KR20090110831A - Methods for high figure-of-merit in nanostructured thermoelectric materials - Google Patents

Abstract

Thermoelectric materials with high figures of merit, ZT values, are disclosed In many instances, such materials include nano-sized domains (e g, nanocrystalhne), which are hypothesized to help increase the ZT value of the material (e g, by increasing phonon scattering due to interfaces at grain boundaries or grain/inclusion boundaries) The ZT value of such materials can be greater than about 1, 1.2, 1.4, 1.5, 1.8, 2 and even higher Such materials can be manufactured from a thermoelectric starting material by generating nanoparticles therefrom, or mechanically alloyed nanoparticles from elements which can be subsequently consolidated (e g, via direct current induced hot press) into a new bulk material Non-limiting examples of starting materials include bismuth, lead, and/or silicon-based materials, which can be alloyed, elemental, and/or doped Various compositions and methods relating to aspects of nanostructured theromoelect'c materials (e g, modulation doping) are further disclosed.

Description

Methods for high figure-of-merit in nanostructured thermoelectric materials

Cross Reference to Related Application

This application is a partial-continued application of US patent application Ser. No. 10 / 977,363, filed October 29, 2004, entitled "Nanocomposites with High Thermoelectric Figures of Merit." US Provisional Application No. 60 / filed Dec. 1, 2006, entitled "Methods for High Figure-of-Merit in Nanostructured Thermoelectric Materials," entitled "Methods for High Figure-of-Merit in Nanostructured Thermoelectric Materials." Claims 872,242. The contents of all these applications are incorporated herein by reference.

The present application generally relates to thermoelectric materials and methods for their preparation, and more particularly to thermoelectric materials exhibiting improved thermoelectric properties.

The thermoelectric property of a material is the figure of merit Z (or no), 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. It can be characterized by an amount called the dimensional performance index ZT). It is desirable to prepare materials with high ZT values (with low thermal conductivity k and / or high power factor S ² σ). By way of example, such materials can be used to fabricate potentially high quality power generation and cooling devices.

The gist of the invention

In one aspect, the present invention produces a plurality of nanoparticles from a starting material, such as a thermoelectric bulk material, and consolidates these nanoparticles under reduced pressure at elevated temperatures, for example, less than about 2000 ° C., less than about 1000 ° C. And a method for producing a thermoelectric material by forming a thermoelectric material exhibiting a ZT value higher than the thermoelectric starting material at a temperature below about 600 ° C., below about 200 ° C. or below about 20 ° C. In some cases, the peak ZT value of the formed material may be about 25 to about 1000% greater than the peak ZT value of the starting material. In other cases, the peak ZT of the formed material may be substantially greater than 1000% of the peak ZT of the starting material.

The term “nanoparticles” is generally known in the art, which has a size (eg, average or maximum size) in the range of less than about 1 micron, for example, from about 1 to about 1000 nm. Used to mean material particles. Preferably, the size may be less than about 500 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 grinding the starting material into nano-sized pieces (eg, grinding using dry milling, wet milling or other suitable technique). In one example, ball milling can be used to achieve the desired nanoparticles. Optionally, cooling can also be used (eg, cooling the starting material while grinding it), while producing nanoparticles, in order to reduce the size of the particles again. Other methods of producing nanoparticles may include condensation from the gas phase, wet chemical methods, and other methods of forming nanoparticles. In some cases, nanoparticles of different elemental materials (eg, bismuth or tellurium) may be produced separately and then solidified with the resulting thermoelectric material, as discussed again below.

Nanoparticles can solidify under selected temperature and selected pressure to induce electrical coupling between nanoparticles sufficient to form the resulting thermoelectric material. For example, the current drawn (known as The plasma pressure ^{compression, "P 2 C (plasma pressure} compaction)", or spark plasma sintering, SPS (spark plasma sintering)) hot press temperature compression comprising a unidirectional hot pressing And an isothermal hot press process can be used to achieve the solidification of the nanoparticles. The pressure selected can be, for example, in the range of about 10 to about 900 MPa or in the range of about 40 to about 300 MPa and preferably in the range of about 60 to about 200 MPa. The temperature selected is in the case of a Bi ₂ Te ₃ based material, for example, in the range of about 200 to about the melting point of the thermoelectric material (eg, 200 to about 2000 ° C.) or in the range of about 400 to about 1200 ° C. or about 400 To about 600 ° C or about 400 to about 550 ° C.

In a related aspect, in the method, the solidification of the nanoparticles compresses the nanoparticles (eg, porosity of about 10 to provide a material exhibiting a density ranging from about 90 to about 100% of each theoretical density). Less than or less than about 1%).

In a related aspect, as discussed above, the thermoelectric material produced by the method of the present invention has a ZT value (eg, a peak ZT value) of about 1 or more, about 1.2 or more, about 1.4 or more, preferably At least about 1.5 and most preferably at least about 2. Further, in many embodiments, the thermoelectric material is high at a certain operating temperature, which may depend, for example, on the melting point of the material, for example, at a temperature below about 300 ° C. for Bi ₂ Te ₃ based materials. ZT values are shown. The increased ZT value may also depend on the level of doping and / or the microstructure of the material.

In many cases, the starting material of the thermoelectric material (eg, starting bulk material or fluidic material for particle synthesis) exhibits a ZT value of less than about 1 and optionally greater than about 0.1, producing nanoparticles from the starting material, The final thermoelectric material obtained by solidifying these nanoparticles (eg, grinding the starting material by grinding or other suitable technique) may comprise at least about 1, at least about 1.1, at least about 1.2, at least about 1.3, at least about 1.4, ZT values of at least about 1.5 or at least about 2.

Various thermoelectric materials can be used as starting materials in the practice of the present invention. The starting material of the thermoelectric material may be p-doped or n-doped. Examples of starting materials for thermoelectric materials include, but are not limited to, bismuth based, lead based or silicon based materials. For example, starting materials for thermoelectric materials include bismuth-antimony-tellurium alloys, bismuth-selenium-tellurium alloys, lead-tellurium alloys, lead-selenium alloys, or silicon-germanium (eg, SiGe) alloys. It may include. By way of example, in some embodiments, the starting material of the thermoelectric material can be a Bi ₂ Te _3-x Se _x alloy, where x ranges from about 0 to about 0.8. Or, in some other embodiments, the starting material of the thermoelectric material is Bi _x Sb _{2 -} may be a _{3 x} Te alloy, wherein x is in the range of about 0 to about 0.8. In some embodiments, starting materials of thermoelectric materials having a polycrystalline structure may be used, which may optionally include an average grain size (eg, at least about 1 micron).

In another aspect, the nanoparticles have a size (eg, average or maximum size) of the resulting nanoparticles of less than about 1000 nm or less than about 500 nm, or less than about 200 nm and preferably less than about 100 nm, For example, it may be produced from the starting material of the thermoelectric material to be in the range of about 1 to about 200 nm or in the range of about 1 to about 100 nm and preferably in the range of about 1 to about 50 nm. Such particle size may be produced by any of the techniques discussed herein, such as grinding the starting material by ball milling or other suitable technique.

In a related aspect, in the method, the nanoparticles are maintained at elevated temperature, for example, under pressure for a time ranging from about 1 second to about 10 hours, to produce a resulting thermoelectric material with improved thermoelectric properties. Let's do it. In another aspect, the selected temperature is applied while maintaining the nanoparticles at low or ambient pressure for a time sufficient to allow the resulting thermoelectric material to be produced. In another aspect, the nanoparticles can be solidified under high pressure at room temperature to form a sample having a high theoretical density (eg, about 100%) and then annealed at high temperature to form the final thermoelectric material.

Another aspect relates to a method of forming a thermoelectric material comprising producing a plurality of nanoparticles. As an example, even particles may be produced by grinding one or more bulk elemental materials. For example, nanoparticles can be produced by grinding 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 in a workable ratio. Can be. In this case, two or more types of nanoparticles may be formed. If different types of particles are produced separately, these particles can be mixed and ground again (eg by a ball mill) to form mechanically alloyed particles. Alternatively, all of the various bulk materials can be ground simultaneously to form mechanically alloyed particles. A mixture of nanoparticles formed using mechanically alloyed nanoparticles from elements, compounds or alloys or separately produced nanoparticles can be compressed at elevated temperature under pressure to produce the resulting thermoelectric material with a ZT value of at least about 1. have. Dopants may optionally be added to the mixture of nanoparticles. In another embodiment, the nanoparticles are particles from a raw material having a good ZT value (eg, about 0.5 or greater) and / or micron-sized particles (eg, an average size of about 1 to about 10, Particles of other types, such as 50, 100 or 500 microns).

In another aspect, a thermoelectric material is provided that includes a material structure that includes a plurality of inclusions having an average size in the range of about 1 to about 500 nm, wherein the structure has a ZT value of about 1 or greater (eg, , Peak ZT values) and preferably ZT values of at least about 1.2 or at least about 1.5, or even at least about 2.

In a related aspect, the thermoelectric material may exhibit the ZT value at a temperature that is 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. In addition, the average grain size may range from about 1 to about 500 nm. The structure may be substantially free of grain greater than about 500 nm (eg substantially free of grains having an average and / or maximum dimension greater than about 500 nm), or of larger size grains (eg, approximately 1 μm or more).

