JP2010512011A - A method for high explicit numbers in thermoelectric materials with nanostructures - Google Patents

Abstract

Thermoelectric materials with high modulus numbers and ZT values are disclosed. Such materials are often assumed to help increase the ZT value of the material (eg, by increasing phonon scattering by the interface at the coarse grain boundary or the coarse / inclusion interface). Containing nanosized domains (eg, nanocrystals). The ZT value of such materials can be greater than about 1, 1.2, 1.4, 1.5, 1.8, 2, and more. Such materials form nanoparticles from them or nanoparticles mechanically alloyed from the elements that can then be consolidated into new bulk materials (eg, by direct current induction hot pressing). Can be produced from thermoelectric starting materials. Non-limiting examples of starting materials include bismuth, lead and / or silicon based materials that can be alloyed, atomic and / or doped. Further disclosed are various compositions and methods (eg, controlled doping) relating to embodiments of thermoelectric materials having nanostructures.
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Description

Cross-reference of related applications

  This application is a continuation-in-part of US patent application Ser. No. 10 / 977,363, filed Oct. 29, 2004, entitled “Nanocomposites with high thermoelectric properties”. Claims the benefit of US Provisional Patent Application No. 60 / 872,242, filed Dec. 1, 2006, entitled "Method for High Indicative Numbers". The contents of all these applications are hereby incorporated by reference in their entirety.

  The present application generally relates to thermoelectric materials and methods for their processing, and more specifically to such thermoelectric materials that exhibit high thermoelectric properties.

The thermoelectric property of any material is defined as Z = S ² σ / k, where S is the Seebeck coefficient, σ is the electrical conductivity, and k is the total thermal conductivity, A feature can be represented by an amount called the figure number Z (or dimensionless figure number ZT). It is desirable to construct materials with high ZT values (eg, with low thermal conductivity k and / or high power factor S ² σ). As an example, such materials could be used to construct high quality power generation and cooling devices.

  In one embodiment, the present invention produces a plurality of nanoparticles from a starting material, such as a thermoelectric bulk material, and the nanoparticles are consolidated under pressure at an elevated temperature, for example, less than about 2000 ° C., less than about 1000 ° C. Relates to a method of processing a thermoelectric material by forming a thermoelectric material that exhibits a higher ZT value than a thermoelectric starting material at a temperature of less than about 600 ° C., less than about 200 ° C., or less than about 20 ° C. In some cases, the peak ZT value of the formed material can be about 25% to about 1000% greater than the peak ZT value of the starting material. In other cases, the peak ZT value of the material formed can be substantially greater than 1000% of the peak ZT of the starting material.

  The term “nanoparticle” is generally known in the art, and as used herein is a material having a size (eg, average or maximum size) of less than about 1 micron, such as in the range of about 1 nm to about 1000 nm. Used to represent particles. The size can preferably be less than about 500 nanometers (nm), preferably in the range of about 1 to about 200 nm, and more preferably in the range of about 1 to about 100 nm. Nanoparticles can be produced, for example, by breaking the starting material into nanosized pieces (eg, by dry grinding, wet grinding, or grinding using any other suitable method). As an example, a ball milling method can be used to achieve the desired nanoparticles. In order to further reduce the size of the particles, additional cooling can optionally be used during the production of the nanoparticles (eg, the starting material can be cooled during milling). Some other methods of nanoparticle production can include condensation from the gas phase, wet chemical methods, and other methods of forming nanoparticles. Optionally, nanoparticles of different elemental materials (eg, bismuth or tellurium) can be produced separately and then consolidated into the resulting thermoelectric material as discussed further below.

The nanoparticles can be consolidated under a selected temperature and selected pressure to induce sufficient electrical coupling between the nanoparticles to form the thermoelectric material produced. As an example, current induced hot pressing (also known as plasma pressure compression, “P ² C” or spark plasma sintering, SPS), unidirectional hot pressing and iso- Hot presses including the static hot press method can be used. The selected pressure can be, for example, in the range of about 10 MPa to about 900 MPa, or in the range of about 40 MPa to about 300 MPa, and preferably in the range of about 60 MPa to about 200 MPa. The temperature selected is, for example, in the temperature range between about 200 ° C. to about the melting point of the thermoelectric material (eg, 200 ° C. to about 2000 ° C.), or about 400 ° C. to about 2 ° C. for Bi ₂ Te ₃ based materials. It can be in the range of about 1200 ° C, or in the range of about 400 ° C to about 600 ° C, or in the range of about 400 ° C to about 550 ° C.

  In a related embodiment of the above method, the step of consolidating the nanoparticles comprises a density within the range of about 90% to about 100% of the respective theoretical density (eg, a porosity of less than about 10% to less than about 1%. ) Represents the step of compacting the nanoparticles to provide a material exhibiting

In related embodiments, the thermoelectric material produced by the method of the present invention as discussed above is greater than about 1, or greater than about 1.2, or greater than about 1.4, and preferably about 1.5. And most preferably greater than about 2 ZT values (eg, peak ZT values). Further, in many embodiments, the thermoelectric material is at a specific operating temperature that may depend, for example, on the melting point of the material, eg, less than about 300 ° C. for a Bi ₂ Te ₃ -based material. High ZT value at temperature. High ZT values can also depend on the doping level and / or the microstructure of the material.

  In many cases, the starting thermoelectric material (eg, starting bulk material or fluid phase material for synthesizing particles) exhibits a ZT of less than about 1, and optionally more than about 0.1, and is nano-sized from the starting material. The final thermoelectric material obtained by generating particles (eg, breaking the starting material by grinding or other suitable method) and consolidating these nanoparticles is about 1, 1.1, 1.2. ZT values exceeding 1.3, 1.4, 1.5 or 2 are indicated.

Various thermoelectric materials can be used as starting materials in the practice of the invention. The starting thermoelectric material can be p-doped or n-doped. Exemplary starting thermoelectric materials include, but are not limited to, bismuth-based, lead-based or silicon-based materials. For example, the starting thermoelectric material may comprise a bismuth-antimony-tellurium alloy, a bismuth-selenium-tellurium alloy, a lead-tellurium alloy, a lead-selenium alloy, or a silicon-germanium alloy (eg, SiGe). it can. As an example, in some embodiments, the thermoelectric material can be an alloy of Bi ₂ Te _3-x Se _x, where x is in the range of about 0 to about 0.8. Alternatively, in some other embodiments, the thermoelectric material can be an alloy of _{Bi x Sb 2-x Te 3} [ where x is in the range of about 0 to about 0.8. In some embodiments, a starting thermoelectric material having a polycrystalline structure that can optionally include an average grain size (eg, greater than about 1 micron) can be used.

  In other embodiments, the nanoparticles are produced in less than about 1000 nm, or less than about 500 nm, or less than about 200 nm, and preferably less than about 100 nm, such as in the range of about 1 nm to about 200 nm, or about 1 nm to It can be generated from the starting thermoelectric material to have a size (eg, average or maximum size) in the range of about 100 nm, and preferably in the range of about 1 nm to about 50 nm. Such a particle size can be produced by any method discussed herein, such as grinding the starting material by a ball mill or other suitable method.

In a related aspect of the above method, the nanoparticles are maintained under pressure and elevated temperature for a period of time, for example from about 1 second to about 10 hours, to produce a thermoelectric material with resultant enhanced thermoelectric properties. The In other embodiments, the nanoparticles are exposed to a selected temperature while being maintained at low pressure or atmospheric pressure for a time sufficient to result in the formation of a thermoelectric material. In other embodiments, the nanoparticles are consolidated at room temperature under high pressure to form a sample with a high theoretical density (eg, about 100%) and then annealed at a high temperature to produce a final thermoelectric material. Can be formed.

  Another aspect relates to a method of forming a thermoelectric material that includes generating a plurality of nanoparticles. As an example, the particles can be generated by a process of grinding one or more bulk elemental materials. For example, nanoparticles can grind at any workable proportion of at least two different bulk elemental materials, such as bismuth and tellurium, bismuth and selenium, antimony and tellurium, antimony and selenium, and silicon and germanium. Can be generated. In such a case, at least two types of nanoparticles can be formed. If the different types of particles are produced separately, the particles can be mixed and further ground (eg, a ball mill) to form mechanically alloyed particles. Alternatively, the various bulk materials can all be ground simultaneously to form mechanically alloyed particles. Nanoparticles formed using mechanical alloying or a mixture of nanoparticles produced separately from elements, compounds or alloys are consolidated under pressure and elevated temperature to exhibit a ZT value greater than about 1 A thermoelectric material can be produced as a result. Optionally, a dopant can be added to the mixture. In other embodiments, the nanoparticles are particles from a source material with good ZT values (eg, greater than about 0.5) and / or micron-sized particles (eg, from about 1 micron to about 10, 50, It can be consolidated with other types of particles, such as particles having an average size of 100 or 500 microns.

  In other embodiments, the structure has a ZT value greater than about 1 (eg, a peak ZT value), and preferably greater than about 1.2, or greater than about 1.5, or even greater than about 2. A thermoelectric material is provided that includes a structure of material comprising a plurality of inclusions having an average size in the range of about 1 nm to about 500 nm.

  In related embodiments, the thermoelectric material can exhibit the ZT value at a temperature of less than about 2000 ° C, or less than about 1000 ° C, or less than about 600 ° C, or less than about 200 ° C, or less than about 20 ° C. Further, the average particle size can be in the range of about 1 to about 500 nm. The structure is substantially free of coarse grains greater than about 500 nm (eg, substantially free of coarse grains having an average and / or maximum dimension greater than about 500 nm), or some larger (eg, Coarse grains (with a particle size greater than about 1 μm) can be included.

