JPWO2018117045A1 - Thermoelectric materials and thermoelectric modules - Google Patents

Abstract

Provided are a thermoelectric material and a thermoelectric module with an improved figure of merit, which do not require a process for producing raw materials of nanoparticles, can improve electric conductivity and Seebeck coefficient by quantum confinement effect, and can be expected to be put to practical use To do. The structure comprises a first crystal phase and a second crystal phase having a thermoelectric effect. The first crystal phase 11 forms a eutectic structure with the second crystal phase 12. The first crystal phase 11 and the second crystal phase 12 are present continuously or dispersed on the two opposing surfaces of the structure. The first crystal phase 11 is located around the second crystal phase 12, or the second crystal phase 12 is located around the first crystal phase 11, and the first crystal The phase 11 decreases the thermal conductivity of the second crystalline phase 12, or the electrical conductivity or Seebeck coefficient of the second crystalline phase 12 increases. [Selection] Figure 1

Description

  The present invention relates to a thermoelectric material, in particular, a thermoelectric material that generates power due to a temperature difference, and a thermoelectric module using the thermoelectric material.

  In a thermoelectric module used for effectively utilizing unused thermal energy, a thermoelectric material generates an electromotive force by the Seebeck effect and generates power in an environment where a temperature difference exists. In addition, two types of n-type and p-type thermoelectric materials are alternately arranged, and each thermoelectric material is installed so as to cause a temperature difference (see, for example, Patent Document 1).

  And the electric power generation amount of the thermoelectric module greatly depends on the figure of merit of the thermoelectric material. The figure of merit is a value determined by thermal conductivity, electrical conductivity, and Seebeck coefficient. Generally, the figure of merit is improved by decreasing the thermal conductivity, increasing the electrical conductivity, and increasing the Seebeck coefficient.

  Conventional thermoelectric materials need to improve the amount of power generated as a thermoelectric module by improving the figure of merit determined by thermal conductivity, electrical conductivity, and Seebeck coefficient. However, a decrease in thermal conductivity and an increase in electrical conductivity are generally incompatible, and means for reducing only the thermal conductivity is required to improve the figure of merit. Therefore, as a thermoelectric material that improves the figure of merit by reducing only the thermal conductivity by forming a phonon scatterer, a nanoparticle impurity phase dispersed in the thermoelectric material phase or the nanometer of the thermoelectric material The thing comprised by particle | grains is developed (for example, refer patent document 2 or 3).

JP, 2006-181564, A International Publication WO2013 / 094598 Japanese Patent Laid-Open No. 2006-58558

  However, the thermoelectric materials described in Patent Documents 2 and 3 are limited to substances that can form nanoparticles, and there is a problem that the dispersion of nanoparticles requires a search for precise conditions and complicated processes. there were. Attempts have also been made to improve the figure of merit using the quantum confinement effect by lowering the thermoelectric material, and as a result, improvements in electrical conductivity and Seebeck coefficient have been reported by turning the thermoelectric material into nanowires. ing. However, making nanowires of thermoelectric materials requires a complicated manufacturing process, and further technological development is required for lengthening and modularization, and technology that cannot be used for practical use yet. It is.

  The present invention has been made paying attention to such a problem, and does not require a process for producing a raw material of nanoparticles, can reduce thermal conductivity by phonon scattering, and has an electrical conductivity by a quantum confinement effect. It is an object to provide a thermoelectric material and a thermoelectric module having an improved figure of merit, which can improve the Seebeck coefficient and can be expected to be put to practical use.

  In order to achieve the above object, the thermoelectric material according to the present invention includes a eutectic structure. In particular, the thermoelectric material according to the present invention preferably has a eutectic structure obtained by unidirectional solidification at the eutectic point. The thermoelectric material according to the present invention is a structure composed of a first crystal phase and a second crystal phase having a thermoelectric effect, and the first crystal phase is a eutectic with the second crystal phase. It is preferable to form a tissue. The second crystal phase preferably has a smaller particle size than the first crystal phase.

  The thermoelectric material according to the present invention has a process for producing a nanoparticle raw material by forming a eutectic structure obtained by dispersing the second phase in the phase of the thermoelectric material directly by unidirectional solidification from the melt. It is unnecessary. In addition, it is possible to realize a structure in which two phases are uniformly dispersed using a eutectic structure.

  Moreover, the thermoelectric material which concerns on this invention can improve an electrical conductivity and a Seebeck coefficient by the quantum confinement effect by a reduction in dimension, when the 2nd crystal phase in a eutectic structure has a thermoelectric effect. In addition, the nanorod phase of the thermoelectric material can be formed in the second phase, so that the electrical conductivity and Seebeck coefficient can also be improved, and the practical application as a bulk body can be expected. In addition, since the first crystal phase in the eutectic structure also has a thermoelectric effect, phonons in the first crystal phase are scattered by the second crystal phase located around the first crystal phase, and as a result, thermal conductivity is increased. Can be reduced. Thus, the thermoelectric material according to the present invention can improve the figure of merit.