In another aspect, one or more of the grains comprises one or more precipitation zones or other inclusions in the particles, wherein the precipitation zones or other inclusions are, for example, in the range of about 1 to about 50 nm or about 1 to about It may have a size in the range of 20 nm. The precipitation zone may be characterized by different compositions and / or different phases for the same composition with different crystal directions and / or the remainder of the grain.

In another aspect, the thermoelectric material can have a density in the range of about 90 to about 100% of each density theory. By way of example, the thermoelectric material may exhibit a porosity of less than about 10% and preferably less than about 1%.

In a related aspect, the thermoelectric material has small crystal grains randomly oriented relative to each other (eg, an average size of less than about 500 nm, or less than about 200 nm, preferably in the range of about 1 to about 100 nm. Polycrystalline structure formed from

One aspect of the invention relates to thermoelectric materials that may include a material structure having a plurality of grains. The grains may have an average size in the range of about 1 to about 10 microns, or in the range of about 1 to about 5 microns, or in the range of about 1 to about 2 microns. At least some of the grains may comprise one or more precipitation zones or other types of inclusions. Such regions may have an average size of about 1 to about 100 nm, or about 1 to about 50 nm. The thermoelectric material may have a ZT value of at least about 1, at least about 1.2, at least about 1.5 or at least about 2. For example, the ZT value may also range from about 1 to about 5. The thermoelectric material may exhibit the ZT value at an operating 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. The grains may 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 is to derive a thermoelectric material comprising a host material having a plurality of inclusions or particles dispersed throughout the host. The particles or inclusions may have a size that is less than the threshold, for example, less than about 20 microns. The host material may comprise one or more grains, wherein at least a portion of the grains have a size (eg, a maximum size and / or average size in a particular dimension) that is at least about 1 micron or less than about 1 micron. In some embodiments, the host material is not excessively doped as in conventional thermoelectric materials, which means that a large portion of the charge carriers, such as 50%, 80%, 90% and preferably 99% of the host material, This is due to the presence of these inclusions. In some embodiments, the particles can be doped more than the host material. The thermoelectric material may exhibit a carrier concentration and / or charge carrier mobility that is greater than the respective carrier concentration and / or charge carrier mobility of the host material in the absence of the particles or inclusions, resulting in a higher power factor (S ^2). σ). In addition, or alternatively, the thermoelectric material may have an energy band (eg, conduction band or valence band) for the charge carrier type having a higher energy than the associated energy band of the host material for the corresponding charge carrier type. It 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 may exhibit a ZT value of at least about 1, at least about 1.1, at least about 1.2, at least about 1.3, at least about 1.4, at least about 1.5, or at least about 2.

Some aspects of the invention may be better understood with reference to the following figures, which are not necessarily drawn to scale.

1A is a schematic of a plurality of grains in a thermoelectric material, with some grains comprising one or more precipitation zones, consistent with some aspects of the present invention;

1B is a schematic diagram of a host material having inclusions embedded therein, consistent with some aspects of the present disclosure;

1C is a schematic of a conduction energy diagram for the material shown in FIG. 1B;

2 is an XRD pattern of p-type BiSbTe nanoparticles produced by ball milling, consistent with some embodiments;

3A is an SEM image of the p-type BiSbTe nanoparticle of FIG. 2;

3B is a lower resolution TEM micrograph of the BiSbTe nanoparticle of FIG. 2;

FIG. 3C is a higher resolution TEM micrograph of the BiSbTe nanoparticles shown in FIG. 3B;

4 is a diagram and photograph of a DC hot press (plasma pressure or spark plasma sintering) apparatus that may be used with some aspects of the present invention;

FIG. 5 is a graph showing the temperature dependence of electrical conductivity for thermoelectric materials made from the particles of FIG. 2 and bulk materials of the current state of the art p-type BiSbTe alloy, consistent with some embodiments;

FIG. 6 is a graph showing the temperature dependence of the Seebeck coefficients for thermoelectric materials made from the particles of FIG. 2 and bulk materials of the current state of the art p-type BiSbTe alloy, consistent with some embodiments;

FIG. 7 is a graph showing the temperature dependence of power factor for thermoelectric materials made from the particles of FIG. 2 and bulk materials of the current state of the art p-type BiSbTe alloy, consistent with some embodiments;

FIG. 8 is a graph showing the temperature dependence of thermal conductivity for thermoelectric materials prepared from the particles of FIG. 2 and bulk materials of the current state of the art p-type BiSbTe alloy, consistent with some embodiments;

FIG. 9 is a graph showing the temperature dependence of ZT, the figure of merit for thermoelectric materials made from the particles of FIG. 2 and bulk materials of the current state of the art p-type BiSbTe alloy, consistent with some embodiments;

FIG. 10 is a TEM micrograph of a thermoelectric material made from the particles of FIG. 2; FIG.

FIG. 11 is an enlarged TEM micrograph of the thermoelectric material prepared from the particles of FIG. 2, showing the nano size of densely packed nano grains; FIG.

FIG. 12 is a TEM micrograph of a thermoelectric material made from the particles of FIG. 2, showing the presence of grains larger than the nano grains shown in FIG. 11;

FIG. 13 is a TEM micrograph of a thermoelectric material made from the particles of FIG. 2, illustrating the presence of nanodots; FIG.

FIG. 14 is a TEM micrograph of a thermoelectric material made from the particles of FIG. 2, illustrating the presence of nano dots with small angle boundaries; FIG.

FIG. 15 is an illustration of a TEM micrograph of a thermoelectric material made from the particles of FIG. 2, showing the Te diffraction, the electron diffraction pattern of the Te precipitate; FIG.

FIG. 16 is a graph showing the temperature dependence of electrical conductivity for thermoelectric materials prepared from p-type SiGe bulk starting materials, consistent with some embodiments;

FIG. 17 is a graph showing the temperature dependence of the Seebeck coefficient for thermoelectric materials made from p-type SiGe bulk starting materials, consistent with some embodiments;

18 is a graph showing the temperature dependence of thermal conductivity for thermoelectric materials prepared from p-type SiGe bulk starting materials, consistent with some embodiments;

FIG. 19 is a graph showing the temperature dependence of ZT, figure of merit, for thermoelectric materials made from p-type SiGe bulk starting materials, consistent with some embodiments;

20 is a graph showing the temperature dependence of electrical conductivity for thermoelectric materials prepared from n-type SiGe bulk starting materials, consistent with some embodiments;

FIG. 21 is a graph showing the temperature dependence of the Seebeck coefficient for thermoelectric materials prepared from n-type SiGe bulk starting materials, consistent with some embodiments;

FIG. 22 is a graph showing the temperature dependence of thermal conductivity for thermoelectric materials prepared from n-type SiGe bulk starting materials, consistent with some embodiments;

FIG. 23 is a graph showing the temperature dependence of ZT, figure of merit, for thermoelectric materials made from n-type SiGe bulk starting materials, consistent with some embodiments;

24 is a TEM micrograph of a ball mill treated sample of SiGe bulk starting material, consistent with some embodiments of the present invention;

FIG. 25 is a TEM micrograph of the particles of FIG. 24 after hot compression, with illustrations showing corresponding electron diffraction patterns for the samples; FIG.

FIG. 26 is a high resolution TEM micrograph of the hot compressed sample shown in FIG. 25;

Figure 27 is consistent with some embodiments, p- type Bi _{0 .3 1 .7} Sb Te ₃ showing the temperature dependence of the electrical conductivity of the graph for the thermoelectric material prepared from the bulk starting material and;

Figure 28 is consistent with some embodiments, p- type Bi _{0 .3 1 .7} Sb Te claim ₃ illustrates the temperature dependence of the coefficient vectors in the graph for the thermoelectric material prepared from the bulk starting material and;

Figure 29 is consistent with some embodiments, p- type Bi _{0 .3 1 .7} Sb Te ₃ showing the temperature dependence of the thermal conductivity of the graph for the thermoelectric material prepared from the bulk starting material and;

Figure 30 is consistent with some embodiments, p- type Bi _{0 .3 1 .7} Sb Te ₃ merit for a bulk thermoelectric material prepared from the starting material, showing the temperature dependence of ZT and the graph;

Figure 31 is consistent with some embodiments, p- type Bi _{0 .5} Sb _{1 .5} Te ₃ showing the temperature dependence of the electrical conductivity of the graph for the thermoelectric material prepared from the bulk starting material and;

Figure 32 is consistent with some embodiments, p- type Bi _{0 .5} Sb _{1 .5} Te ₃ showing the temperature dependence of the coefficient vectors in the graph for the thermoelectric material prepared from the bulk starting material and;

Figure 33 is consistent with some embodiments, p- type Bi _{0 .5} Sb _{1 .5} Te ₃ showing the temperature dependence of the thermal conductivity of the graph for the thermoelectric material prepared from the bulk starting material and;

34 is showing a, p- type Bi _{0 .5} Sb _{1 .5} Te ₃ the figure of merit, ZT for the temperature dependence of the thermoelectric material prepared from the bulk starting material that matches some aspect graph.

