JP3132956B2 - Method for producing oxide single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an oxide single crystal comprising lithium tantalate or lithium niobate,
In particular, the present invention relates to a method for producing a high-quality oxide single crystal by preventing deterioration of a furnace body and a holder during high-temperature heat treatment for removing thermal strain generated during growth of the oxide single crystal.

[0002]

2. Description of the Related Art A single crystal of oxide such as lithium tantalate or lithium niobate is produced by bringing a rotating seed crystal into contact with a melt of these raw materials.
The seed crystal is grown using a pulling method (Czochralski method) in which the seed crystal is pulled from the melt, and in this method, the heat accompanying the crystallization is utilized by utilizing the heat conduction of the crystal itself. From the crystal to the upper surface of the crystal and further to the atmosphere, and the growth interface is solidified, thereby growing the crystal. For this reason, there is a temperature gradient between the crystal portion grown earlier and the growth interface, so that thermal distortion occurs inside the crystal, and cracks are generated in the subsequent cutting and processing steps due to the thermal distortion. Because of the disadvantages, a method is employed in which a single crystal grown by the pulling method is annealed at a high temperature to release thermal strain inside the crystal.

[0003]

However, even in this annealing, when this oxide single crystal is heat-treated in a support such as a crucible, cracks occur in this portion due to the contact between the single crystal and the support. A method has been proposed in which a powder of this oxide single crystal is interposed between the single crystal and the support to perform high-temperature treatment (Japanese Patent Publication No. 56-36160).
No., JP-A-59-227799). That is, according to this, since the oxide single crystal does not come into direct contact with the holder, the disadvantage of crack generation can be avoided, but in this case, lithium tantalate or lithium niobate as the oxide single crystal and Lithium (Li) mainly composed of lithium oxide (Li ₂ O) volatilizes at a high temperature from this powder, and a high-temperature furnace for high-temperature treatment and a support made of ceramic such as alumina are severely deteriorated in an alkaline atmosphere. It has been found that the life of the obtained single crystal is remarkably shortened, and that the obtained single crystal also has disadvantages in that the composition is non-uniform and the quality is poor.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method for producing an oxide single crystal which has solved the above-mentioned disadvantages, and relates to an oxide comprising lithium tantalate single crystal or lithium niobate grown by a pulling method. The product single crystal is held on a holding body via the oxide single crystal powder,
A method for producing an oxide single crystal, which is heat-treated at a high temperature, is characterized in that the oxide single crystal powder has a composition (Ta / Li or Ta / Nb = X) of 1.2 ≦ X ≦ 1.5. Is what you do.

That is, the present inventors have conducted various studies to solve the disadvantages caused by high-temperature treatment of an oxide single crystal composed of lithium tantalate single crystal or lithium niobate single crystal. The composition of the oxide single crystal powder used to avoid direct contact with the support and the Ta / Li or Ta / Nb value (X) is 1.
When 2 ≦ X ≦ 1.5, surplus Ta ₂ O ₅ is converted to Li
Is trapped and the volatilization of Li from now on is reduced, so that the deterioration of the holder and the furnace body made of alumina is no longer observed. The present inventors have completed the present invention by conducting research on such factors. This will be described in more detail below.

[0006]

The present invention relates to a method for producing a single crystal of lithium tantalate or a single crystal of lithium niobate. This single crystal of this type grown by the pulling method is placed on a support. In a method for producing an oxide single crystal, which is held via an oxide single crystal powder and heat-treated at a high temperature, the powder of the oxide single crystal has a composition (Ta
/ Li or Ta / Nb = X) is such that 1.2 ≦ X ≦ 1.5. According to this, even if the heat treatment at a high temperature, lithium (Li)
Since the volatilization of the sulfur is suppressed, the high-temperature furnace and the holder are prevented from being deteriorated due to the volatilized Li, and the life is prolonged, and the obtained oxide single crystal has an advantage of high quality. Is given.

The oxide single crystal comprising lithium tantalate single crystal or lithium niobate single crystal used in the present invention is obtained by melting tantalum oxide or niobium oxide as a material for growing these single crystals and lithium carbonate. The seed crystal made of lithium tantalate or lithium niobate is brought into contact with the liquid, and the seed crystal is pulled up from the melt to grow a single crystal. The crystal has the formula
Since they are represented by LiTaO ₃ and the lithium niobate single crystal is represented by the formula LiNbO ₃ , they have the composition Ta /
Li or Nb / Li = X is where X = 1.

Therefore, in LiTaO ₃ or LiNbO ₃ , when it is heated to a high temperature, only Li is volatilized from this, and this erodes the heating furnace and the holder.
The oxide single crystal powder used in the present invention has the composition Ta
If X / Li or Nb / Li = X is less than X = 1.2, the amount of excess Ta ₂ O ₅ that still traps the Li content is small, so that the Li content volatilizes during high-temperature heating and becomes larger than X = 1.5. The resulting oxide single crystal is Li
It is necessary that X is 1.2 ≦ X ≦ 1.5, since the dissociation of these components is increased and becomes non-uniform, but these are usually LiTaO ₃ or LiNbO ₃ where X = 1. The Li content is smaller than that of Li, and the Li content is trapped in the surplus Ta ₂ O ₅ , which suppresses the amount of Li content that evaporates when heated to a high temperature, thus preventing erosion due to this volatilization. In addition, the obtained single crystal has the advantage of being of high quality.