  In other embodiments, the one or more coarse grains can have a size, for example, in the range of about 1 to about 50 nm, or in the range of about 1 nm to about 20 nm. Or other inclusions are included therein. The precipitate regions are different compositions and / or the same composition, but can be characterized by different crystal orientations and / or different phases for the rest of the particles.

  In other embodiments, the thermoelectric material can have a density in the range of about 90% to about 100% of the respective theoretical density. As an example, the thermoelectric material can exhibit a porosity of less than about 10%, and preferably less than about 1%.

  In related embodiments, the thermoelectric material is formed of small crystalline grains that are randomly oriented with respect to each other (eg, less than about 500 nm, or less than about 200 nm, and preferably from about 1 nm to about 100 nm). A polycrystalline structure (with an average size in the range).

  One aspect of the invention relates to a thermoelectric material that can include a material structure having a plurality of coarse grains. The coarse particles can have an average size in the range of about 1 micron to about 10 microns, or in the range of about 1 micron to about 5 microns, or in the range of about 1 micron to about 2 microns. At least some of the coarse grains can include one or more precipitate regions or other types of inclusions. Such regions can have an average size of about 1 nm to about 100 nm, or about 1 nm to about 50 nm. The thermoelectric material can have a ZT value greater than about 1, 1.2, 1.5 or 2. For example, the ZT value can also be in the range of about 1 to about 5. Thermoelectric materials can exhibit such ZT values at operating temperatures of less than about 2000 ° C, or less than about 1000 ° C, or less than about 600 ° C, or less than about 200 ° C, or less than about 20 ° C. Coarse grains can be formed from a variety of materials such as any combination of bismuth-based alloys, lead-based alloys and silicon-based alloys.

Another aspect of the invention reaches a thermoelectric material comprising a host material having a plurality of inclusions or particles dispersed throughout the host. The particles or inclusions can have a size below a certain threshold, for example, less than about 20 microns. The host material comprises one or more coarse particles having a size (eg, maximum particle size and / or average size of any dimension) of which at least some of the coarse particles are greater than about 1 micron or less than about 1 micron. Can be included. In some embodiments, the majority of charge carriers in the host material, eg, greater than 50%, 80%, 90%, and preferably 99%, are due to the presence of these inclusions. The host material is not as highly doped as in typical thermoelectric materials. In some embodiments, the particles can be more highly doped than the host material. Thermoelectric materials have a higher carrier concentration and / or charge carrier mobility than the host material carrier concentration and / or charge carrier mobility, respectively, in the absence of particles or inclusions, and consequently higher power factor (S ² σ ). Additionally or alternatively, the thermoelectric material has an energy band (eg, conduction band or valence band) for the charge carrier type that has a higher energy compared to the associated energy band of the host material for the corresponding charge carrier type. Can be characterized by inclusions having The thermoelectric material can optionally include a number of properties discussed herein with respect to the thermoelectric material. For example, the thermoelectric material can exhibit a ZT value greater than about 1, 1.1, 1.2, 1.3, 1.4, 1.5, or 2.

Some embodiments of the present invention can be better understood with reference to the following drawings, which are not necessarily drawn to actual measurements.
FIG. 5 is a scheme of multiple coarse grains in a thermoelectric material, where some coarse grains include one or more precipitate regions, in accordance with some embodiments of the present invention. FIG. 3 is a schematic diagram of a host material with an inclusion embedded therein, according to some embodiments of the present invention. 1B is a scheme of the conduction energy diagram of the material represented in FIG. 1B. FIG. 4 is an XRD diagram of p-type BiSbTe nanoparticles prepared by ball milling, according to some embodiments. 3 is a SEM image of the p-type BiSbTe nanoparticles of FIG. 3 is a relatively low resolution TEM micrograph of the BiSbTe nanoparticles of FIG. 3B is a relatively high resolution TEM micrograph of BiSbTe nanoparticles shown in FIG. 3B. 2 is a diagram and photograph of a DC hot press (plasma pressure or spark plasma sintering process) that can be used with some embodiments of the present invention. FIG. 3 is a graph illustrating the temperature dependence of the electrical conductivity of a current state of the art bulk material of a thermoelectric material prepared from the particles of FIG. 2 and a p-type BiSbTe alloy according to some embodiments. FIG. 3 is a graph representing the temperature dependence of the Seebeck coefficient of a current state of the art bulk material of a thermoelectric material prepared from the particles of FIG. 2 and a p-type BiSbTe alloy according to some embodiments. FIG. 3 is a graph depicting the temperature dependence of the power factor of a current state of the art bulk material of a thermoelectric material prepared from the particles of FIG. 2 and a p-type BiSbTe alloy according to some embodiments. FIG. 3 is a graph representing the temperature dependence of the thermal conductivity of a current state of the art bulk material of a thermoelectric material prepared from the particles of FIG. 2 and a p-type BiSbTe alloy according to some embodiments. FIG. 3 is a graph showing the temperature dependence of ZT of thermoelectric materials prepared from the particles of FIG. 2 and the current state of the art bulk material of p-type BiSbTe alloys according to some embodiments. 3 is a TEM micrograph of a thermoelectric material prepared from the particles of FIG. 3 is an enlarged TEM micrograph of a thermoelectric material prepared from the particles of FIG. 2 showing the nanosize of the closely packed nanoparticles. FIG. 12 is a TEM micrograph of a thermoelectric material prepared from the particles of FIG. 2, showing the presence of larger coarse particles than the nanoparticles shown in FIG. FIG. 3 is a TEM micrograph of a thermoelectric material prepared from the particles of FIG. 2 showing the presence of nanodots. 3 is a TEM micrograph of a thermoelectric material prepared from the particles of FIG. 2 showing the presence of nanodots with small angle boundaries. FIG. 3 is a TEM micrograph of a thermoelectric material prepared from the particles of FIG. 2 showing a Te precipitate, where the inset in the figure shows an electron diffraction pattern of the Te precipitate. 6 is a graph depicting the temperature dependence of the electrical conductivity of a thermoelectric material prepared from a p-type SiGe bulk starting material, according to some embodiments. 2 is a graph depicting the temperature dependence of the Seebeck coefficient for thermoelectric materials prepared from p-type SiGe bulk starting material, according to some embodiments. 2 is a graph depicting the temperature dependence of the thermal conductivity of a thermoelectric material prepared from a p-type SiGe bulk starting material, according to some embodiments. FIG. 4 is a graph illustrating the temperature dependence of ZT, the thermometric material prepared from p-type SiGe bulk starting material, according to some embodiments. 6 is a graph depicting the temperature dependence of the electrical conductivity of thermoelectric materials prepared from n-type SiGe bulk starting materials, according to some embodiments. 2 is a graph depicting the temperature dependence of the Seebeck coefficient for thermoelectric materials prepared from n-type SiGe bulk starting material, according to some embodiments. 6 is a graph depicting the temperature dependence of the thermal conductivity of thermoelectric materials prepared from n-type SiGe bulk starting materials, according to some embodiments. FIG. 6 is a graph showing the temperature dependence of ZT, the thermoelectric material prepared from n-type SiGe bulk starting material, according to some embodiments. 2 is a TEM micrograph of a ball mill sample of SiGe bulk starting material, in accordance with some embodiments of the present invention. FIG. 25 is a TEM micrograph of the particles of FIG. 24 after hot pressing, with the inset showing the corresponding electron diffraction pattern on the sample. It is a high-resolution TEM micrograph of the hot press sample shown in FIG. 6 is a graph depicting the temperature dependence of the electrical conductivity of thermoelectric materials prepared from bulk starting materials of p-type Bi _0.3 Sb _1.7 Te ₃ according to some embodiments. 6 is a graph depicting the temperature dependence of the Seebeck coefficient of thermoelectric materials prepared from bulk starting material of p-type Bi _0.3 Sb _1.7 Te ₃ according to some embodiments. 6 is a graph depicting the temperature dependence of the thermal conductivity of a thermoelectric material prepared from a bulk starting material of p-type Bi _0.3 Sb _1.7 Te ₃ according to some embodiments. FIG. 4 is a graph showing the temperature dependence of ZT, a thermoelectric material prepared from bulk starting material of p-type Bi _0.3 Sb _1.7 Te ₃ according to some embodiments. 6 is a graph depicting the temperature dependence of the electrical conductivity of a thermoelectric material prepared from p-type Bi _0.5 Sb _1.5 Te ₃ bulk starting material, according to some embodiments. 6 is a graph illustrating the temperature dependence of the Seebeck coefficient of thermoelectric materials prepared from bulk starting material of p-type Bi _0.5 Sb _1.5 Te ₃ according to some embodiments. 6 is a graph depicting the temperature dependence of the thermal conductivity of a thermoelectric material prepared from a bulk starting material of p-type Bi _0.5 Sb _1.5 Te ₃ according to some embodiments. FIG. 6 is a graph showing the temperature dependence of ZT, the thermoelectric material prepared from bulk starting material of p-type Bi _0.5 Sb _1.5 Te ₃ according to some embodiments.