In one aspect, the present invention relates to thermoelectric materials having high ZT values and methods of making such materials. In general, such thermoelectric materials typically comprise a plurality of grains. Such grains can be present in the form of nano-sized grains, which can be obtained from bulk materials such as, for example, starting materials of thermoelectric materials. In general, thermoelectric materials consistent with aspects of the present invention may include grains of various sizes. For example, the thermoelectric material may have grains larger than 1 μm and grains smaller than 1 μm. In some embodiments, the thermoelectric material is substantially free of grain that may adversely affect the ZT value of the thermoelectric material (eg, about 5%, about 10%, about 15%, Does not include adverse grains that can be reduced by at least about 20%, about 25%, about 30%, about 40%, or about 50%). Some embodiments relate to thermoelectric materials having multiple grains with an average grain size of the order of micron (eg, greater than about 1 micron). In some cases, the thermoelectric material is substantially free of large grains. Non-limiting examples include grains greater than about 5000 nm, grains greater than 1000 nm, grains greater than 300 nm, grains greater than 100 nm, grains greater than 50 nm, grains greater than 20 nm, or grains greater than 10 nm. Include nonexistent ones. In many cases, such grains may optionally include one or more precipitation regions or other forms of inclusions, the average size being in the range of, for example, about 1 to about 50 nm. In some preferred embodiments, at least some, preferably substantially all of the grains comprise precipitation regions, nanoparticles and / or other forms of inclusions; These various inclusions may be formed by chemical reactions and / or insertion of such inclusions in situ. Further embodiments relate to materials having multiple grain sizes (eg, at least some are nano size grains and some grains are greater than 1 micron), where some grains optionally include precipitation regions or other types of inclusions. can do. In other words, the thermoelectric material of the present invention has sub-micron sized grains with or without precipitation zones, grains greater than 1 micron with or without precipitation zones (e.g., using modulation doping), Or any combination of a mixture of sub-micron grains with grains greater than 1 micron, with or without precipitation zones. Any of these grains can be formed by a number of mechanisms, including but not limited to formation of precipitation zones during material compaction, particle insertion into the host matrix, and / or formation by solid-state chemical reactions. .

The ZT value of the thermoelectric material of the present invention may have various values. For example, the peak ZT value or average ZT value of a thermoelectric material is the peak ZT value of the corresponding starting material that forms the thermoelectric material by converting the starting material into nanoparticles and then compressing the nanoparticles at elevated temperature under pressure or Can be greater than the average ZT value. For example, the ZT value of the thermoelectric material may be about 25 to about 1000% greater than the ZT value of the starting material. As another example, the ZT value of the thermoelectric material may be substantially greater than 1000% substantially than the ZT value of the starting material. The starting material may have a range of ZT values. In some embodiments, the ZT values of the formed thermoelectric materials are at least about 0.8, at least about 0.9, at least about 1, at least about 1.1, at least about 1.2, at least about 1.3. At least about 1.4, at least about 1.5, at least about 1.6, at least about 1.7, at least about 1.8, at least about 1.9, or at least about 2. In some embodiments, the thermoelectric material may exhibit a ZT value in the range of a lower limit of one of the ZT values and an upper limit of about 4, about 5, or about 6.

These improved ZT values can be identified without being limited to temperature, while in some embodiments thermoelectric materials can exhibit the improved ZT values at particular temperatures or within a range of temperatures. For example, the thermoelectric material may exhibit improved 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 another example, the thermoelectric material begins to reach room temperature or includes a temperature range that includes room temperature (eg, 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., about 30 ° C.). Less than or less than about 20 ° C.). As another example, the thermoelectric material may exhibit improved ZT values in a temperature range up to or including cryogenic temperatures (eg, temperatures below about 0 ° C., below about −50 ° C. or below about −100 ° C.). And such materials may be useful for special cooling applications such as air conditioners, refrigerators or superconductors. In some embodiments, the temperature range exhibiting improved ZT values may depend on the composition of the thermoelectric material. In some non-limiting examples, the boron-carbide based composition may, in some embodiments, exhibit improved ZT values below about 2000 ° C., and the SiGe based composition may exhibit improved ZT values below about 1000 ° C., in some embodiments. And, in some embodiments, the PbTe based composition may exhibit improved ZT values below about 600 ° C., and / or the Bi ₂ Te ₃ based composition may exhibit improved ZT values below about 200 ° C. in some embodiments. . As another non-limiting example, the thermoelectric material includes Bi _x Sb _{1- x} and exhibits improved ZT below room temperature (eg, below about 20 ° C.).

Without wishing to be bound by a particular theory, the high ZT values of such thermoelectric materials may be the result of changes in any combination of thermal conductivity, Zeebeck coefficient, and electrical conductivity. Thermal conductivity has two contributing factors: lattice contributing factor and electron contributing factor. In monocrystalline or polycrystalline samples with large grains, lattice thermal conductivity is fixed for a particular material. However, if the bulk material consists of nano-sized grains and / or nanoparticles enclosed in grains larger than nanoparticles, three effects resulting from nano grains and / or encapsulated nanoparticles can be envisioned. First, the grating portion of thermal conductivity is degraded due to interference scattering of the phonons. Secondly, the Seebeck coefficient can be increased due to the carrier filtration effect (usually by low energy electron / hole scattering, thereby increasing the Seebeck coefficient), and thirdly, the electrical conductivity can be increased due to the modulation doping effect. Can act as carrier (electron and hole) contributing factors, thereby reducing impurity scattering compared to homogeneously doped conventional materials. The contribution of electrons to thermal conductivity can potentially be reduced by interfacial barrier scattering of electrons, in particular by bipolar contribution to thermal conductivity, with the barrier preferentially scattering one form of charge (electron or hole) This is because it may not substantially affect other types of carriers. In addition, quantum size effects can further affect the Seebeck coefficient and electrical conductivity such that S ² α is increased. Thus, some aspects of the invention provide for the preparation of dense samples (eg, about 90 to about 100% of the density theory) by, for example, hot presses comprising P ² C, unidirectional hot presses, isostatic hot presses. For the preparation, nanoparticles prepared by ball milling the starting material can be used. These hot compressed samples typically exhibit lower thermal conductivity compared to bulk counterparts, thereby improving ZT values; Although the power factor may be lowered when ZT obtained due to the decrease in thermal conductivity is sufficient, the power factor is usually maintained or improved.

In some embodiments, the thermoelectric material may include grain generated from a bulk starting material (eg, bulk thermoelectric material). Examples include bulk starting materials with high power factor and / or starting materials with good ZT values (eg, ZT values greater than about 0.1). For example, the ZT of the starting material may be greater than about 0.05, greater than about 0.1, greater than about 0.2, greater than about 0.3, greater than about 0.4, greater than about 0.5, or greater than this. have. In some non-limiting cases, the starting material has a ZT value lower than about 0.8, lower than about 0.9, lower than about 1, lower than about 1.1, lower than about 1.2, lower than about 1.3, or about It may be lower than 1.4, lower than about 1.5, or lower than about 2. As another example, the starting material of a thermoelectric material may not only have a high power factor (eg, S ² α of at least 20 kW / cm-K ² , preferably at least 40 kW / cm-K ² ), but also high thermal conductivity (eg, For example, greater than 2 W / mK). Such bulk thermoelectric materials may be specially prepared or commercially available materials may be used. Although many bulk starting materials are solids that can be pulverized to produce grain, when producing grains from gas phase condensation, bulk starting materials may be produced from other thermodynamic conditions, such as gas, and produce grains by chemical means. The bulk starting material can be produced from other thermodynamic conditions such as liquids. It is also understood that grain can be produced from one or more forms of bulk starting materials or mixtures of materials with different thermodynamic phases (eg, a mixture of liquid and gas).

Although many starting materials may be used, in some embodiments, the bulk starting material may be selected from any combination of bismuth based materials, lead based materials, and / or silicon based materials. In some embodiments, the bulk starting material can be a variety of alloys, such as bismuth-antimony-tellurium alloys, bismuth-selenium-tellurium alloys, bismuth-antimony-tellurium-selenium alloys, lead-tellurium alloys, lead- And selenium alloys, silicon-germanium alloys or any combination thereof. Particular embodiments can be derived using bulk starting materials that are p-type or n-type materials. For example, such starting material may be in a compositionally modified form of a parent composition, for example Bi ₂ Te ₃ . As an example, the n-type material may substitute tellurium in Bi ₂ Te ₃ with selenium so that the stoichiometry of the bulk material is determined by the formula Bi ₂ Te _{3 − x} Se _x where x is in the range of about 0 to about 0.8. It can obtain by having it. In the case of a p- type material, for example, the stoichiometry of the bulk material the formula Bi _x Sb _{2 -} is replaced with antimony in order to have a _bi-x Te ₃ (where, x is in the range of about 0 to about 0.8) Can be used. In a particular embodiment, the bulk starting material used is a _{Bi 0 .5 Sb 1 .5 Te 3} . In general, the bulk starting material may be a crystalline material or a polycrystalline material (eg, a polycrystalline having an average crystal grain size greater than about 1 micron). Other examples of starting materials include MgSi ₂ , InSb, GaAs, CoSb ₃ , Zn ₄ Sb ₃ , and the like. In some cases, the bulk starting material may be a material having a critical power factor value S ² σ, for example, at least about 20 kW / cmK ² . In such cases, the bulk starting material may have a suitable ZT value (eg greater than about 0.1) due to the low thermal conductivity of the bulk starting material, or the power factor may be at or above a threshold, but the ZT value of the starting material may be It may be low due to the relatively high thermal conductivity of the starting material.

