JP2020057727A - Thermoelectric material and manufacturing method therefor, and thermoelectric generation element - Google Patents

Abstract

To provide a thermoelectric material which is made into p-type and n-type by composition control, showing a thermoelectric effect in a range from a room temperature to 600 K and having a binary compound of Cr and Se as a main component, and to provide a manufacturing method therefor and thermoelectric generation element.SOLUTION: The thermoelectric material is at least a binary compound of Cr and Se and is expressed by the following general formula: CrSe, where p satisfies -0.1≤p<0 or 0<p≤0.2 and q satisfies -0.1≤q≤0.05, with the binary compound which is a phase expressed by CrSehaving a crystalline structure of a trigonal system.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a thermoelectric material, a method for producing the same, and a thermoelectric generator using the same.

  Even in Japan, where energy conservation has been particularly advanced in the world, at present, about 3/4 of the primary supply energy is discarded as heat energy, and establishment and diffusion of waste heat recovery technology is desired. Under such circumstances, thermoelectric power generation elements are in great demand, such as power generators, because they can recover heat energy and directly convert it to electrical energy. Further, such a thermoelectric conversion technology is also expected to be used as a cooling element for cooling a computer, air conditioning of an automobile, and the like.

Thermoelectric materials applied to such thermoelectric generators have been actively studied and variously developed. In recent years, thermoelectric materials using Cr ₂ Se ₃ have been developed (for example, see Non-Patent Documents 1 and 2). Non-Patent Document 1 reports that a material in which the Se site of Cr ₂ Se ₃ is partially substituted with S is a p-type thermoelectric material. Non-Patent Document 2 reports that a material in which the Cr site of Cr ₂ Se ₃ is partially substituted with Mn, Nb or Ni and the Se site is partially substituted with S is a p-type thermoelectric material. I have.

According to Non-Patent Documents 1 and 2, non-doped Cr ₂ Se ₃ shows p-type thermoelectric characteristics, but has a small absolute value of the Seebeck coefficient, and it is difficult to put it to practical use as it is. For application, a pair of p-type thermoelectric material and n-type thermoelectric material of the same type of material are required. However, as shown in Non-Patent Documents 1 and 2, an n-type thermoelectric material using Cr ₂ Se ₃ is Not developed.

  From the viewpoint of thermal matching and the like, it is most desirable that the p-type thermoelectric material and the n-type thermoelectric material be made of the same compound, but generally it is difficult. Therefore, it would be advantageous if a thermoelectric material consisting of a binary compound of Cr and Se and having p-type and n-type thermoelectric properties could be developed. In addition, although the heat of 600K or less occupies most of the unused heat, it is desirable to develop a thermoelectric material suitable for collecting such so-called poor heat.

Tinting Zhang et al. Mater. Chem. C, 2018, 6, 833-846 Tingting Zhang et al., ACS Appl. Mater. Interfaces, 2018, 10, 22389-22400

  As described above, an object of the present invention is to provide a thermoelectric material containing a binary compound of Cr and Se as a main component, exhibiting a thermoelectric effect from room temperature to 600 K, and being p-type and n-type by composition control, a method for producing the same, and a thermoelectric material. It is to provide a power generating element.

The thermoelectric material of the present invention contains at least a binary compound of Cr and Se, and the binary compound has a general formula of Cr _{2 + p} Se _{3 + q} (where p is −0.1 ≦ p <0 or 0 <p ≦ 0.2, q satisfies −0.1 ≦ q ≦ 0.05), and the binary compound is represented by Cr ₂ Se ₃ having a trigonal crystal structure. This solves the above problem.
In the binary compound, an atomic ratio of the Cr to the Se may satisfy 0.623 or more and 0.759 or less.
The space group of the crystal structure may be R3-.
The p satisfies -0.1 ≦ p <0 or 0 <p <0.05, and may show p-type in a temperature range from room temperature to 600 K or less.
In the binary compound, an atomic ratio of the Cr to the Se may satisfy 0.623 or more and less than 0.707.
The p may satisfy -0.05 ≦ p ≦ −0.02 or 0 <p ≦ 0.04.
In the binary compound, an atomic ratio of the Cr to the Se may satisfy 0.639 or more and 0.703 or less.
The above p satisfies 0.05 ≦ p ≦ 0.2 and may be n-type in a temperature range from room temperature to 600K or less.
In the binary compound, an atomic ratio of the Cr to the Se may satisfy 0.672 or more and 0.759 or less.
The p may satisfy 0.06 ≦ p ≦ 0.15.
In the binary compound, the atomic ratio of Cr to Se may satisfy 0.675 or more and 0.741 or less.
The binary compound may contain 70% by weight or more of the phase represented by Cr ₂ Se ₃ .
The binary compound may not contain a different element other than Ce and Se.
In the method for producing a thermoelectric material of the present invention, a raw material containing Cr and a raw material containing Se are converted to a general formula Cr _{2 + x} Se ₃ (where x is −0.1 ≦ x <0 or 0 <x ≦ 0). .2), and firing the mixture obtained in the mixing step, thereby solving the above-mentioned problems.
In the mixing, the Cr-containing raw material and the Se-containing raw material may be mixed such that the atomic ratio of Cr to Se satisfies 0.633 or more and 0.733 or less.
In the firing step, the mixture may be fired in an inert atmosphere or in a vacuum at a temperature ranging from 1073K to 1773K.
Following the mixing step, the method may further include a step of forming the mixture.
After the firing step, the method may further include a step of rapidly cooling the fired body obtained in the firing step.
The thermoelectric power generation element of the present invention includes a p-type thermoelectric material and an n-type thermoelectric material connected alternately in series, and at least one of the p-type thermoelectric material and the n-type thermoelectric material is the thermoelectric material described above. Solves the above problem.
The p-type thermoelectric material may be the above-described thermoelectric material, and the n-type thermoelectric material may be the above-described thermoelectric material.

