KR101872424B1 - Quaternary Zintl Compounds Including Ca and Yb Mixed Cation Sites And Manufacturing Method Thereof - Google Patents

Abstract

The present invention relates to a four-component zeolitic compound containing Ca ^{2 +} / Yb ^{2 +} at a mixed position and a process for producing the same. The present invention relates to a method for producing a thin film of Ca _{5 - x} Yb _x Al ₂ Sb ₆ Ca _{5 - x} Yb _x Al ₂ Sb ₆ with low lattice thermal conductivity ( κ _lat ) and improved thermoelectric performance index ( ZT ) by introducing Ca ^{2 +} / Yb ^{2 +} mixed cations into the solid solution system The system provides the compound in a frame. The present invention relates to a method of preparing a Ca _{5 - x} Yb _x Al ₂ Sb ₆ compound having a low thermoelectric performance index by introducing Ca ^{2 +} / Yb ^{2 +} mixed cations and having a metal conduction behavior according to the molar ratio of Ca ^{2 +} / Yb ^{2 +} It is possible to economically produce a thermoelectric material having excellent thermoelectric performance by suggesting a method of converting the compound into a Ca _{5 - x} Yb _x Al ₂ Sb ₆ compound exhibiting an improved thermoelectric performance index due to a semiconductor conduction behavior by a simple heat treatment. Therefore, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ The system is expected to be used as a new thermoelectric material because of its excellent economical efficiency and thermoelectric efficiency compared to the conventional Ca ₅ Al ₂ Sb ₆ system compound.

Description

[0001] The present invention relates to a quartz-containing zirconium compound having a calcium / ytterbium mixed cation position and a method for producing the same. [0002]

The present invention relates to a four-component zeolitic compound containing Ca ^{2 +} / Yb ^{2 +} mixed cation positions and a method for producing the same, and more specifically, to Ca _{5 - x} Yb _x Al ₂ Sb ₆ Ca _{5 - x} Yb _x Al ₂ Sb ₆ reduced the lattice thermal conductivity ( κ _lat ) by introducing Ca ^{2 +} / Yb ^{2 +} mixed cations into the solid solution system And performing a heat treatment method after preparation of the compound for changing the system compound and the conductor-semiconductor property.

Thermoelectric (TE) materials and devices based on these thermoelectric materials have been considered as one of the excellent methods for reducing energy consumption around the world because they recover waste heat produced from various kinds of heat sources and convert them into electricity. The performance of a thermoelectric material is expressed by the thermoelectric figure of merit ( ZT ). The thermoelectric performance index, ZT, is expressed as σS ² T / κ , where σ means electrical conductivity; S denotes the Seebeck coefficient; T is the absolute temperature; κ means thermal conductivity. To increase ZT , the σ and S values should be high and the κ value should be low. However , a direct correlation between the above-mentioned ?, S and ? Values is hard to be found. Therefore , decoupling between the sigma, S and kappa values is a very important factor in improving ZT .

The main research directions for maximizing the thermoelectric performance of thermoelectric materials are 1) intrinsically low lattice thermal conductivity ( κ _latt ) characteristics through nano-structuring or hierarchical architecturing Studies for the discovery of thermally conductive materials; And 2) electronic band structure engineering studies to improve the power factor (PF =? S ² ) including resonance level effect and band convergence. Of the various candidate materials for thermoelectric applications, the titania is a relatively new material. The nipped-in phase is characterized not only by satisfying the conditions of the thermoelectric material due to complicated crystal structure and semiconductor behavior, but also showing excellent ZT. Recent studies have shown that A ₅ M ₂ Pn ₆ Series (system) has been actively studied. The A ₅ M ₂ Pn ₆ The series of thermoelectric materials are composed of Yb ₅ M ₂ Sb ₆ ( M = Al, Ga, In; Ba ₅ Al ₂ Bi ₆ A ₅ M ₂ Sb ₆ ( A = Ca, Sr, Eu; M = Al, Ga, In; Ca ₅ Ga ₂ Sb ₆ Type structure) system exists. In particular, the above A ₅ M ₂ Sb ₆ ( A = Ca, Eu; M = Al, Ga, In; Ca ₅ Ga ₂ Sb ₆ Type structure) p with respect to the A and M in the system is to perform the type of doping (p-type doping) was found to be the successful contributes to maximizing the ZT value _{Yb 5 Al 2 Sb 6 (Ba} 5 Al 2 Bi ₆ - type structure) It was confirmed that substitution of Yb with Sr in the system also helps to improve the ZT value. According to recent studies, loss of σ and S is not severe but Ca _x Yb _{1 - x} Zn ₂ Sb ₂ It was confirmed that the phonon scattering was increased due to the large amount of cation contrast in the system. Although cation-mixing using Ca ^{2 +} and Yb ^{2 +} as described above can improve ZT, A ₅ M ₂ Sb ₆ There were only a few attempts to mix the cation to the system.

The patent documents and references cited herein are hereby incorporated by reference to the same extent as if each reference was individually and clearly identified by reference.

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The inventors of the present invention have found that cationic mixing using Ca ^{2 +} and Yb ^{2 +} can improve ZT by using Ca _{5 - x} Yb _x Al ₂ Sb ₆ The incorporation of Ca ^{2 +} / Yb ^{2 +} mixed cations into the solid solution system reduced the lattice conductivity ( κ _lat ) and improved the thermoelectric performance index Ca _{5 - x} Yb _x Al ₂ Sb ₆ The present inventors have completed the present invention by experimentally confirming that the compound can be used as a new thermoelectric material by preparing a system compound. Also chemically identical Ca _{5 - x} Yb _x Al ₂ Sb ₆ The present inventors have experimentally confirmed that it is possible to induce structural modification to a compound having an improved thermoelectric performance by performing additional heat treatment on a compound having a low thermoelectric performance due to the difference in structure type despite the system compound.

Accordingly, an object of the present invention is to provide a process for preparing a compound represented by the formula Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0? X ? 2.0].

Another object of the present invention is to provide a process for the preparation of compounds of the formula Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X < 5.0].

 Ca is Ca; Yb is Ytterbium; The Al may be aluminum (Al); Sb is antimony.

It is still another object of the present invention to provide a composition for a thermoelectric material containing the above-mentioned groundnut compound.

Other objects and technical features of the present invention will be described in more detail with reference to the following detailed description, claims and drawings.

According to one aspect of the present invention, the present invention provides a composition comprising a compound represented by the formula Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0? X ? 2.0].

According to an embodiment of the present invention, the Ca may be calcium (Ca); Yb is Ytterbium; The Al may be aluminum (Al); Sb is antimony.

According to another embodiment of the present invention, the graft compound represented by the above formula is Ca ₄ YbAl ₂ Sb _{6 ,} Ca _{3 . 5} Yb _{1 . 5} Al ₂ Sb ₆ , and Ca ₃ Yb ₂ Al ₂ Sb ₆ .

According to another embodiment of the present invention, the crystal structure of the graft compound is composed of a Ca ₂ Ga ₂ Sb ₆ -type orthorhombic Pbam space group, and seven crystallographically independent atoms I have a position.

According to another embodiment of the present invention, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≦ x ≦ 2.0] The compound is prepared by preparing a raw material containing ytterbium (Yb), calcium (Ca), aluminum (Al), antimony (Sb) and aluminum (Al) By performing a heat treatment at a high temperature.

According to another aspect of the present invention, the present invention provides a composition comprising a compound represented by the formula Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X < 5.0].

According to an embodiment of the present invention, the Ca may be calcium (Ca); Yb is Ytterbium; The Al may be aluminum (Al); Sb is antimony.

According to one embodiment of the present invention, the graft compound represented by the above formula is CaYb ₄ Al ₂ Sb _{6 ,} Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb _{6 ,} and Ca ₂ Yb ₃ Al ₂ Sb ₆ .

According to another embodiment of the present invention, the crystal structure of the graft compound is composed of a Ca ₂ Ga ₂ Sb ₆ -type orthorhombic Pbam space group and has seven crystallographically independent atomic positions have and independent atom position in the seven crystallographic three calcium (Ca ^{2 +)} / Ytterbium (Yb ^{2 +)} mixture atom positions, one of aluminum (Al) atom position and three antimony (Sb) atom position to be.

According to another embodiment of the present invention, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 ≤ x <5.0] The compound is prepared by preparing a raw material containing ytterbium (Yb), calcium (Ca), aluminum (Al), antimony (Sb) and aluminum (Al) And then subjected to a first heat treatment to form Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X < 5.0] compound; And performing the secondary heat treatment (annealing) at 673-1023K for 14-30 days using a muffle furnace with the Ca _{5- x} Yb _x Al ₂ Sb ₆ [2.5? X <5.0] compound &Lt; / RTI &gt;

The present invention relates to a four-component zeolitic compound containing Ca ^{2 +} / Yb ^{2 +} at a mixed position and a process for producing the same. The present invention relates to a method for producing a thin film of Ca _{5 - x} Yb _x Al ₂ Sb ₆ Ca _{5 - x} Yb _x Al ₂ Sb ₆ with low lattice thermal conductivity ( κ _lat ) and improved thermoelectric performance index ( ZT ) by introducing Ca ^{2 +} / Yb ^{2 +} mixed cations into the solid solution system The system provides the compound in a frame. The present invention relates to a method of preparing a Ca _{5 - x} Yb _x Al ₂ Sb ₆ compound having a low thermoelectric performance index by introducing Ca ^{2 +} / Yb ^{2 +} mixed cations and having a metal conduction behavior according to the molar ratio of Ca ^{2 +} / Yb ^{2 +} It is possible to economically produce a thermoelectric material having excellent thermoelectric performance by suggesting a method of converting the compound into a Ca _{5 - x} Yb _x Al ₂ Sb ₆ compound exhibiting an improved thermoelectric performance index due to a semiconductor conduction behavior by a simple heat treatment. Therefore, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ The system is expected to be used as a new thermoelectric material because of its excellent economical efficiency and thermoelectric efficiency compared to the conventional Ca ₅ Al ₂ Sb ₆ system compound.

