JP7028076B2 - Manufacturing method of p-type thermoelectric conversion material, thermoelectric conversion module and p-type thermoelectric conversion material - Google Patents

Description

The present invention relates to a p-type thermoelectric conversion material, a thermoelectric conversion module, and a method for manufacturing a p-type thermoelectric conversion material.

A thermoelectric conversion module is known as a technique for converting exhaust heat energy into electric power, and in particular, Fe-V is a typical thermoelectric conversion material applicable to exhaust heat recovery in a temperature range of 300 ° C. or lower. -Al-based full-Wheeler alloys and Bi-Te-based semiconductors can be mentioned. Among them, Fe—V—Al-based full-Wheeler alloys are known as materials having lower toxicity and less environmental load than Bi—Te-based semiconductors.

Generally, a thermoelectric conversion module is configured by combining an n-type thermoelectric conversion material and a p-type thermoelectric conversion material. Therefore, in order to obtain high thermoelectric conversion characteristics in the thermoelectric conversion module, it is required to obtain a high figure of merit ZT in both n-type and p-type. At present, the figure of merit ZT of the p-type thermoelectric conversion material is lower than that of the n-type, so improvement of the value is required.

In Patent Document 1, it can be produced by using only a material containing Fe (iron), Ti (titanium), and Si (silicon), which has a low toxicity and a large reserve without using a high-cost element such as Te, and is high. A Fe—Ti—Si based full-Whisler alloy has been proposed as a thermoelectric conversion material capable of obtaining a performance index ZT.
Further, in Patent Document 2, the thermoelectric material particles are dispersed in the binder resin, and the thermoelectric material having metal fine particles formed on the surface of the thermoelectric material particles is formed into a flexible and thin material while maintaining the thermoelectric characteristics. Technology has been proposed.

International Publication No. 2016/185852 Special Table 2012-523121 Gazette

In Patent Document 1, in a Fe—Ti—Si based full-Whisler alloy having a composition ratio centered on Fe: Ti: Si = 2: 1: 1, the n-type and ZT have a maximum thermoelectric conversion characteristic of 0.98. Although the thermoelectric conversion material to be possessed is described, there is no disclosure that such a high ZT can be obtained for the p-type thermoelectric conversion material.

Patent Document 2 discloses a technique in which ZT is improved as compared with before compounding by using a thermoelectric conversion material in which thermoelectric conversion material particles and metal fine particles are composited in a binder. In this technique, since it is molded with a binder without using a sintering method, the electrical resistivity is very high, the ZT is 0.0001 at the maximum, and sufficient thermoelectric conversion characteristics cannot be obtained.

Therefore, an object of the present invention is to provide a p-type thermoelectric conversion material, a thermoelectric conversion module, and a method for manufacturing a p-type thermoelectric conversion material, which can obtain high thermoelectric conversion characteristics.

The p-type thermoelectric conversion material according to one aspect of the present invention contains a matrix phase which is a Fe—Ti—Si based full-Whisler alloy and a second phase M, and the second phase M is dispersed in the matrix phase. The average particle size of the second phase M is smaller than the average particle size of the parent phase and is 50 nm or less, and the content x of the second phase M is 0 at% <x <2.5 at%.

The thermoelectric conversion module according to one aspect of the present invention is a thermoelectric conversion module having a plurality of thermoelectric conversion elements and electrodes for electrically connecting the thermoelectric conversion elements, and the thermoelectric conversion element is a p-type thermoelectric conversion element. The p-type thermoelectric conversion element includes a conversion element and an n-type thermoelectric conversion element connected to the p-type thermoelectric conversion element. The second phase M is dispersed in the mother phase, and the average particle size of the second phase M is smaller than the average particle size of the mother phase and is 50 nm or less, and the second phase. The content x of M is 0 at% <x <2.5 at%.

The method for producing a p-type thermoelectric conversion material according to one aspect of the present invention mixes Fe raw material powder, Ti raw material powder, Si raw material powder, and M raw material powder to produce a mixture containing Fe, Ti, Si, and M. A step, a step of amorphizing Fe, Ti, and Si in the mixture to form an alloy in which M is dispersed in an Fe—Ti—Si based amorphous alloy while maintaining the crystal structure of M, and the alloy. Is to be heated to produce a p-type thermoelectric conversion material of a thermoelectric conversion material.

