KR101874391B1 - CaMnO₃ BASED THERMOELECTRIC MATERIAL AND PRODUCING METHOD OF THE SAME - Google Patents

Abstract

It relates to a method of producing a CaMnO ₃ based thermoelectric material using a tape casting method and hence a CaMnO ₃ based thermoelectric material prepared by.

Description

TECHNICAL FIELD The present invention relates to a CaMnO 3 based thermoelectric material and a method for manufacturing the same,

The present application is directed to a method of producing a CaMnO ₃ based thermoelectric material using a tape casting method and hence a CaMnO ₃ based thermoelectric material prepared by.

Since the nineteenth century, human beings have begun to use electricity to change the time and space of mankind, change the working time and working environment, and have a great influence on all aspects of society. Currently, global warming problems are constantly emerging due to the rapid increase in high oil prices and CO ₂ gas emissions. Korea's energy dependency is 97% of total energy, and energy problems are expected to further intensify in the future. In order to solve these problems, recently, there has been much interest in the effective utilization of the waste heat energy used and abandoned. Among them, thermoelectric power generation is one of the fields that are actively researched recently, and solar energy, geothermal heat, waste heat, And the like. However, since the energy conversion efficiency of the thermoelectric power generation is 10% or less, practical use is insignificant.

A thermoelectric material is a material used in a thermoelectric generator by utilizing the action of heat and electricity. The thermoelectric module has low energy conversion efficiency and high manufacturing cost, which is less economical than a fuel cell or a solar cell. However, it has a merit of being able to design and manufacture various sizes of system because there is no mechanical parts, and the selection range of heat source is wide as well as the middle and low temperature regions as well as the high temperature region. It is possible to generate noiseless power without any separate parts, and it is not environmentally friendly since no secondary byproducts are generated during the power generation process. Also, natural heat energy, heat and geothermal heat such as waste heat of power plants, steelworks, automobiles, The power generation system can be constructed with the thermoelectric element used.

In the 1970s, it was studied mainly on metal alloy thermoelectric materials (Bi-Te system, Sb-Te system, Fe-Si system, etc.) and this thermoelectric material is known to have a large performance index value at medium and low temperatures. However, metal alloy type thermoelectric materials have problems in that they are oxidized or thermally decomposed in a high temperature atmosphere to deteriorate performance, and recently, they have a great interest in oxide-based thermoelectric materials.

The oxide based thermoelectric material is stable at a high temperature and can be used in the air for a long time, and is less toxic than a metal alloy type thermoelectric material and is safe. Terasaki et al. Reported that NaCo ₂ O ₄ oxide thermoelectric materials have low resistance and high thermal conductivity at high temperatures. Then, Ca ₃ CO ₄ O ₉ , Bi ₂ Sr ₂ Co ₂ O _y , Oxides have been reported to possess excellent thermoelectric performance [I. Terasaki, Y. Sasago, K. Uchinokura, Phys. Rev. B56, R12685 (1997)]. Although the above-mentioned oxide thermoelectric material has been studied as a p-type oxide thermoelectric material, the n-type oxide thermoelectric material has insufficient thermoelectric properties compared to the p-type oxide thermoelectric material, and research is lacking. As of the n-type oxide thermoelectric materials research is carried out to a lot may include ZnO, SrTiO _3, and CaMnO _3-δ. Among them, ZnO has a disadvantage in that it is difficult to greatly improve the electrical characteristics due to the dopant due to low employment and SrTiO ₃ must be produced in an inert atmosphere. On the other hand perovskite (perovskite) CaMnO _{3 -δ} having a crystal structure is manufacturable and have got very promising as an n-type oxide thermoelectric materials with high solubility in an air atmosphere [M. Ohtaki, H. Koga, T. Tokunaga, K. Eguchi, H. Arai, J. Solid State Chem. 120,105 (1995)].

The present invention provides a method for producing a CaMnO ₃ thermoelectric material by using a tape casting method, and a CaMnO ₃ thermoelectric material and a sheet produced thereby.

However, the problems to be solved by the present invention are not limited to the problems described above, and other problems not described can be clearly understood by those skilled in the art from the following description.

The first aspect of the present invention provides a method of manufacturing a CaMnO ₃ thermoelectric material by a tape casting method.

A second aspect of the present invention provides a CaMnO ₃ based thermoelectric material produced by a tape casting method and represented by the following Chemical Formula 1:

[Chemical Formula 1]

Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ

In the above formulas,

R is Ce or Bi,

x is 0? x? 0.1.

A third aspect of the invention provides a sheet comprising a CaMnO ₃ based thermoelectric material according to the second aspect of the present application.

The conventional n-type oxide thermoelectric material has a disadvantage in that it is difficult to improve the electrical characteristics due to the dopant due to low employment, or it must be manufactured in an inert atmosphere. On the other hand, the CaMnO _{3 - ?} -Type thermoelectric material having the petrobeacite crystal structure of the present invention is a promising n-type oxide-based thermoelectric material because it can be produced in an atmospheric environment and has a high solubility.

In particular, the present application uses a tape casting method CaMnO _3-δ system, by producing a thermoelectric material, CaMnO ₃ which is produced by the cold pressure molding method that were conventionally used _- show a greater density, and better thermal characteristics than the _δ-based thermoelectric material .

