AFFECTING THE THERMOELECTRIC FIGURE OF MERIT (ZT) AND THE POWER FACTOR BY HIGH PRESSURE, HIGH TEMPERATURE SINTERING
A method for increasing the ZT of a semiconductor, involves creating a reaction cell including a semiconductor in a pressure-transmitting medium, exposing the reaction cell to elevated pressure and elevated temperature for a time sufficient to increase the ZT of the semiconductor, and recovering the semiconductor with an increased ZT.
1 . A method of increasing the ZT of a semiconductor, comprising:
exposing a semiconductor to elevated pressure and elevated temperature for a time sufficient to increase the ZT of the semiconductor; and
recovering the semiconductor with an increased ZT when measured at the pressure and temperature of use.
2 . The method of claim 1 , wherein the elevated pressure ranges from about 1 GPa to 20 GPa and the elevated temperature ranges from about 500° C. to about 2500° C.
3 . The method of claim 2 , wherein the pressure ranges from about 2 GPa to about 10 GPa.
4 . The method of claim 2 , wherein the pressure ranges from about 4 GPa to about 8 GPa.
5 . The method of claim 2 , wherein the temperature ranges from about a third of the melting temperature to about 500° C. above the melting point of the semiconductor at process pressures.
6 . The method of claim 2 , wherein the temperature ranges from a sintering temperature of the semiconductor to about a melting point of the semiconductor at process pressures.
7 . The method of claim 1 , wherein the semiconductor is selected from the group consisting of selenides, antimonides, tellurides, sulfides, germanium compounds, and alloy mixtures thereof.
8 . The method of claim 1 , wherein the semiconductor is selected from the group consisting of lead selenide, lead sulfide, lead telluride, tin sulfide, tin telluride, and alloy mixtures thereof.
9 . The method of claim 1 , wherein the semiconductor comprises lead telluride.
10 . The method of claim 1 , wherein the time is from about 30 seconds to about 24 hours.
11 . The method of claim 1 , wherein the semiconductor further comprises dopants.
12 . The method of claim 1 , wherein the time is about 5 minutes to about 30 minutes.
13 . The method of claim 1 , wherein the semiconductor comprises a semiconductor starting powder, wherein the semiconductor starting powder has an average particle size of about 0.05 mm to about 4 mm.
14 . The method of claim 1 , wherein prior to exposing the semiconductor to elevated pressure and elevated temperature, the semiconductor comprises a powder, a polycrystalline mass, one or more discrete single crystals, or a combination thereof.
15 . A method for increasing the ZT of lead telluride, comprising:
exposing the reaction cell to a pressure ranging from about 4 GPa to about 8 GPa and a temperature from about 600° C. to about 1300° C. for a time sufficient to increase the ZT of the lead telluride; and recovering the lead telluride with an increased ZT.
16 . The method of claim 15 , wherein the time is from about 5 minutes to about 24 hours.
17 . The method of claim 15 , wherein the lead telluride comprises a lead telluride starting powder having an average particle size of about 0.05 mm to about 4 mm.
18 . An HPHT-treated semiconductor material, wherein said material has a ZT that is higher than a semiconductor material of the same composition that is not HPHT-treated.
19 . The semiconductor material of claim 18 , wherein the semiconductor is selected from the group consisting of selenides, antimonides, tellurides, sulfides, germanium compounds, and alloy mixtures thereof.
20 . The semiconductor material of claim 18 , wherein the material is selected from the group consisting of lead selenide, lead sulfide, lead telluride, tin sulfide, tin telluride, and alloy mixtures thereof.