Here, the thermoelectric conversion material contains a matrix phase which is a Fe—Ti—Si based full-Whisler alloy and a second phase M, and the second phase M is dispersed in the matrix phase, and the second phase M The average particle size of the second phase M is smaller than the average particle size of the parent phase and is 50 nm or less, and the content x of the second phase M is 0 at% <x <2.5 at%.

According to the present invention, it is possible to realize a p-type thermoelectric conversion material, a thermoelectric conversion module, and a method for manufacturing a p-type thermoelectric conversion material that can obtain high thermoelectric conversion characteristics.

It is a flowchart explaining the procedure of the manufacturing method of the p-type thermoelectric conversion material which concerns on Example. It is a schematic diagram which shows the structure of the thermoelectric conversion module which concerns on Example. It is a figure which shows the X-ray diffraction pattern in a sample 5. It is a figure which shows the TEM-EDX image in the sample 5. It is a graph which shows the relationship between the amount of W and the thermal conductivity κ in the p-type thermoelectric conversion material. It is a graph which shows the relationship between the amount of W and the figure of merit ZT in a p-type thermoelectric conversion material.

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the drawings.
The p-type thermoelectric conversion material according to the present invention uses a Fe—Ti—Si based full-Whisler alloy as a parent phase. The full-Whisler alloy is represented by the general formula E1 ₂ E2 E3. The present invention is a p-type thermoelectric conversion material using a Fe—Ti—Si based full-Whisler alloy having a full-Whisler structure mainly using Fe element in E1, Ti element in E2, and Si element in E3 as a parent phase. These E1, E2, and E3 elements may be replaced with other elements to the extent that the composition of each element does not exceed half, and the Fe—Ti—Si based full-Whisler alloy includes these elements. Fe—Ti—Si based full-Whisler alloys are non-toxic, inexpensive, composed only of elements with large reserves, and have a small environmental load. As described above, the Fe—Ti—Si based full-Whisler alloy can conventionally have a sufficiently large thermoelectric conversion characteristic in the n-type, but the present invention also has a sufficiently large thermoelectric conversion characteristic in the p-type. It makes it possible.

As a result of the study by the present inventors, it is a thermoelectric conversion material containing a Fe—Ti—Si based full-Whisler alloy as a matrix phase and a matrix phase and a second phase M, and the second phase M is dispersed in the matrix phase. The average particle size of the second phase M is smaller than the average particle size of the parent phase and is 50 nm or less, and the content x of the second phase M is 0 at% <x <2.5 at%. In terms of materials, it has been found that high thermoelectric conversion performance can be obtained even with p-type thermoelectric conversion materials. The average particle size was determined by analyzing the X-ray diffraction pattern of the sample using Scherrer's equation represented by the following equation [Equation 1].

[Number 1]
L = Kλ / βcosθ

In [Equation 1], L is the average particle size, K is a constant of 0.94, λ is the wavelength of the X-ray, β is the half width of the diffraction peak, and θ is the diffraction angle. The Fe—Ti—Si based full-Whisler alloy can have high thermoelectric conversion characteristics even if the composition ratio deviates from Fe: Ti: Si = 2: 1: 1. This is not limited to the case where the thermoelectric conversion material is p-type, and the same applies even when the thermoelectric conversion material is n-type.

The maximum output of the thermoelectric conversion module depends on the dimensionless figure of merit ZT of the thermoelectric conversion material. Therefore, the performance of the thermoelectric conversion material is evaluated by the dimensionless figure of merit ZT of the following equation [Equation 2].

[Number 2]
ZT = (S ² / ρκ) T

In the following, the "dimensionless figure of merit ZT" is simply referred to as "figure of merit ZT". In [Equation 2], S is the Seebeck coefficient, ρ is the electrical resistivity, κ is the thermal conductivity, and T is the temperature. Therefore, in order to improve the maximum output P of the thermoelectric conversion module, it is desirable to increase the Seebeck coefficient S of the thermoelectric conversion material, decrease the electrical resistivity ρ, and decrease the thermal conductivity κ.

