JPS61101495A - Preparation of rutile single crystal - Google Patents

Abstract

PURPOSE:To obtain a high-quality rutile single crystal free from sub-grain texture, by keeping the oxygen partial pressure in the growth atmosphere below a specific pressure, and growing the single crystal of TiO2 from the molten liquid, thereby developing only one kind of crystal phase. CONSTITUTION:A single crystal of TiO2 is made to grow from the molten liquid of TiO2 keeping the oxygen partial pressure in the atmosphere to <=3X10<-2>atm. There is no particular restriction in the crystal growth method, however, a floating zone process is preferable from the viewpoint of the contamination from the crucible, etc. The oxygen partial pressure in the crystal growth atmosphere can be maintained to <=3X10<-2>atm, e.g. by the high-temperature thermal equilibrium reaction or heat-decomposition reaction near the temperature of crystal growth, or by the use of gas emitting a specific amount of free oxygen, e.g. CO2, NOX, etc. Only one kind of a crystal phase can be crystallized by the above process, and a high-quality rutile crystal free from sub-grain texture can be prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing rutile (TjO2) single crystal.

[Problems to be solved by the prior art and the invention] Calcite, which has large birefringence and is used in high-precision optical equipment parts such as polarizing prisms, is rounded and natural products are used for which the forming technology has not been fully established. has been done. However, high-quality natural calcite has recently been in short supply, and its low hardness causes problems such as inconvenience in handling.

Recently, rutile (TiO), which has a high birefringence of 0.3, has been
2) is attracting attention and is expected to be a substitute for calcite. However, the rutile currently on the market is a product made by the Bernoulli method, and has large optical distortion due to thermal distortion.
It has drawbacks such as a large number of bubble-containing products, making it unsuitable as a component for high-precision optical equipment.

Attempts have also been made to grow crystals using six growth methods, such as the pulling method. This method often produces crystals of inferior quality to those produced by the Bernoulli method.

Therefore, the present invention seeks to propose a method for producing an optically undistorted and bubble-free rutile single crystal that can also be used as a component of high-precision optical equipment.

[Reason why good quality crystals could not be obtained by the conventional method] In titanium oxide, Ti'0 and Ti3+ coexist, which is expressed as Tin01n-1 (n is an integer of 1 or more).

The existence of a series of independent crystal phases with similar crystal structures is known. Each phase exists stably only under a specific range of oxygen partial pressure. Therefore, when crystals solidify from the melt.

The composition of the solidified crystal, that is, the crystal structure, depends on the oxygen partial pressure in the atmosphere. That is, when the oxygen partial pressure is high, a crystal with a large n is obtained, and when the oxygen partial pressure is low, a crystal phase with a small n is obtained. Depending on the value of the oxygen partial pressure, two types of crystal phases having adjacent compositions may crystallize simultaneously. In such a case, it is obvious that a single crystal cannot be obtained even if ordinary crystal growth techniques from melt are applied.

The crystal phase of the composition Tln01n-+ is when n is large.

That is, when the composition is very close to T-0H, it easily changes to a rutile structure while remaining a single crystal by slow cooling or annealing. it is,
This is because the structure of Tin02n,H has oxygen-deficient lattice defects introduced into the rutile structure in an orderly manner, and these are easily removed by oxygen diffusion at low temperatures. Furthermore, under the same oxygen partial pressure, the permissible growth rate of low-temperature phase Ti3+ is reduced. Therefore, the crystal solidified in the above two-phase coexistence state.

When slowly cooled to room temperature, K contains subgrain structure even though it has a rutile structure.

This is the reason why good quality crystals have not been obtained by conventional melt growth methods.

Therefore, the means to obtain high-quality rutile crystals without subgrain structure is to supply oxygen partial pressure such that only one type of crystal phase crystallizes during solidification.

[Means for solving problems]

The present invention is based on the above-mentioned concept, and is designed to grow a single crystal of titanium oxide from a melt while maintaining the oxygen partial pressure in the atmosphere within a range of 13×10 −2 atmospheres or less.

According to the present invention, it has been revealed for the first time that the oxygen partial pressure range in which only one type of titanium oxide crystallizes falls within this range.

The methods of growing crystals from melt applied in the present invention include the pulling method, the Bernoulli method, and the Brillaman method.

Although any method such as the 70-Ting zone method may be used, the pulling method and the 70-Ting zone method are preferable because it is easy to achieve high quality grown crystals, and the floating zone method, which is free from 1% contamination by impurities from the container, is preferable.

TiO2 as a starting material used in the present invention may be a commercially available special grade reagent, but the higher the purity, the more preferable it is as a raw material for optical crystals. In addition, Fe, Ni, and Oo are used to control the physical and chemical properties depending on the application.