Figure 1 shows the crystal structures of the Ba ₅ Al ₂ Bi ₆ -type phase and the Ca ₅ Ga ₂ Sb ₆ -type phase observed along the c-axis direction by ball and stick and polyhedral representation methods. The same ideal unit sets on both types are indicated in rhombus. The tetrahedron [AlSb ₄ ] block and Sb-Sb cross-linking are represented by blue polyhedra and orange dumbbells, respectively. The atoms are represented by the following colors: M-gray, Al-blue, Sb-orange. The center of the table shows the change in the electrical conductivity with temperature and shows the metallic conduction behavior in the case of Ba ₅ Al ₂ Bi ₆ - type (blue dot) and Ca ₅ Ga ₂ Sb ₆ - type (red dot) Showing the conduction behavior.
2 is Ba ₅ Al ₂ Bi ₆ - type, Ca _{1. 58 (2)} Yb _{3 . 42} Al ₂ Sb ₆ and Ca ₅ Ga ₂ Sb ₆ -type Ca _{1 . 55 (1)} Yb _{3 . 45} Al ₂ Sb ₆ [Al ₂ Sb ₈ ] unit surrounded by eight M positions. The panel (a) is a Ba ₅ Al ₂ Bi ₆ -type Ca _{1 . 58 (2)} Yb _{3 . 42} Al ₂ Sb ₆ and the panel (b) shows the structure of Ca ₅ Ga ₂ Sb ₆ - type Ca _{1.55 (1)} Yb _3.45 Al ₂ Sb ₆ .
Figure 3 schematically shows the different packing patterns of the cation and anion polyhedrons observed between the Ba ₅ Al ₂ Bi ₆ -type (panel (a)) and the Ca ₅ Ga ₂ Sb ₆ -type (panel b) Show. The polyhedra are represented by the following colors: M 1 position - yellow, M 2 position - red, M 3 position - green, Al position - blue.
4 is Ca _{1. 55 (1)} Yb _{3 . 45} Al ₂ Sb ₆ (Ca ₅ Ga ₂ Sb ₆ - type). The atoms were marked with the following colors: M-gray, Sb-orange.
5 is annealed prior to performing (third heat _{treatment) Ba 5 Al 2 Bi 6 -} Ca 1 having a structure _{type. 5} Yb _{3 . 5} Al ₂ Sb ₆ compounds were subjected to PXRD pattern (panel (a)) and annealing (tertiary heat treatment) to form Ca ₁ Ga ₂ Sb ₆ -type converted Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ compound (panel (b)) with each of the simulated PXRD patterns.
FIG. 6 shows a phase diagram of a Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0? X <5.0] solid solution system. Ten compounds which were synthesized by arc melting method and were not annealed and 11 compounds synthesized by arc melting method and annealed were displayed according to their structures. The dashed line represents a temporary boundary between the Ca ₅ Ga ₂ Sb ₆ -type phase and the Ba ₅ Al ₂ Bi ₆ -type phase.
FIG. 7 shows a graph of the composition of CaYb ₄ Al ₂ Sb ₆ with a crystal structure of Ba ₅ Al ₂ Bi ₆ -type phase (panel (a)) and Ca ₅ Ga ₂ Sb ₆ -type phase (panel (b) DOS curve for compound, PDOS curve and COHP curve. In the DOS curve, PDOS curve, and COHP curve, the entire DOS curve is black-bold; Yb PDOS curves are in gray areas; The Ca PDOS curve is in the purple area; The Sb PDOS curve is in the orange region; Al PDOS curves are marked as green areas. PDOS curves (panel (a)) for p-orbital of Sb2 and Ca3 and PDOS curves (channel (b)) for p-orbital of Sb1 and Yb1 are shown for each type. The two COHP curves of panel (a) show the atomic interactions of Sb-Sb and Sb-Ca bridges, and the two COHP curves of panel (b) show Sb-Sb bridges and Sb-Yb bridges It shows the interatomic interaction of the bonds. The inner boxes of panels (a) and (b) show enlarged E _F 2eV to 1eV sections, and the dotted line shows the point where E _F is 0eV.
Panel (a) of Figure 8 shows the change in the electric conductivity (σ) according to the temperature of the panel (b) shows the change in ssibek coefficient (S) according to the temperature.
Panel of Figure 9 (a) shows the change in the total thermal conductivity is also according to the temperature (κ _tot) Panel (b) shows the change in the thermal performance index (figure-of-merit ZT) with temperature.

According to one aspect of the present invention, the present invention provides a Zintl compound represented by the following formula:

[Chemical Formula]

Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0? X ? 2.0]

Where Ca is calcium; Yb is Ytterbium; Al is aluminum; Sb is Antimony.

The above-mentioned groundnut compound means an intermetallic compound formed by an alkali metal and an alkaline earth metal and a group 13 (3B) to 15 (5B) group element, and has an intermediate property between an ionic crystal and a metal.

The _{Ca 5 - x Yb x Al 2} Sb 6 system compound is a compound showing semiconductor behavior _{A 5 M 2 Sb 6 (A} = Ca, Sr, Eu; M = Al, Ga, In) Ca and Yb cations to the system a compound And the thermoelectric performance index is improved.

According to one embodiment of the present invention, the graft compound represented by the above formula is Ca ₄ YbAl ₂ Sb _{6 ,} Ca _{3 . 5} Yb _{1 . 5} Al ₂ Sb ₆ , and Ca ₃ Yb ₂ Al ₂ Sb ₆ .

According to another embodiment of the present invention, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≦ x ≦ 2.0] The compound is prepared by preparing a raw material containing ytterbium (Yb), calcium (Ca), aluminum (Al), antimony (Sb) and aluminum (Al) Followed by heat treatment.

According to one embodiment of the present invention, Ca _{5 - x} Yb _x Al ₂ Sb ₆ (1.0 ≤ x ≤ 2.0) The compound is prepared by mixing raw materials Ca, Yb, Al, Sb and Al in a weight ratio of Ca: Ye: Al: Sb), followed by heat treatment using an arc melting method. (Ca: Yb: Al: Sb) at a weight ratio of 3: 2: 2: 6, and heat treatment (electric furnace) The Ca _{2 . 78 (2)} Yb _{2 . 22} Al ₂ Sb ₆ It has been confirmed that a compound can be synthesized. Therefore, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≦ x ≦ 2.0] can be prepared by mixing the raw materials at a weight ratio (Ca: Yb: Al: Sb) of 3: 2: 2: 6 to 4: 1: 2: 6 . Preferably, Ca ₄ YbAl ₂ Sb ₆ can be prepared by mixing raw materials at a weight ratio of Ca: Yb: Al: Sb = 4: 1: 2: 6 and performing heat treatment; The Ca _3.5 Yb _1.5 Al ₂ Sb ₆ may be prepared by mixing raw materials at a weight ratio of Ca: Yb: Al: Sb = 3.5: 1.5: 2: 6 and performing heat treatment; The Ca ₃ Yb ₂ Al ₂ Sb ₆ may be prepared by mixing raw materials at a weight ratio of Ca: Yb: Al: Sb = 3: 2: 2: 6 and performing heat treatment.

According to an embodiment of the present invention, the compound synthesized using the arc-melting method may be synthesized by performing the heat treatment on the mixture of the same raw materials at a temperature range of 1100-1500K. Preferably in the temperature range of 1200-1400K. More preferably at a temperature of 1323K. In the heat treatment process, the mixture of the raw materials is put into a muffle furnace, and the temperature is raised to 1323K at a temperature elevation temperature of 5K per hour, followed by heating for 24 hours.

According to one embodiment of the present invention, when the heat treatment is performed, Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≤ x ≤ 2.0] can be identified. The X-ray diffraction experiment using this can confirm the chemical composition and crystallographic structure of the compound synthesized through heat treatment. If the heating temperature is less than 1100K difficult to melt the raw material the Ca _{2. 78 (2)} Yb _{2 . 22} Al ₂ Sb ₆ It is difficult to crystallize the synthesized Ca _{2.78 (2)} Yb _2.22 Al ₂ Sb ₆ compound if the heating temperature exceeds 1500 K. Therefore, it is difficult to confirm the result of synthesis of the compound using X-ray diffraction .

According to one embodiment of the present invention, Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≤ x ≤ 2.0] The crystal structure of the compound consists of Ca ₂ Ga ₂ Sb ₆ -type orthorhombic Pbam space group and has seven crystallographically independent atomic positions.

In further embodiments, the above jinteul compound crystal structure is independent of atomic positions three calcium into seven crystallographic with (Ca ^{2 +)} / Ytterbium (Yb ^{2 +)} mixture atom positions, one of aluminum (Al) atomic position and three antimony (Sb) atomic positions.

