KR102269412B1 - Thermoelectric materials thermoelectrically enhanced by doping materials - Google Patents

Abstract

A technical gist of the present invention is that a doping material made of M'Q' is added to a thermoelectric material made of MQ in a thermoelectric material whose thermoelectric performance is improved by adding a dopant. (The M and M' are metal materials, and Q and Q' are selected from the group consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and mixtures thereof.) Accordingly, it is possible to obtain a thermoelectric material with improved thermoelectric performance by comparing the lattice state and energy barrier values between the thermoelectric material and the dopant, and adding the selected dopant through this. In addition, it is possible to obtain a thermoelectric material with improved thermoelectric performance by adding a doping material in which the content to be added to the thermoelectric material can be selected according to the thermoelectric properties of the doping material.

Description

Thermoelectric materials thermoelectrically enhanced by doping materials

The present invention relates to a thermoelectric material with improved thermoelectric performance by adding a dopant, and more particularly, to a thermoelectric material with improved thermoelectric performance by comparing the lattice state and energy barrier values between the thermoelectric material and the doping material, and adding a doping material selected through this. It's about the material.

The thermoelectric effect is due to the fact that kinetic energy or thermal energy is transferred together with the electric charge when electrons or holes in the solid move. The thermoelectric phenomenon is a direct energy conversion between electrical energy and thermal energy, and can be used for thermoelectric power generation and thermoelectric cooling. In a thermoelectric material, as thermoelectric properties are improved, the efficiency of a thermoelectric element is improved. Thermoelectric characteristics that determine such thermoelectric performance are thermoelectric (V), Seebeck coefficient (S), Peltier coefficient (π), Thomson coefficient (τ), Nernst coefficient (Q), Ettingshausen coefficient (P), electrical conductivity ( σ), output factor (PF), figure of merit (Z), dimensionless figure of merit (ZT), thermal conductivity (κ), Lorentz number (L), and electrical resistivity (ρ).

Among them, the dimensionless figure of merit (ZT) is an important index that determines the thermoelectric conversion energy efficiency and can be expressed through the following equation.

ZT=S ² σT/κ

Here, S is the Seebeck coefficient [μV/K], σ is the electrical conductivity [1/(ohm×cm)], T is the temperature [K], and κ is the thermal conductivity [W/mK ² ]. In this formula, the part excluding T is an output factor (power factor), which is a measure that can evaluate the thermoelectric conversion characteristics. The output factor is a value indicating the output of the unit length per unit area of the material, and a high ZT value can be obtained only when the output factor is excellent. In other words, the Seebeck coefficient and electrical conductivity are excellent at the same time, and a material with low thermal conductivity has excellent thermoelectric properties. By manufacturing such a thermoelectric material, it is possible to increase the efficiency of cooling and power generation.

Among thermoelectric materials, AgPb _m SbTe _{m +2} alloy is known to have excellent thermoelectric properties, and recently, a lot of research has been done on a technique for manufacturing an alloy by adding a metal dopant to the thermoelectric material. However, these studies have limitations in determining a thermoelectric material whose thermoelectric performance is improved by adding a dopant because there is no standard for selecting a dopant according to the physical properties of the thermoelectric material.

Korean Intellectual Property Office Registered Patent No. 10-1417968 Korean Intellectual Property Office Registered Patent No. 10-1417965

Accordingly, an object of the present invention is to provide a thermoelectric material with improved thermoelectric performance by comparing lattice state and energy barrier values between a thermoelectric material and a dopant, and adding a doping material selected through this.

Another object of the present invention is to provide a thermoelectric material with improved thermoelectric performance by adding a doping material in which the content to be added to the thermoelectric material can be selected according to the thermoelectric characteristics of the doping material.

The above object is achieved by a thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that a doping material made of M'Q' is added to a thermoelectric material made of MQ. (The M and M' are metal materials, and Q and Q' are selected from the group consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and mixtures thereof.)

Here, the M'Q' is selected by comparing the lattice state and energy barrier values of the MQ and the M'Q', and the lattice state of the MQ and the M'Q' is a lattice constant (Lattice constant) And it is preferable to compare including at least one of the lattice structure (Lattice structure).

The M'Q' is preferably selected to have a lattice constant value of -10% to 10% with respect to the lattice constant value of the MQ, or is selected to have the same lattice structure as the lattice structure of the MQ.

In addition, the energy barrier values of MQ and M 'Q' are less than or equal to 0.3 eV in the conduction band, and greater than or equal to 0.3 eV in the valence band, or greater than or equal to 0.3 eV in the conduction band, The valence band is preferably 0.3 eV or less.

