JP2011210845A - BULK TYPE MANGANESE SILICIDE SINGLE CRYSTAL OR POLYCRYSTAL DOPED WITH Ga OR Sn, AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive bulk type manganese silicide single crystal or polycrystal doped with Ga or Sn that is effectively used as a thermoelectric conversion material, an optical sensor, an optical element, etc., expected to have a high performance index at an intermediate temperature of approximately 300 to 600°C, and to provide a method of manufacturing the same in which the manufacture is easily and safely achieved in a short time.SOLUTION: The problem is solved with the bulk type manganese silicide single crystal or polycrystal doped with Ga or Sn characterized in being expressed by formula (1) or formula (2). Formula (1): Mn11Si19-xGax [where x is larger than 0 and equal to or less than 0.1]; and formula (2): Mn4 Si7-y Sny [where y is larger than 0 and equal to or less than 0.1].

Description

  The present invention relates to a bulk manganese silicide single crystal or polycrystalline body doped with Ga or Sn, and a method for producing the same, and more particularly, a P-type thermoelectric conversion material and an optical sensor that can be expected to have a high performance index, The present invention relates to an inexpensive Ga or Sn-doped bulk manganese silicide single crystal or polycrystal that can be effectively used as an optical element or the like, and a method for manufacturing the same.

In recent years, development of power generation systems using waste heat generated from factory facilities, power generation facilities, and the like has become active toward an energy-saving society. In particular, with the increase in industrial waste, etc., effective utilization of waste heat generated when these are incinerated has become a problem. For example, large-scale waste incineration facilities recover waste heat, such as burning boilers with waste heat and generating electricity with steam turbines, but medium- and small-sized waste incineration facilities, which account for the majority, depend on scale melt. Because of its high performance, it cannot be used to generate power with a turbine.
Therefore, a thermoelectric conversion element using a thermoelectric conversion material that reversibly performs thermoelectric conversion using the Seebeck effect or the Peltier effect, which has no scale merit dependency, has been proposed as a power generation method using such exhaust heat. .

As the thermoelectric conversion element, for example, an n-type semiconductor and a p-type semiconductor having low thermal conductivity are used as the thermoelectric conversion materials of the n-type thermoelectric conversion unit and the p-type thermoelectric conversion unit, respectively, as shown in FIG. 5 and FIG. Electrodes 5 and 6 are respectively provided at the upper end and the lower end of the n-type thermoelectric conversion unit 101 and the p-type thermoelectric conversion unit 102, and the electrodes 5 at the upper ends of the thermoelectric conversion units 101 and 102 are connected and integrated. In addition, the thermoelectric conversion elements configured by separating the electrodes 6 and 6 at the lower ends of the thermoelectric conversion units 101 and 102 can be given.
An electromotive force can be generated between the electrodes 5 and 6 by generating a temperature difference between the electrodes 5 and 6.

  On the other hand, by causing a direct current to flow between the electrodes 6 and 6 at the lower ends of the thermoelectric converters 101 and 102, heat generation and heat absorption are generated in the electrodes 5 and 6, respectively.

The thermoelectric conversion performance of such a thermoelectric conversion part is generally evaluated by a figure of merit Z (unit: K ⁻¹ ) expressed by the following formula (1).
Z = α ² / (κρ) (1)
In equation (1), α, κ, and ρ represent the Seebeck coefficient (thermoelectromotive force), thermal conductivity, and specific resistance, respectively.
It is considered that the dimensionless figure of merit ZT obtained by multiplying the figure of merit Z by the temperature T is, for example, 0.5 or more, preferably 1 or more, for practical use.

  That is, in order to obtain excellent thermoelectric conversion performance, a material having a large Seebeck coefficient α and a small thermal conductivity κ and specific resistance ρ may be selected.

That is, as shown in FIG. 5, when a positive temperature difference (Th−Tc) is generated between the electrodes 5 and 6 by heating the electrode 5 side or radiating the electrode 6 side, p is generated by the thermally excited carriers. The p-type thermoelectric conversion unit 102 is connected to the n-type thermoelectric conversion unit 101 by connecting the resistor 3 as a load between the left and right electrodes 6 and 6. Current flows to the side.
On the other hand, as shown in FIG. 6, when a direct current is passed from the p-type thermoelectric conversion unit 102 to the n-type thermoelectric conversion unit 101 by the DC power supply 4, an endothermic action and a heat generation action are generated in the electrodes 5 and 6, respectively.
Conversely, by causing a direct current to flow from the n-type thermoelectric conversion unit 101 to the p-type thermoelectric conversion unit 102, it is possible to cause the electrodes 5 and 6 to generate heat and heat, respectively.

