JP3631415B2 - Method for producing oxide single crystal - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing an oxide single crystal, and more particularly to a method for producing a single crystal of a substance that has been difficult to grow due to a narrow liquidus.
[0002]
[Prior art]
Superconducting materials are expected to be widely applied to superconducting magnets, superconducting power transmission and high-speed computer elements. J. et al. G. Bednorz and K.M. A. Muller's research on high-temperature superconducting materials originated from the discovery of a high-temperature superconductor composed of La-Ba-Cu-O (1986) greatly increased the possibilities of the above-mentioned applications. Among them, a substance having a CuO ₂ plane of 3 sheets such as Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10+ δ} phase and HgBa ₂ Ca ₂ Cu ₃ O _{8+ δ} phase has the highest superconducting transition temperature (Tc) ( 100K ≦ Tc ≦ 135K) (A. Schilling, M. Cantoni, JD Guo and HR Ott: Nature 363, 56 (1993)) Not obtained.
[0003]
On the other hand, as a method for growing a single crystal of a high-temperature superconductor, a flux method has been widely used because of its simplicity. However, the Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10+ δ} phase has a very narrow liquidus, so a single crystal cannot be obtained by the normal self-flux method. By adding KCI as an additive, a micrometer-sized crystal can be obtained. It was only there.
[0004]
The solvent transfer floating zone method (TSFZ) is promising in principle as a large-scale single crystal growth method, but its successful example has so far been La _{2 with} a wide liquidus line and easy single crystal growth. _-X Sr _X CuO ₄ (I. Tanaka and H. Kojima: Nature 337, 21 (1989)) and Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{8+ δ} (S. Takekawa, H. Nozaki, A. Umezono, K. Kosuda and M. Kobayashi: J. Cryst. Growth 92, 687 (1988)).
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a single crystal capable of growing even a substance having a very narrow liquidus line such as Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10+ δ} phase and generally difficult to grow a single crystal. is there.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems, the oxide single crystal production method according to the present invention uses a solvent transfer floating zone method, a growth rate is 0.05 mm / h or less, and a temperature gradient at a solid-liquid interface is 300 ° C./cm or more. It is characterized by. In addition, the method for producing an oxide single crystal according to the present invention is a method for producing an oxide single crystal having a CuO ₂ plane in units of three pieces , using a solvent transfer floating zone method, and a growth rate of 0.1 mm / h. The temperature gradient of the solid-liquid interface is 300 ° C./cm or more. Furthermore, it is a method for producing a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} phase oxide single crystal, using a solvent transfer floating zone method, a growth rate of 0.1 mm / h or less, and a temperature gradient at a solid-liquid interface Is 300 ° C./cm or more.
[0007]
According to the present invention, there is an advantage that even a substance that has a very narrow liquidus line such as Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10+ δ} phase and is generally difficult to grow a single crystal can be grown.
[0008]
The present invention will be described in more detail. In systems where single crystal growth is difficult due to the narrow liquidus, the yield of crystals will be very low when using the normal flux method. There are limits.
[0009]
Since the TSFZ method can in principle continue crystal growth at one point on the temperature-composition phase diagram, it is considered that large single crystals can be grown even in systems with narrow liquidus lines if conditions are adjusted. However, since the driving force for crystal growth is given by the degree of supersaturation of the solution, the narrow liquidus means that low-speed growth is forced. In a commercially available infrared concentrated heating furnace, the low-speed growth limit is usually about 0.3 mm / h. Therefore, we modified (1) the device to enable low-speed growth of 0.03 mm / h. The growth rate of such a single crystal is 0.1 mm / h or less. When the growth rate exceeds 0.1 mm / h, a single crystal having a narrow liquidus cannot be grown. Especially preferably, it is 0.05 mm / h or less.
[0010]
In the TSFZ method, since the melting zone is supported by surface tension, the size of the zone is usually determined to be about 4 mm. This means that the growth temperature cannot be arbitrarily adjusted under a finite temperature gradient. Therefore, (2) by using a small lamp (300 W, usually 1500 W), the condensing property of the lamp was improved and a temperature gradient about twice as large as that of the conventional one was realized. The large temperature gradient makes it possible to adjust the growth temperature, and also promotes thermal convection in the melting zone to increase the degree of supersaturation and avoids cell growth due to compositional supercooling.
[0011]
The temperature gradient at the solid-liquid interface is 300 ° C./cm or more in the present invention. It is because it is difficult to grow the above-mentioned single crystal when it is less than 300 ° C./cm. Particularly preferred is 370 ° C./cm or more.
[0012]
【Example】
Hereinafter, the manufacturing method of the oxide single crystal of this invention is demonstrated concretely based on an Example.
[0013]
[Example 1]