The composition ratio Ta / Li or Nb /
The powder of lithium tantalate or lithium niobate in which Li = X and X = 1.2 to 1.5 is prepared by mixing tantalum oxide or niobium oxide with lithium carbonate such that the ratio of tantalum or niobium to lithium is 1.2 to 1.5. What is necessary is just to bake the adjusted thing at about 1,000 degreeC, According to this, X = 1.2
Since an oxide single crystal having a size of ~ 1.5 can be easily obtained, it may be pulverized.

The method for producing an oxide single crystal of lithium tantalate single crystal or lithium niobate single crystal by heat treatment according to the present invention is performed by the apparatus shown in FIG.
FIG. 1 is a longitudinal sectional view of an example of an oxide single crystal heat treatment apparatus according to the present invention, which is an oxide such as a lithium tantalate single crystal or a lithium niobate single crystal grown by a pulling method. The single crystal 1 placed on the powder 2 of these oxide single crystals is housed in a holder 4 made of alumina via a platinum foil 3, and this holder 4 is not shown. Predetermined temperature by a heater arranged outside the holder, for example, 1,300 for LiTaO ₃ single crystal
It is designed to be heated to ~ 1,400 ° C.

However, in this case, when the single crystal is heated by the heater, the single crystal of the oxide is annealed by the heating to eliminate the growth distortion and the thermal distortion given to the single crystal during the crystal growth. Although the single crystal does not come into direct contact with the support due to the presence of the single crystal powder, it is possible to avoid cracks there, but the single crystal powder used here has a composition of T
Assuming that the ratio of a / Li or Nb / Li is 1.0, there is a disadvantage that the high-temperature furnace and the alumina support are eroded by Li content volatilized from the oxide single crystal and the powder during the heating. Occurs.

However, according to the present invention, the powder of this oxide single crystal is made to have a composition (Ta / Li or Nb / L
Assuming that i = X) is X = 1.2 to 1.5, since the content of Li is smaller than that of a conventionally known oxide single crystal, the volatilization is suppressed, and therefore, the high heat furnace and the support This has the advantage of reducing the erosion due to the volatile Li content of the metal, and has the advantage that it has a long life. However, even in this case, if this holding body is made to be a box with a lid, it can be compared with one that is opened. The Li content can be prevented from being volatilized, and a better result can be obtained by providing a trap in the system for recovering the Li content volatilized here.

[0013]

Next, examples of the present invention and comparative examples will be described. Example, Comparative Example A platinum foil with a thickness of 0.5 mm was placed on the floor of a box-shaped holder with a lid made of alumina having a size of 250 mm × 400 mm and a depth of 100 mm,
Spread lithium tantalate single crystal powder on top of it to a thickness of 20 mm and grow it here by the Czochralski method with a diameter of 80 mm.
A lithium tantalate single crystal rod having a length of 120 mm was placed and heat-treated at a high temperature of 1,400 ° C. for 16 hours. The powder of the lithium tantalate single crystal at this time was made up of the composition (Ta / L
i = X) as shown in Table 1, where X = 1.0, 1.2, 1.5,
Assuming that there were four types of 1.7, the results shown in Table 1 were obtained for the deterioration of the furnace body and the holder and the quality of the crystals.

That is, according to the present invention, this lithium tantalate single crystal powder has the composition (Ta / Li = 1.2 to 1.
When the value was 5, no deterioration was observed in the high-temperature furnace body and the holder, and the obtained crystals were of good quality.
For comparison, when the composition was Ta / Li = 1.0, the obtained crystal was of good quality, but the furnace body and the holder were deteriorated, and the composition was Ta / Li = 1.0. 1.
No deterioration was observed in the furnace body and the holder in the case of No. 7, but since the Li component was desorbed from the crystal surface obtained, the composition of the 3-inch wafer formed from this crystal caused non-uniformity, When the lattice constant was measured with a lattice constant precision measuring device, the disadvantage that the difference in lattice constant between the central part and the four points at the peripheral part was large was recognized.

[0015]

[Table 1]

[0016]

The present invention relates to a method for producing an oxide single crystal, which holds an oxide single crystal composed of a lithium tantalate single crystal or a lithium niobate single crystal grown by the pulling method as described above. In a method for producing an oxide single crystal, which is held on a body via the oxide single crystal powder and heat-treated at a high temperature, the oxide single crystal powder has a composition (Ta / Li or Nb / Li). = X)
Is characterized by 1.2 ≦ X ≦ 1.5. However, according to this, since the volatilization of Li from this oxide single crystal powder is suppressed, the Li
This provides the advantage that the erosion due to impurities is prevented and the obtained oxide single crystal has a high quality.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an example of an oxide single crystal heat treatment apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxide single crystal 2 Oxide single crystal powder 3 Platinum foil 4 Alumina holder

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshihiko Nagao 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Research Laboratories (56) References JP-A-54-5900 JP, A) JP-A-3-218996 (JP, A) JP-A-59-227799 (JP, A) JP-A-56-54300 (JP, A) JP-A-6-211600 (JP, A) (58) ) Field surveyed (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 CA (STN) JICST file (JOIS)

Claims (1)

(57) [Claims] 1. An oxide single crystal composed of lithium tantalate or lithium niobate single crystal grown by a pulling method is held on a holder via a powder of the oxide single crystal, and is heat-treated at a high temperature. In the method for producing an oxide single crystal, the powder of the oxide single crystal is mixed with its composition (Ta / L
i or Nb / Li = X) wherein 1.2 ≦ X ≦ 1.5. A method for producing an oxide single crystal comprising lithium tantalate or lithium niobate.