JP2018067590A - Copper gallium tellurium-based p-type thermoelectric semiconductor and thermoelectric generation element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper gallium tellurium-based p-type thermoelectric semiconductor and thermoelectric generation element, having a high thermoelectric conversion efficiency even in a relatively low temperature region substantially from a room temperature to 400°C as a thermoelectric semiconductor.SOLUTION: The copper gallium tellurium-based p-type thermoelectric semiconductor is a p-type thermoelectric semiconductor including a copper gallium tellurium compound containing at least any one element of chromium, manganese, iron, cobalt and nickel. It is also a p-type thermoelectric semiconductor including a copper gallium tellurium compound containing the element and a thermoelectric semiconductor element integrated with an n-type semiconductor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a copper gallium tellurium-based p-type thermoelectric semiconductor and a thermoelectric power generation element using the same.

In the past, thermoelectric semiconductors have been actively researched in order to use energy efficiently in modern society, and there has been a great demand for use in reliable and quiet cooling devices and generators. ing.
A copper gallium tellurium compound is known as one of thermoelectric semiconductors. As shown in Patent Document 1 and Non-Patent Document 1, the copper gallium tellurium compound exhibits low electrical resistance, a large Seebeck coefficient, and a relatively low thermal conductivity at high temperatures, and exhibits excellent performance as a thermoelectric semiconductor in high temperature regions. Show. However, it is a performance at a high temperature of 800 K or more (about 500 ° C. or more). On the other hand, there is a high demand for effective use of heat in the low and medium temperature ranges close to room temperature. In order to meet such demand, a new thermoelectric conversion material as a thermoelectric semiconductor has been required. In addition, a thermoelectric power generation element having high power generation efficiency in a low temperature and medium temperature range close to room temperature has been demanded.

JP2013-016685A

Advanced Materials, vol. 24 (2012) pp. 3622-3626 Inorganic Materials, vol. 43 (2007) pp. 12-17

  An object of the present invention is to provide a thermoelectric semiconductor and a thermoelectric power generation element having a high thermoelectric conversion efficiency even in a relatively low temperature range as a thermoelectric semiconductor at around room temperature to about 400 ° C.

  As a result of various investigations, the present inventors have compared the above object by adding one or more magnetic elements selected from the group consisting of chromium, manganese, iron, cobalt, and nickel to a copper gallium tellurium compound. It has been found that a p-type thermoelectric semiconductor having high thermoelectric conversion efficiency can be provided even in a low operating temperature range. The configuration of the present invention is as follows.

(Configuration 1)
A p-type thermoelectric semiconductor containing a copper gallium tellurium compound,
A p-type thermoelectric semiconductor comprising one or more elements selected from the group consisting of chromium, manganese, iron, cobalt, and nickel.

(Configuration 2)
The p-type thermal semiconductor according to Configuration 1, wherein the element is contained as a total amount of the element in a molar ratio of more than 0% and less than 5% with respect to the copper gallium tellurium compound.

(Configuration 3)
2. The p-type thermoelectric semiconductor according to Configuration 1, wherein the element is contained in a molar ratio of 1% to 3% with respect to the copper gallium tellurium compound as a total amount of the element.

(Configuration 4)
4. A p-type thermoelectric semiconductor according to any one of Structures 1 to 3, wherein the composition is a tetragonal p-type thermoelectric semiconductor having a composition represented by Formula 1.
_{CuGa 1-x M x Te 2} ( Equation 1)
(M is 1 or more consisting of Cr, Mn, Fe, Co, and Ni, and x is greater than 0 and less than 1.)

(Configuration 5)
5. The p-type thermal semiconductor according to Configuration 4, wherein x is greater than 0 and less than 0.05.

(Configuration 6)
The p-type thermoelectric semiconductor according to Configuration 4, wherein x is 0.01 or more and 0.03 or less.

(Configuration 7)
A thermoelectric power generation element obtained by integrating a p-type semiconductor and an n-type semiconductor, wherein the p-type thermoelectric semiconductor according to any one of configurations 1 to 6 is used as the p-type semiconductor. .