FIG. 1 shows the crystal structure of a CaMnO _{3 - ?} -Type oxide according to an embodiment of the present invention.
2 is a schematic diagram of a tape casting process in accordance with one embodiment of the present application.
FIG. 3 is a schematic view showing a cutting process of a CaMnO _{3 - ?} -Type thermoelectric material according to an embodiment of the present invention.
4 is a according to one embodiment of the invention, produced by the cold pressure molding method Ca _{0. 9} shows the XRD pattern of the La _{1 -x} Ce _x MnO _{3 -δ} thermoelectric material.
FIG. 5 is a graph showing the relationship between the Ca _{0 . 9} is an FE-SEM (field emission-scanning electron microscope) image of La _{1 -x} Ce _x MnO _3-δ thermoelectric material.
FIG. 6 is a graph showing the relationship between the Ca _{0 . 9} is a graph showing the electrical conductivity of a La _{1 -x} Ce _x MnO _{3 -δ} thermoelectric material.
FIG. 7 is a graph showing the relationship between the Ca _{0 . 9} is a graph showing the relationship between the temperature and the thermal conductivity (Seebeck coefficient) of the La _{1 -x} Ce _x MnO _{3 -δ} thermoelectric material.
FIG. 8 is a graph showing the relationship between the Ca _{0 . 9} is a graph showing output factors in cold pressing of La _{1 -x} Ce _x MnO _3-δ thermoelectric material.
FIG. 9 is a graph showing the relationship between the content of Ca _{0 . 9} La _{1- x} Ce _x MnO _3-δ thermoelectric material.
FIG. 10 is a graph _{showing the relationship} between the thermal conductivity of the Ca _0.9 La _1-x Ce _x MnO _{3 -δ} thermoelectric material produced by the cold press forming method and the dimensionless figure of merit ZT).
Fig. 11 shows an XRD pattern of a Ca _0.9 La _1-x Ce _x MnO _{3 -δ} thermoelectric material produced by a tape casting method in one embodiment of the present invention.
12 is an FE-SEM (field emission-scanning electron microscope) image of a Ca _0.9 La _1-x Ce _x MnO _{3 -δ} thermoelectric material produced by a tape casting method in an embodiment of the present invention.
13 is a graph showing an electric conductivity of a Ca _0.9 La _1-x Ce _x MnO _{3 -?} Thermoelectric material produced by a tape casting method according to an embodiment of the present invention.
14 is a graph showing the relationship between the temperature and thermal conductivity (Seebeck coefficient) of Ca _0.9 La _1-x Ce _x MnO _{3 -?} Thermoelectric material produced by the tape casting method in one embodiment of the present invention.
Fig. 15 is a graph showing output factors in a tape casting process of a Ca _0.9 La _1-x Ce _x MnO _{3 -?} Thermoelectric material produced by a tape casting method in one embodiment of the present invention.
16 is a graph showing the thermal conductivity of Ca _0.9 La _1-x Ce _x MnO _{3 -?} Thermoelectric material produced by the tape casting method in one embodiment of the present invention.
FIG. 17 is a graph _{showing the relationship} between the output factor and the thermal conductivity value of the Ca _0.9 La _1-x Ce _x MnO _{3 -δ} thermoelectric material produced by the tape casting method and the dimensionless figure of merit ZT).
18 is an XRD pattern of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -δ} thermoelectric material produced by a cold press forming method according to an embodiment of the present invention.
19 is an FE-SEM (field emission-scanning electron microscope) image of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -?} Thermoelectric material produced by the cold press forming method according to one embodiment of the present invention.
20 is a graph showing an electric conductivity of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -?} Thermoelectric material produced by a cold press forming method according to an embodiment of the present invention.
FIG. 21 is a graph showing the relationship between the temperature and the thermal conductivity (Seebeck coefficient) of the Ca _0.9 La _0.1-x Bi _x CaMnO ₃ -δ thermoelectric material produced by the cold pressing method in one embodiment of the present invention.
22 is a graph showing output factors in cold pressing of Ca _0.9 La _0.1-x Bi _x MnO _{3 -?} Thermoelectric material produced by the cold press forming method in one embodiment of the present invention.
23 is a graph showing the thermal conductivity of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -?} Thermoelectric material produced by a cold press forming method in one embodiment of the present invention.
Fig. 24 is a graph showing the relationship between the dimensionless figure of merit (Fig. 24) calculated by using the output factor and the thermal conductivity value of the Ca _0.9 La _0.1-x Bi _x MnO _{3 -δ} thermoelectric material produced by the cold pressing method ZT).
25 shows XRD patterns of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -δ} thermoelectric material produced by a tape casting method in one embodiment of the present invention.
26 is an FE-SEM (field emission-scanning electron microscope) image of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -δ} thermoelectric material produced by a tape casting method in one embodiment of the present invention.
FIG. 27 is a graph showing the electrical conductivity of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -?} Thermoelectric material produced by a tape casting method in one embodiment of the present invention.
28 is a graph showing the relationship between the temperature and thermal conductivity (Seebeck coefficient) of the Ca _0.9 La _0.1-x Bi _x MnO _{3 -δ} thermoelectric material produced by the tape casting method in one embodiment of the present invention.
29 is a graph showing output factors in a tape casting process of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -?} Thermoelectric material produced by a tape casting method in one embodiment of the present invention.
30 is a graph showing the thermal conductivity of a Ca _0.9 La _0.1-x Bi _x MnO _{3 -?} Thermoelectric material produced by a tape casting method in one embodiment of the present invention.
Fig. 31 is a graph showing the relationship between the dimensionless figure of merit (Fig. 31) calculated by using the output factor and the thermal conductivity value of the Ca _0.9 La _0.1-x Bi _x MnO _{3 -δ} thermoelectric material produced by the tape casting method ZT).

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains.

It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout this specification, when a member is " on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as " including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms " about ", " substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) " or " step " used to the extent that it is used throughout the specification does not mean " step for.

Throughout this specification, the term " combination thereof " included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

Throughout this specification, the description of "A and / or B" means "A or B, or A and B".

Throughout the specification of the present application, "CaMnO _{3 - δ} system oxide" means an oxide having a perovskite crystal structure (FIG. 1), and forms an orthorhombic perovskite crystal structure at room temperature. When heat is applied in the atmosphere, oxygen deficiency occurs in the crystal structure, and it has a tetragonal crystal structure at 896 ° C or higher, and a cubic crystal structure at 913 ° C or higher. It has been reported that the addition of +3 or +4 elements to the Ca position in CaMnO _{3 -δ} leads to polaron hopping conduction, and the main carrier (electrons or holes), depending on the amount of the added substance, . This phenomenon is caused by the interaction of Mn with +3 valence and Mn with +4 valence. When the amount of the added material is large, Mn ⁺³ (3d ⁴ )> Mn ⁺⁴ (3d ³ ) When the amount of the added substance is small, Mn ⁺³ (3d ⁴ ) <Mn ⁺⁴ (3d ³ ) becomes, and the carrier becomes an electron. Depending on the amount of the added material, the type of the carrier is changed and the pn transition occurs.

Throughout the specification of the present application, the term " tape casting " refers to a ceramic tape casting method that is commonly used in the manufacture of thin and flat ceramic sheets in the electronics industry. A representative method is doctor blade casting, in which a slurry composed of a ceramic raw material, a solvent, and an organic additive (binder, plasticizer, dispersant, etc.) is sent onto a carrier film to produce a green sheet (Fig. 2). For separating the carrier film and the sheet, it is required to have appropriate mechanical strength and flexibility of the sheet. The size of the sheet must be small due to temperature and humidity, and finally, it can be adhered by cold pressing or hot pressing. Should be. Tape casting applications include solid oxide fuel cells, piezoelectric devices, capacitors, and multilayer electronic ceramics. The advantage of tape casting is that it can be mass-produced and continuous, and that various organic additives can be used. Further, the thickness of the sheet can be freely adjusted, and a sheet having a high filling density can be produced.

Throughout this specification, "electrical conductivity" refers to the degree to which a current flows well in a material, and is the reciprocal of the resistivity. Generally, the electric conductivity σ is expressed by the following Equation 1:

,

,

Where n is the concentration of the charge, e is the unit charge, and μ is the mobility of the charge.

Throughout the present description, the " figure of merit " can be expressed as " Z "

,

,

In the above formula (2),? Represents electrical conductivity,? Represents thermal conductivity, and? Represents thermal conductivity. Here, ZT multiplied by the absolute temperature is called a dimensionless figure of merit. The dimensionless figure of merit (ZT) is a measure of the performance at the temperature of use and is used as a measure to compare the performance of thermoelectric materials.

The three factors representing the figure of merit are interrelated. For example, as the number of electrons increases, the electrical conductivity in Equation 2 increases, but at the same time, the thermal conductivity decreases and the thermal conductivity increases.

The first aspect of the present invention provides a method for manufacturing a CaMnO ₃ based thermoelectric material using a tape casting method.

In one embodiment of the present application, the CaMnO ₃ -based thermoelectric material may comprise a CaMnO _{3 - δ-} based oxide, for example, a metal selected from the group consisting of La, Ce, Bi, Doped CaMnO _{3 - δ-} based oxides, although the present invention is not limited thereto. The CaMnO ₃ based thermoelectric material may have a perovskite crystal structure (FIG. 1), and may form an orthorhombic perovskite crystal structure at room temperature, but the present invention is not limited thereto. When heat is applied in the atmosphere, oxygen deficiency occurs in the crystal structure, and it has a tetragonal crystal structure at 896 ° C or higher, and a cubic crystal structure at 913 ° C or higher. Among CaMnO _{3 - δ} , it has been reported that when +3 or +4 element is added to the Ca position, the polaron hopping conduction occurs, and depending on the amount of the added substance, the main carrier (electron or hole ) Is changed. This phenomenon is caused by the interaction of Mn with +3 valence and Mn with +4 valence. When the amount of the added material is large, Mn ⁺³ (3d ⁴ )> Mn ⁺⁴ (3d ³ ) When the amount of the added substance is small, Mn ⁺³ (3d ⁴ ) <Mn ⁺⁴ (3d ³ ) becomes, and the carrier becomes an electron. Depending on the amount of the added material, the type of the carrier is changed and the pn transition occurs.

In one embodiment of the present invention, the CaMnO ₃ -based thermoelectric material may be represented by the following chemical formula 1, but is not limited thereto:

[Chemical Formula 1]

Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ

In the above formulas,

R is Ce or Bi,

x is 0? x? 0.1.

In one embodiment of the present invention, the tape casting method may be used without limitation as long as it is a tape casting method used in the electronics industry, and may include, for example, doctor blade casting. .

