JPH0669918B2 - Rare earth gallium perovskite single crystal and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a rare earth gallium perovskite single crystal, particularly a rare earth / gallium perovskite single crystal which is useful as a superconducting substrate material because a segregation coefficient is close to 1.00 and twins are unlikely to occur. The present invention relates to a gallium perovskite single crystal and a method for manufacturing the same.

(Prior Art) Rare earth gallium perovskite single crystals are used for superconducting substrate materials, etc., but rare earth gallium perovskite single crystals used for these applications have high quality, that is, uniform and uniform. Lattice constant and defect-free are required.

In order to produce a single compound crystal such as a rare earth gallium perovskite single crystal, a method of growing a single crystal from a melt having a stoichiometric composition is usually adopted. In addition to ensuring high quality, the problem is to prevent cracks from occurring in crystals. In other words, increasing the diameter and length of the single crystal causes a large nonuniformity of the composition and characteristic values in the single crystal ingot, and the single crystal ingot is not only disadvantageous not only in the substrate processing step but also in the thin film forming step. Will be accompanied.

(Problems to be solved by the invention) However, since the segregation coefficient of the single crystal produced by the above-described known method largely deviates from 1.00, the composition of the melt and the single crystal do not match, and Since crystals do not grow stably, long ones cannot be pulled up, and twins are likely to occur, which also means that each device using a wafer cut from the single crystal thus obtained as a substrate There is also the disadvantage that the characteristic values are not constant.

(Means for Solving the Problems) The present invention relates to a rare earth gallium perovskite single crystal and a method for producing the same, in which such disadvantages are solved, and it is Re ₂ O ₃ (where Re represents a rare earth element). x, y in the composition consisting of x mol% and Ga ₂ O ₃ y mol%
Is 50.00 <x ≦ 52.00 and 48,00 ≦ y <50.00, and x is 5 in a composition consisting of Re ₂ O ₃ x mol% and a rare earth gallium perovskite single crystal.
R consisting of congruent composition with 0.00 <x ≤ 52.00
From the mixed melt of e ₂ O ₃ and Ga ₂ O ₃ , rare earth gallium
The present invention relates to a method for producing a rare earth gallium perovskite single crystal, which comprises growing a perovskite single crystal.

That is, as a result of various studies on the rare earth gallium perovskite single crystal and the method for producing the same without the above disadvantages, the present inventors have found that the melt used in pulling the single crystal by the Czochralski method has a congruent composition. When a rare earth gallium perovskite single crystal is grown from this assuming that Re ₂ O ₃ x mol% x is 50.00 <x ≦ 52.00 and the balance is substantially Ga ₂ O ₃ .
X of Re ₂ O ₃ x mol% of the obtained single crystal is 50.00 <x ≦ 52.00
It was confirmed that the content was mol% and that the segregation coefficient of this product was approximately 1.00 and the composition of the single crystal was constant in each part, so the crack rate was small and twins were also small. The present invention was completed by finding out that.

This will be described in more detail below.

(Function) The rare earth gallium perovskite single crystal of the present invention has a composition of Re ₂ O ₃ x mol% and Ga ₂ O ₃ y mol%.
x, y is 50.00 <x ≦ 52.00, 48.00 ≦ y <50.00, which means that x is Re ₂ O ₃ x mol% and x is
It is produced by growing from a mixed melt of Re ₂ O ₃ and Ga ₂ O ₃ having a congruent composition of 50.00 <x ≦ 52.00. The rare earth element (Re) is La,
Pr and Nd are appropriate. Also used here
Re ₂ O ₃ and Ga ₂ O ₃ are preferably as high in purity as possible, and therefore, it is preferable that all of them are 99.99% or more. Congruent composition Re ₂ O ₃ x mol% x
Should be 50.00 <x ≦ 52.00, and the balance should be substantially Ga ₂ O ₃ . Each of these is weighed and then stored in a crucible to be melted. Since the melting temperature of these crucibles is 1,600 ° C. or higher, they may be made of iridium. This material may be melted by high-frequency induction heating according to a conventional method. Therefore, for this, for example, a high frequency of 7 kHz, 10 kw is used to melt these at 1,700 to 1,8
It may be heated to 00 ° C to melt.