The raw materials were pre-fired high-purity (99.999% or 99.999% equivalent) Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO at about 800 ° C. for 2 to 3 times, and then in air at 860 ° C. for 50 hours. The raw material rod was produced by carrying out the main firing. The raw material rod thus produced was once melted and solidified at a high speed of 20 mm / h for the lower spindle and 16 mm / h for the upper spindle (so-called zone pass) to increase the density. A part of this high-density raw material rod was used instead of the seed crystal.
[0014]
Crystal growth was performed at a feed rate of 0.05 mm / h for the lower spindle and 0.04 mm / h for the upper spindle. The rotation speeds of the upper and lower spindles were 10.5 rpm and 10.0 rpm, respectively. Although the solvent was not used, it is thought that it formed spontaneously with the crystal growth. As described in the section on how to solve the problem, since two 300 W halogen lamps were used for heating (double elliptical infrared central heating furnace), the temperature gradient of the solid-liquid interface was about 370 ° C./cm. It was about twice as large.
[0015]
As shown in FIG. 1, a 15-fold micrograph shows that the size of the produced crystal is about 4 × 2 × 0.1 mm, which is about the same size as Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{8+ δ} . FIG. 2 shows the temperature dependence of the magnetization of an as-grown single crystal (about 0.1 mg). The magnetic field used is 30 gauss. This characteristic suggests that a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10+ δ} single crystal having a Tc of about 105 K is almost composed of a single phase.
[0016]
FIG. 3 shows an X-ray diffraction pattern. Since (002n) reflection is selectively observed, it can be seen that it is a single-phase single crystal. From the value of 2θ, the c-axis length was found to be 37.08 mm, and it was confirmed to be a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10+ δ} single crystal because it coincided with the literature value.
[0017]
4 and 5 show the in-plane resistivity and the inter-surface resistivity, respectively, of the samples heat-treated in various atmospheres.
[0018]
In Figure 4, the sample a is what is heat treated 225 h _{O 2 400 ℃ (a; O} 2 400 ℃ 225 hours, and hereinafter), and so on _b; O 2 500 ℃ 50 hours, _c; O 2 600 ° C 12 hours, d; O ₂ -10% 600 ° C 20 hours, e; O ₂ -1% 600 ° C 15 hours, f; O ₂ -0.1% 600 ° C 20 hours, g; O ₂ -0.01 % 600 ° C. Indicates the in-plane resistivity of the sample heat-treated at 15 ° C. (samples a to g).
[0019]
In FIG. 5, the inter-surface resistivity of samples h to O that have been heat-treated under the following conditions is shown.
h; O ₂ 400 ° C. 250 hours, i; O ₂ 500 ° C. 75 hours, j; O ₂ 600 ° C. 12 hours, k; O ₂ −10% 600 ° C. 40 hours, l; O ₂ −1% 600 ° C. 20 hours , M; O ₂ −0.1% 600 ° C. for 20 hours, n; O ₂ −0.01% 600 ° C. for 20 hours, o; O ₂ 5 × 10 ⁻³ torr.
[0020]
Interestingly, on the overdoped side, Tc does not drop from the highest value of 109 K, although the carriers are definitely doped. This is presumably because carrier doping proceeds only on the outer _two CuO ₂ surfaces of the three CuO ₂ surfaces, and the inner CuO ₂ surface is maintained in an almost optimally doped state. This shows the possibility that anisotropy can be reduced while maintaining a high Tc.
[0021]
【The invention's effect】
As described above, if the oxide single crystal growth method of the present invention is used, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} single crystal having a high Tc can be grown, so that the possibility of superconductivity application is expanded. There are advantages. In particular, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} single crystal is considered to be able to reduce anisotropy while maintaining a high Tc, and is expected to be applied to a high Jc practical wire. Needless to say, the single crystal growth method of the present invention is applicable not only to superconducting materials but also to general substances.
[Brief description of the drawings]
1 is a 15 × photomicrograph of an oxide superconductor single crystal produced in Example 1. FIG.
2 is a graph showing a change in temperature of magnetization of an oxide superconductor single crystal manufactured by the method of Example 1. FIG.
3 is a diagram showing an X-ray diffraction pattern of an oxide superconductor single crystal manufactured by the method of Example 1. FIG.
4 is a graph showing the temperature change of in-plane resistivity when an oxide superconductor single crystal manufactured by the method of Example 1 is heat-treated in various atmospheres. FIG.
5 is a graph showing a change in interfacial resistivity with temperature when an oxide superconductor single crystal manufactured by the method of Example 1 is heat-treated in various atmospheres. FIG.

Claims (5)

A method for producing an oxide single crystal, characterized by using a solvent transfer floating zone method, a growth rate of 0.05 mm / h or less, and a temperature gradient at a solid-liquid interface of 300 ° C./cm or more. 3 CuO units ₂ A method for producing an oxide single crystal having a surface, characterized by using a solvent transfer floating zone method, a growth rate of 0.1 mm / h or less, and a temperature gradient of a solid-liquid interface of 300 ° C./cm or more. A method for producing an oxide single crystal. Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} A method for producing a single-phase oxide crystal, characterized by using a solvent transfer floating zone method, a growth rate of 0.1 mm / h or less, and a solid-liquid interface temperature gradient of 300 ° C./cm or more. A method for producing an oxide single crystal. The method for producing an oxide single crystal according to claim 2 or 3 , wherein the growth rate is 0.05 mm / h or less. The said temperature gradient is 370 degrees C / cm or more, The manufacturing method of the oxide single crystal in any one of the Claims 1 thru | or 4 characterized by the above-mentioned.

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