KR20190088764A - Semiconductor compound and thermoelectric element including the same - Google Patents

Abstract

In a semiconductor compound according to one embodiment of the present invention part of Fe is substituted by Zn in a semi-Hoisler material based on p-type NbFeSb. An objective of the present invention is to provide a semiconductor compound exhibiting the excellent output factor and reducing thermal conductivity and a thermoelectric element including the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a semiconductor compound and a thermoelectric device including the same. BACKGROUND OF THE INVENTION [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor compound and a thermoelectric device including the same, and more particularly, to a semiconductor compound and a thermoelectric device having a new composition in which a part of an element of the Semi-Hosler material is substituted.

Recently, researches on thermoelectric conversion materials using waste heat as one of alternative energy have been accelerated due to environmental problems due to resource depletion and combustion.

The energy conversion efficiency of the thermoelectric conversion material depends on ZT which is the thermoelectric performance index value of the thermoelectric conversion material. Here, ZT is determined according to Seebeck coefficient, electric conductivity and thermal conductivity as shown in the following equation (1). More specifically, it is proportional to the square of the Seebeck coefficient and the electric conductivity, and is inversely proportional to the thermal conductivity.

[Equation 1]

ZT =? S ² T / K,

(In the above equation (1),? Is the electric conductivity, S is the Seebeck coefficient, K is the thermal conductivity, and T is the absolute temperature.)

Therefore, in order to increase the energy conversion efficiency of a thermoelectric element, development of a thermoelectric conversion material exhibiting a high output factor (PF = σS ² ) or a low thermal conductivity (K) due to a high heat transfer coefficient (S) need.

In particular, Half-Heusler materials as thermoelectric conversion materials have a high output factor (PF = sigma S ² ) due to their high electrical conductivity. However, due to the interdependence of the electrical and thermal properties of thermoelectric materials, they have a higher thermal conductivity than other materials and thus lower the ZT value.

In recent years, a composition obtained by replacing a part of Fe with Co in a material based on NbFeSb has been disclosed in the prior art publication US Publication No. 2015-0270465. However, since the Co substitution imparts an n type property, the electric conductivity decreases and the output factor can be reduced.

Embodiments are to provide a new composition semiconductor compound and a thermoelectric device including the same which can reduce the thermal conductivity while exhibiting excellent output factors by increasing the electrical conductivity by replacing a part of Fe in the Semi-Hoistler material.

However, the problems to be solved by the embodiments of the present invention are not limited to the above-mentioned problems, but can be variously extended within the scope of the technical idea included in the present invention.

Semiconductor compounds according to one embodiment of the present invention are partially substituted with Zn in the semi-Hoesler material based on p-type NbFeSb.

The semiconductor compound may be represented by the following general formula (I).

Fe _1-x Zn _x Nb _1-y A _y Sb _{1 -z} ????? (I)

Here, 0 <x <0.1, 0 <y <1.0, 0 <z <0.1, and A is a transition metal.

In formula (I), A may be at least one transition metal selected from the group consisting of Ti, Zr, Hf, V, Ta, Mo, W, Co and Cr.

In the formula (I), the second phase of Zn is not present or the content of the second phase of Zn may be 0.05 wt% or less.

The content of the second phase of ZnSb in the above formula (I) may be 0.20 wt% or less.

The semiconductor compound represented by Formula (I) may have a cubic system structure.

The semiconductor compound represented by the above formula (I) may have a space group of F-43m.

A thermoelectric device according to an embodiment of the present invention includes the above-described semiconductor compound.

According to the embodiments, by realizing the semiconductor compound and the thermoelectric element having the composition formed by replacing the Fe part of the Semi-Hoistler material with Zn, it is possible to increase the electrical conductivity, to exhibit excellent output factors and to reduce the thermal conductivity.

