Tin selenide single crystals for thermoelectric applications

1. A thermoelectric material having a length and comprising SnSe single crystals having an a-axis, a b-axis and a c-axis, wherein not all crystalline orientations of the SnSe single crystals are represented equally along the length of the material, such that SnSe single crystals oriented along their b-axial direction or their c-axial direction, as defined with respect to the room temperature crystal structure of the SnSe, are selectively favored relative to those oriented along their a-axial direction; and further wherein the thermoelectric material has a ZT max value of at least about 1.3 at a temperature of greater than 800 K, as measured along the length of the thermoelectric material.

2. The material of claim 1 having a ZT max value of at least 1.4 at a temperature of 973 K, as measured along the length of the material.

3. The material of claim 1 , wherein greater than 80% of the SnSe single crystals are oriented, to within ±10°, along their b-axial direction along the length of the material, as defined with respect to the room temperature crystal structure of the SnSe, and the thermoelectric material has a ZT max value of at least about 2 at a temperature of greater than 800 K, as measured along the length of the material.

4. The material of claim 1 , wherein greater than 90% of the SnSe single crystals are oriented, to within ±5°, along their b-axial direction along the length of the material, as defined with respect to the room temperature crystal structure of the SnSe, and the thermoelectric material has a ZT max value of at least about 2 at a temperature of greater than 800 K, as measured along the length of the material.

5. The material of claim 1 , wherein the thermoelectric material consists of SnSe single crystals.

6. The material of claim 1 , wherein the SnSe single crystals are extrinsically p-type doped and the material has a ZT max value of at least 1.4 at a temperature of 600 K, as measured along the length of the material.

7. The material of claim 6 , wherein the material has a ZT ave value of at least 2 over the temperature range from 300 K to 923 K, as measured along the length of the material.

8. The material of claim 7 , wherein the SnSe single crystals have a hole concentration of at least 1×10 19 cm −3 .

9. The material of claim 7 , wherein the SnSe single crystals are doped with sodium and have a hole concentration in the range from about 1×10 19 cm −3 to about 1×10 20 cm −3 .

10. A thermoelectric cell comprising:

a thermoelectric material having a length defined between a first end and a second end, the thermoelectric material comprising SnSe single crystals having an a-axis, a b-axis and a c-axis, wherein not all crystalline orientations of the SnSe single crystals are represented equally along the length of the material, such that SnSe single crystals oriented along their b-axial direction or their c-axial direction, as defined with respect to the room temperature crystal structure of the SnSe, are selectively favored relative to those oriented along their a-axial direction; and further wherein the thermoelectric material has a ZT max value of at least about 1.3 at a temperature of greater than 800 K, as measured along the length of the thermoelectric material;

a first contact comprising a thermally and electrically conductive material at the first end of the thermoelectric material; and

a second contact comprising a thermally and electrically conductive material at the second end of the thermoelectric material.

11. The cell of claim 10 , wherein the material has a ZT max value of at least 1.4 at a temperature of 973 K, as measured along the length of the material.

12. The cell of claim 10 , wherein greater than 80% of the SnSe single crystals in the thermoelectric material are oriented, to within ±10°, along their b-axial direction along the length of the thermoelectric material, as defined with respect to the room temperature crystal structure of the SnSe, and the thermoelectric material has a ZT max value of at least about 2 at a temperature of greater than 800 K, as measured along the length of the material.

13. The cell of claim 10 , wherein the SnSe single crystals are extrinsically p-type doped and the thermoelectric material has a ZT max value of at least 2 at a temperature of 600 K, as measured along the length of the material.

14. A method of powering an external device using a thermoelectric cell comprising:

a thermoelectric material comprising an SnSe powder comprising SnSe single crystals and having a first end and a second end, wherein the thermoelectric material has a ZT max value of at least about 1.3 at a temperature of greater than 800 K, as measured between the first end and the second end;

a first contact comprising a thermally and electrically conductive material at the first end; and

a second contact comprising a thermally and electrically conductive material at the second end;

the method comprising:

connecting an external electrical device to the thermoelectric cell; and

exposing the thermoelectric material to a temperature gradient between its first end and its second end that results in the generation of electricity in the thermoelectric material, wherein the external electrical device is powered by the electricity.

15. The method of claim 14 , wherein the SnSe single crystals have an a-axis, a b-axis, and a c-axis and not all crystalline orientations of the SnSe single crystals are represented equally along the length of the material, such that SnSe single crystals oriented along their b-axial direction or their c-axial direction, as defined with respect to the room temperature crystal structure of the SnSe, are selectively favored relative to those oriented along their a-axial direction; and further wherein the thermoelectric material has a ZT max value of at least about 1.3 at a temperature of greater than 800 K, as measured along the length of the material.

16. The method of claim 14 , wherein the thermoelectric cell is operated at a temperature of at least 800 K.

17. The method of claim 14 , wherein the thermoelectric material has a ZT max value of at least 1.4 at a temperature of 973 K, as measured along the length of the material.

18. The method of claim 14 , wherein greater than 80% of the SnSe single crystals in the thermoelectric material are oriented, to within ±10°, along their b-axial direction along the length of the thermoelectric material, as defined with respect to the room temperature crystal structure of the SnSe, and the thermoelectric material has a ZT max value of at least about 2 at a temperature of greater than 800 K, as measured along the length of the material.

19. The method of claim 14 , wherein the SnSe single crystals are extrinsically p-type doped and the thermoelectric material has a ZT max value of at least 1.4 at a temperature of 600 K, as measured along the length of the material.

20. A method of powering an external device using a thermoelectric cell comprising:

a thermoelectric material consisting essentially of SnSe single crystals and having a first end and a second end, wherein the thermoelectric material has a ZT max value of at least about 1.3 at a temperature of greater than 800 K, as measured between the first end and the second end;

a first contact comprising a thermally and electrically conductive material at the first end; and

a second contact comprising a thermally and electrically conductive material at the second end;

the method comprising:

connecting an external electrical device to the thermoelectric cell; and

exposing the thermoelectric material to a temperature gradient between its first end and its second end that results in the generation of electricity in the thermoelectric material, wherein the external electrical device is powered by the electricity.