JP2000261045A - Manufacture of thermoelectric conversion material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease thermal conductivity for making high performance, or enhancing the Seebeck coefficient by a method, wherein an added element to Si powder is coated in a vapor growth method, or a discharge plasma process, to form powder containing a predetermined amount of the annexed element in order to make a semiconductor, so as to sinter them. SOLUTION: An added element to Si powders is coated in a vapor growing method, such as a deposition or the like, or a discharge plasma process, to form powders containing sole or composite annexed element of 0.001 atom% to 20 atom% in order to make a P-type on N-type semiconductor, so as to sinter them, thereby obtaining a thermoelectric conversion material composed of a sintered composition having a structure forming rich in the added element in the grain boundary of a Si-rich phase in which Si is a main body. Namely, with the structure forming rich phase of the annexed element in the grain boundary of the Si-rich phase, the annexed element is condensed into a crystal grain boundary, and conduction of carrier is increased therein, and a high Seebeck coefficient in the Si-rich phase in the crystalline grains can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a novel thermoelectric conversion material composed of a sintered body having a variety of additional element is contained 20 atomic% or less Si, or vapor phase growth deposition on Si powder, GeH ₄
Plasma treatment with gas is used to obtain a Si-based material powder of the required composition, which is sintered to form a structure in which the rich phase of the added element is dispersed at the grain boundaries of the Si-rich phase, so that the Seebeck coefficient is extremely high. Polycrystalline Si-based thermoelectric conversion made of sintered body characterized by large size, low thermal conductivity, remarkable increase in thermoelectric conversion efficiency, and characterized by extremely low environmental pollution with mainly Si rich in resources About the material.

[0002]

2. Description of the Related Art Thermoelectric conversion elements are devices that are expected to be put to practical use from the viewpoint of effective use of thermal energy, which is required in recent industries. For example, thermoelectric conversion elements convert waste heat into electric energy. A very wide range of applications are being studied, such as systems, small portable generators for easily obtaining electricity outdoors, and flame sensors for gas appliances.

[0003] The conversion efficiency from heat energy to electric energy is a function of the figure of merit ZT, and increases as ZT increases. This figure of merit ZT is expressed as in equation (1). ZT = α ² σT / κ (1) where α is the Seebeck coefficient of the thermoelectric material, σ is the electrical conductivity, κ is the thermal conductivity, and T is the high-temperature side (T _H ) and low-temperature side ( It is the absolute temperature represented by the average value of T _L ).

[0004] FeSi, a thermoelectric conversion material known so far,
₂ , silicides such as SiGe are abundant in resources, but the former has a figure of merit (ZT) of 0.2 or less, its conversion efficiency is low and the operating temperature range is very narrow, and the latter contains Ge which is poor in resources. If the amount is not about 20 to 30 at%, no decrease in heat conduction is observed, and Si and Ge have a wide range of liquid-solid and solid-phase lines of totally controlled solid solution, dissolution and ZL method (Zone-Leveling ) Is not widely used because it is difficult to produce a uniform composition and it is difficult to industrialize.

At present, chalcogen-based compounds such as BiTe and PbTe, such as IrSb ₃ having a skutterudite-type crystal structure exhibiting the highest figure of merit, are known to have high-efficiency thermoelectric conversion capabilities. From the viewpoint of environmental protection, it is expected that the use of these heavy metal elements will be regulated in the future.

[0006]

On the other hand, while Si has a high Seebeck coefficient, it has a very high thermal conductivity,
It is not considered suitable for high-efficiency thermoelectric materials, and the study of its thermoelectric properties has been limited to Si with a carrier concentration of 10 ¹⁸ (Mm ³ ) or less.