Detailed Description of the Invention

  In one aspect, the present invention relates to thermoelectric materials having high ZT values and methods for making such materials. In general, such thermoelectric materials typically comprise a plurality of coarse grains. Such coarse grains can be in the form of nano-sized coarse grains that can be obtained, for example, from a bulk material such as a starting thermoelectric material. Thermoelectric materials according to embodiments of the present invention can generally include coarse particles of various sizes. For example, the thermoelectric material can include some coarse particles larger than 1 μm and some coarse particles smaller than 1 μm. In some embodiments, the thermoelectric material can be substantially free of coarse grains that can adversely affect the ZT value of the material (eg, about 5%, 10%, 15%, 20% 25%, 30%, 40% or more than 50%, substantially free of inconvenient coarse grains that can reduce the ZT value of the total material). Some embodiments relate to thermoelectric materials that include a plurality of coarse grains having an average grain size in the micron dimension (eg, greater than about 1 micron). In some cases, the material may be substantially free of large coarse grains. Non-limiting examples include examples that are substantially free of coarse grains greater than about 5000 nm, 1000 nm, 300 nm, 100 nm, 50 nm, 20 nm, or 10 nm. In many cases, such coarse particles can optionally include one or more precipitate regions or other types of inclusions having, for example, an average size in the range of about 1 nm to about 50 nm. In some preferred embodiments, at least some, and preferably substantially all of the coarse particles comprise precipitate regions, nanoparticles and / or other types of inclusions, these various inclusions being Can be formed in situ by chemical reactions and / or by insertion of such inclusions. Further embodiments provide for materials with multiple particle sizes (eg, at least some nano-sized coarse particles and some of which some coarse particles can optionally include precipitate regions or other types of inclusions. Coarse particles exceeding 1 micron). In other words, the thermoelectric material of the present invention includes coarse particles of sub-micron size with or without a precipitate region, coarse particles having a size greater than 1 micron with or without a precipitate region (e.g., controlled doping). any combination of sub-micron coarse particles and coarse particles of greater than 1 micron, with or without precipitate regions. Any of these coarse grains include a plurality of mechanisms including, but not limited to, formation of precipitate regions during compression of the material, insertion of particles into the host matrix and / or formation of solid state chemical reactions. Can be formed.

The ZT value of the thermoelectric material of the present invention can take various values. For example, the peak ZT value or average ZT value of the material is then converted from the starting material into nanoparticles and the thermoelectric material is formed by consolidating the nanoparticles under pressure and high temperature. Greater than the peak ZT value or the average ZT value. For example, the ZT value of the material can be about 25% to about 1000% greater than the ZT value of the starting material. In other examples, the ZT value of the material can be substantially greater than 1000% of the ZT value of the starting material. The starting material can have a range of ZT values. In some embodiments, the formed material has a ZT value of about 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, It can be greater than 1.7, 1.8, 1.9 or 2. In some embodiments, the thermoelectric material can exhibit a ZT value in a range where the lower limit is one of the ZT values and the upper limit reaches a value of about 4, 5 or 6.

Although these elevated ZT values can be specified without temperature constraints, in some embodiments, thermoelectric materials can exhibit elevated ZT values at specific temperatures or within a temperature range. . For example, thermoelectric materials can exhibit elevated ZT values at temperatures below about 2000 ° C., below about 1000 ° C., below about 800 ° C., below about 600 ° C., or below about 400 ° C. In other examples, the thermoelectric material is at room temperature (eg, a temperature of less than about 200 ° C, less than about 150 ° C, less than about 100 ° C, less than about 60 ° C, less than about 40 ° C, less than about 30 ° C, or less than about 20 ° C). A ZT value can be shown that rises in a temperature range that begins to approach or includes it. In yet another example, the thermoelectric material may exhibit an increased ZT value in a temperature range approaching or including cryogenic temperatures (eg, temperatures below about 0 ° C., less than about −50 ° C., or less than about −100 ° C.). Such materials can be useful for certain cooling devices such as air conditioners, refrigerators or superconductors. In some embodiments, the temperature range within which elevated ZT values are exhibited can depend on the composition of the thermoelectric material. In some non-limiting examples, the boron-carbide group composition can exhibit an increased ZT value below about 2000 ° C. in some embodiments, and in some embodiments, the SiGe group composition The article can exhibit an elevated ZT value below about 1000 ° C., and in some embodiments, the PbTe-based composition can exhibit an elevated ZT value below about 600 ° C. and / or In this embodiment, the Bi ₂ Te ₃ based composition can exhibit an elevated ZT value below about 200 ° C. In other non-limiting examples, the thermoelectric material comprises Bi _x Sb _1-x and exhibits an elevated ZT value below room temperature (eg, below about 20 ° C.).

Although not necessarily limited by any particular theory, it is believed that the high ZT value of such thermoelectric materials can be the result of changes in any combination of thermal conductivity, Seebeck coefficient and electrical conductivity. Thermal conductivity has two contributions: lattice and electron contributions. In single crystal or polycrystalline samples containing large coarse grains, the thermal conductivity of the lattice is fixed to a specific substance. However, if the bulk material consists of nano-sized coarse particles and / or nanoparticles embedded in larger coarse particles, consider the three effects that result from nanoparticles and / or embedded nanoparticles can do. First, the portion of the thermal conductivity lattice is degraded by phonon interfacial scattering. Secondly, the Seebeck coefficient can be increased due to the filter effect of the carrier (usually low energy electrons / vacancies are scattered thereby increasing the Seebeck coefficient), and thirdly the electrical conductivity is It can be increased due to the controlled doping effect—particles act as carriers (electrons and vacancies) and thus reduce the scattering of impurities compared to uniformly doped conventional materials. Because the barrier can preferentially scatter one type of charge (electrons or vacancies) without substantially affecting other types of carriers, the contribution of electrons to thermal conductivity, especially heat The bipolar contribution to conductivity can be reduced by interfacial barrier scattering of electrons. In addition, the quantum size effect can further affect the Seebeck coefficient and electrical conductivity such that S ² σ is increased. Thus, some embodiments of the present invention may be used to produce denser samples (eg, theoretical density) by hot pressing including, for example, ball milling the starting material and P ² C, unidirectional hot pressing, isostatic hot pressing. From about 90% to about 100%) can be utilized. These hot pressed samples typically exhibit low thermal conductivity compared to their bulk counterparts, thus increasing the ZT value and power factor if ZT acquisition from a decrease in thermal conductivity is sufficient. Can also be reduced, but the power factor is usually maintained or increased.

In some embodiments, the thermoelectric material can comprise coarse particles produced from a bulk starting material, such as a bulk thermoelectric material. Examples include bulk starting materials with large power factors and / or starting materials with good ZT values (eg, ZT values greater than about 0.1). For example, the starting ZT can be greater than about 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 or more. In some non-limiting examples, the starting material has a ZT value less than about 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or 2. Can do. In other examples, the starting thermoelectric material has a high thermal conductivity (eg, greater than 2 W / mK) but a high power factor (eg, greater than 20 μW / cm-K ² and preferably 40 μW / cm-K). ⁽ S ² σ) greater than ² . Such bulk thermoelectric materials can be specially prepared or commercially available materials can be used. Many bulk starting materials are solids that can be broken to produce coarse grains, but loose starting materials are also from gas or wet chemical methods when producing coarse grains from gas phase condensates. Coarse grains can be produced from other thermodynamic states, such as liquid. Furthermore, it is understood that coarse grains can be generated from more than one bulk starting material, or a mixture of materials with different thermodynamic phases (eg, a mixture of liquid and gas).

Although a number of starting materials can be used in some embodiments, the bulk starting material can be selected from any combination of bismuth-based materials, lead-based materials, and / or silicon-based materials. In some embodiments, the bulk starting material is a bismuth-antimony-tellurium alloy, a bismuth-selenium-tellurium alloy, a bismuth-antimony-tellurium-selenium alloy, a lead-tellurium alloy, a lead-selenium alloy, It can be derived from various alloys such as silicon-germanium alloys or any combination thereof. Specific embodiments may relate to using bulk starting materials that are either p-type or n-type materials. For example, such starting materials can be a modified form of a parent composition such as Bi ₂ Te ₃ . As an example, an n-type material may have a bulk material stoichiometry of the formula Bi ₂ Te _3-x Se _x where x is in the range of about 0 to about 0.8. In addition, it can be obtained by replacing tellurium in Bi ₂ Te ₃ with selenium. For p-type materials, for example, using antimony, the stoichiometric composition of the bulk material is of the formula Bi _x Sb _2-x Te ₃ [where x is from about 0 to about 0.8. Bismuth can be substituted to have [in range]. In a specific embodiment, the bulk starting material used is Bi _0.5 Sb _1.5 Te ₃ . In general, the bulk starting material can be a crystalline material or a polycrystalline material (eg, a polycrystalline having an average grain size greater than about 1 micron). Other examples of the starting _{material, MgSi 2, InSb, GaAsCoSb 3} , Zn 4 Sb 3, and the like. In some cases, the bulk starting material can be a material with a threshold power factor value S ² σ, for example, greater than about 20 μV / cm K ² . In such cases, the bulk starting material can have a significant ZT value (eg, greater than about 0.1) due to the low thermal conductivity of the bulk starting material, or the power factor is a threshold Although this can be the case, the ZT value of the starting material can be low due to the relatively high thermal conductivity of the material.

  In some embodiments, particles of thermoelectric material (eg, nanoparticles) can be generated from bulk starting material or elemental material by methods other than grinding / milling one or more starting materials. The particles can be produced by a number of methods, including methods known to those skilled in the art. Non-limiting examples include gas phase condensation, laser ablation, chemical synthesis (eg, wet or dry methods), rapid cooling of sprays, and the like. Accordingly, the scope of this application is not limited to the specific particle production methods discussed herein. It will be appreciated that the particle generation methods can be combined in any way to produce a material for consolidation. For example, some particles can be produced by a ball mill (eg, to produce a host material), while other particles can be one or more other methods (eg, gas phase condensation, laser ablation, etc. ).