  The thermoelectric material according to the present invention comprises a structure having a first crystal phase and a second crystal phase having a thermoelectric effect, and the first crystal phase has a eutectic structure with the second crystal phase. The first crystal phase and the second crystal phase are continuously present on the two opposing surfaces of the structure, and the first crystal phase is the second crystal phase. Or the second crystalline phase is located around the first crystalline phase, and the first crystalline phase has a thermal conductivity of the second crystalline phase. The electrical conductivity or Seebeck coefficient of the second crystal phase may be increased. In addition, the thermoelectric material according to the present invention includes a rectangular parallelepiped structure having a first crystal phase and a second crystal phase having a thermoelectric effect, and the first crystal phase includes the second crystal phase. The first crystal phase and the second crystal phase are dispersed on the two opposing surfaces of the structure, and the first crystal phase is the second crystal phase. Or the second crystal phase is located around the first crystal phase, and the first crystal phase is the second crystal phase of the second crystal phase. The thermal conductivity may be decreased, or the electrical conductivity or Seebeck coefficient of the second crystal phase may be increased. The thermoelectric material according to the present invention includes an oxide and metal structure having a first crystal phase and a second crystal phase having a thermoelectric effect, and the first crystal phase is the second crystal phase. The first crystal phase and the second crystal phase are present continuously or dispersed on the two opposing faces of the structure, respectively, and the first crystal A phase is located around the second crystalline phase, or the second crystalline phase is located around the first crystalline phase, and the first crystalline phase is the first crystalline phase. The thermal conductivity of the second crystal phase may be reduced, or the electrical conductivity or Seebeck coefficient of the second crystal phase may be increased. In any of these cases, the first crystal phase and the second crystal phase may be present continuously or dispersed on two opposing surfaces of the structure.

  The method for producing a thermoelectric material according to the present invention includes a step of mixing a material constituting the first crystal phase and a material constituting the second crystal phase, and a material constituting the mixed first crystal phase. And a material constituting the second crystal phase, and a material constituting the melted first crystal phase and a material constituting the second crystal phase are solidified along one direction to be shared. And a step of generating a crystal. In the thermoelectric material according to the present invention, the two opposing surfaces of the structure are, for example, two surfaces perpendicular to the solidification direction when generating a eutectic structure or two surfaces parallel to the solidification direction.

  In the thermoelectric material according to the present invention, the shape of the first crystal phase or the shape of the second crystal phase is preferably a columnar shape or a plate shape. In this case, the first crystal phase having a columnar shape or a plate shape or a plurality of second crystal phases having a columnar shape or a plate shape are included, and the plurality of crystal phases are out of two opposing surfaces of the structure. Are periodically arranged along at least one of the surfaces, and the period is preferably 5 nm or more and 50 μm or less.

  Further, in the thermoelectric material according to the present invention, it is preferable that the second crystal phase generates power by a temperature difference. Further, in the thermoelectric material according to the present invention, the composition ratio between the first crystal phase and the second crystal phase is ± eutectic composition ratio between the first crystal phase and the second crystal phase. It is preferable to be within the range of 5 mol%.

In the thermoelectric material according to the present invention, the first crystal phase or the second crystal phase may contain SrTiO ₃ . In this case, the crystal phase composed of SrTiO ₃ among the first crystal phase and the second crystal phase is Nb, Ta, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, It contains at least one of Ho, Er, Tm, Yb, and Lu, and the content thereof is preferably in the range of more than 0 mol% and less than 50 mol%. In particular, the second crystal phase may consist of SrTiO ₃ and the first crystal phase may consist of TiO ₂ .

  In the thermoelectric material according to the present invention, the first crystal phase or the second crystal phase may be made of ZnO. In this case, the crystal phase composed of ZnO among the first crystal phase and the second crystal phase contains at least one of Al and Ga, and the content is in the range of more than 0 mol% and less than 50 mol%. It may be. The first crystal phase or the second crystal phase may be made of ZnO, and the other phase of the crystal phase may contain any of Nb, Si, and P. In the thermoelectric material according to the present invention, the first crystal phase may have a thermoelectric effect, and the first crystal phase and the second crystal phase may be reversed. In this case, the actions and effects of the first crystal phase and the second crystal phase are interchanged.

  The thermoelectric module according to the present invention is a thermoelectric module using a thermoelectric material, wherein the thermoelectric material is the thermoelectric material according to the present invention. In particular, in the thermoelectric module according to the present invention, two types of n-type and p-type thermoelectric materials according to the present invention are alternately arranged, and each thermoelectric material is installed so as to generate a temperature difference. preferable.

  According to the present invention, the process for producing the raw material of the nanoparticles is unnecessary, the thermal conductivity can be reduced by phonon scattering, and the electrical conductivity and Seebeck coefficient can be improved by the quantum confinement effect. Therefore, it is possible to provide a thermoelectric material with improved performance index. Moreover, according to this invention, the thermoelectric module using the thermoelectric material which improved the figure of merit can be provided.