According to the configuration of the present invention described above, it is possible to obtain a thermoelectric material with improved thermoelectric performance by comparing the lattice state and energy barrier values between the thermoelectric material and the dopant, and adding the selected doping material through this.

In addition, it is possible to obtain a thermoelectric material with improved thermoelectric performance by adding a doping material in which the content to be added to the thermoelectric material can be selected according to the thermoelectric properties of the doping material.

1 is a graph showing the lattice constant value according to the material,
2a and 2b are schematic views showing the flow of electrons and holes in n and p-type thermoelectric devices,
3 is a graph showing the conduction band and valence band values according to the material,
4 is a graph of FIG. 3 arranged in the order of conduction band values;
5 is a graph in which the valence band values of FIG. 3 are arranged in order,
6 is a view showing the lattice form of ZnO and Bi2Te3,
7 is a _{(Bi 2 Te 2 .7 Se 0} .3) / (ZnO) a view of the electron barrier and the hole barrier in the thermal material,
8 is a graph showing the electrical resistivity of the thermoelectric material according to the amount of ZnO added;
9 is a graph showing the Seebeck coefficient of the thermoelectric material,
10 is a graph showing the thermal conductivity of the thermoelectric material,
11 is a graph showing the dimensionless figure of merit of the thermoelectric material.

Hereinafter, a thermoelectric material with improved thermoelectric performance by adding a dopant according to an embodiment of the present invention will be described in detail with reference to the drawings.

In an MQ thermoelectric material consisting of a metal material M and Q selected from the group consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and mixtures thereof, M′ and oxygen ( O), sulfur (S), selenium (Se), tellurium (Te), and a new thermoelectric material is obtained by adding an M'Q' dopant composed of Q' selected from the group consisting of mixtures thereof. Here, as the metal materials M and M', a metal alloy in which a plurality of metals are mixed may also be used. In some cases, MQ thermoelectric material and M'Q' doping material may be selected so that M and M' are the same metal material or Q and Q' are the same material.

When the M'Q' dopant is added, it is placed between MQ thermoelectric materials having a specific lattice state to change the lattice state, thereby improving thermoelectric performance. In order to be disposed between the MQ thermoelectric materials in this way, the M'Q' dopant must have a lattice state similar to that of the MQ thermoelectric material. Lattice state refers to a lattice constant or a lattice structure, and if one of them is similar to MQ thermoelectric material or both are similar, it is suitable as an M'Q' dopant. That is, when the lattice constant values of the MQ thermoelectric material and the M'Q' dopant are compared, the thermoelectric performance of the new thermoelectric material can be increased only when they are similar or identical.

Comparing the lattice constant, it is preferable that the M'Q' dopant has a lattice constant value of -10% to 10% with a high possibility of forming a coherent interface with respect to the lattice constant value of the MQ thermoelectric material. This will be described in detail through the graph in which the lattice constant of FIG. 1 is described. The materials described in FIG. 1 may be an MQ thermoelectric material or an M'Q' doping material, and when the content is high, the MQ thermoelectric material is used, and when the content is lower than the MQ thermoelectric material, the M'Q doping material is used.

The lattice constant of MQ thermoelectric material can be calculated by performing the following method. A quantum computational simulation calculation method based on Density functional theory was performed. We used VASP DFT code and planewave basis, PAW potential, and PBE exchange-correlation energy approximation. Structure relaxation calculations were performed for a given lattice structure to obtain the lattice constant and atomic structure with the minimum total energy value. This can also be applied to the method of obtaining the lattice constant of the M'Q' dopant.

In FIG. 1 , in the case of h-Bi ₂ Te ₃ , the lattice constant value is 6.29 Å. When this is used as an MQ thermoelectric material, since the constant value of the MQ thermoelectric material is 6.29 Å, the lattice constant value that can be used as the M'Q' dopant is 5.66 Å to 6.92 Å, which is -10% to 10%. Materials within this range include BaS, BaSe, CaS, CaSe, CaTe, etc., which are h-Bi ₂ Te ₃ It is suitable as a doping material for thermoelectric materials. In addition, in the case of PbTe having a lattice constant of 6.56 Å, a material having a lattice constant value of 5.90 Å to 7.22 Å may be used as an M'Q' dopant. Here, when the lattice constant value of the M'Q' dopant is out of -10% to 10% compared to the MQ thermoelectric material, it cannot be placed between the MQ thermoelectric materials and is separated from each other, so it does not play a role in increasing the thermoelectric performance. Rather, it may act as an obstruction and adversely affect the flow of current.