[0007] However, the inventors have found that adding various elements to Si alone, for example, adding a small amount of a group 3 or 5 element and a small amount of Ge to Si can lower the thermal conductivity. It is possible to find that the Seebeck coefficient is equal to or higher than that of conventionally known Si-Ge and Fe-Si systems, or that it is extremely high at a given carrier concentration, impairing the essential advantages of Si alone. Instead, it was found that the thermoelectric conversion material exhibited a large figure of merit and could be improved in performance.

[0008] The inventors have also added various elements to Si to add P
As a result of investigating the relationship between the amount of addition and the thermoelectric properties, the Seebeck coefficient decreased with the increase of the carrier up to the addition amount, that is, the carrier concentration of 10 ¹⁸ (M / m ³ ). , 10 ¹⁸ to 10 ¹⁹ (M / m ³ ).

[0009] The present invention is based on this novel Si which the inventors have found.
The object is to have a high Seebeck coefficient possessed by a system thermoelectric conversion material, to further lower the thermal conductivity without deteriorating the electric conductivity, to improve the performance, or to further improve the Seebeck coefficient.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies on the mechanism of obtaining a high Seebeck coefficient in a Si-based thermoelectric conversion material to which various additive elements are added.
It has been found that this novel Si-based material has a structure in which a rich phase of the additive element is formed at a grain boundary of a Si-rich phase mainly composed of Si.

The inventors further studied the crystal structure. As a result, the increase in the Seebeck coefficient was caused by the addition of the added element at the crystal grain boundaries, which increased the carrier conduction. It was found that a high Seebeck coefficient was obtained in the rich phase.

[0012] Then, the inventors examined the control of the crystal structure other than the component system as a method of keeping the Seebeck coefficient high and lowering the thermal conductivity. The raw material is pulverized, and the pulverized powder is formed and sintered by, for example, hot pressing or plasma sintering, so that the crystal grain size can be reduced to 1 to 50 μm, and a Si-rich phase and an additive element-rich phase are required in the material. It has been found that a material having a structure dispersed in the arrangement and having a high figure of merit can be obtained.

[0013] Further, the inventor has proposed a method of obtaining a Si-based powder for sintering by vapor phase growth such as vapor deposition, sputtering, CVD or discharge plasma treatment on Si powder or Si powder containing an additive element to Si. The additional element for coating the additional element by plasma treatment using a gas containing the additional element, or for embedding the additional element by mechanofusion treatment to form a P-type or N-type semiconductor 0.001 atom% to 20 atoms in single or compound
% To obtain a thermoelectric conversion material consisting of a sintered body having a structure in which a rich phase of the additive element is formed at a grain boundary of a Si-rich phase mainly composed of Si. The inventors have found that the present invention can be performed, and have completed the present invention.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the thermoelectric conversion material according to the present invention, in which a rich phase of the additive element is formed at a grain boundary of a Si-rich phase mainly composed of Si, will be described.
Various amounts of Ge (4N) added to high-purity Si (10N) were varied to produce a melt of Si _1-x Ge _x (at%) by arc melting, and the cooling rate after the melting was 50 K / sec to 200 K /. A sample substrate was prepared by rapid cooling with sec and the crystal structure was observed by EPMA.When x = 0.03, as shown in Fig. Is the main Si-rich phase, the white part in the photograph is the rich phase of the additive element Ge, and it can be seen that the structure is such that the Ge-rich phase is dispersed or formed at the grain boundaries of the Si-rich phase.

[0015] In addition, although a small amount of P was doped into the above _- mentioned Si _1-x Ge _x molten metal, only this P was observed.
As shown in B, the white portion indicates the location of the doped P, and it can be seen that P is segregated at the same position as the grain boundary of the Si-rich phase where the Ge-rich phase shown in FIG. 1A was formed.

[0016] In short, the structure of the thermoelectric conversion material according to the present invention is, as shown in the schematic diagram of FIG. 2, only Si or an Si-rich phase containing an additive element but mostly Si, This is a structure in which an additive element-rich phase in which an additive element segregates at the grain boundary of the Si-rich phase.