It is a perspective view which shows (A) 1st structure, (B) 2nd structure, (C) 3rd structure of the thermoelectric material of embodiment of this invention. It is a schematic longitudinal cross-sectional view which shows the manufacturing apparatus of the thermoelectric material of embodiment of this invention. A thermoelectric material embodiment of the present _invention, is a side view showing a SrTiO 3 -TiO ₂ based thermoelectric material crystals. (A) Scanning electron microscope (SEM) image showing a structure perpendicular to the solidification direction of the SrTiO ₃ —TiO ₂ -based thermoelectric material crystal shown in FIG. 3, (B) Energy dispersive type of columnar crystals in (A) X-ray analysis (EDX) spectrum, (C) EDX spectrum around columnar crystal in (A), (D) SEM image showing a structure parallel to the solidification direction. Of SrTiO ₃ -TiO ₂ based thermoelectric material crystal body shown in FIG. 3 is a powder X-ray diffraction (XRD) patterns. SrTiO ₃ -TiO ₂ system and shown in Figure 3, of SrTiO ₃ -TiO ₂ based thermoelectric material crystals with the addition of Nb, is a graph showing the temperature dependence of the electrical resistivity ([rho). A thermoelectric material embodiment of the present invention, is a side view showing the (A) Nb added, (B) Pr addition, (C) La added SrTiO ₃ -TiO ₂ based thermoelectric material crystals. A thermoelectric material embodiment of the present _invention, is a side view showing a Zn ₃ Nb ₂ O 8 -ZnO based thermoelectric material crystals. (A) SEM image of Zn ₃ Nb ₂ O ₈ —ZnO-based thermoelectric material crystal body shown in FIG. 8, (B) EDX spectrum of columnar crystal in (A), (C) Columnar crystal periphery in (A) This is an EDX spectrum.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
There are various forms (various configurations and various materials) for carrying out the present invention, but what is common to all the embodiments is that the first crystal phase and the first A thermoelectric material having a eutectic structure having a particle size smaller than that of the crystal phase and having a second phase with a second crystal phase having a thermoelectric effect is formed by the first crystal phase and the second crystal on two opposite sides. The phases are present continuously or dispersed. Accordingly, when the first crystal phase has a thermoelectric effect, the phonons in the first crystal phase are scattered by the second crystal phase located around the first crystal phase, and as a result, the thermal conductivity is lowered. On the other hand, since the second crystal phase has a thermoelectric effect, the electrical conductivity and Seebeck coefficient are improved by the quantum confinement effect due to the reduction in dimension. In this way, all embodiments of the present invention improve the figure of merit of the thermoelectric crystal itself.
Each embodiment will be described below.

[First Embodiment: Columnar Crystal or Dispersed Crystal Structure, Form in which Main Component of Second Crystal Phase is Thermoelectric Crystal]
1A, 1B, and 1C are schematic views showing an embodiment of a thermoelectric material according to an embodiment of the present invention. Note that, as shown in FIG. 1A, a first crystal phase 11 having a number of columnar crystals or dispersed crystals having unidirectionality, and a second crystal phase 12 filling the side surfaces of the first crystal phase 11. Hereinafter, the case where the two layers are configured is referred to as a first configuration. Further, as shown in FIG. 1B, a second crystal phase 12 having a number of columnar crystals or dispersed crystals having unidirectionality, and a first crystal phase 11 filling the side surfaces of the second crystal phase 12. Hereinafter, a case where the two phases are configured is referred to as a second configuration. Further, as shown in FIG. 1C, both the first crystal phase 11 and the second crystal phase 12 are composed of plate crystals standing in one direction, and they are configured to be alternately in close contact. This case is hereinafter referred to as a third configuration.

  FIG. 1A is a schematic view showing a thermoelectric material according to the first embodiment of the present invention. In the thermoelectric crystal body (structure) having two eutectic structures of this embodiment shown in FIG. 1A, the first crystal phase 11 and the second crystal phase 12 are continuous on two opposing surfaces, Or they are distributed. In the form shown in FIG. 1A, the second crystal phase 12 has a first crystal phase 11 composed of a number of columnar crystals or dispersed crystals having unidirectionality. Specifically, it is composed of a two-phase phase separation structure of a first crystal phase 11 and a second crystal phase 12 filling the side surface of the first crystal 11. The phase separation structure is a structure obtained by separating into a plurality of phases when the situation is changed from a uniform state. In this embodiment, when the constituent material is melted from a uniform liquid state without a structure to a solidified state, two crystal phases are simultaneously crystallized and formed with a certain degree of periodicity. Represents.

  The cross-sectional shape of the columnar crystal constituting the first crystal phase 11 is not limited to a circle, an ellipse, and a quadrangle, and may be composed of a plurality of crystal planes to form a polygon. The diameter 13 of the columnar crystals is 5 nm to 50 μm, preferably 5 nm to 10 μm. Further, the period 14 of the columnar crystals of the first crystal phase 11 is 5 nm or more and 50 μm or less, preferably 5 nm or more and 10 μm or less. Further, the thickness 15 of the thermoelectric crystal body can be adjusted to an arbitrary thickness although it depends on the manufacturing method.

  The columnar crystals preferably continue straight across the thickness direction 16, but are interrupted in the middle, branching and fusion occur, include bent portions that are not straight, and the diameter changes partially. You may do it. Columnar crystals can be bent by appropriately controlling the direction of the solid-liquid interface during solidification.

The second crystal phase 12 is preferably composed of a material containing SrTiO ₃ . The content of SrTiO ₃ contained in the second crystal phase 12 with respect to the amount of the first crystal phase 11 is 50 mol% or more, preferably 80 mol% or more and 100 mol% or less.

The first crystal phase 11 preferably contains TiO ₂ as a main component. Here, the main component means a material having a content of 50 mol% or more in the first crystal phase 11, and more preferably, the main component material is 80 mol% or more and 100 mol% in the first crystal phase 11. It is desirable that it is contained in the following.

  The composition of the material constituting the first crystal phase 11 and the second crystal phase 12 contained in the thermoelectric material of the first embodiment of the present invention is preferably a composition at the eutectic point. The eutectic point is a point at which an eutectic reaction occurs in the equilibrium diagram, and represents a point at which solidification is completed by simultaneously discharging two solid solutions from the liquid phase. Table 1 shows examples of composition ratios of preferable combinations of the material systems of the first crystal phase 11 and the second crystal phase 12 of the present embodiment.

