KR20150029570A - Thermoelectric materials and their manufacturing method - Google Patents

Abstract

Disclosed is a thermoelectric conversion material with improved performance. A thermoelectric material according to the present invention can be expressed as the following chemical formula 1: Cu_xSe, wherein 2<x<=2.6. The thermoelectric material can include an induced nano DOT (INDOT) as a copper containing particle. Here, INDOT represents a particle with a diameter, for example, between 1 nanometer and 100 nanometers which is spontaneously generated during a thermal material formation process. This nano DOT, which is INDOT, can exist on a grain boundary of a semiconductor.

Description

TECHNICAL FIELD [0001] The present invention relates to thermoelectric materials,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric conversion technology, and more particularly, to a thermoelectric conversion material having excellent thermoelectric conversion characteristics, a manufacturing method thereof, and a use thereof.

A compound semiconductor is a compound that is not a single element such as silicon or germanium but is operated as a semiconductor by combining two or more elements. Various kinds of compound semiconductors are currently being developed and used in various fields. Typically, a compound semiconductor can be used for a thermoelectric conversion element using a Peltier effect, a light emitting element such as a light emitting diode or a laser diode using a photoelectric conversion effect, and a solar cell.

In particular, the thermoelectric conversion element can be applied to thermoelectric conversion power generation, thermoelectric conversion cooling, and the like. In general, the N type thermoelectric semiconductor and the P type thermoelectric semiconductor are electrically connected in series and thermally connected in parallel. Among them, the thermoelectric conversion power generation is a type of power generation that converts thermal energy into electric energy by using the thermoelectric power generated by placing a temperature difference in the thermoelectric conversion element. The thermoelectric conversion cooling is a cooling type in which electric energy is converted into thermal energy by utilizing the effect that a temperature difference occurs at both ends when a direct current flows in both ends of the thermoelectric conversion element.

It can be said that the energy conversion efficiency of such a thermoelectric conversion element is generally dependent on ZT, which is a figure of merit of the thermoelectric conversion material. Here, ZT can be determined according to Seebeck coefficient, electric conductivity and thermal conductivity, and it can be said that the higher the ZT value, the better the thermoelectric conversion material.

Many thermoelectric materials have been proposed and developed so far to be used as thermoelectric conversion elements, and Cu _x Se (x? 2) has been proposed and developed as a Cu-Se thermoelectric material to date. This is thought to be because Cu _x Se having a composition of x 2 or less is already known.

Recently, relatively low thermal conductivity and high ZT value have been reported in Cu _x Se (1.98? _X ? 2). Typically, the Lidong Chen group reported that Cu ₂ Se shows ZT = 1.5 at 727 ° C (Nature Materials, 11, (2012), 422-425). In addition, MIT's Gang Chen group reported high ZT values at x = 1.96 (Cu ₂ Se _{1 .02} ) and x = 1.98 (Cu ₂ Se _{1 .01} ), where x is less than ₂ (Nano Energy ) 1, 472-478).

However, in both of these results, although a relatively good ZT value is observed at 600 ° C to 727 ° C, the ZT value is very low at a temperature lower than 600 ° C. As such, thermoelectric materials having a low ZT value at a low temperature are not preferable even though they have a high ZT at a high temperature, and are not particularly suitable for a thermoelectric material for electric power generation. This is because even if such a thermoelectric material is applied to a high-temperature heat source, a part of the material experiences a temperature much lower than the desired temperature due to a temperature gradient generated in the material itself. Therefore, a thermoelectric material capable of maintaining a high ZT value over a wide temperature range by having a high ZT value even in a low temperature range of less than 600 DEG C such as 100 DEG C to 600 DEG C It needs to be developed.

Accordingly, it is an object of the present invention to provide a thermoelectric material having a high thermoelectric conversion performance in a wide temperature range, a method of manufacturing the thermoelectric material, and a device using the thermoelectric material.

Other objects and advantages of the present invention will become apparent from the following description, and it will be understood by those skilled in the art that the present invention is not limited thereto. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

In order to achieve the above object, the inventor of the present invention has succeeded in synthesizing a thermoelectric material represented by the following Chemical Formula 1 after repeated researches on a thermoelectric material and confirmed that such a novel thermoelectric conversion material can have excellent thermoelectric conversion performance Thereby completing the present invention.

&Lt; Formula 1 >

Cu _x Se

In the above formula (1), 2 < x &lt;

Preferably, x in the above formula (1) is x? 2.2.

Also preferably, x in the above formula (1) is x? 2.15.

Also preferably, x in the above formula (1) is x? 2.1.

Also preferably, x in Formula 1 is 2.01? X.

Preferably, x in the above formula (1) is 2.025? X.

Preferably, x in the formula (1) is 2.04 < x.

Preferably, x in the formula (1) is 2.05? X.

Preferably, x in the formula (1) is 2.075 x.

According to another aspect of the present invention, there is provided a thermoelectric conversion device comprising a thermoelectric material according to the present invention.

According to another aspect of the present invention, there is provided a thermoelectric generator including a thermoelectric material according to the present invention.

According to the present invention, a thermoelectric material having excellent thermoelectric conversion performance can be provided.

In particular, the thermoelectric material according to one aspect of the present invention can achieve low thermal diffusivity, low thermal conductivity, high whiteness factor, and high ZT value in a wide temperature range of 100 ° C to 600 ° C.

Therefore, the thermoelectric material according to the present invention can be used as another material in place of the conventional thermoelectric material or in addition to the conventional thermoelectric material.

Furthermore, the thermoelectric material according to the present invention can maintain a higher ZT value than that of the conventional thermoelectric material even at a temperature of 600 ° C or lower, and even at a low temperature close to 100 ° C to 200 ° C. Therefore, when the thermoelectric material according to the present invention is used for a thermoelectric device for power generation or the like, a stable thermoelectric conversion performance can be secured even in the case of a material exposed to a relatively low temperature.