According to another aspect of the present invention, the present invention provides a Zintl compound represented by the following formula:

[Chemical Formula]

Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X <5.0]

Where Ca is calcium; Yb is Ytterbium; Al is aluminum; Sb is Antimony.

The Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 < x < 2.0] compound and the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 ≤ x <5.0] Compounds have the same kinds of constituent materials but differ in the composition of cation atoms (Ca ^{2 +} and Yb ^{2 +} ) according to the mixing ratio of raw materials, and a unique structure type formed by the cation atoms The thermoelectric performance index of each compound is determined.

According to one embodiment of the present invention, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0? X < 2.0] compound exhibits relatively superior thermoelectric performance index because it is thermodynamically stable due to improved local symmetry compared to the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X <5.0] . The structural differences between the compounds are determined by the molar ratio of Ca / Yb when prepared by performing the same heat treatment step. Depending on the molar ratio of Ca / Yb this type of structure of the compound is Ca ₂ Ga ₂ Sb ₆ - type _{(Ca 5- x Yb x Al 2} Sb 6 [1.0 ≤ x <2.0] compound) or Ba ₅ Al ₂ Bi ₆ - Type (Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 ≤ x <5.0] compound), and the thermodynamic stability difference results in a difference in the thermoelectric performance index. Therefore, if a compound having a Ba ₅ Al ₂ Bi ₆ - type crystal structure can be converted to a compound having a Ca ₂ Ga ₂ Sb ₆ - type crystal structure by a suitable synthesis method, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ It is expected that the synthesis efficiency of the [1.0? X < 2.0] compound can be greatly improved.

According to an embodiment of the present invention, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 < x &lt; 5.0] The compound represented by the formula is any one selected from the group consisting of CaYb ₄ Al ₂ Sb _6, Ca _1.5 Yb _3.5 Al ₂ Sb _6, and Ca ₂ Yb ₃ Al ₂ Sb ₆ .

According to another embodiment of the present invention, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 ≤ x <5.0] The method for preparing the compound is to prepare a raw material containing ytterbium (Yb), calcium (Ca), aluminum (Al), antimony (Sb) and aluminum (Al) - Primary heat treatment is carried out by the melting method to obtain Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X < 5.0] compound; And Ca _{5 - x} Yb _x Al ₂ Sb ₆ (Annealing) at 673-1023K for 14-30 days using a muffle furnace after the [2.5 < x &lt; 5.0] compound is prepared by the arc-melting method.

Step 1: Primary heat treatment is performed to produce Ca _{5- x} Yb _x Al ₂ Sb ₆ [2.5? x  &Lt; 5.0] compound

The Ca of the present invention_{5 - x} Yb _x Al₂Sb₆ [2.5?x &Lt; 5.0 &gt;] compound is the Ca_{5 - x} Yb _x Al₂Sb₆ [1.0?x &Lt; 2.0 &gt; compound, the description is omitted to avoid duplication of the present specification. However,_{5 - x} Yb _x Al₂Sb₆ [2.5?x &Lt; 5.0 &gt; The production method of the compound is not limited to the Ca_{5 - x} Yb _x Al₂Sb₆ [1.0?x &Lt; 2.0 &gt;], there is a difference in the blending ratio of the raw materials. The Ca_{5 - x} Yb _x Al₂Sb₆ [2.5?x <5.0] may be prepared by mixing the raw materials at a weight ratio (Ca: Yb: Al: Sb) of 3.5: 1.5: 2: 6 to 1: 4: 2: 6. Preferably Ca_{One . 5}Yb_{3 . 5}Al₂Sb₆Can be prepared by mixing raw materials at a weight ratio of Ca: Yb: Al: Sb = 1.5: 3.5: 2: 6 and performing heat treatment; The Ca₂Yb₃Al₂Sb₆Can be prepared by mixing raw materials at a weight ratio of Ca: Yb: Al: Sb = 2: 3: 2: 6 and performing heat treatment; The CaYb₄Al₂Sb₆Can be prepared by mixing raw materials at a weight ratio of Ca: Yb: Al: Sb = 1: 4: 2: 6 and performing heat treatment.

Second step: Second heat treatment (annealing) is performed to form Ca _{5- x} Yb _x Al ₂ Sb ₆ [2.5? x  &Lt; 5.0] compound

The Ca _{2 . 78 (2)} Yb _{2 . 22} Al ₂ Sb ₆ The compound was subjected to a secondary heat treatment to produce Ca _{2 . 78 (2)} Yb _{2 . 22} Al ₂ Sb ₆ Compounds are synthesized. The Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≤ x ≤ 2.0] The compound has a Ca ₂ Ga ₂ Sb ₆ - type crystal structure. On the contrary, the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 ≤ x ≤ 5.0] The compound has a crystal structure of Ba ₅ Al ₂ Bi ₆ - type. The Ca ₂ Ga ₂ Sb ₆ - type crystal structure and the Ba ₅ Al ₂ Bi ₆ - type crystal structure are Ca _{5 - x} Yb _x Al ₂ Sb _{6 -} They have the same chemical composition but different crystallographic structures and different thermoelectric properties. The difference in crystallographic structure is due to the difference in Sb-Sb bonding distance and geometric arrangement.

According to an embodiment of the present invention, the Ca ₂ Ga ₂ Sb ₆ -type crystal structure has a shorter Sb-Sb bond distance than the Ba ₅ Al ₂ Bi ₆ -type crystal structure, The local coordination geometry structure of the crystal is not greatly changed due to the long bonding distance, and the local symmetry is improved, thereby improving the thermodynamic stability. The Ca _{5 - x} Yb _x Al ₂ Sb ₆ having the Ba ₅ Al ₂ Bi ₆ - type crystal structure prepared in the first step [2.5 ≤ x ≤ 5.0] The compound is Ca _{5 - x} Yb _x Al ₂ Sb ₆ with the Ca ₂ Ga ₂ Sb ₆ - type crystal structure There is a disadvantage in that the thermodynamic performance index is low because the thermodynamic stability is low compared with the compound. In the present invention, the compound of Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 ≦ x ≦ 5.0] prepared in the first step is subjected to an additional heat treatment (secondary heat treatment, annealing) ₅ Al ₂ Bi ₆ -type to Ca ₂ Ga ₂ Sb ₆ -type.

According to one embodiment of the present invention, the secondary heat treatment is performed at 673-1023K for 14-30 days in a tertiary heat treatment (annealing). If the heat treatment temperature is less than 673 K, the crystal structure transformation is not efficient. If the heat treatment temperature is 1023 K or higher, the crystals produced in the first step may be dissolved.

According to another embodiment of the present invention, the Ba ₅ Al ₂ Bi ₆ -type and Ca ₂ Ga ₂ Sb ₆ -type Ca _{5 - x} Yb _x Al ₂ Sb ₆ -type prepared in the first and second steps [2.5 ≤ x ≤ 5.0] crystal with the compound structure is made by orthorhombic space group Pbam (orthorhombic space group Pbam), and has an independent atom in position 7 crystallographic. In addition, an independent atom position as significant of the seven decision is a three calcium (Ca ^{2 +)} / Ytterbium (Yb ^{2 +)} mixture atom positions, one of aluminum (Al) atom position and three antimony (Sb) atom position.

According to still another aspect of the present invention, there is provided a thermoelectric material composition comprising a hydrate compound produced by the above-described process.

Example

Materials and Methods

1. Ca _{2.78 (2)} Yb _2.22 Al ₂ Sb ₆  Compound synthesis

Preparation of all samples was carried out in a glove box filled with inert argon (Ar) gas, in an atmosphere in which oxygen and water were present at 0.1 ppm or less, or in a vacuum state. The raw materials used in the experiment were Yb-ingot, 99.9%; Ca-shot, 99.5%; Al-piece, 99.9%; And Sb-shot, 99.9%. The weakly browned portions of the Yb and Ca surfaces were removed using a skelpper or metal brush in the glove box prior to use in the reaction. Ca _{2.78 (2)} Yb _2.22 Al ₂ Sb ₆ was prepared using a conventional high temperature reaction (electric furnace method). (Ca: Yb: Al: Sb) at a weight ratio of 3: 2: 2: 6 in an atmosphere containing argon gas, and then sealed in an Nb- ampule (length 4 cm, diameter 1 cm) . In the Nb-ampoule, a vacuum fused silica jacket was used as a secondary container to prevent the oxidation of the raw material that has entered the inside of the Nb-ampule. The Nb-ampoule into which the Ca, Yb, Al and Sb mixture (reaction mixture) was injected was inserted into the secondary container and then sealed. The secondary container having the reaction mixture inserted therein was placed in a muffle furnace, and then heated to 1323 K at a heating rate of 5 K (Kelvin, Kelvin) per hour and heated for 24 hours. After the heat treatment, the muffle was cooled to room temperature at a cooling rate of 10K per hour. The heat treatment results, Ca _{2. 78 (2)} Yb _{2 . 22} Al ₂ Sb ₆ was formed as a small single crystal with an irregular shape and metallic luster.