In some embodiments, particles of thermoelectric material (eg, nanoparticles) can be produced from the bulk starting material or elemental material by a method other than grinding / milling one or more starting materials. Particles can be prepared 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), rapid spray cooling, and the like. Thus, the scope of the present application is not limited to the particular particle preparation methods discussed herein. It is understood that particle generation techniques can be combined in a manner to produce a material for solidification. For example, some particles may be produced by ball milling (eg, to produce a host material), while other particles may be produced by one or more other techniques (eg, gas phase condensation, laser ablation, etc.). Can be generated by

The grains forming the thermoelectric material may have various properties. In some embodiments, each grain has a crystal structure. In such cases, the thermoelectric material may include a polycrystalline-like structure that is generally lacking (eg, randomly dispersed) in the grains. In some cases, the grains may also exhibit a form of predominant orientation due to the grain morphology, where the general crystallographic direction of the grains may be random or may indicate a somewhat dominant orientation with respect to each other. Thus, this embodiment exhibits a large number of representative crystal structures (including, for example, a superlattice structure formed as a stack of multiple semiconductor layers) despite small defects or compositional heterogeneity in the average crystal structure. It is quite different from known thermoelectric materials.

The grains that make up the various thermoelectric materials discussed herein can have a variety of sizes. In some embodiments, the size is generally nanometer-scale and generally less than 1 micron. For example, the average grain size of the grains may be less than about 500 nm, or less than about 200 nm, or less than about 100 nm, or about 50 nm, or less than about 20 nm. In this embodiment, the average grain size may be larger than the somewhat lower threshold (eg, about 1 nm). In some cases, the average grain size can be measured using a variety of methods, including methods understood by those skilled in the art. For example, transmission electron microscopy (herein referred to as "TEM (Transmission electron micrograph)") can be used to image grain, and then the size of the grain can be measured and averaged. Since the particles are typically in an irregular shape, the size of the particles measured can be determined using a number of techniques, including those known to those skilled in the art. For example, the maximum dimension of grain from an image (eg, SEM and / or TEM image) can be used, or the effective diameter can be calculated based on surface area measurements or the effective-cross-sectional area of grain from the image.

In many aspects of the invention, the grains of the thermoelectric material can be compressed so that the final product exhibits the desired properties (eg, improved ZT values). In some embodiments, the thermoelectric material includes grains compressed into a structure that exhibits low porosity (eg, the actual density of the final product is used to prepare nanoparticles in the composition, eg, in some embodiments). Close to the theoretical density of the bulk starting material), which can help to obtain improved ZT values. Porosity is defined as the difference between the theoretical density and the actual density of the material divided by the theoretical density. In general, the phrase "theoretical density" is known to those skilled in the art. The porosity of the thermoelectric material is less than about 10%, less than about 5%, or less than about 4%, or less than about 3%, or less than about 2%, or less than about 1%, or less than about 0.5%, or about 0.1% May be less than. In some embodiments, the thermoelectric material exhibits a density up to 100% of the theoretical density. In some embodiments, the density of the thermoelectric material may be between 100%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9%, or each theoretical density. While not necessarily bound by theory, it is believed that compression can help maintain contact between grains, which can help maintain the electrical conductivity of thermoelectric materials.

Some embodiments relate to thermoelectric materials formed from a plurality of grains, where one or more grains may comprise one or more precipitation zones. As an example, FIG. 1 schematically illustrates such a thermoelectric material exhibiting a polycrystalline structure comprising a plurality of grains 110. The grains may also include one or more precipitation zones 120, which may improve the thermoelectric properties of the thermoelectric material. The precipitation zone may be characterized by a heterogeneity of the composition, such as having a composition and / or phase different from the rest of the grain. The precipitation zones may also be characterized by having a crystal structure similar to the matrix in which the precipitation zones are enclosed, although the precipitation zones are also oriented in different crystal directions. In some embodiments, despite the defects due to the presence of precipitation zones, one or more precipitation zones are embodied as discrete particles (eg, nanoparticles) enclosed in grains, or the whole grains are embodied as crystals. Can be. In some embodiments, the thermoelectric material may include other grains that do not have a precipitation zone. In an alternative embodiment, substantially all of the grains constituting the thermoelectric material comprise precipitation zones. The precipitation zone typically has a size (eg, a maximum average size) of about 10 nm or less or about 50 nm or less (eg, in the range of about 1 to about 50 nm). The formation of the precipitation zone is a US patent filed October 29, 2004 entitled "Nanocomposites with High Thermoelectric Figures of Merit", which is hereby incorporated by reference in its entirety. This can be accomplished in a variety of ways, including the techniques discussed in US Patent Publication No. US 2006/0102224 to US Pat. No. 10 / 977,363.

In some cases, precipitation zones are created spontaneously, for example, through the formation of thermoelectric materials by the methods discussed herein. In other cases, precipitation zones are created by mixing two types of nanoparticles with different melting points. For example, one type may have a lower melting point than another type. By mixing nanoparticles and heating / solidifying them (e.g., at a temperature close to the melting point of one type of nanoparticles but below the other type of melting point), the nanoparticles with lower melting points become different types of nanoparticles. Grain may form around the particles. In other words, grains formed from one type of nanoparticle may encapsulate another type of nanoparticle. Examples of ensemble materials that can be used to form such encapsulated nanoparticles include bismuth-telluride material systems, lead-telluride material systems, silicon-germanium material systems, and the like.

Although the above-mentioned discussion is explicitly about forming precipitates in thermoelectric materials, it should be understood that other materials are formed by using other types of inclusions in the matrix (eg, using nanoparticles in the host). For example, two or more types of nanoparticles that may be mixed together to form a thermoelectric material may not contain precipitates but may still have useful properties (eg, using modulation doping). Thus, the disclosure herein may be used for other forms of inclusions, as the case may be. For example, precipitation zones or inclusion zones can be formed through solid phase chemical reactions of particles and hoses (eg, Si and Mo, Fe, Mn, Mg, Ag, Cr, W, Ta, Ti in SiGe hosts). , Cu, Ni or V metal particles react to form particles such as MoSi ₂ , FeSi ₂ , MgSi ₂ ).

While not wishing to be bound by any particular theory, it is believed that precipitation zones or other types of inclusions can enhance phonon scattering in the thermoelectric material, which can lead to a decrease in the thermal conductivity of the thermoelectric material. In addition, n-doped or p-doped regions can enhance the electrical conductivity of the thermoelectric material, for example, via a modulation doping mechanism. In such cases, some or all of the charge carriers (electrons and holes) may be donated by precipitation inclusions or other inclusions enclosed in larger grains. Since the distance between the inclusion regions can be greater than the distance between atomic dopants in the homogeneously doped material, the impurity scattering of the charge carriers is reduced compared to the impurity scattering of the homogeneously doped material. Such a modulation doping like mechanism can increase electrical conductivity through enhancement of carrier mobility. In some cases, these precipitation zones or other inclusions may improve the Seebeck coefficient by scattering more low energy carriers than high energy carriers. Thus, precipitation zones or other inclusions can enhance the ZT of the thermoelectric material.

In other embodiments, the precipitation zone, or the grain zone or other inclusions may be preferentially doped. In such a case, carriers in these regions can fall into the surrounding host medium when they are at higher potential energy. For example, in the case of modulation doping, the doping in the host material can be correspondingly reduced or eliminated, thereby reducing the scattering of ionized impurities to improve electron mobility in the host.

Embodiments that include precipitation zones or other inclusions in the grain may exhibit multiple particle sizes. In some embodiments, the particle size is consistent with the size described herein for grains generally smaller than microns. For example, the average grain size may be less than about 500 nm, less than about 200 nm, less than about 100 nm, less than about 50 nm or less than about 20 nm. Alternatively or in addition, the average grain size may be greater than about 1 nm. In other embodiments with one or more inclusions, the grain size may be larger than microns. For example, many grains may have an average size of about 2 microns, about 5 microns, or about 10 microns. In particular embodiments, the plurality of grains have an average size in the range of about 1 to about 10 microns, in the range of about 1 to about 5 microns, or in the range of about 1 to about 2 microns.

The size of the precipitation zone or inclusions may vary. For example, the size of the precipitation zone may be limited by the size of the grains in which the precipitation zone is enclosed. In many embodiments, the precipitation zone or inclusions may preferably have an average size in the range of about 1 to about 50 nm, or in the range of about 1 to about 20 nm. As another example, where, for example, a modulation doping mechanism is used to increase electronic performance, the precipitation region or inclusion may have a larger size, for example, between 1 nm and 10 microns, while The reduction in phonon thermal conductivity of the region is achieved by alloying or nanograining.

Some aspects relate to manufactured thermoelectric materials exhibiting modulation doping to achieve improved performance indices. In some embodiments, the thermoelectric material may include particles (eg, nanoparticles) or other inclusions encapsulated in a host material, wherein the inclusions are provided by donating charge carriers (eg, electrons or holes) to the host. Increasing carrier mobility in the host. This can usefully improve the electrical conductivity of the entire thermoelectric material, and thus improve the thermoelectric performance of the thermoelectric material, for example the thermoelectric performance characterized by the ZT value of the thermoelectric material. In many such cases, the host is first chosen to have an n-type or p-type doping level (typically, a spatially substantially uniform doping level) that is undoped or below the typical doping value for the thermoelectric material. For example, the initial doping level of the host can be a factor of less than 1.5, less than 2, less than 5, less than 10, less than 100 or less than 1000 than conventional thermoelectric materials. In addition, the enclosed inclusions (eg, precipitation sites or individual particles) may be formed of doped or undoped materials.

