JP2000247777A - Method for producing rutile single crystal - Google Patents

Abstract

(57) [Problem] To produce a high-quality, large-diameter rutile single crystal free of bubbles and small-angle grain boundaries. SOLUTION: A first step of continuously supplying granular TiO ₂ raw material into a crucible, melting by high-frequency heating, and solidifying a melt flowing out from a hole at the bottom center of the crucible;
In this method, the raw material crystal 26 is suspended in the crucible 18, melted by high-frequency heating, and solidified from a melt flowing out of a central hole at the bottom of the crucible to pass through a second step of growing a single crystal 32. In addition, a high-density raw material rod is supplied to the upper crucible and is sufficiently melted by high-frequency heating. There is also a method in which a single crystal is grown by continuously supplying the melt so as to be guided to the bottom and solidifying the melt flowing out from the hole at the bottom center of the lower crucible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rutile single crystal by a raw material continuous supply type reduction method using high-frequency heating. The present invention relates to a method for producing a rutile single crystal devised so as to improve the crystal quality.
The rutile single crystal produced by the method of the present invention is useful for, for example, a polarizer of an optical isolator.

[0002]

2. Description of the Related Art As is well known, a rutile single crystal (Ti
O ₂ ) has a very large birefringence and is excellent in chemical durability, so that it is useful as a polarizer material, and is used as an optical isolator, an optical circulator, an optical switch,
It is built into various optical devices such as optical attenuators. This rutile single crystal is generally grown by the FZ method (floating zone method) or the Bernoulli method, but the diameter of the obtained single crystal is limited and cannot be too large. For example, the crystal diameter that can be grown by the FZ method is limited to about 15 mm.

[0003] One of the methods of growing a single crystal is a pulling-down method. This is a method of growing a single crystal by solidifying the melt flowing out of a hole provided at the center of the bottom of the crucible, and has an advantage that a single crystal having a diameter equivalent to the diameter of the crucible can be obtained relatively easily. is there.

The conventional pulling-down method is a batch method, in which raw materials are filled in a crucible, melted by high-frequency heating, and the melt flowing out of a hole provided at the center of the bottom of the crucible is solidified. Because of this method, it is difficult to make the diameter of the single crystal to be grown uniform, and there is a problem that the method is not suitable for making the single crystal to have a straight body.

[0005] Recently, a technique for growing a rutile single crystal using a continuous material supply type pulling-down method which solves this problem has been reported ("29th National Conference on Crystal Growth" Vol.25 No.3).
199814aA1 "Growth of rutile single crystals by continuous feed-down method". In addition, the continuous raw material supply type means that the raw material is continuously supplied into the crucible during the growth. Here, a sintered rod or granular TiO ₂ is used as a raw material. When the raw material is a sintered rod, the lower end is melted above the crucible and then drops as a droplet. By continuously supplying the raw materials into the crucible in this way, the length of the grown single crystal can be increased.

[0006]

As described above, the pulling-down method of the continuous material supply type has an advantage that a large-diameter and uniform-diameter rutile single crystal can be efficiently grown. When the crystal was observed in detail, bubbles and small-angle grain boundaries were present inside, and there was a problem that the crystal quality was not always sufficient as a material for a polarizer.

An object of the present invention is to provide a method for producing a high-quality, large-diameter rutile single crystal free of bubbles and small-angle grain boundaries.

[0008]

Means for Solving the Problems The present invention basically comprises:
This is a method of producing a rutile single crystal by a raw material continuous supply type pulling-down method using high-frequency heating.

In the first method of the present invention, a granular TiO ₂ raw material is continuously supplied into a crucible, is melted by high-frequency heating, and solidifies a melt flowing out from a central hole at the bottom of the crucible. A first step of growing a raw material crystal, and suspending the raw material crystal in a crucible and melting by high-frequency heating;
A second step of growing the single crystal by continuously supplying the lower end of the raw material crystal in contact with the melt in the crucible, and solidifying the melt flowing out of the hole at the bottom center of the crucible; ,
This is a method for producing a rutile single crystal through two steps.

In the raw material crystal grown in the first step, bubbles and small-angle grain boundaries are observed as in the prior art. However, in the second step using the raw material crystal, bubbles are newly introduced. Since there is no room for further uniformity, the rutile single crystal obtained in the second step has a high quality without bubbles or small tilt grain boundaries.

