JP4393412B2 - Thermoelectric conversion material - Google Patents

Description

  The present invention relates to a thermoelectric conversion material.

  Conventionally, thermoelectric conversion elements capable of mutual conversion between thermal energy and electrical energy are known. This thermoelectric conversion element is configured using two types of thermoelectric conversion materials, p-type and n-type, and the two types of thermoelectric conversion materials are electrically connected in series and are arranged in parallel thermally. It is said that. In this thermoelectric conversion element, when a voltage is applied between both terminals, hole movement and electron movement occur, and a temperature difference occurs between both surfaces (Peltier effect). Moreover, if this thermoelectric conversion element gives a temperature difference between both surfaces, the movement of a hole and the movement of an electron will also occur, and an electromotive force will generate | occur | produce between both terminals (Seebeck effect). For this reason, it is considered to use the thermoelectric conversion element as an element for cooling a CPU, refrigerator, car air conditioner, etc. of a personal computer, or as an element for a power generation apparatus using waste heat generated from a waste incinerator or the like. ing.

Conventionally, Bi ₂ Te ₃ , PbTe, and the like have been put to practical use as thermoelectric conversion materials constituting thermoelectric conversion elements. In addition, Se is generally added when forming an n-type thermoelectric conversion material using a Bi-Te-based material. The elements Bi, Te, Pb and Se constituting these thermoelectric conversion materials are highly toxic and may cause environmental pollution.

As a thermoelectric conversion material with little environmental pollution, at least a part of at least one element of Fe, V, and Al is replaced with another element with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and the element is replaced Have been controlled so as to be n-type with electrons as carriers (see, for example, Patent Document 1). The other element to be substituted in place of Fe is selected from the group consisting of groups 9 and 10 of the 4th to 6th periods in the periodic table, and the other element to be substituted in place of V is the 4th to 6th in the periodic table. Selected from the group consisting of groups 6 and 7 of the period, and other elements substituted for Al are selected from the group consisting of groups 14 to 16 of the 3rd to 6th periods in the periodic table.

In Patent Document 1, at least a part of at least one element of Fe, V, and Al is substituted with another element with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and the element to be substituted has an atomic weight. Some have been proposed that are controlled to be p-type with holes as carriers by being made large. Then, the other element to be substituted in place of V is selected from the group consisting of Group 4 of the 4th to 6th periods in the periodic table, and the other element to be substituted in place of Al is 2 in the 3rd to 6th periods in the periodic table. Selected from the group consisting of tribes.

Further, as a p-type thermoelectric conversion material, it has a composition represented by Fe _x Al _y V _100-xy (where 40 ≦ x ≦ 49, 26 ≦ y ≦ 40), and has a Heusler structure as a main component. A compound in which a part of Fe or a part of Al is substituted with another element has been proposed (see, for example, Patent Document 2). Patent Document 2 includes Ti, Cr, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Hf, Ta, W, Y, and rare earth elements as elements for substituting part of Fe. Examples of elements that substitute a part of Al include C, N, Si, P, S, Mg, Ga, Ge, Sn, Sb, In, and Bi. And as an element which substitutes a part of Al, since the effect of reducing thermal conductivity is high, it describes that Sn, Sb, In, and Bi are especially preferable.
JP 2004-253618 A (paragraphs [0012] to [0014], [0020] to [0022] of the specification) JP 2004-119648 A (paragraphs [0016] to [0021] of the specification)

However, research on a thermoelectric conversion material in which a part of Fe ₂ VAl having a Heusler alloy type crystal structure is replaced with another element is not yet sufficient. As a result of intensive studies on the Fe ₂ VAl having a Heusler alloy type crystal structure, the present inventor has reached the present invention.

An object of the present invention is to provide a thermoelectric conversion material having the same basic structure as Fe ₂ VAl having a Heusler alloy type crystal structure and capable of making a power factor P larger than Fe ₂ VAl without containing harmful elements. It is to provide.