The thermoelectric material according to the present invention can also be used in a solar cell, an IR window, an infrared sensor, a magnetic device, a memory, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given below, serve to further the understanding of the technical idea of the invention, And should not be construed as limiting.
1 is a graph showing XRD analysis results of thermoelectric materials according to various embodiments of the present invention.
2 is a graph showing an enlarged view of a portion A in Fig.
3 to 7 are SEM / EDS analysis results of the thermoelectric material according to an embodiment of the present invention.
FIG. 8 is a graph showing XRD analysis results of a thermoelectric material according to an embodiment of the present invention. FIG.
9 is a flowchart schematically showing a method of manufacturing a thermoelectric material according to an embodiment of the present invention.
10 is a graph showing a comparison of results of measurement of thermal diffusivity with temperature of a thermoelectric material according to Examples and Comparative Examples of the present invention.
FIG. 11 is a graph showing the results of measurement of the whitening coefficient according to the temperature of the thermoelectric material according to the example of the present invention and the comparative example.
FIG. 12 is a graph comparing the results of measurement of ZT values according to temperatures of thermoelectric materials according to Examples and Comparative Examples of the present invention.
13 is a SIM image of a thermoelectric material according to an embodiment of the present invention.
14 is a SIM image of a thermoelectric material according to a comparative example.
FIG. 15 is a graph showing the scale change of the y-axis only for the embodiments in FIG.
FIG. 16 is a graph showing the scale change of the y-axis only for the embodiments in FIG.
FIG. 17 is a graph comparing XRD analysis results of thermoelectric materials according to different embodiments of the present invention prepared by different synthesis methods. FIG.
18 is a graph showing an enlarged view of the portion D in Fig.
FIG. 19 is a graph comparing the results of measurement of lattice thermal conductivity according to different temperatures of thermoelectric materials according to different embodiments of the present invention produced by different synthesis methods.
FIG. 20 is a graph comparing power factor measurement results according to temperature of a thermoelectric material according to different embodiments of the present invention produced by different synthesis methods. FIG.
FIG. 21 is a graph comparing the results of measurement of ZT values according to different temperatures of thermoelectric materials according to different embodiments of the present invention manufactured by different synthesis methods.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

The thermoelectric material according to one aspect of the present invention can be represented by the following formula (1).

&Lt; Formula 1 >

Cu _x Se

In the above formula (1), 2 < x &lt;

Preferably, in the above formula (1), x < / = 2.2. In particular, in Formula 1, x &lt; 2.2.

More preferably, in the above formula (1), it is preferable that the condition of x? 2.15 is satisfied.

In particular, in the above formula (1), x &lt; / = 2.1 may be satisfied.

Further, it is preferable that the condition of 2.01? X is satisfied in the above formula (1). In particular, in Formula 1, 2.01 < x.

More preferably, in the above formula (1), it is preferable that the condition of 2.025? X is satisfied. Under these conditions, the thermoelectric conversion performance of the thermoelectric material according to the present invention can be further improved.

Particularly, in the above formula (1), it is preferable that the condition of 2.04 < x is satisfied.

Preferably, in the above formula (1), it is preferable that the condition of 2.05? X is satisfied.

More preferably, in the above formula (1), it is preferable that the condition of 2.075? X is satisfied.

On the other hand, the thermoelectric material represented by Formula 1 may include a part of the secondary phase, and the amount thereof may vary depending on the heat treatment conditions.

The thermoelectric material according to the present invention may also be referred to as a thermoelectric material containing copper-containing particles. That is, the thermoelectric material according to one aspect of the present invention may include a Cu-Se matrix including Cu and Se, and Cu-containing particles. Here, the Cu-containing particles means particles containing at least Cu, and it can be said that not only particles composed of Cu but also particles including one or more elements other than Cu are included therein.

Preferably, the Cu-containing particles may comprise at least one of Cu particles consisting only of a single Cu composition and Cu oxide particles bound to Cu and O, such as Cu ₂ O particles.

In particular, the thermoelectric material according to the present invention may include INDOT (Induced Nano DOT) as the Cu-containing particles. Here, INDOT refers to particles of a nanometer size (such as a diameter of 1 to 100 nanometers) spontaneously generated during thermoelectric material formation. In other words, in the present invention, INDOT is not particles injected into the thermoelectric material artificially from the outside during the process of forming the thermoelectric material, but may be a particle induced by itself in the thermoelectric material.

Furthermore, in the present invention, such a nanodot, that is, INDOT, may exist in the grain boundary of a semiconductor. INDOT in the present invention can be produced at grain boundaries during the formation of a thermoelectric material, particularly in the sintering process. INDOT contained in the thermoelectric material according to the present invention may be defined as an induced nano-dot on grain boundary which is spontaneously induced in a grain boundary of a semiconductor during a sintering process. In this case, the thermoelectric material according to the present invention can be said to be a thermoelectric material including a Cu-Se matrix and INDOT.

The thermoelectric material according to the present invention can be said to contain a relatively large amount of Cu compared to a conventional Cu-Se based thermoelectric material, based on the chemical formula. At this time, at least a part of Cu may be present as a single element without constituting Se and a matrix, or in a form in which it is bonded with another element, such as oxygen, and Cu present alone or in combination with other elements It can be included in the form of nano dot. This will be described in more detail with reference to experimental results.

FIG. 1 is a graph showing XRD analysis results of a thermoelectric material according to various embodiments of the present invention, and FIG. 2 is an enlarged graph showing part A of FIG.

1 and 2 illustrate the XRD pattern for a Cu _x Se (x = 2.025, 2.05, 2.075, 2.1) thermoelectric material (manufactured by the same method as in Examples 2 to 5 below) (X-axis unit is degree). In particular, in FIG. 1, for convenience of description, XRD pattern analysis graphs for the respective embodiments are shown to be spaced apart from each other by a predetermined distance in the vertical direction. In FIG. 2, the graphs of the respective embodiments are shown so as to be superimposed on each other without being separated for convenience of comparison. Further, in Fig. 2, the Cu peak appearing when Cu exists in a single composition is indicated by B.

