Manufacturing method and manufacturing apparatus for ruthenium oxide single crystal

Abstract

To provide a method for manufacturing a ruthenium oxide single crystal, capable of obtaining a ruthenium oxide single crystal having high quality and larger than a conventional one.SOLUTION: A method for manufacturing a ruthenium oxide single crystal by a molten zone method comprises using lamps 13 and 14 capable of heating a molten zone up to a temperature of 2000°C or more and setting the length of the molten zone in a single crystal growth process to 5 mm or less to grow a ruthenium oxide single crystal. When the lamps include a plurality of filaments 23, the plurality of filaments 23 preferably have a single layer type constitution juxtaposed in the horizontal direction; the thickness of the single layer of the single layer type constitution is preferably 1-3 mm; and the ruthenium oxide is Sr2RuO4, Ca3Ru2O7, CaRuO3, SrRuO3 or Sr3Ru2O7.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for producing a ruthenium oxide single crystal. [Background technology]

[0002] Ruthenium oxide Sr2RuO4 has been the subject of much research since it was discovered to exhibit superconductivity in 1994. However, the superconducting state has yet to be fully elucidated, and research into this issue is still being actively pursued as an important issue in the field of superconductivity.

[0003] The molten zone method (floating zone (FZ) method) is known as a method for growing single crystals of oxides and alloys. In this method, a part of a polycrystalline raw material rod is heated to create a molten zone between the single crystal rod that serves as the seed crystal and the polycrystalline raw material rod, and the molten zone is cooled while being held in place by surface tension to obtain a single crystal. This method has the advantage that no crucible is used, so the inclusion of impurities from the crucible is avoided, and high-purity crystals can be obtained. Titanium oxide (density: 4.25 g / cm 3 ) and silicon (density: 2.33g / cm 3 ) is a representative example of single crystal growth using the molten zone method, and is also used as a test melt when introducing floating zone single crystal growth equipment.

[0004] As a single crystal manufacturing (growing) device used in the melting zone method, a concentrated heating type is known (see, for example, Patent Document 1). This single crystal manufacturing device is equipped with a heating furnace having an ellipsoidal mirror, and an infrared lamp with a filament is installed at one focus of the ellipsoidal mirror, and the material is melted by the light emitted from the infrared lamp being reflected by the inner surface of the ellipsoidal mirror and concentrated at the other focus. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-89263 A Summary of the Invention [Problem to be solved by the invention]

[0006] Although Sr2RuO4 has the same layered perovskite structure as copper oxide superconductors, its superconductivity is more strongly suppressed by impurities than that of copper oxide superconductors. Therefore, high-quality single crystals are required for research on Sr2RuO4, but until now, only small samples have been guaranteed to have high-quality single crystals, making it difficult to conduct comprehensive research.

[0007] As a result of extensive research, the inventors of the present invention discovered a method for obtaining high-quality Sr2RuO4 single crystals that are larger than conventional ones in the molten zone method using a concentrated heating system, and arrived at the present invention. In addition, Patent Document 1 describes a superconducting material called Bi2Sr2Ca2CuO, which has a melting point of about 1400°C. 8+δ It is described that high-quality single crystals can be obtained (see paragraph 0013).

[0008] The present invention has been made in view of the above circumstances, and has an object to provide a method and an apparatus for producing a ruthenium oxide single crystal, which can obtain a high-quality ruthenium oxide single crystal that is larger than conventional crystals. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides the following means.

[0010] (1) A method for producing a ruthenium oxide single crystal according to a first aspect of the present invention is a method for producing a ruthenium oxide single crystal by a molten zone method, in which a lamp capable of heating a molten zone to a temperature of 2000°C or higher is used to grow the ruthenium oxide single crystal, with the length of the molten zone during the single crystal growth step being set to 5 mm or less.

[0011] (2) In the method for producing a ruthenium oxide single crystal according to the above aspect, when the lamp includes a plurality of filaments, the plurality of filaments may have a single-layer configuration in which the filaments are arranged in parallel in the horizontal direction.

