Methods for high figure-of-merit in nanostructured thermoelectric materials
Thermoelectric materials with high figures of merit, ZT values, are disclosed. In many instances, such materials include nano-sized domains (e.g., nanocrystalline), 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 thermoelectric materials (e.g., modulation doping) are further disclosed.
1. A method of forming a semiconductor alloy thermoelectric material, comprising:
providing at least two different elemental powders;
mechanically alloying the at least two different elemental powders to form a semiconductor alloy powder comprising semiconductor alloy nanoparticles; and
compacting the semiconductor alloy powder under pressure and at an elevated temperature to generate the semiconductor alloy thermoelectric material with a ZT value greater than 1.2 for at least one temperature in a range of room temperature to 300° C.;
wherein:
a current is passed through the semiconductor alloy powder during the step of compacting;
the semiconductor alloy thermoelectric material comprises randomly oriented grains having an average grain size below 5000 nm and precipitation regions having an average size of 1 nm to 100 nm; wherein the semiconductor alloy thermoelectric material comprises a bismuth telluride or bismuth antimony telluride based material; and the step of providing at least two different elemental powders comprises providing at least a bismuth elemental powder and a tellurium elemental powder, or at least a bismuth elemental powder, an antimony elemental powder and a tellurium elemental powder.
2. The method of claim 1 , wherein:
the step of mechanically alloying comprises milling the at least two different elemental powders;
the semiconductor alloy nanoparticles have an average size of about 1 to about 200 nm.
3. The method of claim 1 , wherein the precipitation regions are formed by solid state chemical reaction.
4. The method of claim 1 wherein the provided elemental powders comprise nanoparticles.
5. The method of claim 1 , further comprising modulation doping the semiconductor alloy thermoelectric material.
6. A method of forming a semiconductor alloy thermoelectric material, comprising: providing at least two different elemental powders; mechanically alloying the at least two different elemental powders to form a semiconductor alloy powder comprising semiconductor alloy nanoparticles; and compacting the semiconductor alloy powder under pressure and at an elevated temperature to generate the semiconductor alloy thermoelectric material with a ZT value greater than 1.2 for at least one temperature in a range of 400° C. to 1200° C.; wherein: a current is passed through the semiconductor alloy powder during the step of compacting; the semiconductor alloy thermoelectric material comprises randomly oriented grains having an average grain size below 5000 nm and precipitation regions having an average size of 1 nm to 100 nm; wherein the semiconductor alloy thermoelectric material comprises a silicon germanium based material; and the step of providing at least two different elemental powders comprises providing at least a silicon elemental powder and a germanium elemental powder.
7. The method of claim 6 , wherein: of mechanically alloying comprises milling the at least two different elemental powders; the semiconductor alloy nanoparticles have an average size of about 1 to 200 nm.
8. The method of claim 6 , wherein the precipitation regions are formed by solid state chemical reaction.
9. The method of claim 6 , wherein the provided elemental powders comprise nanoparticles.
10. The method of claim 6 , further comprising modulation doping the semiconductor alloy thermoelectric material.
11. A method of forming a semiconductor alloy thermoelectric material, comprising:
providing a mixture of at least two different elemental powders each comprising elemental nanoparticles; and
compacting the mixture under pressure and at an elevated temperature to alloy the elemental powders and to form the semiconductor alloy thermoelectric material with a ZT value greater than 1.2 for at least one temperature in a range of room temperature to 300° C.;
wherein:
a current is passed through the mixture during the step of compacting;
the semiconductor alloy thermoelectric material comprises randomly oriented grains having an average grain size below 5000 nm and precipitation regions having an average size of 1 nm to 100 nm; wherein the semiconductor alloy thermoelectric material comprises a bismuth telluride or bismuth antimony telluride based material; and the step of providing a mixture of at least two different elemental powders comprises providing at least a bismuth elemental powder and a tellurium elemental powder, or a bismuth elemental powder, an antimony elemental powder and a tellurium elemental powder.
12. The method of claim 11 , wherein the elemental nanoparticles have an average size of about 1 to about 200 nm.
13. A method of forming a semiconductor alloy thermoelectric material, comprising: providing a mixture of at least two different elemental powders each comprising elemental nanoparticles; and compacting the mixture under pressure and at an elevated temperature to alloy the elemental powders and to form the semiconductor alloy thermoelectric material with a ZT value greater than 1.2 for at least one temperature in a range of 400° C. to 1200° C.; wherein a current is passed through the mixture during the step of compacting; the semiconductor alloy thermoelectric material comprises randomly oriented grains having an average grain size below 5000 nm and precipitation regions having an average size of 1 nm to 100 nm; wherein the semiconductor alloy thermoelectric material comprises a silicon germanium based material; and the step of providing a mixture of at least two different elemental powders comprises providing a mixture of at least a silicon elemental powder and a germanium elemental powder.
14. The method of claim 13 , wherein the elemental nanoparticles have an average size of about 1 to about 200 nm.
15. A method of forming a semiconductor alloy thermoelectric material, comprising:
providing a semiconductor alloy powder comprising semiconductor alloy nanoparticles; and
compacting the semiconductor alloy powder under pressure and at an elevated temperature while passing a current through the semiconductor powder to generate the semiconductor alloy thermoelectric material with a ZT value greater than 1.2 for at least one temperature in a range of room temperature to 300° C.;
wherein the semiconductor alloy thermoelectric material comprises randomly oriented grains having an average grain size below 5000 nm and precipitation regions having an average size of 1 nm to 100 nm; and wherein the semiconductor alloy thermoelectric material comprises a bismuth telluride or bismuth antimony telluride based material.
16. The method of claim 15 , wherein the semiconductor alloy nanoparticles have an average size of about 1 to about 200 nm.
17. The method of claim 15 , wherein the precipitation regions are formed by solid state chemical reaction.
18. A method of forming a semiconductor alloy thermoelectric material, comprising: providing a semiconductor alloy powder comprising semiconductor alloy nanoparticles; and compacting the semiconductor alloy powder under pressure and at an elevated temperature while passing a current through the semiconductor powder to generate the semiconductor alloy thermoelectric material with a ZT value greater than 1.2 for at least one temperature in a range of 400° C. to 1200° C.; wherein the semiconductor alloy thermoelectric material comprises randomly oriented grains having an average grain size below 5000 nm and precipitation regions having an average size of 1 nm to 100 nm; and wherein the semiconductor alloy thermoelectric material comprises a silicon germanium based material.
19. The method of claim 18 , wherein the semiconductor alloy nanoparticles have an average size of about 1 to about 200 nm.
20. The method of claim 18 , wherein the precipitation regions are formed by solid state chemical reaction.