In order to achieve the above object, according to the first aspect of the present invention, a part of Al is substituted with rare earth elements and Si with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure , When the rare earth element is M, it is a thermoelectric conversion material having a composition represented by Fe ₂ VAl _1-mn M _m Si _n , the rare earth element is Y, and the composition m and the composition n are m + n = 0.07 and 0.002 ≦ m ≦ 0.03.
According to the second aspect of the present invention, when a part of Al is substituted with a rare earth element and Si with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, ₂ VAl _1-mn M _m Si _n is a thermoelectric conversion material having a composition represented by the formula, wherein the rare earth element is one selected from Nd, Sm, Gd, and Tb, and the composition m and the composition n is 0 <m <1, 0 <n <1, 0 <m + n <1.
In the inventions according to claims 1 and 2 , the power factor P may be made larger than Fe ₂ VAl in the presence of an additive element that is not harmful to Fe ₂ VAl having a Heusler alloy type crystal structure. it can. Further, when manufacturing a thermoelectric conversion material, by adding Fe, V, in addition to rare earth elements and Si in Al as a raw material, it can be produced by the same method as the manufacturing method of Fe 2 _VAl.

In addition to the fact that the output factor P becomes larger than Fe ₂ VAl, the thermal conductivity of the thermoelectric conversion material is reduced. Therefore, even if the output factor P is the same, the thermoelectric conversion material does not decrease the thermal conductivity. In comparison, the figure of merit increases. Here, the “performance index” is defined as a value (Z) obtained by dividing the output factor P by the thermal conductivity, and is expressed by the following equation.

Z = α ² / (ρκ) (1)
P = α ² / ρ (2)
Where α is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity.

According to the present invention, compared with Fe ₂ VAl having a Heusler alloy type crystal structure, a part of Al is substituted with rare earth elements and Si , so that a power factor does not contain harmful elements. P can be made larger than Fe ₂ VAl.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described.
In this embodiment, in the thermoelectric conversion material, a part of Al (aluminum) is substituted with a rare earth element with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and the rare earth element is M The composition is represented by Fe ₂ VAl _1-x M _x . However, 0 <X <1. In the thermoelectric conversion material having this composition, the rare earth element acts as a donor and becomes an n-type thermoelectric conversion material.

The output factor P of the thermoelectric conversion material having a composition represented by Fe ₂ VAl _1-x M _x becomes a large value near room temperature, and decreases as the temperature increases.
When a part of Al is substituted with a rare earth element, the output factor P increases as the substitution ratio increases until the composition X is 0.02 to 0.03 except Sm, but 0.02 to 0.03. It becomes a peak, and the output factor P decreases as the replacement ratio increases further. On the other hand, in the case of substitution with Sm (samarium), the output factor P increases as the substitution ratio increases up to 0.05, but the increase ratio is small.

When the maximum values of the output factors P of the thermoelectric conversion materials having the composition represented by Fe ₂ VAl _1-x M _x are compared, the case where M is Y (yttrium) is the maximum, and hereinafter, Nd (neodymium), Gd (Gadolinium), Tb (terbium), and Sm (samarium) decrease in this order. However, when any rare earth element is substituted, the value of the output factor P in the reference Fe ₂ VAl not substituted with the rare earth element is 5 times or more over a range where the composition X changes by 0.03 or more. become.

  When a part of Al is substituted with a rare earth element, when Y, Nd, and Tb are used as the rare earth element, the thermal conductivity decreases as the substitution ratio, that is, the composition X increases. Therefore, even when the magnitude of the output factor P is the same, the figure of merit becomes larger than that of a thermoelectric conversion material in which the thermal conductivity does not decrease.

For Sm, there is a peak of the thermal conductivity of the composition X is in the vicinity of 0.01, the peak value is greater than the thermal conductivity of the _Fe 2 VAl is not replaced until the composition X is 0.02 _strong, the Fe 2 VAl The thermal conductivity is larger than the thermal conductivity. In the case of Gd (gadolinium), the composition X has a peak of thermal conductivity in the vicinity of 0.02, the peak value is larger than the thermal conductivity of Fe ₂ VAl that is not substituted, and the peak value is 0 when the composition X of Sm is 0. It is almost equal to the value of thermal conductivity of just over .02.

Hereinafter, the embodiment will be described in more detail. However, these are examples and do not limit the present invention.
<Sample preparation>
A sample of the thermoelectric conversion material was prepared by an arc melting method. As a starting material, a material having a purity of Fe (99% by mass), V (99% by mass), Al (99.9% by mass), rare earth (Y, Nd, Sm, Gd, Tb) (99.9% by mass) (Raw materials) were prepared, and these were weighed in the atmosphere so as to have the composition shown in Table 1 (about 16 g was used at a time) to obtain a raw material mixture. This raw material mixture was melted by a non-consumable arc melting furnace manufactured by Nippon Special Machinery Co., Ltd. Dissolution was performed in a high purity Ar atmosphere (99.9999%). After re-melting a plurality of times (for example, 5 times) so that the composition of the alloy obtained by arc melting was uniform, cooling was performed to obtain an ingot.