The thermoelectric semiconductor of the present invention has characteristics such as low electrical resistance (high electrical conductivity), high Seebeck coefficient, and low thermal conductivity even in a relatively low operating temperature range from near room temperature to 400 ° C. Therefore, high thermoelectric conversion efficiency can be obtained.
Moreover, the thermoelectric power generation element using the thermoelectric semiconductor of the present invention can obtain high thermoelectric power generation efficiency even in the low operating temperature region as described above. For this reason, it becomes possible to recover heat from a lower temperature range than before, and the range of available heat is greatly expanded.

The crystal structure schematic diagram of the semiconductor material of this invention. The powder X-ray-diffraction pattern figure of a copper gallium tellurium compound sample. The thermoelectric characteristic figure which investigated the electrical conductivity characteristic of the copper gallium tellurium compound. The thermoelectric characteristic figure which investigated the Seebeck coefficient characteristic of the copper gallium tellurium compound. The thermoelectric characteristic figure which investigated the output factor characteristic of the copper gallium tellurium compound. The thermoelectric characteristic figure which investigated the thermal conductivity characteristic of the copper gallium tellurium compound. The thermoelectric characteristic figure which investigated the dimensionless figure of merit ZT characteristic of a copper gallium tellurium compound. The thermoelectric characteristic figure which investigated the output factor characteristic of the copper gallium tellurium compound. The thermoelectric characteristic figure which investigated the dimensionless figure of merit ZT characteristic of a copper gallium tellurium compound. The thermoelectric characteristic figure which investigated the power factor characteristic of the copper gallium tellurium compound which added iron. FIG. 4 is a schematic cross-sectional view showing a thermoelectric power generation element of Example 3.

(Thermoelectric semiconductor)
Initially, the manufacturing method of the thermal semiconductor of this invention is demonstrated.
1 selected from the group consisting of copper (Cu), manganese (Mn), tellurium (Te), and chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) as a raw material The above magnetic element M is prepared. Here, the case where manganese is prepared as the magnetic element M will be mainly described, but the magnetic element M may be obtained by replacing manganese with chromium, iron, cobalt, or nickel. Two or more selected from manganese, chromium, iron, cobalt, and nickel may be used as the magnetic element M.

Next, Cu, Ga, M, and Te are weighed so that the molar ratio is 1: 1-x: x: 2. Here, when the magnetic element M is composed of the plurality of elements described above, the total amount is weighed so that the molar ratio is x. x is preferably more than 0 and less than 0.05. Here, the meaning of “beyond 0” means that the magnetic element M is substantially included, and for example, it is not included when it is unintentionally contained in a very small amount as an impurity. When a very small amount is included unintentionally, the amount and distribution are likely to vary, and the thermoelectric characteristics are likely to vary.
x is particularly preferably from 0.01 to 0.03 because an impurity phase is not generated, thermoelectric conversion efficiency is high, and thermoelectric characteristics are stable.
After mixing the above-mentioned weighed elements, the mixture is heated to a temperature at which Cu, Ga, M and Te are sufficiently melted, and then at a temperature that forms a solid phase such as 600 ° C., the atoms move. Cool slowly so that homogeneous crystal growth proceeds to a temperature at which homogeneous crystals tend to form.
Then, it cools to room temperature and the ingot in which the magnetic element M was added to the copper gallium tellurium compound is obtained.
Next, the ingot is pulverized using, for example, a ball mill, a sintered body is obtained by a discharge plasma sintering method, a hot press method, or the like, and a copper gallium tellurium compound CuGa ₁ to which a predetermined amount of a predetermined magnetic element M is added. _A p-type thermoelectric semiconductor composed of _{-xM x} Te ₂ is manufactured.

A schematic diagram of a manganese (Mn) copper gallium was added tellurium compounds _CuGa 1-x _Mn x Te ₂ crystal structures (chalcopyrite structure) the magnetic element M shown in FIG. Since only a few percent of manganese is added at a molar ratio, only one gallium (Ga) site in some unit cells is replaced with manganese (Mn). The same applies when the other magnetic element M is added instead of manganese.