  The coarse grains forming the thermoelectric material can have various characteristics. In some embodiments, each coarse grain has a crystalline structure. In such cases, the thermoelectric material may comprise a polycrystalline-like structure whose coarse grains generally lack a suitable orientation (eg, randomly distributed). In some cases, the coarse grains also have a certain type of preferred orientation, depending on the shape of the coarse grains, whose overall crystallographic direction may be random with respect to each other or exhibit some preferred direction. Can show. Thus, such embodiments include superlattice structures formed as an average crystal structure (eg, a stack of multiple semiconductor layers) despite small defects or compositional non-uniformities in the average crystal structure. Is substantially different from many known thermoelectric materials.

  Coarse grains composed of the various thermoelectric materials discussed herein can have various sizes. In some embodiments, the size is generally on a nanometer scale and is generally less than 1 micron. For example, the coarse particles can have an average particle size of less than about 500 nm, or less than about 200 nm, or less than about 100 nm, or less than about 50 nm, or less than about 20 nm. In such embodiments, the average particle size can be greater than some lower threshold (eg, about 1 nm). In some cases, the average particle size can be determined using a variety of methods, including methods understood by those skilled in the art. For example, in that case, coarse particles can be photographed using a transmission electron microscope (herein “TEM”) whose size can be determined and an average calculated. Since coarse particles typically have an irregular shape, the measured size of the coarse particles can be determined using a number of methods, including methods known to the expert. For example, the largest dimension of the coarse grain from the image (eg, SEM and / or TEM image) can be used, or the effective particle size can be based on a coarse particle surface area measurement or effective cross-sectional area from the image. Can be calculated.

  In many embodiments of the present invention, the coarse grain of the thermoelectric material can be consolidated so that the final product exhibits desired properties such as elevated ZT values. In some embodiments, the thermoelectric material comprises consolidated coarse particles in a structure that exhibits a low porosity that can assist in obtaining elevated ZT values (eg, the actual product of the final product). The density can approach the theoretical density of the composition, for example, the bulk starting material used in some embodiments to produce nanoparticles). Porosity is defined as the difference between the theoretical and actual density of a material divided by the theoretical density. The term “theoretical density” is generally known to those skilled in the art. The porosity of the material can be about 10%, 5% or 4%, or 3%, or 2%, or 1%, or 0.5% or less than 0.1%. In some embodiments, the thermoelectric material exhibits a density close to 100% of the theoretical density. In some embodiments, the density of the thermoelectric material is 100% of the respective theoretical density and 90%, 95%, 96%, 97%, 98%, 99%, 99.5% or 99.9%. Can be between. While not necessarily constrained by theory, it is believed that increasing the density can help maintain the electrical conductivity of the material, and can help maintain contact between the coarse grains.

Some embodiments relate to thermoelectric materials formed from a plurality of coarse particles, wherein the one or more coarse particles can include one or more precipitate regions. As an example, FIG. 1 schematically illustrates a thermoelectric material that exhibits a polycrystalline structure including a plurality of coarse grains 110. The coarse particles further include one or more precipitate regions 120, which can increase the thermoelectric properties of the material. The precipitate region can be characterized by a compositional non-uniformity such that it has a different composition and / or phase than the rest of the coarse grain. The precipitate region can also be characterized by having a similar crystal structure with respect to the matrix in which it is oriented, although oriented in different crystal directions. In some embodiments, the one or more precipitate regions can be embodied as separate particles (eg, nanoparticles) embedded in the coarse particles or the presence of the precipitate region The entire coarse grain can be embodied as a crystal despite the defects due to. In some embodiments, the thermoelectric material can include other coarse grains that do not have a precipitate region. In an alternative embodiment, substantially all of the coarse particles comprising the thermoelectric material include a precipitate region. The precipitate region typically has a size (eg, maximum average size) of less than about 10 nm, or less than about 50 nm (eg, in the range of about 1 nm to about 50 nm). The formation of a precipitate region is a U.S. patent filed Oct. 29, 2004 entitled “Nanocomposites with High Thermoelectric Properties”, which is incorporated herein by reference in its entirety. This can be accomplished in a variety of ways, including those discussed in U.S. Patent Application Publication No. 2006/0102224, carrying application number 10 / 977,363.

  In some cases, the precipitate region is generated spontaneously, for example, by formation of a thermoelectric material by the methods discussed herein. In other cases, the precipitate region is generated by mixing two nanoparticles with different melting points. For example, one type can have a lower melting point than the other. Nanoparticles with a lower melting point by mixing the nanoparticles and heating / consolidating them (eg, near the melting point of one type of nanoparticle but below the melting point of the other type) Can form coarse particles around other types of nanoparticles. In other words, coarse particles formed of one type of nanoparticles can embed the other type of nanoparticles. Examples of ensemble materials that can be used to form such embedded nanoparticles include bismuth-tellurium material systems, lead-tellurium material systems, silicon-germanium material systems, and the like.

The above discussion is clearly related to precipitate formation in thermoelectric materials, but other materials are formed by utilizing other types of inclusions in the matrix (eg, using nanoparticles in the host). Must be understood. For example, two or more types of nanoparticles can be mixed together to form a thermoelectric material that may be free of precipitates but still have beneficial properties (eg, use of controlled doping). . Accordingly, the disclosure herein regarding precipitates can also be utilized with other types of inclusions where appropriate. For example, the precipitate or inclusion region reacts with Si in the SiGe host to form particles such as MoSi ₂ , FeSi ₂ , MgSi ₂ , Mo, Fe, Mn, Mg, Ag, Cr, W, It can be formed by solid state chemical reaction of particles with a host such as Ta, Ti, Cu, Ni or V metal particles.

  Although not limited to any specific theory, it is believed that the sediment region or other type of inclusion increases phonon scattering in the thermoelectric material, which can lead to a decrease in the thermal conductivity of the material. It is done. Furthermore, the n-doped or p-doped regions can increase the electrical conductivity of the material, for example, by a controlled doping mechanism. In such cases, some or all of the charge carriers (electrons and vacancies) can be donated by precipitate regions or other inclusions embedded in larger coarse grains. Since the distance between the inclusion regions may be greater than the distance between the dopants of the atoms in the uniformly doped material, the charge carrier impurity scattering is compared to that in the uniformly doped material. Will be reduced. Such a controlled doping-like mechanism can increase the electrical conductivity by improving the mobility of the support. In some cases, these precipitate regions or other inclusions can also improve the Seebeck coefficient by scattering lower energy carriers than higher energy carriers. Thus, the sediment region or other inclusion can improve the ZT of the thermoelectric material.

  In other embodiments, the precipitate region, or the coarse region or other inclusions can be preferentially doped. In such an environment, the carriers in these regions can fall into the surrounding host medium when they are at higher potential energy. For example, in the case of controlled doping, doping in the host material is correspondingly reduced or eliminated entirely, thus increasing electron mobility in the host by reducing the scattering of ionized impurities.

Embodiments that include precipitate regions or other inclusions in the coarse particles can exhibit multiple particle sizes. In some embodiments, the particle size follows any size described herein for coarse particles, generally less than 1 micron. For example, the average particle size can be less than about 500 nm, about 200 nm, about 100 nm, about 50 nm, or about 20 nm. Alternatively or additionally, the average particle size can be greater than about 1 nm. In other embodiments comprising one or more inclusions, the particle size can be greater than 1 micron. For example, the plurality of coarse grains can have an average size of up to about 2, 5, or 10 microns. In specific embodiments, the plurality of coarse grains have an average size in the range of about 1 micron to about 10 microns, or in the range of about 1 micron to about 5 microns, or in the range of about 1 micron to about 2 microns.

  The size of the sediment area or inclusion can also vary. For example, the size of the precipitate region may be limited by the size of the coarse grain in which it is embedded. In many embodiments, the precipitate region or inclusion can preferably have an average size in the range of about 1 nm to about 50 nm, or in the range of about 1 nm to about 20 nm. In other cases, for example, when a controlled doping mechanism is used to increase electronic performance, the precipitate region or inclusion can have a larger size, eg, 1 nm to 10 microns, On the other hand, alloy formation or nanoparticle formation achieves a decrease in the thermal conductivity of the phonons in the surrounding region.

  Some embodiments relate to engineered thermoelectric materials that exhibit controlled doping to achieve high modulus numbers. In some embodiments, the thermoelectric material can include particles (eg, nanoparticles) or other inclusions embedded in the host material, where the inclusions are charged carriers (eg, electrons or pores) to the host. ), Thereby increasing the mobility of the support in the host. This can advantageously increase the overall electrical conductivity of the material, thus improving its thermoelectric performance, which is characterized, for example, by the ZT value of the material. In many such cases, the host is initially undoped or has an n-type or p-type doping level (typically spatially substantially lower than typical doping values for thermoelectric materials). The doping level being uniform). For example, the initial doping level of the host can be lower by a factor of 1.5, 2, 5, 10, 100 or 1000 than conventional thermoelectric materials. Furthermore, embedded inclusions (eg, precipitate sites or distinguishable particles) can be formed of doped or undoped materials.

  According to one example, FIG. 1B schematically depicts a thermoelectric material that includes a host 130 in which a plurality of particles 140 are embedded—the particles acting as inclusions. In this case, the host optionally has a plurality of grains 135 having a size of less than about 1 micron (eg, maximum particle size of any dimension), eg, a size in the range of about 500 nm to less than about 1 micron. For example, it contains a plurality of crystalline coarse grains. In other cases, the particle size can be larger, for example, in the range of about 1 micron to about 20 microns. Further, in some cases, the particles can have a size (eg, maximum size in any direction) less than about 1 micron, such as in the range of about 1 nm to about 200 nm, or in the range of about 2 nm to about 100 nm, In some cases, the size can be greater than 1 micron, for example in the range of about 1 micron to about 10 microns. The enclosure 140 can be formed by various methods. For example, they can be formed as a precipitate region using any suitable method, including those discussed with respect to other embodiments herein. In other cases, they are different from the host material, for example by using the method discussed in the above cited patent application entitled “Nanocomposites with high thermoelectric number”. Can be formed. In still other cases, the particles can be formed, for example, by solid state chemical reactions during the consolidation phase.

