JP4496365B2 - Thermoelectric material and manufacturing method thereof - Google Patents

Description

The present invention relates to a thermoelectric material mainly composed of an Mg ₂ Si-based compound and a method for producing the same. In particular, the present invention relates to a thermoelectric material in which Al and Zn are added as dopant elements to an Mg ₂ Si-based compound, a thermoelectric material for producing the thermoelectric material by a melting method, and a method for producing the thermoelectric material.

  Thermoelectric conversion elements that convert thermal energy into electrical energy and convert the opposite electrical energy into cold energy can be used not only for moving parts and miniaturization of equipment, but also for precise temperature control. easy. For this reason, utilization is spreading to waste heat recovery, temperature control of electronic devices, sensors, and the like.

As a thermoelectric material used for the thermoelectric conversion element, Bi—Te, Pb—Te, Si—Ge, Fe—Si, Mg—Si, and the like are known. Elements such as Bi, Te, Pb, and Ge have a small abundance on the earth, and in particular, Bi and Te have a strong toxicity, which is a difficulty in large-scale commercialization. On the other hand, the Fe—Si system has a high melting point and a wide use temperature range and is excellent in environmental characteristics, and is regarded as a promising thermoelectric material. However, its figure of merit is 0.1 × 10 ⁻³ (1 / K) About as low as practical and poor in practicality.

This figure of merit is calculated by Z = α ² σ / κ, Z: figure of merit (1 / K). Here, σ is electrical conductivity (1 / m · Ω), α is electromotive force (V / K), and κ is thermal conductivity (W / m · K). On the other hand, the Mg-Si system is low in cost, its constituent elements are light and environmentally friendly, lightweight, high strength and high melting point, and is considered to have a wide use temperature range. One of the materials.

  Therefore, in order to improve the low figure of merit, which is one of the problems of the Mg-Si system, an impurity called a dopant is added to develop semiconductor characteristics in the Mg-Si system material at high temperatures. The thermoelectric characteristics are improved by exhibiting a high electrical conductivity at. Known dopants added to the Mg—Si-based material include Al, Sb, etc., which develop N-type semiconductor characteristics, and Ag, Cu, etc., which develop P-type semiconductor characteristics.

However, Mg ₂ Si thermoelectric material has not been developed so far because Mg is an active metal and there is a risk of ignition and the like. Conventionally, as a method for producing this type of Mg ₂ Si-based compound, a mixed powder obtained by adding dopant element powder to Mg and Si powder in which Mg and Si are in an atomic ratio of 2: 1, or prepared in advance. A mixed powder composed of Mg ₂ Si powder and dopant element powder is heated to a melting point (Tm: 1358K) or higher of Mg ₂ Si in an atmosphere several times higher than atmospheric pressure in a pressure heating apparatus, and then cooled to Mg ₂ Si based compound There is a high pressure melting method that produces

As another method for producing the Mg ₂ Si-based compound, a mixed powder obtained by adding a dopant element powder to Mg and Si powder in which Mg and Si are in an atomic ratio of 2: 1, or a Mg ₂ Si powder prepared in advance. And a mixed powder composed of a dopant element powder is placed in a carbon crucible in a pressurized container substituted with an inert gas, and high-frequency heating / dissolution is exemplified.

As another method for producing the Mg ₂ Si-based compound, there is a method called a mechanical alloying method. In this method, Mg and Si powders are weighed so that the atomic ratio of Mg and Si is 2: 1, and these powders are ball milled for a long time (for example, 300 hours) with iron or ceramic balls. By doing so, the Mg ₂ Si powder is mechanically synthesized. A Mg ₂ Si based compound is produced by mixing the Mg ₂ Si powder thus obtained and a dopant element and subjecting the mixture to heat treatment.

Still another method for producing an Mg ₂ Si-based compound is called a discharge plasma method. This method includes a mixing step of mixing Mg powder and Si powder and dopant element powder such that the atomic ratio of Mg and Si is 2: 1, and the mixed powder obtained in the mixing step is mixed with the melting point of Mg ( Tm: 923K) and heated and held for a predetermined time within a temperature range of 1073K or less to form Mg ₂ Si by reaction between molten Mg and Si particles, and a dopant element is dissolved in molten Mg to form a Mg ₂ Si crystal structure. Mg ₂ Si based compound having a non-equilibrium structure is produced by substitution and solid solution with a part of Mg or Si.