2. Ca by using arc-melting synthesis method _{5- x} Yb _x Al ₂ Sb ₆  Synthesis of solid solution series compounds

The Ca _{2 . 78 (2)} Yb _{2 . X} Yb _{- 22} Al ₂ different Ca in solution composition on the Sb ₆ compound and Yb molar ratio Ca ₅ having the (Ca / Yb ratio = 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.3, 4.5, 5.0) of _x Al ₂ Sb ₆ solid solution series compounds were synthesized. The synthesis of the above various types of Ca _{5 - x} Yb _x Al ₂ Sb ₆ solid solution series compounds is the same as the synthesis of Ca _{2.78 (2)} Yb _2.22 Al ₂ Sb ₆ compounds except that the arc melting method There is a difference. Also unlike the conventional Yb ₅ Al ₂ Sb ₆ system, the target compound series was successfully synthesized without the additional use of Ge or Si used as a catalyst for crystal formation. The compounds prepared by each reaction were found to form mono-phase crystals of Ba ₅ Al ₂ Bi ₆ -type or Ca ₅ Ga ₂ Sb ₆ -type depending on the Ca / Yb molar ratio, It was confirmed that it was stable to air or moisture for 3 weeks. In order to perform the single-crystal X-ray diffraction (SXRD) experiment, larger single crystal growth was attempted. For this, Yb-rich Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ (nominal composition) was annealed at 1023 K for 2 weeks (second heat treatment). As a result of the annealing, it was confirmed that the solid phase structure transformation from the original Ba ₅ Al ₂ Bi ₆ -type phase to the Ca ₅ Ga ₂ Sb ₆ -type phase was achieved. Five different Yb-rich Ca _{5 - x} Yb _x Al ₂ Sb ₆ ( x = 3.0, 4.0, and 1.0) were synthesized through an arc-melting synthesis method and identified as Ba ₅ Al ₂ Bi ₆ - 4.3, 4.5, and 5.0) compounds also exhibited the Yb-rich Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ (nominal composition) at 1023 K for two weeks. Results Ca ₂ Yb ₃ Al ₂ Sb ₆ And CaYb ₄ Al ₂ Sb ₆ (nominal composition) were found to have undergone a solid phase transformation on the Ca ₅ Ga ₂ Sb ₆ -type phase. The combined Ca ₁ to confirm that the appropriate annealing temperature and time required for the conversion of a structure type based on the _{result. 5} Yb _{3 . 5} Al ₂ Sb ₆ samples were annealed at 673 K and 873 K for 2 weeks and 1023 K for one month, respectively. The reason why the annealing temperature is set at 1023K is that the crystal is decomposed when the annealing temperature exceeds 1073K as a result of thermal gravimetric analysis.

3. Structure analysis by X-ray diffraction analysis

Powder X-ray diffraction (PXRD) experiments were performed on all 10 representative compounds of Ca _{5 - x} Yb _x Al ₂ Sb ₆ (1.0 ≤ x ≤ 5.0) solid solution systems. In addition, single crystal X-ray diffraction (SXRD) experiments were performed on four of the ten compounds. The PXRD pattern was collected at room temperature using a Bruker D8 diffractometer equipped with monochromatic Cu K α ₁ radiation ( λ = 1.54059 A) and an area detector. The step size for collecting the pattern was set at 0.05 deg. In a range of 15 deg. 2 &amp;thetas; 85 deg. And the sample was exposed to X-rays for a total of 1 hour. The purity of the representative compound for X-ray diffraction was confirmed by comparing the collected powder pattern with the pattern simulation results of one or two structure types. In order to check the lattice parameter of each unit cell, all peaks of each powder pattern were indexed using a Reitica program. Single crystal X-ray diffraction (SXRD) data was obtained from Mo Kα ₁ Were collected using a Bruker SMART APEX2 CCD-based diffractometer fitted with radiation ( lambda = 0.71073A). First, from a crushed crystal sample, a silver single crystal with a silver metallic luster was selected and a rapid scan was performed to simply confirm the quality of the crystal. The best quality crystal was selected through the quick scan and the entire data was collected using Bruker's APEX2 program. Data summarization, integration, and unit grid analysis were performed using the SAINT program, and an equivalent semi-empirical absorption correction was performed using the SADABS program. The complete diffraction data sets of the four compounds are in good agreement with the tetragonal crystal system and all of the crystal structures suitable for the Ba ₅ Al ₂ Bi ₆ -type or Ca ₅ Ga ₂ Sb ₆ -type are all in the Pbam space group ( space group). The detailed crystal structures were determined using the direct method and converged using the full matrix least-squares method for F ² . The refined parameter includes a scale factor, an atomic position with respect to an anisotropic displacement parameter, an extinction coefficient, and an occupancy factor of the Yb / Ca mixed site . During the last structural analysis phase, atomic positions were normalized using STRUCTURE TIDY. Important crystal data, the atomic position of the atom transfer parameter and the distance between the selected atoms are listed in Tables 1-3. Additional details on each crystal structure can be found at Fachinformationszentrum Karlsruhe. The deposit number of each crystal structure is CSD-432095: Ca _{3 . 60 (2)} Yb _{1 . 40} Al ₂ Sb ₆ ; CSD-432096: Ca _{2 . 78 (2)} Yb _{2 . 22} Al ₂ Sb ₆ ; CSD-432097: Ca _{1.58 (2)} Yb _3.42 Al ₂ Sb ₆ ; And CSD-432098: Ca _{1.55 (1)} Yb _3.45 Al ₂ Sb;

4. Computation and analysis of electronic structures

A series of TB-LMTO-ASA calculations were performed using the Stuttgart TB-LMTO47 program to verify the overall electronic structure and chemical bonding of representative compounds. Theoretical structural model corresponding to Ba ₅ Al ₂ Bi ₆ -type structure or Ca ₅ Ga ₂ Sb ₆ -type structure (Model 1: Ba ₅ Al ₂ Bi ₆ - type structure corresponding to the ideal compound "CaYb ₄ Al ₂ Sb ₆ " Type structure, Model 2: Ca ₅ Ga ₂ Sb ₆ - type structure). The lattice parameters for Model 1 and Model 2 are Ca _{1 . 58 (2)} Yb _{3 . 42} Al ₂ Sb ₆ And Ca _{1 . 55 (1)} Yb _{3 . 45} Al ₂ Sb _{6 from} the SXRD results. The lattice parameters of Model 2 were adjusted to be similar to the total unit cell volume of Model 1 by fine modification (see Table 1). To apply &quot; CaYb ₄ Al ₂ Sb _{6 &} quot ;, which is an ideal composition for the above models, Ca atoms were assigned to the M 3 position ( Wyckoff 2 a site). According to the SXRD results, it was confirmed that the M 3 position was the largest Ca position among the three mixed cation positions. The local density approximation was used for the transformation and correlation, and all relative effects were calculated taking into account the scalar relativistic approximation except spin-orbit coupling. The space in the ASA method was filled with the overlap of Wigner-Seitz (WS) atoms. The symmetry of the potential was considered inside each WS atomic region, and the integrated calibration was used to calibrate the embedded part. The radius of the WS atomic radius was determined by an automated procedure and was calculated taking into account the superimposition potential which can be used to predict the most complete potential. The overlay should not be too large. Because the error of the kinetic energy reflected by the integrated calibration is proportional to the quadrature of the relative spherical overlap. The WS atomospheres used for the above structure type area were Ca = 2.14A, Yb = 2.14A, Al = 1.55A, and Sb = 1.72A. The orbitals used in each atom are as follows; Ca is 4 s , 4 p and 3 d orbitals; Yb is 6 s , 6 p , and 5 d orbitals; Al s is 3, p 3 and 3 d orbitals; Sb is 5 s , 5 p , 5 d and 4 f orbitals. Yb 6 p , Ca 4 p , Al 3 d and Sb 5 d and 4 f orbitals And processed using the Lowdin downfolding technique. The k-space integration was also performed using the tetrahedron method and the self-consistent charge density was calculated using the 343 k-point, which is no longer reducible in the Brillouin zone .

5. Thermal analysis

Ca ₁ using a thermal analyzer, _{SDT2960. 5} Yb _{3 . 5} Al ₂ Sb ₆ were subjected to thermal gravimetric analysis to analyze the thermal stability of the compounds. About 20 mg of the sample was placed in an alumina crucible and sealed, and then heated at a rate of 10 K / min at a room temperature to 1273 K under a constant nitrogen flow. Thereafter, it was naturally cooled to room temperature.

6. Electrical conduction characteristics

Three samples of Ca _1.5 Yb _3.5 Al ₂ Sb ₆ (nominal composition) employed on the Ba ₅ Al ₂ Bi ₆ -type or Ca ₅ Ga ₂ Sb ₆ -type subjected to different annealing to determine the electrical conductivity characteristics Was cut into a rectangular shape (3 mm x 3 mm x 9 mm) and then washed. The long direction of the rectangular sample corresponds to the specified electrical conductivity. The electrical conductivity (σ) and The Seebeck coefficient ( S) was measured simultaneously at room temperature up to 700 K using a ULVAC-RIKO ZEM-3 instrument system under helium atmosphere.

7. Thermal conductivity

The thermal diffusivity (D) is the ratio of the three Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ Samples were measured by a flash diffusivity method using a Netzsch LFA457 micro flash device and were performed under an inert atmosphere of 700K at room temperature. The flash diffusion method was performed by irradiating a front surface of a disc-shaped sample with a short laser burst and recording the temperature of the back surface of the sample on the back surface using an infrared detector. The thermal conductivity (κ) was calculated from the equation κ = DCPρ . In the above equation, ρ and Cp denote density and heat capacity, respectively. In the calculation of the thermal conductivity, Dulong-Petit value (3R / atom, R is the gas constant), the sum was used as Cp the total thermal conductivity (κ _tot) is lattice conductivity (κ _latt) and electronic conductivity (κ _elec) Respectively. κ _elec is expressed by the Wiedemann-Franz law ( κ _elec = L s σT ), where L is the Lorentz number with temperature. The L value was estimated from a single parabolic band (SPB) model from a temperature dependent Seebeck coefficient based on the assumption of acoustic phonon scattering. The κ _latt was _calculated from the relation ( κ _latt = κ _tot - κ _elec ).