Accordingly, Mg2 Si (see Non-Patent Documents 1, 2, and 3), which has abundant resources, is non-toxic, and has a low environmental load, has been studied as a thermoelectric conversion material, and Mg2 Si is suitable as an n-type thermoelectric conversion material. .
MnSi1.7 (manganese silicide) has begun to attract attention as a p-type thermoelectric conversion material that is compatible with the n-type Mg2 Si thermoelectric conversion material.

However, MnSi1.7 manufactured by the conventional manufacturing method has a problem that the thermoelectric conversion performance is poor.
That is, in the conventional manufacturing method of growing MnSi1.7 crystal from a melt of Mn and Si, Si and Mn are used as raw materials, the crystal growth temperature is as high as 1200 ° C. Since a heterogeneous phase called Si or Si single phase is precipitated in the crystal, the thermoelectric conversion performance is poor (see Non-Patent Document 4).
On the other hand, a chemical vapor deposition method (see Non-Patent Document 5) or a solution method in which MnSi1.7 crystal is grown using Mn and Si as raw materials and Ga, Sn, Pb and Cu melts as solvents. (See Non-Patent Document 6), there is a report that single-phase MnSi1.7 can be obtained, but the maximum diameter is about 0.1 mm, and Si or MnSi phase is precipitated in the same powder. In addition, it is difficult to use as a thermoelectric conversion material, and the crystal growth temperature is as high as 1200 ° C.

Semiconducting Properties of Mg2Si Single Crystals Physical Review Vol.109, No.6 March 15,1958, P.1909-1915 Seebeck Effect In Mg2Si Single Crystals J.Phys.Chem.Solids Pergamon Press 1962.Vol.23, pp.601-610 Bulk crystal growth of Mg2Si by the vertical Bridgman method Science Direct Thin Solid Films 461 (2004) 86-89 J.Materials Sci.16 (1981) 355 J. Crystal Growth 47 (1979) 589 J. Crystal Growth 229 (2001) 532

The first object of the present invention is to provide a bulk manganese silicide doped with inexpensive Ga or Sn that can be effectively used as a thermoelectric conversion material, optical sensor, optical element or the like that can be expected to have a high performance index at a medium temperature of about 300 to 600 ° C. It is to provide a single crystal or a polycrystal.
The second object of the present invention is to easily and safely manufacture such a bulk manganese silicide single crystal or polycrystal doped with Ga or Sn in a short time without using an expensive apparatus. It is to provide a manufacturing method that can be used.

  As a result of diligent research to solve the above-mentioned problems, Ga represented by the following formula (1) or the following formula (2), which will be described later, using a mixture of Mn and Si as a raw material and Ga melt or Sn melt. Alternatively, in a solution method for growing bulk manganese silicide single crystal or polycrystal (hereinafter sometimes referred to as MnSi1.7 crystal) doped with Sn, a crystal growth portion between a raw material portion and a crystal precipitation portion By attaching an appropriate temperature gradient ΔT to the film, it promotes convection and diffusion in Ga melt or Sn melt, and makes the synthesis rate of MnSi1.7 crystal overwhelmingly fast, even at a relatively low temperature of about 900 ° C. It has been found that a large crystal having a diameter of about 1 mm or more, preferably about 1 cm or more, more preferably about 10 to 20 cm can be synthesized, and the present invention has been achieved.

  The invention according to claim 1 of the present invention is a bulk manganese silicide single crystal or polycrystal doped with Ga or Sn, characterized by being represented by the following formula (1) or (2): is there.

Mn11Si19-xGax formula (1)
[In Formula (1), x is more than 0 and 0.1 or less. ]
Mn4 Si7-y Sny formula (2)
[In Formula (2), y exceeds 0 and is 0.1 or less. ]

  The invention according to claim 2 of the present invention includes the following steps (1) to (6), and is produced in a vacuum, wherein the bulk manganese silicide unit doped with Ga or Sn according to claim 1 is used. A method for producing a crystal or polycrystal.