As a technology related to this, for example, Japanese Patent Laid-Open No. 2002-285274 (Patent Document 1) proposes an invention related to “Mg—Si-based thermoelectric material and manufacturing method thereof”. Mixing step of mixing Mg powder and Si powder with an atomic ratio of 2: 1 and the dopant element powder, and mixing powder obtained in the mixing step within a temperature range of Mg melting point Tm (Mg) to 1073 K And heated for a predetermined time to form Mg ₂ Si by reaction of molten Mg and Si particles, and the dopant element is dissolved in molten Mg to replace part of Mg or Si in the Mg ₂ Si crystal structure - a heating holding step of generating a more Mg 2 _Si based compound be a solid solution, cooled Engineering stopping the extent that Si particles of unreacted remains a heating holding step after the predetermined time Is produced. "It has been disclosed by the.
JP 2002-285274 A

However, this Patent Document 1 discloses an example of Al as dopan, but according to the knowledge of the present inventor, segregation increases when only Al is added, and only P becomes p-type when Zn alone. It is not a type. On the other hand, cracks are likely to occur in Mg ₂ Si ingots produced by a conventional melting process such as the conventional high pressure melting method and the melting method under atmospheric pressure (atmospheric pressure melting method). is there. Further, the Mg ₂ Si based compound containing 0.15 at% Al dopant having a non-equilibrium structure produced by the conventional discharge plasma method shows excellent thermoelectric properties, but the above-described direct melting method such as high pressure and normal pressure is used. In the Mg ₂ Si ingot of the same composition prepared in (1), since this has an equilibrium structure, most of the dopant element segregates as an Al compound in the final solidified part, and the amount of solid solution in the Mg ₂ Si compound becomes extremely small. The conductivity of the Mg ₂ Si ingot is very low. Therefore, the optimum chemical composition of the Mg ₂ Si based thermoelectric material used in the discharge plasma method cannot be applied directly to the melting process.

  The present invention has been made in view of the above-described circumstances, and achieves the following objects.

  An object of the present invention is to provide a thermoelectric material capable of improving the safety of the manufacturing process and reducing the manufacturing cost by focusing on the melting method under atmospheric pressure and the manufacturing method thereof.

Another object of the present invention is to provide a thermoelectric material comprising a thermoelectric semiconductor in which Al and Zn are added in combination as dopant elements to a Mg ₂ Si based compound having an excellent figure of merit, and a method for producing the thermoelectric material.

  In order to achieve the above object, the thermoelectric material according to the present invention is characterized by comprising an N-type thermoelectric semiconductor formed by adding Al and Zn as dopant elements to an Mg—Si based compound. In the thermoelectric material according to the present invention, it is preferable that the Mg—Si based compound has Mg and Si in an atomic ratio of 2: 1 and the addition amount of Al and Zn is 0.21 at% to 2 at%.

The method for producing a thermoelectric material of the present invention accommodates massive Mg and Si that forms a compound with Mg in a melting chamber of a graphite container having a buffer cavity on the atmosphere side, and adds Al and Zn as dopant elements in combination. Then, with the inert gas substituted in the buffer cavity, the graphite container is held for a certain period of time in a temperature range not lower than the melting point of the Mg ₂ Si compound and not higher than the boiling point of Mg, thereby allowing the compound melt or the combined liquid to be obtained. It is characterized by producing an ingot by cooling the compound melt or combined liquid, and sintering the Mg ₂ Si raw material powder produced by pulverizing the ingot.

  Further, in the method for producing a thermoelectric material according to the present invention, the graphite container is a container made of a bottomed cylindrical body, and is placed in the graphite container by a semi-sealing punch that divides the space of the container. The buffer cavity for introducing and storing the inert gas, and the dissolution chamber for storing the Mg-Si based compound and the Al and Zn are formed on the bottom side, and heated while being blocked from the atmosphere by the inert gas. By holding, a compound melt or a combined financial liquid of the thermoelectric material may be made.