In the Fe—Ti—Si based full-Whisler alloy, by substituting a part of Si having a valence electron number of 4 with Al having a valence electron number of 3, the number of valence electrons of the entire thermoelectric conversion material is reduced and becomes a carrier. The holes are doped. When the total valence electron number VEC per unit cell of the full-Whisler alloy is 23.8 or more and 24.1 or less, a high figure of merit ZT can be obtained in the p-type thermoelectric conversion material.

Further, it is a thermoelectric conversion material containing a Fe—Ti—Si based full-Whisler alloy as a matrix phase and a matrix phase and a second phase M. The second phase M is dispersed in the matrix phase, and the second phase M The average particle size of the mother phase is smaller than the average particle size of the parent phase and is 50 nm or less. Here, "dispersion" means that the second phase M is separated from the crystal structure of the Fe—Ti—Si based full-Whisler alloy, and the distribution state and density are different from the distribution state and density of the alloy crystals. It is used in a broad sense to the extent that it exists in an alloy.

In such a Fe—Ti—Si based full-Whisler alloy in which the second phase M is dispersed, the parent phase is compared with the single phase of the conventional Fe—Ti—Si based full-Whisler alloy that does not contain the second phase M. Since phonons having a short mean free path are scattered at the interface between the phase 2 and the phase M, energy propagation by the lattice is suppressed. This suppresses heat conduction in the thermoelectric conversion material. Further, as will be described later, the electrical conductivity is also ensured by obtaining the sintered body. Due to these effects, the figure of merit ZT of the p-type thermoelectric conversion material can be increased.

In such a Fe—Ti—Si based full-Whisler alloy in which the second phase M is dispersed, when the mean particle size of the second phase M is larger than the mean particle size of the mother phase, the average of phonons scattered by the mother phase Since phonons having a mean free path shorter than the free path are not scattered at the interface between the parent phase and the second phase M, the thermal conductivity of the thermoelectric conversion material does not decrease sufficiently, and it becomes difficult to obtain a high performance index ZT. Even when the average particle size of the second phase M is smaller than the average particle size of the parent phase and exceeds 50 nm, phonons having a short mean free path are not effectively scattered, so that the thermal conductivity of the thermoelectric conversion material is high. It does not drop sufficiently, making it difficult to obtain a high performance index ZT.
As mentioned above
(A) Mother phase of Fe—Ti—Si based full-Whisler alloy (b) Phase 2 M
(C) The second phase M is dispersed in the mother phase (d) The p-type in which the average particle size of the second phase M is smaller than the average particle size of the mother phase and is 50 nm or less. It is understood that a high performance index can be obtained by combining thermoelectric conversion materials.

In addition,
(E) The content x of the second phase M with respect to the Fe—Ti—Si based full-Whisler alloy is preferably 0 at% <x <2.5 at%. As a result, heat conduction in the thermoelectric conversion material is suppressed as compared with the single phase of the conventional Fe—Ti—Si based full-Whisler alloy that does not contain the second phase M. In addition, electrical conductivity is ensured by obtaining a sintered body. Due to these effects, a large figure of merit ZT can be obtained.

When the content x of the second phase M with respect to the Fe—Ti—Si based full-Whisler alloy is 2.5 at% or more, the influence of the Seebeck coefficient of the second phase M cannot be ignored, and the Seebeck coefficient of the thermoelectric conversion material decreases. In addition, as the number of interfaces between the parent phase and the second phase M increases, electrons are scattered and the electrical resistivity increases. Therefore, it is more preferable to suppress the content x to less than 2.5 at% from the viewpoint of obtaining a high figure of merit ZT.

As described above, from the viewpoint of mechanical properties and element diffusion coefficient, the second phase M is a metal composed of at least one element of W (tungsten) and Ta (tantalum), or at least of Ta and W. Compounds containing one or more elements are preferred.

