JP4413323B2 - Thermoelectric material, manufacturing method thereof, and thermoelectric module using thermoelectric material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a clathrate compound, a high-efficiency thermoelectric material using the clathrate compound, a production method thereof, and a thermoelectric module, and relates to a technique capable of providing a thermoelectric material having excellent conductivity and Seebeck coefficient and low thermal conductivity. .
[0002]
[Prior art]
Conventionally, various methods of using thermoelectric materials have been studied, but conventional thermoelectric materials have poor thermoelectric conversion efficiency, and are limited to applications that require reliability or special applications. Accordingly, it has been considered difficult to provide thermoelectric materials for the purpose of waste heat power generation, which is considered as a general use.
[0003]
In order to improve the efficiency of this type of thermoelectric material and use it as a high-efficiency thermoelectric material,
1) low thermal conductivity,
2) High Seebeck coefficient
3) High electrical conductivity,
It is necessary to satisfy the conditions.
[0004]
However, with conventional thermoelectric material development techniques, material development has been carried out by selecting the composition empirically. For this reason, an example in which the dimensionless index (ZT) exceeds 1 at a temperature of 700 K or higher in the currently developed thermoelectric material is GeTe-AgSbTe known as a p-type thermoelectric material.₂It was only.
[0005]
[Problems to be solved by the invention]
Considering the conventional thermoelectric material in such a background, there is no situation that completely satisfies the conditions for becoming a highly efficient thermoelectric material. For example, a metal has a large electrical conductivity as an advantage, but has a large thermal conductivity as a disadvantage and a small Seebeck coefficient. In the case of a semiconductor, it has a small thermal conductivity and a large Seebeck coefficient as advantages, but it does not hold as a high-efficiency thermoelectric material because the electrical conductivity is small. BiTe is known as a thermoelectric material, but it is inefficient and cannot be practically used.
[0006]
In addition, in order to use for general power generation as a thermoelectric material, a p-type thermoelectric material and an n-type thermoelectric material must be combined to form a power generation system. However, the conventional GeTe-AgSbTe is used.₂In this case, it is said that there is no n-type.
[0007]
The present invention has been made in view of the above circumstances, and a highly efficient thermoelectric material having a figure of merit exceeding 1 to satisfy the three conditions of high thermal conductivity, high Seebeck coefficient and high electrical conductivity. One of the objects is to provide a clathrate compound which is expected to be applied to the above.
Furthermore, it is an object of the present invention to provide a highly efficient thermoelectric material having a figure of merit exceeding 1 in order to satisfy the three conditions of high thermal conductivity, high Seebeck coefficient, and high electrical conductivity. .
[0008]
An object of the present invention is to provide an excellent thermoelectric material and thermoelectric module that can be used for general uses such as waste heat power generation.
[0009]
An object of the present invention is to provide a method capable of easily producing the excellent clathrate compound and the high-efficiency thermoelectric material as described above.
[0010]
[Means for Solving the Problems]
  P-type of the present inventionHeat ofThe electric material was made in view of the above circumstances, and a clathrate lattice mainly composed of Si or Ge, and doping of Ba contained in the lattice gap of the clathrate lattice and having a mass larger than the constituent atoms of the clathrate lattice. It is characterized by comprising mainly atoms and Al substituted with at least a part of the atoms constituting the clathrate lattice.
[0011]
  IVB group elementSi or GeThe clathrate lattice basically has a semiconducting or insulating property and a high Seebeck coefficient, but has low electrical conductivity and high thermal conductivity. Therefore, the clathrate lattice has 1 to 3 valence electrons. Atom with high specific gravity of elements of group IA to IIIB elementsBaBy suppressing the vibration of the clathrate lattice by lowering the thermal conductivity, metal conductivity is imparted and electrical conductivity is improved. Further, in order to adjust the provision of metallic properties by atoms that have penetrated into the clathrate lattice, a part of the clathrate lattice is changed to IA to IIIBAlBy substituting with, the metallic properties are close to semi-metallic, i.e. semiconducting properties, and as a synergistic effect of these, the appropriate thermal conductivity, high Seebeck coefficient and electrical conductivity are balanced, and the performance coefficient is excellent. Get things.