Without loss of generality, in this example, the host 130 may have multiple micron sizes and / or
Or it can be estimated to be a SiGe alloy with nano-sized grains 135 and the particles 140 can be MoSi ₂ (molybdenum silicide) particles embedded in the SiGe alloy. . Such a thermoelectric material can be produced, for example, by the following method: adding molybdenum to SiGe, melting the material, and cooling the material (eg, as described above) to produce an ingot, optionally It can be formed by a method of pulverizing and compacting. In this way, MoSi ₂ particles are formed by a solid state chemical reaction of Mo with Si, for example during the cooling process. In this example, the SiGe host is not highly doped, but in other cases it can be highly doped, e.g., p-type doped, but less than in conventional SiGe thermoelectric materials. Low by a factor of 5, 10 or 100. Furthermore, vacancies can be generated by the presence of MoSi ₂ . Such provision of vacancies to the host increases the vacancy mobility within the material, and thus can improve the electrical conductivity of the material and consequently the thermoelectric performance. In other cases, the particles may be obtained by grinding Si and Ge elements or SiGe crystal alloys with Fe, Mn, Mg, Cr, W, Ta, Ti, Cu, Ni, or V, such as FeSi ₂ , MgSi ₂ , etc. It can be formed by solid-state chemical reaction of Si (eg, SiGe) in the host by forming particles or grinding each silicide together with Si and Ge or SiGe alloys. Some of them are applicable to n-type, while others are applicable to p-type materials. Other nanoparticles that do not react with Si (eg, metal and / or semiconductor nanoparticles) can also be used to form a controlled doping such as Ag as an encapsulation.

For further explanation of such donation of charge carriers from the particle to the host, without being limited to any particular theory, FIG. 1C shows portions 151, 152, 153 corresponding to the host material and Of charge carriers corresponding to hypothetical thermoelectric materials (eg, the SiGe-based materials described above embedded with MoSi ₂ particles) representing portions 161, 162 corresponding to the particles embedded in The energy diagram is represented by a scheme. It is understood that the figure is a scheme and is provided for illustrative purposes only. The charge carriers (eg, electrons or vacancies) in the energy band (eg, conduction band or valence band) of the particles 161, 162 are the energy of the hosts 151, 152, 153, which can be the conduction band or valence band. Can have higher energy than that of the band. Thus, multiple charge carriers in a particle (such as in a metal or metalloid), either by further doping in the particle or by its inherent high density of electrons, migrate to the host and their Energy can be reduced. This transfer of charge carriers from the particle to the host can advantageously increase the mobility of the carrier, for example, by reducing the dopant in the host material and thus reducing the scattering of ionized impurities. In this way, higher electrical conductivity can be achieved. In some cases, overall higher electron mobility may not be achieved, but this controlled doping method may be used for electron grain boundary scattering because the grain boundaries still scatter electrons. Can still be beneficial by compensating for the reduced mobility. The particles used for controlled doping can also result in higher Seebeck coefficients because they can scatter low energy carriers and reduce the thermal conductivity of both phonons and electrons. In some other cases, rather than donating electrons to the host, the particles can donate vacancies to the host. Again, without being limited to any particular theory, the mechanism of such donation of charge carriers from the particle to the host is that some vacancies are due to the host's higher energy level in the valence band. It can be based on the mechanism of moving to a lower energy level of the valence band or the mechanism of attracting electrons in the valence band of the host into the particles to form more vacancies in the host.

In general, the type of starting material, the temperature at which elevated ZT is measured, the composition of the coarse particles, the formation method and other properties and methods that can be associated with these embodiments are described in terms of particle size, precipitate area and / or Including all traits and methods discussed within this application according to other inclusions. For example, the coarse grains can be formed of any suitable thermoelectric material as discussed above, and can further include an n-type or p-type dopant. In other examples, the thermoelectric material formed has a ZT value in the range of greater than about 1.0, greater than about 1.5, greater than about 2, or from about 1 to about 5. In still other examples, the thermoelectric material formed has a ZT value at an operating temperature of less than about 2000 ° C., less than about 1000 ° C., less than about 600 ° C., less than about 200 ° C. or less than about 20 ° C. Have risen). In other examples, the coarse particles of the thermoelectric material can include at least one of a bismuth-based material (eg, Bi ₂ Te ₃ and / or related alloys), a silicon-based material, and a lead-based material. With respect to the process of producing such materials, the method of forming nanoparticles from bulk starting materials or elemental materials can include grinding speed, duration and / or temperature (polarity) to obtain the desired nanoparticle size for compression. By adjusting parameters such as low temperature, but can be applied as discussed herein. Further, such adjustment of the nanoparticle size can be used to obtain the desired particle size of the final thermoelectric material (eg, less than 1 micron, or greater than 1 micron but less than 10 microns). Furthermore, consolidation methods as discussed herein and applied by those skilled in the art can be applied.

  Another embodiment of the present application relates to a method for processing a thermoelectric material. In such a method, a plurality of nanoparticles are generated from the thermoelectric material. The nanoparticles can be consolidated at elevated temperatures under pressure to form a thermoelectric material. The types of thermoelectric starting materials that can be used to produce the nanoparticles include, but are not limited to, any bulk material disclosed herein and others known to those skilled in the art. Thus, embodiments can include a thermoelectric material having a ZT value greater than about 1 (eg, at a temperature less than about 2000 ° C.). Additionally or alternatively, the method can use n-doped or p-doped starting materials (eg, bulk thermoelectrics that are elemental and / or alloys).

  Various methods can be used to produce nanoparticles from thermoelectric materials. In some embodiments, the nanoparticles are produced by grinding a thermoelectric material. Grinding can be performed using a mill such as a ball mill that uses a planetary movement, an eight-shaped movement or some other movement. When producing nanoparticles, some methods, such as some milling methods, generate substantial heat, which can affect the size and properties of the nanoparticles (eg, particle aggregation ( agglomeration)). Thus, in some embodiments, cooling of the thermoelectric material can be performed while the material is being ground. Such cooling may make the thermoelectric material more brittle and facilitate the generation of nanoparticles. Cooling and particle generation can be accomplished by a wet mill and / or a cryogenic mill (eg, in the presence of dry ice or liquid nitrogen around the mill). Embodiments of the invention can also use other methods of forming nanoparticles. Such methods may include gas phase condensation, wet chemical methods, spinning of molten material at high speeds and other suitable methods.

Consolidation of nanoparticles under pressure and elevated temperature can be performed in different ways under different conditions. A method such as hot pressing (herein “P ² C”), also known as spark plasma sintering, can be used to apply the desired pressure and temperature during the consolidation period. A description of this method and an apparatus for carrying out this method are described in US patent application Ser. No. 10/977, filed Oct. 29, 2004, which is hereby incorporated by reference in its entirety. No. 363, which is available in U.S. Patent Application No. 2006/0102224.

The pressure used is typically superatmospheric, allowing the use of low temperatures to achieve nanoparticle consolidation. In general, the pressure used can be in the range of about 10 MPa to about 900 MPa. In some embodiments, the pressure is in the range of about 40 MPa to about 300 MPa. In other embodiments, the pressure is in the range of about 60 MPa to about 200 MPa.

  For high temperatures, a certain temperature range can be used. In general, the temperature is typically in the range of about 200 ° C. to about the melting point of the thermoelectric material. In some exemplary embodiments, the temperature is in the range of about 400 ° C to about 2000 ° C, about 400 ° C to about 1200 ° C, about 400 ° C to about 600 ° C, about 400 ° C to about 550 ° C. The temperature for some typical n-doped materials is in the range of about 450 ° C. to about 550 ° C., but the range for some typical p-doped materials is several degrees higher (eg, about 475 ° C. to 580 ° C. Within range). Other temperature ranges can also be used in connection with processing of n and p-type materials. These specific pressure and temperature ranges are preferably applicable to materials such as BiSbTe alloys and BiSeTe alloys, but they can be used for any material.

  The pressure and temperature can be maintained for a time sufficient to allow consolidation of the nanoparticles. In some embodiments, the time is in the range of about 1 second to about 10 hours.

Other consolidations can also be used to form the thermoelectric materials described in this application. For example, nanoparticles can be collided with other fine particles at high speed to achieve low temperature consolidation. In some cases, subsequent heat treatment can be used to form the thermoelectric material. Other consolidation methods can use annealing of particles (eg, nanoparticles) with little or no pressure to compact the particles. In such cases, the temperature can be selected to induce particle annealing no matter what pressure the sample is maintained during the annealing period. In other cases, the particles can be consolidated at a relatively low temperature and pressure to form a consolidated material, such as a material having a density close to 100% theoretical density. The consolidated material can then be annealed at a high temperature to form a thermoelectric material. Therefore, the consolidation method need not be limited to P ² C or hot press methods.

As an exemplary embodiment, nano-powders of various substances from commercially available materials can be produced by a high energy ball mill to obtain nanoparticles having a particle size as small as 1 nm. Optionally, the dry mill can be combined with a wet mill and / or a cryogenic mill to prevent the agglomeration of the ground particles into larger size particles due to the heat generated during the mill. In this way, more dispersed particles can be obtained. These powders can be consolidated into a solid sample by hot pressing including a P ² C method. In many embodiments, a density of approximately 100% of theory can be achieved by this method within a short period of time (typically about 1 to about 10 minutes per sample). The lattice thermal conductivity of hot pressed samples prepared by these methods is reduced to some of the initial values in both n-type and p-type, while maintaining a power factor comparable to the bulk material, Thus, the ZT value can be substantially increased.