When the mechanical strength of the second phase M is small, the crystal structure of M is not maintained when the Fe—Ti—Si based amorphous alloy is produced, and the Fe—Ti—Si based amorphous alloy and M are alloyed to form the second phase. Since the phase M is not formed in a dispersed form in the Fe—Ti—Si based full-Whisler alloy of the parent phase, it becomes difficult to obtain a high performance index ZT.

When the element diffusion coefficient of the second phase M is large, when the Fe—Ti—Si based amorphous alloy is produced, M is elementally diffused and alloyed in the Fe—Ti—Si based amorphous alloy by the generated heat, and the second phase is alloyed. Since the phase M is not formed in a dispersed form in the Fe—Ti—Si based full-Whisler alloy of the parent phase, it becomes difficult to obtain a high performance index ZT.

Since the mechanical strength is high and the element diffusion coefficient is small, M is preferably a compound containing W, Ta, or W, Ta.

The Fe—Ti—Si based full-Whisler alloy, which is the parent _phase in the thermoelectric conversion material, has an L21 type crystal structure and is preferable because excellent thermoelectric conversion characteristics can be obtained as a p-type thermoelectric conversion material.

According to the p-type thermoelectric conversion material according to the embodiment described above, the figure of merit ZT when applied as a p-type thermoelectric conversion material is the maximum value indicated by the conventional Fe—Ti—Si based full-Whisler alloy. A figure of merit ZT of 0.20 or more can be obtained.

The p-type thermoelectric conversion material according to the present embodiment can be described by composition analysis by inductively coupled plasma emission spectroscopy (ICP-AES) or energy dispersive X-ray spectroscopy (EDX), and a scanning electron microscope (SEM). Alternatively, it can be easily confirmed by structural analysis using a transmitted electron microscope (TEM).

Next, the method for manufacturing the above-mentioned p-type thermoelectric conversion material will be described with reference to FIG.
First, Fe raw material powder, Ti raw material powder, Si raw material powder, and M raw material powder are prepared at a ratio according to the composition of the Fe—Ti—Si based alloy to be finally obtained (step S1).

Next, each of the above-mentioned raw material powders is mixed to produce a mixture containing Fe, Ti, Si, and M, and the obtained mixture is amorphized Fe, Ti, and Si by, for example, a mechanical alloying method to form Fe-. A Ti—Si-based amorphous alloy is used (step S2). Mechanical alloying is a method in which a pulverizing medium such as a hard ball is loaded into a closed container together with a mixture and milled by mechanical stirring to form an alloy. The mechanical alloying method can obtain an amorphous phase in a wide composition range as compared with other techniques capable of producing an amorphous phase such as a quenching method. On the other hand, even after Fe, Ti, and Si have changed to an amorphous phase, the M raw material powder is finely divided and dispersed in an Fe—Ti—Si-based amorphous alloy with an average particle size of 50 nm or less while maintaining the crystal structure. As a result, an alloy powder in which the second phase M is dispersed in the Fe—Ti—Si-based amorphous alloy is formed. As another method for forming Fe, Ti, and Si into an amorphous alloy, a melt spinning method, an atomizing method, or the like can also be used. When the alloy is not obtained as a powder, for example, a method of performing hydrogen embrittlement treatment and pulverizing in an environment where oxidation is prevented may be used.

Next, the alloy powder is molded by a method such as pressure molding (step S3). The pressure at the time of molding can be, for example, 40 MPa to 5 GPa.

Next, the alloy powder is heated and sintered while being pressurized at a temperature of 450 ° C. or higher and 800 ° C. or lower (step S4). As a result, the Fe—Ti—Si based amorphous alloy forms a full-Whisler alloy having an L2 type ₁ crystal structure. At this time, the pressure is preferably 40 MPa to 5 GPa, whereby the density of the sintered body is increased, the electrical resistivity is decreased, and the thermoelectric figure of merit is increased. The second phase M is dispersed in the matrix as a full-Whisler alloy as before sintering, and the average particle size of the second phase M is smaller than the average particle size of the matrix and is 50 nm or less.