Referring to FIGS. 1 and 2, it can be seen that as the relative content x of copper in Cu _x Se increases from 2.025 to 2.05, 2.075, and 2.1, the height of the Cu peak gradually increases. Therefore, according to the results of XRD analysis, it can be seen that as _x is more than 2 and included more and more, Cu contained in excess does not constitute a matrix such as Se and Cu _x Se, and can exist alone.

On the other hand, Cu present without constituting the Se and the matrix in this way can exist in the form of nanodots. Such Cu-containing nanodots can exist in the form of aggregation within the thermoelectric material, particularly at the grain boundaries of the Cu-Se matrix. That is, in the thermoelectric material according to the present invention, the Cu-Se matrix may be composed of a plurality of grains, and the Cu-containing INDOT may be located at the grain boundary of the matrix.

3 to 7 are SEM / EDS analysis results of the thermoelectric material according to an embodiment of the present invention.

More specifically, Figure 3 is a SEM photograph taken of a portion of the Cu ₂ Se _.075 In one embodiment of the present invention, 4 and 5 are on a different part of the Cu _2.1 Se according to another embodiment of the present invention This is a SEM photograph. FIG. 6 is a graph showing an EDS analysis result for the C1 portion in FIG. 3, and FIG. 7 is a graph showing the EDS analysis result for the C2 portion in FIG.

3 to 5, a plurality of grains having a size of about several micrometers to several tens of micrometers (for example, 1 to 100 micrometers) and a plurality of nanometer-sized grains smaller in size than the grains It can be seen that there is a nano-dot. At this time, it can be confirmed that the nanodots can be formed along the grain boundaries of the matrix having a plurality of crystal grains as shown in the figure, and at least some of them can exist in the form of cohesion with each other as indicated by C2 . In particular, the SEM photographs of FIGS. 4 and 5 clearly show that nanodots, such as nanodots having an average particle size of 1 nm to 500 nm, are distributed along the grain boundaries of the Cu-Se matrix.

Next, when the results of FIG. 6 in which nano dot is not observed are analyzed in the C1 portion of FIG. 3, that is, the inside of the grain, Cu and Se peaks are mainly formed. From this, it can be seen that in the portion C1 of FIG. 3, Cu constitutes a matrix with Se. In other words, the grains shown in Fig. 3 can be referred to as Cu-Se grains whose main component is Cu and Se. It is also found through quantitative analysis that the Cu-Se matrix exists in the form of Cu _x Se, where x has a value close to 2 or 2.

On the other hand, when the result of FIG. 7 analyzing the C2 portion of FIG. 3 observed that the nano dot is clustered, it can be seen that the Cu peak is dominantly formed. This indicates that nano dot is present as Cu rather than Cu-Se matrix. A few Se peaks were observed in the Cu-Se matrix near or below the nanodot due to limitations in the resolution of the analytical instrument or limitations of the analytical method.

Based on these results, it can be confirmed that the particles aggregated in the portion C 2 in FIG. 3 are Cu-containing nanodots. Therefore, the thermoelectric material according to one aspect of the present invention can be said to be a thermoelectric material containing Cu particles, especially Cu-containing INDOT, together with a Cu-Se matrix composed of Cu and Se. Particularly, at least a part of such Cu-containing INDOT can exist in the form of agglomerated with each other in the thermoelectric material. Here, such a Cu-containing INDOT may exist in a form composed of Cu alone, but may be present in the form of a Cu oxide such as Cu ₂ O in combination with O as a slight O peak is observed in FIG.

As such, the thermoelectric material according to one aspect of the present invention may include Cu-containing nano-dots, particularly INDOT and Cu-Se matrices. Here, the Cu-Se matrix can be expressed by the formula Cu _x Se, where x is a positive rational number. In particular, x can have a value around 2, such as 1.8 to 2.2. Furthermore, x can have a value of 2 or less, such as 1.8 to 2.0. For example, the thermoelectric material according to the present invention may comprise a Cu ₂ Se matrix and a Cu-containing nanodat. Cu-containing nanodots can cause phonon scattering to reduce heat diffusivity.

Here, the Cu-containing nanodots can exist between the crystal interfaces of the Cu-Se matrix as described above. For example, the thermoelectric material according to the present invention may comprise a single composition of copper particles between the crystal interfaces of such a matrix with a Cu ₂ Se matrix. Of course, some of the Cu-containing nanodots may also be present inside the crystals of the Cu-Se matrix.

The thermoelectric material according to one aspect of the present invention may also be referred to as a thermoelectric material including Cu and Se and including a plurality of crystal structures at a predetermined temperature. That is, in the thermoelectric material according to the present invention, the structure of the crystal composed of Cu atoms and Se atoms may exist in two or more forms at a predetermined temperature.

In particular, the thermoelectric material according to the present invention may have a plurality of different crystal lattice structures at a predetermined temperature in a temperature range of 100 ° C to 300 ° C.

FIG. 8 is a graph showing XRD analysis results of a thermoelectric material according to an embodiment of the present invention. FIG.

More specifically, FIG. 8 shows an example of the present invention in which Cu _{2 .1} Se is subjected to various temperature conditions of 25 ° C., 50 ° C., 100 ° C., 150 ° C., 200 ° C., 250 ° C., 300 ° C. and 350 ° C. XRD &lt; / RTI &gt;

In FIG. 8, Cubic_Fm-3m, Cubic_F-43m, Monoclinic_C2 / C, and Cu_Cubic_Fm-3m are representative representations of peaks corresponding to four phases. For example, in FIG. 8, the Cubic_Fm-3m crystal structure is determined as a square at the peak, the inverted triangle at the peak for the Cubic_F-43m crystal structure, and the Cu_Cubic_Fm-3m crystal at the corresponding peak for the Monoclinic_C2 / C crystal structure The structure was displayed as rhombus on the peak.