As shown in Example 1 below, the copper gallium tellurium compound CuGa _1-x Mn _x Te ₂ to which less than 5 mol% of manganese is added becomes a homogeneous crystal having a chalcopyrite structure that is one of the tetragonal systems. When 5 mol% of manganese is added, an impurity phase appears in the crystal.
When the impurity phase appears, the thermoelectric characteristics are difficult to stabilize, and therefore it is not preferable that the copper gallium tellurium compound contains manganese as the magnetic element M in a molar ratio of 5% or more. As shown in this example, from the viewpoint of obtaining a crystal of sufficient purity, in the copper gallium tellurium compound CuGa _1-x M _x Te _{2 to} which the magnetic element M, which is the p-type thermoelectric semiconductor of the present invention, is added, x Is preferably less than 0.05.

Next, the thermoelectric characteristics of a thermoelectric semiconductor made of a copper gallium tellurium compound to which a predetermined amount of magnetic element M is added will be described.
The thermoelectric characteristics are measured as follows, for example.
The electrical conductivity (σ), Seebeck coefficient (S), thermal diffusivity (α), thermal capacity (C _p ), and sample density of a thermoelectric semiconductor comprising a copper gallium tellurium compound to which a predetermined amount of magnetic element M has been added ( d) is measured, and the output factor (PW), thermal conductivity (κ), and dimensionless figure of merit (ZT) are calculated from the measurement results. Here, the output factor PW can be calculated by the equation PW = S ² σ, the thermal conductivity κ can be calculated by the equation κ = α · C _p · d, and the dimensionless figure of merit ZT can be calculated by the equation ZT = S ² σT / κ. Here, T is an absolute temperature.

As shown in Example 1 below, by adding, for example, manganese as the magnetic element M, the electrical conductivity σ increases by an order of magnitude. This is thought to be mainly due to the increased carrier concentration.
When the carrier concentration is significantly increased, normally, the Seebeck coefficient S is significantly reduced, and the output factor PW calculated by S ² σ does not simply increase. However, as shown in Example 1, the Seebeck coefficient S is not reduced so much in the sample to which manganese is added, and is only reduced by about half at the maximum. Moreover, thermal conductivity (kappa) is lower than the case where manganese is not added, and has a preferable characteristic as a thermoelectric semiconductor.
From these facts, as shown in Example 1, the addition of manganese doubles the output factor PW and increases the dimensionless figure of merit ZT by about 3 times in a relatively low temperature range from around room temperature to about 400 ° C.

Such a large increase in the output factor PW is due to the fact that carriers (electrons and holes) responsible for electrical conduction in the semiconductor interact with added magnetic elements (magnetic ions), resulting in an increase in effective mass. It is presumed that a large Seebeck coefficient was maintained despite the increase in carrier density.
In order to support this, the effective mass of the carrier was calculated from the Hall coefficient measurement for the sample added with manganese. As a result, the copper gallium telluride without the addition of manganese, effective mass of electrons was calculated from the Hall coefficient measurement and Seebeck coefficient value was 0.22 m o _{(m o} is the free electron mass). In contrast, 1 mol% of manganese, 2 mol%, and the effective electron mass at 3 mol% added sample, respectively 0.62 meters _o, 1.0 m _o, was 0.92 m _o. Therefore, it is considered that the interaction between the magnetic ions and the carriers in the semiconductor caused an increase in effective mass, which led to an improvement in thermoelectric characteristics. Since the same interaction works even when a similar magnetic ion is added, the same effect can be obtained even when chromium, manganese, iron, cobalt, and nickel are used as transition metal elements exhibiting ferromagnetism or antiferromagnetism.
On the other hand, rare earth elements exhibiting magnetism (neodymium (Nd), gadolinium (Gd), dysprosium (Dy), etc.) have little effect because the permissible content in the copper gallium tellurium compound is on the order of ppm.

  In addition, in Non-Patent Document 2, an experiment in which manganese is added to a copper gallium tellurium compound is performed, but only magnetic measurement is performed there. Its purpose is to search for new ferromagnets and spintronics applications, not to thermoelectric semiconductors. There are no measurements of electrical conductivity σ above room temperature, Seebeck coefficient S, and thermal conductivity κ, and it is difficult to analogize how non-patent literature 2 affects the addition of manganese to thermoelectric properties. .