The thermoelectric material of the present invention contains at least a binary compound of Cr and Se. Since it is composed of two elements, Cr and Se, it is a very simple thermoelectric material, which is advantageous for element design. Further, this binary compound has a general formula of Cr _{2 + p} Se _{3 + q} (where p satisfies −0.1 ≦ p <0 or 0 <p ≦ 0.2, and q satisfies −0.1 ≦ q ≦ 0 0.55) and a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure. In addition, if the above-mentioned general formula is satisfied and the above-mentioned phase is used, excellent thermoelectric properties can be exhibited in a temperature range from room temperature to 600 K or less. In particular, since the n-type and p-type can be controlled by controlling the parameter x, n-type and p-type thermoelectric materials can be provided with the same element. If n-type and p-type thermoelectric materials made of the same element are used, they have the same coefficient of thermal expansion, which is extremely advantageous for designing a thermoelectric power generation element.

In the method for producing a thermoelectric material according to the present invention, a raw material containing Cr and a raw material containing Se are converted to a general formula Cr _{2 + x} Se ₃ (where x is −0.1 ≦ x <0 or 0 <x ≦ 0. 2) and firing the mixture. In the preparation of the raw materials, the above-mentioned thermoelectric material can be obtained only by mixing so as to satisfy the above-mentioned general formula. Therefore, a special technique is not required, and the thermoelectric material can be provided at low cost and with high yield.

Schematic diagram showing a Cr ₂ Se ₃ crystal Flow chart showing steps for manufacturing the thermoelectric material of the present invention Schematic diagram showing a thermoelectric power generation element using the thermoelectric material of the present invention The figure which shows the X-ray diffraction pattern of the sample by Examples 1-7. The figure which shows the temperature dependence of the electric conductivity of the sample of Examples 1-7. The figure which shows the temperature dependence of the Seebeck coefficient of the sample of Examples 1-7. The figure which shows the temperature dependence of the electric power factor of the sample of Examples 1-7. The figure which shows the temperature dependence of the thermal conductivity of the sample of Examples 1-7. The figure which shows the temperature dependence of the dimensionless figure of merit ZT of the sample of Examples 1-7.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the same reference numerals are given to the same elements, and the description thereof will be omitted.

(Embodiment 1)
Embodiment 1 describes a thermoelectric material of the present invention and a method for manufacturing the same.

  The inventors of the present application focused on a binary compound of chromium (Cr) and selenium (Se), and found that a variety of compositions provided a thermoelectric material. In particular, it was found that the p-type thermoelectric material as well as the n-type thermoelectric material can be obtained only by controlling the composition. This will be described in detail below.

The thermoelectric material of the present invention contains at least a binary compound of chromium (Cr) and selenium (Se). Such a binary compound has a general formula of Cr _{2 + p} Se _{3 + q} (where p satisfies −0.1 ≦ p <0 or 0 <p ≦ 0.2, and q satisfies −0.1 ≦ q ≦ 0 0.55) and a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure. When the binary compound is a phase that satisfies the above general formula and has the above crystal structure, excellent thermoelectric properties can be exhibited in a temperature range from room temperature to 600 K or less.

  In the thermoelectric material of the present invention, the binary compound does not contain intentional foreign elements other than Cr and Se (excluding unavoidable impurities contained in the raw material). For example, as shown in Non-Patent Documents 1 and 2, it is known to improve the thermoelectric properties by adding a different element, but in the present invention, the composition is simply controlled without using a different element. Since p-type and n-type thermoelectric characteristics can be exhibited, the coefficient of thermal expansion does not change, which is extremely advantageous for designing a thermoelectric power generation element.

FIG. 1 is a schematic diagram showing a Cr ₂ Se ₃ crystal.

FIG. 1 shows a Cr ₂ Se ₃ crystal as a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure, but Se is omitted for clarity. In the thermoelectric material of the present invention, the binary compound has a predetermined composition as described above, and includes a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure. Here, the phase represented by Cr ₂ Se ₃ (hereinafter referred to as “Cr ₂ Se ₃ phase for simplicity”) is represented by the crystal structure in FIG. 1 and satisfies the crystal parameters and atomic coordinate positions in Table 1.