Figure 2 schematically illustrates a tape casting process wherein a slurry comprising a material, a solvent, and an organic additive is dispensed onto a carrier film to produce a green sheet. The solvent may include, but is not limited to, water, methyl alcohol, ethyl alcohol, n-butyl alcohol, acetone, ethylene glycol, n-hexane, toluene, glycerol and the like. The organic additives may include, but are not limited to, binders, plasticizers, dispersants, and the like. Such binders can be used without limitation as long as they are used in the art and include, for example, natural gums, polysaccharides, purified alginates, cellulose ethers, polymerized alcohols, polymerized butyrals, acrylic resins, glycols, waxes, Silicates, organosilicates, soluble phosphates, soluble aluminates, and the like, but the present invention is not limited thereto. The plasticizers may be used without limitation as long as they are commonly used in the art, and may include, for example, phthalate plasticizers. A suitable mechanical strength and flexibility of the sheet are required for separating the carrier film and the sheet and a change in size due to temperature and humidity must be small. Finally, adhesion between the carrier film and the sheet is required by cold pressing or hot pressing. Should be possible. Due to the use of the tape casting method, mass production and continuous production are possible, and various organic additives can be used. Further, the thickness of the sheet can be freely adjusted, and a sheet having a high filling density can be produced.

In one embodiment of the present invention, the method for preparing a CaMnO ₃ based thermoelectric material includes the steps of: firstly calcining an oxide of a metal selected from the group consisting of Ca, La, Ce, Bi, Mn and combinations thereof; Crushing and drying the first calcined powder and then calcining the second calcined powder; Mixing the second calcined powder, the solvent and the organic additive to form a slurry; And forming the slurry into a sheet form using a tape casting method and then cutting the slurry.

In one embodiment of the present invention, for example, the CaMnO ₃ based thermoelectric material may be one prepared by mixing Ca oxide and Mn oxide with La, Ce, Bi, and a metal selected from the group consisting of Ca, .

In one embodiment of the invention, the solvent may include, but is not limited to, water, methyl alcohol, ethyl alcohol, n-butyl alcohol, acetone, ethylene glycol, n-hexane, toluene, glycerol and the like.

In one embodiment of the invention, the organic additive may include, but is not limited to, binders, plasticizers, dispersants, and the like. Such binders can be used without limitation as long as they are used in the art and include, for example, natural gums, polysaccharides, purified alginates, cellulose ethers, polymerized alcohols, polymerized butyrals, acrylic resins, glycols, waxes, Silicates, organosilicates, soluble phosphates, soluble aluminates, and the like, but the present invention is not limited thereto. The plasticizers may be used without limitation as long as they are commonly used in the art, and may include, for example, phthalate plasticizers.

In one embodiment herein, the primary calcination and the secondary calcination may be performed at a temperature ranging from about 900 &lt; 0 &gt; C to about 1,500 &lt; 0 &gt; C, but may not be limited thereto. For example, the primary calcination and the secondary calcination may be carried out at a temperature of from about 900 캜 to about 1,500 캜, from about 900 캜 to about 1,300 캜, from about 900 캜 to about 1,100 캜, from about 1,100 캜 to about 1,500 캜, Lt; 0 &gt; C to about 1,300 &lt; 0 &gt; C, or from about 1,300 &lt; 0 &gt; C to about 1,500 &lt; 0 &gt; C.

A second aspect of the present invention provides a CaMnO ₃ based thermoelectric material produced by a tape casting method and represented by the following Chemical Formula 1:

[Chemical Formula 1]

Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ

In the above formulas,

R is Ce or Bi,

x is 0? x? 0.1.

In one embodiment of the present application, the CaMnO ₃ -based thermoelectric material may comprise a CaMnO _{3 - δ-} based oxide, for example, a metal selected from the group consisting of La, Ce, Bi, Doped CaMnO _{3 - δ-} based oxides, although the present invention is not limited thereto. The CaMnO ₃ based thermoelectric material may have a perovskite crystal structure and may form an orthorhombic perovskite crystal structure at room temperature, but the present invention is not limited thereto. When heat is applied in the atmosphere, oxygen deficiency occurs in the crystal structure, and it has a tetragonal crystal structure at 896 ° C or higher, and a cubic crystal structure at 913 ° C or higher. In the CaMnO _{3 -δ} , it has been reported that when +3 or +4 element is added to the Ca position, polaron hopping conduction occurs, and depending on the amount of the added substance, the main carrier (electron or hole ) Is changed. This phenomenon is caused by the interaction of Mn with +3 valence and Mn with +4 valence. When the amount of the added material is large, Mn ⁺³ (3d ⁴ )> Mn ⁺⁴ (3d ³ ) When the amount of the added substance is small, Mn ⁺³ (3d ⁴ ) <Mn ⁺⁴ (3d ³ ) becomes, and the carrier becomes an electron. Depending on the amount of the added material, the type of the carrier is changed and the pn transition occurs.

In one embodiment of the present invention, the tape casting method may be used without limitation as long as it is a tape casting method used in the electronics industry, and may include, for example, doctor blade casting. .

In one embodiment of the present invention, the tape casting process may be to produce a green sheet by sending a slurry containing a material, a solvent, and an organic additive onto a carrier film. The solvent may include, but is not limited to, water, methyl alcohol, ethyl alcohol, n-butyl alcohol, acetone, ethylene glycol, n-hexane, toluene, glycerol and the like. The organic additives may include, but are not limited to, binders, plasticizers, dispersants, and the like. Such binders can be used without limitation as long as they are used in the art and include, for example, natural gums, polysaccharides, purified alginates, cellulose ethers, polymerized alcohols, polymerized butyrals, acrylic resins, glycols, waxes, Silicates, organosilicates, soluble phosphates, soluble aluminates, and the like, but the present invention is not limited thereto. The plasticizers may be used without limitation as long as they are commonly used in the art, and may include, for example, phthalate plasticizers. A suitable mechanical strength and flexibility of the sheet are required for separating the carrier film and the sheet and a change in size due to temperature and humidity must be small. Finally, adhesion between the carrier film and the sheet is required by cold pressing or hot pressing. Should be possible. Due to the use of the tape casting method, mass production and continuous production are possible, and various organic additives can be used. Further, the thickness of the sheet can be freely adjusted, and a sheet having a high filling density can be produced.

In one embodiment of the present invention, the method for preparing a CaMnO ₃ based thermoelectric material includes the steps of: firstly calcining an oxide of a metal selected from the group consisting of Ca, La, Ce, Bi, Mn and combinations thereof; Crushing and drying the first calcined powder and then calcining the second calcined powder; Mixing the second calcined powder, the solvent and the organic additive to form a slurry; And forming the slurry into a sheet form using a tape casting method and then cutting the slurry.

In one embodiment of the present invention, for example, the CaMnO ₃ based thermoelectric material may be one prepared by mixing Ca oxide and Mn oxide with La, Ce, Bi, and a metal selected from the group consisting of Ca, .

In one embodiment of the invention, the solvent may include, but is not limited to, water, methyl alcohol, ethyl alcohol, n-butyl alcohol, acetone, ethylene glycol, n-hexane, toluene, glycerol and the like.

In one embodiment of the invention, the organic additive may include, but is not limited to, binders, plasticizers, dispersants, and the like. Such binders can be used without limitation as long as they are used in the art and include, for example, natural gums, polysaccharides, purified alginates, cellulose ethers, polymerized alcohols, polymerized butyrals, acrylic resins, glycols, waxes, Silicates, organosilicates, soluble phosphates, soluble aluminates, and the like, but the present invention is not limited thereto. The plasticizers may be used without limitation as long as they are commonly used in the art, and may include, for example, phthalate plasticizers.

In one embodiment herein, the primary calcination and the secondary calcination may be performed at a temperature ranging from about 900 &lt; 0 &gt; C to about 1,500 &lt; 0 &gt; C, but may not be limited thereto. For example, the primary calcination and the secondary calcination may be carried out at a temperature of from about 900 캜 to about 1,500 캜, from about 900 캜 to about 1,300 캜, from about 900 캜 to about 1,100 캜, from about 1,100 캜 to about 1,500 캜, Lt; 0 &gt; C to about 1,300 &lt; 0 &gt; C, or from about 1,300 &lt; 0 &gt; C to about 1,500 &lt; 0 &gt; C.