  In order to obtain a good phase separation structure as shown in FIG. These compositions correspond to eutectic points. However, it should not be deviated from the above composition at all, and a range of ± 5 mol% with respect to the composition is preferably an allowable range. More preferably, it is in the range of ± 2 mol%. The reason for limiting the range in the vicinity of these compositions is that each phase has a eutectic relationship in the formation of the structure, and in the vicinity of the eutectic composition, a good-quality structure as shown in FIG. 1A can be obtained by unidirectional solidification. It is. In other composition ranges, that is, when deviating by 5 mol% or more, one phase is crystallized first, which is a factor disturbing the structure from the viewpoint of structure formation. However, since the eutectic composition shown in Table 1 also has measurement errors, it is important that the eutectic composition is ± 2 mol% from the eutectic composition. However, if a substantially good structure is obtained, it deviates by about ± 5 mol%. May be. Further, the eutectic temperatures shown in Table 1 also have a measurement error or the like, and thus indicate that the temperature is around the above temperature and do not impose any limitation.

Next, the first crystal phase 11 and the second crystal phase 12 may contain components other than those described above. In particular, the components contained in the material constituting the first crystal phase 11 are It is preferable that the component is a solid solution in one crystal phase 11 and is not a solid solution in the second crystal phase 12. For example, SiO ₂ may be added to TiO ₂ . Further, the component contained in the material constituting the second crystal 12 is preferably a component that does not dissolve in the first crystal phase 11 but dissolves in the second crystal phase 12. For example, as described above, BaTiO ₃ can be dissolved in SrTiO ₃ .

Further, additive materials other than SrTiO ₃ and TiO ₂ may be added or added alone. Moreover, if there is no hindrance to the formation of the eutectic structure, a component that dissolves in both may be added. In this way, the purpose in the case of adding 1 mol% or more instead of adding a trace amount is to control the carrier amount, the lattice constant, and the band structure.

  In the phase separation structure in the present embodiment, the second crystal phase 12 whose main component is a material having a thermoelectric effect has an electromotive force due to a temperature difference and generates electric power. However, the present invention is not limited to this, and in the present invention, at least one of the first crystal phase 11 and the second crystal phase 12 may generate power due to a temperature difference, and both may generate power. In particular, in order to increase the power generation efficiency, a component for controlling the carrier amount may be added to the base material constituting the first crystal phase 11 and the second crystal phase 12, or reduction treatment may be performed. preferable.

  A large number of additive elements for controlling the carrier amount can be selected depending on the application and the like, and a single element or a plurality of elements may be added. For example, Nb, Ta, Sc, Y, Zr, and Hf rare earth elements La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Ho, Er, which can be trivalent or more expensive ions. It is preferable to select from Tm, Yb, and Lu. When adding the said element, it can select suitably with respect to requirements, such as an electromotive force, an electrical resistivity, and a Seebeck coefficient, according to a use. Moreover, there is no problem even if a concentration distribution occurs due to the addition of such an element, such as easy addition to one phase due to the phase separation structure.

[Second Embodiment: Columnar Crystal Structure, Form in which Main Component of Second Crystal Phase is Thermoelectric Crystal]
Next, a second embodiment will be described. In the second embodiment, ZnO or SrTiO ₃ was used as the main component of the second crystal phase 12 to obtain the eutectic structure shown in FIG. This will be described in detail below.

  The diameter 13 of the first crystal phase 11 in the first configuration shown in FIG. 1A or the diameter 13 of the second crystal phase 12 in the second configuration shown in FIG. The preferable range of the period 14 in (B) is as described in the first embodiment. Further, in the third configuration shown in FIG. 1C, a plate-like crystal is used, but when the short side is defined as a diameter and a period, the diameter 13 of the first crystal phase 11 of the plate-like crystal is The structural period 14 is preferably in the same range of values as in the first configuration.

The thermoelectric material thickness 15 shown in FIG. 1B is the same as in the first embodiment.
In the present embodiment, the second crystal phase 12 is realized by containing ZnO or SrTiO ₃ as a main component. However, more preferably, the material constituting the first crystal phase 11 is the same as ZnO or SrTiO ₃ . A material system having a crystal relationship is preferable for forming the structure of this embodiment. An example of the relationship that can be taken by the materials of the first crystal phase 11 and the second crystal phase 12 is as shown in Table 2. That is, in the case of a combination of ZnO and Nb ₂ O ₅ , the second configuration (FIG. 1B) is obtained, the second crystal phase 12 is ZnO, and the first crystal phase 11 is Zn ₃ Nb ₂ O _8. It is. In the case of a combination of ZnO and SiO ₂ , the second configuration is adopted, and the first crystal phase 11 is Zn ₂ SiO ₄ and the second crystal phase 12 is ZnO. In the case of a combination of ZnO and P ₂ O ₅ , the second configuration is adopted, where the first crystal phase 11 is Zn ₃ (PO ₄ ) ₂ and the second crystal phase 12 is ZnO. Further, in the case of a combination of SrTiO ₃ and Sr ₂ TiO ₄ , the second configuration is adopted, and the first crystal phase 11 is Sr ₂ TiO ₄ and the second crystal phase 12 is SrTiO ₃ .