For example, in a p-type commercial material of Bi _x Sb _2-x Te ₃ where x can range from about 0 to about 0.8, the commercial material has a maximum ZT value of about 1. So, after ball milling and hot pressing, it can be higher than 1.4. These increases are mainly due to the reduced thermal conductivity resulting from the presence of nanostructures in the sample.

In some embodiments, instead of converting the thermoelectric starting material into nanoparticles (or using some other particle generation method) and consolidating these nanoparticles, the nanoparticles are converted into at least two types of nanoparticles. Generated from elemental material (eg, elemental Bi and elemental Te) (eg, by grinding). The nanoparticles are then mixed and compressed at pressure and elevated temperature (eg, pressure and temperature discussed above) to exceed about 1, and preferably about 1.2, or about 1
. A final thermoelectric material (e.g., having a polycrystalline structure including coarse grains having a size less than about 500 nm, and preferably in the range of about 1 to about 100 nm) exhibiting a ZT value greater than 5, or about 2 Generate.

  In an alternative embodiment, two or more bulk materials can be ground simultaneously to produce a variety of nanoparticles having different compositions. Grinding methods can be used to “mechanically alloy” the nanoparticles. Mechanical alloys also produce two or more different particles separately and then mix the particles together and further grind, alloy and reduce the particle size of the alloy nanoparticles Can be carried out. The particles can be consolidated to form a thermoelectric material having one or more of the properties discussed in this application.

In yet other embodiments, any of the methods discussed herein may be used to separately generate different types of nanoparticles (e.g., grinding bulk elemental material such as bismuth or tellurium). And then mixed together and consolidated, a thermoelectric material can be formed. Optionally, further grinding of the mixture may be applied before consolidation. Final compaction material formed by any of these methods, for _{example, Bi 2 Te 3-x Se} x [ wherein x is from about 0 to about 0.8, such as Bi ₂ Te 2.8 _{Se 0.2} Or Bi _x Sb _2-x Te ₃ such as Bi _0.5 Sb _1.5 Te ₃ where x is in the range of about 0 to about 0.8. It can have all the characteristics of the composition described in the application.

  Other embodiments for the purpose of forming thermoelectric materials use one or more process iterations used to form thermoelectrics as discussed herein. For example, particles (eg, nanoparticles) can be generated from one or more starting materials (eg, bulk starting thermoelectric material or elemental material) and consolidated into a material structure. The resulting structure is then used to generate a new plurality of particles (eg, by crushing the material structure), which is then consolidated to form another material structure Can do. This process may be repeated any number of times to form the final thermoelectric material. Such a process helps to produce a fully mixed small particle size.

  For some embodiments, it may be beneficial to protect the particles being produced (eg, during the ball mill process) from oxidation. A non-limiting example of a protection method involves exposing the produced particles (eg, the environment in which the grinding of the material is performed) to an oxygen-depleted environment, such as an environment containing low oxygen relative to a relative vacuum or atmospheric pressure. Including. The microparticles produced can also be exposed to certain chemical coatings to reduce oxygen exposure to the surface, which can optionally be removed later in the thermoelectric material manufacturing process. Thus, the protection scheme can include a number of suitable methods, including those known to those skilled in the art.

The following experimental division is provided for further illustration of various embodiments of the present invention and to demonstrate the feasibility of using the method of the present invention to produce thermoelectric materials exhibiting high thermoelectric properties. However, it should be understood that the following examples are provided for display purposes only and do not necessarily represent the optimal results achievable by performing the method of the present invention.
[Example]

Nanocrystalline bulk p-type Bi _x Sb _2-x Te ₃ material commercial material (p-type BiSbTe alloy ingot) was ground and filled into zirconia jars in a glove box under argon atmosphere to avoid oxidation . Several zirconia balls (5-15 mm particle size) were also added and sealed. The sealed jar was placed in a ball mill and ground at a speed of 100-2000 rpm for a total of about 0.5-50 hours. The powder was characterized using a scanning electron microscope (SEM), transmission electron microscope (TEM) and x-ray diffraction (XRD).

FIG. 3 shows an x-ray diffraction (XRD) diagram of the nanopowder after ball milling. The XRD diagram shows that the powder is single phase and matches well with that of Bi _0.5 Sb _1.5 Te ₃ . A broadened diffraction peak indicates that the particles are small. The small size is confirmed by the scanning electron microscope (SEM) image of the nanopowder represented in FIG. 2A and the low magnification transmission electron microscope (TEM) image of the powder presented in FIG. 2B. The low resolution TEM image of FIG. 2B clearly shows that the nanoparticles have a size of a few nm to about 50 nm, an average size of about 20 nm. The high resolution TEM image presented by FIG. 2C confirmed the good crystallinity of the nanoparticles and the obvious particle surface desired for good thermoelectric properties. The inset in FIG. 2C also shows that some nanoparticles are even less than 5 nm.

Once the powder is obtained, the powder sample is processed into a 2-12 mm thick bulk disk sample at 1/2 "diameter by hot pressing nanopowder filled in a 1/2" diameter die. did. The ground powder stored in the glove box to prevent oxidation was filled into a graphite die and compressed into pellets using a DC hot press method (see FIG. 4). The parameters of the hot press conditions are 40 to 160 MPa and 450 ° C. to 600 ° C. The density is close to 100% of theory for all compositions. A 1/2 "diameter and 2 mm thick disk and approximately 2 x 2 x 12 mm ³ bars were cut from the compressed disk for measurement of electrical and thermal conductivity and Seebeck coefficient using both DC and AC methods. Polished.

  In preparing a hot pressed sample, the powder is typically exposed to a selected pressure and the apparatus is operated at a target heating rate. Upon reaching the selected high temperature, the sample may be between about 0 minutes to about 60 minutes, preferably about 0 minutes to about 30 minutes, about 0 minutes to about 10 minutes, or about 0 minutes to less than 5 minutes. Maintain that temperature and pressure during (for example, 2 minutes). Next, cooling is started. However, it is understood that pressure can be applied during or after the sample reaches a high temperature.

  FIGS. 5-9 compare the temperature dependence of various properties of hot-pressed nanocrystalline material (labeled BP0572) and commercially available material (labeled com ingot) p-type BiSbTe alloy ingots. 5-9 all properties are measured from the same sample. A cylindrical thick disc is hot pressed, cut along the pressing direction and vertically, and then measured. To test the temperature stability of the bulk sample of nanocrystals, the same sample was measured repeatedly up to 250 ° C. No significant degradation of properties was observed.

  FIG. 5 compares the temperature dependence of the electrical conductivity of the nanocrystal and the commercial sample. The electrical conductivity was measured by a four-point current-switching method. The electrical conductivity of the nanocrystal bulk sample is slightly higher than that of the commercial ingot.

FIG. 6 shows the temperature dependence of the Seebeck coefficient between the nanocrystal and the commercial sample, while FIG. 7 compares the temperature dependence of the sample power factor (S ² σ). The Seebeck coefficient was measured using a commercially available device (ZEM-3, Ulvac, Inc.) on the same rod-shaped sample with a 2 × 2 mm ² cross section cut along the disk surface and a 12 mm length dimension. Used to measure by the static DC method based on the slope of the voltage vs. temperature difference curve. These properties were also measured on a handmade device on the same sample. The two sets of measurements are within 5% of each other. The Seebeck coefficient of the nanocrystal sample is slightly lower or higher than the ingot coefficient depending on the temperature, which makes the power factor of the nanocrystal sample comparable to that of a commercial ingot below 75 ° C. and above 75 ° C. The coefficient is higher than that of a commercially available ingot.

  FIG. 8 represents the temperature dependence of the thermal conductivity of nanocrystals and commercial samples. Thermal conductivity is derived from measurements of the thermal diffusivity and heat capacity of the sample. The thermal diffusivity was measured by a laser-flash method on the disk along the axial direction of the disk using a commercially available device (Netzsch Instruments, Inc.). After laser-flash measurement, the bars were diced from the disk, and their thermal diffusivity was measured along the bar (disk surface) direction using an angstrom method in a handmade device. The thermal diffusivity values of the bars and disks agree within 5%.

FIG. 9 records the change in the figure of merit, ZT, as a function of temperature for nanocrystals and commercial samples. The thermal conductivity of the bulk sample of nanocrystals is significantly lower than that of commercial ingots, and more importantly, because the difference increases with increasing temperature, this is significantly greater in the temperature range of 20-250 ° C. High ZT results. FIG. 9 also shows that the peak ZT value moves to a higher temperature (100 ° C.). The peak ZT of the nanocrystalline bulk sample is about 1.4 at 100 ° C., which is significantly higher than the value of commercially available Bi ₂ Te ₃ -based alloys. The ZT value of commercial ingots begins to drop above 75 ° C and drops below 0.25 at 250 ° C. In contrast, a bulk sample of nanocrystals exhibits a ZT of greater than 0.8 at 250 ° C. Since there is no good material currently available with high ZT in this temperature range, such ZT features are highly desirable for power generation applications.

  A detailed microstructure test was performed on a bulk sample of nanocrystals using a transmission electron microscope (TEM). TEM specimens were prepared by dicing, polishing, and ion milling bulk nanocrystal samples. Hot pressed nanocrystalline bulk pellets were cut into 2 × 3 × 1 mm blocks and ground to 2 × 3 × 0.002 mm using a mechanical Tripod Polisher. The sample was glued to a copper grid and ground using a Precision Ion Polishing System (Gatan Inc.) for 30 minutes with an incident energy of 3.2 kV and a beam current of 15 μA at an incident angle of 3.5 degrees. Figures 10-15 show some representative TEM micrographs showing the major structural features observed.