A third aspect of the invention provides a sheet comprising a CaMnO ₃ based thermoelectric material according to the second aspect of the present application. Although the description of the sheet according to the third aspect of the present invention is omitted from the description of the second aspect of the present invention, the description of the second aspect of the present application is the same as the third aspect of the present application Lt; / RTI &gt;

In one embodiment of the present invention, the CaMnO ₃ -based thermoelectric material is produced by a tape casting method, and may be represented by the following Formula 1, but is not limited thereto:

[Chemical Formula 1]

Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ

In the above formulas,

R is Ce or Bi,

x is 0? x? 0.1.

In one embodiment of the present invention, the tape casting method may be used without limitation as long as it is a tape casting method used in the electronics industry, and may include, for example, doctor blade casting. .

In one embodiment of the present application, the CaMnO ₃ -based thermoelectric material may comprise a CaMnO _{3 - δ-} based oxide, for example, a metal selected from the group consisting of La, Ce, Bi, Doped CaMnO _{3 - δ-} based oxides, although the present invention is not limited thereto. The CaMnO ₃ based thermoelectric material may have a perovskite crystal structure and may form an orthorhombic perovskite crystal structure at room temperature, but the present invention is not limited thereto. When heat is applied in the atmosphere, oxygen deficiency occurs in the crystal structure, and it has a tetragonal crystal structure at 896 ° C or higher, and a cubic crystal structure at 913 ° C or higher. In the CaMnO _{3 -δ} , it has been reported that when +3 or +4 element is added to the Ca position, polaron hopping conduction occurs, and depending on the amount of the added substance, the main carrier (electron or hole ) Is changed. This phenomenon is caused by the interaction of Mn with +3 valence and Mn with +4 valence. When the amount of the added material is large, Mn ⁺³ (3d ⁴ )> Mn ⁺⁴ (3d ³ ) When the amount of the added substance is small, Mn ⁺³ (3d ⁴ ) <Mn ⁺⁴ (3d ³ ) becomes, and the carrier becomes an electron. Depending on the amount of the added material, the type of the carrier is changed and the pn transition occurs.

In one embodiment of the present invention, the tape casting method may be used without limitation as long as it is a tape casting method used in the electronics industry, and may include, for example, doctor blade casting. .

In one embodiment of the present invention, the tape casting process may be to produce a green sheet by sending a slurry containing a material, a solvent, and an organic additive onto a carrier film. The solvent may include, but is not limited to, water, methyl alcohol, ethyl alcohol, n-butyl alcohol, acetone, ethylene glycol, n-hexane, toluene, glycerol and the like. The organic additives may include, but are not limited to, binders, plasticizers, dispersants, and the like. Such binders can be used without limitation as long as they are used in the art and include, for example, natural gums, polysaccharides, purified alginates, cellulose ethers, polymerized alcohols, polymerized butyrals, acrylic resins, glycols, waxes, Silicates, organosilicates, soluble phosphates, soluble aluminates, and the like, but the present invention is not limited thereto. The plasticizers may be used without limitation as long as they are commonly used in the art, and may include, for example, phthalate plasticizers. A suitable mechanical strength and flexibility of the sheet are required for separating the carrier film and the sheet and a change in size due to temperature and humidity must be small. Finally, adhesion between the carrier film and the sheet is required by cold pressing or hot pressing. Should be possible. Due to the use of the tape casting method, mass production and continuous production are possible, and various organic additives can be used. Further, the thickness of the sheet can be freely adjusted, and a sheet having a high filling density can be produced.

In one embodiment of the present invention, the method for preparing a CaMnO ₃ based thermoelectric material includes the steps of: firstly calcining an oxide of a metal selected from the group consisting of Ca, La, Ce, Bi, Mn and combinations thereof; Crushing and drying the first calcined powder and then calcining the second calcined powder; Mixing the second calcined powder, the solvent and the organic additive to form a slurry; And forming the slurry into a sheet form using a tape casting method and then cutting the slurry.

In one embodiment of the present invention, for example, the CaMnO ₃ based thermoelectric material may be one prepared by mixing Ca oxide and Mn oxide with La, Ce, Bi, and a metal selected from the group consisting of Ca, .

In one embodiment of the invention, the solvent may include, but is not limited to, water, methyl alcohol, ethyl alcohol, n-butyl alcohol, acetone, ethylene glycol, n-hexane, toluene, glycerol and the like.

In one embodiment of the invention, the organic additive may include, but is not limited to, binders, plasticizers, dispersants, and the like. Such binders can be used without limitation as long as they are used in the art and include, for example, natural gums, polysaccharides, purified alginates, cellulose ethers, polymerized alcohols, polymerized butyrals, acrylic resins, glycols, waxes, Silicates, organosilicates, soluble phosphates, soluble aluminates, and the like, but the present invention is not limited thereto. The plasticizers may be used without limitation as long as they are commonly used in the art, and may include, for example, phthalate plasticizers.

In one embodiment herein, the primary calcination and the secondary calcination may be performed at a temperature ranging from about 900 &lt; 0 &gt; C to about 1,500 &lt; 0 &gt; C, but may not be limited thereto. For example, the primary calcination and the secondary calcination may be carried out at a temperature of from about 900 캜 to about 1,500 캜, from about 900 캜 to about 1,300 캜, from about 900 캜 to about 1,100 캜, from about 1,100 캜 to about 1,500 캜, Lt; 0 &gt; C to about 1,300 &lt; 0 &gt; C, or from about 1,300 &lt; 0 &gt; C to about 1,500 &lt; 0 &gt; C.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited by these Examples.

[ Example ]

Cold pressing  Used Ca _{0 . 9} La _{0 .One- x} R _x MnO _{3 -δ} ( R: Ce  or Bi ; 0? x &Lt; / RTI &gt; Manufacture of thermoelectric materials

_{CaO, Mn 3 O 4, CeO} 2 And Bi ₂ O ₃ (purity 99.9%, High Purity Chemicals Co., Japan) using a powder Ca _{0. The} thermoelectric materials were prepared by the cold press forming method after forming the thermoelectric materials into the compositions shown in Table 1 and forming La _{0 .1- x} R _x MnO _{3 -δ} (R: Ce, Bi; 0 ≦ x ≦ 0.1). The powders, ethyl alcohol, and zirconia balls weighed to the composition of Table 1 were put together into a zirconia jar and milled at 350 rpm for 3 hours using a planetary mill. Into the mixed powder to a 60 ℃ dryer and dried for 12 hours body having a size of less than 100 μm sieve manure to Ca _{0. 9} La _{0 .1 - x} R _x MnO _{3 - delta} . The obtained mixed powder was first calcined at 1100 ° C. for 10 hours, and the first calcined powder was pulverized, dried and sieved. The sieved primary calcined powder was subjected to secondary calcination at 1200 ° C. for 10 hours and pulverized, dried and sieved in the same manner as the primary calcination. The second calcined powder was placed in a disk and bar mold and uniaxially pressurized at a pressure of 90 MPa to form a powder having a diameter of 10 mm (Φ) × 5 mm (t), 20 mm (Φ) × 5 mm (t), and a size of 5 mm (w) x 25 mm (l) x 5 mm (t). Then, after keeping the molded body at 1300 ℃ at a heating rate of 5 ℃ / min to room temperature for 10 hours to ronaeng Ca _{0. 9} La _{0 .1 - x} R _x MnO _{3 - δ} thermoelectric material specimens were prepared.