Referring to FIG. 8, at a temperature of 25 ° C and 50 ° C, a crystal structure mainly composed of monoclinic (C 2 / C) crystals except for a peak corresponding to a cubic structure (Cu_Cubic_Fm-3m) It can be seen that only the corresponding peak exists. Therefore, it can be seen that, in the case of the thermoelectric material according to the present invention, crystals composed of Cu atoms and Se atoms are present in a monophasic form of a monoclinic C2 / C structure at a temperature of 50 DEG C or lower.

However, as a result of measurement at a temperature of 100 ° C, it can be seen that there is a peak corresponding to a cubic crystal structure together with a peak corresponding to a monoclinic crystal structure. That is, although the monoclinic crystal structure is predominant at a temperature of 100 ° C, a cubic crystal structure appears. Therefore, the thermoelectric material according to the present invention may include a plurality of crystal structures including both a monoclinic crystal structure and a cubic crystal structure simultaneously at a temperature of 100 ° C. In addition, in the embodiment of Fig. 8, peaks for two cubic crystal structures (Cubic_Fm-3m, Cubic_F-43m) having different space groups are observed at all peaks corresponding to cubic crystal structures have. Therefore, it can be said that the thermoelectric material according to the present invention has a crystal structure including one kind of monoclinic crystal structure (Monoclinic_C2 / C) and two types of cubic crystal structure at a temperature condition of 100 ° C. Therefore, in this case, it may be said that the thermoelectric material according to this aspect of the present invention has three or more crystal structures at a temperature condition of 100 캜, wherein the crystal is composed of Cu atoms and Se atoms. In addition, when the temperature of the thermoelectric material according to the present invention is raised from 50 ° C to 100 ° C, a part of the monoclinic crystal structure may undergo a phase transition to two kinds of cubic crystal structures.

In addition, as a result of measurement at temperatures of 150 ° C, 200 ° C and 250 ° C, it can be seen that the peak corresponding to the monoclinic phase almost disappeared and only the peak corresponding to the two cubic phases existed. Therefore, the thermoelectric material according to the present invention is a thermoelectric material in which crystals composed of Cu atoms and Se atoms are different from each other in space groups at different temperatures under at least one of temperature conditions of 150 ° C to 250 ° C, particularly 150 ° C, 200 ° C and 250 ° C It can be said to be formed in a form including two kinds of cubic crystal structures (Cubic_Fm-3m, Cubic_F-43m). At this time, the space group of two kinds of cubic crystal structures can be expressed by Fm-3m and F-43m, respectively.

Therefore, it can be said that most of the monoclinic crystal structure is phase-changed to cubic crystal structure as the temperature rises from 100 ° C to 150 ° C in the thermoelectric material according to the present invention.

Further, referring to the measurement results of FIG. 8, the thermoelectric material according to the present invention may have a relatively increased proportion of the F-43m cubic crystal structure as the temperature rises from 150 ° C to 200 ° C.

Referring to the measurement results of FIG. 8, the thermoelectric material according to the present invention may have a relatively reduced ratio of the F-43m cubic crystal structure as the temperature rises from 200 ° C to 250 ° C.

On the other hand, from the measurement results of FIG. 8, it can be seen that only the peak corresponding to Cubic_Fm-3m exists mainly at temperatures of 300 ° C and 350 ° C. Therefore, it can be seen that the thermoelectric material according to the present invention exists in the form of a single crystal structure of Cubic_Fm-3m type at a temperature of 300 ° C or more. As a result, the thermoelectric material according to the present invention showed that the F-43m cubic crystal structure disappeared and the Fm-3m cubic crystal structure appeared as a single phase as the temperature increased from 250 ° C to 300 ° C or higher Able to know.

As seen from the XRD measurement results, the thermoelectric material according to the present invention is characterized in that the crystal structure composed of Cu atoms and Se atoms is mixed in a plurality of different forms at a predetermined temperature of 100 ° C to 300 ° C can do.

On the other hand, the thermoelectric material according to one aspect of the present invention is a Cu-Se-based thermoelectric material containing Cu and Se, which has a lower thermal conductivity and a higher ZT value than a conventional Cu-Se- .

In particular, the thermoelectric material according to the present invention may be composed of Cu and Se, and in this case, the formula of Cu _x Se (where x is a rational number) can be expressed.

The thermoelectric material according to the present invention may have a thermal diffusivity of 0.5 mm ² / s or less in a temperature range of 100 ° C to 600 ° C.

The thermoelectric material according to the present invention may have a ZT value of 0.3 or more over the whole temperature range of 100 deg. C to 600 deg.

In particular, the thermoelectric material according to the present invention may have a ZT value of 0.3 or higher under a temperature condition of 100 캜. Preferably, the thermoelectric material according to the present invention may have a ZT value of 0.4 or higher under a temperature condition of 100 캜.

Further, the thermoelectric material according to the present invention may have a ZT value of 0.4 or higher under a temperature condition of 200 캜. Preferably, the thermoelectric material according to the present invention may have a ZT value of 0.5 or higher under a temperature condition of 200 캜. More preferably, the thermoelectric material according to the present invention may have a ZT value of more than 0.6 under a temperature condition of 200 ° C.

Further, the thermoelectric material according to the present invention may have a ZT value of 0.6 or higher at a temperature condition of 300 캜. Preferably, the thermoelectric material according to the present invention may have a ZT value of 0.75 or higher at a temperature condition of 300 캜. More preferably, the thermoelectric material according to the present invention may have a ZT value of more than 0.8 under a temperature condition of 300 ° C. More preferably, the thermoelectric material according to the present invention may have a ZT value of more than 0.9 at a temperature condition of 300 캜.