Experiment result

1. Crystal structure of a compound

The solid solution system of Ca _{5 - x} Yb _x Al ₂ Sb ₆ (1.0 ≤ _x ≤ 5.0) with Ca ^{2 +} / Yb ^{2 +} mixed cation was synthesized by arc melting and analyzed by PXRD and SXRD It was confirmed that the two kinds of crystallization were slightly different structure types. Table 1 shows the SXRD analysis results for Ca _{5 - x} Yb _x Al ₂ Sb ₆ (1.40 (2) ≤ x ≤ 3.45 (1)) systems. In the table below, ^a R ₁ is Σ || F _o | - | F _c || / Σ | F _o |. In addition, wR ₂ is ^{_{[Σ [w (F o 2}} - F c 2] / Σ [w (F o 2) 2]] 1/2 means wherein w is ^{_{1 / [σ 2 F o 2}} + (A- P ² + B - P ], P means ( F _o ² +2 F _c ² ) / 3, and A and B mean weight coefficients.

Empirical formula Ca _{3.60 (2)} Yb _1.40 Al ₂ Sb ₆ Ca _{2.78 (2)} Yb _2.22 Al ₂ Sb ₆ Ca _{1.58 (2)} Yb _3.42 Al ₂ Sb ₆ Ca _{1.55 (1)} Yb _3.45 Al ₂ Sb ₆ Structure-type Ca ₅ Ga ₂ Sb ₆ Ca ₅ Ga ₂ Sb ₆ Ba ₅ Al ₂ Bi ₆ Ca ₅ Ga ₂ Sb ₆ Crystal system Orthorhombic Space group Pbam (No. 55) Unit cell dimensions (A) a = 11.962 (6) a = 12.032 (1) a = 7.325 (1) a = 12.001 (1) b = 13.929 (8) b = 14.023 (1) b = 22.904 (2) b = 13.993 (1) c = 4.427 (2) c = 4.453 (1) c = 4.409 (1) c = 4.446 (1) Volume (A ³ ) 737.50 (70) 751.37 (3) 739.82 (11) 746.51 (3) _calcd d (g / cm ³⁾ 5.273 5.655 6.459 6.419 Data / restraints / parameters 922/0/44 972/0/45 1040/0/44 1274/45 R ^a indices ( I > 2 σ _I ) R ₁ = 0.0321 R ₁ = 0.0214 R ₁ = 0.0300 R ₁ = 0.0217 wR ₂ = 0.0752 wR ₂ = 0.0536 wR ₂ = 0.0624 wR ₂ = 0.0394 R ^a indices (all data) R ₁ = 0.0454 R ₁ = 0.0225 R ₁ = 0.0327 R ₁ = 0.0284 wR ₂ = 0.0824 wR ₂ = 0.0541 wR ₂ = 0.0643 wR ₂ = 0.0408 Goodness-of-fit on F ² 1.134 1.218 1.212 1.127 Largest diff. peak / hole
(e / A ³ ) 1.672 / -1.568 1.467 / -1.110 2.813 / -2.643 1.298 / -1.553

Ca _{5 - x} Yb _x Al ₂ Sb ₆ Three compounds with x = 1.0, 1.5 and 2.0 (nominal composition) in the representative solid solution compounds were crystallized into Ca ₅ Ga ₂ Sb ₆ -type structure and x = 2.5, 3.0, 3.5, 4.0, 4.3, 4.5 and 5 Nominal composition) were crystallized into a Ba ₅ Al ₂ Bi ₆ -type structure as in FIG. The two structural types belong to the orthorhombic Pbam space group (Pearson code oP 26, Z = 2) and were confirmed to contain seven crystallographically independent atomic positions in each unit cell. The seven crystallographically independent atomic positions were confirmed to consist of three Ca ^{2 +} / Yb ^{2 +} mixed positions, one Al position and three Sb positions (see Table 2).

Atom Wyckoff site Occupation
(Ca ^{2 +} / Yb ^{2 +} ) x y z U _eq ^a (A ² ) Ca _{3.60 (2)} Yb _1.40 Al ₂ Sb ₆ (Ca ₅ Ga ₂ Sb ₆ -type) M 1 ^b 4 g 0.71 (1) /0.29 0.0921 (1) 0.2477 (1) 0 0.0145 (4) M 2 ^b 4 g 0.69 (1) / 0.31 0.3261 (1) 0.0134 (1) 0 0.0155 (4) M 3 ^b 2 a 0.81 (1) /0.19 0 0 0 0.0166 (7) Al 4 h One 0.3308 (3) 0.2118 (3) 1/2 0.0159 (7) Sb1 4 h One 0.0240 (1) 0.4001 (1) 1/2 0.0147 (2) Sb2 4 h One 0.1565 (1) 0.0943 (1) 1/2 0.0140 (2) Sb3 4 g One 0.3390 (1) 0.3211 (1) 0 0.0140 (2) Ca _{2.78 (2)} Yb _2.22 Al ₂ Sb ₆ (Ca ₅ Ga ₂ Sb ₆ -type) M 1 ^b 4 g 0.53 (1) /0.47 0.0916 (1) 0.2478 (1) 0 0.0095 (2) M 2 ^b 4 g 0.51 (1) /0.49 0.3266 (1) 0.0141 (1) 0 0.0118 (2) M 3 ^b 2 a 0.71 (1) /0.29 0 0 0 0.0098 (3) Al 4 h One 0.3306 (1) 0.2123 (2) 1/2 0.0106 (4) Sb1 4 h One 0.0239 (1) 0.4001 (1) 1/2 0.0094 (1) Sb2 4 h One 0.1564 (1) 0.0944 (1) 1/2 0.0086 (1) Sb3 4 g One 0.3387 (1) 0.3212 (1) 0 0.0081 (1) Ca _{1.58 (2)} Yb _3.42 Al ₂ Sb ₆ (Ba ₅ Al ₂ Bi ₆ -type) M 1 ^b 4 g 0.66 (1) /0.34 0.2662 (1) 0.2523 (1) 0 0.0062 (2) M 2 ^b 4 g 0.69 (1) / 0.31 0.4479 (1) 0.0888 (1) 0 0.0070 (2) M 3 ^b 2 a 0.73 (1) /0.27 0 0 0 0.0060 (3) Al 4 h One 0.3141 (5) 0.3782 (2) 1/2 0.0071 (7) Sb1 4 h One 0.0133 (1) 0.3122 (1) 1/2 0.0053 (2) Sb2 4 h One 0.1992 (1) 0.4944 (1) 1/2 0.0097 (2) Sb3 4 g One 0.0230 (1) 0.1358 (1) 0 0.0054 (2) Ca _{1.55 (1)} Yb _3.45 Al ₂ Sb ₆ (Ca ₅ Ga ₂ Sb ₆ -type) M 1 ^b 4 g 0.28 (1) /0.72 0.0911 (1) 0.2477 (1) 0 0.0063 (1) M 2 ^b 4 g 0.26 (1) /0.74 0.3273 (1) 0.0146 (1) 0 0.0076 (1) M 3 ^b 2 a 0.46 (1) /0.54 0 0 0 0.0060 (2) Al 4 h One 0.3305 (2) 0.2127 (1) 1/2 0.0071 (4) Sb1 4 h One 0.0244 (1) 0.3998 (1) 1/2 0.0064 (1) Sb2 4 h One 0.1561 (1) 0.0942 (1) 1/2 0.0061 (1) Sb3 4 g One 0.3380 (1) 0.3220 (1) 0 0.0059 (1)

Table 2 above shows the Equivalent Isotropic Displacement Parameters ( U ) determined from the SXRD refinement results for the Ca _{5 - x} Yb _x Al ₂ Sb ₆ (1.40 (2) ≤ x ≤ 3.45 _eq ) and atomic coordinates. Wherein ^a U _eq of Table 2 are defined as one of three signs of the orthogonal U _ij tensor (tensor) ^b wherein M is defined as the position of the mixed cations Ca ^{2 +} / Yb ^{2 +.} It has been found that the overall crystal structure of the compounds corresponding to the two peculiar phases is closely related to the respective structural building blocks, and the structural building blocks are composed of the dimerized tetrahedral [AlSb ₄ ] moieties, And [AlSb ₄ ] units were filled by isolated Ca ^{2 +} / Yb ^{2 +} mixed cations. In particular, the [Al ₂ Sb ₈ ] units of the two structural types share an Sb atom at four corners and are connected together along the c-axis direction to form an infinite one-dimensional (1D) double chain . There are several structural differences in the two phases. The difference includes the geometry of the [Al ₂ Sb ₈ ] unit and the geometry between the one-dimensional double chain and the Ca ^{2 +} / Yb ^{2 +} mixed cation. For example, the Sb-Sb bond distance connecting the dimerized [AlSb ₄ ] moieties is Ca _{1 . 58 (2)} Yb _{3 . 42} Al ₂ Sb ₆ (Ba ₅ Al ₂ Bi ₆ - type), whereas Ca _{1 . 58 (2)} Yb _{3 . 42} Al ₂ Sb ₆ (Ca ₂ Ga ₂ Sb ₆ - type) (see FIG. 2). In _{addition, Ca 1.58 (2) Yb 3.42} Al 2 Sb 6 (Ba 5 Al 2 Bi 6 - type) Sb- M bond distance and Sb-Al _1.58 Ca coupling distance from each 3.12A (1) and 2.79A (4) of ₍₂₎ Yb _3.42 Al ₂ Sb ₆ (Ca ₂ Ga ₂ Sb ₆ -type) to 3.18A (2) and 2.81A (2), respectively, so that the specific binding (Sb -Sb bond) (see Table 3).