Further, in the manufacturing method of the thermoelectric material of the present invention, the sintering, the Mg 2 _Si raw material powder voltage and current is applied to, produce a sintered body by a discharge phenomenon occurring at the particle gap of the Mg 2 _Si raw material powder If the discharge plasma sintering method is used, a more effective one can be produced. Furthermore, in the method for producing a thermoelectric material of the present invention, the additive amount of Al and Zn is preferably 0.21 at% to 2 at%.

According to the present invention, a thermoelectric material composed of an Mg ₂ Si-based thermoelectric semiconductor having an excellent figure of merit can be achieved by improving the safety of the manufacturing process and reducing the manufacturing cost by a melting method under atmospheric pressure. Can be manufactured.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to this embodiment. The structure of a semi-sealed container (graphite container) used for manufacturing the thermoelectric material according to the present invention will be described with reference to FIG. As shown in the figure, the semi-sealed container 1 used in the present embodiment is a container having a bottomed cylindrical shape, and the container body 2 is made of graphite. The opening of the container body 2 is closed by a graphite lid 3, and the lid 3 is provided with a tubular gas inlet 4 so as to penetrate the lid 3.

  Further, a semi-sealing punch 5 made of graphite is attached to the middle part of the container body 2 in the longitudinal direction. In this case, a melting chamber 7 capable of accommodating a raw material is defined on the bottom side with a buffer cavity 6 that can be accommodated by introducing an inert gas to the atmosphere side. The semi-sealing punch 5 is slightly smaller in size than the inner diameter of the inner hole of the container body 2.

  The semi-sealing punch 5 can be fixed at an arbitrary position by a frictional force with the container body 2. By interposing the semi-sealing punch 5, the internal space of the container body 2 can be partitioned into upper and lower spaces. That is, the space above the container body 2 is a buffer cavity 6 that is a space for introducing an inert gas from the atmosphere side, and the bottom side that is the lower space of the semi-sealing punch 5 is a melting chamber 7 that can accommodate a raw material. A compartment is formed.

  The semi-sealing punch 5 has an effect of suppressing the evaporation of the compound melt or the combined financial liquid. In particular, when the melting point is 923K and the boiling point is 1380K, for example, magnesium, it evaporates when the melting point is exceeded. By forming a semi-sealed space with the punch 5, this evaporation is suppressed, and a magnesium alloy having a uniform target component Can be manufactured.

In the manufacturing method according to the present embodiment, Mg and Si that forms a compound with Mg and the compound are accommodated in the dissolution chamber 7 of the semi-sealed container 1 having the buffer cavity 6 on the atmosphere side. In a state in which Al and Zn as dopant raw materials are added in combination and the inert gas is replaced in the buffer cavity 6, the semi-sealed container 1 is kept at a temperature range between the melting point of the Mg ₂ Si compound and the boiling point of Mg. By holding for a time, a compound melt or a combined liquid is produced, and the melt is cooled to produce a polycrystalline ingot.

In the present embodiment, Mg is not used in an easily ignited powder state, but a lump is put into the melting chamber 7 of the semi-sealed container 1. In addition, Si that forms a compound with Mg is preferably one having a small particle size in order to reduce the heating and holding time. In particular, if there is no risk of ignition or explosion, a powdery one may be used. I do not care. On the other hand, since Mg is sufficiently dissolved at the heating and holding temperature, there is little influence on the holding time of the shape and size of the raw material. In order to produce an Mg ₂ Si-based compound ingot, a massive Mg raw material and an irregular granular Si raw material are weighed so as to have an atomic ratio of 2: 1 and charged into the melting chamber 7.

Moreover, in this Embodiment, Al and Zn are compound-added as a dopant element, and it is preferable that the compound addition amount is 0.21 at%-2 at%. Here, the reason why Al and Zn are added in combination is to obtain a thermoelectric material composed of a Mg ₂ Si-based thermoelectric semiconductor having an excellent figure of merit, as shown in the data below, while suppressing macrosegregation of the dopant element. .