When selecting the M'Q' dopant, it may be selected by comparing the lattice structure instead of the lattice constant. For the lattice structure, the MQ thermoelectric material and the M'Q' doping material must have the same lattice structure. When the MQ thermoelectric material having the same lattice structure and the M'Q' dopant are mixed, a coherent or semi-coherent interface is formed in the micro or nanometer region, thereby reducing electrical conductivity loss.

In the case of MQ thermoelectric materials, the lattice structure consists of MQ with rock-salt-type or distorted rock-salt-type, M ₂ Q with antifluororite or distorted antifluororite shape, M ₂ Q _{3 with} rhombohedral or tetradymite shape, MQ ₂ and mixtures thereof. selected from the group. In the case of the M'Q' dopant, like the MQ thermoelectric material, the lattice structure is selected from the group consisting _{of M'Q', M' 2} Q', M' ₂ Q' ₃ , M'Q' _{2 and mixtures thereof.} Therefore, the doping material added to the thermoelectric material having a lattice structure of M _{2 O preferably has a lattice structure of M′ 2} Q′ like the thermoelectric material. If the lattice constants are not similar and the lattice structure is not identical, the thermoelectric material and the dopant do not mix and act as an obstacle.

Therefore, if the MQ thermoelectric material and the M'Q' dopant have similar lattice constants or are mixed with the same lattice structure, the thermoelectric performance can be improved. Alternatively, when both the lattice constant and the lattice structure have desirable values, the thermoelectric performance is expected to be further improved.

MQ thermoelectric material and M'Q' doping material should be selected by comparing not only the lattice state but also the energy barrier value. The energy barrier value can be compared through the difference between the conduction band and the valence band between the MQ thermoelectric material and the M'Q' dopant. If the conduction band difference between the MQ thermoelectric material and the M'Q' dopant is 0.3 eV or less, the valence band difference must be 0.3 eV or more, and when the conduction band difference is 0.3 eV or more, the valence band difference must be 0.3 eV or less. This is because in MQ thermoelectric material, the flow of the majority carrier is not interrupted through the M'Q' dopant, and the minority carrier of the MQ thermoelectric material is prevented from flowing through the M'Q' doping material. This is because electrical conductivity must be maintained. Through this, the Seebeck coefficient and thermal conductivity are improved, and finally, the dimensionless figure of merit increases, thereby improving the thermoelectric performance.

The energy barrier value was calculated using the following method. The surface atomic structure of each MQ thermoelectric material or M'Q' dopant is implemented, the electronic structure of the DFT is calculated, and the electronic structure is calculated in comparison with the vacuum energy (Evac), and the valence band maximum obtained through this : Ev) and conduction band minimum (Ec) values were calculated. And energy barrier values were obtained by calculating the Evac-Ev and Evac-Ec values of each material.

If the conduction band difference and the valence band difference are both less than 0.3 eV, the thermoelectric performance improvement is insignificant even with the addition of M'Q' doping material. If the conduction band difference and the valence band difference are both 0.3 eV or more, it is not placed between MQ thermoelectric materials. Since they are separated from each other, they cannot serve to increase the thermoelectric performance, but also act as an obstacle and adversely affect the flow of current.

This can be explained by applying it to a thermal semiconductor device as shown in FIG. 2 . Figure 2a shows an n-type thermal semiconductor device E _{B . major} represents electrons, which are majority charges in n-type. Electrons, which are majority-charged, can move smoothly when the conduction band difference or the valence band difference is 0.3 eV or less. E _{B . minor} represents a hole, which is a minor charge in the n-type, and should be greater than the level that blocks electrons, which is 0.3 eV or less, since it should be made at a level that is higher than the level that blocks electron movement. That is, in the case of a minor charge, the difference between the conduction band and the valence band must be 0.3 eV or more.

On the contrary, as shown in FIG. 2b , the p-type thermal semiconductor device is E _{B . Major} becomes hole and E _B.minor becomes electron. Therefore, when the hole conduction band difference or the valence band difference is 0.3 eV or less, the electron becomes 0.3 eV conversely. In an n-type thermal semiconductor, heat moves according to the flow of electrons, and in a p-type thermal semiconductor, heat moves according to the flow of holes to lower the temperature of the heat absorbing part. It is preferable that the energy barrier values of n-type and p-type are opposite to each other.

As such, when the conduction band difference between the MQ thermoelectric material and the M'Q' doping material is 0.3 eV or less, the valence band difference must be 0.3 eV or more, and when the conduction band difference is 0.3 eV or more, the valence band difference must be 0.3 eV or less.