As an example, FIG. 1B schematically illustrates a thermoelectric material comprising a host 130 in which a plurality of particles 140 are enclosed-the particles act as inclusions. In this case, the host comprises a number of grains 135, for example a number of crystalline grains, which in some cases are less than about 1 micron, for example, in the range of about 500 nm to less than about 1 micron. Size (eg, maximum particle size in all dimensions). In other cases, the grain size may be larger, for example in the range of about 1 to about 20 microns. In addition, in some cases, the particles may have a size (eg, a maximum size in all directions) of less than about 1 micron, such as in the range of about 1 to about 200 nm or in the range of about 2 to about 100 nm. In other cases, the particle size may range from 1 micron or greater, such as from about 1 to about 10 microns. The inclusion 140 may be formed in various ways. For example, they can be formed as precipitation zones using appropriate techniques including those discussed for other aspects herein. In other cases, they may be formed from materials different from those of the host using, for example, the techniques discussed in the above referenced patent application entitled "Nanocomposites with High Thermoelectric Performance Index". In another case, the particles can be formed, for example, through a solid phase chemical reaction during the solidification step.

Without loss of generality, in this example, the host 130 is assumed to be a SiGe alloy having a number of micron-sized and / or nano-sized grains 135, and the particles 140 are MoSi ₂ (encapsulated in SiGe alloys). Molybdenum silicide). Such thermoelectric materials can be formed, for example, in the following manner: molybdenum is added to SiGe, the material is melted, and the material is cooled (eg, in the manner discussed above) to produce an ingot. Which can be ground and compressed as necessary. In this approach, MoSi ₂ particles are formed, for example, through solid-state chemical reactions of Mo and Si during the cooling process. The SiGe host is not excessively doped in this example, although it may be in other cases, for example, the SiGe host may be p-type doped, but 2, 5, 10 or more than in conventional SiGe thermoelectric materials. It can be as small as 100 factors. Holes can also be produced by the presence of MoSi ₂ . Such donation of holes to the host can improve hole mobility in the thermoelectric material, thus improving electrical conductivity and consequently improving the thermoelectric performance of the thermoelectric material. In other cases, the particles may be used to form particles of FeSi ₂ , MgSi _2, etc. by grinding elemental Si and elemental Ge or SiGe crystalline alloy with Fe, Mn, Mg, Cr, W, Ta, Ti, Cu, Ni or V. By forming, or by grinding together each of the above silicides and elemental Si and elemental Ge or SiGe alloys, through solid-state chemical reactions of Si in a host (eg SiGe). Some of these can be applied to the n-type, while others can be applied to the p-type material. Other nanoparticles (eg, metallic nanoparticles and / or semiconductor nanoparticles) that do not react with Si may be used to produce a modulation doping such as Ag as inclusions.

While not wishing to be bound by any particular theory, for further explanation of this donation of charge carriers from the particles to the host, FIG. 1C corresponds to the portions 151, 152, 153 corresponding to the host material and to the particles encapsulated in the host. Diagrammatically shows a charge carrier energy diagram corresponding to a hypothetical thermoelectric material (eg, the SiGe based material with MoSi ₂ particles encapsulated therein) representing portions 161 and 162. The diagram is schematic and is shown for illustrative purposes only. The charge carriers (eg, electrons or holes) in the energy bands (eg, conduction bands or valence bands) of the particles 161, 162 may be formed by the host 151, 152, 153, which may be conduction bands or valence bands. It may have a higher energy than the energy in the energy band. Thus, many charge carriers in a particle, which may be due to additional doping in the particle or due to the particle's inherent large electron density (such as in metals or semimetals), may be directed to the host to lower their energy. I can move it. Such charge carrier transport from the particles to the host can advantageously increase carrier mobility, for example, by reducing dopants in the host material, thereby reducing scattering of ionized impurities. In this way, higher electrical conduction can be achieved. In some cases, since grain boundaries still scatter electrons, even if overall higher electron mobility is not achieved, this modulation doping method is still beneficial by compensating for the reduction in mobility due to electron grain boundary scattering. Particles used for modulation doping may potentially induce higher Zeebbeck coefficients because they may scatter low energy carriers, and may also potentially induce reduced thermal conductivity of both phonons and electrons. . In other cases, the particles can donate holes to the host rather than donating electrons to the host. In addition, without wishing to be bound by any particular theory, the mechanism for this donation of charge carriers from the particle to the host shifts from the higher energy level of the particle's valence band to the lower energy level of the host's valence band. Can be based on some of the holes, or some of the holes by attracting electrons from the host's valence band into the particles, creating more holes in the host, or drawing electrons from the host's valence band into the particles It can be based on creating more holes in the host.

In general, the type of starting material, temperature at which enhanced ZT is measured, grain components, formation method, and other properties and processes that may be associated with these embodiments include all the features and methods discussed in this application. They are consistent with the grain size, precipitation zone, and / or other inclusions described. For example, the grains may be formed from suitable thermoelectric materials, as discussed above, and may further include n-type or p-type dopants. In another example, the formed thermoelectric material has a ZT value of at least about 1.0, at least about 1.5, at least about 2, or in the range of about 1 to about 5. In another example, the thermoelectric material formed may exhibit ZT values (eg, improved relative to the starting material) at operating temperatures 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 As another example, the grains of the thermoelectric material may include one or more of bismuth based materials (eg, Bi ₂ Te ₃ and / or related alloys thereof), silicon based materials, and lead based materials. In connection with the production of such thermoelectric materials, the method of forming nanoparticles from bulk starting materials or elemental materials may be characterized by parameters (eg, grinding speed, duration and / or temperature) in order to obtain the desired nanoparticles for compaction. Cryogenic)), but may be applied as discussed herein above. In addition, this control of the nanoparticle size can be used to obtain the desired grain size (eg, less than 1 micron, or greater than 1 micron and less than 10 microns) in the final thermoelectric material. Compression methods may also be applied as discussed herein and as applied by those skilled in the art.

Another aspect of the present application relates to a method of making a thermoelectric material. In this method, many nanoparticles are produced from thermoelectric materials. Nanoparticles can solidify at elevated temperatures under pressure to form thermoelectric materials. Types of thermoelectric starting materials that can be used to produce nanoparticles include, but are not limited to, any of the bulk materials described herein and others known to those skilled in the art. Thus, embodiments can include a thermoelectric material having a ZT value of at least about 1 (eg, at a temperature below about 2000 ° C.). In addition or alternatively, the methods may use n-doped or p-doped starting materials (eg, bulk thermoelectric materials that are elements and / or alloys).

Various techniques can be used to generate nanoparticles from thermoelectric materials. In some embodiments, nanoparticles are prepared by grinding a thermoelectric material. Grinding can be performed using a mill, for example, a ball mill using planetary motion, figure-eight-like motion or other motion. In the case of producing nanoparticles, some techniques, such as grinding techniques, generate significant heat, which can affect nanoparticle size and properties (eg, cause particle agglomeration). Thus, in some embodiments, cooling of the thermoelectric material may be performed while grinding the thermoelectric material. Such cooling may make the thermoelectric material more brittle, and may facilitate the production of nanoparticles. Cooling and particle generation can be accomplished by wet milling and / or cryomilling (eg, in the presence of dry-ice or liquid nitrogen surrounding the mill). Aspects of the present invention may also use other methods for forming nanoparticles. Such methods may include gas phase condensation, wet chemistry, high speed spinning of the molten material, and other suitable techniques.

Solidification of the nanoparticles at elevated temperature under pressure can be carried out in a variety of ways under a variety of conditions. Processes, such as hot presses (“P ² C” herein), also known as spark plasma sintering, may be used to impose the desired pressure and temperature during solidification. The disclosure of this process and the apparatus for carrying out the process are described in US Patent Publication No. 2006/0102224, filed Oct. 29, 2004, filed Oct. 29, 2004, which is incorporated by reference in its entirety herein. It is available from.

The pressure used is usually superatmospheric pressure, which allows the use of low temperatures to achieve solidification of the nanoparticles. In general, the pressure used may range from about 10 to about 900 MPa. In some embodiments, the pressure is in the range of about 40 to about 300 MPa. In another embodiment, the pressure is in the range of about 60 to about 200 MPa.

In connection with the above elevated temperatures, a range of temperatures may be used. In general, temperatures typically range from 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 to about 2000 ° C, about 400 to about 1200 ° C, about 400 to about 600 ° C, about 400 to about 550 ° C. For some exemplary n-doped materials, the temperature ranges from about 450 to about 550 ° C., while for some exemplary p-doped materials, the range is several degrees higher (eg, about 475 to about 580 ° C). Other temperature ranges may also be used in connection with the processing of the n- and p-type materials. These particular pressure and temperature ranges may be used for any material, although they may preferably be applied to materials such as BiSbTe alloys and BiSeTe alloys.

The pressure and temperature can be maintained for a time sufficient to allow for the solidification of the nanoparticles. In some embodiments, the time ranges from about 1 second to about 10 hours.

Other solidification conditions may be used to form the thermoelectric materials described herein. For example, to achieve low temperature compression, nanoparticles can be collided with other particles at high speed. Subsequent heat treatment can optionally be used to form the thermoelectric material. Another solidification process may utilize annealing the particles (eg, nanoparticles) with little or no pressure to solidify the particles. In such a case, the temperature can be selected to induce annealing of the particles at whatever pressure the sample is held during annealing. In other cases, the particles can be solidified at high pressure at relatively low temperatures to form a solidifying material, such as a material approaching 100% theoretical density. Subsequently, the solidified material may be annealed at elevated temperature to form a thermoelectric material. Thus, the solidification technique need not be limited to P ² C or high temperature compression.

