Method for producing Mg2Sn-based single crystals and Mg2Sn-based single crystal ingots

Abstract

To provide a method for producing Mg2Sn-based single crystals with a larger diameter, more stably than conventional methods. [Solution] The method for producing Mg2Sn-based single crystals is a method for producing Mg2Sn-based single crystals by unidirectional solidification crystal growth, using a crucible comprising: a small diameter section located at the bottom and having a bottomed cylindrical shape; a single crystal growth section located at the top and having a cylindrical shape with a larger inner diameter than the small diameter section; and a diameter-increasing section growth section connecting the small diameter section and the single crystal growth section, having a cylindrical shape with an increasing inner diameter from the small diameter section toward the single crystal growth section, and having an angle between the inner wall and the central axis of the crucible of 30° or less. A single crystal is grown by solidifying the molten raw material in the crucible from the small diameter section toward the single crystal growth section, and the growth rate in the diameter-increasing section is 0.8 mm / hour or less.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a Mg2Sn-based single crystal and a Mg2Sn-based single crystal ingot.

Background Art

[0002] With the recent power saving of IoT devices, the development of replacing the power source of IoT devices with a self-powered power source is in progress. In addition, the demand for technologies that reuse factory waste heat, etc. as power for suppressing greenhouse gas emissions is increasing. There is growing expectation for thermoelectric power generation elements using thermoelectric elements to meet these demands.

[0003] Mg2Sn is an alloy of magnesium and tin. Mg2Sn is a semiconductor with a band gap of 0.23 eV and is expected to be applied as a thermoelectric material in the medium temperature range from 350K to 500K. In addition, unlike Bi2Te3 and PbTe, which are commonly used as thermoelectric materials, it is composed mainly of elements with low toxicity to the human body and environment, so it has high safety.

[0004] Single crystals of this substance are grown by the VGF method and the vertical Bridgman method. In Patent Document 1, it is described that a MgSn-based single crystal can be obtained by storing raw materials in a tantalum tube, heating them to the melting temperature until the raw materials melt, and then cooling them at a predetermined cooling rate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Mg2Sn is a material that has a proven track record of relatively high thermoelectric performance in small single crystal form. Conventionally, the sample diameter of Mg2Sn single crystals has been small, around φ10-12 mm. When growing single crystals, the high vapor pressure of Mg makes it difficult to grow large crystals, as the composition of the melt changes constantly. For this reason, the size of conventionally grown single crystals is small, intended for property evaluation, and the yield relative to the manufacturing cost is quite poor, making it unsuitable for mass production. In other words, conventionally, due to the above problems, it has been difficult to obtain Mg2Sn single crystals with a large diameter.

[0007] Therefore, one aspect of the present invention, made in view of the above problems, provides a method for growing Mg2Sn-based single crystals that can produce single crystals with a larger diameter more stably than conventional methods. Furthermore, one aspect of the present invention makes it possible to increase the diameter of the single crystal in Mg2Sn-based single crystals. [Means for solving the problem]

[0008] According to one aspect of the present invention, a method for producing an Mg2Sn-based single crystal by unidirectional solidification crystal growth is provided, comprising a crucible having a small diameter section located at the bottom and having a bottomed cylindrical shape, a single crystal growth section located at the top and having a cylindrical shape with a larger inner diameter than the small diameter section, and a diameter-increasing section connecting the small diameter section and the single crystal growth section, having a cylindrical shape with an increasing inner diameter from the small diameter section toward the single crystal growth section, and having an angle between the inner wall and the central axis of the crucible of 30° or less, wherein a single crystal is grown by solidifying the molten raw material in the crucible from the small diameter section toward the single crystal growth section, and the growth rate in the diameter-increasing section is 0.8 mm / hour or less.

[0009] According to one aspect of the present invention, an ingot of a Mg2Sn-based single crystal is provided, comprising a small diameter portion, a diameter-increasing portion, and a straight body portion, wherein the angle between the diameter-increasing portion and the growth axis of the single crystal is 30° or less, and the diameter of the straight body portion is 20 mm or more. [Effects of the Invention]

[0010] According to an aspect of the present invention, a method for growing Mg2Sn alloys can be provided that allows for the stable production of Mg2Sn single crystals with larger diameters compared to conventional methods. Furthermore, one aspect of the present invention allows for the increase in the diameter of the single crystal in Mg2Sn single crystals. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an example of a crucible according to this embodiment. [Figure 2] This flowchart shows an example of a single crystal manufacturing method according to this embodiment. [Figure 3] An example of a single crystal ingot according to this embodiment is shown in Figure 3. [Modes for carrying out the invention]

[0012] Specific embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments and can be modified as appropriate without altering the gist of the invention. In each drawing, some or all of the invention is depicted schematically, and the scale is changed as appropriate. Furthermore, in the following description, directions in the figures will be explained using the XYZ coordinate system. In this XYZ coordinate system, the plane parallel to the horizontal plane is defined as the XY plane. Any direction parallel to this XY plane is denoted as the X direction, and the direction perpendicular to the X direction is denoted as the Y direction. The direction perpendicular to the XY plane (up and down) is denoted as the Z direction. In the X, Y, and Z directions, the direction of the arrow in the figure is the + direction, and the direction opposite to the direction of the arrow is the - direction. Furthermore, in the following description, "A~B" means "A or greater and B or less" or "B or greater and A or less" as appropriate.