  Next, in the selection of the material system, what is important in the present embodiment is the composition of the material constituting each of the first crystal phase 11 and the second crystal phase 12. In the four types of combinations of the material systems of this embodiment shown in Table 2, the preferred composition ratio is as shown in Table 3 below, and is preferably a composition at the eutectic point.

  The permissible range of the composition is the same as that of the first embodiment described above in the range of ± 5 mol%, more preferably ± 2 mol% with respect to the composition.

  As described in the first embodiment, materials other than those described above may be added to the first crystal phase 11 and the second crystal phase 12. Moreover, if there is no hindrance to the structure formation, a material that dissolves in both may be added. Further, the content of the material constituting each crystal phase in each crystal phase is preferably 50 mol% or more and 80 mol% or more and 100 mol% or less.

  In the present embodiment, it is preferable that at least one of the crystal phases generates power due to a temperature difference, but it is more preferable that both generate power. In particular, in order to increase the power generation efficiency, it is also preferable to add an element for forming a carrier to the base material constituting the first crystal phase 11 or the second crystal phase 12. As the additive element, the same elements as in the first embodiment can be applied.

[Third embodiment: Lamellar structure, main component of second crystal phase is made of thermoelectric material]
Next, a third embodiment will be described. In the third embodiment, SrTiO ₃ was used as the main component of the second crystal phase 12, and a lamellar structure phase separation structure shown in FIG. 1C was obtained. This will be described in detail below. Since the outline of FIG. 1C has already been described in the above-described embodiment, only the features of this embodiment will be described below.

The thermoelectric material crystal according to the present embodiment is a phase-separated structure composed of a first crystal phase 11 and a second crystal phase 12 having unidirectionality, and the second crystal phase 12 is a main component of SrTiO. ₃ is composed of a material having ₃ . And at least one phase of this structure is characterized by generating electric power by a temperature difference.

  Moreover, it is preferable that at least one of the first crystal phase 11 or the second crystal phase 12 contains at least one element for controlling the amount of carriers. The compositions of the first crystal phase 11 and the second crystal phase 12 are preferably compositions at the eutectic point. An example of the relationship that the first crystal phase 11, the second crystal phase 12, and the material can take is as shown in Table 4.

  Next, in the selection of the material system, what is important in the present embodiment is the composition of the material constituting each of the first crystal phase 11 and the second crystal phase 12. In the combination of the material systems of the present embodiment shown in Table 4, the preferred composition ratio is as shown in Table 5 below, and is preferably a composition at the eutectic point.

  The permissible range of the composition is the same as that of the first embodiment described above in the range of ± 5 mol%, more preferably ± 2 mol% with respect to the composition. In the present embodiment, it is preferable that at least one of the crystal phases generates power based on a temperature difference, but both may generate power. In particular, in order to increase the power generation efficiency, it is also preferable to add an element for controlling the carrier amount to the base material constituting the first crystal phase 11 or the second crystal phase 12.

  Next, a method for manufacturing the thermoelectric material crystal body (thermoelectric material) of each of the above-described embodiments will be described. The manufacturing method of the thermoelectric material crystal according to the present embodiment includes a step of mixing a material constituting the first crystal phase 11 and a material constituting the second crystal phase 12, and a mixed first crystal phase. 11 and the material constituting the second crystal phase 12 are melted together with the material constituting the melted first crystal phase 11 and the material constituting the second crystal phase 12. And a step of solidifying along a direction to form a eutectic.

  The method for producing the thermoelectric material crystal body of the present embodiment can be any method as long as it is a method in which a desired material system is melted and solidified with an optimal composition and unidirectionality. In particular, it is required to control the temperature gradient so as to smooth the solid-liquid interface, and it is preferable that the temperature gradient at the solid-liquid interface of the mixture is 10 ° C./mm or more. However, in order to eliminate cracks and the like due to thermal stress on the crystal, the temperature gradient may be lowered within a range that does not hinder the structure formation of each of the embodiments described above. It is also desirable to suppress cracks and the like by reheating the portion that has already become a crystal body so as not to melt. The composition range in which the eutectic structure can be formed is described as eutectic composition ± 5 mol%, preferably ± 2 mol%, as described above, but between this range and the temperature gradient and solidification rate. Argues that this crystalline material should be fabricated in a category called the so-called Coupled Eutectic Zone, where there is a material-specific correlation.

  FIG. 2 is a schematic view showing a method for producing a thermoelectric material crystal of the present embodiment. In the micro pull-down method, a material is placed in a crucible having a hole at the bottom, the crucible is heated by a heater or a high frequency induction power source, and then the molten material is pulled from the bottom of the crucible using a seed crystal or the like. Thus, since a solid-liquid interface can be formed immediately below the bottom of the crucible, it is possible to manufacture the thermoelectric material crystal having the eutectic structure of the present embodiment.

  In particular, the apparatus shown in FIG. 2 has a high-temperature induction coil 21 comparable to the length of the crucible 23 and a heat insulating material 22 for realizing a temperature gradient of 10 ° C./mm or more as a temperature gradient at the solid-liquid interface of the sample 25 that is a mixture. Consists of The melt at the bottom of the crucible 23 is solidified in one direction by being pulled downward by a seed crystal 24 installed below the crucible 23.

  In addition, the temperature gradient at the solid-liquid interface can be controlled to an optimum value for crystal production by the after heater 26 installed at the lower part of the crucible 23. Furthermore, the manufacturing method which takes an equivalent means is also possible. However, the temperature gradient may be less than 10 ° C./mm as long as the solid-liquid interface can be made smooth.