＜測定試料の作製＞
試料作製で得られた合金インゴットから、所定の大きさの試料をbrother （株）製のワイヤー放電加工機ＨＳ−３００によって切り出した。その試料を石英管に入れ、真空封入した後、１２７３Ｋで４８時間の均質化熱処理を施したものを測定試料とした。

<Preparation of measurement sample>
A sample of a predetermined size was cut out from the alloy ingot obtained by the sample preparation using a wire electric discharge machine HS-300 manufactured by brother. The sample was put in a quartz tube, vacuum sealed, and subjected to homogenization heat treatment at 1273K for 48 hours as a measurement sample.

<Hardness test>
In order to evaluate the mechanical properties due to the addition of rare earth elements, hardness was measured with an MVK-GI microhardness meter manufactured by Akashi Seisakusho. Twelve points were measured at 1 mm intervals along the longitudinal direction of the sample, and the average value of 10 points excluding the maximum value and the minimum value was taken as the hardness. The load was 100 g. A sample for measurement was prepared by polishing the prepared alloy up to # 1500 with emery paper and then buffing with an alumina powder having a particle size of 0.05 μm.

<X-ray diffraction>
The phase of the prepared sample was identified by X-ray diffraction (XRD). The homogenized sample was pulverized in an agate bowl. Thereafter, distortion was removed for 1 hour at 1273K, and this alloy powder was spread flat on a glass holder and fixed with collodion to obtain a sample.

<Composition analysis>
The composition analysis of the produced alloy was performed using an energy dispersive X-ray spectrometer (EDX) attached to a scanning electron microscope (SEM) manufactured by JEOL. The analysis conditions were a magnification of 1000 times and an acceleration voltage of 20 kV. 12 points were measured from end to end along the longitudinal direction of the sample, and the average value of 10 points excluding the maximum and minimum values was taken as the composition of the sample. One point was measured for 100 seconds. A sample for measurement was prepared by polishing the prepared alloy up to # 1500 with emery paper and buffing with alumina powder having a particle diameter of 1 μm.

<Measurement of electrical properties>
The electrical characteristics of the sample were measured by a thermoelectric power measuring device ZE-1 manufactured by ULVAC Riko Co., Ltd. This apparatus is composed of a heating furnace for heating the entire sample, a measuring instrument, a personal computer, and an evacuation apparatus, and can measure the thermoelectromotive force E ₀ and the electrical resistivity ρ. FIG. 1 schematically shows the configuration of the measuring unit of the thermoelectric power measuring apparatus. The measurement unit 10 includes a pair of electrodes 11 and 12 that sandwich the sample S, a pair of probes 13 a and 13 b, and an interprobe voltage measurement unit 14.

The sample for a measurement was cut out to a sample of about 4 × 4 × 18 mm using a brother electric wire electric discharge machine HS-300. Each side of the sample was polished with emery paper to # 1500. The contact surface between the sample, the probe, and the electrode was further buffed with alumina powder having a particle size of 1 μm. This sample was fixed between the high temperature end electrode and the low temperature end electrode and brought into contact with the probe. The high temperature end temperature Th, the low temperature end temperature Tc, and the inter-probe voltage are measured with a set of probes. The measurement was performed in a temperature range of about 313 to 1073 K and a temperature difference between probes of about 10 K with He gas being put into the furnace at 0.05 MPa. During measurement, a steady current of 100 mA was supplied. The average temperature T = (T _h + T _c ) / 2 of the probe was used as the sample temperature.

The Seebeck coefficient α is obtained from the following equation (3).
α = E ₀ / ΔT (3)
However, _{E 0} is thermoelectromotive force, [Delta] T between the probe is a temperature difference between the probe _(T h -T _c).

  The electrical resistivity ρ was measured by a four-terminal method, which is a typical measurement method. That is, the voltage drop caused by the steady current (100 mA) was measured between the voltage terminals, in this case, between the probes. Using the cross-sectional area A of the sample, the electrical resistivity ρ was determined by the following equation (4).