[0013] A method for manufacturing Mg2Sn-based single crystals according to one aspect of this embodiment (hereinafter sometimes abbreviated as "single crystal manufacturing method") will be described below. The method for manufacturing Mg2Sn-based single crystals according to this embodiment is a method that uses unidirectional solidification growth (unidirectional solidification method). In the unidirectional solidification method, the VB method (vertical Bridgman method), VGF method (vertical temperature gradient method), and micro-down method can be used. In this embodiment, an example of growing a single crystal using the VB method will be described.

[0014] Conventionally, as mentioned above, it has been difficult to obtain Mg2Sn single crystals with large diameters. As described in Patent Document 1, Mg2Sn can be obtained by melting the raw material directly in a Tammann tube or the like without using a seed crystal, and then gradually cooling it from below. Small diameter Mg2Sn single crystals of around φ10 mm could be manufactured. However, when the single crystal diameter becomes larger, crystal growth becomes difficult for the reasons mentioned above.

[0015] Therefore, the inventors of the present invention conducted research and discovered that problems arise during the growth of the diameter-increasing portion of a Mg2Sn single crystal. As a result of further research, they found that the above problem can be solved by changing the shape of the diameter-increasing portion and the growth conditions of the diameter-increasing portion. One embodiment was completed based on the above findings. It will be described below.

[0016] In the single crystal manufacturing method of this embodiment, a predetermined crucible is used, and a single crystal is grown under predetermined conditions, while increasing the crystal diameter until it reaches a predetermined diameter.

[0017] First, the crucible used in the single crystal manufacturing method of this embodiment will be described. Figure 1 shows an example of the crucible according to this embodiment. Figure 1 shows a cross-sectional view of the crucible in a plane (XZ plane) parallel to the vertical direction (Z direction).

[0018] The crucible 1 shown in Figure 1 comprises a narrow-diameter section 2, a diameter-increasing section 3, and a single-crystal growth section 4. The overall shape of the crucible 1 is cylindrical. When in use, the crucible 1 is positioned as shown in Figure 1, with the central axis AX1 of the crucible parallel to the vertical direction (Z direction). The central axis of the narrow-diameter section 2, the central axis of the single-crystal growth section 4, and the central axis of the diameter-increasing section 3 are all coaxial AX1. The upper end of the crucible 1 is open, and the lower end is closed. The crucible 1 is capable of storing and holding raw materials and molten raw materials that have been heated.

[0019] The narrow-diameter section 2 is located at the bottom of the crucible 1 in Figure 1. The narrow-diameter section 2 has a bottomed cylindrical shape with a base at its lower end. The narrow-diameter section 2 contains the raw material and the raw material melt. The narrow-diameter section 2 also contains the seed crystal if seed crystal growth is carried out using a seed crystal as needed. The narrow-diameter section 2 is intended to obtain a bulk single crystal by inducing single crystallization through the movement of the melt interface during the solidification of the melt. The cylindrical shape, inner diameter L1, and length H1 of the narrow-diameter section 2 are not particularly limited as long as they are thin and long enough to induce the movement of the melt interface for single crystallization of the polycrystalline portion. The dimension H1 in the Z direction of the narrow-diameter section 2 is, for example, 10 mm or more, preferably 10 mm to 50 mm, and more preferably 20 mm to 30 mm. The inner diameter L1 of the narrow-diameter section 2 is smaller than the inner diameter L3 of the single crystal growth section 4, which will be described later. The inner diameter L1 (parallel to the X direction) of the narrow-diameter section 2 is not particularly limited, but is, for example, 8 mm or more, preferably 10 mm or more, and more preferably 8 mm or more and 12 mm or less. When the inner diameter L1 of the narrow-diameter section 2 is within the above range, the raw material melt is more reliably filled into the narrow-diameter section 2. The cylindrical shape of the narrow-diameter section 2 is not particularly limited, but is, for example, cylindrical, or cylindrical with a regular polygonal cross-section (e.g., square cylinder). In the example shown in Figure 1, the narrow-diameter section 2 is cylindrical. The wall thickness of the cylinder of the narrow-diameter section 2 is not particularly limited, but is, for example, substantially uniform.