As an exemplary embodiment, nanopowders consisting of various materials from commercially available materials can be prepared by high energy ball milling to obtain nanoparticles with particle sizes as small as 1 nm. In some cases, dry milling can be combined with wet milling and / or cryomilling to prevent the milled particles from agglomerating into larger sized particles due to the heat generated during milling. In this way, even more dispersed particles can be obtained. These powders can be compressed into solid samples by hot presses including P ² C technology. In many embodiments, approximately 100% density, in theory, can be achieved in a short time (typically from about 1 to about 10 minutes per sample). The hot compressed samples produced by this method can reduce the lattice thermal conductivity to only a fraction of the original value in both n-type and p-type, while maintaining a power factor comparable to the bulk counterpart, thus ZT The value is significantly improved.

On the other hand in the p- type commercially available materials of the _x Te ₃ (where, x may range from about 0 to about 0.8), the commercially available materials having a maximum ZT value of about _1, for example, Bi _x Sb ₂ After ball milling and hot pressing, the ZT value of the commercially available material may be 1.4 or higher. This improvement is mainly due to the reduced thermal conductivity due to the presence of nanostructures in the sample.

In some embodiments, rather than converting the thermoelectric starting material into nanoparticles (or using other particle generation methods) to compress these nanoparticles, the nanoparticles are extracted from two or more elemental materials (eg, Elemental Bi and Elemental Te). To produce (eg by grinding). The nanoparticles are then mixed and compressed under elevated pressure (eg, the pressure and temperature discussed above) so that the ZT value is at least about 1, preferably at least about 1.2, or at least about 1.5, or about The resulting thermoelectric material of two or more (eg, a thermoelectric material having a polycrystalline structure having grains of less than about 500 nm in size and preferably in the range from about 1 to about 100 nm) can be produced.

In an alternative embodiment, two or more bulk materials can be ground simultaneously to produce various nanoparticles with different compositions. Grinding processes can be used to “mechanically alloy” nanoparticles. Mechanical alloying may also be performed by producing two or more different particles separately, then mixing the particles together and further grinding them to form an alloy and reducing the size of these particles to form alloyed nanoparticles. . These particles may be solidified to form a thermoelectric material having one or more of the properties discussed herein.

In another embodiment, different types of nanoparticles are produced separately using any of the techniques discussed herein (eg, grinding of bulk elemental materials (eg, bismuth or tellurium)), and then mixed together It can be solidified to form a thermoelectric material. Further grinding of the mixture may optionally be applied prior to solidification. The final-solidified material formed by any of these processes may be any of the compositional properties described herein, eg, Bi ₂ Te _{3 -x} Se _x. (Where x is in the range of about 0 to about 0.8; for example, Bi ₂ Te _2.8 Se _0.2 ) or Bi _x Sb _{2 -x} Te ₃ (where x is in the range of about 0 to about 0.8): g., may have a _{Bi 0 .5 Sb 1 .5 Te 3} ).

Another aspect of forming a thermoelectric material uses one or more repetitions of the steps used to form the thermoelectric material as discussed herein. For example, particles (eg, nanoparticles) can be produced from one or more starting materials (eg, starting material or elemental material of a bulk thermoelectric material) and solidified to be a material structure. The resulting structure can then be used to produce a new large number of particles (eg, by grinding of the material structure), and these new particles can subsequently be solidified to form another material structure. This process can be repeated several times to form the final thermoelectric material. This process can assist in the production of small grain sizes mixed thoroughly.

In some embodiments, it may be advantageous to protect particles resulting from oxidation (eg, during the ball milling process). Non-limiting examples of protection techniques include exposing the resulting particles (eg, the environment in which the grinding of the material occurs) to a relatively oxygen-depleted environment, such as a vacuum, or an environment with low oxygen content relative to atmospheric pressure. The resulting particles can also be exposed to some form of chemical coating to reduce oxygen exposure of the surface; The coating may optionally be removed later in the thermoelectric material manufacturing process. Thus, protection schemes may include a number of suitable techniques, including those known to those skilled in the art.

The following example section provides further description of various aspects of the present invention and a description of the possibility of using the method of the present invention to produce thermoelectric materials exhibiting improved thermoelectric properties. However, the following examples are provided for illustrative purposes only and do not represent the optimal results achievable by practicing the method of the present invention.

Example  1: Nanocrystalline Bulk p-type Bi _x Sb _{2 - x} Te ₃  matter

Commercial materials (p-type BiSbTe alloy ingots) are powdered and introduced into zirconia jars inside a glove box under an argon atmosphere to avoid oxidation. Several zirconia balls (5 to 15 mm in size) are also added and sealed. The sealed ruler is placed in a ball mill and milled for a total of about 0.5 to 50 hours at a speed of 100 to 2000 rpm. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD) are used to verify the properties of the powder.

3 shows the x-ray diffraction (XRD) pattern of nanopowder after ball milling. The XRD pattern proves that the powder two days sangyigo, Bi _{0 .5} Sb _{1 .5} pattern corresponds well with the Te _3. Magnified diffraction peaks indicate that the particles are small. This small size is confirmed by scanning electron microscopy (SEM) images of the nanopowders shown in FIG. 2A and low magnification transmission electron microscopy (TEM) images of the powders shown in FIG. 2B. The low resolution TEM image of FIG. 2B clearly shows that the minority of the sizes of the nanoparticles reaches about 50 nm and the average size is about 20 nm. The high resolution TEM image shown in FIG. 2C confirms good crystallinity and clean particle surface of the nanoparticles, which is desirable for good thermoelectric properties. The illustration of FIG. 2C also shows that some nanoparticles are even smaller than 5 nm.

Once the powder is obtained, the powder sample is processed into a bulk disk sample having a diameter of 1/2 "and a thickness of 2 to 12 mm by introducing nanopowder into a 1/2" diameter die and hot compressing it. After milling the powder (stored inside the glove box to prevent oxidation) is introduced into the graphite die and compacted to pellets using DC hot press technique (see FIG. 4). Parameters for hot compression conditions are 40 to 160 MPa and 450 to 600 ° C. Density is close to 100% of theory of all compositions. For the measurement of electrical and thermal conductivity and the Seebeck coefficient using both the DC and AC methods, a disk with a diameter of 1/2 "and a thickness of 2 mm and about 2 x 2 x 12 mm 3 from the compressed disk Cut and polish the bar.

Typically, in the preparation of hot pressed samples, the powder is exposed to a selected pressure and the device is activated at a set heating rate. Once the selected elevated temperature is reached, the sample is brought to said temperature for about 0 to about 60 minutes, preferably about 0 to about 30 minutes, about 0 to about 10 minutes, or less than about 0 to 5 minutes (eg, for 2 minutes). And at pressure. Then, cooling is started. However, it should be understood that the pressure may be imposed during or after the sample reaches an elevated temperature.

5 to 9 compare the temperature dependence of various properties of hot compressed nanocrystalline material (shown as BP0572 in the figure) and commercial material (shown as a commercial ingot in the figure) p-type BiSbTe alloy ingot. All properties in FIGS. 5-9 are measured from the same sample. The cylinder-shaped disk is hot pressed, cut along the direction of compression and perpendicular to the direction of compression, and then measured. To test the temperature stability of the nanocrystalline bulk sample, the same sample is measured repeatedly until it reaches 250 ° C. No substantial degradation is observed.

5 compares the temperature dependence of the electrical conductivity of nanocrystalline and commercial samples. Electrical conductivity is measured by a four point current-switching technique. The electrical conductivity of the nanocrystalline bulk sample is somewhat higher than that of commercial ingots.

FIG. 6 compares the temperature dependence of the Seebeck coefficients of the nanocrystalline and commercial samples, while FIG. 7 compares the temperature dependence of the power factor (S ² sigma) of the sample. The Seebeck coefficients are calculated using a commercially available device (ZEM-3, Ulvac, Inc.) on the same bar-shaped samples with dimensions of 2 x 2 mm 2 and 12 mm in length cut along the disk face. Measured by the electrostatic DC method based on the slope of the temperature difference curve. These properties are also measured for home-made systems on the same sample. The two sets of measurements are within 5% of each other. The Zeebek coefficient of the nanocrystalline sample is somewhat lower or higher than the Zeebek coefficient of the ingot, which is temperature dependent, making the nanocrystalline sample comparable to that of commercial ingots when the power factor of the nanocrystalline sample is below 75 ° C. If the power factor of the sample is 75 ° C. or higher, the power factor is higher than that of a commercial ingot.

8 shows the temperature dependence of the thermal conductivity of nanocrystalline and commercial samples. Thermal conductivity is derived from the measurement of thermal diffusivity and thermal capacity of the sample. Thermal diffusivity is measured by a laser-flash method on a disc along the disc axis direction using a commercial system (Netzsch Instruments, Inc.). After laser-flash measurement, the bars are cut from the disk and their thermal diffusivity is measured along the bar (disk-plane) direction using the Angstrom method in a home-built system. The thermal diffusivity values of the bars and discs are consistent within 5%.