Further, the thermoelectric material according to the present invention may have a ZT value of 0.7 or higher under a temperature condition of 400 캜. Preferably, the thermoelectric material according to the present invention may have a ZT value of 0.8 or higher under a temperature condition of 400 ° C. More preferably, the thermoelectric material according to the present invention may have a ZT value of 1.0 or higher at a temperature condition of 400 ° C.

Further, the thermoelectric material according to the present invention may have a ZT value of 0.6 or higher under a temperature condition of 500 캜. Preferably, the thermoelectric material according to the present invention may have a ZT value of 0.7 or higher under a temperature condition of 500 ° C. More preferably, the thermoelectric material according to the present invention may have a ZT value of 1.1 or higher under a temperature condition of 500 캜. More preferably, the thermoelectric material according to the present invention may have a ZT value of 1.3 or higher under a temperature condition of 500 캜.

Further, the thermoelectric material according to the present invention may have a ZT value of 0.6 or higher under a temperature condition of 600 캜. Preferably, the thermoelectric material according to the present invention may have a ZT value of 0.8 or higher under a temperature condition of 600 캜. More preferably, the thermoelectric material according to the present invention may have a ZT value of 1.4 or higher at a temperature of 600 ° C. More preferably, the thermoelectric material according to the present invention may have a ZT value of 1.8 or higher at a temperature condition of 600 ° C.

The thermoelectric material according to the present invention can be produced by the following thermoelectric material production method.

9 is a flowchart schematically showing a method of manufacturing a thermoelectric material according to an embodiment of the present invention.

As shown in FIG. 9, the method for producing a thermoelectric material according to the present invention represented by Formula 1 may include a mixture forming step (S110) and a compound forming step (S120).

The mixture forming step (S110) is a step of mixing Cu and Se as raw materials to form a mixture. Particularly, in the step S110, a mixture can be formed by weighing Cu and Se according to the chemical formula of the formula 1, namely, Cu _x Se (x is a positive number of ratios, particularly 2 <x? 2.6) It is a step.

Here, in step S110, powdered Cu and Se may be mixed. In this case, the mixing of Cu and Se is better accomplished, and the synthesis of Cu _x Se can be made better.

Meanwhile, in the mixture forming step (S110), the mixing of Cu and Se may be performed by hand milling using a mortar, ball milling, planetary ball mill, or the like However, the present invention is not limited by such a specific mixing method.

The compound forming step (S120) is a step of synthesizing a substance represented by Cu _x Se (2 < _x &lt; = 2.6) by heat-treating the mixture formed in the step S110. For example, in step S120, a mixture of Cu and Se is put into a furnace and heated at a predetermined temperature for a predetermined time to synthesize a Cu _x Se compound.

Preferably, the step S120 is performed by a solid state reaction (SSR) method. In the case of the synthesis by such a solid phase reaction method, the raw material used for synthesis, that is, the mixture does not change into the liquid state during the synthesis, and the reaction can occur in the solid state.

For example, the step S 120 may be performed at a temperature ranging from 200 ° C to 650 ° C for 1 hour to 24 hours. Since this temperature is lower than the melting point of Cu, when it is heated in this temperature range, Cu _x Se can be synthesized without dissolving Cu. In particular, the step S120 may be performed at a temperature of 500 DEG C for 15 hours.

In step S120, a mixture of Cu and Se for Cu _x Se synthesis is put into a carbide mold to form a pellet. The pellet-like mixture is put into a fused silica tube, Can be sealed. Then, the vacuum-sealed first mixture can be put into a furnace and heat-treated.

Preferably, the method for producing a thermoelectric material according to the present invention may further comprise a step (S130) of pressing and sintering the composite after the compound forming step (S120).

Here, the step S130 may be performed by a hot press (HP) method or a spark plasma sintering (SPS) method. In the case of the thermoelectric material according to the present invention, when sintered by this pressure sintering method, a high sintering density and thermoelectric performance improving effect can be easily obtained.

For example, the pressure sintering step may be performed under a pressure condition of 30 MPa to 200 MPa. Also, the pressure sintering step may be performed at a temperature of 300 ° C to 800 ° C. And, the pressure sintering step may be performed under the pressure and temperature conditions for 1 minute to 12 hours.

Also, the step S130 may be performed while flowing a gas such as Ar, He, or N _{2 in a} vacuum state or partially containing hydrogen or not containing hydrogen.

Also, preferably, the step S130 may be performed by pulverizing the compound formed in the step S120 into a powder form, followed by pressure sintering. In this case, the sintering density and the sintering density can be further increased while improving the convenience in sintering and measurement.

In particular, in the thermoelectric material according to one aspect of the present invention, the Cu-containing particles may be spontaneously formed in the pressure sintering step (S130). That is, the Cu-containing particles of the thermoelectric material according to the present invention may not be forcibly injected from the outside, but may be spontaneously induced in the manufacturing process, particularly the sintering process. Therefore, the Cu-containing particles according to the present invention may be INDOT (Induced Nano DOT). In particular, the thermoelectric material according to the present invention may be a thermoelectric material including an induced nano-dot on grain boundary during the sintering process. According to this aspect of the present invention, it is not necessary to exert a high degree of effort to introduce the Cu-containing particles into the thermoelectric material, particularly the crystal interface, so that the formation of the Cu-containing particles can be facilitated.

The thermoelectric conversion element according to the present invention may include the thermoelectric material described above. Particularly, the thermoelectric material according to the present invention can effectively improve the ZT value over a wide temperature range as compared with a conventional thermoelectric material, particularly a Cu-Se thermoelectric material. Therefore, the thermoelectric material according to the present invention can be used for a thermoelectric conversion element in addition to a conventional thermoelectric conversion material or in addition to a conventional compound semiconductor.

Furthermore, the thermoelectric material according to the present invention can be used in a thermoelectric generator that generates thermoelectric power using a waste heat source or the like. That is, the thermoelectric generator according to the present invention includes the thermoelectric material according to the present invention described above. The thermoelectric material according to the present invention exhibits a high ZT value in a wide temperature range, such as a temperature range of 100 ° C to 600 ° C, and thus can be more effectively applied to thermoelectric power generation.