Distance Structure-type Atomic pair Ca _{3.60 (2)} Yb _1.40 Al ₂ Sb ₆ Ca _{2.78 (2)} Yb _2.22 Al ₂ Sb ₆ Ca _{1.58 (2)} Yb _3.42 Al ₂ Sb ₆ Ca _{1.55 (1)} Yb _3.45 Al ₂ Sb ₆ Ca ₅ Ga ₂ Sb ₆
and
Ba ₅ Al ₂ Bi ₆ Al-Sb1 2.789 (4) 2.811 (2) 2.673 (4) 2.809 (2) Al-Sb2 2.651 (4) 2.670 (2) 2.792 (4) 2.671 (2) Al-Sb3 (x2) 2.688 (3) 2.702 (1) 2.703 (2) 2.699 (1) Ca ₅ Ga ₂ Sb ₆ Sb1-Sb1 2.837 (2) 2.859 (1) - 2.866 (1) Ba ₅ Al ₂ Bi ₆ Sb2-Sb2 - - 2.930 (1) - Ca ₅ Ga ₂ Sb ₆ M 1-Sb 2 (x 2) 3.171 (2) 3.193 (1) - 3.188 (1) M 1-Sb 1 (× 2) 3.175 (2) 3.191 (1) - 3.179 (1) M 2 -Sb 1 (× 2) 3.456 (2) 3.470 (1) - 3.460 (1) M 2 -Sb 3 3.329 (2) 3.358 (1) - 3.347 (1) M 3-Sb 2 (× 4) 3.182 (1) 3.202 (1) - 3.191 (1) M 3-Sb 3 (× 2) 3.150 (2) 3.170 (1) - 3.160 (1) Ba ₅ Al ₂ Bi ₆ M 1-Sb 1 (× 2) - - 3.212 (1) - M 1-Sb 1 (× 2) - - 3.190 (1) - M 2 -Sb 2 (× 2) - - 3.448 (1) - M 2 -Sb 3 - - 3.293 (1) - M 3-Sb 2 (× 4) - - 3.120 (1) - M 3-Sb 3 (× 2) - - 3.114 (1) -

FIG different geometric arrangement of the two represents a one-dimensional chain double anion and Ca ^{2 +} / Yb ^{2 +} cation mixing between, as shown in Figure 3 may be represented schematically by the packing pattern of the three cations polyhedron. Sb-Sb binding distances in the structural units present on the Ba ₅ Al ₂ Bi ₆ -type phase and the Ca ₅ Ga ₂ Sb ₆ -type as shown in the following thermoelectric performance measurements, Lt; / RTI &gt; and &lt; RTI ID = 0.0 &gt; semiconductor conduction behavior. &Lt; / RTI &gt; Interestingly, Ca ^{+ 2} and Yb ^{2 +} particular preference location (site-preference) between the Ca ₅ Ga ₂ Sb ₆ - have been identified in the process of analyzing the structure of crystal type on the structure. The position preference is Ca ^{2 +} M 3 is the preferred location, and Yb ^{2 +} has been found to prefer a location M 2 (see Table 2). The position preference can be easily understood by considering a criterion based on a size factor. The criterion can be established based on whether the size between the central cation and the local coordination environment around the cation coincides. As shown in Figure 4, the Ca ₅ Ga ₂ Sb ₆ -type phase comprises three different types of cation positions. Both the M 1 and M 3 positions are surrounded by six Sb atoms forming two finely distorted octahedra, and the M 2 position consists of seven Sb atoms forming a square pyramid with two sides covered by one atom. Therefore, relatively large coordinated to M 2 7 position according to the size factor is based on Ca ^{2 +} cations _{(r (Ca 2 +) =} 1.00A) is greater Yb ^{2 +} cation is relatively large compared to the ^{(r (Yb 2 +) =} 1.02 A). Moreover, the two 6-coordination in the octahedral positions M 3 position is found to be slightly more symmetrical than M 1 position in the torsion angle (0.00 ° vs 0.75 °) of the coupling distance of M and Sb-Sb-Sb-Sb- M (See FIG. 4). Therefore, it is judged that the M 3 position on the Ca ₅ Ga ₂ Sb ₆ - type is occupied by the Ca ^{2 +} cation having a relatively small size.

2. Solid State Conversion

Performing the annealing in the two weeks 1023K Yb-rich compound solid structure conversion of _{(Ca 1 5 Yb 3 5 Al} 2 Sb 6.. The nominal composition), i.e., _{Ba 5 Al 2 Bi 6 - Ca} 5 Ga 2 Sb from the type of the ₆ - type structural transformation occurs. The PXRD patterns and Ca _{1 . 58 (2)} Yb _{3 . 42} Al ₂ Sb ₆ (Ba ₅ Al ₂ Bi ₆ - type) and Ca _{1 . 55 (1)} Yb _{3 .} SXRD results for ₄₅ Al ₂ Sb ₆ (Ca ₅ Ga ₂ Sb ₆ - type) confirmed that the two compounds had unique crystal structures (see FIG. 5 and Table 1). Interestingly, it has been confirmed that the above structural transformation is observed only in some Yb-rich Ba ₅ Al ₂ Bi ₆ -type compounds and has irreversible properties. It was also confirmed that the Ca-rich Ca ₅ Ga ₂ Sb ₆ -type compound did not undergo structural modification to the Ba ₅ Al ₂ Bi ₆ -type structure. The irreversible structural transformation is understood in that the Ca ₅ Ga ₂ Sb ₆ -type crystal structure is relatively more symmetric. 1, the same imaginary unit cell (red shaded rhombus box) can be selected for each structure type. However, the arrangement of the unit cells is relatively simpler and symmetrical on the Ca ₅ Ga ₂ Sb ₆ -type than on the Ba ₅ Al ₂ Bi ₆ -type phase. In the case of the Ca ₅ Ga ₂ Sb ₆ -type, the unit cells are located one above the other and form one kind of one-dimensional (1D) "strip" along the b-axis direction. Further, two adjacent 1D strips are pushed up and down by a quarter length of the unit cell along the b-axis direction. On the other hand, in the case of the Ba ₅ Al ₂ Bi ₆ -type, the same unit cells form a 1D strip of a similar type along the a-axis direction. However, the 1D strips located above and below the center strip are pushed left or right and are directed in opposite directions from the center as if there were a glide-plane between two adjacent 1D strips. In conclusion, the post-annealing process is a thermodynamically stable Ba ₅ Al ₂ Bi ₆ -type phase which is dynamically stable and has relatively low local symmetry, and has a relatively high local symmetry ₅ Ga ₂ Sb ₆ -type phase. Based on the results of the solid phase structure modification, the appropriate annealing temperature and duration were determined to enable the modification of the structure type. To this end, the five Ca _{1 . 5} Yb _{3 .} Experiments were conducted on various experimental conditions in which an annealing temperature range of 673 to 1023 K and an annealing duration of 1 week to 1 month were combined for ₅ Al ₂ Sb ₆ samples. The PXRD pattern for the five samples shows that successful structural modifications were made in all the samples, particularly the annealing temperature was reduced to 673 K and annealing continued for one week to activate the structural strain. Finally, experiments were conducted on the minimum Ca requirements for structural transformation. Four Ca _{5 - x} Yb _x Al ₂ Sb _{6 with} x = 4.0, 4.3, 4.5 and 5.0 The compound (Yb-rich compound) was prepared and annealed at 1023 K for 2 weeks. It was analyzed by collecting a PXRD pattern for the compound prepared through the above experiment Ca _{0. 7} Yb _{4 . 3} Al ₂ Sb ₆ , Ca _{0 . 5} Yb _{4 . 5} Al ₂ Sb ₆ And Yb ₅ Al ₂ Sb ₆ is original Ba ₅ Al ₂ Bi ₆ after annealing - while maintaining type phase, CaYb ₄ Al ₂ Sb ₆ is _{Ba 5 Al 2 Bi 6 - Ca} 5 Ga 2 Sb 6 from the type of phase- It was confirmed that the structural conversion into the type was performed. Detailed structural information including the phase boundary and phase transition temperature between the Ca ₅ Ga ₂ Sb ₆ type phase and the Ba ₅ Al ₂ Bi ₆ -type phase is shown in Ca _{5 - x} Yb _x Al ₂ Sb ₆ solid solution since optimize the thermal performance of the system, the above two-phase crystal in a direction forming the phase equilibrium between the (phase) on the basis of the series of experiments _{Ca 5- x Yb x Al 2 Sb} 6 [1.0 ≤ x <5.0] system, (Fig. 6). The crystallographic phase-diagram of Fig. The Ca ₅ Ga ₂ Sb ₆ -type structure exhibiting the above semiconductor behavior can be obtained by post heat treatment ( T ≥ 673K), ca, x = 2 of Ca _{5 - x} Yb _x Al ₂ Sb ₆ structure up to x = 4 While the non - annealed compound was found to be a Ba ₅ Al ₂ Bi ₆ - type structure with metal conduction behavior at x ≥ 2.5.