9 records the change in figure of merit ZT as a function of temperature of nanocrystalline and commercial samples. Since the thermal conductivity of the nanocrystalline bulk sample is significantly lower than that of commercial ingots and, more importantly, the difference increases further as the temperature increases, this leads to a significantly improved ZT in the temperature range of 20 to 250 ° C. 9 also shows that the peak ZT values shift to higher temperatures (100 ° C.). The peak ZT of the nanocrystalline bulk sample is about 1.4 at 100 ° C., which is significantly higher than the peak ZT of commercially available Bi ₂ Te ₃ based alloys. The ZT values of commercial ingots begin to drop at temperatures above 75 ° C. and fall below 0.25 at 250 ° C. In comparison, nanocrystalline bulk samples show ZT higher than 0.8 at 250 ° C. These ZT properties are even more desirable for power generation applications, because good materials with high ZT in the above temperature range are not currently available.

Detailed microstructure inspection is performed on nanocrystalline bulk samples using transmission electron microscopy (TEM). The bulk nanocrystalline sample is cut, polished and ion milled to prepare a TEM specimen. The hot pressed nanocrystalline bulk pellets are cut into blocks of 2 × 3 × 1 mm and ground to 2 × 3 × 0.002 mm using a mechanical tripod grinder. The sample is glued to a copper grid and milled for 30 minutes using a Precision Ion Polishing System (Gatan Inc.) with an incident energy of 3.2 kW and a beam current of 15 kW at an angle of incidence of 3.5 °. 10-15 show representative TEM micrographs, which represent the key structural features observed.

In general, as shown in FIGS. 10 and 11, most grains are nano-sized. Moreover, the nanograins are quite crystalline and randomly oriented with very clear boundaries (large angles between the grid faces). As shown in FIG. 11, the nanograins can be intimately packed and match the density measurements suggesting a fully dense sample. There are also larger particles as shown in FIG. 12. As shown in FIG. 13, the high resolution TEM brown rice technique shows that these grains consist of nano dots with a borderless size of 2 to 10 nm. These nanodots are typically Sb-rich with an exemplary composition approaching Bi: Sb: Te = 8:44:48, with Sb replacing Te. Some nanodots have no borders with the matrix as shown in FIG. 13, while other nanodots observed have small angle borders with the matrix as shown in FIG. 14. As shown in FIG. 15, pure Te precipitates in sizes ranging from 5 to 30 nm are also observed. The selected-area electron diffraction pattern shown in the illustration of FIG. 15 confirms the Te phase. Generally speaking, nano dots can be found within an area of 50 nm diameter each.

While not necessarily tied to a particular theory, it can be assumed that these nanodots can be formed during the hot-press heating and cooling process. As shown in FIG. 12, larger grains containing nano dots can cause non-uniform milling of the ingot during ball milling. These large grains can grow much larger during hot-press compaction through Oswald Ripening. If there is a large population of nano interface features (eg nano grains) in the material of the present invention, nano dots may not be the only reason for strong phonon scattering.

Example  2: nanocrystalline SiGe  matter

Elemental silicon and germanium element materials, both p-type and n-type, are used as starting materials and are milled using a ball mill to form nanoparticles having a size of about 1 to about 200 nm. These elemental materials may in some cases have a ZT lower than about 0.01. It is also understood that SiGe alloys can be used to form particles, possibly leading to further improvements in the finally produced material. The sample is hot pressed at a pressure of about 40 to about 200 MPa and a temperature of about 900 to 1300 ° C. to form a thermoelectric material sample.

16-19 show graphs showing the temperature dependence of various properties of hot pressed nanocrystalline materials formed from p-type SiGe ball milled bulk materials. Properties are measured using the same technique described above with respect to FIGS. 5-9. FIG. 16 shows the temperature dependence of the electrical conductivity of nanocrystalline p-type SiGe samples. FIG. 17 shows the temperature dependence of the Seebeck coefficients of nanocrystalline p-type SiGe samples. FIG. 18 shows the temperature dependence of thermal conductivity for p-type SiGe samples. 19 records the change in the figure of merit ZT of the nanocrystalline p-type SiGe sample as a function of temperature.

20-23 show graphs showing the temperature dependence of various properties of hot pressed nanocrystalline materials formed from n-type SiGe ball milled bulk materials. 20 shows the temperature dependence of the electrical conductivity of nanocrystalline n-type SiGe samples. FIG. 17 shows the temperature dependence of the Seebeck coefficients of nanocrystalline n-type SiGe samples. FIG. 18 shows the temperature dependence of thermal conductivity for n-type SiGe samples. 19 records the change in figure of merit ZT of the nanocrystalline n-type SiGe sample as a function of temperature.

24-26 show TEM micrographs of p-type SiGe materials associated with nanocrystalline materials. FIG. 24 shows a TEM micrograph of a ball milled powder sample of SiGe bulk material, showing nano-sized microparticles of milled microparticles. FIG. 25 shows TEM micrographs of SiGe powder samples after hot compression. Micrographs show a large number of grains in the tightly packed nano-size range of hot pressed materials. The illustration of FIG. 25 shows the selected-area electron diffraction pattern taken for the sample. FIG. 26 shows a high resolution TEM of a high temperature compressed SiGe sample, which also shows the nano size of a number of grains in the sample, indicating a number of grain boundaries set for phonon scattering.

Example  3: nanocrystalline p-type BiSbTe  Change the temperature of the material ( tailoring )

To illustrate how the figure of merit ZT can be customized for various temperature conditions, samples of nanocrystalline p-type BiSbTe alloy materials were prepared. In particular, Bi _x Sb _{2 -} can be prepared in a variety of stoichiometric which influence the _x Te ₃ type material, the chosen value of x. To prepare a two particular exemplary types of samples: the Bi _{0 .3} Sb _{1 .7} Te ₃ of p- type nano-crystalline, high temperature compressed materials having a stoichiometry, and Bi _{0 .5} Sb _{1 .5} Te ₃ P-type nanocrystalline, high temperature compressed material with stoichiometry. The appropriate bulk starting material is ground by a ball mill to form a nanoparticle sample. Samples are compressed at 40-160 MPa and 450-600 ° C. for up to about 5 minutes.

Nanocrystalline Bi ₀ is a 27 to 30 _{1 .3 .7} Sb Te ₃ While electrical conductivity, Zeebeck coefficient, thermal conductivity and temperature dependence of ZT for the samples are shown respectively, FIGS. 31 to 34 show electrical conductivity, Zeebeck coefficient, thermal conductivity for Bi _0.5 Sb _1.5 Te ₃ samples. And temperature dependence of ZT, respectively. The measurement was performed as described in Example 1. As can be seen from Figures 30 and _{34, Bi 0 .3 Sb 1 .7} Te 3 Peak ZT value for the sample is measured while at about _{150 ℃, Bi 0 .5 Sb 1} .5 Te 3 Peak ZT values for the samples were measured at about 75 ° C.

Thus, the results indicate that the peak ZT of the nanocrystalline material can be customized for particular temperature range applications. For example, cold peak materials can be used in applications that are tuned closer to room temperature use, such as cooling, while hot peak materials can be used in applications for high temperatures such as power generation.

In conjunction with the above experimental results, it should be understood that the various aspects discussed herein disclose only a variety of methods and materials that are representative of the scope of the invention. Indeed, those skilled in the art will readily recognize that many other modifications to the methods and materials described herein may be made. All such modifications represent relevant aspects that also fall within the scope of the invention. In addition, all numbers indicating the amounts of components used in the specification and claims, reaction conditions, and the like, should be understood as being changed in all cases by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth herein and in the appended claims are approximations that may vary depending upon the desired properties.

Claims (92)