  After the completion of the charging of the raw material, a semi-sealing punch 5 is arranged in the container body 2 and its opening is closed with a lid 3 having a gas introduction port 4. An inert gas such as argon (Ar) is introduced from the port 4 and the inside of the buffer cavity 6 is replaced with the inert gas during heating / holding and cooling. In the present embodiment, Ar is used as the inert gas introduced into the buffer cavity 6, but the present invention is not limited to this, and other gases that do not react with the raw material at a high temperature such as helium (He) may be used. .

After replacing the buffer cavity 6 of the semi-sealed container 1 with an inert gas, the semi-sealed container 1 is stored in a heating furnace and kept for a certain time in a temperature range between the melting point of the Mg ₂ Si compound and the boiling point of Mg. By doing so, a compound melt or a combined financial liquid is generated. Here, the heating and holding at a temperature equal to or higher than the melting point of the Mg ₂ Si compound is to obtain a uniform compound by melting the raw material, and the heating and holding at a temperature not higher than the boiling point of Mg is due to evaporation of Mg. This is to prevent ignition and explosion.

In the present embodiment, an electric furnace is used as the heating means of the semi-sealed container 1, but the present invention is not limited to this, and other heating means such as induction heating or heating by crucible energization may be used. In order to produce an ingot of an Mg ₂ Si-based compound, for example, 1361K in the temperature range of the melting point of Mg ₂ Si (Tm (Mg ₂ Si): 1358K) and the boiling point of Mg (Tb (Mg): 1363K). And a melt of Mg ₂ Si based compound is generated by maintaining the temperature for 2 hours.

  In this heating and holding step, the gas and vapor generated in the melting chamber 7 escape to the outside through the gap between the inner surface of the container body 2 and the outer peripheral surface of the semi-sealing punch 5, but the heating and holding temperature is below the boiling point of Mg. Since it is set, the safety of the semi-sealed container 1 is sufficiently high. On the other hand, the melting chamber 7 is semi-sealed by the semi-sealing punch 5, and the convection of gas between the melting chamber 7 and the buffer cavity 6 can be greatly suppressed, so that the amount of evaporation of Mg to the outside is extremely small, There is also very little change in the melt composition. Furthermore, not only in the above heating and temperature maintenance, but also in the subsequent cooling, by continuously flowing Ar gas into the buffer cavity 6, external oxygen is mixed into the dissolution chamber 7 through the buffer cavity 6. Can be suppressed.

As described above, in the present embodiment, in the semi-sealed container 1, the gap between the inner surface of the container body 2 and the outer peripheral surface of the lid 3 is used as an outlet for releasing the gas and vapor generated in the buffer cavity 6. However, pores may be formed in the lid 3. Thereafter, the Mg ₂ Si melt is cooled (furnace cooled) to obtain a polycrystalline Mg ₂ Si ingot. Then, to prepare a _Mg 2 Si raw material powder using the _Mg 2 Si ingot grinding devices ball mill or the like.

Next, using the obtained Mg ₂ Si raw material powder, sintering is performed for a short time (for example, 5 minutes) by a discharge plasma sintering method, thereby producing a sintered body of the Mg ₂ Si compound semiconductor. As described above, according to the manufacturing method of the present embodiment, Mg ₂ Si ingots are produced using bulk Mg as a raw material, which is difficult to handle as compared with a manufacturing method using a conventional powder metallurgy method. Therefore, the production safety can be improved and the product cost can be greatly reduced.

Moreover, since it is not necessary to use a high-temperature and high-pressure-resistant heating device as compared with the manufacturing method using the conventional high-pressure melting method, the product cost can be reduced. Furthermore, compared with the manufacturing method using the conventional mechanical alloying method, since it is possible to prevent impurities from being mixed in the mixing process using the ball mill, a high-purity Mg ₂ Si ingot can be manufactured.

  Then, a semi-sealed container 1 having a dissolution chamber 7 capable of accommodating a raw material on the bottom side is used with a buffer cavity 6 that can be accommodated by introducing an inert gas to the atmosphere side. When heating and holding in the above-mentioned temperature range in an electric furnace (not shown), the inside of the buffer cavity 6 is replaced with an inert gas such as Ar, so there is no need to use a vacuum device, and the raw material is directly applied under atmospheric pressure. It can be dissolved and the product cost can be greatly reduced.