The binary compound is a Cr ₂ Se ₃ phase having a trigonal crystal structure. As shown in Table 1, the trigonal crystal structure is, in detail, a space group R-3 (specification of the present application). In the description, “3-” represents an overline of 3, and has a symmetry of International Tables for Crystallogy (No. 148 space group), and the lattice constants a, b, and c are:
a = 0.625 ± 0.05 nm,
b = 0.625 ± 0.05 nm, and c = 1.738 ± 0.2 nm
Those that satisfy are stable. Outside this range, the crystals may be unstable.

The fact that the binary compound is a Cr ₂ Se ₃ phase in the thermoelectric material of the present invention can be identified by X-ray diffraction or neutron diffraction. As described above, the binary compound of the present invention has a composition that satisfies the predetermined general formula, but the constituent elements Cr and Se become rich or poor with respect to the Cr ₂ Se ₃ crystal. In this case, the lattice constant changes, but the crystal structure and the atomic position given by the site occupied by the atom and the atomic position given by the coordinates do not change so much as to break the bond between the skeleton atoms. Therefore, in the present invention, the length of the chemical bond of Cr—Se calculated from the atomic coordinates and the lattice constant obtained by Rietveld analysis of the results of X-ray diffraction and neutron beam diffraction in the space group of R 3 — When the distance between atoms is within ± 5% of the length of the chemical bond calculated from the lattice constant and atomic coordinates of the Cr ₂ Se ₃ crystal shown in Table 1, it is defined as having the same crystal structure, It is determined whether the phase is Cr ₂ Se ₃ phase. If the length of the chemical bond changes by more than ± 5%, the chemical bond may be broken and another crystal may be formed.

Conveniently, the powder X-ray diffraction pattern of the composite article obtained, _Cr 2 Se ₃ crystal powder X-ray diffraction pattern (e.g., the calculated value of FIG. 4) and by comparing the or _Cr 2 Se _3-phase Can be determined. In this case, the main peak of the powder X-ray diffraction pattern of the Cr ₂ Se ₃ crystal may be determined based on about 10 strong diffraction intensities (may be small or large depending on conditions). Table 1 is a reference in specifying the Cr ₂ Se ₃ phase in that sense. Further, an approximate structure of the Cr ₂ Se ₃ phase crystal structure can be defined by using another crystal system other than the trigonal system. In this case, the expression uses a different space group, lattice constant, and plane index, but the X-ray diffraction pattern (the calculated value in FIG. 4) and the crystal structure (FIG. 1) remain unchanged. Therefore, even if the identification method uses another crystal system, the identification result is essentially the same. Therefore, in this specification, the analysis of X-ray diffraction is assumed to be a trigonal system.

In the thermoelectric material of the present invention, in the binary compound, the atomic ratio of Cr to Se (Cr / Se ratio) preferably satisfies 0.623 or more and 0.759 or less. As described above, when the atomic ratio of Se to Ce satisfies the predetermined range as well as the composition of the general formula, excellent thermoelectric properties can be exhibited in a temperature range from room temperature to 600 K or less. In particular, a binary compound that is a Cr ₂ Se ₃ crystal itself is known as a p-type thermoelectric material. However, the present inventors have controlled the Cr ₂ Se ₃ crystal only by controlling the atomic ratio of Cr to Se. It has been found that the inherent thermoelectric properties are improved.

  In the specification of the present application, the thermoelectric material of the present invention contains the above-described binary compound as a main phase, and the ratio may be 70% by weight or more as a weight ratio. When the main phase is less than 70% by weight, a sufficient thermoelectric effect may not be obtained. The proportion of the main phase is preferably 80% by weight or more, and more preferably 90% by weight or more. Naturally, since the binary compound is preferably composed of a main phase single phase, the upper limit of the proportion of the main phase is 100% by weight. However, in order to generate thermoelectric properties, it is not necessarily required to be a single phase. . The method of measuring the proportion of such a phase is based on the diffraction pattern observed within the range of d value (1.54 ° -5.80 °) by X-ray diffraction measurement, based on the peak position and peak intensity. From the above, phase identification (main phase and second phase) can be performed, the precipitation ratio can be calculated from the integrated intensity ratio of the strongest peak, and the main phase can be determined (for example, RIR (Reference Intensity Ratio) method). . Further, the thermoelectric material of the present invention may contain a small amount of chromium, chromium oxide, or the like as the second phase in addition to the above-described binary compound.

  Furthermore, when p satisfies -0.1 ≦ p <0 or 0 <p <0.05 in the above general formula, the thermoelectric material of the present invention may exhibit p-type in a temperature range from room temperature to 600K. it can. More preferably, the atomic ratio of Cr to Se satisfies 0.623 or more and less than 0.707. Thus, a p-type thermoelectric material having excellent thermoelectric properties in a temperature range from room temperature to 600K.

  More preferably, in the thermoelectric material of the present invention, in the above general formula, p satisfies −0.05 ≦ p ≦ −0.02 or 0 <p ≦ 0.04. By further restricting the composition, a p-type thermoelectric material having more excellent thermoelectric properties can be obtained in a temperature range from room temperature to 600K. Still more preferably, the atomic ratio of Cr to Se satisfies 0.639 or more and 0.703 or less. Thereby, a p-type thermoelectric material having a large Seebeck coefficient (absolute value) in a temperature range from room temperature to 600 K is obtained. More preferably, in the thermoelectric material of the present invention, in the above general formula, p satisfies −0.04 ≦ p ≦ −0.02 or 0 <p ≦ 0.04, and the atomic ratio of Cr to Se is , 0.643 or more and 0.703 or less. q preferably satisfies -0.05 ≦ q ≦ 0.05.