[0020] The diameter increasing part growing part 3 is a part that grows the so-called diameter increasing part in the single crystal to be grown. The diameter increasing part growing part 3 is arranged above the small diameter part 2 and below the single crystal growing part 4 in the vertical direction of the crucible 1 in FIG. 1. It is provided between the small diameter part 2 and the single crystal growing part 4. The diameter increasing part growing part 3 connects the small diameter part 2 and the single crystal growing part 4.

[0021] The diameter increasing part growing part 3 has a cylindrical shape in which the inner diameter L2 increases as it goes from the small diameter part 2 toward the single crystal growing part 4 (as it goes in the +Z direction in FIG. 1). The diameter increasing part growing part 3 has a tapered shape. The angle θ formed between the inner wall of the diameter increasing part growing part 3 and the central axis AX1 (parallel to the Z direction) of the crucible 1 (the "θ" shown in FIG. 1, hereinafter this angle may also be referred to as the "diameter increasing part angle") is a specific angle.

[0022] The inventor of the present invention found that crystal growth in the raw material melt can increase the growth rate as the temperature gradient at the growth interface becomes larger. However, in the VB method, unlike the temperature gradient in the vertical direction, the temperature gradient becomes smaller in the horizontal direction. Regarding the diameter increasing part where crystal growth occurs in the horizontal direction, if the growth rate in the horizontal direction is not made smaller than that in the vertical direction, polycrystallization will be induced. Therefore, the inventor conceived that it is necessary to reduce the diameter increasing part angle θ of the diameter increasing part growing part 3 of the crucible.

[0023] This diameter increasing part angle θ is 30° or less, and preferably 27° or less. The diameter increasing part angle θ may be 11° to 27° as shown in the examples. When the diameter increasing part angle θ is within the above range, polycrystallization occurring during single crystal growth can be significantly suppressed compared to outside the above range (refer to the results of Example 1 and Comparative Example 1).

[0024] The cylindrical shape in the shape of the diameter increasing part growing part 3 is not particularly limited as long as it is within the range of the above diameter increasing part angle θ. For example, it may be a conical cylinder, a pyramidal cylinder, or a cylinder having a regular polygonal cross-section (XY cross-section) (e.g., a square cylinder). In the example shown in FIG. 1, the diameter increasing part growing part 3 is a frustum-shaped cylinder. Also, the wall thickness (wall thickness) of the diameter increasing part growing part 3 is not particularly limited, but for example, it is substantially uniform.

[0025] The Z-direction dimension H2 of the diameter-increasing section 3 is determined by the inner diameter L1 of the thin section 2, the inner diameter L3 of the single crystal growth section 4, and the diameter-increasing angle θ of the diameter-increasing section 3. For example, a length from the same as the inner diameter L1 of the thin section 2 to four times the inner diameter L1 of the thin section 2 can be used. In the example shown in Figure 1, the Z-direction dimension H2 of the diameter-increasing section 3 is 40 mm. The inner diameter L2 (parallel to the X direction) of the diameter-increasing section 3 is not particularly limited. At the lower end (-Z side) of the diameter-increasing section 3, the inner diameter L2 is the inner diameter L1 of the thin section 2, and at the upper end (+Z side) of the diameter-increasing section 3, it is the inner diameter L3 of the single crystal growth section 4. The inner diameter L2 of the diameter-increasing section 3 is, for example, 8mm to 12mm at the lower end (-Z side) of the diameter-increasing section 3 and 20mm to 50mm at the upper end (+Z side) of the diameter-increasing section 3. In the example shown in Figure 1, the inner diameter L2 of the diameter-increasing section 3 is 10mm at the lower end (-Z side) of the diameter-increasing section 3 and 25mm at the upper end (+Z side) of the diameter-increasing section 3.

[0026] The single crystal growth section 4 will now be described. The single crystal growth section 4 is located above (on the +Z side) the diameter-increasing section growth section 3 and is connected to the diameter-increasing section growth section 3. The single crystal growth section 4 is the part that grows the so-called straight section of the single crystal. The shape and length of the single crystal growth section 4 are not particularly limited. The cylindrical shape of the single crystal growth section 4 is not particularly limited, but for example, it can be cylindrical, or a cylindrical shape with a regular polygonal cross-section (XY cross-section) (e.g., rectangular cylinder, square cylinder). In the example shown in Figure 1, the diameter-increasing section growth section 3 is cylindrical. The wall thickness of the single crystal growth section 4 is not particularly limited, but for example, it is approximately uniform.

[0027] In this embodiment, the inner diameter L3 of the single crystal growth section 4 can be 20 mm or more, for example, φ25 mm as shown in the embodiment, or 25 mm or more. The height H3 of the single crystal growth section 4 is not particularly limited.