[0012] (3) In the method for producing a ruthenium oxide single crystal according to the above aspect, the thickness of the single layer of the single-layer structure may be 1 mm or more and 3 mm or less.

[0013] (4) In the method for producing a ruthenium oxide single crystal according to the above aspect, the ruthenium oxide may be Sr2RuO4, Ca3Ru2O7, CaRuO3, SrRuO3, or Sr3Ru2O7.

[0014] (5) A ruthenium oxide single crystal manufacturing apparatus according to a second aspect of the present invention comprises an ellipsoidal mirror, a lamp disposed at one focus of the ellipsoidal mirror, a feed rod support drive shaft that supports and drives a feed rod, and a seed crystal rod support drive shaft that supports and drives a seed crystal rod, and the lamp is capable of heating a molten zone to a temperature of 2000°C or more. Effect of the Invention

[0015] According to the method for producing a ruthenium oxide single crystal of the present invention, it is possible to provide a method for producing a ruthenium oxide single crystal that is high quality and larger than conventional ruthenium oxide single crystals. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a vertical sectional view of an example of a ruthenium oxide single crystal manufacturing apparatus according to an embodiment of the present invention. [Diagram 2] 2 is a horizontal cross-sectional view taken along line AA of the ruthenium oxide single crystal manufacturing apparatus 10 of FIG. 1. [Diagram 3] 2 is an enlarged plan view of a lamp in the ruthenium oxide single crystal manufacturing apparatus of FIG. 1. [Figure 4] 2 is a schematic plan view of a coiled filament in the center of the ruthenium oxide single crystal manufacturing apparatus of FIG. 1 and an enlarged front view of a heated portion. FIG. [Diagram 5] This is a photograph of the vicinity of the molten zone (FL) during crystal growth. [Figure 6] 1(a) is a photograph of the halogen lamp used in producing the single crystal sample of Example 1, and (b) is a photograph of the halogen lamp used in producing the single crystal sample of the comparative example. [Figure 7] 1A is a photograph of the vicinity of the molten zone during growth of the single crystal sample of Example 1, and FIG. 1B is a photograph of the vicinity of the molten zone during growth of the single crystal sample of the comparative example. [Figure 8] 1(a) is a photograph of the single crystal sample obtained in Example 1, and (b) is a photograph of the single crystal sample obtained in the comparative example. [Figure 9] 1 is an X-ray Laue photograph of the single crystal sample obtained in Example 1. [Figure 10] 2 is a graph showing the results of specific heat measurement of the single crystal sample obtained in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts may be denoted by the same reference numerals in the drawings. In addition, the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the features easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. In addition, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. The present invention can be implemented by appropriately changing the materials, dimensions, etc. within the scope of the effects of the present invention. The configuration shown in one embodiment can also be applied to other embodiments.

[0018] [Ruthenium oxide single crystal manufacturing equipment] Fig. 1 is a vertical cross-sectional view of an example of an apparatus for producing ruthenium oxide single crystal according to an embodiment of the present invention, and Fig. 2 is a horizontal cross-sectional view taken along line AA of the apparatus 10 for producing ruthenium oxide single crystal in Fig. 1.

[0019] The ruthenium oxide single crystal manufacturing apparatus 10 has two symmetrical spheroid mirrors 11 and 12. Each of the spheroid mirrors 11 and 12 has one focus F1, F2 and the other focus F0, and is connected to face each other so that the other focus F0 (see FIG. 2) coincides to form a heating furnace. The inner surfaces of the spheroid mirrors 11 and 12, i.e., the reflective surfaces, are gold-plated to reflect infrared rays with a high reflectance.

[0020] Infrared lamps (lamps) 13, 14, such as halogen lamps having a coiled filament 23 (described later), are fixedly disposed near one of the focal points F1, F2 of each of the spheroidal mirrors 11, 12. A heated portion 15 is located at the other coincident focal point F0 of each of the spheroidal mirrors 11, 12, and a quartz tube 16 is disposed vertically so as to include this heated portion 15.