[0015]
  The present inventionHeat ofIn the electric material, the clathrate lattice is composed of Si dodecahedron.₂₀Si composed of clusters and tetrahedrons of Si atoms₂₄The silicon clathrate 46 is a mixed lattice of clusters. The present inventionHeat ofIn the electric material, the clathrate lattice is composed of Si dodecahedron.₂₀Si consisting of a cluster and a 16-hedron of Si atoms₂₈The silicon clathrate 34 is a mixed lattice of clusters.
  The present inventionHeat ofIn the electric material, the Si₂₀A structure in which Ba doping atoms are penetrated into the 2a site of the cluster or the 6d site of the Si24 cluster can be employed.
  The present inventionHeat ofThe figure of merit (ZT) can be set to a value exceeding 1 at 700K.
[0017]
  P-type of the present inventionHeat ofA method for producing an electric material includes a clathrate lattice mainly composed of Si or Ge, a doping atom of Ba contained in a lattice gap of the clathrate lattice and having a mass larger than that of constituent atoms of the clathrate lattice, and the clathrate. P-type mainly composed of at least part of atoms constituting the lattice and substituted Al atoms substitutedHeat ofWhen manufacturing an electric material, the atoms for constituting the clathrate lattice and the doping atoms are mixed at a predetermined ratio, subjected to pressure forming into a desired shape, subjected to a preliminary heat treatment, and further subjected to pressure sintering. It is characterized by sintering.
  The present inventionHeat ofIn the method for manufacturing an electric material, the clathrate lattice may be made of Si consisting of a dodecahedron of Si atoms.₂₀Si composed of clusters and tetrahedrons of Si atoms₂₄A silicon clathrate 46 which is a mixed lattice of clusters can be obtained.
  The present inventionHeat ofIn the method for manufacturing an electric material, the clathrate lattice may be made of Si consisting of a dodecahedron of Si atoms.₂₀Si consisting of a cluster and a 16-hedron of Si atoms₂₈It can be a silicon clathrate 34 which is a mixed lattice of clusters.
  The present inventionHeat ofIn the method of manufacturing an electrical material, the Si₂₀Cluster 2a site or Si₂₄A configuration can be adopted in which Ba doping atoms enter the 6d sites of the cluster.
  The present inventionHeat ofIn the method for producing an electric material, a thermoelectric material having a figure of merit (ZT) exceeding 1 at 700K can be obtained.
[0018]
  In the thermoelectric material of the present invention, one or more pairs of p-type thermoelectric elements and n-type thermoelectric elements are combined via electrodes, a heat exchanging portion is formed on the connection portion side of both thermoelectric elements, and the connection portions are opposed to each other. As a constituent material of the p-type thermoelectric element, an electric circuit is connected to the sidePreviousAny one of the high-efficiency thermoelectric materials described above is applied.
  The thermoelectric material of the present invention is characterized in that the figure of merit (ZT) of the constituent material of the p-type thermoelectric element is a value exceeding 1 at 700K.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The clathrate compound according to the present invention is doped with clathrate lattice (basic constitutional unit of clathrate) composed of at least one kind of group IVB elements such as C, Si, Ge, Sn and the like and doped inside this clathrate lattice It is comprised from a doping atom and the substituted atom which substituted at least one part of the some atom which comprises the said clathrate lattice.
[0020]
“First Embodiment”
FIGS. 1 and 2 show a first embodiment in which a silicon clathrate lattice is applied to the present invention. The silicon clathrate lattice 1 of the first embodiment is formed from a dodecahedron of Si atoms shown in FIG. Si₂₀Si composed of cluster 2 and tetrahedron of Si atoms_{twenty four}A plurality of structural units 4 combined with the clusters 3 are combined to form a silicon clathrate lattice 1 as shown in FIG.
Of the silicon clathrate lattice 1 shown in FIG.₂₀2a site of cluster 2 or Si_{twenty four}At least part of at least one of the 6d sites of cluster 3 is doped with at least one of atoms of Group IA, IIA, IIIA, IB, IIB, and IIIB having a mass greater than Si .
FIG. 3 shows the lattice structure of the silicon clathrate lattice 1, and Si is present at the apex of the basic unit structure of each lattice. FIG. 4 shows the 2a site (Si₂₀FIG. 5 shows the 6d site (Si) of the silicon clathrate lattice 1._{twenty four}A state in which Ba atoms have invaded the inside of the cluster.