(1) Mn: Si element ratio calculated from the following formula (3), a mixture of Mn particles and Si particles formed into pellets by a sintering method or the like, or melted above the melting point Preparing a raw material made of an alloyed MnSi _1.7 alloy.
(2) The bottom portion in the reaction vessel is a crystal precipitation portion, and after filling the reaction vessel with a predetermined amount of Ga particles or Sn particles, the reaction vessel is heated to a melting point of Ga or Sn to increase the Ga particles or A step of melting the Sn particles to form a crystal growth portion made of Ga or Sn melt.
(3) A step of bringing the raw material prepared in step (1) into contact with the upper surface of the Ga melt or Sn melt in the reaction vessel prepared in step (2) and filling it to form a raw material portion made of the raw material. .
(4) The reaction vessel is further heated so that the temperature of the raw material portion is at least higher than that of the crystal growth portion and at most 1200 ° C., and the crystal growth portion is set to 600 to 1150 ° C. And a step of setting the temperature gradient between the raw material part and the crystal precipitation part to be 5 to 100 ° C./cm.
(5) While maintaining the reaction vessel in the state set in step (4), a crystal is grown for a predetermined time in the crystal growth portion, and a bulk manganese silicide unit doped with Ga or Sn in the crystal precipitation portion. A process of depositing a crystal or bulk manganese silicide polycrystal.
(6) After the crystal growth is completed, it is cooled to room temperature, and the bulk manganese silicide single crystal or polycrystal doped with Ga or Sn is taken out from the reaction vessel.

MnSi1.75-x Formula (3)
[In Formula (3), x is 0 or more and 0.13 or less. ]

  The invention according to claim 1 of the present invention can be manufactured without using an inert gas introduction device or the like, and doped with Ga or Sn represented by the above formula, for example, an average diameter of about 1 mm or more, preferably about 1 cm. More preferably, it is a bulk manganese silicide single crystal or polycrystal that reaches about 10 to 20 cm, is inexpensive, and is doped with Ga or Sn, so it has a high performance index at a medium temperature of about 300 to 600 ° C. In addition to being able to be effectively used as a thermoelectric conversion material that can be expected, there is a remarkable effect that it can be effectively used as an optical sensor, an optical element, or the like.

The invention according to claim 2 of the present invention includes the steps (1) to (6), and is produced in a vacuum. The bulk manganese silicide unit doped with Ga or Sn according to claim 1, A method for producing a crystal or polycrystal,
There is a remarkable effect that it can be manufactured easily and safely in a short time without using an expensive inert gas introduction device or the like.

  The temperature of the raw material portion is at least higher than the temperature of the crystal growth portion and at most 1200 ° C., the crystal growth portion is set to 600 to 1150 ° C., and the raw material portion reaches the crystal precipitation portion. By setting the temperature gradient between 5 to 100 ° C./cm and maintaining this state, the crystal is grown for a predetermined time in the crystal growth part, and the crystal is deposited in the crystal precipitation part, Since the convection and diffusion in the crystal growth portion were promoted and the crystal growth rate could be remarkably increased, a bulk manganese silicide single crystal doped with Ga or Sn reaching an average diameter of about 10 to 20 cm or a multi-crystal. Crystals could be produced in a short time.

It is explanatory drawing explaining the manufacturing method of the bulk-like manganese silicide single crystal or polycrystal doped with Ga or Sn of the present invention. 4 is a graph showing an X-ray diffraction result of a bulk manganese silicide single crystal doped with Ga according to the present invention in Example 1. FIG. It is a graph which shows the X-ray-diffraction result of the bulk-like manganese silicide single crystal body doped with Sn of this invention of Example 2. The graph which shows the electrical resistivity measurement result with respect to the temperature of the bulk manganese silicide single crystal doped with Ga according to the present invention of Example 1 and the bulk manganese silicide single crystal doped with Sn according to the present invention of Example 2. It is. It is explanatory drawing explaining the structural example of the thermoelectric conversion element provided with the n-type thermoelectric conversion part and the p-type thermoelectric conversion part. It is explanatory drawing explaining the structural example of the other thermoelectric conversion element provided with the n-type thermoelectric conversion part and the p-type thermoelectric conversion part.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory view for explaining a method for producing a bulk manganese silicide single crystal doped with Ga according to the present invention in a vacuum.