The sample was cooled at a cooling rate of 50 K / sec after melting to prepare a sample substrate.
30 μm powder, Si _1-x Ge _x (at%) powder coated with additional elements by discharge plasma treatment, and
Observation by EPMA of the crystal structure of the sample obtained by sintering at 250-1350 ° C showed that it had the same structure as in Fig. 1 due to melt solidification, and that the size of the Si-rich phase was relatively small, 10-100 μm. It was confirmed.

Further, when the relationship between the precipitation of added elements of P and B instead of Ge at the crystal grain boundaries and the carrier concentration of n-type and p-type Si was investigated, the correlation between the added amount and the carrier concentration was found to be one. It was confirmed that the additive element was agglomerated at the crystal grain boundary by the structure in which the rich phase of the additional element was formed at the grain boundary of the Si-rich phase, where the carrier conduction was increased and the It was confirmed that a high Seebeck coefficient can be obtained in the Si-rich phase.

Further, the thermal conductivity of this Si-based thermoelectric conversion material is:
It was confirmed that it decreased as the carrier concentration increased. This is considered to be because κ _ph decreased due to scattering of localized phonons of impurities due to the added element in the crystal.

[0020] It is a feature of the Si-based thermoelectric conversion material composed of a sintered body.
A structure in which a rich phase of an additional element such as Ge is dispersed and formed at a grain boundary of a Si-rich phase is formed due to the deflection of the additional element attached to or inside the raw material powder particles during sintering. It is also effective to make the crystal structure of the sintering powder itself the same as that obtained by controlling the cooling rate after smelting. Moderate segregation of additional elements other than Si occurs in the field, resulting in materials and powders that exhibit a high Seebeck coefficient despite high electrical conductivity. The bending of the added element at the time becomes easier and more effective, and a sintered Si-based thermoelectric conversion material having a high Seebeck coefficient can be obtained.

In the present invention, even if the raw material powder has a small amount of additional elements other than Si at the crystal grain boundaries as described above, the required deviation occurs during sintering to obtain the desired structure. Therefore, the cooling rate of the Si-based melting material is not particularly limited.

[0022] In the present invention, as a cooling method for obtaining Si or Si-based powder, a method of cooling in an ingot, or a method of cooling while pulling up, for example, a CZ method for obtaining a known single crystal silicon, Using the FZ method, a method of pulling and cooling under conditions that can obtain polycrystalline silicon can be adopted. Further, it can be manufactured by the ZL method described above.

Further, the cooling rate is adjusted so that a thin plate having a required thickness can be obtained by using a method of producing a thinner plate by pouring the Si-based molten material into a shallow plate and cooling it, or a roll cooling method such as a known melt quenching method. And any other method can be adopted.

Further, in order to obtain Si or Si-based powder, a ribbon can be produced by a roll cooling method such as melt quenching or the like and powdered, or a powder can be directly obtained by a spraying method such as gas atomization. Also, the crystal grain size can be made as fine as 1 to 50 μm, and the thermal conductivity can be reduced.

According to the present invention, only Si or a required composition is obtained.
Si-based raw materials are melted by the arc melting method or high-frequency melting method.
Insufficient additional elements are adhered to the surface of Si or Si-based powder particles, and this is sintered to obtain the required composition and Si as shown in FIG.
This is to obtain a structure in which the additive element rich phase is dispersed and formed at the grain boundaries of the rich phase.

The method of coating the surface of the Si powder or the Si powder containing the additive element with the additive element includes a known vapor deposition method such as vapor deposition, sputtering, and CVD, a discharge plasma treatment method, and a method including the additive element. Any growth, film formation, fixation, and adhesion means such as a plasma treatment method using a gas can be employed, and a method of embedding an additional element on the surface of Si powder by mechanofusion treatment can also be employed.