ρ = (R · A) / L (4)
However, L is a distance between probes, R is a resistance value of a sample, and is given by R = V1 / (V2 / R1). However, V1 is an interprobe voltage, V2 is a reference resistor voltage, and R1 is a reference resistance value.

<Measurement of thermal conductivity>
The thermal conductivity of the prepared sample was calculated from the thermal diffusivity and specific heat using a laser flash method thermal constant measuring device TC-7000 manufactured by ULVAC Riko Co., Ltd. The sample used in the laser flash method was cut out to have a diameter of about 10 mm and a thickness of about 1.2 mm using a wire electric discharge machine HS-300, and the surface was polished with emery paper to # 400. The thermal conductivity is measured by irradiating an instantaneous heat source with a laser beam on the surface of a disk-shaped sample having a thickness d placed in a vacuum and measuring the temperature of the back of the sample to obtain the thermal diffusivity. The thermal conductivity is obtained from the specific heat of. When the amount of heat given by the instantaneous laser beam is Q, and the density and specific heat of the sample are D and Cp, respectively, the maximum value T _max of the back surface temperature rise of the sample is given by the following equation (5).

T _max = Q / (DCpd) (5)
The thermal diffusivity λ is obtained by the following equation (6), where t / 2 is the time required for the temperature of the back surface to reach 1/2 of the maximum value after the instantaneous laser light is irradiated on the sample surface.

λ = 1.37d ² / (π ² t / 2) (6)
Therefore, the thermal conductivity κ is expressed by the following equation (7) from the specific heat Cp and the thermal diffusivity λ of the sample.
κ = λCpD (7)
<Evaluation as thermoelectric material>
Evaluation as a thermoelectric material was performed using an output factor P represented by the following formula (8).

P = α ² / ρ (8)
Where α is the Seebeck coefficient and ρ is the electrical resistivity.
<Example I to Example V>
The raw materials are weighed so as to have the composition shown in Table 1, and a part of Al is Y (Example I), Tb (Example II), Nd (Example III), Gd (Example IV), Sm ( An alloy substituted in Example V) was prepared. As a result of performing X-ray diffraction and composition analysis on each sample, it was confirmed that each of the samples was an alloy having a Heusler alloy type crystal structure and a composition represented by Fe ₂ VAl _1-x M _x .

As a result of measuring the hardness of the alloy obtained in each of Examples I to V, the hardness increased in comparison with Fe ₂ VAl (hardness 385 Hv) as a reference in each of Examples I to V. In the case of Example III, the increase rate was about 5%, but in other Examples, the increase rate was 10% or more.

For the samples obtained in Examples I to V, the thermoelectromotive force E ₀ and the temperature difference ΔT (T _h −T _c ) were measured at 313 K using a thermoelectric power measuring device, and the Seebeck coefficient α and the electrical resistivity were measured. ρ was obtained, and the output factor P [Wm ⁻¹ K ⁻² ] was obtained from the equation (8). The results are shown in Table 2 and FIGS. 2 shows a case where Y is a substitution element, FIG. 3 shows a case where Nd is a substitution element, FIG. 4 shows a case where Sm is a substitution element, and FIG. 5 shows a case where Gd is a substitution element. FIG. 6 shows a case where Tb is used as a substitution element. Table 2 shows the maximum value of the output factor P in each of Examples I to V.

図２〜図６及び表２に示すように、Ｆｅ_２ＶＡｌ_１−ｘＭ_ｘで表される熱電変換材料の出力因子Ｐは、ＭがＹの場合は組成Ｘが０．０２で最大値４．０２×１０^−３［Ｗｍ^−１Ｋ^−２］となり、ＭがＮｄの場合は組成Ｘが０．０２で最大値３．２１×１０^−３［Ｗｍ^−１Ｋ^−２］となった。また、ＭがＳｍの場合は組成Ｘが０．０５で最大値２．４９×１０^−３［Ｗｍ^−１Ｋ^−２］となり、ＭがＧｄの場合は組成Ｘが０．０３で最大値３．１２×１０^−３［Ｗｍ^−１Ｋ^−２］となり、ＭがＴｂの場合は組成Ｘが０．０３で最大値２．８４×１０^−３［Ｗｍ^−１Ｋ^−２］となった。即ち、熱電変換材料の出力因子Ｐの最大値同士を比較すると、Ｙを置換元素とした場合に出力因子Ｐが最大となり、Ｙ＞Ｎｄ＞Ｇｄ＞Ｔｂ＞Ｓｍの順に小さくなった。