In FIG. 1, 1 is an apparatus for producing a bulk manganese silicide single crystal doped with Ga according to the present invention in vacuum, 2 is a heating furnace, 3 is a heater for heating provided on the outer periphery of the heating furnace 2 4 is a reaction vessel, 5 is a crystal growth portion made of a Ga melt in the reaction vessel 4, 6 is a raw material MnSi _1.7 alloy formed by being placed in contact with the upper surface of the Ga melt in the crystal growth portion 5, etc. The raw material portion 7 is composed of a growing manganese silicide single crystal deposited on the crystal precipitation portion without forming a seed crystal portion on the bottom portion of the reaction vessel 4 and using the bottom portion of the reaction vessel 4 as a crystal precipitation portion. Reference numeral 8 denotes a thermometer, and 9 denotes a control means.

Next, the manufacturing method of this invention is demonstrated for every process for every process.
In step (1), first, a raw material composed of pellets obtained by sintering Mn particles and Si particles or an MnSi _1.7 alloy having an element ratio of Mn: Si calculated from the above equation (3) is prepared. .

  In step (2), the bottom of the reaction vessel 4 is used as a crystal precipitation portion, and after filling a predetermined amount of Ga particles in the reaction vessel 4, the heater 3 is driven by a signal from the control means 9 to drive the reaction vessel 4. Is heated to the melting point of Ga or higher to melt the Ga grains to form the crystal growth part 5 made of Ga melt. Although the bottom portion of the reaction vessel 4 is a crystal precipitation portion, a seed crystal such as a quartz plate may be disposed on the bottom portion to form a crystal precipitation portion.

In the step (3), the raw material prepared in the step (1) is brought into contact with the upper surface of the crystal growth part 5 made of a Ga melt in the reaction vessel 4 prepared in the step (2), and is filled with the raw material. Forming the raw material portion 6;
An appropriate spacer such as a mesh or a porous body may be provided between the upper surface of the crystal growth part 5 and the raw material part 6.

In step (4), the heater 3 for each zone is appropriately driven by a signal from the control means 9 to further heat the reaction vessel 4 so that the temperature of the raw material portion 6 is at least higher than the temperature of the crystal growth portion 5. The temperature is set to 1200.degree. C. or lower, preferably 1100.degree. C. or lower, and the crystal growth portion 5 is set to 600 to 1150.degree. C., preferably 650 to 1100.degree. The temperature gradient ΔT between the bottom and the crystal precipitation part is set to 5 to 100 ° C./cm, preferably 10 to 90 ° C./cm.
If the temperature exceeds 1200 ° C., the melting point of the raw material is exceeded, so that the entire raw material becomes a melt and crystal growth may not be possible. If the temperature of the crystal growth part 5 is less than 600 ° C., the raw material is not sufficiently dissolved in Ga or Sn solvent, so that the crystal growth is remarkably slow and the crystal may not grow. The non-uniform portion may melt and hinder crystal growth.
If the temperature gradient ΔT is less than 5 ° C./cm, the solute dissolved in the solution is not sufficiently supplied to the crystal growth part, so that there is a risk that crystal growth may be significantly inhibited. There is a risk of getting worse.

  In the step (5), while maintaining the reaction vessel 4 in the state set in the step (4), a crystal is grown for a predetermined time in the crystal growth portion 5, and the bulk manganese silicide doped with Ga in the crystal precipitation portion A single crystal 7 is deposited.

  In step (6), after the crystal growth is completed, the crystal is cooled to room temperature, and the bulk manganese silicide single crystal 7 doped with Ga is taken out from the reaction vessel 4.

  On the left side of FIG. 1, the vertical axis indicates the distance (cm) from the raw material part 6 to the crystal precipitation part at the bottom of the reaction vessel 4 (that is, the distance between XS and XG), and the horizontal axis indicates the reaction from the raw material part 6. The relationship with the temperature (degreeC) (namely, temperature between TG-TS) until it reaches the crystal precipitation part of the bottom part of the container 4 is shown. And it sets so that the temperature gradient (DELTA) T from the raw material part 6 to the crystal precipitation part of the bottom part of the reaction container 4 may be set to 5-100 degreeC / cm.