Using tape casting Ca _{0 . 9} La _{0 .One- x} R _x MnO _{3 -δ} (R: Ce  or Bi ; 0? x ≤0.1) Manufacture of thermoelectric materials

Ca ₀ by tape casting method _{. 9 La 0 .1- x R x MnO} 3 -δ (R: Ce or Bi; 0≤ x ≤0.1), thereby manufacturing a thermal material. In order to prepare the ceramic slurry, the Ca _{0 . 9} La _{0 .1 - x} R _x MnO _{3 - delta} . The dry powder for preparing Ca _0.9 La _{0.1- x} R _x MnO _3-δ has the composition shown in Table 1 above. Toluene and ethyl alcohol were used as solvents and PVB (binder), α-tepineol (dispersant) and Di-n-butyl phthalate (DBP, plasticizer) were used as organic additives. First, Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ for preparing secondary calcined powder into a solvent, a dispersant, and zirconia balls with a diameter of 5 mm to a polyethylene bottle were mixed by ball milling (ball milling) for 5 hours. The remaining organic additives were then added to the resulting slurry and ball milled again for 24 hours to obtain a final slurry. The resulting slurry was stirred for 1 hour using a stirrer to remove bubbles. The bubble-free slurry and a tape casting device (Hansung System, STC-14A) were used to carry out the Ca _{0 . A} green sheet (thickness: 1 mm) of La _{0 .1 - x} R _x MnO _{3 -? Was prepared} . Then, a green sheet manufactured using a Lamination Machine (Hansung System, HMM-04-12) was laminated. The laminated green sheet was cut into a size of 20 mm x 80 mm as shown in Fig. 3, and 20 sheets were put into a bar mold and a pressure of 40 MPa was applied for 30 minutes to measure a size of 20 mm x 80 mm x 5 mm Was obtained. At this time, the temperature of the upper and lower plates of the laminator was 40 ° C for the first 5 minutes, and then maintained at 80 ° C. The laminated molded body was placed in a 4 mm (w) x 4 mm (l) x 5 mm (t), 5 mm (w) x 25 mm (l) x 5 mm (t), and 20 mm l) × 5 mm (t), and the cut specimens were placed in a heating furnace and sintered at 1300 ° C. for 10 hours. The sampling direction of the thermoelectric property measuring specimen having a size of 5 mm (w) × 25 mm (l) × 5 mm (t) is shown in FIG.

Ca _{0 . 9} La _{0 .One- x} R _x MnO _{3 -δ} (R: Ce  or Bi ; 0? x ≤0.1) Characteristic analysis of thermoelectric material

Ca _{0 . 9} La _{0 .One- x} R _x MnO _{3 -δ} Thermal analysis of mixed powders for manufacturing

The Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ preparative DTG-60H (Shimadzu) thermogravimetric analysis using a thermal analysis equipment in order to understand the thermal behavior according to a temperature change of the mixed powder (Thermogravimetric Analysis: TGA) and differential Differential Thermal Analysis (DTA) was performed. The mixed powder was subjected to thermal analysis while being heated at a temperature raising rate of 10 캜 / min in an air atmosphere at a temperature of 25 캜 to 1200 캜.

Ca _{0 . 9} La _{0 .One- x} R _x MnO _{3 -δ} Crystal Structure and Microstructure Analysis of Thermoelectric Materials

The Ca _{0 . 9 La 0 .1- x R x MnO} 3 - _δ the thermal X-ray diffraction (XRD, Rigaku DMAX 2500) for crystal structure analysis of the material was used. In this analysis, Cu Kα ₁ (λ: 1.54056 Å) was used as the target, and the scan speed was 10 ° / min and the step was 0.02 ° at an angle of 20 ° to 80 °. Further, using a scanning electron microscope (Hitachi S4700), the Ca _{0 . 9} La _{0 .1 - x} R _x MnO _{3 - δ} The grain size, grain shape and porosity of the thermoelectric materials were analyzed.

Ca _{0 . 9} La _{0 .One- x} R _x MnO _{3 -δ}  Measurement of porosity of thermoelectric material

Using Archimedes' principle, the Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ to measure the porosity of the thermoelectric material. When weighing the prepared specimens in a dry atmosphere, the dry weight W _d (g) was measured accurately to 1 mg. The dried specimens were placed in distilled water, heated for 3 hours and cooled to room temperature. Specimens with distilled water infiltrated into the pores of the specimen were called catcher samples. After gaining suspended weight W _susp (g) a catcher sample weighed in the distilled water, obtain a function the weight W _sat (g) weighed and then taken out of the catcher, a sample of the water, wipe out the sample surface with a towel, an expression 3 And the porosity (P _a ) was calculated.

.

.

Ca _{0 . 9} La _{0 .One- x} R _x MnO _{3 -δ}  Thermoelectric properties of thermoelectric materials

The Ca _{0 . 9} was processed in the thermal property test specimen having a size of La _{0 .1- x} R _x MnO _{3 -δ} to measure the thermal properties of the thermal transfer material 5 mm (w) × 20 mm (l) × 5 mm (t) . The thermoelectric properties were measured at 500 ° C to 800 ° C in the atmosphere, and the electric conductivity was measured by flowing a current of 10 mA using the 4-probe method. The resulting electrical conductivity σ was calculated by the following equation (4).

,

,

Where d is the distance between both ends of the platinum wire wound to measure electrical conductivity, A is the cross-sectional area of the specimen, V is the voltage difference across the platinum wire, and I is the current flowing through the specimen.

K-type thermocouples were brought into contact with the two grooves at both ends of the specimen to increase the temperature. Then, the temperature difference and the electromotive force of the two grooves generated by flowing Ar gas to one end of the specimen were measured. The thermal conductivity? Was calculated by the following equation (5).

,

,

In the above equation (5),? T represents the temperature difference between two grooves generated when Ar gas is flowed into the specimen, and? V represents the electromotive force according to the temperature difference. The temperature difference between both ends of the specimen was 1 to 3 占 폚.

In order to measure the thermal conductivity, the specimen was machined to a diameter of 12.7 mm and a thickness of 1.75 mm. Then, the coated specimen was coated with carbon to minimize thermal reflection on both sides of the specimen, and the specimen was measured using a DXF-900 (TA Instrument) Thermal conductivity was measured at intervals of 100 DEG C in a temperature range of 500 DEG C to 800 DEG C. Thermal conductivity κ was calculated using Equation 6 below.

,

,

In the formula 6 λ is thermal diffusivity, specific heat c _p is, ρ represents a density. Where C _p and λ are obtained from the monitor of the thermal conductivity measuring instrument. The principle of the measurement of the thermal diffusivity λ is that when a carbon coated specimen is mounted on a thermal conductivity device and a xenon pulse is projected onto one side of the specimen, heat is transferred to the opposite side after a certain period of time. The transmitted heat was measured with a thermal sensor before and after the Xenon pulse projection to obtain the thermal diffusivity. Specific heat c _p was measured using the same apparatus used for thermal diffusion.

The figure of merit (Z) is calculated from Equation (7) using the obtained electrical conductivity, thermal conductivity and thermal conductivity.

.

.

Comparative Example  One. By cold pressing  Manufactured Ca _{0 . 9} La _{0 .One- x} Ce _x MnO _{3 -δ}  (0? X? 0.1) Characteristic analysis result of thermoelectric material

Crystal structure and microstructure

Ca ₀ produced by cold pressing _{. 9} are shown in _{La 0 .1- x Ce x MnO 3} -δ (0≤ x ≤0.1) 4 to XRD analysis of the thermoelectric material. As shown in FIG. 4, all of the thermoelectric materials have orthorhombic perovskite crystal structure and Pnma (62) space group. No second phase was found in all the specimens. As the content of Ce increases, the diffraction peak moves at an elevated angle because the Ce ^{3 +} ionic radius (0.97 Å) is smaller than the La ³⁺ ionic radius (1.16 Å).

Ca _{0 . 9 La 0 .1- x Ce x MnO} 3 -δ (0≤ x ≤0.1) The microstructure of the thermoelectric material was observed by FE-SEM, and the results obtained are shown in Fig. In FIG. 5, it can be seen that as the Ce content increases, the grain size increases and the porosity tends to decrease. This means that Ce improves sinterability of Ca _0.9 La _{0.1- x} Ce _x MnO _3-δ . The grain size of the prepared specimen is 1.2 to 7.9 탆, and the porosity is 3 to 10%. Ca _{0 . 9 La 0 .1- x Ce x MnO} 3 -δ (0≤ x ≤0.1) to the composition by the grain size and the porosity of the thermoelectric material are shown in Table 2 below.