  As shown in FIGS. 10 and 11, most of the coarse grains are generally nano-sized. Furthermore, the nanoparticles are highly crystalline and randomly oriented (large angles in the lattice plane) with very clear boundaries. As shown in FIG. 11, the nanoparticles may be densely compressed, consistent with density measurements suggesting a fully consolidated sample. Some larger coarse grains are also shown in FIG. A high-resolution TEM microscope as shown in FIG. 13 shows that these coarse particles consist of nanodots with a particle size of 2 to 10 nm with no boundaries. These nanodots typically have a typical composition close to Bi: Sb: Te = 8: 44: 48 with a high Sb concentration, and Sb is replaced by Te. Some nanodots have no matrix and boundary as shown in FIG. 13, while other observed nanodots included a matrix and small angle boundary as shown in FIG. As shown in FIG. 15, pure Te precipitates with sizes in the range of 5-30 nm were also observed. An electron diffractogram of selected regions, shown in the inset of FIG. 15, confirmed the Te phase. In general, nanodots could be seen in each 50 nm diameter region.

Although not necessarily limited to any particular theory, it can be assumed that these nanodots could be formed during the hot press heating and cooling process. As shown in FIG. 12, it is believed that larger coarse grains containing nanodots can be the result of non-uniform grinding of the ingot during the ball mill. These large coarse grains are Oswald R
It may have grown even more during hot press compression due to ipening. Nanodots may not be the only reason for strong phonon scattering, as many nano-sized interface features were given in our materials such as nanoparticles.

As nanocrystalline SiGe material starting material, both p and n-type silicon and germanium elemental materials were used and ground using a ball mill to form nanoparticles having a particle size of about 1 to about 200 nm. These elemental materials can have a ZT of less than about 0.01 in some cases. Furthermore, it is understood that using SiGe alloys to form particles could have resulted in further improvements in the final manufactured material. The sample was hot pressed at a pressure of about 40 to about 200 MPa and a temperature of about 900 ° C. to 1300 ° C. to form a sample of thermoelectric material.

  FIGS. 16-19 represent graphs showing the temperature dependence of various properties of hot-pressed nanocrystalline materials formed from p-type SiGe ball milled bulk materials. Properties were measured using methods similar to those previously described in FIGS. FIG. 16 shows the temperature dependence of the electrical conductivity of the nanocrystalline p-type SiGe sample. FIG. 17 represents the temperature dependence of the Seebeck coefficient of a nanocrystalline p-type SiGe sample. FIG. 18 represents the temperature dependence of the thermal conductivity of the p-type SiGe sample. FIG. 19 records the change in the characteristic number, ZT, as a function of temperature for the nanocrystalline p-type SiGe sample.

  20-23 represent graphs illustrating the temperature dependence of various properties of hot pressed nanocrystalline materials formed from n-type SiGe ball milled bulk materials. FIG. 20 shows the temperature dependence of the electrical conductivity of the nanocrystalline n-type SiGe sample. FIG. 17 represents the temperature dependence of the Seebeck coefficient of a nanocrystalline n-type SiGe sample. FIG. 18 shows the temperature dependence of the thermal conductivity of the n-type SiGe sample. FIG. 19 records the change in the characteristic number, ZT, as a function of temperature for a nanocrystalline n-type SiGe sample.

  24-26 represent TEM micrographs of p-type SiGe materials associated with nanocrystalline materials. FIG. 24 represents a TEM micrograph of a ball mill powder sample of SiGe bulk material showing nano-sized particles of ground particles. FIG. 25 shows a TEM micrograph of the SiGe powder sample after hot pressing. The micrograph shows a large number of coarse grains of hot pressed material that are densely consolidated and in the nano-sized range. The inset of FIG. 25 gives an electron diffractogram of selected areas taken on the sample. FIG. 26 represents a high resolution TEM of a hot-pressed SiGe sample further illustrating the nano-size of the various coarse grains of the sample, showing a number of coarse grain boundaries targeted for phonon scattering.

Samples of nanocrystalline p-type BiSbTe alloy materials were prepared to show how the temperature-tuning index of nanocrystalline p-type BiSbTe material , ZT can be tuned to various temperature states did. In particular, Bi _x Sb _2-x Te ₃ type materials can be prepared in various stoichiometric amounts depending on the value of x selected. Samples of two specific examples: p-type nanocrystals with a stoichiometric amount of Bi _0.3 Sb _1.7 Te ₃ , hot pressed material and Bi _0.5 Sb _1.5 Te ₃ A p-type nanocrystalline, hot-pressed material with a stoichiometric amount of Appropriate loose starting materials were ground with a ball mill to form a nanoparticle sample. The sample was compressed at 40-160 MPa and 450 ° C.-600 ° C. for up to about 5 minutes.

FIGS. 27-30 show the temperature dependence of the electrical conductivity, Seebeck coefficient, thermal conductivity and ZT of the nanocrystalline Bi _0.3 Sb _1.7 Te ₃ sample, while FIGS. 31-34 show the nanocrystals The electrical conductivity, Seebeck coefficient, thermal conductivity, and temperature dependence of each of ZT of the characteristic Bi _0.5 Sb _1.5 Te ₃ sample are shown. Measurements were performed as described in Example 1. As can be seen in FIGS. 30 and 34, the peak ZT value of the Bi _0.3 Sb _1.7 Te ₃ sample was measured at about 150 ° C., whereas the peak of the Bi _0.5 Sb _1.5 Te ₃ sample The ZT value was measured at about 75 ° C.

  Thus, the results show that the peak ZT of the nanocrystalline material can be adjusted for a specific temperature range application. For example, lower temperature peak materials can be used for applications intended for near room temperature use such as cooling-while higher temperature peak materials can be used for higher temperature applications such as power generation. it can.

  It is understood that the various embodiments discussed herein, along with experimental results, describe various methods and materials that are merely representative of the scope of the invention. Indeed, those skilled in the art will readily appreciate that numerous other modifications to the methods and materials disclosed herein can be implemented. All such modifications represent related embodiments which are also within the scope of the invention. Similarly, all numerical values representing amounts of ingredients, reaction conditions, etc. used in the specification and claims can be understood as being modified in all cases by the term “about”. Thus, unless stated to the contrary, the numerical parameters presented herein and in the appended claims are approximations that can vary depending on the desired properties.

Claims (92)