[0027] In the present invention, the coating of the additive element means from complete film formation on the surface of the Si particle to a state in which the additive element particle is simply attached to the surface of the Si particle. In other words, even if not complete, it is sufficient that the additive element particles adhere to the surface of the Si particles until the sintering process, and as described later, any of the additional elements can be added. From the case where the means to be selected is selectable, various cases such as limitation are assumed, and further, the processing conditions of the means selected according to the element to be combined in the case of composite addition are variously varied, so that depending on the intended composition, It is necessary to appropriately select the above means and conditions.

[0028] For example, the example shown in FIG.
An additive element is fixed on the Si grain surface of a Si plate obtained by pulverizing a thin plate to a predetermined particle size or a Si powder directly obtained by a spraying method. The fixing amount may be appropriately selected so that the desired composition is obtained after sintering. In addition, the same treatment can be applied to a Si-based particle in which a required additive element is contained in the Si particle itself. By sintering using Si powder consisting of Si particles having such required additive elements fixed to the surface,
A structure in which the additive element-rich phase is dispersed and formed at the grain boundary of the Si-rich phase shown in FIG. 2 can be obtained.

In the example shown in FIG. 3B, an additional element is buried in the surface of the Si grain by mechanofusion treatment to make the Si grain into a Si-rich grain, and the required additional element is buried in the surface.
By sintering using Si-rich powder composed of Si-rich grains, a structure in which the additive element-rich phase is dispersed and formed at the grain boundary of the Si-rich phase shown in FIG. 2 can be obtained.

In the present invention, any sintering method may be used as long as it can be fired at about 1200 to 1350 ° C. near the melting point of Si. Known sintering means such as hot pressing and spark plasma sintering can be appropriately selected. Depending on the selected sintering means, suitable conditions for maintaining the temperature in a vacuum or an inert gas atmosphere at a temperature of 1200 to 1350 ° C. and a sintering time of 0.5 hour or more may be appropriately selected.

[0031] The thermoelectric conversion material according to the present invention is obtained by sintering.
By forming a structure in which various impurities are added to a polycrystalline Si semiconductor having a diamond-type crystal structure and adjusting the carrier concentration, the Seebeck coefficient can be reduced by lowering the electric resistance without impairing the intrinsic advantages of Si alone. It is a high-efficiency Si-based thermoelectric conversion material of P-type semiconductor and N-type semiconductor that has dramatically improved its figure of merit by improving its performance index.

Here, considering the application of the thermoelectric conversion material, the Seebeck coefficient, the electric conductivity, the thermal conductivity, etc. may be varied depending on the conditions such as the heat source, the place of use, the form, the current to be handled, and the magnitude of the voltage. Although it is necessary to place emphasis on any of the characteristics, in the thermoelectric conversion material of the present invention, the carrier concentration can be selected by the addition amount of the selected element.

For example, a P-type semiconductor having a carrier concentration of 10 ¹⁷ to 10 ²⁰ (M / m ³ ) containing 0.001 atomic% to 0.5 atomic% of the above-mentioned additive element α alone or in combination is obtained. And
A P-type semiconductor having a carrier concentration of 10 ¹⁹ to 10 ²¹ (M / m ³ ) containing 0.5 to 5.0 atomic% of the additional element α is obtained.

Similarly, an N-type semiconductor containing 0.001 atomic% to 0.5 atomic% of the aforementioned additive element β alone or in combination and having a carrier concentration of 10 ¹⁷ to 10 ²⁰ (M / m ³ ) is Obtained and also
An N-type semiconductor containing 0.5 to 10 atomic% of the additive element β and having a carrier concentration of 10 ¹⁹ to 10 ²¹ (M / m ³ ) is obtained.

When the additive element α or the additive element β is contained and 0.5 to 5.0 atomic% is added so that the carrier concentration becomes 10 ¹⁹ to 10 ²¹ (M / m ³ ), a highly efficient thermoelectric Although the conversion element is obtained and has excellent thermoelectric conversion efficiency, its thermal conductivity is about 50 to 150 W / mK at room temperature, and if the thermal conductivity can be reduced, the figure of merit ZT is further improved. I can expect that.