As shown in FIGS. 2 to 6 and Table 2, the output factor P of the thermoelectric conversion material represented by Fe ₂ VAl _1-x M _x is the maximum value 4 when the composition X is 0.02 and M is Y. 0.02 × 10 ⁻³ [Wm ⁻¹ K ⁻² ], and when M is Nd, the composition X was 0.02 and the maximum value was 3.21 × 10 ⁻³ [Wm ⁻¹ K ⁻² ]. Further, when M is Sm, the composition X is 0.05 and the maximum value is 2.49 × 10 ⁻³ [Wm ⁻¹ K ⁻² ], and when M is Gd, the composition X is 0.03 and the maximum value is 3 .12 × 10 ⁻³ [Wm ⁻¹ K ⁻² ], and when M is Tb, the composition X was 0.03 and the maximum value was 2.84 × 10 ⁻³ [Wm ⁻¹ K ⁻² ]. That is, when the maximum values of the output factors P of the thermoelectric conversion materials are compared, the output factor P is maximized when Y is a substitution element, and decreases in the order of Y>Nd>Gd>Tb> Sm.

As shown in FIG. 2, the thermoelectric conversion material represented by Fe ₂ VAl _1-x Y _x has an output factor P of 2.0 × 10 ⁻³ [Wm when the composition X is in the range of 0.006 to 0.079. ⁻¹ K ⁻² ] or more, and the output factor P was 2.8 × 10 ⁻³ [Wm ⁻¹ K ⁻² ] or more in the range where the composition X was 0.01 to 0.05. The output factor P of Fe ₂ VAl is 0.04 × 10 ⁻³ [Wm ⁻¹ K ⁻² ], and the output factor P is not less than 2.0 × 10 ⁻³ [Wm ⁻¹ K ⁻² ]. This means that the output factor P is 5 times or more as compared with Fe ₂ VAl.

As shown in FIG. 3, the thermoelectric conversion material represented by Fe ₂ VAl _1-x Nd _x has an output factor P of 2.0 × 10 ⁻³ [Wm in a range where the composition X is 0.015 to 0.05. ⁻¹ K ⁻² ] or more.

As shown in FIG. 4, the thermoelectric conversion material represented by Fe ₂ VAl _1-x Sm _x has an output factor P of 2.0 × 10 ⁻³ [Wm ⁻¹ K in a range where the composition X is 0.02 or more. ^-2 ] or more.

As shown in FIG. 5, the thermoelectric conversion material represented by Fe ₂ VAl _1-x Gd _x has an output factor P of 2.0 × 10 ⁻³ [in the range where the composition X is about 0.018 to 0.08. Wm ⁻¹ K ⁻² ] or more.

As shown in FIG. 6, the thermoelectric conversion material represented by Fe ₂ VAl _1-x Tb _x has an output factor P of 2.0 × 10 ⁻³ [Wm in the range where the composition X is 0.02 to 0.05. ⁻¹ K ⁻² ] or more.

FIG. 7 shows the relationship between the output factor P and the temperature for the samples obtained in Examples I to V. The power factor P of the thermoelectric conversion material having a composition represented by Fe ₂ VAl and Fe ₂ VAl _1-x M _x becomes a large value near room temperature, and decreases as the temperature increases.

FIG. 8 shows the results of measuring the thermal conductivity κ of the samples obtained in Examples I to V. When Y, Nd, and Tb are used as the rare earth elements, the thermal conductivity decreases as the composition X increases. For Sm, there is a peak of the thermal conductivity of the composition X is in the vicinity of 0.01, the peak value is greater than the thermal conductivity of the _Fe 2 VAl is not replaced until the composition X is 0.02 _strong, the Fe 2 VAl The thermal conductivity is larger than the thermal conductivity. In the case of Gd (gadolinium), the composition X has a peak of thermal conductivity in the vicinity of 0.02, the peak value is larger than the thermal conductivity of Fe ₂ VAl that is not substituted, and the peak value is 0 when the composition X of Sm is 0. It is almost equal to the value of thermal conductivity of just over .02. FIG. 8 confirms that, regardless of the type of substituted rare earth element, if the composition X of the rare earth element is 0.03 or more, the thermal conductivity is higher than that of Fe ₂ VAl not replacing Al. it can.