  Various studies have been conducted to improve thermoelectric properties by adding elements having different valences to semiconductors. This utilizes the fact that "carrier density optimization" occurs, and this method is well known. However, the present invention is not merely “optimization of carrier density” but utilizes a completely new mechanism of enhancement effect by the interaction between magnetism and carrier.

  The fact that the present invention is not based on “optimization of carrier density” has been confirmed by an experiment in which a part of gallium (Ga) is replaced with iron (Fe) having no difference in formal valence. Ga and Fe are both trivalent ions, and there is no change in the number of carriers. The details are shown in Example 2 below.

(Thermoelectric generator)
It is known that about 3/4 of the energy is wasted as waste heat. Thermoelectric conversion is a technique that can recover thermal energy and convert it directly into useful electrical energy, and has advantages such as ease of maintenance and scalability due to the absence of moving parts. In order to use for such power generation, it is necessary to form an element with p-type and n-type thermoelectric materials having high thermoelectric conversion efficiency.

As shown in FIG. 11, the thermoelectric power generation element 31 includes an n-type semiconductor 32 and a p-type semiconductor 33 electrically connected between an electrode 35 on the low temperature side and an electrode 34 on the high temperature side via these electrodes. This is an element having a structure arranged in series.
As the p-type semiconductor 33, a copper gallium tellurium compound added with a predetermined amount of the magnetic element M of the present invention is used. As a result, it becomes possible to recover heat from a lower temperature range than before, and the range of heat that can be used is greatly expanded, and energy recovery from a low temperature range, which has been difficult in the past, becomes possible.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

Example 1
Example 1 shows a p-type thermoelectric semiconductor when 1%, 2%, and 3% of manganese (Mn) are added in a molar ratio to a copper gallium tellurium compound.

((Production of thermoelectric semiconductor))
First, copper (Cu) (powder, Furuuchi Chemical Co., Ltd., 99.99%), gallium (Ga) (granular, Furuuchi Chemical Co., Ltd., 99.999%), manganese (Mn) (powder) , Furuuchi Chemical Co., Ltd., 99.99%) and Tellurium (Te) (granular, High Purity Chemical Laboratory, 99.9999%) were prepared.
Next, Cu, Ga, Mn, and Te were weighed using an electronic balance so that the molar ratio was 1: 0.99: 0.01: 2.
Then, it heated to 900 degreeC in the vacuum quartz tube over 3 days, and after hold | maintaining for 2 hours, it cooled to 600 degreeC. Thereafter, it was cooled to room temperature in 6 hours to obtain an ingot of CuGa _0.99 Mn _0.01 Te ₂ .
Next, this ingot is pulverized in a mortar, filled into a graphite die (inner diameter 10 mm), a sintered body is obtained by a discharge plasma sintering method, and consists of a copper gallium tellurium compound to which 1 mol% of manganese is added. A p-type thermoelectric semiconductor was produced. Here, for the sintering, Dr. Fuji Electric Koki Co., Ltd. SINTER was used, and the sintering conditions were a pressure of 50 MPa, a temperature of 600 ° C., and 5 minutes.

  Further, Cu, Ga, Mn and Te were weighed so that the molar ratios were 1: 0.98: 0.02: 2 and 1: 0.97: 0.03: 2, and the same steps were performed. Then, a p-type thermoelectric semiconductor made of a copper gallium tellurium compound to which 2 mol% and 3 mol% of manganese were added was produced.

((Characteristic evaluation of thermoelectric semiconductor))
FIG. 2 shows a powder X-ray diffraction pattern of a copper gallium tellurium compound sample added with 1 mol%, 2 mol%, and 3 mol% of manganese. In this figure, x represents the molar ratio of manganese. The figure also shows the case of x = 0 without adding manganese (Comparative Example 1) and the case of x = 0.05 with 5% added manganese (Comparative Example 2). Yes.