  Moreover, it can be similarly produced by crystal pulling as in the Czochralski method. In this case, since the crystal is not pulled downward as in the micro pulling method, it is more preferable in that a large sample can be manufactured. Furthermore, as in the Bridgman method, crystals can be similarly produced in the crucible. In this case, it is more preferable in that a large sample can be manufactured with good yield by optimizing the manufacturing conditions. Further, it can be similarly produced by the floating zone method. In this case, it is not necessary to use a crucible, and it is more preferable in that no impurities are mixed from the crucible and the cost of the crucible is not increased. Furthermore, it can be similarly produced by crystal pulling using a die as in the EFG method. In this case, it is more preferable in that it can be manufactured while controlling the shape of the sample to be manufactured.

Further, the diameter of the columnar crystals of the phase-separated thermoelectric material crystal and its period depend on the solidification rate of the sample, and in particular, the period of the columnar crystals has the following correlation. If the period is λ and the solidification rate is v, λ ² · v = constant. Therefore, if there is a desired structural period, the solidification rate is inevitably limited. Conversely, as a limitation on the manufacturing method, there is a solidification rate at which the solid-liquid interface can be controlled flat and smooth, and therefore the range of the period λ is in the range of 5 nm to 50 μm. Correspondingly, the diameter of the columnar crystal is in the range of 5 nm to 50 μm.

  Here, the diameter of the columnar crystal may not be circular, and if it is indefinite, the shortest diameter is included in the above range. Moreover, it is preferable that the ratio of the longest diameter to the shortest diameter is 10 or less as an average value of many columnar crystals. Above this, a lamellar structure is appropriate. However, even if only some of the innumerable columnar crystals have a value of 10 or more, it is acceptable if the average value is below. Also, on the production conditions, the closer the molar ratio of the materials constituting the first crystal phase and the second crystal phase is to 1: 1, the easier it is to adopt a lamellar structure. It is preferable to select. Further, if the molar ratio of the materials constituting the first crystal phase and the second crystal phase is between the value at which columnar crystals are easily taken and the value at which lamellar structures are easily taken, whether the columnar crystals are taken depending on the growth rate. It is possible to take or control the lamellar structure.

  Next, the preparation composition of the raw material of the sample to be produced will be described. The composition ratios of the materials constituting the first crystal phase and the second crystal phase of the above phase-separated thermoelectric material crystal are the values shown in each table, but the charged composition deviates to ± 5 mol% or more. It does not matter. In other words, in the case of the micro pull-down method, if the whole sample is melted and then unidirectionally solidified downward in the crucible, the material that deviates from the eutectic composition in the initial stage of solidification is precipitated first. As a result, the remaining melt has a eutectic composition. Therefore, it is also preferable to pull it down with a dummy once and then pull it down again after the melt has a eutectic composition. What is necessary is just to cut away an unnecessary part after crystal body preparation.

  Next, the thermoelectric module of each of the above-described embodiments includes the thermoelectric material crystal body and the electrode, and the thermoelectric material crystal body is arranged so that n-type and p-type are alternately opposed to each other. It is characterized by. The thermoelectric material crystal is preferably arranged on the electrode directly or via one or more protective layers.

  The thermoelectric module of the present embodiment is a power generation device using unused heat discharged from a power generation facility, industrial device, automobile, etc., by combining the p-type and n-type phase-separated thermoelectric material crystals with electrodes. It can be used as In particular, since the phase-separated thermoelectric material crystal of the present embodiment has high thermoelectric properties, it is preferably applied to a situation where higher power generation efficiency is required. In addition, since there is no need for steps such as nano-scaling of raw materials used for sample preparation and nano-wires of thermoelectric materials, it can be manufactured at low cost compared to conventional nanostructure bulk or nanowires, etc. It is also preferable to apply to a situation where cost reduction is required. In the above applications, it is possible to adjust by adding other materials and controlling the amount of carriers so as to meet the required characteristics.

  Furthermore, it is also preferable that the electrode and the phase-separated thermoelectric material crystal body of the present embodiment are joined or arranged via a film or layer having a function of each protective layer or the like, instead of directly.

Examples described below are examples corresponding to the first embodiment described above. The description will be made sequentially from the first embodiment. In Example 1, first, a powder obtained by mixing SrO ₂ with SrO ₂ : TiO ₂ = 20: 80 with respect to TiO ₂ (material constituting the first crystal phase) is prepared, and these are made of iridium. In a crucible. The iridium crucible used has a 3 × 3 mm ² die on the bottom and a 0.5 mm capillary in the center of the die. This crucible was installed in a micro-pulling furnace as shown in FIG. 2, and the mixed sample in the crucible was completely dissolved by heating the crucible to a temperature of 1440 ° C. or higher using a high frequency induction heating power source. Thereafter, the molten raw material in the crucible passed through the capillary at the bottom, appeared on the bottom of the crucible, and spread wet. The wet raw material melt was brought into contact with an alumina ceramic rod, and the raw material melt was pulled downward together with the ceramic rod to solidify the raw material melt while forming a solid-liquid interface immediately below the bottom of the crucible. The speed at which the raw material melt was pulled down was about 5 mm / min.

  In this way, the eutectic was produced by solidifying the raw material melt directly under the crucible along one direction. The obtained crystal rod is shown in FIG.