In the second method of the present invention, the firing density is 99.5.
% Of TiO ₂ raw material rod is supplied to the upper crucible and is sufficiently melted by high-frequency heating. This is a method for producing a rutile single crystal in which a single crystal is grown by continuously supplying the melt to be guided to the bottom and solidifying a melt flowing out of a hole at the bottom center of the lower crucible.

In the second method, a plurality of holes having a diameter of several mm or less (for example, about 1 mm) are formed at the bottom of the upper crucible in a dispersed manner.
The lower end of the guide rod vertically suspended in the vicinity of each hole is configured to contact the melt in the lower crucible, and the melt flowing out of each hole of the upper crucible travels along the guide rod to the lower crucible. Ensure that it flows smoothly without dripping (and therefore without entraining gas).

Using a raw material rod having a high firing density, the material is melted in the upper crucible with sufficient time. Although this melt flows into the lower crucible, it flows down the guide rod, so that there is no risk of air bubbles and the like being mixed. Therefore, the melt flowing out of the lower crucible has no air bubbles and is sufficiently homogenized because it has been melted sufficiently for a long time. The solidified rutile single crystal has bubbles and small-angle grain boundaries. Does not exist. However, it is not preferable to use a raw material rod having a low sintering density (for example, 99.3%) because bubbles and small-angle grain boundaries are generated in the solidified rutile single crystal even when the above method is used.

[0014]

(Embodiment 1) The growing apparatus used in the first step is shown in FIG. 1, and the growing apparatus used in the second step is shown in FIG. These devices may be basically the same, and may be the same as a conventional growing device. A high-frequency coil 12 for heating is arranged outside the quartz tube 10, an alumina tube 14 and a porous zirconia 16 are arranged inside the quartz tube 10, and an iridium crucible 18 is provided at the center. The crucible 18 has a structure in which a hole having a diameter of 2 mm is formed in the center of the bottom. A rotary pulling-down device (only the shaft is denoted by reference numeral 20) is provided below the crucible 18. In order to adjust the thermal gradient in the furnace, the crucible 18
The heat shield plate 22 is provided horizontally so as to face the bottom of the heat shield.

The raw material is commercially available granular TiO with a purity of 99.9%.
₂ (diameter 1 to 5 mm) was used. The granular TiO ₂ raw material was continuously supplied from above into an iridium crucible 18 having a diameter of 25 mm in the growing apparatus shown in FIG. The supplied raw material is subjected to high-frequency heating to become a melt 24 and flows downward through a hole having a diameter of 2 mm at the bottom center of the crucible 18. The seed crystal was brought into contact with this, and was lowered while rotating, so that the raw material crystal 24 was grown. The breeding condition is 15
mm / h, the number of rotations was 10 rpm, the growth orientation was C axis, and the growth atmosphere was nitrogen. As a result, a rutile single crystal having a diameter of 15 mm was obtained. As a result of observing the rutile single crystal, bubbles and small-angle grain boundaries were confirmed inside the crystal.

The raw material crystal 26 produced in the first step
Is, as shown in FIG.
The sample was suspended from above in a crucible made of iridium with a platinum wire 28, and was continuously supplied in contact with the melt 30. The melt 30 flows downward through a 2 mm diameter hole at the bottom center of the crucible 18. A seed crystal cut out of the raw material crystal prepared in the first step was brought into contact with this, and was lowered while rotating, whereby a rutile single crystal 32 was grown. The growth conditions were a growth speed of 4 mm / h, a rotation speed of 8 rpm, a growth direction of C axis, and a growth atmosphere of nitrogen. As a result, the diameter 18
A rutile single crystal of mm was obtained. As a result of observing the rutile single crystal in detail, no bubbles or small-angle grain boundaries were present inside the crystal.

(Embodiment 2) FIG. 3 shows a growing apparatus used in this embodiment. A high-frequency coil 12 for heating is arranged outside the quartz tube 10, an alumina tube 14 and a porous zirconia 16 are arranged inside, and a crucible 40 made of iridium is placed above and below the center (that is, in two steps). 42 are provided. The upper crucible 40 has a structure in which a plurality of holes are dispersedly formed at the bottom. Here, two holes having a diameter of 1 mm are formed point-symmetrically at a position 8 mm away from the center. A guide rod 44 made of iridium and having a diameter of 2 mm is provided vertically from the vicinity of both holes toward the vicinity of the bottom surface of the lower crucible 42. A hole having a diameter of 2 mm is formed at the bottom center of the lower crucible 42. Below the lower crucible 42, a rotary pull-down device (only the shaft is indicated by reference numeral 20) is provided. In order to adjust the thermal gradient in the furnace, a heat shielding plate 22 is provided horizontally at the upper end of the shaft 20.