The raw material Si used in the present invention is a chunk having an average particle diameter of about 2 to 3 mm obtained by crushing a high-purity silicon raw material for semiconductors, a high-purity silicon raw material for LSI, a high-purity silicon raw material for solar cells, high-purity metallic silicon, or the like. And powder having an average particle size of about 5 to 50 μm.
The raw material Mn used in the present invention is preferably a highly purified 99.9% or more chunk-like particle having an average particle size of about 2 to 3 mm or a powder having an average particle size of about 5 to 50 μm. Can be used.
Examples of the raw material MnSi _1.7 alloy used in the present invention include those obtained by melting chunk-like Si particles and chunk-like Mn particles at a melting point or higher and cooling them to form an alloy. Furthermore, examples of the raw material include bulk mixed sintered pellets obtained by homogeneously mixing and sintering Si particles and Mn particles.

In the present invention, a raw material made of a mixed sintered pellet of Mn particles and Si particles or an MnSi _1.7 alloy having an element ratio calculated from the above equation (3) is prepared.
In the above formula (3), x is adjusted according to the crystal composition to be precipitated, and is preferably 0.023 when growing the Mn11Si19 phase, and preferably 0 when growing the Mn4Si7 phase.
When x exceeds 0.13, a monosilicide MnSi phase may be precipitated, which is not preferable.

The reaction vessel used in the present invention is not particularly limited as long as it has heat resistance and mechanical properties that can withstand the reaction conditions of the chemical reaction, and has oxygen impermeability and the crystal growth temperature in the atmosphere. Such as high-purity quartz, BN, densely processed graphite, and alumina, etc., which have heat resistance that can withstand heat, and does not react with Ga or Sn as a solvent and does not supply impurities to the product MnSi1.7 crystal. A reaction vessel having an inner surface made in (1) can be preferably used.

As described above, in step (4), the temperature of the raw material portion 6 is at least higher than the temperature of the crystal growth portion 5 and at most 1200 ° C. or less, the crystal growth portion 5 is 600 to 1150 ° C., The temperature gradient ΔT from the part 6 to the crystal precipitation part at the bottom of the reaction vessel 4 is set to be 5 to 100 ° C./cm, and the crystal is grown for a predetermined time in the crystal growth part 5 while maintaining the set state. The MnSi1.7 crystal 7 is deposited on the crystal precipitation part.
The heating of the reaction vessel used in the present invention is not particularly limited, and a known heating method can be used using a heating device such as a known electric furnace or gas combustion furnace.

The reaction vessel is evacuated. The degree of vacuum in the container is 0.06 Pa or less, preferably 1 × 10 ⁻³ or less.

The cooling may be natural cooling, forced cooling, or a combination thereof, and is not particularly limited, and a known cooling method can be used by using a known cooling device.
Care should be taken because if the cooling is too rapid, the reaction vessel may break.

When using MnSi1.7 crystal as a thermoelectric conversion material, pulverize Ga or Sn-doped MnSi1.7 crystal obtained in the synthesis step, and if the doping is insufficient, the obtained powder will have an appropriate dopant. After adding a predetermined amount, it has high physical strength and is stably high by sintering at a sintering pressure of 5 to 60 MPa and a sintering temperature of 600 to 1000 ° C. in a reduced pressure atmosphere by a pressure compression sintering method. A P-type thermoelectric conversion material that can exhibit thermoelectric conversion performance, is not weathered, has excellent durability, and has high stability and reliability can be obtained.
The pulverization is preferably carried out to particles having a fine particle size, a uniform particle size, and a narrow particle size distribution. Sintering particles with fine, well-aligned particle size and narrow particle size distribution by the following pressure compression sintering method allows the particles to be fused together with at least a part of their surfaces fused together. Sintering can be performed satisfactorily, and a sintered body having approximately the theoretical density can be obtained from about 70% of the theoretical density.

Specifically, the particle size of the pulverized MnSi1.7 crystal is, for example, 65 μm on a 75 μm pass, 20 μm on a 30 μm pass, or an average particle size of 0.1 to 0.2 μm. It is preferable to select appropriately according to the purpose of use.
A sintered body having an almost theoretical density can be obtained from 70%, and a P-type thermoelectric conversion material can be produced, which is preferable.