  Furthermore, when p satisfies 0.05 ≦ p ≦ 0.2 in the above general formula, the thermoelectric material of the present invention can exhibit n-type in a temperature range from room temperature to 600K. More preferably, the atomic ratio of Cr to Se satisfies 0.672 or more and 0.759 or less. Thus, an n-type thermoelectric material having excellent thermoelectric properties in a temperature range from room temperature to 600K is obtained.

  More preferably, in the thermoelectric material of the present invention, in the above general formula, p satisfies 0.06 ≦ p ≦ 0.15. By further restricting the composition, an n-type thermoelectric material having more excellent thermoelectric properties can be obtained in a temperature range from room temperature to 600K. Still more preferably, the atomic ratio of Cr to Se satisfies 0.675 or more and 0.741 or less. Thus, an n-type thermoelectric material having a large Seebeck coefficient (absolute value) in a temperature range from room temperature to 600 K is obtained. Preferably, p satisfies 0.06 ≦ p ≦ 0.12, and the atomic ratio of Cr to Se satisfies 0.675 or more and 0.731 or less. q preferably satisfies -0.05 ≦ q ≦ 0.05.

  By controlling the composition of Cr and Se to have a very limited composition, n-type and p-type thermoelectric materials can be provided with the same element. Note that the composition can be analyzed by fluorescent X-ray analysis or the like.

  The form of the thermoelectric material of the present invention is not limited to a sintered body, powder, thin film, etc., as long as it contains the binary compound represented by the above general formula. Although the thermoelectric material of the present invention has the above-mentioned binary compound as a main component, for example, when it is a sintered body or a powder, it may contain an additive in addition to the above-mentioned binary compound. From such a viewpoint, in the present specification, the amount of the main component of the intermetallic compound may be 70% by weight or more. If it is less than 70% by weight, a sufficient thermoelectric effect cannot be obtained. The additive may be a sintering aid, a binder, or the like. It is also intended that the thermoelectric material of the present invention contains unavoidable impurities such as C (carbon), metal or its oxide, which are mixed during production. The content of such inevitable impurities is not limited as long as the thermoelectric performance is not reduced, but is preferably 0.15% by weight or less.

Next, an exemplary manufacturing method for manufacturing the thermoelectric material of the present invention will be described. Here, the case where the thermoelectric material is a bulk body or a powder will be described.
FIG. 2 is a flowchart showing steps of manufacturing the thermoelectric material of the present invention.

Step 210: The raw material containing Cr and the raw material containing Se are mixed so as to satisfy the general formula Cr _{2 + x} Se ₃ . Here, x satisfies −0.1 ≦ x <0 or 0 <x ≦ 0.2. The present inventors have found that a thermoelectric material containing the above-described binary compound of the present invention can be obtained only by mixing a raw material containing Cr and Se so as to satisfy the above general formula.

  The raw material containing Cr and the raw material containing Se may be a Cr metal simple substance and a Se metal simple substance, respectively, for example, Cr silicide, oxide, carbonate, nitride, oxynitride, chloride , Fluoride or oxyfluoride, silicide of Se, oxide, carbonate, nitride, oxynitride, chloride, fluoride or oxyfluoride may be used. Also in this case, the respective metal elements may be mixed so as to satisfy the above general formula. Raw materials are preferably powders, granules, and small lumps from the viewpoint of mixing properties and handling.

  Further, the present inventors have found that the thermoelectric material of the present invention in which the n-type and p-type conductivity types are controlled by the same element as described above can be produced by adjusting the mixed composition represented by the general formula. .

  In the above general formula, the raw materials are preferably mixed so that the atomic ratio of Cr to Se (Cr / Se ratio) satisfies 0.6330 or more and 0.733 or less. Thereby, a thermoelectric material having excellent thermoelectric properties in a temperature range from room temperature to 600 K or less can be provided.

  In the above general formula, when the raw materials are mixed such that x satisfies −0.1 ≦ x <0 or 0 <x <0.05, a p-type thermoelectric material can be provided in a temperature range from room temperature to 600K. . More preferably, they are mixed so that the atomic ratio of Cr to Se satisfies 0.633 or more and less than 0.683. Thus, a p-type thermoelectric material having excellent thermoelectric properties can be provided in a temperature range from room temperature to 600K.

  More preferably, in the above general formula, the raw materials are mixed so that x satisfies −0.05 ≦ x ≦ −0.02 or 0 <x <0.05. By further limiting the composition of the raw material, a p-type thermoelectric material having further excellent thermoelectric properties can be provided in a temperature range from room temperature to 600K. Still more preferably, they are mixed so that the atomic ratio of Cr to Se satisfies 0.650 or more and less than 0.683. Thereby, a p-type thermoelectric material having a large Seebeck coefficient (absolute value) in a temperature range from room temperature to 600 K can be provided. More preferably, in the above general formula, x satisfies −0.04 ≦ x ≦ −0.02 or 0 <x ≦ 0.04, and the atomic ratio of Cr to Se is 0.653 or more. Mix to satisfy 680 or less.