3. Electronic structure and chemical bonding

A series of theoretical calculations were performed using the TB-LMTO-ASA method to understand the relationship between the total electron energy of the two structural types, the structural transformation between the overall electronic structure and the individual atomic orbital distribution, and the total electron energy. First, Ca ₁ in the Ba ₅ Al ₂ Bi ₆ - type structure _{. 5} Yb _{3 . 5} Al ₂ Sb ₆ - type structure, the total electron energies of the two structural types were compared with each other to confirm which structural type was more advantageous in terms of energy. Type structure, and Ca ₅ Ga ₂ Sb ₆ - - type gujoeul with selecting any one of the structures Ba ₅ Al ₂ Bi ₆ - type of the virtual structure model, and Ca ₅ Ga ₂ Sb ₆ - type Ba ₅ Al ₂ Bi ₆ For this , Respectively, and an ideal composition of "CaYb ₄ Al ₂ Sb ₆ " was applied to all of these models according to the experimental need. Calculation conditions, including the calculation conditions related to the WS radius and the total number of k-points that can no longer be reduced, except for some essential structural differences described above, were calculated and maintained in both models. As a result of the calculation, it was confirmed that the total electron energy of the Ca ₅ Ga ₂ Sb ₆ -type virtual structure model is 0.66eV / fu as low as the total electron energy of the Ba ₅ Al ₂ Bi ₆ -type virtual structure model. A difference between the total energy E is _{Ca 5 Ga 2 Sb 6 - x} Yb x Al 2 Sb 6 - Ca 5 with the type Ca _{5 - x} Yb _x Al ₂ Sb _{6 where the} compound has a Ba ₅ Al ₂ Bi ₆ - type phase Which is energetically advantageous compared to the compound (Yb-rich CaYb ₄ Al ₂ Sb ₆ compound). The above results also indicate that the Ba ₅ Al ₂ Bi ₆ -type Ca _{5- x} Yb _x Al ₂ Sb ₆ compound is a Ca ₅ Ga ₂ Sb ₆ -type Ca _{5- x} Yb _x Al ₂ Sb ₆ compound.

Next, in order to understand the distribution of individual atomic orbits in the entire energy range, the DOS calculation is performed using the virtual structure model of Ba ₅ Al ₂ Bi ₆ -type and the virtual structure model of Ca ₅ Ga ₂ Sb ₆ -type The total DOS (Total DOS, TDOS) curves and partial DOS (PDOS) curves of each virtual structure model were analyzed. The analysis confirmed that the shapes of the TDOS curves for the two virtual structure models were very similar (see FIG. 7). Particularly, it has been confirmed that the valence band region is divided into two parts in both of the above virtual structure models. The first part was the lower part of ca.-11 eV and 9 eV, and the second part was the higher part of ca. -7 eV and 0 eV, while the second part was the part containing stronger contribution by s-orbital of Al and Sb. Including the major contributions of The two TDOS curves show different electrical conductivities of the two virtual structure models. The TDOS (panel (a) in FIG. 7) of the Ba ₅ Al ₂ Bi ₆ -type virtual structure model exhibits a metal conduction behavior with a significant DOS value at the Fermi level ( E _F ) whereas the Ca ₅ Ga ₂ Sb ₆ - TDOS of the type of virtual structure model (panel (b) of FIG. 7) exhibits a semiconductor behavior with a small bandgap at Fermi level ( E _F ) (see panels (a) and (b) of FIG. 7). Therefore, if the crystal structure of the Ca _{5 - x} Yb _x Al ₂ Sb ₆ compound is converted into the Ba ₅ Al ₂ Bi ₆ - type to the Ca ₅ Ga ₂ Sb ₆ - type through the above annealing process, It is changed from conduction behavior to semiconductor behavior. Further analysis was performed to understand the correlation between the size of the bandgap and the structural transformation. According to the PDOS curves, the greatest contribution to the valence band existing just below E _F is mainly due to the Sb-Sb cross-linking of the [Al ₂ Sb ₈ ] unit with added cation in both of these virtual structure models. However, in the case of the Ba ₅ Al ₂ Bi ₆ -type virtual structure model, the cross-linked Sb-Sb anti-bonding state located at the bottom of the conduction band existing in both virtual structural models is E _F And in the case of the Ca ₅ Ga ₂ Sb ₆ -type virtual structure model, the cross-linked Sb-Sb anti-bonding state has a higher conduction band than E _F And it was confirmed that they did not intersect with E _F (see panel (a) of Fig. 7). The different behaviors of such semi-bonded states are explained by the bonding distance of the Sb-Sb crosslinks. The Ca ₅ Ga ₂ Sb ₆ -type phase has a relatively short Sb-Sb bond distance compared to the Ba ₅ Al ₂ Bi ₆ -type phase, thereby inducing stronger bond interactions. Since the strong coupling interaction separates the valence band and the conduction band more widely, the Ba ₅ Al ₂ Bi ₆ - type phase exhibits a metallic conduction behavior and the Ca ₅ Ga ₂ Sb ₆ - type phase with a small band gap Behavior.

4. Thermoelectric properties

In order to confirm the effect of the solid phase transformation and annealing duration on the thermoelectric properties of the two representative phases, annealing was not performed and Ca ₁ with Ba ₅ Al ₂ Bi ₆ - type structure _{. 5} Yb _{3 . 5} Al ₂ Sb ₆ compound (the first compound) was annealed at 1023K for 2 weeks (14 days) to form Ca ₁ Ga ₂ Sb ₆ -type Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ compound (second compound), and a 1-month (30-day) annealing at 1023K to form Ca ₁ Ga ₂ Sb ₆ -type structure Ca _{1 . 5} Yb _{3 . The} electrical conductivity () and the Seebeck coefficient ( S ) were measured and the PXRD and SXRD analyzes were performed on the ₅ Al ₂ Sb ₆ compound (the third compound). As a result of measurement of electrical conductivity (), the electrical conductivities (?) Of the first compound, the second compound and the third compound were ca. 300, 75 and 2 S / cm (see panel (a) of FIG. 8). In particular, the electrical conductivity of the first compound tends to decrease with increasing temperature, indicating that typical metal conduction behavior is exhibited. On the contrary, the electrical conductivity of the second compound and the third compound tends to increase as the temperature increases, and it is confirmed that typical semiconductor behavior is exhibited. The results show that the conventional Yb ₅ Al ₂ Sb ₆ adopting the Ba ₅ Al ₂ Bi ₆ -type phase exhibits metallic conduction behavior and the conventional Ca ₅ Al ₂ Sb ₆ adopting the Ca ₅ Ga ₂ Sb ₆ -type phase It is in good agreement with the results of the semiconductor behavior. Panel (a) of FIG. 8 shows the measurement results of the temperature-dependent electrical conductivity of Yb ₅ Al ₂ Sb ₆ /0.5Ge and Ca ₅ Al ₂ Sb ₆ . The results show that the Ca ₅ Ga ₂ Sb ₆ -type phase or the Ba ₅ Al ₂ Bi ₆ -type phase and the Ba ₅ Al ₂ Bi ₆ -type phase do not depend on the chemical composition differences such as how much the electrical conductivities of the three compounds include Yb or Ca It is shown that the Ba ₅ Al ₂ Bi ₆ - type structure of Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ compound is annealed for 14 to 30 days, the bonding state between the valence band and the conduction band is remarkably decreased and the electrical conductivity is further reduced. As a result, the Ba ₅ Al ₂ Bi ₆ - Ca ₁ with type structure _{. 5} Yb _{3 . 5} Al ₂ Sb ₆ Compound Ca ₅ Ga ₂ Sb ₆ - Ca ₁ with type structure _{. 5} Yb _{3 . 5} Al ₂ Sb ₆ compound to show semiconductor behavior.

Panel (b) of FIG. 8 shows the result that the Seebeck coefficient S shows temperature dependency. The Seebeck coefficients of the first, second and third compounds show holes as the major charge carrier (p-type) within the measured temperature range. In particular, the first compound has a Seebeck coefficient of ca. 20 μV / K and at ca 700 K the temperature increases to ca. 50 μV / K, and the absolute value of the Seebeck coefficient is relatively small. Also in the second compound, a change in the Seebeck coefficient similar to that of the first compound lasts, presumably due to the presence of the above-mentioned defect state. On the contrary, in the case of the third compound subjected to one month of annealing, a significantly improved ca. 120 180 μV / K was observed.

According to the PXRD and SXRD analysis, it is considered that there is no possibility that there is an intermediate structure between the two types of phases because both the second compound and the third compound undergo annealing at 1023 K and complete structural transformation is performed. Therefore, Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ It can be concluded that the electron transfer between the electropositive atom and the electronegative atom is facilitated by an increase in the annealing duration.

As a result of measuring a power factor ( PF ) corresponding to the first, second and third compounds, the room temperature power factor of the first compound, the second compound and the third compound is 0.11μW / cmK ^2, was confirmed by 0.002μW / cmK ^2, and 0.03μW / cmK ^2. However, the first compound, the second compound and the third compound in that the power factor is raised in proportion to the temperature increase and reaches the maximum value of each ^{0.62μW / cmK 2, 0.36μW / cmK} 2 and 0.77μW / cmK ² at 700K . The reason why the three compounds have a relatively small power factor is that the first compound and the second compound have a relatively low Seebeck coefficient and the third compound has a relatively low electric conductivity. Therefore, it is expected that an appropriate doping is performed to increase the electric conductivity, and in particular, an improved power factor can be confirmed from the third compound.