In addition, since a sintered body of Mg ₂ Si compound semiconductor is produced by short-time sintering of the discharge plasma sintering method using Mg ₂ Si raw material powder free of impurities, a dense Mg ₂ Si thermoelectric semiconductor is manufactured. And no cracks or macrosegregation occur in the sintered body.

  In the present embodiment, the semi-sealed container 1 in which the semi-sealed punch is disposed in the bottomed cylindrical container body 2 is used. However, the present invention is not limited to this, and the buffer cavity 6 is provided on the atmosphere side. If the dissolution chamber 7 is a semi-sealed container, another shape container may be used. Moreover, although the semi-sealed container 1 of the present invention has one buffer cavity 6, the present invention is not limited to this, and a container having two or more chambers may be configured.

Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.
(Manufacture of thermoelectric materials)
The Mg—Si based thermoelectric material according to the present invention is composed of Mg and Si and two kinds of dopant elements. In the manufacturing method of the thermoelectric material of the present embodiment, first, Mg _66.67-xy Si _33.33 Al _x Zn _y (x) is _placed in the melting chamber 7 of the semi-sealed container 1 having the buffer cavity 6 on the atmosphere side. The bulk Mg (99.5%, totalMg + Ca), the irregular particulate Si (99.9%), and the dopant powder raw material are accommodated so that + y = 0.21 to 2).

  In this example, the Si particles having a particle diameter in the range of 1 to 5 mm were used, but it is preferable to use a Si raw material having a small particle diameter in order to reduce the high temperature holding time. On the other hand, since the Mg raw material is sufficiently dissolved at the holding temperature, the shape and size of the raw material have little influence on the holding time. After the completion of the charging of the raw material, a semi-sealing punch 5 is arranged in the container body 2 and its opening is closed with a lid 3 having a gas introduction port 4. Ar is introduced from the port 4 as an inert gas, and the inside of the buffer cavity 6 is replaced with the inert gas during heating, holding and cooling.

Then, _Mg 2 Si melting point _{(Tm (Mg 2 Si):} 1358K) or at the boiling point of Mg (Tb (Mg): 1363K ) was heated to 1361K at the following temperatures and held for about two hours. In this heating and holding step, only Mg reaching the melting point is melted, and a reaction (liquid phase-solid phase reaction) as shown in the following chemical formula at the interface between molten Mg and Si in a solid state (non-solidified state) ) Proceeds, Mg ₂ Si melting is obtained.

2Mg (liquid phase) + Si (solid phase) → Mg ₂ Si (liquid phase)
As described above, in the heating and holding step, the gas and vapor generated in the melting chamber 7 escape to the outside through the gap between the inner surface of the container body 2 and the outer peripheral surface of the semi-sealing punch 5, but the heating and holding temperature is Mg. Therefore, the safety of the semi-sealed container 1 is sufficiently high. On the other hand, the melting chamber 7 is semi-sealed by the semi-sealing punch 5, and the convection of gas between the melting chamber 7 and the buffer cavity 6 can be greatly suppressed, so that the amount of evaporation of Mg to the outside is extremely small, There is also very little change in the melt composition.

Furthermore, not only in the above heating and temperature maintenance, but also in the subsequent cooling, by continuously flowing Ar gas into the buffer cavity 6 at a flow rate of 0.5 ml / min, external oxygen passes through the buffer cavity 6. Thus, mixing into the melting chamber 7 can be sufficiently suppressed. Thereafter, the Mg ₂ Si melt is cooled (furnace cooled) to obtain a polycrystalline Mg ₂ Si ingot. In the obtained Mg ₂ Si ingot, macrosegregation by visual observation was not recognized. Further, as a result of analyzing the Mg ₂ Si raw material powder by X-ray diffraction, the ingot has an almost simple Mg ₂ Si structure and very little unreacted Mg and Si.