[0021] This quartz tube 16 replaces the internal space m1 of the quartz tube 16 with an atmosphere suitable for single crystal growth and makes it easier to maintain the atmospheric state by separating the internal space m1 of the quartz tube 16 from the internal spaces m2 of the other spheroid mirrors 11, 12. On the other hand, it is useful for cooling the infrared lamps 13, 14 in the internal spaces m2 of the spheroid mirrors 11, 12 without affecting the heated parts 15 in the internal space m1 of the quartz tube 16.

[0022] In the heated section 15 located at the coincident focal point F0 of the spheroid mirrors 11, 12, a feed rod 18 fixed to the lower end of a feed rod support drive shaft 17 extending vertically from above is butted against a seed crystal rod 20 fixed to the upper end of a seed crystal rod drive shaft 19 extending vertically from below. The feed rod support drive shaft 17 and the seed crystal rod drive shaft 19 are held airtight by holding members 21, 22 as shown in the figure, and are held so as to be rotatable by a drive motor such as a servo motor (not shown) and to be able to move up and down synchronously or at a relative speed. The raw material rod 18 may have a diameter D2 (see FIG. 4) of, for example, about 4 to 8 mm. The seed crystal rod 20 may have a diameter D1 (see FIG. 4) of about 3 to 8 mm.

[0023] In the ruthenium oxide single crystal manufacturing apparatus 10, the infrared lamps 13, 14 are capable of heating the molten zone to a temperature of 2000° C. or higher, and the length of the molten zone during the growth process of the ruthenium oxide single crystal can be set to 5 mm or less.

[0024] 3, the infrared lamps 13 and 14 each have a plurality of (four in the illustrated example) coil filaments 23a, 23b, 23c, and 23d arranged side by side in a plane and disposed horizontally (left and right) near one of the focal points F1 and F2 of the ruthenium oxide single crystal manufacturing apparatus 10. The plurality of coil filaments 23a to 23d are, for example, connected in series with the coil filaments 23a and 23b in the center and the coil filaments 23c and 23d on both sides (left and right) and are sealed with quartz 24, with terminals 25 and 26 at both ends of the series connection of the coil filaments 23a and 23b in the center and terminals 27 and 28 at both ends of the series connection of the coil filaments 23c and 23d on both sides (left and right).

[0025] Each of the infrared lamps 13 and 14 shown in FIG. 3 includes four coiled filaments, but the number of coiled filaments may be one or any number other than four. Furthermore, when the infrared lamps 13, 14 have multiple coil-shaped filaments, a single-layer (single-stage) configuration in which the filaments are arranged side by side in a plane is shown as an example in FIG. 3, but a double-layer (two-stage) configuration in which the filaments are arranged side by side in two stages, or a multiple-layer (multiple-stage) configuration in which the filaments are arranged side by side in three or more stages, may also be used. In the case of a two-layered configuration in which two tiers are arranged side by side, adjacent coil filaments may be arranged above and below each other in a staggered pattern. In the case of a multi-layer type in which three or more layers are arranged side by side, adjacent coil filaments may be arranged above and below each other in a staggered manner.

[0026] Whether the infrared lamps 13 and 14 have a single-layer, double-layer, or multiple-layer configuration, the thickness of the configuration is preferably 1 mm or more and 3 mm or less, which means that in the case of a single-layer configuration, the diameter of each coiled filament is 1 mm or more and 3 mm or less. By setting the thickness within this range, it is possible to suppress the spread of the temperature distribution at the focal point, and it becomes easier to keep the length of the molten zone during single crystal growth to 5 mm or less.

[0027] The material of the coiled filament may be, for example, tungsten or a tungsten alloy containing tungsten as a main component.

[0028] As the infrared lamp, a known infrared lamp such as a halogen lamp or a xenon lamp can be used.

[0029] The terminals 25, 26 of the series connection of the coiled filaments 23a and 23b in the center are connected to a power source (V1) 29, and the terminals 27, 28 of the series connection of the coiled filaments 23c and 23d on both sides (left and right) are selectively connected to a power source (V2) 30.