[0028] Let's describe crucible 1. Crucible 1 is, for example, a single-piece molded structure. The material of crucible 1 is not particularly limited, but any crucible material that can withstand temperatures exceeding 1000°C in a reducing atmosphere is acceptable, such as alumina, or other materials such as yttria, aluminum titanate, magnesia, or pyrolysis boron nitride, and has a coefficient of thermal expansion of 10 × 10⁻¹⁰. -6 Materials that do not exceed / K are preferable. Crucible 1 may have a lid that covers the opening at the top end (+Z side) of the crucible, if necessary. The material of the lid of crucible 1 is preferably the same as the material of crucible 1. In addition, the inner wall of the crucible may be surface-treated to suppress the adhesion of crystals to the crucible. Examples of surface treatments include the application of a boron nitride coating agent.

[0029] Next, an example of the single crystal manufacturing method of this embodiment will be described. In the single crystal manufacturing method of this embodiment, the single crystal is grown (manufactured) using the crucible described above. Figure 2 is a flowchart of an example of the single crystal manufacturing method of this embodiment.

[0030] In the single crystal manufacturing method of this embodiment, first, the raw materials are prepared and adjusted as shown in step S1 of Figure 2. The raw materials are adjusted to have the composition of the Mg2Sn-based single crystal to be grown. Powdered, lumpy, or shot-type Mg and Sn can be used as raw materials. The raw materials do not necessarily have to be elemental metals; alloys or mixtures of alloys and elemental metals can be used.

[0031] Furthermore, if the diameter of Mg is small, it becomes flammable and is designated as a hazardous material under the Fire Service Act. For this reason, it is preferable to use Mg with a diameter of 2 mm or more, which does not fall under the category of a hazardous material under the Fire Service Act. However, in this case, the smaller the inner diameter L1 of the narrow-diameter section 2 of the crucible 1, the more difficult it is to fill the narrow-diameter section 2 of the crucible 1 with the molten Mg raw material. When the inner diameter L1 of the narrow-diameter section 2 of the crucible 1 is within the range described above, the molten Mg raw material can be easily filled into the narrow-diameter section 2.

[0032] For example, the mixing ratio of Mg and Sn in the raw materials should be such that the molar ratio of Mg to Sn is 2.0:1.0 to 2.2:1.0. Considering that Mg has high vapor pressure properties and evaporates during growth, it is preferable that the molar ratio of Mg to Sn be 2.1:1.0 to 2.2:1.0. The raw materials adjusted to the above mixing ratio are placed into the crucible 1 described above. At this time, additives containing elements such as Sb, Ag, Ga, Bi, Li, and P may be added depending on the intended use of the material. If the added additives replace Mg, the molar ratio of Mg for that portion may be less than the above 2.0. When using a seed crystal, the seed crystal is placed in the narrow diameter section 2 of the crucible 1, and then the raw materials are placed into the crucible 1. For example, a seed crystal with the same orientation as the single crystal to be grown is placed.

[0033] Following step S1 in Figure 2, in step S2, the crucible 1 filled with raw materials is placed into the growth furnace (single crystal growth apparatus). At this time, a lid may be attached to the crucible 1 if necessary.

[0034] In this embodiment, the growth furnace (single crystal growth apparatus) can be any growth furnace (single crystal growth apparatus) capable of performing known unidirectional solidification methods (VB method, VGF method). For example, the growth furnace may be a resistor heating furnace using a carbon heater, or an indirect heating type growth furnace such as high-frequency heating of a carbon outer crucible may be used. The growth furnace (single crystal growth apparatus) is preferably an apparatus capable of controlling the atmosphere and pressure inside the furnace. As such a growth apparatus capable of performing unidirectional solidification methods (VB method, VGF method), for example, the apparatus described in Japanese Patent Application Publication No. 2024-158672, etc., can be used. In addition, an insulating material such as carbon felt may be installed between the crucible and heater (resistor) and the outside thereof.

[0035] The atmosphere used for single crystal growth is, for example, Ar gas. This atmosphere can be created by evacuating the furnace and then replacing the vacuum with Ar gas. A vacuum of 1 Pa or less is desirable. The Ar gas should preferably be of high purity, preferably 5 N or higher. Note that the atmosphere is not limited to Ar; a gas with a different composition may be used as long as it does not react with the raw material at high temperatures. The pressure of the Ar gas in the furnace should preferably be 0.1 MPa or higher, but it may be lower.