When no manganese is added and when the amount of manganese is 1 mol%, 2 mol%, and 3 mol% (x = 0 to 0.03), all the samples agree with the calculation assuming a chalcopyrite structure. This shows that a uniform sample could be produced. On the other hand, in the case of x = 0.05 with 5% molar ratio of manganese, a small impurity phase peak was observed in the portion indicated by the arrow, and a completely uniform sample could not be obtained. .
When the impurity phase appears, there are cases where thermoelectric properties such as a decrease in electrical conductivity are difficult to stabilize, so it may not be preferable that the copper gallium tellurium compound contains 5% or more of manganese in a molar ratio.

Next, the sintered body was cut into a rod shape, and the electrical conductivity (σ) and Seebeck coefficient (S) were measured. The output factor (PW) was calculated by the equation PW = S ² σ. Moreover, the thermal diffusivity ((alpha)) was measured using the sample cut out on the disk. Furthermore, the heat capacity C _p was measured by a DSC (Differential Scanning Calorimetry) method using a small sample piece. The thermal conductivity (κ) was calculated from κ = α · C _p · d from the thermal diffusivity (α), the heat capacity (C _p ), and the density (d) of the sample. Thereafter, the dimensionless figure of merit (ZT) was calculated by ZT = S ² σT / κ. Here, T is an absolute temperature.

  The relationship between the electrical conductivity σ, the Seebeck coefficient S, the output factor PW, the thermal conductivity κ, and the dimensionless figure of merit ZT with respect to the temperature from 324K to 669K is shown in FIG. As shown in FIG.

By adding manganese, the electrical conductivity σ is greatly improved. In particular, when 3 mol% (x = 0.03) of manganese is added, the improvement rate reaches about 10 times (see FIG. 3). This is thought to be mainly due to the increased carrier concentration.
When the carrier concentration is significantly increased, normally, the Seebeck coefficient S is significantly reduced, and the output factor PW calculated by S ² σ does not simply increase. However, as shown in FIG. 4, the Seebeck coefficient S is not reduced so much even in the sample added with manganese, and is only reduced to a maximum of 50%.
From this, as shown in FIG. 5, the output factor PW greatly increased by the addition of manganese. In particular, the increase rate in a low temperature range from room temperature to 500 K is large, and particularly when 2 mol% (x = 0.02) or more of manganese is added, the increase rate exceeds 100%.

  As shown in FIG. 6, the temperature dependence of the thermal conductivity κ of the copper gallium tellurium compound sample to which manganese is added is lower than that in the case where manganese is not added, and has favorable characteristics as a thermoelectric semiconductor.

From these, as shown in FIG. 7, the dimensionless figure of merit ZT calculated by ZT = S ² σT / κ is obtained by adding manganese to the copper gallium tellurium compound from a low temperature region close to room temperature. A value almost twice as high as that obtained when no manganese was added was obtained.
Moreover, the change of the output factor PW with respect to manganese addition density | concentration and the dimensionless figure of merit ZT is shown in FIG.8 and FIG.9, respectively. By adding manganese, the thermoelectric characteristics such as the output factor PW and the dimensionless figure of merit ZT were rapidly improved.

(Example 2)
Example 2 is an example where it was confirmed that the improvement in thermoelectric characteristics described in Example 1 was not due to “optimization of carrier density”.

The experimental results of adding iron (Fe) to the copper gallium tellurium compound are shown in FIG. Fe in the form of replacing a part of _Ga, are added as _{CuGa 1-x Fe x Te 2} . Here, CGFT0, CGFT1, CGFT2, and CGFT3 described in FIG. 10 indicate cases where _{x of} CuGa _1-x Fex Te ₂ is 0, 0.01, 0.02, and 0.03, respectively. That is, the case where iron is added to the copper gallium tellurium compound at 0 mol%, 1 mol%, 2 mol% and 3 mol%, respectively. Samples were prepared in the same manner as in Example 1 except that manganese was replaced with iron.
Since Ga and Fe are both trivalent ions and there is no change in formal valence, there is no change in the number of carriers. Therefore, it can be said that Example 2 does not correspond to “optimization of carrier density”.

  As a result of the experiment, good electrical conductivity (electric resistance) and a large Seebeck coefficient were observed even in the compound added with Fe, and as shown in FIG. 10, the increase of the output factor PW occurred near room temperature. It was confirmed. This result indicates that the improvement in thermoelectric properties is not due to “optimization of carrier density”.