[0030] Therefore, when the power source (V1) 29 energizes only the coil-shaped filaments 23a, 23b in the center, a heated area having a small cross-sectional area is formed in the heated portion 15. On the other hand, when the coil-shaped filaments 23a, 23b in the center, which are connected in series, are kept in an energized state, and electricity is passed through the coil-shaped filaments 23c, 23d on both sides (left and right) from a power source (V2) 30, the radiant energy caused by the energization of the coil-shaped filaments 23a, 23b in the center is added to the radiant energy caused by the energization of the coil-shaped filaments 23c, 23d on both sides (left and right), thereby making it possible to increase the cross-sectional area of ​​the heating region in the heated portion 15.

[0031] The ruthenium oxide single crystal manufacturing apparatus shown in FIG. 1 is a bi-ellipsoidal type having two ellipsoidal mirrors, but it may also be a single-ellipsoidal type having one ellipsoidal mirror.

[0032] [Method for producing ruthenium oxide single crystal] The method for producing a ruthenium oxide single crystal of the present invention is a method for producing a ruthenium oxide single crystal by a molten zone method, in which a lamp capable of heating the molten zone to a temperature of 2000°C or higher is used, and the length of the molten zone during the single crystal growth step is set to 5 mm or less to grow the ruthenium oxide single crystal.

[0033] The method for producing a ruthenium oxide single crystal of the present invention using the ruthenium oxide single crystal production apparatus 10 will be described. First, the inside of the quartz tube 16 is replaced with an appropriate atmosphere such as an inert gas (e.g., argon), and then only the coil-shaped filaments 23a and 23b in the center of the infrared lamps 13 and 14 arranged near one of the focal points F1 and F2 of the spheroid mirrors 11 and 12 are energized by a power source (V1) 29. The infrared rays irradiated from the infrared lamps 13 and 14 are reflected by the spheroid mirrors 11 and 12 and focused on the heated part 15 located at the other common focal point F0 for infrared heating. The radiant energy from this infrared heating heats and melts the lower end of the raw material rod 18 and the upper end of the seed crystal rod 20 of the heated part 15, and brings them into smooth contact with each other, forming a molten zone (hereinafter sometimes referred to as FZ) 31 in the heated part 15 between the raw material rod 18 and the seed crystal rod 20, as shown in FIG. 4. The molten zone can be heated to a temperature of 2000°C or more.

[0034] In the method for producing a ruthenium oxide single crystal of the present invention, the length of FZ31 is L, and the ruthenium oxide single crystal is grown by heating so that the length L of FZ31 is 5 mm or less. Since the molten zone is held by the surface tension between the feed rod and the seed crystal rod, it is usually difficult to hold it in a stable state, but by setting the length L of FZ31 to 5 mm or less, the molten zone can be held in a more stable state. As a result, it has become possible to produce a ruthenium oxide single crystal that is longer than before.

[0035] In order to adjust the length L of FZ31 to 5 mm or less, whether the filament structure is a single-layer structure, a two-layer structure, or a multi-layer structure, the thickness of the structure is preferably 3 mm or less, more preferably 2 mm or less. In principle, the length L of FZ31 can be set to about the thickness of the filament structure. Even if the thickness of the filament configuration exceeds 3 mm, it is possible to adjust the length L of FZ31 to 5 mm or less; however, setting it to 3 mm or less makes it easier to adjust the length L of FZ31 to 5 mm or less.

[0036] In FIG. 4, the coil-shaped filaments 23a to 23d are actually arranged in a direction perpendicular to the axial direction (plane of the paper) of the raw material rod 18 and the seed crystal rod 20, but for convenience of explanation, they are drawn parallel to the plane of the paper.