  Furthermore, when the raw materials are mixed so that x satisfies 0.05 ≦ x ≦ 0.2 in the above general formula, a thermoelectric material exhibiting n-type can be provided in a temperature range from room temperature to 600K. More preferably, the raw materials are mixed such that the atomic ratio of Cr to Se satisfies 0.683 or more and 0.733 or less. Thus, an n-type thermoelectric material having excellent thermoelectric properties can be provided in a temperature range from room temperature to 600K.

  More preferably, in the above general formula, x is mixed with the raw materials so that x satisfies 0.06 ≦ x ≦ 0.15. By further limiting the composition, it is possible to provide an n-type thermoelectric material having further excellent thermoelectric properties in a temperature range from room temperature to 600K. Still more preferably, the raw materials are mixed so that the atomic ratio of Cr to Se satisfies 0.687 or more and 0.717 or less. Thus, an n-type thermoelectric material having a large Seebeck coefficient (absolute value) in a temperature range from room temperature to 600 K can be provided. Preferably, x satisfies 0.06 ≦ x ≦ 0.12, and the atomic ratio of Cr to Se satisfies 0.687 or more and 0.707 or less.

  As described above, since the n-type and p-type can be controlled only by controlling the parameters of the general formula, the thermoelectric material of the present invention can be manufactured with a high yield without requiring any skilled technique.

  Step 220: firing the mixture obtained in step S210. The sintering may be performed by heating to a temperature at which the mixture reacts. For example, the firing is performed in a temperature range of 1073K to 1773K. The calcination is preferably performed in an inert atmosphere of nitrogen or a rare gas such as argon or helium, or in vacuum. The firing time varies depending on the firing temperature, but is illustratively in the range of 30 minutes to 48 hours. The heating rate is not particularly limited, but a heating rate in a range of 5 K / hour to 20 K / hour can be employed.

  Prior to firing, the mixture obtained in the mixing step may be shaped. This is preferable because the reaction is accelerated. Press molding can be used for such molding. After firing, the fired body may be rapidly cooled. Thereby, a uniform fired body is obtained. The rapid cooling may be performed at a cooling rate of 223 K / sec or more from the firing temperature to room temperature. The fired body thus obtained is the thermoelectric material of the present invention.

  The thermoelectric material of the present invention can be provided as a sintered body by crushing and sintering the fired body obtained in step S220. The sintering is, for example, performed by pulverizing the fired body and shaping the formed body into a predetermined shape in a pressure range of 10 MPa to 100 MPa and a temperature range of 1073 K to 1273 K ° C. The sintering time may be 5 minutes or more and 12 hours or less. For sintering, a normal hot press method, a pulse current sintering method, or a spark plasma sintering (SPS) can be adopted.

  The pulverization of the fired body for sintering is preferably performed until the particle diameter (d50) becomes 50 μm or less. Thereby, sintering described later can be promoted. Preferably, the fired body is pulverized to particles having a particle diameter of 45 μm or less. Thereby, sintering and heat treatment can be promoted, and the processing time can be shortened. The pulverization is performed by a known method such as a ball mill, an automatic mortar, and a vibration mill.

  Generally, the average particle size can be defined as follows. The particle diameter is defined as the diameter of a sphere having an equivalent sedimentation velocity in the measurement by the sedimentation method, and is defined as the diameter of a sphere having an equivalent scattering characteristic in the laser scattering method. Further, the distribution of the particle size is referred to as a particle size (particle size) distribution. In the particle size distribution, the particle size when the sum of masses larger than a certain particle size occupies 50% of that of the whole powder can be defined as the average particle size D50. These definitions and terms are all well known to those skilled in the art, and are described in, for example, JISZ8901 “Test powder and test particles” or “Basic physical properties of powder” edited by Japan Society of Powder Technology (ISBN4-526-05544). It is described in the literature such as Chapter 1 of 1). The particle diameter corresponding to 50% in the integrated (cumulative) frequency distribution was determined and defined as the average particle diameter D50. Various means other than those described above have been developed as means for determining the average particle size, and these conditions are still continuing at present, and there may be slight differences in the measured values. It should be understood that the meaning is clear and is not necessarily limited to the above means.

  The obtained sintered body may be formed (formed) by a high-speed cutter or the like, and may be employed for a thermoelectric power generation element (may be referred to as a thermoelectric power generation module). Further, if the obtained sintered body is used as a target in a physical vapor deposition method, the thermoelectric material of the present invention can be provided as a thin film.

(Embodiment 2)
In the second embodiment, a thermoelectric element using the thermoelectric material of the present invention described in the first embodiment will be described.

  FIG. 3 is a schematic view showing a thermoelectric power generation element using the thermoelectric material of the present invention.

  The power generation thermoelectric element 300 according to the present invention includes a pair of n-type thermoelectric material 310 and p-type thermoelectric material 320, and electrodes 330 and 340 at their respective ends. The electrodes 330 and 340 electrically connect the n-type thermoelectric material 310 and the p-type thermoelectric material 320 in series.