Next, the obtained Mg ₂ Si ingot was pulverized with a planetary ball mill for 30 minutes to produce a Mg ₂ Si raw material powder. As a result of analyzing the raw material powder by X-ray diffraction, it was found that the ingot had a substantially simple Mg ₂ Si structure, and that there was very little unreacted Mg and Si. Then, using the Mg ₂ Si raw material powder, a dense sample of Mg ₂ Si compound semiconductor was produced in the atmosphere by a discharge plasma sintering method. The sintering temperature of Mg ₂ Si was 1293 K, the sintering load was 15 MPa, and the holding time was 5 minutes. The discharge plasma sintering method is a well-known sintering method that can bond and sinter composite materials and functional materials, and obtains a sintered body by heating by self-heating of the powder due to the discharge phenomenon. To do.

FIG. 2 is a photomicrograph showing the observation results of the crystal structure of the Mg ₂ Si sintered body with an optical microscope. As shown in the figure, it can be seen that the structure of the obtained sintered body is composed of coarse Mg ₂ Si crystals and fine Mg ₂ Si crystals. When polishing a sample for microscopic observation, coarse crystals were preferentially scraped off, and thus showed relatively low hardness. However, the hardness of a sintered body having a finer structure is considered to be higher than that of an ingot.

In the heating step in the present embodiment, sintering is performed in an air atmosphere, but a sintering process in another atmosphere (for example, a vacuum or an inert gas atmosphere) may be used. Further, according to the preliminary experimental results of the present invention, it is known that when the Mg ₂ Si raw material powder is used, the influence of the sintering atmosphere on the thermoelectric characteristics of the sintered body is small.
(Characteristics of thermoelectric material obtained in Examples)
3 to 7 show the electromotive force (α), conductivity (σ), output factor P, thermal conductivity (κ), and performance index (Mg) of the Mg ₂ Si-based sintered body produced by the production method of the present invention. Z) is an explanatory diagram showing isothermal characteristics. The horizontal axis in FIG. 3 is the temperature T, and the vertical axis is the electromotive force α, which shows the characteristics of the relationship between the temperature T and the electromotive force α of the thermoelectric material obtained by the manufacturing method of the above-described embodiment. The electromotive force α means an electromotive force obtained when a thermoelectric semiconductor material has a temperature difference of 1K. The electromotive force α of the conductive material of the present example shows a peak around a temperature of 700K. However, the electromotive force and conductivity are measured using a general-purpose specific resistance, Hall coefficient, and thermoelectric temperature-dependent simultaneous measurement system (for example, thermoelectric conversion system technology overview: issued by Realize Co., Ltd., p.33 (1995)), the thermal conductivity was measured by a laser flash method using a thermal constant measuring device TC7000Win manufactured by Vacuum Riko Co., Ltd.

  The horizontal axis in FIG. 4 is the temperature T, and the vertical axis is the electrical conductivity σ, which shows the characteristics of the relationship between the temperature and the electrical conductivity of the thermoelectric material obtained by the manufacturing method of the above-described embodiment. The electric conductivity σ of the thermoelectric material of this example shows high characteristics in a low temperature region. The horizontal axis in FIG. 5 is the temperature T, and the vertical axis is the output factor P, which shows the characteristics of the relationship between the temperature of the thermoelectric material and the output factor P obtained by the manufacturing method of the embodiment described above. The peak value is shown from the temperature 400K to the temperature 700K.

  The horizontal axis in FIG. 6 is the temperature T, and the vertical axis is the thermal conductivity κ, which shows the characteristics of the relationship between the temperature K and the thermal conductivity κ of the thermoelectric material obtained by the manufacturing method of the above-described embodiment. The thermal conductivity κ of the thermoelectric material of this example shows high characteristics in a low temperature range. The horizontal axis in FIG. 7 is the temperature T, and the vertical axis is the performance index Z, which shows the characteristics of the relationship between the temperature of the thermoelectric material obtained by the manufacturing method of the above-described embodiment and the performance index Z. The peak value is shown from the temperature 400K to the temperature 700K. The temperature range where the numerical value of the figure of merit Z is 0.5 or more indicates a temperature range of 450K to 750K, indicating that it can be used in a wide temperature range.