The sample thus prepared was cut out and structurally observed with a scanning electron microscope (SEM). As a result, in the SrTiO ₃ —TiO ₂ system, the structure perpendicular to the solidification direction (growth direction) (the structure viewed from the first main surface and the second main surface) is shown in FIG. The structure was as shown in FIG. Further, from the composition analysis using energy dispersive X-ray spectroscopy (EDX) attached to the SEM, as shown in FIG. 4B, the columnar crystals have TiO ₂ , and FIG. As shown in FIG. 5, it was found that the peripheral portion has SrTiO ₃ . Thus, it was shown that a large number of columnar crystals of TiO ₂ have unidirectionality and a structure in which the periphery thereof is surrounded by SrTiO ₃ is formed.

  Here, as the explanation of the thermoelectric material structure composed of the first crystal phase and the second crystal phase, it has been explained with reference to one figure. Since the structure viewed from the surface is very similar, only one of them is shown as a representative, and the first crystal phase, which is a columnar crystal, and the first surrounding the peripheral portion are formed on each of the opposing surfaces. It has been confirmed that both of the two crystal phases are exposed.

  In other embodiments described below, a thermoelectric material structure composed of a first crystal phase and a second crystal phase will be described with reference to only some drawings. It should be understood that this is due to the fact that the surface structure is very similar.

After the prepared sample was crushed into powder, the phase was identified by powder X-ray diffraction (XRD) measurement. As a result, as shown in FIG. 5, only diffraction peaks attributable to SrTiO ₃ and TiO ₂ could be confirmed. Therefore, it was found that the prepared sample was composed of only two phases of SrTiO ₃ and TiO ₂ .

The effect of the carrier amount control by the additive element with respect to the SrTiO ₃ —TiO ₂ system produced in Example 1 is shown. FIG. 6 shows the temperature dependence of the electrical resistivity (ρ) of the SrTiO ₃ —TiO ₂ sample containing no additive element and the SrTiO ₃ —TiO ₂ sample added with Nb prepared in Example 1. Indicates. In FIG. 6, xtal STO is SrTiO ₃ single crystal, STO-TO (Nb-free) is SrTiO ₃ / TiO ₂ eutectic without Nb, and Nb-5 (reduced) is SrTiO with 5% Nb added. ₃ / TiO ₂ eutectic (after reduction annealing), Nb-5 (as-received) is SrTiO ₃ / TiO ₂ eutectic with 5% Nb added (without post-treatment), Nb-20 (as -received) is SrTiO ₃ / TiO ₂ eutectic with 20% Nb added (without post-treatment), poly STO is SrTiO ₃ polycrystal, poly Y-doped STO is SrTiO ₃ polycrystal with Y added Is the result of The poly STO and poly Y-doped STO data are the thermophysical properties database system (TPDS) published by the National Institute of Advanced Industrial Science and Technology (AIST). ) Is used. First, as shown in FIG. 6, in the STO-TO (Nb-free) of the sample containing no additive element prepared in Example 1, since the amount of carriers is small, an insulating high electrical resistivity (ρ) showed that.

Next, as shown in FIG. 7A, a sample in which 10 mol% of Nb ₂ O ₅ was added to the SrTiO ₃ —TiO ₂ system was manufactured by the same manufacturing method as in Example 1. Similarly, when the structure was observed by SEM, it had the same eutectic structure as in the case where there was no added element. From the composition analysis using EDX, the columnar crystals had TiO ₂ and the surroundings. Part was found to have SrTiO ₃ . Here, the composition of the additive element is not limited to 10 mol%.

When the electrical resistivity of the SrTiO ₃ —TiO ₂ -based sample added with Nb was measured, as shown in FIG. 6, Nb-5 (reduced) and Nb-5 (as-received) of the sample added with Nb were obtained. , And Nb-20 (as-received), the electrical resistivity decreased significantly compared to STO-TO (Nb-free) of the sample containing no added element. As a result, the carrier amount could be controlled by actually adding Nb.

Further, a sample prepared by adding 10 mol% of Pr ₆ O ₁₁ to a SrTiO ₃ —TiO ₂ system and a sample added with 10/3 mol% (3.3 mol%) of La ₂ O ₃ were prepared by the same manufacturing method. As a result, the sample rods shown in FIGS. 7B and 7C can be obtained, respectively, and it becomes clear that the sample bar has the same eutectic structure as the SrTiO ₃ —TiO ₂ system to which Nb is added. It was.

When the thermal conductivity of the SrTiO ₃ —TiO ₂ -based sample to which Nb was added was measured, it was about 4.2 W / m · K at room temperature, and the heat of SrTiO ₃ to which Nb without eutectic structure was added The value was less than half of the conductivity.

Examples described below are examples corresponding to the second embodiment described above. As the composition of the thermoelectric material crystal body having the eutectic structure of this example, a Zn ₃ Nb ₂ O ₈ —ZnO-based sample shown in Table 3 was produced using the same apparatus as that of Example 1 shown in FIG. However, this time, since the melting point at the eutectic point was 1300 ° C., a crucible for crystal growth was made of platinum-rhodium (Pt—Rh). The obtained crystal rod is shown in FIG.

The structure of the Zn ₃ Nb ₂ O ₈ —ZnO-based crystal rod was observed by SEM in the same manner as in the SrTiO ₃ —TiO ₂ system. As a result, the structure perpendicular to the solidification direction (the structure viewed from the first main surface and the second main surface) became a structure as shown in FIG. Further, from the composition analysis using energy dispersive X-ray spectroscopy (EDX) attached to the SEM, as shown in FIG. 9B, the columnar crystals have ZnO, and FIG. As shown, the peripheral portion was found to have Zn ₃ Nb ₂ O ₈ . Thus, it was shown that a structure in which Zn ₃ Nb ₂ O ₈ surrounds the periphery of a large number of ZnO columnar crystals is formed.