Generally, the thermal conductivity of a solid is given by the sum of phonon conduction and carrier conduction. In the case of a Si-based semiconductor thermoelectric conversion material, phonon conduction is dominant because the carrier concentration is low. Therefore, in order to reduce the thermal conductivity, it is necessary to increase the absorption or scattering of phonons. In order to increase the absorption or scattering of phonons, it is effective to disturb the regularity of the crystal grain size and the crystal structure.

At least one of a Group 3 element and a Group 5 element is added to Si.
By adding the seeds one by one and controlling the carrier concentration to 10 ¹⁹ to 10 ²¹ (M / m ³ ), it is possible to disturb the crystal structure without changing the carrier concentration in Si, and to increase the thermal conductivity by 30%. ~ 90
% At room temperature to 150 W / m · K or less, and a highly efficient thermoelectric conversion material can be obtained.

[0038] In the thermoelectric conversion material having the above structure, a P-type semiconductor is obtained when the Group 3 element is contained in an amount of 0.3 to 5 atomic% more than the Group 5 element, and the Group 5 element is contained in an amount of 0.3 to 5 atomic% than the Group 3 element. If a large amount is contained, an N-type semiconductor can be obtained.

Further, it was examined whether a reduction in thermal conductivity could be achieved with elements other than Group 3 elements and Group 5 elements, and it was found that adding a Group 3-5 compound semiconductor or Group 2-6 compound semiconductor to Si further
By adding at least one of a Group 3 element or a Group 5 element and controlling the carrier concentration to 10 ¹⁹ to 10 ²¹ (M / m ³ ),
The crystal structure can be disturbed without changing the carrier concentration in Si, the thermal conductivity can be reduced to 150 W / mK or less at room temperature, and a highly efficient thermoelectric conversion material can be obtained.

Further, as a result of various studies on other additional elements to Si, it was found that Si contained a Group 4 element of Ge, C, and Sn in an amount of 0.1 to 5 atomic%,
By substituting a part of the element i with a group 4 element with a different atomic weight, the scattering of phonons in the crystal increases,
Reduces the thermal conductivity of semiconductors by 20 to 90%, 150 W / mK at room temperature
It is possible to make
A thermoelectric conversion material containing a P-type semiconductor by containing 5.05.0 at% and a N-type semiconductor containing a Group V element by 0.1 to 10 at% can be obtained.

In the thermoelectric conversion material of the present invention, it was investigated whether elements other than the above-mentioned Group 3 elements and Group 5 elements can be added to Si in the same manner. For example, although there is no particular limitation, if an element having a very different ionic radius is added, most of the element is precipitated in the grain boundary phase. As an additive element α for forming, and as an additional element β for forming an N-type semiconductor,
It has been confirmed that the single or combined addition of the following groups of elements is particularly effective.

As the additional element α, the additional element A (Be, Mg, Ca, Sr,
Ba, Zn, Cd, Hg, B, Al, Ga, In, Tl), transition metal element M ₁ (M ₁ ; Y, M
o, Zr), and the additive element β is the additive element B
(N, P, As, Sb, Bi, O, S, Se, Te), transition metal element M ₂ (M ₂ ; Ti, V, C
r, Mn, Fe, Co, Ni, Cu, Nb, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, P
t, Au, where Fe is 10 atomic% or less), rare earth element RE (RE; La, Ce,
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu).

Further, the additive element α for forming a P-type semiconductor and the additional element β for forming an N-type semiconductor contain at least one kind from each group in a total amount of 0.002 to 20 atomic%, for example, In order to obtain a P-type semiconductor, the combination of each group can be arbitrarily selected as long as the total amount of the additional element α exceeds that of the additional element β and is contained in a necessary amount to become a P-type semiconductor.