This is because the Fe—Ti—Si based L2 type ₁ crystal structure is a semi-stable structure, so that the L2 type ₁ crystal structure can be produced as an intermediate product by passing through the amorphous structure in a high energy state. Is. The sintering temperature is preferably 550 ° C. or higher and 750 ° C. or lower so that the full-Whisler alloy is sufficiently crystallized and does not undergo thermal decomposition. Further, the sintering temperature is more preferably 600 ° C. or higher and 700 ° C. or lower so that the relative density of the full-Whisler alloy increases and the crystal grain size does not become too coarse.

If the sintering temperature is less than 450 ° C., an L2 type ₁ crystal structure cannot be obtained in the matrix. On the other hand, if the sintering temperature exceeds 800 ° C., the L2 type ₁ crystal structure may be thermally decomposed to form another stable alloy. In this case, it becomes difficult to use the obtained sintered body as a thermoelectric conversion material. Therefore, the sintering temperature of the alloy powder is set to a temperature of 450 ° C. or higher and 800 ° C. or lower.

The holding time of the above-mentioned sintering temperature is not particularly limited, but can be approximately 1 to 600 minutes. As the sintering step, a discharge plasma sintering method or a hot press method, which can simultaneously perform the pressure forming step and the heating step, can also be used.

If the holding time is too long, the sample may oxidize and the thermoelectric properties may deteriorate, and if the holding time is too short, the full-Whisler alloy may not be formed. The holding time is preferably 5 to 400 minutes from the viewpoint of reducing temperature unevenness and preventing oxidation. Further, the holding time is more preferably 10 to 200 minutes in order to form a uniform L2 type ₁ crystal structure and to prevent the crystal grain size from becoming too coarse.

<Thermoelectric conversion module>
Next, a thermoelectric conversion module using the p-type thermoelectric conversion material according to the embodiment of the present invention will be described. FIG. 2 is a cross-sectional view showing the configuration of the thermoelectric conversion module according to the present embodiment. The thermoelectric conversion module shown in FIG. 2 includes an upper substrate 14a and a lower substrate 14b, and is adjacent to a p-type thermoelectric conversion element 11 and a p-type thermoelectric conversion element 11 between the upper substrate 14a and the lower substrate 14b. The n-type thermoelectric conversion element 12 is provided.

The p-type thermoelectric conversion element 11 is formed to include a p-type thermoelectric conversion material, and the n-type thermoelectric conversion element 12 is formed to include an n-type thermoelectric conversion material. At least one of the p-type thermoelectric conversion elements 11 is formed of a p-type thermoelectric conversion material of Fe—Ti—Si based full-Whisler alloy in which the second phase M as described above is dispersed.

The p-type thermoelectric conversion element 11 and the n-type thermoelectric conversion element 12 are alternately arranged between the upper substrate 14a and the lower substrate 14b with a predetermined interval. A thermoelectric conversion pair 15 having a π-type structure is formed by a set of a p-type thermoelectric conversion element 11 and an n-type conversion element 12. A plurality of thermoelectric conversion element pairs 15 having this π-shaped structure are electrically connected in series by an upper electrode 13a formed on the upper substrate 14a and a lower electrode 13b formed on the lower substrate 14b. .. Specifically, the p-type thermoelectric conversion element 11 is connected to the adjacent n-type thermoelectric conversion element 12 by the upper electrode 13a. Further, the p-type thermoelectric conversion element 11 is connected by the lower electrode 13b to the n-type thermoelectric conversion element 12 provided on the opposite side of the n-type thermoelectric conversion element 12 connected by the upper electrode 13a.

The p-type thermoelectric conversion element 11 and the n-type thermoelectric conversion element 12 are connected to the upper electrode 13a and the lower electrode 13b by a conductive material. These structures may be provided with stress relaxation structures or may be attached with other accessories.

According to the structure described above, the p-type thermoelectric conversion element 11 and the n-type thermoelectric conversion element 12 are joined so as to be in thermal contact with the upper electrode 13a and the lower electrode 13b, and the upper electrode 13a and the lower electrode 13b are joined. It is joined so as to be in thermal contact with the upper substrate 14a and the lower substrate 14b.