Electrical characteristic

As shown in the above formula (1), Ca _{0 . 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) The electrical conductivity of a thermoelectric material is proportional to the charge concentration and charge mobility. The charge concentration varies with the doping material and its content. In the thermoelectric material prepared in the comparative example, La ^{3 +} and Ce ^{3 +} ions are substituted for the Ca ^{2 +} ion site, and a defect is partially generated in the crystal structure, and Mn ⁴⁺ ions are ^converted into Mn ^{3 +} ions. As a result, mixed ions of Mn ^{4 +} and Mn ^{3 +} increase the charge concentration by Verwey 's controlled ionic valence principle. This mechanism is due to the higher electrical conductivity in specimens doped with pure CaMnO ₃ .

Ca _{0 . 9 La 0 .1- x Ce x MnO} 3 -δ (0≤ x ≤0.1) were measured in the thermal conductivity range of 500 ℃ to 800 ℃ of the material, showing the measured conductivity in Fig. All thermoelectric materials show metallic behavior with decreasing electrical conductivity as temperature increases. This trend is released by Ca ₁ including Yang Wang _- coincides with the thermal properties of the _{x Ce x MnO 3 -δ - x} La x MnO 3 -δ and Ca _1. As the content of Ce ( x ) increases from 0 to 0.075, the electric conductivity increases and it decreases again at 0.1. Electric conductivity at 500 ℃ is the content (x) of Ce is 0, 0.025, ^-1, 0.05, 0.075, and 0.1 days, respectively, when 195.1, 205.8, 254.3, 270.6, and 250.2 Ω ^-1 ㎝, x = 0.075 in the It shows a large electric conductivity. The reason why the conductivity ( x ) of Ce ( x ) increases from 0 to 0.075 is that as the content of Ce increases, the increase of the electric conductivity by the increase of the charge mobility due to the increase of the grain size and the density increases It is presumed that this effect is greater than the effect of decreasing the electrical conductivity. The x = 0.1 specimen is considered to have lower electrical conductivity than the x = 0.075 specimen because x = 0.1 is more effective in decreasing the electrical conductivity due to the decrease of the charge concentration than the electrical conductivity increase effect by increasing the charge mobility.

7 is manufactured Ca _{0. 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) represents the thermal conductivity of the thermoelectric material. In the whole measured temperature range, the thermoelectric power has a _negative (-) value _{. In} La _{0 .1 - x} Ce _x MnO _{3 - δ} thermoelectric materials, electrons are the main charge carriers and n-type conduction. As the temperature increases, the absolute thermal capacity tends to increase. The maximum absolute thermal conductivities at 800 ° C are shown. When the content ( x ) of Ce is 0, 0.025, 0.05, 0.075, and 0.1, the absolute thermal capacity values are 105, 115, 117.5, 120, and 85 μV ^{- 1} .

Using a result of the electrical conductivity and the thermal capacity obtained in the above-mentioned Ca _0. The power factor (PF) of the thermoelectric material was calculated from the _{equation 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≦ x ≦ 0.1). The calculated output factor is shown in FIG. The output factor was calculated using the following equation (8).

,

,

Where σ is the electrical conductivity and α is the thermal conductivity. Ca _{0 .} The output factor of ₉ La _{0 .1 - x} Ce _x MnO _{3 - δ} thermoelectric materials _exhibits a larger output factor when co-doping than when single La and Ce are doped. The specimen with the maximum output factor is x = 0.075 and has a value of 3.22 × 10 ^-4 Wm ^-1 K ^-2 at 800 ℃.

Thermal conductivity

9 is manufactured Ca _{0. 9 La 0 .1- x Ce x MnO} 3 -δ (0≤ x ≤0.1) it is a result of a thermal conductivity measurement of the thermoelectric material at 500 ℃ to 800 ℃. Ca _{0 . 9} La _{0 .1- x} Ce _x MnO _{3 -δ} thermal conductivity of the thermoelectric material showed the smallest thermal conductivity when the content (x) of Ce is zero, as the Ce content increases the thermal conductivity tends to increase . This is probably because the grain size and density increase with increasing Ce content and the phonon scattering decreases. Ce content (x) thermal conductivity at 0, 0.025, 0.05, 0.075, and 0.1 800 ℃ when respectively 2.10, 2.14, 2.31, 2.43, and 2.61 W · m ^-1 K ^{- 1.}

Dimensionless  Performance Index ( ZT )

Figure 10 is, Ca _{0. 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) Indicates the dimensionless figure of merit (ZT) calculated using the output factor and thermal conductivity obtained from the thermoelectric material. When the content ( x ) of Ce is 0, 0.025, 0.05, 0.075, and 0.1, the ZT at 800 ° C is 0.094, 0.107, 0.143, 0.154, and 0.078, respectively. The specimen with the highest ZT among the prepared specimens has a Ce content ( x ) of 0.075 and a value of 0.154 at 800 ° C.

Example  1. Manufactured by tape casting Ca _{0 . 9} La _{0 .One- x} Ce _x MnO _{3 -δ}  (0? X? 0.1) Characteristic analysis result of thermoelectric material

Crystal structure and microstructure

11 is manufactured Ca _{0. 9 La 0 .1- x Ce x MnO} 3 -δ (0≤ x ≤0.1) XRD results of thermoelectric materials are shown. As shown in Fig. 11, the XRD results show that all the thermoelectric materials have an orthorhombic perovskite crystal structure like the specimens prepared by cold pressing. As the content of Ce increases, the diffraction peak shifts to an elevation angle. This can be explained by the reason that the ion radius (1.12 Å) of Ce ^{3 +} is smaller than the ion radius (1.16 Å) of La ^{3 +} , as described above.

Ca _{0 .} FE-SEM results obtained from the surface of ₉ La _{0 .1 - x} Ce _x MnO _{3 - δ} thermoelectric materials can be seen in FIG. Like the specimens prepared by the cold pressing method, the grain size tends to increase as the content of Ce increases. The grain size of the prepared specimen is 2.2 to 8.5 탆, which is larger than that of the specimen prepared by cold pressing (Table 3). Also, as the content of Ce increases, the porosity tends to decrease and the porosity is in the range of 1 to 7%. From these results, it can be seen that the specimen produced by tape casting is denser and the grain size is larger than that produced by the cold pressing method.

Electrical characteristic

Ca ₀ produced by tape casting _{. 9} are shown in _{La 0 .1- x Ce x MnO 3} -δ (0≤x≤0.1) 13 the electric conductivity of the thermoelectric material. Ca _{0 . 9 La 0 .1- x Ce x MnO} 3 _-δ electrical conductivity of the thermoelectric material show a metallic behavior of the electrical conductivity decreases with increasing temperature. The electrical conductivity of the Ca _0.9 La _{0.1- x} Ce _x MnO _{3 -δ} thermoelectric material by the Ce content is the same as that of the thermoelectric material produced by the cold pressing method. In addition, Ca _{0 . 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} thermoelectric materials show higher electrical conductivity than thermoelectric materials produced by cold pressing at the same Ce content. This is probably because the specimen produced by tape casting has larger electron mobility because of the larger density and grain size than the specimen prepared by cold pressing. Content (x) of Ce is 0, 0.025, 0.05, 0.075, and 500 ℃ electrical conductivity of the sample is 0.1, respectively, 283.4, 293.2, 325.6, 345.8, and 310.1 Ω ^-1 ㎝ ^-1.

Fig. 14 is a graph showing the relationship between Ca _{0 . 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) represents the thermal conductivity of the thermoelectric material. The thermal conductivity of all the specimens is negative in the whole temperature range, which is the n-type conduction by electrons. The thermal conductivity of specimens prepared by tape casting method is the same as that of specimens prepared by cold pressing. The absolute thermal conductivity of specimens made by tape casting is about 5 ~ 15 μVK ^{- 1} more than the specimens prepared by cold pressing Respectively. The absolute thermal conductivities at 800 ° C when the Ce content ( x ) is 0, 0.025, 0.05, 0.075, and 0.1 are 110, 115, 120, 125, and 100 μVK ^-1, respectively.