[0021]
Examples of the most preferable doping atom used here include Be, Mg, Ca, Sr, Ba, and Ra among the elements of Group IIA of the periodic table. When these group IIA elements enter the previous site of the Si cluster, the group IIA atoms are divalent, and the two electrons in them move to the atoms constituting the clathrate. Therefore, the clathrate compound as a whole has metallic properties. In addition, since these elements have a mass larger than that of Si constituting the clathrate lattice 1, the vibration of atoms in the clathrate lattice 1 is suppressed, and the lattice vibration is scattered to reduce the heat conduction.
[0022]
In addition to the group IIA atom as the atom doped in the clathrate lattice 1, Li, Na, K, Rb, Cs, Fr can be exemplified as the group IA atom, and Sc, Y as the group IIIA atom La, lanthanoid elements, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, actinoid elements Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr can be exemplified.
Further, Cu, Ag, Au can be exemplified as the group IB doping atom, Zn, Cd, Hg can be exemplified as the group IIB element, and B, Al, Ga, In can be exemplified as the group IIIB doping atom. , Tl can be exemplified.
[0023]
  Next, among the plurality of Si atoms constituting the silicon clathrate lattice 1, at least some of the Si atoms are any of VB group, VIB group, VIIB group, VA group, VIA group, VIIA group, and VIII group in the periodic table. It is substituted with any atom. Replacing a part of Si atoms with these atoms is due to the metallic properties (high thermal conductivity among metallic properties) of the silicon clathrate lattice 1 made metallic by the previous penetration of doping atoms. This is done to suppress or eliminate, and this element substitution gives semiconducting properties and thermal conductivity.LowerAt the same time, the Seebeck coefficient is increased.
[0024]
Of the above-mentioned substitutional elements in each group, the group IIIB atom, which is considered to easily form a compound, is most preferred, and at least one or more of B, Al, Ga, In, and Tl are preferred. Other substituent atoms can include Cu, Ag, and Au as group IB atoms, and Zn, Cd, and Hg as group IIB atoms.
Furthermore, as an outer substitution atom, Li, Na, K, Rb, Cs, Fr of Group IA, Be, Mg, Ca, Sr, Ba, Ra, Group IIIA of Sc, Y, La, and lanthanoid elements of Group IIA, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, actinoid elements such as Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr can be exemplified.
[0025]
Next, the material development guideline which this inventor considers for making the said clathrate compound suitable as a thermoelectric material is described. Conventionally, since there is no clear development guideline in the material design of this type of thermoelectric material, this development guideline is originally proposed by the present inventor.
1). Reduction of thermal conductivity
In order to lower the thermal conductivity of the thermoelectric material of the clathrate compound, it is considered possible to scatter the lattice vibration of the clathrate compound. Specifically, an atom heavier than the mass of the atoms constituting the clathrate skeleton is selected as a doping atom and introduced into a site free of the clathrate skeleton. As a result, the doping atom suppresses vibrations of atoms constituting the skeleton. As a result, phonon scattering occurs and the thermal conductivity can be lowered.
[0026]
Next, according to the calculation of the first principle pseudopotential method using the plane wave basis, the intrinsic energy of Ba (E_Ba)
E_Ba= (1 / x) ・ (Ba_x@Si₄₆-Si₄₆) -Ba₁ ^{(isolate-atom)}It can be expressed by the following formula.
Where x is the number of atoms of solid solution barium, Ba_x@Si₄₆Is the total energy of the electron system in the case where x barium atoms are dissolved in the silicon clathrate 46, Si₄₆Is the total energy of the electronic system of silicon clathrate 46 alone, Ba₁ ^{(isolate-atom)}Is the total energy of an electron system with one barium isolated atom.
The barium solid solution energy when 2, 6, and 8 barium atoms enter the silicon clathrate is shown below.
▲ 1 ▼ Ba₂@Si₄₆(2a site, 12 Hedra)
Barium solid solution energy: -91.150 / (eV / atm)
▲ 2 ▼ Ba₆@Si₄₆(6d site, 14 Hedra)
Barium solid solution energy: -92.805 / (eV / atm)
▲ 3 ▼ Ba₈@Si₄₆(2a site + 6d site)
Barium solid solution energy: −93.628 / (eV / atm)
[0027]
From this result, since it is more energetically stable that many barium atoms are dissolved in the silicon clathrate, Ba can easily enter all the void sites of the silicon clathrate lattice according to the present invention, and the lattice vibration The thermal conductivity can be lowered by scattering.