Generating a plurality of nanoparticles from the thermoelectric starting material and Consolidating the nanoparticles at elevated temperature under pressure to form a compressed thermoelectric material having a higher ZT value than the thermoelectric starting material at at least one temperature. The method of claim 1, further comprising selecting the pressure and elevated temperature such that the thermoelectric material exhibits a ZT value of at least about 1. The method of claim 1, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 2000 degrees Celsius. The method of claim 3, wherein the thermoelectric material exhibits the ZT value at a temperature below about 1000 ° C. 5. The method of claim 4, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 600 ° C. 6. The method of claim 5, wherein the thermoelectric material exhibits the ZT value at a temperature below about 200 ° C. 7. The method of claim 6, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 20 ° C. 8. The method of claim 1, wherein producing a plurality of nanoparticles comprises grinding the thermoelectric starting material. The method of claim 8, further comprising the step of cooling the thermoelectric starting material and cooling it. 10. The method of claim 9, wherein grinding the thermoelectric starting material comprises using ball milling. The method of claim 1, wherein the solidifying of the nanoparticles comprises the use of one or more of a plasma pressure compression process, a unidirectional hot press process, and an isothermal hot press process. The method of claim 1, further comprising selecting the pressure in the range of about 10 to about 900 MPa. The method of claim 12, further comprising selecting the pressure in the range of about 40 to about 300 MPa. The method of claim 13, further comprising selecting the pressure in the range of about 60 to about 200 MPa. The method of claim 1, further comprising selecting the elevated temperature in the melting point range of about 200 ° C. to approximately the thermoelectric starting material. The method of claim 1, further comprising selecting the elevated temperature in the range of about 400 ° C. to about 2000 ° C. 7. The method of claim 1, wherein the step of generating the plurality of nanoparticles comprises using a thermoelectric starting material comprising any one of a p-doped material and an n-doped material. The method of claim 1, wherein the thermoelectric starting material exhibits a polycrystalline structure having an average crystal grain size of at least about 1 micron. The method of claim 1, further comprising selecting the thermoelectric starting material such that the thermoelectric starting material comprises any one of a bismuth based material, a lead based material, and a silicon based material. The thermoelectric starting material of claim 1, wherein the thermoelectric starting material comprises 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. Further comprising the step of producing a thermoelectric material. The thermoelectric material of claim 1, further comprising selecting the thermoelectric starting material such that the thermoelectric starting material is a Bi ₂ Te _{3 − x} Se _x alloy, where x ranges from about 0 to about 0.8. Way. According to claim 1, wherein the heat-starting material is Bi _x Sb _{2 - x} Te ₃ alloy for producing a thermoelectric material further comprises a Selecting the thermal starting materials so that (where, x is from about 0 to the range of about 0.8) Way. The method of claim 1, wherein producing a plurality of nanoparticles comprises producing nanoparticles having an average grain size of less than about 500 nm. The method of claim 23, wherein the average grain size ranges from about 1 to about 200 nm. The method of claim 1, further comprising maintaining the nanoparticles at an elevated temperature for about 1 second to about 10 hours. A material structure comprising a plurality of grains having an average grain size in the range of about 1 to about 1000 nm, wherein the material structure is characterized by a ZT value of at least about 1.0 at a temperature of less than about 2000 ° C. 27. The thermoelectric material of claim 26, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 1000 ° C. 27. The thermoelectric material of claim 26, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 600 ° C. 27. The thermoelectric material of claim 26, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 200 ° C. 27. The thermoelectric material of claim 26, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 20 ° C. The thermoelectric material of claim 26, wherein the average grain size of the plurality of grains ranges from about 1 to about 500 nm. 27. The thermoelectric material of claim 26, wherein at least one of the plurality of grains comprises at least one precipitation region in the grains. 33. The thermoelectric material of claim 32, wherein the one or more precipitation regions have a size in the range of about 1 to about 20 nm. 27. The thermoelectric material of claim 26, wherein substantially no particles are greater than about 100 nm in the material structure. 27. The thermoelectric material of claim 26, wherein the material structure has a porosity of less than about 10%. The thermoelectric material of claim 35, wherein the porosity is less than about 1%. 27. The thermoelectric material of claim 26, wherein the ZT value of the material structure is at least about 1.2. 38. The thermoelectric material of claim 37, wherein the ZT value of the material structure is at least about 1.5. The thermoelectric material of claim 38, wherein the ZT value of the material structure is about 2 or greater. 38. The thermoelectric material of claim 37, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 2000 ° C. 41. The thermoelectric material of claim 40, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 1000 ° C. 43. The thermoelectric material of claim 41, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 600 ° C. 43. The thermoelectric material of claim 42, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 200 ° C. 44. The thermoelectric material of claim 43, wherein the thermoelectric material exhibits the ZT value at a temperature of less than about 20 ° C. 27. The thermoelectric material of claim 26, wherein the thermoelectric material exhibits a density in the range of about 90 to about 100% of each theoretical density. 27. The thermoelectric material of claim 26, wherein the plurality of grains comprises at least one of an n-doped material and a p-doped material. 27. The thermoelectric material of claim 26, wherein the plurality of grains comprise one or more of bismuth based materials, lead based materials, and silicon based materials. 48. The thermoelectric of claim 47, wherein the plurality of grains comprise one or more of bismuth-antimony-tellurium alloys, bismuth-selenium-tellurium alloys, lead-tellurium alloys, lead-selenium alloys, and silicon-germanium alloys. material. 49. The thermoelectric material of claim 48, wherein the plurality of grains comprise a bismuth-antimony-tellurium alloy. 27. The thermoelectric material of claim 26, wherein the plurality of grains comprises a Bi ₂ Te _{3 - x} Se _x alloy, where x ranges from about 0 to about 0.8. 27. The method of claim 26, Bi _x Sb _{2 - x} Te ₃ alloy (where, x is in the range of about 0 to about 0.8) is, the thermoelectric material. 27. The thermoelectric material of claim 26, wherein the plurality of grains comprises two or more grains having different elemental compositions. A thermoelectric material comprising a plurality of compressed crystalline inclusions, Wherein the inclusions are randomly disposed relative to each other, the average size of the inclusions ranges from about 1 to about 500 nm and the compressed inclusions provide a thermoelectric material exhibiting at least about ZT. 54. The thermoelectric material of claim 53, wherein the inclusions comprise grain. The thermoelectric material of claim 53, wherein the average size of the inclusions ranges from about 1 to about 100 nm. The thermoelectric material of claim 53, wherein the average size of the inclusions ranges from about 1 to about 50 nm. The thermoelectric material of claim 53, wherein substantially no inclusions greater than about 500 nm are present. 55. The thermoelectric material of claim 53, wherein the thermoelectric material exhibits a polycrystalline structure. The thermoelectric material of claim 53, wherein the thermoelectric material exhibits ZT of at least about 1.2. 60. The thermoelectric material of claim 59, wherein the thermoelectric material exhibits ZT of at least about 1.5. 61. The thermoelectric material of claim 60, wherein the thermoelectric material exhibits ZT of at least about 2. Grinding at least one bulk elemental material to produce a plurality of nanoparticles, and Compressing the plurality of nanoparticles at elevated temperature under pressure to produce a thermoelectric material exhibiting a ZT value of at least about 1. 63. The method of claim 62, wherein the at least one bulk element material comprises at least two different bulk element materials, and wherein the grinding step comprises producing at least two types of nanoparticles. 64. The method of claim 63, wherein the at least two different bulk element materials comprise bismuth and tellurium. 64. The method of claim 63, wherein the at least two different bulk element materials comprise bismuth, tellurium and antimony. 64. The method of claim 63, wherein the at least two different bulk element materials comprise bismuth, tellurium and selenium. 63. The method of claim 62, further comprising adding a dopant to the plurality of nanoparticles. 63. The method of claim 62, further comprising providing a raw material that is at least one of an alloy and a compound, wherein the raw material has a ZT value of at least about 0.5 and compacting the plurality of nanoparticles comprises: And compressing the particles with the particles from the raw material. 63. The method of claim 62, further comprising providing micron-sized particles, and compacting the plurality of nanoparticles comprises compressing the plurality of nanoparticles with the micron sized particles. Method for producing a thermoelectric material. A thermoelectric material comprising a material structure comprising a plurality of grains having an average size in the range of about 1 nm to about 10 microns, wherein at least some of the plurality of grains have at least one having an average size in the range of about 1 to about 100 nm. And a precipitation zone, wherein the thermoelectric material exhibits a ZT value of at least about 1. The thermoelectric material of claim 70, wherein the average size of the grains ranges from about 1 nm to about 5 microns. The thermoelectric material of claim 71, wherein the average size of the grains ranges from about 1 nm to about 2 microns. 71. The thermoelectric material of claim 70, wherein the thermoelectric material exhibits a ZT value in the range of about 1 to about 5. The thermoelectric material of claim 70, wherein the thermoelectric material exhibits a ZT value of at least about 1.5. The thermoelectric material of claim 70, wherein the thermoelectric material exhibits a ZT value of about 2 or greater. 71. The thermoelectric material of claim 70, wherein the thermoelectric material exhibits the ZT value at an operating temperature of less than about 2000 ° C. 71. The thermoelectric material of claim 70, wherein the precipitation zone exhibits an average size in the range of about 1 to about 50 nm. 71. The thermoelectric material of claim 70, wherein the grain is formed from one or more of bismuth based alloys, lead based alloys, and silicon based alloys. Host material and A thermoelectric material comprising a plurality of particles of less than about 20 microns in size, dispersed throughout the host material, The thermoelectric material exhibits a carrier concentration higher than the respective carrier concentration in the host material in the absence of the particles. 80. The thermoelectric material of claim 79, wherein the charge carrier mobility of the thermoelectric material is greater than each charge carrier mobility in the host material in the absence of the particles. 80. The thermoelectric material of claim 79, wherein the plurality of particles are doped more than the host material. 80. The thermoelectric material of claim 79, wherein the ZT value of the thermoelectric material is at least about 0.8. 80. The thermoelectric material of claim 79, wherein the host material comprises a plurality of grains and at least some of the plurality of grains are less than about 1 micron in size. 80. The thermoelectric material of claim 79, wherein the host material comprises a plurality of grains and at least some of the plurality of grains are at least about 1 micron in size. A host material characterized by a first energy band, and A thermoelectric material dispersed in the host material, less than about 20 microns in size, and comprising a plurality of inclusions characterized by a second energy band, wherein the second energy band has a higher energy than the first energy band; Thermoelectric materials. 86. The thermoelectric material of claim 85, wherein said energy bands are 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 at least about 0.8. 86. The thermoelectric material of claim 85, wherein the host material comprises a plurality of grains and at least some of the plurality of grains are less than about 1 micron in size. 86. The thermoelectric material of claim 85, wherein the host material comprises a plurality of grains, wherein at least some of the plurality of grains are at least about 1 micron in size. 86. The thermoelectric material of claim 85, wherein the plurality of inclusions comprises a doped material. Generating a plurality of nanoparticles using one or more of gas phase condensation, laser ablation, chemical synthesis, rapid spray cooling, and Solidifying the nanoparticles under pressure at elevated temperature to form a compressed thermoelectric material having a ZT value of about 0.8 or greater. 92. The method of claim 91, further comprising ball milling one or more starting materials to produce a plurality of host particles, wherein solidifying the nanoparticles comprises solidifying the nanoparticles and the plurality of host particles. , Thermoelectric material production method.

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