[0036] Following step S2 in Figure 2, a single crystal is grown in step S3. The single crystal is grown by solidifying the molten raw material in the crucible 1 from the narrow diameter section 2 towards the single crystal growth section 4. The crucible 1 is heated by applying power to the heater to reach the melting point of the raw material. The heater is heated so that a solid-liquid interface is formed in the narrow diameter section 2 at the bottom of the crucible 1. The arrangement of the crucible 1 and the heater is adjusted, and the heater is heated to a temperature suitable for that arrangement. Next, the stage on which the crucible 1 is placed is lowered to move the temperature gradient upward, that is, to move the lower part of the crucible 1 away from the heater, thereby lowering the temperature of the lower part of the crucible 1. When using the Bridgman method, the crucible 1 can be moved away from the heater at a predetermined rate, allowing the molten material to be slowly cooled. In this example, the explanation mainly focuses on the example where the temperature gradient is moved by lowering the stage, but the method is not limited to this example. For example, methods such as adjusting the output of a two-zone heater, active slow cooling via a stage on which the crucible constituting the crystal growth apparatus is installed, or the temperature gradient method (VGF method) may be used. When using the temperature gradient method, the melt can be slowly cooled by adjusting the heater output without moving crucible 1.

[0037] Next, in step S3a, the diameter-increasing portion of the single crystal is grown. The diameter-increasing portion of the single crystal (sometimes abbreviated as the diameter-increasing portion) is grown in the diameter-increasing portion growth section 3 of the crucible 1. When growing the diameter-increasing portion of the single crystal, the growth rate (sometimes referred to as the diameter-increasing portion growth rate) should be 0.8 mm / hour or less. The diameter-increasing portion growth rate may be 0.7 mm / hour or less, or 0.5 mm / hour or less. A diameter-increasing portion growth rate of 0.7 mm / hour or less is acceptable, but from an economic standpoint, 0.7 mm / hour to 0.5 mm / hour is desirable. In the case of the VB method, the diameter-increasing portion growth rate can be appropriately adjusted by the descent speed of the stage on which the crucible is placed, and in the case of the temperature gradient method, it can be appropriately adjusted by adjusting the heater output. Note that the growth rate at this time should be maintained within the above range. In the VB method, unlike the vertical temperature gradient, the horizontal temperature gradient is small. Therefore, in growing the diameter-increasing portion where crystal growth occurs horizontally, the growth rate in the horizontal direction must be reduced even more than in the vertical direction to prevent polycrystallization. For this reason, the growth rate in the diameter-increasing portion must be set within the above growth range. Also, since the melt composition in the initial stages of growth deviates from the stoichiometric ratio and is Mg-rich, it is preferable to reduce the growth rate (growth rate) to this extent in order to precipitate Mg2Sn.

[0038] Next, after growing the diameter-increasing portion of the single crystal in step S3a, the straight portion of the single crystal is grown in step S3b. The straight portion of the single crystal (sometimes abbreviated as the straight portion) is grown in the single crystal growth section 4 of the crucible 1. In growing the straight portion of the single crystal, the growth rate (sometimes referred to as the straight portion growth rate) may be the same as the growth rate of the diameter-increasing portion, or it may be a faster rate than the growth rate of the diameter-increasing portion, and a faster rate than the growth rate of the diameter-increasing portion is preferable from the viewpoint of productivity. For example, the straight portion growth rate can be 1.0 mm / hour or more and 5.0 mm / hour or less. In growing the straight portion, the influence of crystal growth in the horizontal direction is less compared to the diameter-increasing portion, and the crystal growth is mainly in the vertical direction, so the growth rate can be increased according to the temperature gradient. For this reason, the growth rate of the straight portion can be set within the above growth range.

[0039] After growing the straight section of the single crystal in step 3b, a cooling process is performed in step S4 to complete the growth (manufacturing) of the single crystal. A single crystal ingot conforming to the shape of the inside of crucible 1 is manufactured. Subsequently, the grown single crystal is removed from the crucible. In addition to the above example, the manufacturing conditions for single crystal growth can be determined by conducting preliminary experiments.

[0040] The single crystals (single crystal ingots) obtained by the manufacturing method of this embodiment can have a diameter of φ20 mm or more, or φ25 mm or more. As described in the examples, the obtained single crystals (single crystal ingots) do not show grain boundaries in the diameter-increasing portion, and even in the straight-body portion, there is no crystal disorder due to back-reflection Laue image. They are larger in diameter and of higher quality than conventional single crystals. The manufacturing method of this embodiment allows for the acquisition of single crystals with a larger diameter and more stable results than conventional methods.

[0041] (Single crystal ingot) Next, the single crystal ingot (sometimes abbreviated as "single crystal") according to this embodiment will be described. The single crystal ingot according to this embodiment is an ingot of Mg2Sn-based single crystal. The single crystal according to this embodiment is obtained by the manufacturing method of this embodiment described above. An example of the single crystal ingot according to this embodiment is shown in Figure 3.