[0028]
2) Improvement of Seebeck coefficient
Any of group IA, group IIA, group IIIA, group IB, group IIB, group IIIB having 1 to 3 valence electrons as doping atoms in the vacant site of silicon clathrate lattice 1 which is a group IVB atom When 1 to 3 atoms are allowed to enter, 1 to 3 valence electrons therein move to the group IVB atoms constituting the clathrate. Therefore, the silicon clathrate lattice 1 can be made metallic as a whole. Here, when at least a part of Si atoms constituting the silicon clathrate lattice 1 is replaced with any atom of Group IA, Group IIA, Group IIIA, Group IB, Group IIB, or Group IIIB, a semiconductor due to metallic properties It is possible to convert the Seebeck coefficient to a higher level.
[0029]
3) Improvement of electrical conductivity
Since the group IVB atoms constituting the silicon clathrate lattice 1 are semiconductors, the electrical conductivity does not increase with the group IVB atoms alone. Therefore, electrical conductivity is increased by introducing any of the group IA, IIA, IIIA, IB, IIB, or IIIB atoms that have metallic properties into the vacant site of the silicon clathrate basic structural unit. Can be made.
[0030]
As a result of these, the silicon clathrate compound of the first embodiment has characteristics that combine a low thermal conductivity, a high Seebeck coefficient and a high electrical conductivity that are not found in conventional thermoelectric materials. Has a better figure of merit. In addition, the silicon clathrate compound of this embodiment is a p-type thermoelectric material.
[0031]
Next, an example of a method for producing the silicon clathrate compound having the above-described configuration will be described.
When the basic constituent unit of silicon clathrate 46 is used, Si and doping atom powder and atomic powder for substitution of the clathrate basic constituent unit are weighed and mixed so as to have a target composition ratio, and these mixed powders are mixed. Is melted by arc melting to obtain an ingot having the desired composition. The raw material powder used here may be a pure powder or a compound powder of each element, but it is preferable to use a pure powder containing as few impurities as possible.
Next, the ingot is pulverized, and the pulverized powder is inspected by X-ray analysis to determine whether or not the desired composition ratio is obtained. That is, if the target composition is obtained, the process proceeds to the next step. If the target composition is not obtained, the ingot is melted again from the powder mixture, and the newly prepared ingot is analyzed. Moreover, it is preferable to use the powder of the pulverized product to be used with a fine particle size as much as possible.
[0032]
Once the powder of the pulverized product having a good composition ratio is obtained, heat treatment (calcination treatment) is performed in an Ar gas atmosphere or a vacuum atmosphere to remove unnecessary components in a gas state, and the powder after the calcination treatment is further removed. After pulverizing, aligning the particle size, analyzing with X-rays, checking whether the composition ratio is correct, selecting the one with the desired composition ratio, aligning the particle size, and discharging the pulverized product into a discharge plasma device Can be used to obtain a desired thermoelectric element composed of a thermoelectric material of a silicon clathrate compound in a desired shape, for example, a columnar sintered product.
In spark plasma sintering, a mixture of powders is pressed with a pair of punches at a pressure of several MPa to several tens of MPa, and at the same time, an electric current is applied and heated to about 1000 ° C. for about several minutes to several hours. It is a kind of pressure sintering method.
[0033]
In addition, when performing the said heat processing, when manufacturing the silicon clathrate 46, it is preferable to heat-process in Ar gas atmosphere, and when manufacturing the silicon clathrate 34, it is preferable to heat-process in a vacuum atmosphere. Moreover, when the composition ratio has deviated from the target composition by the previous X-ray analysis, the same process is repeated by returning to the process of obtaining the ingot from arc melting again.
A silicon clathrate compound thermoelectric element obtained by heat-pressure sintering can be used as a p-type thermoelectric material.
[0034]
By the way, in the above-mentioned manufacturing process, instead of arc melting, a mechanical alloying treatment can be performed to obtain a mixed powder having a desired composition ratio. Mechanical alloying is a process in which powder mixed in a hollow attritor containing a large number of metal balls such as stainless steel balls is mixed, and then the attritor is rotated at high speed to mix the powder, and the powder is pulverized between the metal balls. In this method, mixed powder is obtained by mixing. The thermoelectric element of the silicon clathrate compound according to the present invention can also be obtained by molding the mixed powder obtained by performing the mechanical alloying treatment in this way, preliminarily heat-treating, and further sintering.