This embodiment has the following effects.
(1) In the thermoelectric conversion material, a part of Al is substituted with a rare earth element with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and when the rare earth element is M, Fe ₂ VAl _{1 -X} M _{Expressed as x} . In this case, the output factor P can be made larger than that of Fe ₂ VAl in the presence of an additive element that is not harmful to Fe ₂ VAl having a Heusler alloy type crystal structure. Further, when manufacturing a thermoelectric conversion material, by adding Fe, V, in addition to rare earth element Al as a raw material, it can be produced by the same method as the manufacturing method of Fe 2 _VAl.

(2) The rare earth element substituted for a part of Al with respect to the basic structure of Fe ₂ VAl is one selected from Y, Nd, and Tb. In this case, since the thermal conductivity of the thermoelectric conversion material is decreased in addition to the output factor P being larger than Fe ₂ VAl, the thermoelectric conversion material that does not decrease the thermal conductivity even when the output factor P is the same. The figure of merit is larger than

(3) When the rare earth element substituted with a part of Al is Y with respect to the basic structure of Fe ₂ VAl, the composition X is the same when the composition X of the rare earth element substituted with Al is 0.05 or less. As compared with the case of substituting with other rare earth elements, the output factor P becomes larger and the performance as a thermoelectric conversion material becomes higher.

(4) When the composition X of the rare earth element substituted with a part of Al with respect to the basic structure of Fe ₂ VAl is in the range of 0.02 to 0.05, the output factor P is 2.0 × 10 ^−3. [Wm ⁻¹ K ⁻² ] or more, which is 5 times or more the output factor P of Fe ₂ VAl.

(5) When the rare earth element substituted with a part of Al is Y and the composition X of Y substituted with Al is in the range of 0.006 to 0.079 with respect to the basic structure of Fe ₂ VAl, the output factor P becomes 2.0 × 10 ⁻³ [Wm ⁻¹ K ⁻² ] or more, and becomes 5 times or more the output factor P of Fe ₂ VAl in a wide range of the composition X as compared with other rare earth elements.

(Second Embodiment)
Next, a second embodiment embodying the present invention will be described. In this embodiment, the thermoelectric conversion material is obtained when a part of Al is substituted with rare earth element and Si with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and the rare earth element is M. It has a composition represented by Fe ₂ VAl _1-mn M _m Si _n . A thermoelectric conversion material having this composition also becomes an n-type thermoelectric conversion material.

The output factor P of the thermoelectric conversion material having the composition represented by Fe ₂ VAl _1-mn M _m Si _n becomes a large value near room temperature, and decreases as the temperature increases.
Fe ₂ thermoelectric conversion material of substituted _Fe 2 _{VAl 1-x M x} part of Al in the rare-earth elements to the basic structure of the VAl is, _Fe part of Al is substituted with Si 2 _{VAl 1-x} Since the value of the output factor P becomes large when the composition X is small as compared with Si _x , the value of the output factor P becomes large due to a synergistic effect by replacing a part of Al with rare earth elements and Si. Conceivable.

When the rare earth element M is Y in the composition represented by Fe ₂ VAl _1-mn M _m Si _n , the output factor P is larger than when the rare earth element other than Y is substituted, and the thermoelectric element The performance as a conversion material becomes high. The maximum value of the output factor P of the thermoelectric conversion material represented by Fe ₂ VAl _0.93 Y _X Si _0.07-X (where 0 <X <0.28) is Example I in the first embodiment. greater than _Fe 2 _{VAl 0.98} maximum value of the power factor P of the thermoelectric conversion material represented by Y _0.02 a.

Hereinafter, the embodiment will be described in more detail.
The thermoelectric conversion material of this embodiment can also be manufactured by the same manufacturing method as the thermoelectric conversion material of the first embodiment. In the same manner as in the first embodiment, sample preparation, measurement sample preparation, hardness test, X-ray diffraction, composition analysis, electrical property measurement, thermal conductivity measurement, and evaluation as a thermoelectric material were performed.