3 is a graph showing the conduction band (CB) and the valence band (VB) of materials that can be used as MQ thermoelectric materials or M'Q' doping materials. Through the graph calculated as follows, the conduction band difference and the valence band difference for the two materials can be checked, and a material that can improve the thermoelectric performance through the conduction band difference and the valence band difference can be selected.

Comparing FIG. 3 with FIG. 4 organized according to conduction band values, the _{conduction band difference between Sb 2} Te ₃ and wz-ZnO is 0.3 eV or less, and the valence band difference is 0.3 eV or more. So Sb ₂ Te ₃ Alternatively, it can be predicted that the thermoelectric performance will be improved when one of wz-ZnO is used as an MQ thermoelectric material and the other is used as an M'Q' dopant and mixed.

FIG. 5 is a graph sequentially arranged according to the valence band values of FIG. 3, and when it is confirmed, the _{valence band difference between Bi 2} Se ₃ and zb-ZnS is 0.3 eV or less, and the conduction band difference is 0.3 eV or more. i.e. Bi ₂ Se ₃ Alternatively, if one of zb-ZnS is used as an MQ thermoelectric material and the other is used as an M'Q' dopant, it can be predicted that the thermoelectric performance will be improved.

MQ thermoelectric material and M'Q' doping material are BaS, BaSe, BaTe, CaS, CaSe, CaTe, zb-CdS, zb-CdSe, zb-CdTe, CeS, CeSe, CeTe, EuS, EuSe, EuTe, GeS, GeSe, GeTe, zb-HgS, zb--HgSe, zb-HgTe, LaS, LaSe, LaTe, MgS, MgSe, MgTe, PbS, PbSe, PbTe, SnS, SnSe, SnTe, SrS , SrSe, SrTe, zb-ZnS, zb-ZnSe, zb-ZnTe, m-Ag ₂ Te, c-Ag ₂ Te, Na ₂ Te, h-Bi ₂ Se ₃ , h-Sb ₂ Se ₃ , h-Bi ₂ Te ₂ Se, h-Bi ₂ Te ₃ , h-Sb ₂ Te ₃ , wz-ZnO, graphene, ML H-MoS ₂ and mixtures thereof are preferably selected from the group consisting of, but other materials may be used free of charge

MQ is a thermoelectric material having thermoelectric properties, but in the case of M'Q' doping material, it is possible to select a thermoelectric material or a non-thermoelectric material. If the M'Q' dopant is a non-thermoelectric material, it is preferable to mix 1 to 25 parts by weight based on 100 parts by weight of the MQ thermoelectric material. When the amount of the M'Q' dopant is less than 1 part by weight, the thermoelectric performance improvement effect is insignificant, and when it exceeds 25 parts by weight, the thermoelectric performance may be rather deteriorated by the M'Q' dopant, a non-thermoelectric material.

When the M'Q' dopant is a material having thermoelectric properties, it is preferable to mix 1 to 100 parts by weight based on 100 parts by weight of the MQ thermoelectric material. If it is less than 1 part by weight, the effect of improving the thermoelectric performance is similarly insignificant, and if it exceeds 100 parts by weight, it becomes the main material, not the doping material, and the characteristics of the MQ thermoelectric material, the original main material, may not be obtained.

Through characteristic as described above it can be confirmed through the selected _{(Bi 2 Te 2 .7 Se 0} .3) / (ZnO) 11 6 to the result of measuring the thermal performance of the thermal conductive material. 6 is a Bi ₂ Te _{2 .7} Se _{0 .3} thermal material and doped ZnO As can be seen in the drawing to the drawing showing a material lattice-like thermoelectric materials and doping material grid pattern is similar to each other. 7 is a diagram showing the values predicted through the _{(Bi 2 Te 2 .7 Se 0} .3) / (ZnO) calculating the electron barrier and the hole barrier material of the heat. Here, the predicted electron barrier is 0 to 0.3 eV, and the hole barrier is 2.9 to 3.3 eV.

Thus, by using the _{(Bi 2 Te 2 .7 Se 0} .3) / (ZnO) thermoelectric material having a grid-like barrier and the energy value which is expected to improve the thermal performance of the present invention was the thermal performance testing. Here, ZnO (0.0 vol%) is not added, is ZnO doped material _{(.7 Bi 2 Te 2 Se 0} .3) means the thermal and material, ZnO (1.0 vol%) to 1% of the ZnO-doped material to the total volume volume ratio by means of the addition _{(.7 Bi 2 Te 2 Se 0} .3) / (ZnO) thermal conductive material.