[0035]
In the above manufacturing method, when Ba is selected as the doping atom and Al is selected as the substitution atom, Ba serves as a nucleus, first attracts Si, and a large number of clusters are generated. It seems to constitute. Therefore, a clathrate compound can be produced by an extremely simple method of mixing necessary elements, performing a calcining treatment, and then sintering. Therefore, the clathrate compound of the present invention has a simple production method as compared with conventional thermoelectric materials, and a highly efficient compound having a high figure of merit at 700 K or higher can be obtained.
[0036]
“Second Embodiment”
FIG. 6 is a schematic diagram of the crystal structure of the silicon clathrate 34 constituting the basic structural unit of the second embodiment of the silicon clathrate compound according to the present invention. The crystal structure 10 of the silicon clathrate 34 is composed of Si dodecahedron as shown in FIG.₂₀Si composed of clathrate 11 and Si icosahedron₂₈A plurality of basic structural units 13 composed of the class rate 12 are combined to form a silicon class rate 34.
[0037]
Si constituting the silicon clathrate 34 of the second embodiment₂₀At the 2a site of clathrate 11 or Si_{twenty four}At the 6d site of clathrate 12, atoms in the periodic table IA, IIA, IIIA, IB, IIB, IIIB having a mass larger than that of Si as in the first embodiment For example, Ba is doped.
Further, as in the case of the first embodiment, a part of Si constituting the silicon clathrate 34 is substituted with any atom in the periodic table groups IB, IIB, and IIIB, for example, Al. .
In the silicon clathrate compound of the second embodiment, excellent characteristics as a thermoelectric material can be obtained in the same manner as the silicon clathrate compound of the first embodiment.
[0038]
“Third Embodiment”
FIG. 8 shows an embodiment of a thermoelectric module constructed using the thermoelectric material of the silicon clathrate compound according to the present invention. The thermoelectric module 30 of this embodiment is an insulating substrate disposed vertically opposite to each other. A plurality of thermoelectric elements 33 made of p-type columnar thermoelectric materials and a plurality of thermoelectric elements 34 made of n-type columnar thermoelectric materials are alternately arranged between 31 and 32, and a pair of adjacent ones. The lower end portions of the thermoelectric elements 33 and 34 are connected by the electrode plate 35, and the upper end portions of other adjacent thermoelectric elements 33 and 34 are connected by the electrode plate 36, and at the same time, adjacent p-type thermoelectric elements The end portions of 33 and the end portions of the n-type thermoelectric elements 34 are alternately connected to each other, and are connected by a plurality of electrode plates 35 and 36 so that all the thermoelectric elements are connected in series. Of the plurality of thermoelectric elements 33 between the upper and lower substrates, the connection wiring 37 is bonded to the thermoelectric element 33 at one end, and the connection wiring 38 is bonded to the thermoelectric element 34 at the other end. Has been configured.
Here, among the thermoelectric elements 33, a p-type element is composed of a thermoelectric material made of the clathrate compound described above. Moreover, as an n-type thermoelectric material, it can select from the conventional material as shown in FIG. 12 which shows the thermoelectric performance index of a conventional material, and can use it suitably.
[0039]
The thermoelectric module 30 having the configuration shown in FIG. 8 has a resistor 39 as a load connected between the connection wires 37 and 38 by heating the upper electrode plate 36 side as shown in FIG. 9A. If the electric circuit 41 is configured, the electrode plate 36 side is continuously heated by another heat source, and the electrode plate 35 side is radiated to generate a potential difference between the connection wirings 37 and 38 so that a current flows. Can be used for thermoelectric power generation.
Further, in the thermoelectric module 30 shown in FIG. 8, the power supply 40 is connected to the connection wirings 37 and 38 as shown in FIG. Therefore, it can be used as a thermoelectric cooler by generating heat on the lower electrode plate 35 side.
[0040]
FIG. 10 shows an example of a power generation stack using the thermoelectric material of the present invention. The power generation stack 50 in this example is formed on the outer peripheral portion of an inner shell 51 made of a flat multi-hole tube through which exhaust gas or the like flows. Six power generation modules 52 are mounted, and a flat outer shell 54 is provided on the outside of the power generation module 52 so as to cover them. Power generation is performed using the heat of the exhaust gas flowing inside the inner shell 51. It is comprised so that it can perform.
Also in the power generation stack of this embodiment, the thermoelectric module 30 can be used for power generation by configuring the power generation module 52 similarly to the thermoelectric module 30 of the previous embodiment.