[0042] In the description of the Mg2Sn-based single crystal ingot of this embodiment, the matters described in the above-mentioned method for manufacturing the Mg2Sn-based single crystal shall be applied as appropriate. Furthermore, the matters described in the description of the Mg2Sn-based single crystal ingot of this embodiment shall be described in the above-mentioned method for manufacturing the Mg2Sn-based single crystal and applied as appropriate. Also, similar components shall be denoted by the same reference numerals, and their descriptions shall be omitted or simplified as appropriate. The previously described explanations shall be omitted or simplified as appropriate.

[0043] The single crystal ingot C according to this embodiment, shown in Figure 3, comprises a narrow-diameter section 5, a diameter-increasing section 6, and a straight-bodied section 7. The single crystal ingot C according to this embodiment, shown in Figure 3, is manufactured to conform to the shape of the inside of the crucible 1 described above. The narrow-diameter section 5 of the single crystal ingot C is manufactured in the narrow-diameter section 2 of the crucible 1. The diameter-increasing section 6 of the single crystal ingot C is manufactured in the diameter-increasing section growth section 3 of the crucible 1. The straight-bodied section 7 of the single crystal ingot C is manufactured in the single crystal growth section 4 of the crucible 1. The single crystal ingot C is manufactured by single crystallizing the molten raw material filled inside the cylindrical shape of the crucible 1. Therefore, the shape of the single crystal ingot C is such that the external shape conforms to the shape of the inside of the crucible 1 described above, and it is also columnar in shape. The shape of the single crystal ingot C is a columnar shape with the interior filled in the cylindrical shape described in crucible 1 above.

[0044] The shape and size (L1, H1, L2, H2, etc.) of the thin-diameter portion 5 and the thick-diameter portion 6 of the single-crystal ingot C are the same as the shape and size of the inside of the crucible 1 described above. The shape of the thin-diameter portion 5 is not particularly limited, but for example, it may be cylindrical or a columnar shape with a regular polygonal cross-section (e.g., a rectangular prism). The thin-diameter portion 5 may or may not contain a seed crystal.

[0045] The diameter-increasing portion 6 of the single crystal ingot C has an angle θ between the diameter-increasing portion 6 and the central axis AX1 of the single crystal that is 30° or less. The angle θ between the diameter-increasing portion 6 and the central axis AX1 is the same as the diameter-increasing portion angle θ described above. The central axis AX1 of the crucible corresponds to the central axis (growth axis) of the single crystal ingot C. The shape of the diameter-increasing portion 6 is not particularly limited as long as it is within the range of the diameter-increasing portion angle θ described above, but for example, it can be a columnar shape with a conical (including frustum of a cone) shape, a columnar shape with a pyramidal (including frustum of a pyramidal) shape, or a columnar shape with a regular polygonal cross-section (XY cross-section) (e.g., a quadrangular prism).

[0046] The shape and size (L3, H3, etc.) of the straight section 7 of the single crystal ingot C are the same as the shape and size of the inside of the crucible 1 described above, except for its height H4. The height H4 of the straight section 7 is not particularly limited and is set as appropriate. The diameter L3 of the straight section 7 is φ20 mm or more, as described above, and can be φ25 mm or more. The shape of the straight section 7 is not particularly limited, but for example, it can be cylindrical, or a columnar shape with a regular polygonal cross-section (XY cross-section) (e.g., prismatic, quadrangular prismatic).

[0047] In other words, as shown in Figure 3, the Mg2Sn-based single crystal ingot C of this embodiment has a columnar narrow diameter portion 5, a columnar straight portion 7 positioned at a different location from the narrow diameter portion 5 in the direction of the central axis (growth axis) and having a larger diameter (diameter L3) than the diameter (diameter L1) of the narrow diameter portion 5, and a columnar increasing diameter portion 6 positioned between the narrow diameter portion 5 and the straight portion 7 in the direction of the central axis (growth axis) and connecting the narrow diameter portion 5 and the straight portion 7, with the diameter (diameter L2) increasing as it moves from the narrow diameter portion 5 towards the straight portion 7.

[0048] As described in the examples, single crystal ingot C is a high-quality single crystal with a larger diameter than conventional single crystals, showing no grain boundaries in the diameter-increasing portion 6 and no crystal disorder due to back-reflection Laue image in the straight-body portion 7. In this embodiment, single crystal ingot C can increase the diameter of the single crystal in Mg2Sn-based single crystals.

[0049] Furthermore, the Mg2Sn single crystal may have a stoichiometric composition or a non-stoichiometric composition, and may also contain other elements besides Mg and Sn, such as Sb, Ag, Ga, Bi, Li, and P, as described above. In addition, the method for manufacturing the single crystal ingot according to this embodiment is not limited to the method described in this embodiment.