[0044]

Example 1 In order to prepare mother particles of P-type and N-type Si thermoelectric conversion semiconductors, high-purity Si (10N) and additive elements were blended as shown in Table 1, and then a graphite crucible was used. And vacuum melted in a high frequency melting furnace. After melting, it was cast into a mold having a thickness of 10 mm, and then the ingot was crushed and then crushed by a stamp mill and a ball mill to an average particle size of 10 to 50 μm. The ball mill used a wet xylene solvent. The pulverized powder (base particles) was inserted into a vacuum chamber of 10 ⁻³ Torr, and the surface was coated with an element shown in Table 1 (film thickness: 10 to 100 μm).

The obtained powder was subjected to 1325K × 1 hour, 1000 kgf / cm ² , A
Hot pressing was performed in r to obtain a sintered body. 5 samples of sintered body
It was cut into a shape of × 5 × 15 mm, 10 × 10 × 2 mm, and an outer diameter of 10 × 2 mm, and the Seebeck coefficient, the Hall coefficient (including the carrier concentration and the electric conductivity), and the thermal conductivity were measured. 1
Table 2 shows the measured values at 100 K and the figure of merit (ZT = S ² T / ρκ).

The Seebeck coefficient is set as a value obtained by setting the temperature difference between the high temperature part and the low temperature part to about 6 K while raising the temperature, measuring the thermoelectromotive force of the sample with a digital multimeter, and dividing by the temperature difference. I asked. The Hall coefficient was measured by an AC method, and the electrical resistance was measured by a four-terminal method simultaneously with the carrier concentration. The thermal conductivity was measured by a laser flash method.

Example 2 In order to prepare mother particles of P-type and N-type Si thermoelectric conversion semiconductors, high-purity Si (10N) and additive elements were blended as shown in Table 3, and then the graphite crucible was used. Vacuum melting was performed in a high frequency melting furnace. After melting, it was cast into a 10 mm thick mold to obtain a plate-like ingot. Thereafter, the ingot was pulverized, and further pulverized with a stamp mill and a jet mill to an average particle size of 1 to 10 μm. The jet mill used N ₂ gas at a pressure of 7 kgf / mm ² .

[0048] The obtained powder ((base particles) is put into a chamber, and plasma-treated with SiH ₄ gas or GeH ₄ gas to obtain a powder.
B, Al, Ga, P, As, and Sb were coated.

[0049] The coated raw material powder is 5 x 5 x 15 mm, 10
It was compression molded under a pressure of 2000 kgf / cm ² into a shape of × 10 × 2 mm and an outer diameter of 10 × 2 mm, and sintered in vacuum at 1325 K × 5 hours. The Seebeck coefficient, the Hall coefficient (including the carrier concentration and the electrical conductivity), and the thermal conductivity of the sintered body were measured by the same measurement methods as in Example 1. Measured value at 1100K and figure of merit (ZT = S
² T / ρκ) is shown in Table 4.

Example 3 In order to prepare base particles of P-type and N-type Si thermoelectric conversion semiconductors, high-purity Si (10N) and additive elements were blended as shown in Table 5, and then a graphite crucible was used. Vacuum melting was performed in a high frequency melting furnace. After melting, it was cast into a 10 mm thick mold to obtain a plate-like ingot. Thereafter, the ingot was pulverized, and further pulverized with a stamp mill and a ball mill to an average particle size of 10 to 50 μm. The ball mill used a wet xylene solvent.

Further, in order to produce child particles to be coated around Si, high-purity Si (10N) and additive elements were blended as shown in Table 5, and then vacuum melted in a high-frequency melting furnace using a graphite crucible. did. The melt was discharged from a nozzle having an inner diameter of 3 mm, and the melt was quenched by blowing Ar gas at 30 kgf / cm ³ to have an average particle diameter of 30 to 100 μm. The obtained mother particles were coated with child particles by mechanofusion so that the child particles had a predetermined weight ratio.