(Example 3)
Example 3 is an example in which a thermoelectric power generation element 31 was produced (see FIG. 11).
In the produced thermoelectric power generation element 31, an n-type semiconductor 32, which is a thermoelectric material chip, is joined by solder to an electrode 35 on the low temperature side, and an opposite end of the n-type semiconductor 32 and an electrode 34 on the high temperature side. Are also joined by solder. Further, the same electrode 34 and a p-type semiconductor 33 which is a thermoelectric material chip are joined, and the opposite end of the p-type semiconductor 33 is joined to another electrode 35 to which another n-type semiconductor 32 is joined. With such a configuration, the thermoelectric power generation element 31 electrically connected in series was obtained.
As the p-type semiconductor 33, a copper gallium tellurium compound to which magnetic ions of the present invention were added was used. As a result, it was possible to recover heat from a lower temperature range than before, and the range of available heat was greatly expanded.

(Comparative Example 1)
Comparative Example 1 is an example in which a copper gallium tellurium compound not added with manganese was evaluated. The sample was prepared in the same manner as in Example 1 except that manganese was not added.
As described above, the evaluation results are shown in FIGS. 2 to 9 together with the results of the examples.
This copper gallium tellurium compound also has a chalcopyrite structure (see FIG. 2). As already described, compared to the case where manganese is added, Comparative Example 1 has a dimensionless output factor PW from a low temperature region near room temperature. The figure of merit ZT was also significantly smaller.

(Comparative Example 2)
Comparative Example 2 is an example in which the structure of a powder sample prepared by adding 5 mol% of manganese to a copper gallium tellurium compound was evaluated by X-ray diffraction. The preparation method of the sample was performed by adding 5 mol% of manganese. The process was the same as that of Example 1 except that.
The evaluation results are shown in FIG. 2 together with the results of the examples.
The copper gallium tellurium compound to which 5 mol% of manganese is added has a chalcopyrite structure as a basic skeleton, but an impurity phase was observed as described above.

  As described above, the p-type thermoelectric semiconductor of the present invention in which one or more elements selected from the group consisting of chromium, manganese, iron, cobalt, and nickel are added to the copper gallium tellurium compound has a temperature of about 400 ° C. from around room temperature. The thermoelectric semiconductor is a thermoelectric semiconductor that exhibits high thermoelectric conversion efficiency even in a relatively low temperature region. In addition, the thermoelectric power generation element having this thermoelectric semiconductor can provide high power generation efficiency even in a relatively low operating temperature region such as 500 ° C. or lower. For this reason, it becomes possible to recover heat from a lower temperature range than before, and the range of available heat is greatly expanded.

31 Thermoelectric power generation element 32 n-type semiconductor 33 p-type semiconductor 34 electrode 35 electrode 36 current

Claims (7)

A p-type thermoelectric semiconductor containing a copper gallium tellurium compound,
A p-type thermoelectric semiconductor comprising one or more elements selected from the group consisting of chromium, manganese, iron, cobalt, and nickel.   2. The p-type thermal semiconductor according to claim 1, wherein the element is contained as a total amount of the element in a molar ratio of more than 0% and less than 5% with respect to the copper gallium tellurium compound.   2. The p-type thermoelectric semiconductor according to claim 1, wherein the element is contained in a molar ratio of 1% to 3% with respect to the copper gallium tellurium compound as a total amount of the element. 4. The p-type thermoelectric semiconductor according to claim 1, wherein the p-type thermoelectric semiconductor is a tetragonal p-type thermoelectric semiconductor having a composition represented by Formula 1. 5.
_{CuGa 1-x M x Te 2} ( Equation 1)
(M is one or more of Cr, Mn, Fe, Co, and Ni, and x is greater than 0 and less than 1.)   The p-type thermal semiconductor according to claim 4, wherein x is greater than 0 and less than 0.05.   The p-type thermoelectric semiconductor according to claim 4, wherein x is 0.01 or more and 0.03 or less. A thermoelectric power generation element in which a p-type semiconductor and an n-type semiconductor are integrated, wherein the p-type thermoelectric semiconductor according to any one of claims 1 to 6 is used as the p-type semiconductor. element.