Figure 15 is, Ca _{0. 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) Indicates the output factor of the thermoelectric material. The output factor increases as the content of Ce ( x ) increases from 0 to 0.075, and decreases when it decreases to 0.1. When x = 0.075, the maximum power factor (3.98 × 10 ^-4 Wm ^-1 K ^-2 ) was observed at 800 ° C. It can be seen that, in the same composition, the specimen made by the tape casting method has a larger output factor than the specimen made by cold pressing.

Thermal conductivity

Fig. 16 is a graph showing the relationship between Ca _{0 . 9 La 0 .1- x Ce x MnO} 3 -δ (0≤ x ≤0.1) it is a result of a thermal conductivity measurement of the thermoelectric material at 500 ℃ to 800 ℃ interval. As the content of Ce increases, the thermal conductivity value tends to increase. This trend is consistent with the cold pressing method. It can be seen that, in the same composition, the thermal conductivity of the specimen produced by tape casting is slightly greater than that produced by cold pressing. This is probably due to the decrease in phonon scattering due to the larger density and grain size of the thermoelectric material produced by tape casting. Ce content (x) thermal conductivity at 0, 0.025, 0.05, 0.075, and when 0.1 days, 800 ℃, respectively, 2.18, 2.25, 2.35, 2.49, and 2.70 W · m ^-1 K ^{- 1.}

Dimensionless  Performance Index ( ZT )

Fig. 17 is a graph showing the relationship between Ca _{0 . 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) Indicates the dimensionless figure of merit (ZT) calculated using the output and thermal conductivity of the thermoelectric material. ZT increases as the Ce content ( x ) increases, has a maximum value at 0.075, and tends to decrease at 0.1. The maximum ZT at x = 0.075 specimen is 0.175 at 800 ° C. Specimens made by tape casting show much larger ZT than those prepared by cold pressing. This is because the electrical conductivity and absolute thermal conductivity of the specimen produced by tape casting are larger.

Comparative Example  2. By cold pressing  Manufactured Ca _{0 . 9} La _{0 .One- x} Bi _x MnO _{3 -δ}  (0? X? 0.1) Characteristic analysis result of thermoelectric material

Crystal structure and microstructure

Ca ₀ produced by cold pressing _{. 9} are shown in _{La 0 .1- x Bi x MnO 3} 18 a XRD result of the thermoelectric material of FIG _-δ (0≤ x ≤0.1). Ca _{0 . 9} La _{0 .1 - x} Bi _x MnO _{3 - δ} thermoelectric material has an orthorhombic perovskite crystal structure, and the second phase does not exist. As the content of Bi was changed, it was not possible to observe clear diffraction peaks due to the fact that the difference between the ion radius of Bi ^{3 +} (1.17 Å) and the ion radius of La ³⁺ (1.16 Å) .

19 is manufactured Ca _{0. 9 La 0 .1- x Bi x MnO} 3 -δ shows an FE-SEM results obtained from the surface of the thermoelectric material. It can be seen that grain size and density increase as Bi content increases, and grain size and density increase sharply from 0.075 Bi content ( x ). This is probably because the melting point of Bi ₂ O ₃ (810 ° C) is low. Ca _{0 . 9} La _{0 .1 - x} Bi _x MnO _{3 -?} Thermoelectric material has a grain size of 1.2 to 10.6 μm and a porosity of 2 to 10%. The grain size and porosity of each composition are shown in Table 4 below.

Electrical characteristic

FIG. 20 is a graph showing the results of measurement of the Ca _{0 . 9} La _{0 .1 - x} Bi _x MnO _{3 - δ} (0 _{≤ x ≤} 0.1) This is the electrical conductivity of the thermoelectric material. The Ca _{0 . 9} Electrical conductivity of La _{0 .1 - x} Ce _x MnO _{3 - δ} thermoelectric material The electrical conductivity shows the metallic behavior. Bi content (x) from 0, 0.025, 0.05, 0.075, and 0.1 of the specimen 500 ℃ electrical conductivity, respectively, 195.1, 188.3, 175.4, 223.5, and 248.0 Ω ^-1 ㎝ ^{- 1.} Specimens with x = 0.1 show the highest electrical conductivity. As the Bi content ( x ) increases from 0 to 0.05, the electrical conductivity decreases and the electrical conductivity increases from x = 0.075.

Figure 21 is, Ca _{0. 9} La _{0 .1 - x} Bi _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) The thermal conductivity of the thermoelectric material. The Ca _{0 . 9 La 0 .1- x Ce x MnO} 3 -δ powerful heat the entire temperature range, as the thermoelectric material is (-) has a value, and this means that the main charge carriers of e. Also, as the temperature increases, the absolute thermal power value tends to increase. The absolute thermal osmolality at 800 ° C is 105, 120, 130, 110 and 90, respectively, when the content ( x ) of Bi is 0, 0.025, 0.05, 0.075, a μVK ^-1. Absolute thermal osmolality increases from 0 to 0.05 in the content of Bi ( x ), and absolute thermal osmotion decreases from 0.075.

Figure 22 is, Ca _{0. 9} La _{0 .1 - x} Bi _x MnO _{3 - δ} (0 _{≤ x ≤} 0.1) represents the output factor obtained from the measurement of electrical conductivity and thermal conductivity of the thermoelectric material. The output factor tends to increase with increasing temperature. Ca _{0 . 9 La 0 .1- x Bi x MnO} 3 _-δ output factor of the thermoelectric material, a Bi and La to La or Bi than one days doped specimen co-doped samples have a higher output factor. Among the samples, x = 0.025 specimen has the maximum output factor and has a value of 2.13 × 10-4 Wm ^-1 K ^-2 at 800 ℃.

Thermal conductivity

A Ca ₀ measured at 500 ℃ to 800 ℃ _{temperature. 9} are shown in _{La 0 .1- x Bi x MnO 3} -δ (0≤ x ≤0.1) 23 Thermal conductivity results of the thermoelectric material. As the Bi content increases, the thermal conductivity tends to increase. This is probably due to the increase in grain size and density and the decrease in phonon scattering as the Bi content increases. The thermal conductivity of the specimens with the same Bi content is not significantly affected by temperature and has almost the same value. When the content ( x ) of Bi is 0, 0.025, 0.05, 0.075, and 0.1, the thermal conductivities at 800 ° C are 2.10, 2.21, 2.38, 2.61, and 2.84 W · m ^-1 K ^-1, respectively.

Dimensionless  Performance Index ( ZT )

Ca _{0 . 9 La 0 .1- x Bi x MnO} 3 -δ (0≤ x ≤0.1) it shows the non-dimensional figure of merit (ZT) was calculated using the output parameters and the thermal conductivity of the thermoelectric material obtained in the Figure 24. When the Bi content ( x ) is 0, 0.025, 0.05, 0.075, and 0.1, the ZT at 800 ° C is. 0.094, 0.099, 0.105, 0.086 and 0.056. The specimen with the highest ZT is x = 0.05 and has a value of 0.105 at 800 ℃.

Example  2. With tape casting The Ca _{0 . 9} La _{0 .One- x} Bi _x MnO _{3 -δ}  (0? X? 0.1) Characteristic analysis result of thermoelectric material

Crystal structure and microstructure

Ca ₀ produced by tape casting _{. 9} are shown in _{La 0 .1- x Bi x MnO 3} -δ (0≤ x ≤0.1) 25 the XRD patterns of the thermoelectric material. All specimens have an orthorhombic perovskite crystal structure and a space group of Pnma (62), with a single phase without a second phase. Like the specimens prepared by the cold pressing method, the diffraction peaks did not show a tendency to move as the Bi content varied. This is because the ion radius of Bi ^{3 +} (1.17 Å) is not much different from the ion radius of La ^{3 +} (1.16 Å).

