Thermoelectric devices having reduced thermal stress and contact resistance, and methods of forming and using the same

1. A method of forming a thermoelectric device, the method including:

preparing a thermoelectric material including a p-type or n-type material and first and second caps respectively including first and second cap materials respectively disposed on either side of the p-type or n-type material, the first and second cap materials each respectively including an independently selected transition metal;

wherein the preparing the thermoelectric material includes:

loading a powder precursor of the first cap material into a sintering die;

assembling one or more punches to the powder precursor of the first cap material in the sintering die;

applying a first pre-load via the one or more punches to the powder precursor of the first cap material to form a first pre-pressed structure including a first substantially flat surface;

removing a first punch of the one or more punches to expose the first substantially flat surface;

loading a powder precursor of the p-type or n-type material into the sintering die and onto the exposed first substantially flat surface;

assembling the first punch to the powder precursor of the p-type or n-type material in the sintering die;

applying a second pre-load via the one or more punches to the first pre-pressed structure and the powder precursor of the p-type or n-type material to form a second pre-pressed structure including a second substantially flat surface;

removing the first punch to expose a second substantially flat surface;

loading a powder precursor of the second cap material into the sintering die and onto the exposed second substantially flat surface;

assembling the first punch to the powder precursor of the second cap material in the sintering die;

applying a third pre-load via the one or more punches to the second pre-pressed structure and the powder precursor of the second cap material to form a third pre-pressed structure;

sintering the third pre-pressed structure to form the thermoelectric material; and

coupling at least one of the first and second caps of the thermoelectric material to an electrical connector.

2. The method of claim 1 , including selecting the first and second cap materials so as to respectively include a coefficient of thermal expansion (CTE) that differs by 10% or less from a CTE of the p-type or n-type material.

3. The method of claim 1 , further including dicing the thermoelectric material to form a plurality of individual thermoelectric legs.

4. The method of claim 3 , including respectively coupling at least one of first and second caps of each of four of the individual thermoelectric legs to the electrical connector.

5. The method of claim 3 , further including testing an electrical resistance of each of the individual thermoelectric legs, and sorting the individual thermoelectric legs based on the tested electrical resistance.

6. The method of claim 1 , wherein the p-type or n-type material includes magnesium silicide or manganese silicide.

7. The method of claim 6 , wherein the powder precursor of the p-type or n-type material includes Mg 2 Si ultrafine powder formed based on Si and Mg elemental materials, and wherein the powder precursors of the first and second cap materials include a metallic powder.

8. The method of claim 7 , wherein the metallic powder includes a nickel powder.

9. The method of claim 6 , wherein the powder precursor of the p-type or n-type material includes MnSi x ultrafine powder formed based on Si and Mn elemental materials, and wherein the powder precursors of the first and second cap materials include a metallic powder.

10. The method of claim 9 , wherein the metallic powder includes a chromium powder.

11. The method of claim 1 , wherein the p-type or n-type material includes tetrahedrite or Mg 2 SiSn.

12. The method of claim 1 , wherein a thickness of the thermoelectric material is approximately 0.5 mm to approximately 20 mm.

13. The method of claim 1 , wherein a thickness of each of the first and second caps is approximately 0.2 mm to approximately 2 mm.

14. The method of claim 1 , wherein the first, second, and third pre-loads each are in the range of approximately 2 MPa to approximately 80 MPa.

15. The method of claim 1 , wherein the sintering the third pre-pressed structure includes:

applying a pressure to the third pre-pressed structure while ramping to an intermediate temperature and holding at that temperature for a first pre-determined period of time; and

subsequently ramping to a higher temperature than the intermediate temperature and maintaining that temperature for a second pre-determined period of time.

16. The method of claim 1 , wherein the sintering the third pre-pressed structure includes:

ramping to a first intermediate pressure applied to the third pre-pressed structure;

subsequently reducing to a second intermediate pressure;

subsequently ramping to an intermediate temperature and holding at that temperature for a first pre-determined period of time; and

subsequently ramping to a higher temperature than the intermediate temperature and holding at that temperature for a second pre-determined period of time.

17. The method of claim 16 , the sintering the third pre-pressed structure further includes, subsequently to ramping to the intermediate temperature, ramping to a higher pressure than the second intermediate pressure.

18. The method of claim 1 , wherein the sintering the third pre-pressed structure includes applying a pressure via the one or more punches to the third pre-pressed structure while:

ramping a temperature of the third pre-pressed structure from room temperature to about 850° C. at a rate of about 200° C./min; and

subsequently holding the third pre-pressed structure at about 850° C. for a pre-determined period of time.

19. The method of claim 1 , wherein the sintering the third pre-pressed structure includes applying a pressure via the one or more punches to the third pre-pressed structure while:

ramping a temperature of the third pre-pressed structure from room temperature to about 300° C.;

subsequently holding the third pre-pressed structure at about 300° C. for a first pre-determined period of time;

subsequently ramping the temperature of the third pre-pressed structure from 300° C. to about 850° C.; and

subsequently holding the third pre-pressed structure at about 850° C. for a second pre-determined period of time.

20. The method of claim 1 , wherein the sintering the third pre-pressed structure includes applying a pressure via the one or more punches to the third pre-pressed structure while:

ramping a temperature of the third pre-pressed structure from room temperature to about 500° C.;

subsequently holding the third pre-pressed structure at about 500° C. for a first pre-determined period of time;

subsequently ramping the temperature of the third pre-pressed structure from 300° C. to about 850° C.; and

subsequently holding the third pre-pressed structure at about 850° C. for a second pre-determined period of time.

21. The method of claim 1 , wherein the sintering the third pre-pressed structure includes applying a pressure via the one or more punches to the third pre-pressed structure while:

ramping a temperature of the third pre-pressed structure from room temperature to about 500° C.;

subsequently holding the third pre-pressed structure at about 500° C. for a first pre-determined period of time;

subsequently ramping the temperature of the third pre-pressed structure from 500° C. to about 950° C.; and

subsequently holding the third pre-pressed structure at about 950° C. for a second pre-determined period of time.

22. The method of claim 1 , wherein the sintering the third pre-pressed structure includes:

via the one or more punches, ramping a pressure to the third pre-pressed structure to about 80 MPa and then settling the pressure at 15 MPa;

at the pressure of 15 MPa, subsequently ramping a temperature of the third pre-pressed structure from room temperature to about 300° C. and then holding the third pre-pressed structure at about 300° C. for a first pre-determined period of time;

at the temperature of 300° C., subsequently ramping the pressure to about 80 MPa;

at the pressure of 80 MPa, subsequently ramping the temperature of the third pre-pressed structure from 300° C. to about 900° C.; and

subsequently holding the third pre-pressed structure at about 900° C. for a second pre-determined period of time.

23. The method of claim 22 , wherein the first pre-determined period of time is about 5 minutes, and wherein the second pre-determined period of time is about 15 minutes.