[0050] As described above, the method for manufacturing an Mg2Sn-based single crystal according to one aspect of this embodiment is a method for manufacturing an Mg2Sn-based single crystal by a unidirectional solidification crystal growth method, and uses a crucible comprising: a small diameter section located at the bottom and having a bottomed cylindrical shape; a single crystal growth section located at the top and having a cylindrical shape with a larger inner diameter than the small diameter section; and a diameter-increasing section growth section connecting the small diameter section and the single crystal growth section, having a cylindrical shape with an increasing inner diameter from the small diameter section toward the single crystal growth section, and having an angle between the inner wall and the central axis of the crucible of 30° or less. The method involves growing a single crystal by solidifying the molten raw material in the crucible from the small diameter section toward the single crystal growth section, and setting the growth rate in the diameter-increasing section to 0.8 mm / hour or less. Furthermore, a method for manufacturing Mg2Sn-based single crystals according to one aspect of this embodiment is a method for manufacturing Mg2Sn-based single crystals by unidirectional solidification crystal growth, wherein the grown single crystal comprises a small diameter portion, a diameter-increasing portion, and a straight body portion, the angle between the diameter-increasing portion and the central axis (growth axis) of the single crystal being 30° or less, and the growth rate in the diameter-increasing portion being 0.8 mm / hour or less. In this embodiment, the configuration other than that described above is arbitrary. The method for manufacturing Mg2Sn-based single crystals according to this embodiment allows for the stable acquisition of single crystals with a larger diameter than conventional methods in a method for growing Mg2Sn-based alloys.

[0051] Furthermore, according to one aspect of the present invention, an ingot of a Mg2Sn-based single crystal is provided, comprising a small diameter portion, a diameter-increasing portion, and a straight body portion, wherein the angle between the diameter-increasing portion and the growth axis of the single crystal is 30° or less, and the diameter of the straight body portion is 20 mm or more. In this embodiment, the single crystal ingot C of the Mg2Sn-based single crystal can have a larger single crystal diameter. [Examples]

[0052] [Example 1] Crystal growth was carried out using the method described above. The raw material used was a master alloy consisting of Mg and Sn, with the ratio of Mg to Sn adjusted as described above. The crucible used was the one shown in Figure 1, with the size of each part as described above. In crucible 1 used, the inner diameter of the narrow section 2 was 10 mm, the inner diameter L3 of the single crystal growth section 4 was 25 mm, and the diameter-increasing section angle θ was 11°. In addition, a boron nitride coating agent was applied to the inner wall of the crucible to suppress adhesion between the crystal and the crucible. Growth was started using the vertical Bridgman method at a descent speed of 0.5 mm / h of the stage on which the crucible was placed (crucible stage), and growth was completed at that speed (the growth speed of the diameter-increasing section and the straight section was 0.5 mm / h). This obtained a bulk single crystal (bulk sample).

[0053] The grown bulk sample was evaluated. Visual inspection of a surface cut perpendicular to the growth direction of the grown bulk sample revealed no clear grain boundaries.

[0054] Furthermore, wafers manufactured by cutting from the grown bulk samples were visually inspected to determine whether they were polycrystalline. For wafers determined not to be polycrystalline, at least three Laue images were taken using the back-reflection Laue method (sometimes abbreviated as the Laue method) to determine whether they were single crystals or not.

[0055] When measurements were taken at three points using the Laue method, all showed the same single-domain diffraction pattern. Four more tests were conducted under identical conditions, but no grain boundaries were observed in any of the samples. The manufacturing conditions and evaluation results are shown in Table 1.

[0056] [Example 2] In Example 1, the angle θ of the diameter-increasing section of crucible 1 was changed to 27°, and the descent speed of the crucible stage was changed to 0.7 mm / h (growth speed of the diameter-increasing section and growth speed of the straight section were both 0.7 mm / h). Otherwise, single crystals were manufactured and evaluated in the same manner as in Example 1.

[0057] The grown bulk sample was evaluated in the same manner as in Example 1, and it was confirmed to be a single crystal. The manufacturing conditions and evaluation results are shown in Table 1.

[0058] [Example 3] In Example 1, the descent speed of the crucible stage was changed to 5.0 mm / h (straight body growth rate 5.0 mm / h) during the growth of the straight body section, and single crystals were manufactured and evaluated in the same manner as in Example 1. The descent speed of the stage was changed to 5.0 mm / h when the growth interface had sufficiently entered the straight body section.

[0059] The grown bulk sample was evaluated in the same manner as in Example 1, and it was confirmed to be a single crystal. The manufacturing conditions and evaluation results are shown in Table 1.

[0060] [Example 4] In Example 1, a single crystal was manufactured and evaluated in the same manner as in Example 1, with the only modification being the use of a 10 mm diameter, 30 mm long Mg2Sn single crystal as a seed crystal in the narrow diameter section 2 at the lower end of the crucible.