1 is a graph showing a thermoelectric performance index value (ZT) according to a composition ratio of Sb in a compound semiconductor according to an embodiment of the present invention.
FIG. 2 is a graph showing electrical characteristics in the case where the Fe part of the Semi-Hoistler material is Co-substituted.
3 is a graph showing an XRD pattern according to embodiments of the present invention and a comparative example.
4 is a graph showing electrical conductivity according to embodiments of the present invention and a comparative example.
5 is a graph showing lattice thermal conductivity according to embodiments of the present invention and a comparative example.
FIG. 6 is a graph showing an XRD pattern after attempting to replace a part of Fe of the Semi-Hoistler material with Cu.
7 is a partially enlarged view of the portion "A" in Fig.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Also, throughout the specification, when an element is referred to as "including" an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

The semiconductor compound according to an embodiment of the present invention has a composition in which a part of Fe is substituted with a transition metal in a semi-Hoesler material based on p-type NbFeSb. According to this embodiment, the transition metal may be Zn. Specifically, the semiconductor compound according to this embodiment can be represented by the following formula (I).

Fe _1-x Zn _x Nb _1-y A _y Sb _{1 -z} ????? (I)

Here, 0 <x <0.1, 0 <y <1.0, 0 <z≤0.1, and A is a transition metal.

In the above formula (I), A is at least one transition metal selected from the group consisting of Ti, Zr, Hf, V, Ta, Mo, W, Co and Cr. It is an element included in the semiconductor compound of the example.

Sb in the above formula (I) was synthesized from FeNb _0.85 Ti _0.15 Sb _1-z as z = 0, 0.02, 0.04, 0.06, 0.08 and 0.1 (Zn is unsubstituted) FeSb system secondary phase was observed at x = 0, and it was confirmed that all phases from z = 0.02 to z = 0.1 were synthesized in a single phase.

FeNb _0.85 Ti _0.15 Sb _1-z
powder
rietveld refinement Lattice parameter
(Angstrom) R _wp (%) FeNb _0.85 Ti _0.15 Sb _1-z
(wt%) FeSb
(wt%) Z = 0.1 5.951 4.178 100 - Z = 0.08 5.951 3.849 100 - Z = 0.06 5.951 4.600 100 - Z = 0.04 (Comparative Example 1) 5.950 3.323 100 - Z = 0.02 5.951 4.155 100 - Z = 0 5.950 3.512 94.17 5.03

Accordingly, the semiconductor compound according to an embodiment of the present invention is set to FeNb _0.85 Ti _0.15 Sb _1-z (z is not 0) as a basic composition, and a part of Fe is substituted with Zn.

1 is a graph showing a thermoelectric performance index value (ZT) according to a composition ratio of Sb in a compound semiconductor according to an embodiment of the present invention.

Referring to FIG. 1, the thermocompression index of z = 0.04 to z = 0.1 is the best when z = 0.04, and the value of thermoelectric performance index tends to decrease gradually as z increases to 0.06, 0.08 and 0.1. Therefore, when z is larger than 0.1, the value of the thermoelectric performance index further decreases to deteriorate the performance of the thermoelectric device including the semiconductor compound according to the present embodiment. Therefore, in the compound semiconductor according to the present embodiment, z is greater than 0 and 0.1 Or less.

Semiconductor compounds in which the Fe part of the semi-Hoists type base based on the p-type NbFeSb according to this embodiment is substituted with Zn belong to the semi-hoistler group with a cubic system structure. Also, it can have space group F-43m. Space group is a group made of a combination of elements showing the symmetric structure when there is a crystal structure inside the material. The symmetrical structure affects the appearance and properties of the material and has 230 types.

In the case of the atom substitution in which a part of Fe is substituted with Zn in the present embodiment, since the element is changed to another element at the same site in the crystal structure, the crystal structure can be maintained before and after the substitution. However, the cell parameters, crystallinity, and intensity may vary due to differences in element sizes, differences in chemical properties of the elements, and differences in elemental bonding force. Since the semiconductor compound according to this embodiment has a cubic system structure and belongs to the anti-Hoesler group, it can be regarded as a different material if the basic crystal structure is changed.