Further, the thermoelectric material according to the present invention may be produced in the form of a bulk thermoelectric material.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. It should be understood, however, that the embodiments of the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example  One

In order to synthesize Cu _{2 .01} Se, powders of Cu and Se were weighed in accordance with these formulas and mixed in an alumina mortar. The mixed material was pelletized in a carbide mold, placed in a fused silica tube, and vacuum-sealed. Then, it was placed in a box furnace and heated at 500 ° C. for 15 hours. After heating, the mixture was slowly cooled to room temperature to obtain a Cu _{2 .01} Se composite.

Then, this Cu _{2 .01} Se composite was filled in a cemented carbide mold for hot pressing, and then hot pressed and sintered under a vacuum condition at 650 ° C to obtain a sample of Example 1. At this time, the sintered density was set to be 98% or more of the theoretical value.

Example  2

In order to synthesize Cu _{2 .025} Se, powders of Cu and Se were weighed in accordance with the above formula and then mixed and synthesized in the same manner as in Example 1 to obtain a Cu _2.025 Se composite. On the other hand, a sintering process was performed in the same manner as in Example 1 to obtain a sample of Example 2.

Example  3

In order to synthesize Cu _{2 .05} Se, powders of Cu and Se were weighed according to the above formula, and then mixed and synthesized in the same manner as in Example 1 to obtain a Cu _{2 .05} Se composite. On the other hand, a sintering process was performed in the same manner as in Example 1 to obtain a sample of Example 3.

Example  4

In order to synthesize Cu _{2 .075} Se, powders of Cu and Se were weighed in accordance with the above formula and then mixed and synthesized in the same manner as in Example 1 to obtain a Cu _2.075 Se composite. On the other hand, a sintering process was carried out in the same manner as in Example 1 to obtain a sample of Example 4.

Example  5

In order to synthesize Cu _{2 .1} Se, powders of Cu and Se were weighed in accordance with the above formula, and then mixed and synthesized in the same manner as in Example 1 to obtain a Cu _{2 .1} Se composite. On the other hand, a sintering process was carried out in the same manner as in Example 1 to obtain a sample of Example 5.

Example  6

In order to synthesize Cu _{2 .15} Se, powders of Cu and Se were weighed in accordance with the above formula and then mixed and synthesized in the same manner as in Example 1 to obtain a Cu _{2 .15} Se compound. Then, a sintering process was carried out in the same manner as in Example 1 to obtain a sample of Example 6.

Example  7

In order to synthesize Cu _{2 .2} Se, powder Cu and Se were weighed in accordance with these formulas, and then Cu _{2 .2} Se composite was obtained through mixing and synthesis in the same manner as in Example 1. On the other hand, a sintering process was performed in the same manner as in Example 1 to obtain a sample of Example 7.

Comparative Example  One

In order to synthesize Cu _{1 .8} Se, powders of Cu and Se were weighed according to the formula, and then Cu _{1 .8} Se composite was obtained through mixing and synthesis in the same manner as in Example 1. On the other hand, a sintering process was performed in the same manner as in Example 1 to obtain a sample of Comparative Example 1.

Comparative Example  2

In order to synthesize the _{1 .9} Cu Se, and then weighing the powder in the form of Cu and Se in order to fit these formulas, Through the above Example 1, a synthesis mixture and in the same manner as the process to obtain a Cu Se _{1 .9} composite. On the other hand, a sintering process was performed in the same manner as in Example 1 to obtain a sample of Comparative Example 2.

Comparative Example  3

To synthesize the Cu _{2 .0} Se, it was weighed to meet the formula such a powder in the form of Cu and Se, in Example 1 and after the mixture and the synthesis process in the same manner to obtain a Cu ₂ Se _.0 composite. On the other hand, a sintering process was performed in the same manner as in Example 1 to obtain a sample of Comparative Example 3.

The thus obtained samples of Examples 1 to 7 and Comparative Examples 1 to 3 were measured for thermal diffusivity (TD) at predetermined temperature intervals using LFA457 (Netzsch), and the results are shown in Examples 1 to 7 and Comparative Examples 10 as Examples 1 to 3.

The electrical conductivities and whitening coefficients of the samples were measured at predetermined temperature intervals using ZEM-3 (Ulvac-Riko, Inc) for each of the samples of Examples 1 to 7 and Comparative Examples 1 to 3 , And the results of measurement of the whitening coefficient (S) among them are shown in Fig. 11 as Examples 1 to 7 and Comparative Examples 1 to 3. Then, the ZT values are calculated using the respective measured values, and the results are shown in Fig. 12 as Examples 1 to 7 and Comparative Examples 1 to 3.

10, the thermoelectric materials of Examples 1 to 7, wherein x is more than 2 in the formula of Cu _x Se, are in the range of 100 ° C to 700 ° C It can be seen that the thermal diffusivity is remarkably low over the whole temperature measurement period of the temperature sensor.

In particular, the sample according to the present invention has a thermal diffusivity of less than 0.5 mm ² / s, preferably less than 0.4 mm ² / s over the entire temperature range of 100 ° C to 600 ° C, It can be seen that it is remarkably low.

11, the thermoelectric materials of Examples 1 to 7 according to the present invention had a whiteness coefficient over the entire temperature measurement period of 100 ° C to 700 ° C as compared with the thermoelectric materials of Comparative Examples 1 to 3, Is significantly high.

Referring to the ZT values of the respective samples with reference to the results of FIG. 12, it can be seen that the ZT values of the thermoelectric materials of Examples 1 to 7 according to the present invention are significantly higher than those of the thermoelectric materials of Comparative Examples 1 to 3 .

In particular, in the case of the thermoelectric material according to the comparative example, the ZT value is extremely low in a temperature range of less than 500 ° C., and the ZT value is very low in a low temperature range of 100 ° C. to 300 ° C.