In the composition formula represented by Fe ₂ VAl _0.93 Y _X Si _0.07-X , the raw materials were weighed so that the composition X of Y would be the value shown in Table 3, and a part of the rare earth element (this implementation In the examples, Y) and Si substituted alloys were made. As a result of performing X-ray diffraction and composition analysis on each sample, it is confirmed that both are alloys having a Heusler alloy type crystal structure and represented by Fe ₂ VAl _1-mn Y _m Si _n. It was done.

得られた合金の硬度を測定した結果、基準となるＦｅ_２ＶＡｌ（硬度３８５Ｈｖ）に比較して硬度が１割以上増加した。

As a result of measuring the hardness of the obtained alloy, the hardness increased by 10% or more compared to the reference Fe ₂ VAl (hardness 385 Hv).

About the obtained sample, the thermoelectromotive force E ₀ and the temperature difference ΔT (T _h −T _c ) are measured at 313 K using a thermoelectric power measuring device, and the Seebeck coefficient α and the electrical resistivity ρ are obtained. The output factor P [Wm ⁻¹ K ⁻² ] was determined. The results are shown in FIG. For comparison, the thermoelectric conversion material represented by Fe ₂ VAl _1- XY _X and the thermoelectric conversion material represented by Fe ₂ VAl _1-X Si _X are also shown in FIG. The result of obtaining the output factor P is also shown.

As shown in FIG. 9, the thermoelectric conversion material represented by Fe ₂ VAl _0.93 Y _X Si _0.07-X has a power factor P of 1st when the composition X is in the range of 0.002 to 0.028. In the embodiment, the output factor P of the thermoelectric conversion material represented by Fe ₂ VAl _0.98 M _0.02 having the maximum output factor P is larger than 4.02 × 10 ⁻³ [Wm ⁻¹ K ⁻² ]. became. Further, when the composition X of Y was 0.01, the output factor P was maximized at 5.3 × 10 ⁻³ [Wm ⁻¹ K ⁻² ].

This embodiment has the following effects.
(6) Thermoelectric conversion materials, Fe ₂ part of Al with respect to the basic structure of Fe 2 _VAl having a crystal structure of the Heusler alloy type has been replaced by rare earth elements and Si, a rare earth element when the M It is represented by VAl _1-mn M _m Si _n . In this case, the output factor P can be made larger than that of Fe ₂ VAl in the presence of an additive element that is not harmful to Fe ₂ VAl having a Heusler alloy type crystal structure. Further, when manufacturing a thermoelectric conversion material, by adding Fe, V, in addition to rare earth elements and Al of Al as a raw material, it can be produced by the same method as the manufacturing method of Fe 2 _VAl.

(7) When the rare earth element is Y, the output factor P is increased and the performance as a thermoelectric conversion material is enhanced as compared with the case where other rare earth elements are used.
(8) When the composition of the thermoelectric conversion material is Fe ₂ VAl _0.93 Y _X Si _0.07-X , the output factor P is in the range where the composition X is 0.07 or less near room temperature (for example, 313 K). _but greater than the output factor P of the thermoelectric conversion material represented by _{Fe 2 VAl 1-X Y X} .

(9) When the composition of the thermoelectric conversion material is Fe ₂ VAl _0.93 Y _X Si _0.07-X , the composition X is in the range of 0.002 to 0.028 near room temperature (for example, 313 K). The output factor P becomes greater than the maximum value of the output factor of the thermoelectric conversion material represented by Fe ₂ VAl _1- XY _X.

(10) When the composition of the thermoelectric conversion material is Fe ₂ VAl _0.93 Y _X Si _0.07-X , the composition X is in the range of 0.002 to 0.03 near room temperature (for example, 313 K). The output factor P becomes larger than the output factor P of the thermoelectric conversion material represented by Fe ₂ VAl _1-X Si _X.

The embodiment is not limited to the above, and may be configured as follows, for example.
In the second embodiment, the rare earth substituted with a part of Al together with Si is not limited to Y, but may be other rare earths. In this case, in the first embodiment, the composition X corresponding to the substitution amount for Al is 0.2 or 0.3, and the output factor P is 3.0 × 10 ⁻³ [Wm ⁻¹ K ⁻² ] or more. Or Gd is preferable.