In this embodiment, since a part of the constituent element Fe contained in the Semi-Hoistler material is replaced with Zn, the electrical conductivity can be increased to exhibit an excellent output factor and the thermal conductivity can be reduced. The above effect can be realized by selecting Zn as a transition metal in which a part of Fe is substituted. For comparison with a case where a part of Fe is replaced with Co, which is not Zn, will be described with reference to FIG.

FIG. 2 is a graph showing electrical characteristics in the case where the Fe part of the Semi-Hoistler material is Co-substituted. Fig. 2 (a) shows the whitening coefficient according to the degree of substitution of Fe with Co, and Fig. 2 (b) is a graph showing the electric conductivity according to the temperature.

Referring to FIG. 2, as the ratio of Co increases (x decreases) in the p-type ZrCo _1-x Fe _x Sb of the anti-Hoistler material, the electric conductivity Is decreased. Likewise, when the Fe part of the semi-Hoistler material based on the p-type NbFeSb according to an embodiment of the present invention is substituted with Co, the n-type property is imparted to decrease the hole carrier concentration, The characteristics can be reduced.

3 is a graph showing an XRD pattern according to embodiments of the present invention and a comparative example. In the following Table 2, Comparative Example 1 is a composition of the Fe-substituted Fe-Izeller material, Examples 1, 2 and 3 show the Fe content of the Fe- , And Zn with 10% composition ratio.

Furtherance Comparative Example 1 FeNb0.85Ti0.15Sb0.96 Example 1 Fe0.99Zn0.01Nb0.85Ti0.15Sb0.96 Example 2 Fe0.95Zn0.05Nb0.85Ti0.15Sb0.96 Example 3 Fe _0.90 Zn _0.10 Nb _0.85 Ti _0.15 Sb _0.96

Table 3 below shows the results of secondary phase content analysis by Rietveld refinement of the XRD patterns of Examples 1, 2, and 3. R _wp is one of the reliability factors of the Rietveld method analysis, and if the R _wp is less than 5, the analysis result is regarded as reliable.

Fe _1-x Zn _x Nb _0.85 Ti _0.15 Sb _0.96
powder
rietveld refinement Lattice parameter R _wp (%) Zn
(wt%) ZnSb
(wt%) FeSb
(wt%) Comparative Example 1 x = 0 mol% 5.950 3.323 - - - Example 1 x = 1 mol% 5.951 2.573 0.00 0.17 0.11 Example 2 x = 5 mol% 5.950 2.331 0.03 0.18 0.01 Example 3 x = 10 mol% 5.951 2.105 0.3 1.31 0.21

Referring to FIG. 3 and Table 3, it can be confirmed through the XRD structure analysis that the Zn substitution was successfully performed in Examples 1 and 2 without generating the second phase. In Example 3, a peak indicating a secondary phase is observed in a part, that is, the remaining Zn is present in a secondary phase such as Zn and / or ZnSb.

In the present specification, the term &quot; second phase &quot; means phases different from those of the desired composition. Although the composition represented by the formula (I) according to the present embodiment was intended to be prepared, it was found that the composition of the actually produced compound is not a composition of the general formula (I), but a peak corresponding to a shape capable of representing the formula (I) It indicates that a peak appears. In other words, although it was intended to make a material consisting of 100% of the XRD pattern representing Formula I, it means that the XRD pattern of Formula I is mixed with another secondary phase for some reason.

In Table 3, in the case of Examples 1 and 2, Zn and ZnSb are contained in the second phase in an amount of 0.05 wt% or less and 0.20 wt% or less, respectively, and 0.3 wt% of Zn and 0.18 wt% The ZnSb of ZnSb has a very small level, so that there is no problem in showing the effect of reducing the thermal conductivity in addition to the increase of the electric conductivity according to the embodiment of the present invention. In Example 3, although the secondary phase occurs over a certain level, since the secondary phase Zn is less than 0.5 wt% and the secondary phase ZnSb is less than 1.5 wt%, the electric conductivity is slightly lower than that of Example 2 as described later.