  Here, n-type thermoelectric material 310 and p-type thermoelectric material 320 are the thermoelectric materials of the present invention described in the first embodiment. Since the n-type and p-type thermoelectric materials made of the same element having the same coefficient of thermal expansion are used, it is advantageous to make the thermoelectric power generation element 300 of the present invention an element. The electrodes 330 and 340 may be a normal electrode material, but are exemplified by Al, Ni, Cu and the like.

  In FIG. 3, a chip made of the n-type thermoelectric material 310 is joined to the electrode 340 on the low-temperature side by soldering or the like, and the opposite end of the chip of the n-type thermoelectric material 310 and the electrode 330 on the high-temperature side are connected to each other. Are joined by solder or the like. Similarly, a chip made of the p-type thermoelectric material 320 is joined to the electrode 330 on the high-temperature side by soldering or the like, and the opposite end of the chip of the p-type thermoelectric material 320 is connected to the electrode 340 on the low-temperature side. Are joined by solder or the like.

  When the thermoelectric power generation element 300 of the present invention is installed in an environment where the temperature of the electrode 330 is high and the temperature of the electrode 340 is low compared to the temperature of the electrode 330 and the end electrodes are connected to an electric circuit or the like, the voltage is increased by the Seebeck effect. Occurs, and a current flows in the order of the electrode 340, the n-type thermoelectric material 310, the electrode 330, and the p-type thermoelectric material 320, as shown by arrows in FIG. In detail, the electrons in the n-type thermoelectric material 310 obtain thermal energy from the high-temperature side electrode 330 and move to the low-temperature side electrode 340, where the heat energy is released. Electric current flows according to the principle that the holes 320 obtain thermal energy from the high-temperature side electrode 330 and move to the low-temperature side electrode 340, where the thermal energy is released.

  In the present invention, since the thermoelectric material of the present invention described in Embodiment 1 is used as the n-type thermoelectric material 310 and the p-type thermoelectric material 320, the power generation thermoelectric element 300 having a large power generation in a wide temperature range from room temperature to 600K is realized. it can. Since a thermoelectric material made of the same constituent element is used near room temperature, good heat recovery is possible. When a thin film is used as a thermoelectric material, a flexible thermoelectric power generation module can be provided as an IoT power supply.

  Although FIG. 3 has been described using a π-type thermoelectric power generation element, the thermoelectric material of the present invention may be used for a U-shaped thermoelectric power generation element (not shown). In this case, similarly, the n-type thermoelectric material and the p-type thermoelectric material made of the thermoelectric material of the present invention are alternately electrically connected in series.

  Hereinafter, embodiments of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the scope of these Examples.

[Examples: 1 to 7]
In Examples 1 to 7, the raw materials were mixed so as to satisfy the general formula Cr _{2 + x} Se ₃ (−0.04 ≦ x ≦ 0.12) to produce a thermoelectric material. Cr (powder, purity 99.99%, manufactured by Kojundo Chemical Laboratory Co., Ltd.) and Se (powder, purity 99.99%, manufactured by Kojundo Chemical Laboratory Co., Ltd.) were designed to the design compositions shown in Table 2. Therefore, they were mixed (step S210 in FIG. 2).

  Each mixture was press-molded into pellets (diameter 12 mm, thickness 1-2 mm). The pellet was placed in a quartz tube, and the inside was evacuated with a diffusion pump. Thereafter, under the conditions shown in Table 3, the temperature was raised from room temperature to 1273 K over 100 hours (10 K / hour) and calcined at 1273 K for 24 hours (step S220 in FIG. 2). After firing, the mixture was rapidly cooled to room temperature using water.

  The fired body obtained was wet-ground using ethanol in an agate mortar. The particles of the fired body after pulverization were sieved with a mesh (mesh size: 45 μm), and only particles having a particle size of 45 μm or less that passed through the mesh were taken out. The particles were identified by a powder X-ray diffraction method (manufactured by Rigaku Corporation, Smartlab3), and a composition analysis was performed by fluorescent X-ray analysis (manufactured by Horiba, Ltd., EMAX Evolution EX). The results are shown in FIG. 4, Table 4 and Table 5, and will be described later.

  Next, the particles were sintered by spark plasma sintering (SPS). In detail, a graphite sintering die (inner diameter 20 mm, height 40 mm) was filled with particles, and the temperature was raised at a rate of 100 K / min and a sintering temperature of 923 K for 5 minutes under a uniaxial stress of 80 MPa. Thus, a disk-shaped sintered body having a diameter of about 10 mm and a thickness of about 2 mm was obtained.