[0041]
Here, the figure of merit (ZT) frequently used as a performance index of the thermoelectric material will be described below.
The performance of thermoelectric materials is as follows: α is the thermoelectric power, κ is the thermal conductivity, and ρ is the specific resistance.
Z = α²/ Κρ (1) It is shown by the formula (1).
In addition, the figure of merit of the thermoelectric module shown in FIG.
Z_pn= (Α_p-Α_n)²/ (Κ_pρ_p+ Κ_nρ_n)²    ... indicated by equation (2)
The subscript corresponds to each value of the p-type molded body and the N-type molded body.
The maximum power generation efficiency of the thermoelectric material is the temperature at the high temperature end and the low temperature end respectively._hAnd T_cThen,
η_max= (T_h/ T_h-T_c) ・ {(M−1) / (M + T_h/ T_c)} ... (3) formula,
M = (1 + Z (T_h+ T_c) / 2)^1/2  ... expressed by equation (4).
[0042]
On the other hand, the maximum coefficient of performance for thermoelectric cooling is
φ_max= (T_h/ T_h-T_c) ・ {(MT_h/ T_c) / (M + 1)} (5), and in thermoelectric heating, φ_maxGiven by +1. In addition, if the heat absorption part is completely insulated and there is no inflow of heat, T_cBecomes the most lowered state, φ_max= 0, the maximum cooling temperature difference is
ΔT_max= (T_h-T_c )_max = (1/2) · ZT² _c  ... The relationship of equation (6) is obtained.
[0043]
Here, in general, thermoelectric cooling / heating is performed using a temperature difference (T_h-T_c) Since it is used in the range of ≦ 100K, a higher Z becomes a necessary condition, and now it is 3.4 × 10^-3K^-1More than that is required.
On the other hand, T_hHowever, it is required to be a heat-resistant material that is chemically stable at high temperatures. In general, the figure of merit Z has a temperature dependency inherent to the material, but the temperature at which the maximum value varies depends on the material.
Materials whose maximum value ZT of the figure of merit Z exceeds 1 are currently GeTe-AgSbTe.²And most other materials show ZT values lower than 1.
FIG. 11 and FIG. 12 show the absolute temperature dependence of the figure of merit of the p-type and n-type thermoelectric materials known in the past. As is clear from these figures, the maximum figure of merit is shown. A value exceeding ZT = 1 indicates that in the case of p-type GeTe—AgSbTe in the temperature range of 600 to 900K.²Only and not outside. In the n-type, only SiGe (GaP) is promising in a specific narrow temperature range, and does not exist at room temperature to 700K.
[0044]
On the other hand, if it is a thermoelectric material according to the present invention, it is possible to provide a p-type thermoelectric material having a ZT exceeding 1 as will be apparent from examples described later. Therefore, if a thermoelectric module is configured using the thermoelectric material of the present invention, a highly efficient thermoelectric module that is far superior to that of conventional thermoelectric materials can be provided.
[0045]
FIG. 11 and FIG. 12 show the absolute temperature dependence of the figure of merit of the p-type and n-type thermoelectric materials known in the past. As is clear from these figures, the maximum figure of merit is shown. A value exceeding ZT = 1 indicates that in the case of p-type GeTe—AgSbTe in the temperature range of 600 to 900K.²Only, and there is no outside. In the n-type, only SiGe (GaP) is promising in a specific narrow temperature range, and does not exist at room temperature to 700K.
[0046]
On the other hand, if it is a thermoelectric material according to the present invention, it is possible to provide a p-type thermoelectric material having a ZT exceeding 1 as will be apparent from examples described later. Therefore, if a thermoelectric module is configured using the thermoelectric material of the present invention, a highly efficient thermoelectric module that is far superior to that of conventional thermoelectric materials can be provided.
[0047]
Next, the Seebeck coefficient will be described.
In the thermoelectric module shown in FIG. 9B, when a current flows from the power source 40 in the direction of the arrow, the current I flows through the electric circuit 42 and Peltier heat is generated on the upper electrode plate 36 side, and the Seebeck coefficient of the n-type thermoelectric element 34 -Α_n, The Seebeck constant of the p-type element_p, Α of the Seebeck coefficient of the electrode plate_mThen, the upper electrode plate and the Pn element Peltier heat absorption Q_cpIs
Q_cp  = (-Α_n-Α_m ) T_cI + (α_m -Α_p) T_cI = − (α_n+ Α_p) T_cI
And α_m Can be ignored. Where T_cIs the temperature of the junction. α_e= Α_n+ Α_pAs the absolute value Q of the endothermic quantity._cpQ_cp= Α_eT_cI.