[0037] Then, the feed rod support drive shaft 17, to which the feed rod 18 is fixed at its lower end, and the seed crystal rod drive shaft 19, to which the seed crystal rod 20 is fixed at its upper end, are rotated together (e.g., at 20 to 30 rpm) and moved slowly downward in sync, so that the FZ 31 formed in the heated portion 15 between the feed rod 18 and the seed crystal rod 20 gradually moves toward the feed rod 18 side, thereby growing a single crystal. In Fig. 4, 18a indicates the solid-liquid interface on the feed rod 18 side, and 20a indicates the solid-liquid interface on the seed crystal rod 20 side. The length L of the FZ 31 is the length from the solid-liquid interface 18a on the feed rod 18 side to the solid-liquid interface 20a on the seed crystal rod 20 side. The solid-liquid interface 18a and the solid-liquid interface 20a can be identified as the locations where the molten liquid can be visually confirmed. Figure 5 shows a photograph of the vicinity of the molten zone (FL) 31 during single crystal growth.

[0038] The method for producing a ruthenium oxide single crystal of the present invention can also be applied to ruthenium oxide single crystals other than Sr2RuO4, Ca3Ru2O7, CaRuO3, SrRuO3, and Sr3Ru2O7. For example, ruthenium oxide single crystals other than those having the general chemical formula Sr (n+1) Ru (n) O (3n+1) (n is an integer of 1 or more), Ca (n+1) Ru (n)O (3n+1) (n is an integer of 1 or more). In addition, the present invention is applicable to known ruthenium oxide single crystals for which single crystals have been reported to be produced by the molten zone method. Here, the melting points of Sr2RuO4, Ca3Ru2O7, CaRuO3, SrRuO3, and Sr3Ru2O7 are approximately 2100°C.

[0039] It tends to be difficult to stably maintain the molten zone in low-viscosity or high-density materials. In particular, since the molten material of ruthenium oxide has a low viscosity, the molten zone often falls during growth, making growth difficult. The method for producing a ruthenium oxide single crystal of the present invention makes it possible to stably maintain the molten zone, and thus makes it possible to grow a large ruthenium oxide single crystal. The density of Sr2RuO4 is 5.92g / cm 3 and the density of Ca3Ru2O7 is 4.97g / cm 3 It is. EXAMPLES

[0040] Example 1 (Growth of Sr2RuO4 single crystals) In the bi-elliptical ruthenium oxide single crystal manufacturing apparatus shown in Figure 1, a halogen lamp was used as the infrared lamp, in which four coil-shaped filaments (diameter of each filament: 2 mm, length: 25 mm) were connected horizontally to form a single layer (thickness: 2 mm, width in plan view: 20 mm: 20 mm) as shown in Figure 6(a). The length of the molten zone during the ruthenium oxide single crystal growth process was set to 5 mm or less at a power of 2 W, as shown in Figure 7(a), to grow a Sr2RuO4 single crystal. The diameter of the seed crystal rod was 6 mm, and the diameter of the feed rod was 6 mm. The cross section of the obtained Sr2RuO4 single crystal is often roughly elliptical or circular. If it is elliptical, the long axis is 5 mm or less, averaging about 4 mm, and the short axis is 4 mm or less, averaging about 3 mm.

[0041] The obtained Sr2RuO4 single crystal is shown in Figure 8(a). The length of the single crystal was 130 mm. As will be described later, when the length of the molten zone during the growth process of the ruthenium oxide single crystal was set to about 8 mm (see Figure 7(b)), the length of the single crystal was 70 mm (see Figure 8(b)), which is more than 1.8 times larger. Note that the seed crystal rod is on the right side of the single crystal in the photograph of Figure 8(a).

[0042] (Evaluation of Sr2RuO4 single crystal) (1) Analysis by X-ray Laue diffraction method The X-ray Laue photograph obtained for the grown crystal is shown in Figure 9. From the X-ray Laue photograph, it was confirmed that a high-quality Sr2RuO4 single crystal had been grown. This Laue photograph was taken by irradiating the crystal with X-rays in a direction perpendicular to the crystal growth method. This photograph shows that the irradiation direction is the (001) plane of the crystal, and also provides information on the crystal growth direction. The Laue photographs of the crystals taken in each growth process show that the crystals are often grown in a direction that is about 15 degrees off the (100) direction.