  The sintered body was processed into a 1.5 mm × 1.5 mm × 9 mm rectangular parallelepiped by a high-speed cutter, and electric conductivity and thermoelectric properties were measured. The electric conductivity was measured by a direct current four terminal method. The Seebeck coefficient and the thermal conductivity as thermoelectric properties were measured by a steady-state temperature difference method using a thermoelectric property measurement and evaluation device (ZEM-3, manufactured by Advance Riko Co., Ltd.). The measurement conditions were all measured in a helium gas atmosphere from room temperature to 823K. The electrical output factor was calculated from the thermoelectromotive force obtained from the electrical conductivity and the Seebeck coefficient, and the dimensionless figure of merit ZT was calculated from the Seebeck coefficient, the electrical conductivity, and the thermal conductivity. These results are shown in FIGS. 5 to 9 and Table 5 and will be described later.

The above results will be described.
FIG. 4 is a diagram showing X-ray diffraction patterns of the samples according to Examples 1 to 7.

FIG. 4 also shows the X-ray diffraction pattern of Cr ₂ Se ₃ calculated from the calculation. According to FIG. 4, the XRD pattern of any of the samples (fired bodies) of Examples 1 to 7 was in good agreement with the calculated XRD pattern of Cr ₂ Se ₃ . In the samples of Example 1 and Example 2, as shown in FIG. 4, some unknown phases were found, but when the precipitation ratio was calculated from the integrated intensity ratio of the strongest peak, the main phase was found to be all trigonal. It was a Cr ₂ Se ₃ phase having a crystal structure and contained 90% by mass or more.

  When Rietveldt analysis was performed from the X-ray diffraction pattern of FIG. 4 to determine the crystal structure, as shown in Table 4, all of the samples of Examples 1 to 7 belonged to the trigonal system, and the space group was R3- And it was confirmed that it was space group number 148.

  Table 5 shows the results of composition analysis by X-ray fluorescence analysis.

According to Table 5, Cr in the sample was substantially similar to the charged composition, but Se varied from the time of charging. The composition of the sample obtained in Example 1 was Cr _1.96 Se _3.04 , and the composition of the sample obtained in Example 3 was Cr ₂ Se ₃ . Although not shown in the table, the samples of Examples 2 and 4 to 7 are all binary compounds of Cr and Se, and have the general formula Cr _{2 + p} Se _{3 + q} (where p is −0.1 ≦ p <0 or 0 <p ≦ 0.2, and q satisfies −0.1 ≦ q ≦ 0.05).

From the above, when the method of the present invention is carried out, at least a binary compound of Cr and Se is contained, and the binary compound has a general formula of Cr _{2 + p} Se _{3 + q} (where p is −0.1 ≦ p <0 or 0 <p ≦ 0.2, and q satisfies −0.1 ≦ q ≦ 0.05), and a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure. It was shown that a material containing as a main component was obtained.

  FIG. 5 is a diagram showing the temperature dependence of the electrical conductivity of the samples of Examples 1 to 7.

According to FIG. 5, it was found that all the samples had an electrical conductivity usable as a thermoelectric material and had a temperature dependency in a measurement temperature range. Focusing on the electrical conductivity at room temperature, the electrical conductivity can be changed from 250 (Ωcm) ⁻¹ to 600 (Ωcm) ⁻¹ by controlling the composition. When configuring the thermoelectric conversion element, a material having an electric conductivity required in a use temperature range may be appropriately selected.

  FIG. 6 is a diagram showing the temperature dependence of the Seebeck coefficient of the samples of Examples 1 to 7.

  According to FIG. 6, in the measurement temperature range (300 K to 823 K), the samples of Examples 1 to 4 show a positive Seebeck coefficient and have p-type conductivity, and the samples of Examples 5 to 7 show the negative Seebeck coefficients. The coefficient was shown, and it was confirmed that it was n-type conduction.

That is, the general formula Cr _{2 + p} Se _{3 + q} (where p satisfies −0.1 ≦ p <0 or 0 <p ≦ 0.2, and q satisfies −0.1 ≦ q ≦ 0.05) Thus, it was shown that the binary compound of Cr and Se, which is a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure, is a thermoelectric material. Specifically, Cr ₂ Se having a trigonal crystal structure represented by a general formula Cr _{2 + p} Se _{3 + q} (where p satisfies −0.1 ≦ p <0 or 0 <p <0.05) _The binary compound having the phase represented by ₃ as a main phase functions as a p-type thermoelectric material, and is represented by a general formula Cr _{2 + p} Se _{3 + q} (where p satisfies 0.05 ≦ p ≦ 0.2). The binary compound having a main phase of a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure functions as an n-type thermoelectric material.

Surprisingly, the sample of Example 3 is the Cr ₂ Se ₃ phase itself, but makes Cr slightly rich or slightly poor and deviates from stoichiometric composition (eg, Example 1, Example 2, Example 4). Thus, it was found that a p-type thermoelectric material exhibiting a large Seebeck coefficient (absolute value) of 90 μV / K to 160 μV / K in a temperature range from room temperature to 50 ° C. Here, the atomic ratio of Cr to Se satisfies 0.623 or more and less than 0.707.

  When Cr is further made rich from the stoichiometric composition (for example, Examples 5 to 7), an n-type thermoelectric exhibiting a large Seebeck coefficient (absolute value) of 100 μV / K to 250 μV / K in a temperature range of room temperature to 50 ° C. It turned out to be a material. Here, the atomic ratio of the Cr to Se satisfies 0.672 or more and 0.759 or less.