Hereinafter, the thermoelectric properties according to Examples 1, 2 and 3 and Comparative Example 1 will be evaluated and compared with reference to Figs. 4 and 5. Fig.

4 is a graph showing electrical conductivity according to embodiments of the present invention and a comparative example. 5 is a graph showing lattice thermal conductivity according to embodiments of the present invention and a comparative example.

Referring to FIG. 4, the electric conductivity of Examples 1, 2 and 3 was higher than that of Comparative Example 1. In Example 3 where 10% of Zn was substituted, the electric conductivity was higher than that of Example 2 . &Lt; / RTI &gt;

Referring to FIG. 5, as the Zn substitution amount increases, the lattice thermal conductivity decreases.

FIG. 6 is a graph showing an XRD pattern after attempting to replace a part of Fe of the Semi-Hoistler material with Cu. 7 is a partially enlarged view of the portion "A" in Fig. In the following Table 4, Comparative Example 1 is a composition of the Fe-substituted Hoesler material, and Comparative Examples 3, 4 and 5 are compositions of the Fe part included in the anti- , And Cu with a composition ratio of 10%.

Furtherance Comparative Example 1 FeNb0.85Ti0.15Sb0.96 Comparative Example 2 Fe0.98Cu0.02Nb0.85Ti0.15Sb0.96 Comparative Example 3 Fe0.95Cu0.05Nb0.85Ti0.15Sb0.96 Comparative Example 4 Fe _0.90 Cu _0.10 Nb _0.85 Ti _0.15 Sb _0.96

Table 5 below shows the results of analysis of the secondary phase content by Rietveld refinement of the XRD patterns of Comparative Examples 2, 3 and 4.

Fe _1-x Cu _x Nb _0.85 Ti _0.15 Sb _0.96
powder
rietveld refinement Lattice parameter R _wp (%) Nb ₅ Sb ₄
(wt%) Cu ₂ Sb
(wt%) Cu ₁₀ Sb ₃
(wt%) Ti ₄ Nb
(wt%) Comparative Example 1 x = 0 mol% 5.950 3.323 - - - - Comparative Example 2 x = 2 mol% 5.950 4.257 1.33 1.43 1.30 0.48 Comparative Example 3 x = 5 mol% 5.950 4.154 2.92 2.27 1.46 0.13 Comparative Example 4 x = 10 mol% 5.950 4.443 2.34 2.28 2.29 1.84

6, 7, and Table 5, the semiconductor compound in which a part of Fe-based FeSb based Fe-based Fe-based NbFeSb was replaced with Cu showed that Fe was not easily substituted by Cu as a result of XRD analysis Can be confirmed. Unsubstituted Cu exists as Cu ₂ Sb, Cu ₁₀ Sb _3, etc. As a result, the stoichiometric ratio of the remaining elements is shifted, and secondary phases such as Nb ₄ Sb ₄ and Ti ₄ Nb ₄ are observed together.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

Claims (8)

Semiconductor compound wherein part of Fe is substituted with Zn in semi-Hoesler material based on p-type NbFeSb. The method of claim 1,
Wherein the semiconductor compound is represented by the following formula < RTI ID = 0.0 &gt; (I) <
Fe _1-x Zn _x Nb _1-y A _y Sb _{1 -z} ????? (I)
(0 <x <0.1, 0 <y <1.0, 0 <z≤0.1, A is a transition metal). 3. The method of claim 2,
Wherein A is at least one transition metal selected from the group consisting of Ti, Zr, Hf, V, Ta, Mo, W, Co and Cr. 3. The method of claim 2,
Wherein the second phase of Zn is absent or the content of the second phase of Zn is 0.05 wt% or less. 3. The method of claim 2,
Wherein the content of the second phase of ZnSb in the formula (I) is 0.20 wt% or less. 3. The method of claim 2,
The semiconductor compound represented by Formula (I) has a cubic system structure. The method of claim 6,
Wherein the semiconductor compound represented by Formula (I) has a space group of F-43m. A thermoelectric device comprising the semiconductor compound of any one of claims 1 to 7.

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