Examples described below are examples corresponding to the first embodiment described above. As the thermoelectric material crystal body of this example, Sn—SnSe, SnSe—SnSe ₂ , Bi ₂ Te ₃ —Te, PbTe—Te, Co—CoSb, PbSe—Se, InSb—Sb, Cu ₂ S—PbS, Cu— _{Cu 2 Se, Cu 2 Se-} Se, Mg-Mg 3 Sb 2, Mg 3 Sb 2 -Sb, Sb 2 Te 3 -Te, Zn 3 Sb 4 -Zn, Sb-ZnSb, Bi 2 Te 3 -In 2 Te For each eutectic structure of the _three systems, the structure of the plane perpendicular to the solidification direction when unidirectional solidification was performed was determined from the respective phase diagrams by simulation. Further, from the simulation results, the configuration of the eutectic structure (first configuration, second configuration, third configuration), the first crystal phase, and the second crystal phase were determined. The results are shown in Table 6.

11 First crystal phase 12 Second crystal phase 13 Diameter (such as columnar crystal) 14 Period (such as columnar crystal) Period 15 Thickness (of thermoelectric crystal) 16 Thickness direction

21 High-frequency induction coil 22 Heat insulating material 23 Crucible 24 Seed crystal 25 Sample 26 After heater

Claims (15)

  A thermoelectric material comprising a eutectic structure. Consisting of a structure having a first crystal phase and a second crystal phase having a thermoelectric effect,
The first crystal phase forms a eutectic structure with the second crystal phase;
On the two opposite surfaces of the structure, the first crystal phase and the second crystal phase are respectively present continuously,
The first crystalline phase is located around the second crystalline phase, or the second crystalline phase is located around the first crystalline phase, and the first crystalline phase is 2. The thermoelectric device according to claim 1, wherein the crystal phase decreases the thermal conductivity of the second crystal phase, or the electrical conductivity or Seebeck coefficient of the second crystal phase increases. material. A cuboid structure having a first crystal phase and a second crystal phase having a thermoelectric effect,
The first crystal phase forms a eutectic structure with the second crystal phase;
On the two opposing surfaces of the structure, the first crystal phase and the second crystal phase are present in a dispersed manner,
The first crystalline phase is located around the second crystalline phase, or the second crystalline phase is located around the first crystalline phase, and the first crystalline phase is 2. The thermoelectric device according to claim 1, wherein the crystal phase decreases the thermal conductivity of the second crystal phase, or the electrical conductivity or Seebeck coefficient of the second crystal phase increases. material. Consisting of an oxide and metal structure having a first crystalline phase and a second crystalline phase having a thermoelectric effect,
The first crystal phase forms a eutectic structure with the second crystal phase;
On the two opposite surfaces of the structure, the first crystal phase and the second crystal phase are present continuously or dispersed respectively,
The first crystalline phase is located around the second crystalline phase, or the second crystalline phase is located around the first crystalline phase, and the first crystalline phase is 2. The thermoelectric device according to claim 1, wherein the crystal phase decreases the thermal conductivity of the second crystal phase, or the electrical conductivity or Seebeck coefficient of the second crystal phase increases. material.   The thermoelectric material according to any one of claims 2 to 4, wherein the shape of the first crystal phase or the shape of the second crystal phase is a columnar shape or a plate shape.   The first crystal phase that is columnar or plate-shaped or the second crystal phase that is columnar or plate-shaped is plural, and the plurality of crystal phases is at least one of two opposing surfaces of the structure. 6. The thermoelectric material according to claim 5, wherein the thermoelectric material is periodically arranged along one of the surfaces, and the cycle is 5 nm or more and 50 μm or less.   The thermoelectric material according to any one of claims 2 to 6, wherein the second crystal phase generates power by a temperature difference.   The composition ratio between the first crystal phase and the second crystal phase is within a range of ± 5 mol% of the eutectic composition ratio between the first crystal phase and the second crystal phase. The thermoelectric material according to any one of claims 2 to 7. The thermoelectric material according to any one of claims 2 to 8, wherein the first crystal phase or the second crystal phase contains SrTiO ₃ . Among the first crystal phase and the second crystal phase, the crystal phase composed of SrTiO ₃ is Nb, Ta, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er. The thermoelectric material according to claim 9, wherein the thermoelectric material contains at least one of Tm, Yb, and Lu, and the content thereof is in the range of more than 0 mol% and less than 50 mol%. 9. The thermoelectric material according to claim 2, wherein the second crystal phase is made of SrTiO ₃ , and the first crystal phase is made of TiO ₂ .   The thermoelectric material according to any one of claims 2 to 8, wherein the first crystal phase or the second crystal phase is made of ZnO.   Of the first crystal phase and the second crystal phase, the crystal phase composed of ZnO contains at least one of Al and Ga, and the content thereof is in the range of more than 0 mol% and less than 50 mol%. The thermoelectric material according to claim 12.   The first crystal phase or the second crystal phase is made of ZnO, and the other phase of the crystal phase contains any one of Nb, Si, and P. The thermoelectric material according to any one of the above. A thermoelectric module using a thermoelectric material, wherein the thermoelectric material is the thermoelectric material according to any one of claims 1 to 14.