighed so that the molar ratio of oxides was BaO:Ti(]z = 1:4, and wet mixing was carried out in two bottles. This was dried in air. After that, a raw material powder was obtained by annealing at 1000° in air for 12 hours.
cm' under hydrostatic pressure, diameter 60110, 5501I
It was molded into a round bar shape of II6. This molded round bar is 11300
A rod-shaped raw material was obtained by sintering at ℃ for 2 hours.

Seed crystals are cut out using the backside Lawe method.
The one in the b or c axis direction was used.

The apparatus used was a single-tank circular infrared concentrated heating furnace as shown in the attached FIG. 1, which was equipped with one halogen lamp (1.5 KW). The atmosphere is 60j! It was flowed at a speed of /h.

The rotating shaft is rotated at 30 rpm in the upper and lower directions in opposite directions, and the melting zone is rotated at 1.0 to 2.0 rpm per hour. Move at a speed of Omm,
A transparent single crystal with a diameter of 5III and a length of 50 ma+ was obtained.

The shape of this single crystal was somewhat cylindrical with 77 sets appearing on the 0 face when a seed crystal with an upward direction of a upward direction of bII11 was used. Moreover, when a seed crystal in the C-axis direction was used, a round rod-shaped crystal was obtained.

The obtained single crystal was examined using Buerger's preset camera method, back surface Laue method, and polarizing microscope using X#i, and it was confirmed that the crystal was a single crystal.

Table 1 below shows various properties of the BT4 grown single crystal.

−・−1 Space group PIIlaln Lattice constant a(^) b(^) e(^
) Measured value 3.795 (1) 14.530 (1
) 6,292(1) JCPDS 8-367 3.
79 14,51 6.30Lukaszewia
z book 3.75 (1) 14.53 (2) 6.3
0(1) Analysis value Ti0z [laO
Measured value 68.4 wt% 32. Olllt%
Calculated value 67.6 wt% 32.4IIIt%
Density measurement value 4.40±0.02 g/
ca+: I calculated value 8aTi40* 4.5
3 g7cm'Bao, 5yTi40s, st 4.4
8 g7cm 3 pieces K, Lukasze
wicz* Rocz, Chem, + 3 two one,
11 In addition, the powder X-ray data of the BT4 grown single crystal is shown in Table 2 below.
cz, Rocz.

Chewa,, 31. The lattice constant of the sintered body was in good agreement with the lattice constant of the sintered body published in 1111 (19S 7).

1, =, -1, , , 1 Example 2 A single crystal was grown in the same manner as in Example 1, except that nitrogen was used as the atmosphere and a seed crystal in the six-ring direction was used. The obtained single crystal exhibited a deep blue color, and when this colored crystal was annealed in air at 1000° C. for 5 hours, it became colorless and transparent.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the principle of an apparatus for producing a giant single crystal according to the present invention. In FIG. 1, 1... spheroidal surface value, 2... halogen lamp, 3... rod-shaped raw material, 4... upper rotating shaft,
5... Seed crystal, 6... Lower rotating shaft, 7... Transparent quartz tube, 8... Molten zone.

Claims (1)

[Claims] 1. Compositional formula Ba_xTi_4O_y (where x is 0.
97 to 1.04, and y is a number from 8.97 to 9.04). 2. 1 molar equivalent of barium oxide and titanium oxide 3.8-4.
Compositional formula B characterized in that crystal growth is performed on seed crystals at a growth rate of 0.5 to 4.0 mm/hour by a floating zone melting method using a rod-shaped raw material made of a sintered body with 2 molar equivalents.
a_xTi_4O_y (here, x is 0.97 to 1.0
4 and y is a number from 8.97 to 9.04).