  FIG. 7 is a diagram illustrating the temperature dependence of the electrical output factors of the samples of Examples 1 to 7.

  According to FIG. 7, it was found that by selecting the composition, a high electrical output factor could be achieved in the measurement temperature range. For example, the sample of Example 4 exhibits a high electric power factor in a temperature range of 300K to 823K, and is particularly suitable for collecting poor heat of 600K or less, and can provide a thermoelectric power generation element for consumer use.

  FIG. 8 is a diagram showing the temperature dependence of the thermal conductivity of the samples of Examples 1 to 7.

  According to FIG. 8, it was found that even when the composition was selected, the value of the thermal conductivity was almost constant in the measurement temperature range. Thus, the thermal conductivity of the thermoelectric material of the present invention does not depend on the composition, which is advantageous for element design.

  FIG. 9 is a diagram showing the temperature dependence of the dimensionless figure of merit ZT of the samples of Examples 1 to 7.

  According to FIG. 9, it was found that a high dimensionless figure of merit can be achieved in the measurement temperature range by selecting the composition. For example, the value of the sample of Example 4 exceeded 0.2 in the range of 500K to 600K.

  The above results are summarized in Table 6 for simplicity.

  The thermoelectric material of the present invention exhibits n-type and p-type thermoelectric characteristics and can achieve a high power factor only by controlling the composition in a temperature range of at least up to 600 K. Used for In particular, if the thickness is reduced, a flexible thermoelectric generator can be provided as an IoT power supply.

300 Thermoelectric module for power generation 310 n-type thermoelectric material 320 p-type thermoelectric material 330, 340 Electrode

Claims (20)

At least a binary compound of Cr and Se is contained,
The binary compound has a general formula of Cr _{2 + p} Se _{3 + q} (where p satisfies −0.1 ≦ p <0 or 0 <p ≦ 0.2, and q satisfies −0.1 ≦ q ≦ 0.05. Is satisfied)
The thermoelectric material, wherein the binary compound is a phase represented by Cr ₂ Se ₃ having a trigonal crystal structure.   2. The thermoelectric material according to claim 1, wherein in the binary compound, an atomic ratio of the Cr to the Se satisfies 0.623 to 0.759.   The thermoelectric material according to claim 1, wherein the space group of the crystal structure is R 3-3.   4. The thermoelectric material according to claim 1, wherein p satisfies −0.1 ≦ p <0 or 0 <p <0.05, and indicates p-type in a temperature range from room temperature to 600 K or less. 5.   The thermoelectric material according to claim 4, wherein in the binary compound, an atomic ratio of the Cr to the Se satisfies 0.623 or more and less than 0.707.   The thermoelectric material according to claim 4, wherein the p satisfies −0.05 ≦ p ≦ −0.02 or 0 <p ≦ 0.04.   The thermoelectric material according to claim 6, wherein in the binary compound, the atomic ratio of the Cr to the Se satisfies 0.639 or more and 0.703 or less.   4. The thermoelectric material according to claim 1, wherein p satisfies 0.05 ≦ p ≦ 0.2 and shows n-type in a temperature range from room temperature to 600 K or less. 5.   The thermoelectric material according to claim 8, wherein in the binary compound, an atomic ratio of the Cr to the Se satisfies 0.672 or more and 0.759 or less.   The thermoelectric material according to claim 8, wherein p satisfies 0.06 ≦ p ≦ 0.15.   The thermoelectric material according to claim 10, wherein the atomic ratio of the Cr to Se in the binary compound satisfies 0.675 or more and 0.741 or less. The binary compound contains the _Cr 2 Se ₃ in phases 70 wt% or more homology, thermoelectric material according to any one of claims 1 to 11.   The thermoelectric material according to any one of claims 1 to 12, wherein the binary compound does not contain a different element other than the Ce and the Se. A method for producing a thermoelectric material, comprising:
A raw material containing Cr and a raw material containing Se are mixed so as to satisfy the general formula Cr _{2 + x} Se ₃ (where x satisfies −0.1 ≦ x <0 or 0 <x ≦ 0.2). Steps and
Calcining the mixture obtained in the mixing step.   The mixing step, wherein the Cr-containing raw material and the Se-containing raw material are mixed such that the atomic ratio of the Cr to Se satisfies 0.633 or more and 0.733 or less. The described method.   The method according to claim 14 or 15, wherein the firing step includes firing the mixture in a temperature range from 1073K to 1773K in an inert atmosphere or vacuum.   17. The method of any of claims 14 to 16, further comprising, following the mixing step, shaping the mixture.   The method according to any one of claims 14 to 17, further comprising, after the firing step, rapidly cooling the fired body obtained in the firing step. A thermoelectric generator comprising a p-type thermoelectric material and an n-type thermoelectric material alternately connected in series,
A thermoelectric power generation element, wherein at least one of the p-type thermoelectric material and the n-type thermoelectric material is the thermoelectric material according to claim 1. The p-type thermoelectric material is the thermoelectric material according to any one of claims 4 to 7,
The thermoelectric generator according to claim 19, wherein the n-type thermoelectric material is the thermoelectric material according to any one of claims 8 to 11.