A density-enhanced thermoelectric material that produces a plurality of nanoparticles from a thermoelectric starting material and consolidates the nanoparticles under elevated temperature, pressure, and has a higher ZT value than the thermoelectric starting material at at least one temperature A method of processing a thermoelectric material comprising a step of forming a film. Selecting a pressure and elevated temperature such that the thermoelectric material exhibits a ZT value greater than about 1:
The method of claim 1 further comprising:   The method of claim 1, wherein the thermoelectric material exhibits the ZT value at a temperature less than about 2000 ° C.   The method of claim 3, wherein the thermoelectric material exhibits the ZT value at a temperature less than about 1000 ° C.   The method of claim 4, wherein the thermoelectric material exhibits the ZT value at a temperature less than about 600 ° C.   The method of claim 5, wherein the thermoelectric material exhibits the ZT value at a temperature less than about 200 ° C.   The method of claim 6, wherein the thermoelectric material exhibits the ZT value at a temperature less than about 20 ° C.   The method of claim 1, wherein generating the plurality of nanoparticles comprises grinding the thermoelectric material.   The method of claim 8, further comprising cooling the thermoelectric material while grinding.   10. The method of claim 9, wherein the step of grinding the thermoelectric material comprises using ball milling.   The method of claim 1, wherein the step of consolidating the nanoparticles comprises using at least one of a plasma pressure compression method, a unidirectional hot pressing method and an isostatic hot pressing method. Selecting the pressure to be in the range of about 10 MPa to about 900 MPa:
The method of claim 1 further comprising: Selecting the pressure to be in the range of about 40 MPa to about 300 MPa:
The method of claim 12, further comprising: Selecting the pressure to be in the range of about 60 MPa to about 200 MPa:
14. The method of claim 13, further comprising: Selecting the elevated temperature to be in the range of about 200 ° C. to about the melting point of the thermoelectric starting material:
The method of claim 1 further comprising: Selecting the elevated temperature to be in the range of about 400 ° C to about 2000 ° C:
The method of claim 1 further comprising:   The method of claim 1, wherein generating the plurality of nanoparticles comprises using a thermoelectric starting material comprising any p-doped and n-doped material.   The method of claim 1, wherein the thermoelectric starting material exhibits a polycrystalline structure having an average grain size greater than about 1 micron. The method of claim 1, further comprising selecting the thermoelectric starting material to include any of a bismuth-based material, a lead-based material, and a silicon-based material. Selecting the thermoelectric material to comprise at least one of a bismuth-antimony-tellurium alloy, a bismuth-selenium-tellurium alloy, a lead-tellurium alloy, a lead-selenium alloy, and a silicon-germanium alloy; The method of claim 1 further comprising: The method of claim 1, further comprising selecting the thermoelectric material to be an alloy of Bi ₂ Te _3-x Se _x , where x is in the range of about 0 to about 0.8. The thermoelectric material [where x is in the range of about 0 to about _{0.8] Bi x Sb 2-x} Te 3 alloy which further comprises the step of selecting as a method of claim 1.   The method of claim 1, wherein generating a plurality of nanoparticles comprises generating nanoparticles having an average particle size of less than about 500 nm.   24. The method of claim 23, wherein the average particle size is in the range of about 1 nm to about 200 nm.   The method of claim 1, further comprising maintaining the nanoparticles at the elevated temperature for a period of about 1 second to about 10 hours. Comprising a structure of material comprising a plurality of coarse grains having an average grain size in the range of about 1 nm to about 1000 nm;
A thermoelectric material wherein the structure is characterized by a ZT value greater than about 1.0 at a temperature below about 2000 ° C.   27. The thermoelectric material of claim 26, wherein the material exhibits the ZT value at a temperature less than about 1000 <0> C.   27. The thermoelectric material of claim 26, wherein the material exhibits the ZT value at a temperature less than about 600 degrees Celsius.   27. The thermoelectric material of claim 26, wherein the material exhibits said ZT value at a temperature less than about 200 <0> C.   27. The thermoelectric material of claim 26, wherein the material exhibits the ZT value at a temperature less than about 20 degrees Celsius.   27. The thermoelectric material of claim 26, wherein the average grain size of the plurality of coarse grains is in the range of about 1 nm to about 500 nm.   27. The thermoelectric material of claim 26, wherein at least one of the plurality of coarse grains includes at least one precipitate region therein.   33. The thermoelectric material of claim 32, wherein the at least one precipitate region has a size in the range of about 1 nm to about 20 nm.   27. The thermoelectric material of claim 26, wherein the structure is substantially free of coarse grains greater than about 1000 nm.   27. The thermoelectric material of claim 26, wherein the structure has a porosity of less than about 10%.   36. The thermoelectric material of claim 35, wherein the porosity is less than about 1%.   27. The thermoelectric material of claim 26, wherein the structure has a ZT value greater than about 1.2.   38. The thermoelectric material of claim 37, wherein the structure has a ZT value greater than about 1.5.   40. The thermoelectric material of claim 38, wherein the structure has a ZT value greater than about 2.   38. The thermoelectric material of claim 37, wherein the material exhibits the ZT value at a temperature less than about 2000 degrees Celsius.   41. The thermoelectric material of claim 40, wherein the material exhibits the ZT value at a temperature less than about 1000 <0> C.   42. The thermoelectric material of claim 41, wherein the material exhibits the ZT value at a temperature less than about 600 <0> C.   43. The thermoelectric material of claim 42, wherein the material exhibits said ZT value at a temperature less than about 200 <0> C.   44. The thermoelectric material of claim 43, wherein the material exhibits said ZT value at a temperature less than about 20 <0> C.   27. The thermoelectric material of claim 26, wherein the material exhibits a density in the range of about 90% to about 100% of the respective theoretical density.   27. The thermoelectric material of claim 26, wherein the plurality of coarse grains comprise at least one of an n-doped material and a p-doped material.   27. The thermoelectric material of claim 26, wherein the plurality of coarse grains comprise at least one of a bismuth-based material, a lead-based material, and a silicon-based material.   48. The plurality of coarse grains comprise at least one of a bismuth-antimony-tellurium alloy, a bismuth-selenium-tellurium alloy, a lead-tellurium alloy, a lead-selenium alloy, and a silicon-germanium alloy. Thermoelectric material.   49. The thermoelectric material of claim 48, wherein the plurality of coarse grains comprise a bismuth-antimony-tellurium alloy. A plurality of coarse _{particles, Bi 2 Te 3-x Se} x [ the x is in the range of about 0 to about 0.8] comprising the alloy of the thermoelectric material of claim 26. Thermoelectric material _is an alloy of _{Bi x Sb 2-x Te 3} [ that x is in the range of about 0 to about 0.8, the thermoelectric material of claim 26.   27. The thermoelectric material of claim 26, wherein the plurality of coarse particles comprise at least two particles having different elemental compositions. Comprising a plurality of compressed crystalline inclusions randomly arranged relative to each other, wherein the inclusions have an average size in the range of about 1 nm to about 500 nm;
Providing a thermoelectric material wherein the compressed enclosure exhibits a ZT of greater than about 1;
Thermoelectric material.   54. The thermoelectric material of claim 53, wherein the encapsulant comprises coarse particles.   54. The thermoelectric material of claim 53, wherein the average size of the enclosure is in the range of about 1 nm to about 100 nm.   54. The thermoelectric material of claim 53, wherein the average size of the enclosure is in the range of about 1 nm to about 50 nm.   54. The thermoelectric material of claim 53, wherein the material is substantially free of inclusions greater than about 500 nm.   54. The thermoelectric material of claim 53, wherein the material exhibits a polycrystalline structure.   54. The thermoelectric material of claim 53, wherein the material exhibits a ZT greater than about 1.2.   60. The thermoelectric material of claim 59, wherein the material exhibits a ZT greater than about 1.5.   61. The thermoelectric material of claim 60, wherein the material exhibits a ZT greater than about 2. Grinding at least one bulk elemental material to produce a plurality of nanoparticles and producing a thermoelectric material exhibiting a ZT value greater than about 1 under pressure and at an elevated temperature Consolidating the nanoparticles of
A method of forming a thermoelectric material comprising:   64. The method of claim 62, wherein the at least one bulk elemental material comprises at least two different bulk elemental materials, and further, the step of grinding includes the step of producing at least two types of nanoparticles.   64. The method of claim 63, wherein the at least two different bulk elemental materials comprise bismuth and tellurium.   64. The method of claim 63, wherein the at least two different bulk elemental materials comprise bismuth, tellurium and antimony.   64. The method of claim 63, wherein the at least two different bulk elemental materials comprise bismuth, tellurium and selenium. Adding dopant to a plurality of nanoparticles:
64. The method of claim 62, further comprising: Providing particles from a raw material having a ZT value greater than about 0.5 that is at least one of an alloy and a compound;
The step of consolidating the plurality of nanoparticles comprises consolidating the plurality of nanoparticles together with particles from the source material;
64. The method of claim 62. Further comprising providing micron-sized particles,
64. The method of claim 62, wherein the step of consolidating the plurality of nanoparticles comprises consolidating the micron sized particles and the plurality of nanoparticles. Comprising a structure of a material comprising a plurality of coarse grains having an average size in the range of about 1 nm to about 10 microns;
At least some of the coarse grains include one or more precipitate regions having an average size in the range of about 1 nm to about 100 nm, and the material exhibits a ZT value greater than about 1;
Thermoelectric material.   71. The thermoelectric material of claim 70, wherein the coarse grains have an average size in the range of about 1 nm to about 5 microns.   72. The thermoelectric material of claim 71, wherein the coarse grains have an average size in the range of about 1 nm to about 2 microns.   71. The thermoelectric material of claim 70, wherein the material exhibits a ZT value in the range of about 1 to about 5.   71. The thermoelectric material of claim 70, wherein the material exhibits a ZT value greater than about 1.5.   71. The thermoelectric material of claim 70, wherein the material exhibits a ZT value greater than about 2.   The thermoelectric material of claim 70, wherein the material exhibits the ZT value at an operating temperature of less than about 2000 ° C.   71. The thermoelectric material of claim 70, wherein the precipitate region exhibits an average size in the range of about 1 nm to about 50 nm.   71. The thermoelectric material of claim 70, wherein the coarse grains are formed from at least one of a bismuth-based alloy, a lead-based alloy, and a silicon-based alloy. Comprising a host material and a plurality of particles dispersed in the host having a size of less than about 20 microns;
Wherein the thermoelectric material exhibits a carrier concentration that exceeds the respective carrier concentration in the host material in the absence of the particles,
Thermoelectric material.   80. The thermoelectric material of claim 79, wherein the mobility of charge carriers in the thermoelectric material is greater than the mobility of each charge carrier in the host material in the absence of the particles.   80. The thermoelectric material of claim 79, wherein the plurality of particles are more highly doped than the host material.   80. The thermoelectric material of claim 79, wherein the ZT value of the thermoelectric material is greater than about 0.8.   80. The thermoelectric material of claim 79, wherein the host material comprises a plurality of coarse grains, wherein at least some of the coarse grains are characterized by a size of less than about 1 micron.   80. The thermoelectric material of claim 79, wherein the host material comprises a plurality of coarse grains, wherein at least some of the coarse grains are characterized by a size greater than about 1 micron. A host material characterized by a first energy band and a plurality of inclusions having a size less than about 20 microns and characterized by a second energy band dispersed in the host material;
Comprising
Here, the thermoelectric material in which the second energy band has higher energy than the first energy band.   The thermoelectric material of claim 85, wherein the energy band is at least one of a conduction band and a valence band.   86. The thermoelectric material of claim 85, wherein the ZT value of the thermoelectric material is greater than about 0.8.   86. The thermoelectric material of claim 85, wherein the host material comprises a plurality of coarse grains, at least some of the coarse grains characterized by a size of less than about 1 micron.   86. The thermoelectric material of claim 85, wherein the host material comprises a plurality of coarse grains, wherein at least some of the coarse grains are characterized by a size greater than about 1 micron.   86. The thermoelectric material of claim 85, wherein the plurality of inclusions comprises a doped material. Producing a plurality of nanoparticles using at least one of gas phase condensation, laser ablation, chemical synthesis and rapid spray cooling; and consolidating the nanoparticles under pressure at an elevated temperature Forming a consolidated thermoelectric material having a ZT value greater than about 0.8,
A method of processing a thermoelectric material, comprising: Further comprising the step of ball milling at least one starting material to produce a plurality of host particles;
Wherein the step of consolidating the nanoparticles comprises the step of consolidating the nanoparticles with the plurality of host particles;
92. The method of claim 91.

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