[0061] The grown bulk sample was evaluated in the same manner as in Example 1, and it was confirmed to be a single crystal. The manufacturing conditions and evaluation results are shown in Table 1.

[0062] [Comparative Example 1] In Example 1, the angle θ of the diameter-increasing portion of crucible 1 was changed to 45°, and single crystals were manufactured and evaluated in the same manner as in Example 1.

[0063] When the sample was cut along a plane parallel to the growth direction, a clear domain boundary was observed originating from the diameter-increasing portion. The manufacturing conditions and evaluation results are shown in Table 1.

[0064] [Comparative Example 2] In Example 2, the descent speed of the crucible stage was changed to 1.0 mm / h (growth rate of the diameter-increasing section and growth rate of the straight section were both 1.0 mm / h), and single crystals were manufactured and evaluated in the same manner as in Example 2.

[0065] When the sample was cut along a plane parallel to the growth direction, a clear domain boundary was observed originating from the diameter-increasing portion. The manufacturing conditions and evaluation results are shown in Table 1.

[0066] [Table 1]

[0067] (summary) Examples 1 to 4 were carried out under conditions within the range of the manufacturing method of this embodiment described above, and high-quality bulk single crystals with a diameter of φ25 mm, which is larger than conventional methods, were obtained. On the other hand, in Comparative Example 1, where the diameter-increasing angle θ (45°) was outside the range of this embodiment, and in Comparative Example 2, where the diameter-increasing growth rate (1.0 mm / h) was outside the range of this embodiment, grain boundaries were observed in the diameter-increasing portion of the obtained crystals, and they were not single crystals.

[0068] From the above, it is confirmed that the method for manufacturing Mg2Sn-based single crystals according to this embodiment has the effects described above. Furthermore, it is confirmed that a single crystal ingot of this embodiment can be obtained.

[0069] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. One or more of the requirements described above may be omitted. Also, the requirements described above may be combined as appropriate. In addition, to the extent permitted by law, all disclosures of the documents cited above shall be incorporated as part of the description herein. [Explanation of Symbols]

[0070] 1...crucible 2...Narrow diameter part (crucible) 3. Diameter increase section / Growth section 4. Single Crystal Growth Department 5. Thin section (single crystal) 6. Increased diameter section 7...straight body part θ...Angle of increased diameter part AX1...Center axis C... Single crystal (single crystal ingot)

Claims

1. Mg grown by unidirectional solidification crystal growth method ２ A method for manufacturing Sn-based single crystals, A crucible is used that comprises a narrow diameter section located at the bottom and having a bottomed cylindrical shape, a single crystal growth section located at the top and having a cylindrical shape with a larger inner diameter than the narrow diameter section, and a diameter-increasing growth section connecting the narrow diameter section and the single crystal growth section, having a cylindrical shape with an increasing inner diameter from the narrow diameter section toward the single crystal growth section, and having an angle of 30° or less between the inner wall and the central axis of the crucible. A single crystal is grown by solidifying the molten raw material in the crucible from the small diameter side toward the single crystal growth section. The growth rate in the diameter-increasing growth section is set to 0.8 mm / hour or less, Mg ２ A method for manufacturing Sn-based single crystals.

2. The growth rate in the single crystal growth section is greater than the growth rate in the diameter-increasing section, according to claim 1. ２ A method for manufacturing Sn-based single crystals.

3. The growth rate in the single crystal growth section is 1.0 mm / hour or more and 5.0 mm / hour or less, according to claim 2 of the Mg ２ A method for manufacturing Sn-based single crystals.

4. In the crucible, without using a seed crystal, raw materials are placed and the raw materials are melted, as described in claim 1. ２ A method for manufacturing Sn-based single crystals.

5. In the crucible, a seed crystal is placed in the narrow diameter portion, a raw material is placed above the seed crystal, and the raw material is melted, as described in claim 1. ２ A method for manufacturing Sn-based single crystals.

6. The raw materials to be placed in the crucible are Mg and Sn in a molar ratio of 2.1:1.0 to 2.2:1.0, as described in claim 1. ２ A method for manufacturing Sn-based single crystals.

7. In the crucible, the inner diameter of the narrow portion is 8 mm or more, Mg according to claim 1. ２ A method for manufacturing Sn-based single crystals.

8. Mg ２ An ingot of a Sn-based single crystal, It comprises a narrow diameter section, a diameter-increasing section, and a straight barrel section. The diameter-increasing portion has an angle of 30° or less between the diameter-increasing portion and the growth axis of the single crystal. The diameter of the straight section is 20 mm or more. Mg ２ Sn-based single crystal ingot.

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