On the contrary, the thermoelectric material according to the embodiment of the present invention has a very high ZT value even in a high-temperature zone of 500 ° C or higher and a low-temperature zone of less than 500 ° C, compared with the comparative example.

In general, the thermoelectric materials of Examples 1 to 6 exhibit a ZT value performance improvement of about twice as high as that of the thermoelectric materials of Comparative Examples 1 to 3 at a temperature of 600 ° C.

More specifically, the thermoelectric material of the comparative example exhibits a very low performance of ZT value of approximately 0.15 to 0.1 or less at a temperature of 100 ° C., while the thermoelectric material of the example according to the present invention exhibits 0.3 to 0.4 Or more.

In addition, under the temperature condition of 200 占 폚, the thermoelectric material of the comparative example exhibits a very low ZT value of 0.15 to 0.1 or less, similar to that at 100 占 폚, while the thermoelectric material of the embodiment according to the present invention has a Zr value of 0.4 or more, Of ZT values.

In the temperature condition of 300 ° C, the thermoelectric material of the comparative example has a ZT value of about 0.1 to 0.2, while the thermoelectric material of the embodiment of the present invention has a value of 0.6 or more, more than 0.7 or 0.8 or more, Respectively.

Further, at a temperature condition of 400 ° C, the thermoelectric material of the comparative example showed values of ZT values of 0.1 to 0.2 and as much as 0.35, whereas the thermoelectric materials of the examples of the present invention all showed a value of 0.7 or more, 0.8 or more, and more preferably 1.0 to 1.2.

The thermoelectric material of the comparative example exhibits a value of about 0.5 or less at a temperature of 500 ° C., whereas the thermoelectric material of the embodiment of the present invention shows a very high ZT value of 0.6 or more to 1.0 to 1.4.

The thermoelectric materials of Comparative Examples 1 to 3 showed a ZT value of about 0.4 to 0.9 at a temperature of 600 ° C., while the thermoelectric materials of Examples 1 to 5 according to the present invention had a very high ZT value of 1.4 to 1.7 Showing a large difference from the thermoelectric material of the comparative example.

The thermoelectric material according to each of the embodiments of the present invention has significantly lower thermal diffusivity over the entire temperature range of 100 ° C. to 600 ° C. than the conventional thermoelectric material according to the comparative example, As shown in FIG. Therefore, the thermoelectric material according to the present invention can be said to have excellent thermoelectric conversion performance and can be very usefully used as a thermoelectric conversion material therefor.

On the other hand, as described above, the thermoelectric material according to the present invention may further include Cu-containing particles, particularly INDOT, in addition to the Cu-Se matrix. This will be described with reference to FIGS. 13 and 14. FIG.

FIG. 13 is a SIM (Scanning Ion Microscope) image of the sample prepared in Example 4, and FIG. 14 is a SIM image of the sample prepared in Comparative Example 3. FIG.

Referring to FIG. 13, in the case of the thermoelectric material represented by Cu _2.075 Se according to Example 4 of the present invention, nano dot is present. And, as mentioned above, such a nano dot is a nano dot containing Cu. In particular, as shown in FIG. 13, nanodots can be distributed mainly along the grain boundaries.

On the other hand, referring to FIG. 14, it can be seen that there is no nano dot in the conventional Cu-Se thermoelectric material represented by Cu ₂ Se. However, in FIG. 14, there is a black dot, but it is a pore, not a nano dot.

On the other hand, it was confirmed that Cu-containing nano dot, especially INDOT, was also included in Examples 1 to 3 and 5 to 7 in addition to the above-mentioned Example 4.

In addition, in FIGS. 10 and 11, since it is not easy to distinguish between the embodiments, the comparison between the embodiments will be described with reference to FIG. 15 and FIG.

Figs. 15 and 16 are graphs showing scale changes of the y-axis only for the embodiments in Figs. 10 and 11. Fig.

15 and 16, in the thermoelectric material according to the present invention represented by the formula 1 (Cu _x Se), when the range of x is x> 2.04, more specifically x? 2.05, And the number of the white areas is higher.

Further, the thermal diffusivity (TD) results of FIG. 15 show that the thermal diffusivity of Examples 3 to 7, in which x is more than 2.04, is relatively low compared to Examples 1 and 2 in which x in Formula 1 is less than 2.04 . Particularly, the results of Examples 5 to 7, and more specifically Examples 5 and 6, are remarkably low at a temperature range of 200 ° C to 600 ° C.

16, it can be seen that the whitening coefficients of Examples 3 to 7, where x is more than 2.04, are relatively higher than those of Examples 1 and 2 in which x in Formula 1 is less than 2.04 . In particular, in the case of Examples 5 to 7, the whitening coefficient is significantly higher than in the other embodiments. Moreover, in the section between 100 DEG C and 200 DEG C and in the section between 400 DEG C and 600 DEG C, the number of whiteness in Examples 6 and 7 is much higher than in the other embodiments.

On the other hand, as described above, the thermoelectric material according to the present invention is preferably synthesized by a solid-phase reaction (SSR) method. Hereinafter, the effect of the SSR synthesis method is compared with the melting method.

Example 8

To synthesize Cu _2.025 Se, powders of Cu and Se were weighed according to the formula, and then mixed in an alumina mortar. The mixed material was pelletized in a carbide mold, placed in a fused silica tube, and vacuum-sealed. Then, it was put in a box furnace and heated at 1100 ° C for 12 hours, and the temperature rise time was set at 9 hours. Then, it was heated again at 800 ° C for 24 hours, and the temperature-reducing time was set at 24 hours. After such heating, the mixture was slowly cooled to room temperature to obtain a Cu _2.025 Se composite.

Then, this Cu _2.025 Se composite was filled in a cemented carbide mold for hot pressing, and then hot pressed and sintered under a vacuum condition at 650 ° C to obtain a sample of Example 8. At this time, the sintered density was set to be 98% or more of the theoretical value.