The coated raw material powder was subjected to spark plasma sintering in an Ar atmosphere. The sintering conditions were 1325K × 3 minutes. The sintered sample is 5 × 5 × 15mm, 10 × 10 × 2mm, outer diameter 1
Cut into a shape of 0 x 2 mm, each Seebeck coefficient, Hall coefficient (including carrier concentration and electric conductivity),
The thermal conductivity was measured by the same measuring method as in Example 1. Table 6 shows the measured values at 1100K and the figure of merit (ZT = S ² T / ρκ).

[0053]

【table 1】

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

[0059]

The thermoelectric conversion material according to the present invention comprises
Si is excellent in terms of global environment, global resources and safety, and it is very convenient as a thermoelectric conversion element for automobiles due to its small specific gravity and light weight.Since bulk Si has excellent corrosion resistance Another advantage is that no surface treatment or the like is required.

[0060] Since the thermoelectric conversion material according to the present invention mainly uses Si, it is less expensive than a Si-Ge material containing a large amount of expensive Ge, and a higher figure of merit can be obtained than an Fe-Si material. . Further, since Si used in the present invention has much lower purity than semiconductor devices, the raw material can be obtained relatively inexpensively, and an inexpensive thermoelectric conversion material with good productivity and stable quality can be obtained.

The thermoelectric conversion material according to the present invention makes use of the characteristics of Si having a large Seebeck coefficient and a small electric resistance where the carrier concentration is high, and greatly reduces the defect of a large thermal conductivity, and has a large figure of merit. Is an effective way to get Further, there is an advantage that the physical property value can be controlled by the type and amount of the added element.

[Brief description of the drawings]

FIG. 1 shows the EPMA crystal structure of the thermoelectric conversion material according to the present invention.
In the photograph observed by A, A shows the deflection of the additional element Ge, and B shows the deflection of the additional element P.

FIG. 2 is a schematic explanatory view showing a crystal structure of a thermoelectric conversion material according to the present invention.

FIG. 3 is a schematic explanatory view showing a state of Si grains of the thermoelectric conversion material powder according to the present invention, wherein A shows a case where an additive element is embedded on the surface, and B shows a case where the additive element is embedded.

Claims (4)

[Claims] Claims: 1. An additive element for forming Si into a P-type and / or N-type semiconductor by coating a Si powder with a vapor-phase growth method or a discharge plasma treatment to form a P-type and / or N-type semiconductor. Alone or in a composite to form a Si powder containing 0.001 at% to 20 at%, sintering the same, and forming a structure in which the rich phase of the additional element is formed at the grain boundary of the Si-rich phase mainly composed of Si. A method for producing a thermoelectric conversion material for obtaining a sintered body having the same. 2. The method according to claim 1, wherein the Si powder itself is P-type or N-type.
A method for producing a thermoelectric conversion material containing an additional element for forming a mold semiconductor. 3. A plasma treatment using a gas containing an additive element for forming a Si or P-type or N-type semiconductor in a Si powder containing an additional element for forming a P-type or N-type semiconductor in Si. , Si or an additive element for forming a P-type or N-type semiconductor and coating the additive element for forming a P-type or N-type semiconductor singly or in combination with a Si powder containing 0.001 at% to 20 at%. And sintering the same to obtain a sintered body having a structure in which a rich phase of the additive element is formed at a grain boundary of a Si-rich phase mainly composed of Si. 4. An Si powder or an Si powder containing an additive element for forming a P-type or N-type semiconductor in Si is embedded with an additive element for forming Si or a P-type or N-type semiconductor by mechanofusion treatment. , S containing 0.001 atomic% to 20 atomic% of additional elements alone or in combination to form a P-type or N-type semiconductor
i. A method for producing a thermoelectric conversion material in which a powder is formed and sintered to obtain a sintered body having a structure in which a rich phase of the additive element is formed at a grain boundary of a Si-rich phase mainly composed of Si.