Mn, Or, Li, My, Ou,
Zn, Od*At, Ga*V, Nb
.

Small amounts of elements such as Ta, Si, Ge, Zr, HfoMo, and W can be added.

The crystal growth rate in the present invention is 0.1 to 300 W/hour, preferably 0.5 to 15 m/hour, preferably *3
~8 m/h.

In the present invention, the oxygen partial pressure range in the crystal growth atmosphere is 3
In order to achieve a pressure of 10" atm or less, a predetermined amount of free oxygen must be released through thermal equilibrium reactions and thermal decomposition reactions at high temperatures near crystal growth. Gases such as NOx and NOx are used. In order to correctly set the oxygen partial pressure range, the higher the purity of these gases, the better.

In addition, in order to realize the oxygen partial pressure range, acid! A mixed gas consisting of an inert gas and an inert gas may be used. The inert gas is a rare gas element such as Ar or nitrogen.

The higher the purity of these inert gases, the better in order to set the oxygen partial pressure range correctly.

The crystals obtained according to the present invention are
; The composition is Ti0z, o, but it may contain Ti"+ to the extent that it is difficult to detect by analysis, and the transparency may be insufficient. In such cases, the crystals may be exposed to air or Transparency can be increased by annealing in oxygen.The annealing temperature is 600-1000°C, preferably 7
00-900°C. The longer the annealing time, the better; however, in order to increase production efficiency and ensure sufficient transparency, the annealing time is 3 to 100 hours, preferably 5 to 70 hours.

[Example 1] Commercially available Tl02 (99,98%) powder was
Rubber press molded into a rod shape using hydrostatic pressure of I, and sintered in air at 1400°C. This was loaded as a raw material rod into a condensing floating zone method single crystal manufacturing apparatus using a spheroidal mirror, and a separately prepared rutile single crystal was loaded as a seed crystal. 00 to control the oxygen partial pressure in the atmosphere! was introduced into a crystal elongation chamber and continued to flow at a flow rate of 2 t/min until the end of crystal growth, and nine crystal growth operations were performed according to the conventional floating zone method to obtain blue-black crystals.

The growth conditions were that the rotation speed of the raw material rod and the seed crystal were 25 times/min in opposite directions, and the crystal growth rate was 5/hour.

The obtained crystals were annealed in air at 800° C. for 48 hours to obtain a slightly yellowish transparent crystal body 2. A specimen with planes parallel to the growth direction and a direction perpendicular to it was cut from this crystal, optically polished, and examined using a polarizing microscope.

It was found to be a high-quality rutile single crystal with no detectable distortions, bubbles, or subgrain structure.

[Example 2] In exactly the same operation as in Example 1, a mixed gas containing ultra-high purity R and 02 mixed at a ratio of 100:3 was used for crystal growth to control the oxygen partial pressure in the atmosphere. Introduced into the room, 2t/
The flow rate continued until the end of the growth. Other operations were performed in exactly the same manner as in Example 1 to obtain a high-quality rutile single crystal in which distortion, bubbles, subgrain structure, etc. were hardly detected.

〔Effect of the invention〕

As is clear from the above examples, one of the features of the present invention is when growing a rutile single crystal from a melt.

By keeping the oxygen partial pressure in the atmosphere within the range of 3 x 10'''2 atmospheres or less, only one type of crystal phase is crystallized,
The objective is to obtain high quality rutile crystals without subgrain structure.

On the other hand, if oxygen, air, etc. are supplied to make the oxygen partial pressure higher than the 9 range limited in the present invention, or if ultra-high purity Ar is supplied to make the oxygen partial pressure almost zero, crystallization will occur. The crystals contain many subgrain structures and high quality crystals cannot be obtained. Although it is difficult to determine the lower limit of the oxygen partial pressure, ultra-high purity pLr and 02 are 100 p
1yrf containing pm was mixed at a ratio of 100:1 to create an atmosphere with an oxygen partial pressure of 10-6 atm, and crystals were grown in exactly the same manner as in Example 1. Subdalein was locally detected, but Obtain high quality rutile single crystal.

Claims (2)

[Claims] (1) In a method of growing crystals from a melt of TiO_2 at high temperature, the oxygen partial pressure in the atmosphere is set to 3×10
^-^ A method for producing a rutile (TiO_2) single crystal, characterized by maintaining the pressure in a range of 2 atmospheres or less. (2) In the crystal growth apparatus, a gas that releases a small amount of oxygen, such as CO_2 or NOx, or a mixed gas of oxygen and an inert gas is introduced into the vicinity of the melt and the growing crystal to increase the oxygen partial pressure in the atmosphere. A method for producing a rutile single crystal according to claim 1, characterized in that the pressure is controlled to a range of 10^-^2 atmospheres or less.