Fig. 26 is a graph showing the relationship between Ca _{0 . 9 La 0 .1- x Bi x MnO} 3 -δ a result of observation of the microstructure of the thermoelectric material, [x = (a) 0, (b) 0.025, (c) 0.05, (d) 0.075, and (e) 0.1 (scale bar: 10 mu m)]. Ca ₀ produced by cold pressing _. Compared with the microstructure of ₉ La _{0 .1 - x} Bi _x MnO _{3 - δ} thermoelectric materials, it was observed that specimens produced by tape casting had larger grains and density than those prepared by cold pressing . As the content of Bi increased, the grain size and density increased significantly. Ca _{0 .} The size of the crystal grains of the ₉ La _{0 .1 - x} Bi _x MnO 3 -? Thermoelectric material is 2.2 to 12.1 탆 and the porosity is 1 to 7%. Ca _{0 . 9 La 0 .1- x Bi x MnO} 3 -δ (0≤ x ≤0.1) to the size and porosity of the composition by the crystal grains of the thermoelectric material are shown in Table 5.

Electrical characteristic

Ca ₀ produced by tape casting _{. 9} are shown in _{La 0 .1- x Bi x MnO 3} -δ (0≤ x ≤0.1) 27 the electric conductivity of the thermoelectric material also. Fig. 27 shows the same electrical conductivity behavior as the specimen produced by cold pressing. At the same Bi content, specimens produced by tape casting show greater electrical conductivity than specimens produced by cold pressing. This is thought to be due to the larger grain size and density than the specimens produced by cold pressing. The electrical conductivities at 500 ° C for specimens with Bi content ( x ) of 0, 0.025, 0.05, 0.075, and 0.1 are 283.4, 269.5, 255.4, 275.3, and 315.8 Ω ^-1 ㎝ ^-1, respectively.

Fig. 35 is a graph showing the relationship between Ca _{0 . 9} La _{0 .1 - x} Bi _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) The relationship between thermoelectric material temperature and thermal conductivity is shown. The thermal conductivity of all the specimens shows n-type conduction with a negative value. The thermoelectric behavior of these specimens is the same as the specimens prepared by cold pressing. The absolute thermal conductivities at 800 ° C when the content ( x ) of Bi is 0, 0.025, 0.05, 0.075, and 0.1 are 105, 125, 135, 115, and 85 μV K ^-1, respectively.

Ca ₀ produced by tape casting _{. 9} are shown in _{La 0 .1- x Bi x MnO 3} -δ (0≤ x ≤0.1) 29 the output factor of the thermoelectric material. Output factor while the content (x) of Bi is increased from 0 to 0.05 was reduced from 0.075. The composition with the highest output factor was x = 0.05 and showed a value of 3.01 W · m ^-1 K ^-2 at 800 ° C. In FIG. 29, specimens co-doped with La and Bi show larger output factors than single doped La or Bi specimens. At the same Bi contents, the specimens made by the tape casting method showed larger output factors than the specimens produced by the cold pressing method. This is probably due to the higher electrical conductivity of the specimen made by tape casting than the specimen made by cold pressing.

Thermal conductivity

Fig. 30 is a graph showing the relationship between Ca _{0 . 9 La 0 .1- x Bi x MnO} 3 -δ (0≤ x ≤0.1) it shows a measurement result of thermal conductivity at 500 ℃ to 800 ℃ temperature range of the thermoelectric material. As the content of Bi increased, the thermal conductivity value tended to increase, which was the same as that of the sample prepared by cold pressing. In the same composition, the thermal conductivity of the specimen produced by tape casting was found to be slightly larger than that of the specimen prepared by cold pressing. This is probably due to the decrease in phonon scattering due to the larger grain and density of the thermoelectric material produced by tape casting. When the content ( x ) of Bi was 0, 0.025, 0.05, 0.075, and 0.1, the thermal conductivities at 800 ° C were 2.18, 2.33, 2.45, 2.72, and 2.88 Wm ^-1 K ^-1 , respectively.

Dimensionless  Performance Index ( ZT )

Figure 31, the each of the prepared Ca _{0. 9 La 0 .1- x Bi x MnO} 3 - δ MnO 3 -δ (0≤ x ≤0.1) shows the non-dimensional figure of merit (ZT) value calculated by using the output parameters and the thermal conductivity of the thermoelectric material. ZT shows a tendency that the content ( x ) of Bi increases from x = 0.075 to x = 0.05. The maximum ZT at specimen x = 0.05 was 0.131 at 800 ° C. Specimens made by tape casting show larger ZT than those made by cold pressing.

As it described above, by using a cold pressure molding method and a tape casting method Ca _{0. 9} La _{0 .1 - x} R _x MnO _{3 -?} (R: Ce and Bi; 0? X? 0.1) thermoelectric materials were prepared. All the prepared specimens had an orthorhombic perovskite crystal structure and grain size and density increased with increasing La and Bi contents. The specimens produced by the tape casting method showed larger grain size and density than the specimens prepared by the cold pressing method.

Ca ₀ produced by cold pressing and tape casting method _{. 9} La _{0 .1 - x} Ce _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) The best thermoelectric properties of thermoelectric materials are Ca _{0 . 9} La _{0 . 025} Ce _{0 . 075} MnO _{3 - ?} . Ca ₀ produced by cold pressing _{. 9} La _{0 .025} Ce _{0 .} The output factor, thermal conductivity, and ZT of the ₀₇₅ MMnO _{3- δ} specimen were 3.22 × 10 ^-4 Wm ^-1 K ² , 2.43 Wm ^-1 K ^-1 , and 0.154 at 800 ° C., respectively, Ca _{0 . 9} La _{0 . 025} Ce _{0 .} The output factor, thermal conductivity, and ZT of the ₀₇₅ MnO _{3- δ} specimen were 3.98 × 10 ^-4 Wm ^-1 K ^-2 , 2.49 Wm ^-1 K ^-1 , and 0.175 at 800 ° C., respectively. The specimens produced by the tape casting method showed a higher performance index than the specimens prepared by the cold pressing method.

Ca ₀ produced by cold pressing and tape casting method _{. 9} La _{0 .1 - x} Bi _x MnO _{3 - δ} (0 ≤ x ≤ 0.1) The best thermoelectric properties of thermoelectric materials are Ca _{0 . 9} La _{0 . 05} Bi _{0 . 05} MnO &lt; ₃ &gt; _{- delta} . Ca ₀ produced by cold pressing _{. 9} La _{0 .05} Bi _{0 . 05} MnO _{3 - δ} specimens were 2.01 × 10 ^-4 Wm ^-1 K ^-2 , 2.38 W m ^-1 K ^-1 , and 0.105 at 800 ° C. and the output factors, thermal conductivity, and ZT of the MnO _{3 -} Ca _{0 . 9} La _{0 . 05} Bi _{0 . 05} MnO _{3- δ} specimens were 3.01 × 10 ^-4 W m ^-1 K ^-2 , 2.45 W m ^-1 K ^-1 , and 0.131 at 800 ° C., respectively. The specimens produced by the tape casting method showed a higher performance index than the specimens prepared by the cold pressing method.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (5)

As a method for producing a CaMnO ₃ thermoelectric material using a tape casting method,
The method for manufacturing a CaMnO ₃ based thermoelectric material includes:
Ca, La, Ce, Bi, Mn, and combinations thereof;
Crushing and drying the first calcined powder and then calcining the second calcined powder;
Mixing the second calcined powder, the solvent and the organic additive to form a slurry; And
The slurry is formed into a sheet form by tape casting and then cut to obtain a CaMnO ₃ based thermoelectric material represented by the following Chemical Formula 1
/ RTI &gt;
Method of manufacturing CaMnO ₃ thermoelectric material:
[Chemical Formula 1]
Ca _0.9 La _{0.1 - x} R _x MnO _{3 - ?,}
In the above formulas,
R is Ce or Bi,
x is 0? x? 0.1.
delete delete A CaMnO ₃ thermoelectric material, which is produced by a tape casting method and expressed by the following formula (1)
[Chemical Formula 1]
Ca _{0 . 9 La 0 .1- x R x MnO} 3 -δ
In the above formulas,
R is Ce or Bi,
x is 0? x? 0.1.
A sheet comprising a CaMnO ₃ based thermoelectric material according to claim 4.

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