The thermoelectric conversion module shown in FIG. 2 generates a temperature gradient in the same direction in the p-type thermoelectric conversion element 11 and the n-type thermoelectric conversion element 12 by, for example, heating the upper substrate 14a or bringing it into contact with a high heat portion. be able to. At this time, according to the principle of the Zeebeck effect, in the p-type thermoelectric conversion element 11 and the n-type thermoelectric conversion element 12, thermoelectromotive force is generated in the direction opposite to the temperature gradient. This makes it possible to generate a large thermoelectromotive force. Therefore, by connecting both ends of the electrode (for example, in FIG. 2, the lower electrode 13b at the right end in the figure and the lower electrode 13b at the left end in the figure) with the temperature gradient applied, electrical energy can be efficiently extracted. can.

As the n-type thermoelectric conversion element 12, a Fe—Ti—Si-based full-Whisler alloy may be used, an Fe—V—Al-based full-Whisler alloy may be used, or Bi— as the n-type thermoelectric conversion material. A Te-based semiconductor may be used. When the Fe—Ti—Si based full-Whisler alloy is used as the n-type thermoelectric conversion material, the temperature range in which high mechanical properties and high figure of merit ZT can be obtained is high in the p-type thermoelectric conversion material. It is suitable because it is about the same as the temperature range in which the figure of merit ZT can be obtained. Therefore, from the viewpoint of improving the output characteristics and reliability of the thermoelectric conversion module and reducing the cost, it is preferable to use the Fe—Ti—Si based full-Whisler alloy as the n-type thermoelectric conversion element.

<Example>
Hereinafter, the p-type thermoelectric conversion material according to the examples will be described in detail with reference to the examples.
First, by the following method, as the p-type thermoelectric conversion material according to the embodiment, a Fe—Ti—Si based full-Whisler alloy having an L2 type ₁ crystal structure represented by E1 ₂ E2 E3 is used as a parent phase, and the second phase M is used. A thermoelectric conversion material containing and was prepared.

As the raw material powders constituting the main components of each of the E1 site, E2 site and E3 site, raw material powders containing Fe, Ti and Si as main components were used, respectively. Further, as an example of the raw material powder of the component to be added to the E3 site, the raw material powder containing Al as the main component was used. Even when the additive is not Al, a high P-type Seebeck coefficient can be obtained if the total valence electron number VEC is 23.8 or more and 24.1 or less. Further, W was used for the second phase M. These raw material powders were weighed so that the composition ratios of the finally obtained thermoelectric conversion materials (sample numbers 1 to 6) were shown in Table 1. In sample numbers 1 to 6, the composition ratios of Fe, Ti, and Si are substantially the same, but the composition ratio of W is changed stepwise in the range of 0 to 2.50 at%. The sample of sample No. 1 corresponds to a comparative example because W is not added. Further, the material of sample No. 6 corresponds to a comparative example because a sufficiently high ZT cannot be obtained due to the large amount of W added.

Next, these raw material powders were placed in a stainless steel container in an inert gas atmosphere and mixed with a stainless steel ball or a chrome steel ball (hard ball) having a diameter of 10 mm. Next, this mixture was mechanically alloyed using a planetary ball mill device to obtain an alloy powder containing an amorphous mother phase and the second phase M.

Mechanical alloying was carried out at a revolution rotation speed of 350 rpm for 20 hours or more. Next, the alloy powder was placed in a carbon die or a tungsten carbide die and heated in an inert gas atmosphere under a pressure of 1.5 GPa while applying a pulse current to be sintered.

The sintering treatment was carried out by raising the temperature to 660 ° C. and then holding the temperature at the target temperature (660 ° C.) for 30 minutes. Then, the obtained sintered body was cooled to room temperature to obtain thermoelectric conversion materials (Samples 1 to 6).

[Evaluation methods]
Next, the Zeebeck coefficient and electrical conductivity of each of the obtained thermoelectric conversion materials were measured by a thermoelectric property evaluation device (“ZEM-2”, manufactured by Advance Riko Co., Ltd.), and the thermal conductivity was measured by the laser flash method thermal constant. The performance index ZT of each sample 1 to 6 was calculated by measuring with an apparatus (“LFA447 Nanoflush”, manufactured by Netch Japan Co., Ltd.).

