NANOPARTICLE COMPACT MATERIALS FOR THERMOELECTRIC APPLICATION
A thermoelectric composite and a thermoelectric device and a method of making the thermoelectric composite. The thermoelectric composite is a semiconductor material formed from mechanically-alloyed powders of elemental constituents of the semiconductor material to produce nano-particles of the semiconductor material, and compacted to have at least a bifurcated grain structure. The bifurcated grain structure has at least two different grain sizes including small size grains in a range of 2-200 nm and large size grains in a range of 0.5 to 5 microns. The semiconductor material has a figure of merit ZT, defined as a ratio of the product of square of Seebeck coefficient, S 2 , and electrical conductivity σ divided by the thermal conductivity k, which varies from greater than 1 at 300 K to 2.5 at temperatures of 300 to 500K.
1 . A thermoelectric composite, comprising:
a semiconductor material formed from mechanically-alloyed powders of elemental constituents of the semiconductor material to produce nanoparticles of the semiconductor material, and compacted to have at least a bifurcated grain structure; and
said bifurcated grain structure having at least two different grain sizes including small size grains in a range of 2-200 nm and large size grains in a range of 0.5 to 5 microns.
2 . The composite of claim 1 , wherein the semiconductor material has a figure of merit ZT, defined as a ratio of the product of square of Seebeck coefficient S and electrical conductivity σ divided by the thermal conductivity k, which varies from greater than 1 at 300 K to 2.5 at temperatures of 300 to 500K.
3 . The composite of claim 1 , wherein the semiconductor material comprises nano-size scattering sites including at least one of nano-voids, inclusions, precipitates, and grain boundaries.
4 . The composite of claim 1 , wherein the semiconductor material comprises nano-size scattering sites having dimensions less than 10 nm.
5 . The composite of claim 1 , wherein the semiconductor material comprises nano-size scattering sites having dimensions less than 5 nm.
6 - 12 . (canceled)
13 . The composite of claim 1 , wherein the small size grains have a grain size ranging from 2 to 50 nm.
14 . The composite of claim 1 , wherein said compact comprises at least one of n-type Bi 2 Te 3-x Se x and p-type B y Sb 2-y Te 3 .
15 . The composite of claim 14 , wherein x ranges from 0.1 to 0.9 and y ranges from 0.1 to 0.9.
16 . The composite of claim 14 , wherein x ranges from 0.2 to 0.5 and y ranges from 0.2 to 0.6.
17 . The composite of claim 14 , wherein x ranges from 0.25 to 0.35 and y ranges from 0.35 to 0.45.
18 - 19 . (canceled)
20 . The composite of claim 1 , wherein said semiconductor material comprises n-type Bi 2 Te 3-x Se x and has at least one of the following properties:
a logarithmic slope of resistivity ranging from 1.09 to 1.25/° C.;
a Seebeck coefficient at 125° C. ranging from 225 to 325 μv/K;
a thermal conductivity at 125° C. ranging from 1.1 to 1.6 W/m-K; and
a power factor at 125° C. ranging from 45 to 100 micro W/cm-K.
21 - 45 . (canceled)
46 . The composite of claim 1 , wherein said semiconductor material comprises p-type Bi y Sb 2-y Te 3 and has at least one of the following properties:
a logarithmic slope of resistivity ranging from 1.75 to 2.27/° C.;
a Seebeck coefficient at 125° C. ranging from 250 to 325 μ\7K;
a thermal conductivity at 125° C. ranging from 1.0 to 1.35 W/m-K; and
a power factor at 125° C. ranging from 40 to 100 micro W/cm-K 2 .
47 . A thermoelectric device, comprising:
an n-type compacted thermoelectric element having at least a bifurcated grain structure with at least two different grain sizes including small size grains in a range of 2-200 nm and large size grains in a range of 0.5 to 5 microns; and
a p-type compacted thermoelectric element having at least a bifurcated grain structure with at least two different grain sizes including small size grains in a range of 2-200 nm and large size grains in a range of 0.5 to 5 microns.
48 . The device of claim 47 , wherein:
the n-type compacted thermoelectric element comprises a n-type Bi 2 Te 3-x Se x section having grains consolidated from nanoparticles of Bi 2 Te 3-x Se x ; and
the p-type compacted thermoelectric element comprises a p-type Bi y Sb 2-y Te 3 section having grains consolidated from nanoparticles of p-type Bi y Sb 2-y Te 3 .
49 . The device of claim 47 , wherein said grain size of the n-type Bi 2 Te 3-x Se x section or the p-type Bi y Sb 2-y Te 3 section ranges from 30 to 50 nm.
50 . The device of claim 47 , wherein said grain size of the n-type Bi 2 Te 3-x Se x section or the p-type Bi y Sb 2-x Te 3 section averages 40 nm.
51 . A compacted composite, comprising:
a material formed from mechanically-alloyed powders of elemental constituents of the semiconductor material to produce nanoparticles of the semiconductor material, and compacted to have at least a bifurcated grain structure; and
said bifurcated grain structure having at least two different grain sizes including small size grains in a range of 2-200 nm and large size grains in a range of 0.5 to 5 microns.