In the second embodiment, the composition of Y and Si was changed by setting the Al composition to 0.93, but the composition of Y and Si may be changed by changing the composition of Al to a value other than 0.93. .
○ part of Al with respect to the basic structure of the _Fe 2 VAl having a Heusler alloy type crystal structure is substituted with a rare earth element is represented by _Fe 2 _{VAl 1-X M} X when the rare earth element is M The thermoelectric conversion material is good. However, depending on the method for producing the thermoelectric conversion material, there is a possibility that a part of the obtained alloy partially substitutes a part of Fe or V with a rare earth element. Even in such a case, when viewed as a whole alloy portion represented by Fe 2 _{VAl 1-X} M _X is if main phase, the same effect can be obtained.

○ Thermoelectric conversion represented by Fe ₂ VAl _1-mn M _m Si _{n in} which a part of Al is substituted with rare earth elements and Si with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure Similarly, in the case of the material, even when part of Fe or V constituting the thermoelectric conversion material is locally substituted with a rare earth element, when viewed as the whole alloy, Fe ₂ VAl _1-mn M _m if part main phase represented by Si _n, the same effect can be obtained.

The following technical idea (invention) can be understood from the embodiment or the examples.
(1) before SL composition X is 0.02 to 0.05.
(2) pre-Symbol rare earth element is Y, the composition X is 0.006 to 0.079.

(3) pre-Symbol rare earth element is Y, the composition X is 0.05 or less.
(4) before Symbol rare earth element is Y, m + n = 0.07, and is 0.002 ≦ m ≦ 0.03.

(5) A part of Al is substituted with a rare earth element with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and when the rare earth element is M, Fe ₂ VAl _1-x M _x A thermoelectric conversion material characterized in that a portion having a composition represented is a main phase.

(6) A part of Al is substituted with rare earth elements and Si with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and when the rare earth element is M, Fe ₂ VAl _1-m- thermoelectric conversion material characterized in that _n M _m Si _n is a composition represented by parts is the main phase.

(7) As starting materials, Fe, V, Al and rare earth are represented by Fe: 50 at%, V: 25 at%, Al: (25-α) at% _, M: α at% when the rare earth element is M. A thermoelectric conversion material having a Heusler alloy type crystal structure obtained by weighing so as to have a composition to be obtained and melting them in a melting furnace as a raw material mixture. However, 0 <α <3.0.

(8) Fe: V, Al, rare earth and Si as starting materials, Fe: 50 at%, V: 25 at%, Al: (25-α-β) at% _, M: A thermoelectric conversion material having a Heusler alloy type crystal structure obtained by weighing them so as to have a composition represented by αat%, Si: βat%, and melting them in a melting furnace as a raw material mixture. However, 0 <α <3.0, 0 <β <3.0, and 0 <α + β <3.0.

The schematic diagram which shows the structure of the measurement part of a thermoelectric power measuring apparatus. The graph which shows the relationship between the composition of the thermoelectric conversion material in Example I, and an output factor. The graph which shows the relationship between the composition of the thermoelectric conversion material in Example II, and an output factor. The graph which shows the relationship between the composition of the thermoelectric conversion material in Example III, and an output factor. The graph which shows the relationship between the composition of the thermoelectric conversion material in Example IV, and an output factor. 6 is a graph showing the relationship between the composition of the thermoelectric conversion material and the output factor in Example V. FIG. The graph which shows the relationship between the output factor and temperature in a thermoelectric conversion material. The graph which shows the relationship between the composition and thermal conductivity in the thermoelectric conversion material of each Example. The graph which shows the relationship between the composition of the thermoelectric conversion material in 2nd Embodiment, and an output factor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Measurement part, 11, 12 ... Electrode, 13a, 13b ... Probe, 14 ... Inter-probe voltage measurement part.

Claims (2)

A part of Al is substituted with rare earth elements and Si with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and Fe ₂ VAl _1-mn M _{m where} M is the rare earth element. A composition represented by Si _n ,
The rare earth element is Y, and the composition m and the composition n are m + n = 0.07 and 0.002 ≦ m ≦ 0.03 . A part of Al is substituted with rare earth elements and Si with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure, and Fe ₂ VAl _1-mn M _{m where} M is the rare earth element. A composition represented by Si _n ,
The rare earth element is one selected from Nd, Sm, Gd, and Tb, and the composition m and the composition n are 0 <m <1, 0 <n <1, 0 <m + n <1. thermoelectric conversion material characterized.

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