The total thermal conductivity ( κ _tot ) of the first compound, the second compound and the third compound at room temperature is ca. 4.0 W / mK, 1.4 W / mK, and 1.1 W / mK (see panel (a) of FIG. 9). Wiedemann-Franz law (κ _elec = LσT) used when the electronic conductivity can because lattice thermal conductivity (κ _latt) to estimate (κ _elec) a can be calculated using a simple formula of κ _latt = κ _tot κ _elec. The Lorentz coefficient ( L ) according to the temperature was calculated from the temperature dependent Siebec coefficients based on a single parabolic band model. 6 shows the Lorentz coefficient according to the calculated temperature. The temperature dependent Lorentz coefficient of the third compound was found to have a non-degenerative value corresponding to a range of 1.83 x 10 ^-8 V ² K ^-2 to 1.66 x 10 ^-8 V ² K ^-2 The temperature-dependent Lorentz coefficients of the first and second compounds were found to have a degenerate Lorentz coefficient corresponding to 2.44 x 10 ^-8 V ² K ^-2 to 2.17 x 10 ^-8 V ² K ^-2 . The room temperature lattice thermal conductivities of the first, second and third compounds are ca. 3.8W / mK, 1.3W / mK, and 1.1W / mK, which means that most of the heat is transferred in phonon form by lattice vibration. The first compound (lattice conductivity: ca. 3.8 W / mK) and the second compound (lattice conductivity: ca. 3.8 W / mK) according to the temperature of Yb ₅ Al ₂ Sb ₆ /0.5Ge, Yb ₅ Al ₂ Sb ₆ and Ca ₅ Al ₂ Sb ₆ , A Ba ₅ Al ₂ Bi ₆ -type containing Yb ₅ Al ₂ Sb ₆ /0.56 Ge (lattice conductivity ca. 3.1 W / mK) and Yb ₅ Al ₂ Sb ₆ (lattice conductivity: ca 2.4 W / mK) It was confirmed that the degrees of change of the room temperature lattice thermal conductivity in the compounds were different from each other, and the difference was judged to be caused by the difference in the production method and chemical composition of each compound. The preparation method and the chemical composition of the three compounds were arc fusion method / Ca _1.5 Yb _3.5 Al ₂ Sb ₆ , arc melting method / Yb ₅ Al ₂ Sb ₆ /0.5 Ge and ball milled and spark sintering plasma sintered, BM-SPS method / Yb ₅ Al ₂ Sb ₆ . In particular, the lowest lattice thermal conductivity ( ca. 2.4 W / mK) of the Yb ₅ Al ₂ Sb ₆ compound prepared by the BM-SPS method is due to enhanced grain boundary scattering more effective for phonon scattering . The results are quite remarkable. This is because the structural change by a simple annealing process means that the same stoichiometrically identical material can be produced with a greatly improved thermal insulation. Finally, panel (b) of Figure 9 shows the thermoelectric performance index (ZT) expressed as a function of temperature. Overall, the thermoelectric performance index of the three compounds is proportional to the temperature and shows a maximum value at 700K. In particular, it was confirmed that the third compound subjected to the annealing for 30 days has a relatively low characteristic in the absolute value and the thermoelectric performance index is improved up to 6 times as compared with the first compound not subjected to the annealing process.

conclusion

A total of 10 compounds belonging to the solid solution system were synthesized by the arc melting method, Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≤ x <5.0]. The Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≤ x ≤ 2.0] compounds with a high content of Ca crystallize in the Ca ₅ Ga ₂ Sb ₆ - type structure while the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5 ≤ x <5.0] compound was confirmed to be crystallized into a Ba ₅ Al ₂ Bi ₆ - type structure, and Ca _{5 - x} Yb _x Al ₂ Sb ₆ - type crystallized in the Ca ₅ Ga ₂ Sb ₆ - Compounds and the Ca _{5 - x} Yb _x Al ₂ Sb ₆ compounds crystallized in the Ba ₅ Al ₂ Bi ₆ - type structure were found to exhibit a physical balance of semiconductor conduction behavior and metal conduction behavior, respectively. The difference is due to the difference in the bonding distance of the Sb-Sb cross-linking of the [Al ₂ Sb ₈ ] unit and the geometric arrangement of the various structural building blocks. Ca ₁ with a high content of Yb _{. 5} Yb _{3 . 5,} the thermal activity of the solid solution crystal Al ₂ Sb _6-crystal structure transform the crystal structure by heat treatment Ba ₂ Al _{5 6} Bi - means for converting the type-in type Ca ₂ Ga ₅ Sb _6. The Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb ₆ was first identified through the present invention. It is believed that the annealing process of the present invention is sufficient to provide the activated thermal energy needed to convert the dynamically stable Ba ₅ Al ₂ Bi ₆ -type structure into a thermodynamically stable Ca ₅ Ga ₂ Sb ₆ -type structure. As a result of comparing the total electron energies between virtual structural models adopting Ba ₅ Al ₂ Bi ₆ -type or Ca ₅ Ga ₂ Sb ₆ -type, the Ca ₅ Ga ₂ Sb ₆ -type virtual structure model is Ba ₅ Al ₂ Bi ₆ - type virtual structure model. Unlike the Ba ₅ Al ₂ Bi ₆ -type hypothetical model, the Ca ₅ Ga ₂ Sb ₆ -type hypothetical model induces a large separation between the valence band and the conduction band due to the relatively short Sb-Sb cross- Is opened. It is therefore believed that the electrotransport properties of the compound are determined directly by the type of structure determined by the synthetic route, rather than by chemical composition.

The specific embodiments described herein are representative of preferred embodiments or examples of the present invention, and thus the scope of the present invention is not limited thereto. It will be apparent to those skilled in the art that modifications and other uses of the invention do not depart from the scope of the invention described in the claims.

Claims (12)

Zintl compound represented by the following formula:
[Chemical Formula]
Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0? X ? 2.0]
Where Ca is calcium; Yb is Ytterbium; Al is aluminum; Sb is Antimony.
The compound according to claim 1, wherein the compound represented by the formula is any one selected from the group consisting of Ca ₄ YbAl ₂ Sb _6, Ca _3.5 Yb _1.5 Al ₂ Sb ₆ , and Ca ₃ Yb ₂ Al ₂ Sb ₆ Characterized by a worm compound.
The method according to claim 1, wherein the crystal structure of the graft compound is composed of Ca ₂ Ga ₂ Sb ₆ -type orthorhombic Pbam space group and has seven crystallographically independent atomic positions &Lt; / RTI &gt;
4. The method of claim 3, wherein the crystal structure of the wilttle compound has seven crystallographically independent atomic positions of three calcium (Ca2 ⁺ ) / ytterbium (Yb2 ⁺ ) mixed atom positions, one aluminum (Al) And three antimony (Sb) atomic positions.
The method according to claim 1, wherein the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [1.0 ≦ x ≦ 2.0] The compound is prepared by preparing a raw material containing ytterbium (Yb), calcium (Ca), aluminum (Al), antimony (Sb) and aluminum (Al) And then heating the mixture to heat treatment.
Zintl compound represented by the following formula:
[Chemical Formula]
Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X <5.0]
Where Ca is calcium; Yb is Ytterbium; Al is aluminum; Sb is Antimony.
The method according to claim 6, wherein the graft compound represented by the formula is CaYb ₄ Al ₂ Sb _{6 ,} Ca _{1 . 5} Yb _{3 . 5} Al ₂ Sb _{6 ,} and Ca ₂ Yb ₃ Al ₂ Sb ₆ .
The method of claim 6, wherein the crystalline structure of the graft compound is composed of a Ca ₂ Ga ₂ Sb ₆ -type orthorhombic Pbam space group and has seven crystallographically independent atomic positions &Lt; / RTI &gt;
The method of claim 8 wherein the independent atom position in the seven crystallographic three calcium (Ca ^{2 +)} / Ytterbium (Yb ^{2 +)} mixture atom positions, one of aluminum (Al) atom position and three antimony (Sb ) Atomic position.
The method according to claim 6, wherein the Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X < 5.0]
a) preparing a raw material containing ytterbium (Yb), calcium (Ca), aluminum (Al), antimony (Sb) and aluminum (Al) and subjecting the raw material to a first heat treatment by arc- Ca _{5 - x} Yb _x Al ₂ Sb ₆ [2.5? X < 5.0] compound; And
b) the Ca _{5 - x} Yb _x Al ₂ Sb ₆ Performing a secondary heat treatment (annealing) at 673-1023K for 14-30 days using a muffle furnace [2.5? X <5.0] compound;
&Lt; / RTI &gt;
11. The method of claim 10, wherein the first heat treatment is performed using Ca _{5 - x} Yb _x Al ₂ Sb ₆ having a Ba ₅ Al ₂ Bi ₆ - type crystal structure [2.5? X < 5.0] compound, and the secondary heat treatment is performed using Ca _{5 - x} Yb _x Al ₂ Sb ₆ Wherein the crystal structure of the [2.5 < x &lt; 5.0] compound is converted from a Ba ₅ Al ₂ Bi ₆ -type to a Ca ₂ Ga ₂ Sb ₆ -type.
A composition for a thermoelectric material comprising a winglet compound according to any one of claims 1 to 11.

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