8 is a graph showing the electrical resistivity of the thermoelectric material, and it can be seen that the thermoelectric material to which 1% of the ZnO dopant is added has a higher electrical resistivity than the thermoelectric material to which the ZnO dopant is not added.

9 is a graph showing the Seebeck coefficient of the thermoelectric material to which the ZnO dopant is added in the same proportion as in FIG. 8. It was confirmed that the Seebeck coefficient value of the thermoelectric material to which the ZnO dopant was added at a temperature of 300 to 550K was high, and similar at 600K. However, it can be seen that the Seebeck coefficient value of the thermoelectric material to which the ZnO dopant is added is slightly higher than that of the thermoelectric material to which the ZnO dopant is not added.

10 is a graph showing the measured values of the thermal conductivity of the thermoelectric material. It was confirmed that the thermoelectric material to which the ZnO dopant was added had lower thermal conductivity than the thermoelectric material to which the ZnO dopant was not added.

However, as shown in FIG. 11 , when the dimensionless figure of merit (ZT) value calculated through the values obtained through FIGS. 8 to 10 is checked, it can be confirmed that the thermoelectric material to which the ZnO dopant is added has a high dimensionless figure of merit value. . This means that the thermoelectric performance is improved when the ZnO dopant is added.

As described above, conventionally, a dopant is added to increase the thermoelectric performance of a thermoelectric material, but a standard for selecting a doping material according to the thermoelectric material is not separately provided. To this end, in the present invention, the lattice state and energy barrier value of the thermoelectric material were compared with the doping material, and a thermoelectric material to which a dopant having an appropriate lattice state and energy barrier value was added was obtained. As a result of an actual experiment, it was confirmed that the thermoelectric performance of the thermoelectric material to which the doping material selected through the present invention was added was improved compared to the thermoelectric material to which the dopant was not added.

Claims (13)

A doping material made of M'Q' is added to the thermoelectric material made of MQ,
The M'Q' is selected by comparing the lattice state and energy barrier values of the MQ and M'Q',
The energy barrier values of the MQ and M'Q' are,
(1) Conduction band is 0.3 eV or less and valence band is 0.3 eV or more,
(2) A thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that the conduction band is 0.3 eV or more and the valence band is 0.3 eV or less.
(The above M and M 'is a metal material,
wherein Q and Q' are selected from the group consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and mixtures thereof) delete The method of claim 1,
The lattice state of the MQ and M'Q' is,
A thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that it includes at least one of a lattice constant and a lattice structure. 4. The method of claim 3,
The M'Q' is,
Thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that it is selected to have a lattice constant value of -10% to 10% with respect to the lattice constant value of MQ. 4. The method of claim 3,
The M'Q' is,
Thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that those having the same lattice structure as the lattice structure of the MQ are selected. 6. The method of claim 5,
The lattice structure of the MQ is,
MQ, M ₂ Q, M ₂ Q ₃ , MQ ₂ and mixtures thereof,
The lattice structure of M'Q' is,
A thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that it is selected from the group consisting of M'Q', M' ₂ Q', M' ₂ Q' ₃ , M'Q' _{2 and mixtures thereof.} delete delete The method of claim 1,
Thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that M and M' are the same metal material. The method of claim 1,
Thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that Q and Q' are the same material. The method of claim 1,
The thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that the M'Q' is mixed in an amount of 1 to 25 parts by weight based on 100 parts by weight of the MQ. The method of claim 1,
The M'Q' has thermoelectric properties, and thermoelectric performance is improved by adding a doping material, characterized in that 1 to 100 parts by weight are mixed with respect to 100 parts by weight of MQ. The method of claim 1,
The MQ or the M'Q' is,
BaS, BaSe, BaTe, CaS, CaSe, CaTe, zb-CdS, zb-CdSe, zb-CdTe, CeS, CeSe, CeTe, EuS, EuSe, EuTe, GeS, GeSe, GeTe, zb-HgS, zb--HgSe , zb-HgTe, LaS, LaSe, LaTe, MgS, MgSe, MgTe, PbS, PbSe, PbTe, SnS, SnSe, SnTe, SrS, SrSe, SrTe, zb-ZnS, zb-ZnSe, zb-ZnTe, m-Ag ₂ Te, c-Ag ₂ Te, Na ₂ Te, h-Bi ₂ Se ₃ , h-Sb ₂ Se ₃ , h-Bi ₂ Te ₂ Se, h-Bi ₂ Te ₃ , h-Sb ₂ Te ₃ , wz - A thermoelectric material with improved thermoelectric performance by adding a doping material, characterized in that selected from the group consisting of -ZnO, graphene, ML H-MoS _{2 and mixtures thereof.}

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