Specific examples of the dopant include trivalent dopants such as B, Al, Ga, and In.
Other specific examples include pentavalent dopants such as P and Bi.
Other specific examples include hexavalent dopants such as Cr, Mo, and W.

  The description of the above embodiment is for explaining the present invention, and does not limit the invention described in the claims or reduce the scope. Moreover, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention in detail, unless it deviates from the main point of this invention, it is not limited to these Examples.

(Example 1)
The apparatus 1 shown in FIG. 1 is used, the temperature of the raw material part 6 is set to 880 to 930 ° C., the temperature of the crystal growth part 5 made of Ga melt is set to 850 to 900 ° C. The temperature gradient ΔT between the bottom and the crystal precipitation part is set to 30 to 60 ° C./cm, and the crystal is grown in the crystal growth part 5 for a predetermined time (about one week) while maintaining this state. The bulk manganese silicide single crystal 7 doped with Ga was deposited on the crystal precipitation part. After the crystal growth was completed, it was cooled to room temperature, and the bulk manganese silicide single crystal 7 doped with Ga was taken out from the reaction vessel 4.

Using a scanning electron microscope (SEM-EDX) of bulk manganese silicide single crystal 7 doped with Ga, three points were measured under the following analysis conditions, and the average values are shown in Table 1.
(Analysis conditions)
Device: JEOL JSM-5600LV
Electron beam acceleration voltage: 15KV
Beam size: 44
Sample distance: 15mm

The results of X-ray diffraction measurement of Ga-doped bulk manganese silicide single crystal 7 under the following analytical conditions are shown in FIG.
(Analysis conditions)
Equipment: Rigaku RINT2000
X-ray: CuKα1 40KV / 30mA
Divergent slit: 1 deg.
Scattering slit: 1 deg.
Receiving slit: 0.3mm
Scanning mode: Continuous sample rotation speed: 60 rpm
Scan speed: 2 ° / min
Scan step: 0.02 °
Scanning axis: θ ・ 2θ

FIG. 4 shows the results of measuring the electrical resistivity (Ωcm) of the bulk manganese silicide single crystal 7 doped with Ga with respect to the temperature (K).
(Measurement condition)
Measurement method: Four-terminal method Electrode: Silver paste Device: Keithley 2400 source meter, 2182 nanovolt meter

The results of measuring the thermoelectric properties of the bulk manganese silicide single crystal 7 doped with Ga are shown in Table 3 together with a report example described in Table II of Non-Patent Document 4 [J. Materials Sci. 16 (1981) 355-366]. Shown in
However, the thermoelectric output factor P = α ² / ρ in Table 3 is represented.
α: Seebeck coefficient, ρ represents electric resistance.

(Example 2)
The apparatus 1 shown in FIG. 1 is used, the temperature of the raw material part 6 is set to 880 to 930 ° C., the temperature of the crystal growth part 5 made of Sn melt is set to 850 to 900 ° C. The temperature gradient ΔT between the bottom and the crystal precipitation part is set to 30 to 60 ° C./cm, and while maintaining this state, the crystal is grown in the crystal growth part 5 for a predetermined time (about 2 weeks). The bulk manganese silicide single crystal 7 doped with Sn was deposited on the crystal precipitation part. After the crystal growth was completed, it was cooled to room temperature, and the bulk manganese silicide single crystal 7 doped with Sn was taken out from the reaction vessel 4.

  In the same manner as in Example 1, three points of the bulk manganese silicide single crystal 7 doped with Sn were measured using a scanning electron microscope (SEM-EDX), and the average value is shown in Table 1.

  The results of X-ray diffraction measurement of the bulk manganese silicide single crystal 7 doped with Sn in the same manner as in Example 1 are shown in FIG.

  FIG. 4 shows the results of measuring the electrical resistivity (Ωcm) of the bulk manganese silicide single crystal 7 doped with Sn with respect to the temperature (K) in the same manner as in Example 1.