A raw material TiO ₂ powder having a purity of 99.9% was molded by CIP (cold isostatic pressing) and fired at 1200 ° C. for 3 hours to produce a TiO ₂ raw material rod. This raw material rod is supplied to the upper crucible 40 of the growing apparatus shown in FIG. 3 from above, sufficiently melted by high-frequency heating, and the melt 46 flows out of both holes.
2. The melt 48 supplied to the lower crucible 42 is
Further, it is heated by high frequency and flows downward through a hole at the bottom center. A rutile single crystal was grown by bringing a seed crystal into contact with this and pulling it down while rotating. The growth conditions are
Growth speed 5mm / h, rotation speed 10rpm, growth direction C
The shaft and growth atmosphere were nitrogen.

(Example 2-1) When a single crystal was grown by the above method using a raw material rod having a sintering density of 99.9%, a rutile single crystal having a diameter of 15 mm was obtained. As a result of observation of the rutile single crystal, no bubbles or small-angle grain boundaries were found inside the crystal. (Example 2-2) Using a raw material rod having a firing density of 99.5%,
When a single crystal was grown by the above method, a rutile single crystal having a diameter of 16 mm was obtained. As a result of observation of the rutile single crystal, no bubbles or small-angle grain boundaries were found inside the crystal. (Example 2-3) Using a raw material rod having a firing density of 99.3%,
When a single crystal was grown by the above method, a rutile single crystal having a diameter of 15 mm was obtained. As a result of observing the rutile single crystal, bubbles and small-angle grain boundaries were confirmed inside the crystal.

(Comparative Example) A single crystal was grown using a raw material rod having a firing density of 99.9%. The breeding method is similar to the conventional technology,
In this method, the raw material rods are directly supplied to the lower crucible without using the upper crucible. As a result, a rutile single crystal having a diameter of 15 mm was obtained. However, as a result of observing the grown rutile single crystal,
Bubbles and small-angle grain boundaries were observed inside the crystal.

[0021]

According to the first method of the present invention, as described above,
In this method, the rutile single crystal grown in the first step by the continuous raw material supply type pulling-down method is used as the raw material crystal in the second step. In the second step, the melt is further homogenized. A large-diameter rutile single crystal without bubbles or small-angle grain boundaries can be produced.

In the second method of the present invention, as described above, a raw material rod having a high sintering density is used, crucibles are arranged in two upper and lower stages, and the raw material is continuously supplied. And
Since the crystallization is carried out from the lower crucible, the melt is further homogenized in the lower crucible, so that a large-diameter rutile single crystal having no bubbles or small-angle grain boundaries can be produced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a growing apparatus used in a first step in a first method of the present invention.

FIG. 2 is an explanatory diagram of a growing apparatus used in a second step in the first method of the present invention.

FIG. 3 is an explanatory view of a growing apparatus used in a second method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Quartz tube 12 High frequency coil 14 Alumina tube 16 Porous zirconia 18 Crucible 20 Shaft of rotation lowering device 22 Heat shield plate 26 Raw material crystal 30 Melt 32 Rutile single crystal

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiromitsu Umezawa 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. F-term (reference) 4G077 AA02 BB04 CE02 CE04

Claims (3)

[Claims] 1. A first method for growing a raw material crystal by continuously supplying a granular TiO ₂ raw material into a crucible, melting the raw material by high-frequency heating, and solidifying a melt flowing out of a hole at the bottom center of the crucible. And hanging the raw material crystal in a crucible, melting it by high-frequency heating, continuously supplying the lower end of the raw material crystal in contact with the melt in the crucible, and passing through the hole at the bottom center of the crucible. And a second step of growing a single crystal by solidifying the melt flowing out. A method for producing a rutile single crystal, comprising the following two steps. 2. A TiO ₂ raw material rod having a sintering density of 99.5% or more is supplied to the upper crucible and sufficiently melted by high-frequency heating, and the melt flowing out from the hole at the bottom of the upper crucible is dropped from the vicinity of the hole. A single crystal is grown by continuously feeding the liquid to be guided to the lower crucible through the guide rod, and solidifying the melt flowing out of the hole at the bottom center of the lower crucible. Method for producing crystals. 3. A plurality of holes each having a diameter of several mm or less are dispersedly formed at the bottom of the upper crucible, and the lower end of a guide rod vertically suspended from the vicinity of each hole is in contact with the melt in the lower crucible. The method for producing a rutile single crystal according to claim 2.