As described above, according to the present embodiment, in the semi-sealed container 1 in which the inert gas is replaced, the Mg and Si raw materials and the dopant elements (Al and Zn) such that Mg and Si are in an atomic ratio of 2: 1. Are heated, held, melted, and cooled to obtain an Mg ₂ Si ingot. The ingot is pulverized and sintered for a short time using a discharge plasma sintering method to obtain a dense Mg ₂ Si Semiconductors can be manufactured. In particular, in the manufacturing method described above, by adding Al and Zn as dopants, macrosegregation of the dopant element is suppressed, and as shown in FIGS. 3 to 7, N-type Mg ₂ Si having an excellent figure of merit. A base thermoelectric semiconductor can be manufactured.

FIG. 1 is a longitudinal sectional view showing the structure of a semi-sealed container used for manufacturing the thermoelectric material of this example. FIG. 2 is an explanatory diagram showing the observation results of the crystal structure of the Mg ₆₆ Si _33.33 Al _0.33 Zn _0.33 thermoelectric material sintered body produced in this example, using an optical microscope. FIG. 3 is an explanatory diagram showing the electromotive force (α) of the Mg ₆₆ Si _33.33 Al _0.33 Zn _0.33 thermoelectric material produced in this example. FIG. 4 is an explanatory diagram showing the electrical conductivity (σ) of the Mg ₆₆ Si _33.33 Al _0.33 Zn _0.33 thermoelectric material produced in this example. FIG. 5 is an explanatory diagram showing the output factor P, (α ² σ) of the Mg ₆₆ Si _33.33 Al _0.33 Zn _0.33 thermoelectric material produced in this example. FIG. 6 is an explanatory diagram showing the thermal conductivity (κ) of the Mg ₆₆ Si _33.33 Al _0.33 Zn _0.33 thermoelectric material produced in this example. FIG. 7 is an explanatory diagram showing the figure of merit (Z) of the Mg ₆₆ Si _33.33 Al _0.33 Zn _0.33 thermoelectric material produced in this example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semi-sealed container 2 ... Container main body 3 ... Cover body 4 ... Gas inlet 5 ... Semi-sealing punch 6 ... Buffer cavity 7 ... Dissolution chamber

Claims (5)

A thermoelectric material composed of an N-type thermoelectric semiconductor formed by adding Al and Zn as dopant elements to a Mg-Si based compound ,
The Mg-Si based compound, the atomic ratio of Mg and Si is 2: 1, the thermoelectric material, wherein the amount of the Al and Zn is 0.21at% ~2at%. In a melting chamber of a graphite container having a buffer cavity on the atmosphere side, massive Mg and Si forming a compound with Mg are accommodated, and Al and Zn are added in combination as dopant elements, and an inert gas is contained in the buffer cavity. In a state where the graphite vessel is substituted, the graphite container is maintained in a temperature range not lower than the melting point of the Mg ₂ Si compound and not higher than the boiling point of Mg for a certain period of time, thereby generating a compound melt or a combined financial liquid. A method for producing a thermoelectric material, characterized in that the liquid is cooled to produce an ingot, and the Mg ₂ Si raw material powder produced by pulverizing the ingot is sintered. In the manufacturing method of the thermoelectric material of Claim 2 ,
The graphite container is a container having a bottomed cylindrical body, and the buffer cavity is arranged in the graphite container and introduces an inert gas to the atmosphere side and accommodates it by a semi-sealing punch that divides the space of the container. And forming the melting chamber containing the Mg and Si, and the Al and Zn on the bottom side,
A method for producing a thermoelectric material, characterized in that a compound melt or a combined liquid of the thermoelectric material is prepared by heating and holding while blocking the atmosphere with the inert gas. In the manufacturing method of the thermoelectric material of Claim 2 ,
The sintering, and characterized in that the Mg 2 _Si raw material powder voltage and current is applied to a spark plasma sintering method of producing a sintered body by a discharge phenomenon occurring at the particle gap of the Mg 2 _Si raw material powder A method for manufacturing a thermoelectric material. In the manufacturing method of the thermoelectric material of Claim 3 ,
The method for producing a thermoelectric material, wherein the addition amount of Al and Zn is 0.21 at% to 2 at%.

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