  The results of measuring the thermoelectric properties of the bulk manganese silicide single crystal 7 doped with Sn in the same manner as in Example 1 are shown in Table II of Non-Patent Document 4 [J. Materials Sci. 16 (1981) 355-366]. It is shown in Table 3 with the report example described in.

The bulk manganese silicide single crystal 7 doped with Ga in Example 1 has an average diameter of about 5 cm, and from Table 1, it has a composition of Si 63.1 atom%, Mn 36.6 atom%, Ga 0.3 atom%, and From FIG. 2 and Table 2, it can be seen that unreacted Si, Mn, Ga, Mn4 Si7, MnSi and the like are not contained.
From Table 3, it can be seen that the bulk manganese silicide single crystal 7 doped with Ga of Example 1 has excellent thermoelectric properties.

The bulk manganese silicide single crystal 7 doped with Sn in Example 2 has an average diameter of about 4.5 cm, and has a composition of Si 63.4 atom%, Mn 36.4 atom%, and Sn 0.2 atom% from Table 1. 3 and Table 2 show that unreacted Si, Mn, Ga, Mn4 Si7, MnSi and the like are not contained.
From Table 3, it can be seen that the bulk manganese silicide single crystal 7 doped with Sn in Example 2 has excellent thermoelectric properties.

  The present invention can be manufactured without using an inert gas introduction device or the like, and doped with Ga or Sn represented by the above formula (1) or (2), for example, an average diameter of about 1 mm or more, preferably Bulk manganese silicide single crystal or polycrystal which reaches about 1 cm or more, more preferably about 10 to 20 cm, is inexpensive and is doped with Ga or Sn, so it is high at a medium temperature of about 300 to 600 ° C. In addition to being able to be used effectively as a thermoelectric conversion material that can be expected to have a figure of merit, it has a remarkable effect that it can also be used effectively as an optical sensor, an optical element, etc. Because it has a great effect, it has high industrial utility value.

1 Apparatus for producing a bulk manganese silicide single crystal doped with Ga according to the present invention in vacuum 2 Heating furnace 3 Heating heater 4 Reaction vessel 5 Crystal growth section 6 Raw material section 7 Crystal precipitation section 8 Thermometer 9 Control means

Claims (2)

A bulk manganese silicide single crystal or polycrystal doped with Ga or Sn, which is represented by the following formula (1) or (2):
Mn11Si19-xGax formula (1)
[In Formula (1), x is more than 0 and 0.1 or less. ]
Mn4 Si7-y Sny formula (2)
[In Formula (2), y exceeds 0 and is 0.1 or less. ] The method for producing a bulk manganese silicide single crystal or polycrystal doped with Ga or Sn according to claim 1, comprising the following steps (1) to (6) and producing in vacuum.
(1) Mn: Si element ratio calculated from the following formula (3), a mixture of Mn particles and Si particles formed into pellets by a sintering method or the like, or melted above the melting point Preparing a raw material made of an alloyed MnSi1.7 alloy.
(2) The bottom portion in the reaction vessel is a crystal precipitation portion, and after filling the reaction vessel with a predetermined amount of Ga particles or Sn particles, the reaction vessel is heated to a melting point of Ga or Sn to increase the Ga particles or A step of melting the Sn particles to form a crystal growth portion made of Ga or Sn melt.
(3) A step of bringing the raw material prepared in step (1) into contact with the upper surface of the Ga melt or Sn melt in the reaction vessel prepared in step (2) and filling it to form a raw material portion made of the raw material. .
(4) The reaction vessel is further heated so that the temperature of the raw material portion is at least higher than that of the crystal growth portion and at most 1200 ° C., and the crystal growth portion is set to 600 to 1150 ° C. And a step of setting the temperature gradient between the raw material part and the crystal precipitation part to be 5 to 100 ° C./cm.
(5) While maintaining the reaction vessel in the state set in step (4), a crystal is grown for a predetermined time in the crystal growth portion, and a bulk manganese silicide unit doped with Ga or Sn in the crystal precipitation portion. A process of depositing a crystal or bulk manganese silicide polycrystal.
(6) After the crystal growth is completed, it is cooled to room temperature, and the bulk manganese silicide single crystal or polycrystal doped with Ga or Sn is taken out from the reaction vessel.
MnSi1.75-x Formula (3)
[In Formula (3), x is 0 or more and 0.13 or less. ]

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