In addition, measurement was performed with an X-ray diffractometer (“X'pertPro”, manufactured by PANalytical), and the crystal structure and average particle size of each sample were evaluated. The Scherrer's formula represented by the above [Equation 1] was used for the calculation of the average particle size. A transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy were used to observe the structures of the matrix and the second phase M.

These evaluation results are shown in FIGS. 3 to 6. The composition ratio, average particle size, and figure of merit ZT of each sample 1 to 6 are as shown in Table 1.

[Evaluation results]
3 and 4 show the XRD pattern and the TEM-EDX image of the sintered body for the sample 5 in which the composition ratio of W is 2.0 at%. The composition ratio of Al was set so that the total number of valence electrons was 23.8 or more and 24.1 or less.

As shown in FIG. 3, in the sintered body, in addition to the diffraction peak of the full-Whisler alloy having high strength, the diffraction peak of W having low strength is obtained. Therefore, it can be seen that W is present in the base material as the second phase M dispersed in the mother phase with the full-Whisler alloy as the mother phase. In the composition ratios of Fe, Ti, Si, and Al in [Table 1], when the composition ratio of W is increased from 0 at% to 2.5 at%, the Scherrer's formula represented by [Equation 1] is shown from the X-ray diffraction pattern. The average particle size of the matrix and W calculated using the above is shown in [Table 1]. The particle size of the matrix is approximately 69 nm to 79 nm, whereas the average particle size of W is approximately 20 nm to 23 nm, and the average particle size of W is smaller than the average particle size of the matrix and is 50 nm or less. You can see that.

FIG. 4 shows a TEM-EDX image of the p-type thermoelectric conversion material according to the embodiment. The black region indicates the mother phase, and the lightly concentrated region indicates the W phase. As shown in FIG. 4, W becomes particles in the matrix and is uniformly dispersed in a distribution state and density different from the distribution state and density of the matrix, and its average particle size is 50 nm or less. You can see that it is.

The graphs of FIGS. 5 and 6 show the changes in the thermal conductivity κ and the figure of merit ZT when W is increased from 0 at% to 2.5 at%.
As shown in FIG. 5, when the amount of W increases from 0 at% to 2.5 at%, the thermal conductivity κ decreases as the amount of W increases. When a predetermined amount of W is added, the thermal conductivity κ is smaller than that of the p-type Fe—Ti—Si based full-Whisler alloy single-phase sample (Sample 1) to which W is not added.
Further, as shown in FIG. 6, a figure of merit ZT exceeding that of the conventional p-type full-Whisler alloy single-phase sample (Sample 1) was obtained in the composition region in which the amount of W was 0 at% or more and less than 2.5 at%. There is.

When such a p-type Fe—Ti—Si based full-Whisler alloy is used as the matrix phase and W having an average particle size of 50 nm or less is dispersed in the matrix phase as the second phase M, the performance in the p-type thermoelectric conversion material is achieved. Index ZT is improved. The reason is that, as shown in FIG. 4, the thermal conductivity κ decreases as the amount of W increases. On the other hand, when the content of W in the matrix exceeds 2.5 at%, the influence of the extremely small Seebeck coefficient of W cannot be ignored, the Seebeck coefficient of the p-type thermoelectric conversion material decreases, and W As the number of interfaces with the matrix increases, electrons are scattered and the electrical resistivity increases. By setting the W content in the matrix to 0 at% <x <2.5 at%, a higher figure of merit can be obtained.
Although the embodiment in which W is dispersed in the mother phase as the second phase M has been described above, the same effect can be obtained even when Ta is the second phase M.

Although embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

11 ... p-type thermoelectric conversion element, 12 ... n-type thermoelectric conversion element, 13a ... upper electrode, 13b ... lower electrode, 14a ... upper substrate, 14b ... lower substrate, 15 ... thermoelectric conversion element pair.