Example 9

In order to synthesize Cu _2.1 Se, powders of Cu and Se were weighed according to the above formula, and then Cu _2.1 Se composite was obtained through mixing and synthesis in the same manner as in Example 8. On the other hand, a sintering process was performed in the same manner as in Example 8 to obtain a sample of Example 9.

In the case of the samples according to Examples 8 and 9, the synthesis method was different from those of Examples 1 to 7 above. That is, in the case of the samples according to Examples 1 to 7, the thermoelectric material was synthesized by the SSR method in which the synthesis was performed in a state in which at least a part of the raw material was not dissolved. In the samples according to Examples 8 and 9, And the thermoelectric material was synthesized by a melting method which is heated above the melting point.

XRD analysis was performed on the thus obtained samples of Example 8 and Example 9, and the results are shown in Fig. XRD analysis was also performed on the samples corresponding to Example 2 and Example 5 synthesized by the SSR method, and the results thereof are shown in FIG. 17, and a part thereof is enlarged and shown in FIG. 18 Respectively. In particular, in FIG. 17, the XRD pattern analysis graphs for the respective embodiments are shown to be spaced apart from each other by a predetermined distance in the vertical direction for convenience of classification. 18, the graphs of the respective embodiments are shown to be superimposed on each other without being separated from each other. Further, in Fig. 18, the Cu peak appearing when Cu exists in a single composition is indicated by E.

17 and 18, it is confirmed that the heights of the Cu peaks of Examples 2 and 5 synthesized by the SSR method are much higher than those of the Cu peaks of Examples 8 and 9 synthesized by the melting method . Therefore, according to the results of the XRD analysis, it can be seen that when the thermoelectric material according to the present invention is synthesized by the SSR method, the amount of Cu existing alone is higher than that when the thermoelectric material is synthesized by the melting method. Particularly, in the case of the melting method, copper can be present in the form of nano-dots in the Cu-Se matrix or in the form of precipitates that do not exist in the grain boundaries and escape to the outside. Therefore, in the case of the thermoelectric material according to the present invention, it can be said that the thermoelectric material is preferably synthesized by the SSR method. Advantages of the SSR method for such a melting method will be described in more detail with reference to FIGS. 19 to 21. FIG.

Figs. 19 to 21 are graphs showing measurements of lattice thermal conductivity (虜_L ), power factor (PF) and ZT value according to the temperature for Examples 2, 5, 8 and 9, Fig.

First, in FIG. 19, the lattice thermal conductivity was obtained by using the Biedemann-Franz law, and the Lorentz constant used at that time was 1.86 * 10 ^-8 . More specifically, the lattice thermal conductivity can be calculated using the following equation.

κ _L = κ _total - κ _e

Where κ _L is the lattice thermal conductivity, κ _total is the thermal conductivity, and κ _e is the thermal conductivity due to the electrical conductivity. And, κ _e can be expressed as follows.

κ _e = σLT

Here,? Denotes electric conductivity, and L denotes a Lorentz constant, which indicates 1.86E-8. Further, T means temperature (K).

Referring to the results of FIG. 19, it can be seen that the lattice thermal conductivity of Examples 2 and 5 synthesized by the SSR method is relatively lower than that of Examples 8 and 9 synthesized by the melting method. In particular, when comparing Example 2 and Example 8 of the same composition, the lattice thermal conductivity change pattern according to temperature was similar, but in Example 2, in the entire temperature range of 100 ° C to 600 ° C as compared to Example 8, It can be seen that the lattice thermal conductivity is remarkably low. In addition, even when Example 5 and Example 9 having the same composition are compared, the lattice thermal conductivity of Example 5 by the SSR method is lower than that of Example 9, and the temperature The higher the difference, the greater the difference.

Next, referring to the results of FIG. 20, in the case of Embodiments 2 and 5 synthesized by the SSR method, the power factor PF is relatively high as compared with Embodiments 8 and 9 synthesized by the melting method . In particular, when comparing Example 2 and Example 8 having the same composition, the power factor of Example 2 by the SSR method is higher than that of Example 8 by the melting method in the entire temperature measurement period of 100 to 600 占 폚. Furthermore, even when Example 5 and Example 9 are compared with each other in the same composition, Example 5 is higher than Example 9 in the entire temperature measurement period of 100 ° C to 600 ° C.

Finally, referring to the results of FIG. 21, it can be seen that the ZT is relatively high in Examples 2 and 5 synthesized by the SSR method, as compared with Embodiments 8 and 9 synthesized by the melting method . Particularly, when comparing Example 2 and Example 8 having the same composition, Example 2 by the SSR method shows higher ZT than that of Example 8 by the melting method in the temperature measurement period of 200 ° C to 600 ° C. Furthermore, even when Example 5 and Example 9 are compared with each other in the same composition, Example 5 is higher than Example 9 in the entire temperature measurement period of 100 ° C to 600 ° C.

Taking all these points into consideration, it can be said that the thermoelectric material according to the present invention can have a higher thermoelectric performance than that synthesized by the SSR method, as compared with the thermoelectric material synthesized by the melting method.

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. It will be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (8)

A thermoelectric material represented by the following formula (1).
&Lt; Formula 1 >
Cu _x Se
In the above formula (1), 2 < x &lt; The method according to claim 1,
The thermoelectric material according to claim 1, wherein x satisfies x &amp;le; 2.2. The method according to claim 1,
The thermoelectric material according to claim 1, wherein x is 2.15. The method according to claim 1,
The thermoelectric material according to claim 1, wherein x is 2.1. The method according to claim 1,
The thermoelectric material according to claim 1, wherein x is 2.01? X. The method according to claim 1,
The thermoelectric material according to claim 1, wherein x is 2.025? X. A thermoelectric conversion element comprising the thermoelectric material according to any one of claims 1 to 6. A thermoelectric generator comprising the thermoelectric material according to any one of claims 1 to 6.

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