Thus, since the Seebeck coefficient is an index when the heat calculation of the thermoelectric module is performed, this numerical value is known to have a great influence on the performance improvement of the thermoelectric module.
[0048]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
Each powder was weighed so that the composition ratio (atomic%) of Ba, Si, and Al was Ba: Si: Al = 8: 26: 20, and a mixed powder was prepared by mechanical alloying treatment. This mixed powder is subjected to a preliminary heat treatment of heating to 800 ° C. for 24 hours in an Ar gas atmosphere. Further, after the preliminary heat treatment, the pre-sintered product is pulverized to an average particle size of 100 μm, and this is subjected to a plasma sintering apparatus to 850 Plasma sintering was performed at 40 ° C. and a pressure of 40 MPa for 30 minutes.
As a result of X-ray diffraction of the obtained sintered product,
space group: Pm3m origin at 43m (In the crystallographic analysis, Pm3Usually overlined above 3 of m, but here about overline of 33And a silicon clathrate having a lattice constant of 10.3 ４６ 46 Ba₈@ (Si₂₆, Al₂₀) Was confirmed. Moreover, as a result of measuring the figure of merit (ZT) at 700 K of this sintered product, it was confirmed that the value was 1.01 exceeding 1.
[0049]
【The invention's effect】
  According to the thermoelectric material of the present invention, the basic lattice is Si orGeIt is a clathrate lattice, and its specific gravity is larger than the constituent elements of the clathrate lattice inside the clathrate latticeBa'sSince the atoms are doped, the vibration of the clathrate lattice is suppressed, the thermal conductivity is lowered and the electrical conductivity is improved at the same time, and some of the atoms constituting the clathrate lattice have a valence of 1 to 3AlAs a result of substitution with semiconducting properties, a p-type thermoelectric material with improved Seebeck coefficient can be provided. In the present invention, Si or Ge is selected as the clathrate lattice constituent element, Ba is selected as the doping atom, and Al is selected as the substitution atom, so that the thermal conductivity, electrical conductivity, and Seebeck coefficient are improved in a good balance. be able to.
  In the present invention, the silicon clathrate 46 or the silicon clathrate 34 can be selected as the clathrate lattice.Si ₂₀ Cluster 2a site or Si ₂₄ If the structure is such that Ba doping atoms enter the 6d sites of the cluster, excellent characteristics as a thermoelectric material can be obtained.
  In the present invention, the p-type thermoelectric material described above can provide an excellent value exceeding 1 as a figure of merit (ZT) at 700K.
[0051]
  When producing the thermoelectric material according to the present invention, if the constituent elements are mixed, after pressure forming, preheated, and pressure sintered, the above-described good thermal conductivity, electrical conductivity, and Seebeck coefficient are obtained. An excellent thermoelectric material can be obtained.
  In addition, the present inventionHeat ofExcellent value exceeding 1 at 700K as a figure of merit (ZT) due to the manufacturing method of electrical materialsHeatAn electric material can be obtained.
[0052]
Furthermore, if it is the thermoelectric module of this invention, it has low thermal conductivity, electrical conductivity, a good Seebeck coefficient, and can obtain the thermoelectric performance which has the outstanding performance coefficient as demonstrated previously.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a crystal structure including a clathrate lattice and an intruding atom of a silicon clathrate compound according to the present invention.
2 is a dodecahedron of Si serving as a partial structural unit of the silicon clathrate compound shown in FIG.₂₀And Si tetrahedral Si_{twenty four}FIG.
FIG. 3 is a plan view showing a basic crystal lattice structure of a silicon clathrate compound according to the present invention.
FIG. 4 is a plan view showing a structure in which Ba atoms have entered the 2a site of the basic crystal lattice of the silicon clathrate compound according to the present invention.
FIG. 5 is a plan view showing a structure in which Ba atoms have penetrated into the 6d site of the basic crystal lattice of the silicon clathrate compound according to the present invention.
FIG. 6 is a schematic view showing a crystal structure of a silicon clathrate 34 for constituting a silicon clathrate compound according to the present invention.