The target single crystal may be produced by pulling a single crystal from the melt by the Czochralski method,
The atmosphere in this case is 1 to 5% oxygen or 25 to 100 CO ₂ .
% Nitrogen gas or argon gas atmosphere may be used. Further, the seed crystal used for pulling this single crystal may be of the same quality as the intended single crystal, for example, the one represented by the formula ReGaO ₃ , but this is also a single crystal of the garnet single crystal type crystal body. Of course, the pulling rate of the single crystal in this case may be 1 to 20 mm / hour.

The pulling of this single crystal can be performed in the same manner as the pulling of other single crystals, and after the pulling is completed, the single crystal is separated from the melt and cooled to obtain the desired single crystal.

In the composition of Re ₂ O ₃ x mol% of the single crystal represented by the formula ReGaO ₃ of the present invention thus obtained, x is 50.00 <x ≦ 5
2.00, which has a small crack occurrence rate, extremely few twins, and a segregation coefficient of about 1, so it is for superconductivity of Ba-Y-Cu-O system. It is useful as a substrate single crystal for growing a thin film of an oxide substance.

(Example) Next, the Example of this invention and a comparative example are given.

Example 1 La ₂ O ₃ 25 was placed in an iridium crucible having an outer diameter of 50 mm and a height of 50 mm.
5.8 g (50.50 mol%) and Ga ₂ O ₃ 144.2 g (49.50 mol%) were weighed and charged, and heated to 1,715 ° C. by high frequency induction in a nitrogen gas atmosphere gas containing 1 to 5% oxygen gas. When melted, 5 mm square LaGaO ₃ seed crystals were immersed in this melt, and when this was pulled at a rate of 1 to 10 mm / hour under rotation of 20 rpm to perform single crystal pulling, 200 g of transparent crystals were obtained. Was given.

Next, 1 g of each sample was taken from the melt in the lower part of the crystal and in the crucible after pulling the crystal, and quantitative analysis for La ₂ O ₃ was carried out, and the results shown in Table 1 were obtained.
This was confirmed to have the crystal structure of the formula La _1.01 Ga _0.99 O ₃ , but based on the quantitative analysis results,
The segregation coefficient of La was calculated and found to be 1.00.

For this crystal, a wafer with a thickness of 1 mm was cut out from the upper and lower parts of the crystal, etched with hot phosphoric acid, and the lattice constant precision measurement device APL2 (trade name of Rigaku Denki Co., Ltd.) was used. When constants were measured, they were a = 5.502Å, b = 5.491Å, c = 7.
The value in the range of 773Å ± 0.002Å was shown.

When the crystal was pulled 10 times under the same conditions, no cracks occurred during cooling or during work cutting after pulling, and 1 mm thick wafers cut from the top and bottom of the crystal were hot-phosphorized. After etching with acid, twins were observed, and the area of twins different from the original crystal orientation was 10% or less per cm ² .

Comparative Examples 1 and 2 The same treatment as in Example 1 was carried out except that the amounts of La ₂ O ₃ and Ga ₂ O ₃ in Example 1 were changed to those shown in Table 2. The following single crystals were obtained. The La ₂ O ₃ (wt%) and segregation coefficient of these single crystals were obtained as shown in Table 3, and the crack rate and twin number thereof were shown in Table 4. The results were as shown.

Claims (3)

[Claims] 1. A composition comprising Re ₂ O ₃ (wherein Re represents a rare earth element) x mol% and Ga ₂ O ₃ y mol%, x,
A rare earth gallium perovskite single crystal characterized in that y is 50.00 <x ≦ 52.00, 48.00 ≦ y <50.00. 2. The rare earth gallium perovskite single crystal according to claim 1, wherein the rare earth element is at least one selected from La, Pr and Nd. _3. A mixture of Re ₂ O ₃ and Ga ₂ O ₃ having a composition of Re ₂ O ₃ (Re represents a rare earth element) x mol% and a congruate composition in which x is 50.00 <x ≦ 52.00. A method for producing a rare earth gallium perovskite single crystal, which comprises growing a rare earth gallium perovskite single crystal from a melt.