Claims (11)

It contains a matrix phase which is a Fe—Ti—Si based full-Whisler alloy and a second phase M.
The second phase M is dispersed in the mother phase, and the average particle size of the second phase M is smaller than the average particle size of the mother phase and is 50 nm or less.
The content x of the second phase M is 0 at% <x <2.5 at%, and the content x is 0 at% <x <2.5 at%.
The Fe—Ti—Si based full-Whisler alloy is a p-type thermoelectric conversion material having a total valence electron number VEC per unit cell of 23.8 or more and 24.1 or less . The p-type according to claim 1, wherein the second phase M is a metal composed of at least one element of W and Ta, or a compound containing at least one element of W and Ta. Thermoelectric conversion material. It contains a matrix phase which is a Fe—Ti—Si based full-Whisler alloy and a second phase M.
The second phase M is dispersed in the mother phase, and the average particle size of the second phase M is smaller than the average particle size of the mother phase and is 50 nm or less.
The content x of the second phase M is 0 at% <x <2.5 at%, and the content x is 0 at% <x <2.5 at%.
A part of the Fe—Ti—Si based full-Whisler alloy is characterized in that Si is substituted with Al and the total valence electron number VEC per unit cell is 23.8 or more and 24.1 or less . P -type thermoelectric conversion material. A thermoelectric conversion module having a plurality of thermoelectric conversion elements and electrodes for electrically connecting the thermoelectric conversion elements.
The thermoelectric conversion element is
A p-type thermoelectric conversion element and an n-type thermoelectric conversion element connected to the p-type thermoelectric conversion element are included.
The p-type thermoelectric conversion element is
It contains a matrix phase which is a Fe—Ti—Si based full-Whisler alloy and a second phase M.
The second phase M is dispersed in the mother phase, and the average particle size of the second phase M is smaller than the average particle size of the mother phase and is 50 nm or less.
The content x of the second phase M is 0 at% <x <2.5 at%, and the content x is 0 at% <x <2.5 at%.
The Fe—Ti—Si based full-Whisler alloy has a total valence electron number VEC per unit cell of 23.8 or more and 24.1 or less.
A thermoelectric conversion module characterized by that. The thermoelectric conversion module according to claim 4 , wherein the n-type thermoelectric conversion element includes an n-type thermoelectric conversion material having a Fe—Ti—Si based full-Whisler alloy. A plurality of thermoelectric conversion element pairs having the p-type thermoelectric conversion element, the n-type thermoelectric conversion element, and an electrode connecting the p-type thermoelectric conversion element and the n-type thermoelectric conversion element are arranged. The thermoelectric conversion module according to claim 4 . A step of mixing Fe raw material powder, Ti raw material powder, Si raw material powder, and M raw material powder to produce a mixture containing Fe, Ti, Si, and M.
A step of amorphizing Fe, Ti, and Si in the mixture to form an alloy in which M is dispersed in an Fe—Ti—Si-based amorphous alloy while maintaining the crystal structure of M.
It includes a step of heating the alloy to produce a p-type thermoelectric conversion material of a thermoelectric conversion material.
The thermoelectric conversion material contains a matrix phase which is a Fe—Ti—Si based full-Whisler alloy and a second phase M, and the second phase M is dispersed in the matrix phase M. The average particle size of the second phase M is smaller than the average particle size of the parent phase and is 50 nm or less, and the content x of the second phase M is 0 at% <x <2.5 at% .
In the step of producing the mixture, the Al raw material powder is further mixed so that the total valence electron number VEC per unit cell is 23.8 or more and 24.1 or less.
A method for manufacturing a p-type thermoelectric conversion material. The method for producing a p-type thermoelectric conversion material according to claim 7 , wherein the alloy is sintered at a temperature of 450 ° C. or higher and 800 ° C. or lower. The method for producing a p-type thermoelectric conversion material according to claim 7 or 8 , wherein the mixture is amorphized by a mechanical alloying method. Claims 7 to 9 are characterized in that the M raw material powder is mixed so that the content x of the M element is 0 at% <x <2.5 at% with respect to the whole constituting the p-type thermoelectric conversion material. The method for producing a p-type thermoelectric conversion material according to any one of the above items. The method for producing a p-type thermoelectric conversion material according to any one of claims 7 to 10 , wherein W or Ta is used as the M raw material powder.

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