[0043] (2) Specific heat measurement Figure 10 shows the results of specific heat measurements performed on the grown crystals. The graph confirms a clear superconducting transition at 1.5K. Sr2RuO4 is highly impurity dependent, and the superconducting transition cannot be confirmed when the impurity concentration is high. This result indicates that the impurity concentration is 0.15% or less.

[0044] Comparative Example In the bi-elliptical ruthenium oxide single crystal manufacturing apparatus shown in FIG. 1, conventional halogen lamps were used as infrared lamps, in which eight coil-shaped filaments as shown in FIG. 6(b) were arranged in a two-layer configuration in which adjacent coil-shaped filaments were arranged above and below each other in a staggered pattern (diameter of each filament: 2 mm, length: 20 mm, width in plan view: 20 mm). At a power of 2 W, the same as in the example, the length of the molten zone during the ruthenium oxide single crystal growth process was set to about 8 mm, as shown in FIG. 7(b), and a Sr2RuO4 single crystal was grown.

[0045] Figure 8(b) shows the Sr2RuO4 single crystal obtained with the conventional lamp. The length of the Sr2RuO4 single crystal was 70 mm.

[0046] For the crystal of the comparative example, analysis by the X-ray Laue diffraction method and specific heat measurement were performed in the same manner as in Example 1. As in Example 1, an X-ray Laue photograph showing a high-quality single crystal was obtained, and specific heat measurement results showed a clear superconducting transition at 1.5 K. Considering these results, it can be said that in Example 1, a larger Sr2RuO4 single crystal was obtained compared to the comparative example, and the quality of the Sr2RuO4 single crystal was as high as that of the comparative example in terms of both crystal structure and impurity concentration.

[0047] Example 2 When single crystals of Ca3Ru2O7 were grown in the same manner as in Example 1, a high-quality, large-sized Ca3Ru2O7 single crystal was obtained, as in Example 1. [Explanation of symbols]

[0048] 10 Ruthenium oxide single crystal manufacturing equipment 11,12 Spheroidal mirror 13,14 Infrared lamp 15 Heated part 16 Quartz tube 17 Raw material rod support drive shaft 18 Raw material rod 18a Solid-liquid interface on the feed rod side 19 Seed crystal rod support drive shaft 20 seed crystal rods 20a Solid-liquid interface on the seed crystal rod side 23a-23d Coiled filament 24 Quartz 25~28 Terminal section 29,30 Power supply 31 Fusion Zone (FZ)

Claims

1. A method for producing ruthenium oxide single crystals by a molten zone process, comprising the steps of: Using lamps to heat the melt zone, The length of the molten zone during the single crystal growth step is set to 5 mm or less, and the ruthenium oxide single crystal is grown. The lamp has a plurality of filaments, the filaments being arranged in a single layer configuration in a horizontal direction; The method for producing a ruthenium oxide single crystal, wherein the thickness of the single layer of the single-layer structure is 1 mm or more and 3 mm or less.

2. The ruthenium oxide single crystal is Sr ２ RuO ４ , Ca ３ Ru ２ O ７ , CaRuO ３ , SrRuO ３ , or Sr ３ Ru ２ O ７ The method for producing a ruthenium oxide single crystal according to claim 1,

3. A ruthenium oxide single crystal manufacturing apparatus that can be used in the method for manufacturing a ruthenium oxide single crystal according to claim 1, A rotating spheroid mirror; a lamp disposed at one focus of the spheroidal mirror; a raw material rod support drive shaft that supports and drives the raw material rod; a seed crystal rod support drive shaft that supports and drives the seed crystal rod, The lamp has a plurality of filaments, the filaments being arranged in a single layer configuration in a horizontal direction; The thickness of the single layer of the single-layer type configuration is 1 mm or more and 3 mm or less, The lamp is capable of heating the molten zone to a temperature of 2000° C. or higher.

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