7 is a Si dodecahedron of Si serving as a partial structural unit of the silicon clathrate 34 shown in FIG.₂₀And Si 16-hedron Si₂₈FIG.
FIG. 8 is a cross-sectional view showing one embodiment of a thermoelectric module configured using the thermoelectric element according to the present invention.
FIG. 9 shows an example of how the thermoelectric module shown in FIG. 8 is used. FIG. 9 (a) is a configuration diagram in the case of causing a thermoelectric reaction, and FIG. Diagram.
FIG. 10 is a cross-sectional view showing an example in which the thermoelectric module according to the present invention is used in a power generation stack.
FIG. 11 is a diagram showing the absolute temperature dependence of the figure of merit of a conventional p-type thermoelectric material and the thermoelectric material according to the present invention.
FIG. 12 is a diagram showing the absolute temperature dependence of a figure of merit of a conventional n-type thermoelectric material.
[Explanation of symbols]
1 ... silicon clathrate lattice, 2 ... Si₂₀Cluster, 3 ... Si_{twenty four}Cluster, 10 ... silicon clathrate 34, 11 ... Si₂₈Cluster, 30 ... thermoelectric module, 33 ... p-type thermoelectric element, 34 ... n-type thermoelectric element, 37, 38 ... connection wiring, 41, 42 ... electric circuit, 50 ... power generation stack, 52 ... thermoelectric module.

Claims (11)

A clathrate lattice mainly composed of Si or Ge; a Ba doping atom contained in the lattice gap of the clathrate lattice and having a mass larger than that of the constituent atoms of the clathrate lattice; and at least of the atoms constituting the clathrate lattice p-type thermoelectric material characterized by comprising a substituted part Al mainly. The clathrate lattice is a silicon clathrate 46, which is a mixed lattice of Si ₂₀ clusters composed of a dodecahedron of Si atoms and Si ₂₄ clusters composed of a tetrahedron of Si atoms . thermoelectric material. 2. The clathrate lattice is a silicon clathrate 34, which is a mixed lattice of Si ₂₀ clusters composed of dodecahedrons of Si atoms and Si ₂₈ clusters composed of 16-sided bodies of Si atoms . thermoelectric material. Thermoelectric material according to claim 2, characterized in that the doping atoms of Ba, which are entering the 2a site or Si ₂₄ clusters 6d site of the Si ₂₀ clusters. Thermoelectric material according to claim 2 or 4 merit (ZT) is equal to or more than 1 in 700K. A clathrate lattice mainly composed of Si or Ge; a Ba doping atom contained in the lattice gap of the clathrate lattice and having a mass larger than that of the constituent atoms of the clathrate lattice; and at least of the atoms constituting the clathrate lattice upon manufacturing the part and p-type thermoelectric material comprising mainly a replacement atom has been Al-substituted, by mixing the atom and the doping atoms for constituting the clathrate lattice at a predetermined ratio, the desired after pressure molding into a shape, subjected to a preliminary heat treatment, further p-type thermoelectric material manufacturing method of which is characterized in that sintered by pressure sintering. According to the clathrate lattice, in claim 6, characterized in that the Si ₂₀ clusters of 12 tetrahedral Si atoms, a silicon clathrate 46 is a mixed lattice of Si ₂₄ clusters of 14 tetrahedrons of Si atoms method of manufacturing a thermoelectric material. According to the clathrate lattice, in claim 6, characterized in that the Si ₂₀ clusters of 12 tetrahedral Si atoms, a silicon clathrate 34 is a mixed lattice of Si ₂₈ clusters of 16 tetrahedrons of Si atoms method of manufacturing a thermoelectric material. Thermoelectric material manufacturing method according to claim 7, characterized in that to penetrate the doping atoms of Ba in the 2a site or Si ₂₄ clusters 6d site of the Si ₂₀ clusters. Thermoelectric material manufacturing method according to claim 7 or 9 merit (ZT), characterized in that the obtaining thermoelectric material exceeding 1 at 700K. One or more pairs of p-type thermoelectric elements and n-type thermoelectric elements are combined via electrodes, a heat exchange part is formed on the connection part side of both thermoelectric elements, and an electric circuit is connected to the side facing the connection part. Te becomes, the thermoelectric module, wherein the thermoelectric material is applied according to any one of claims 1 to 5 as a constituent material of the p-type thermoelectric elements.

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