High-performance terbium-based thermoelectric materials
A thermoelectric material, having a formula Tb x M1 y-x M2 z O w where M1 is one of Ca, Mg, Sr, Ba and Ra, M2 is at least one of Co, Fe, Ni, and Mn, x ranges from 0.01 to 5; y is 1, 2, 3, or 5; z is 1, 2, 3, or 4; and w is 1, 2, 3, 4, 5, 7, 8, 9, or 14. The thermoelectric material is chemically stable within 5% for one year and is also non-toxic. The thermoelectric material can also be incorporated into a thermoelectric system which can be used to generate electricity from waste heat sources or to cool an adjacent region.
1. A thermoelectric material, comprising a material having formula (I)
Tb x M1 y-x M2 z O w (I)
where M1 is one of Ca, Mg, Sr, Ba and Ra, M 2 is at least one of Co, Fe, Ni, and Mn, x ranges from 0.01 to 5; y is 1, 2, 3, or 5; z is 1, 2, 3, or 4; and w is 1, 2, 3, 4, 5, 7, 8, 9, or 14;
wherein the material includes Tb having an oxidation state of Tb 3+ , Tb 4+ , and Tb 9+ ; and
wherein the material is air stable within 5% mass for one year and is non-toxic.
2. The material of claim 1 , wherein 0.2≤x≤0.8, and 1<z<4.
3. The material of claim 1 , wherein M1 is Ca.
4. The material of claim 1 , wherein M2 is Co.
5. The material of claim 4 , wherein the Co has an oxidation state of Co 3+ or Co 4+ .
6. The material of claim 1 , wherein the material is polycrystalline.
7. The material of claim 1 , wherein the material has pores having an average pore size ranging from 0.5 μm to 2 μm and a porosity from 1% to 50%.
8. The material of claim 1 , wherein x ranges from 0.01 to 0.7.
9. The material of claim 1 , wherein the material is capable of direct bonding to Au leads, Ag leads, or a combination thereof.
10. A thermoelectric system, comprising:
the thermoelectric material of claim 1 having a zT which is a function of temperature such that zT>0.5 for temperatures greater than 350 K and zT>1.0 for temperatures greater than 700 K; and
a pair of electrodes electrically associated with the thermoelectric material at locations remote from one another forming a temperature differential zone.
11. The thermoelectric system of claim 10 , wherein the pair of electrodes are leads selected from the group consisting of copper, silver, gold, ITO, or a combination thereof.
12. The thermoelectric system of claim 11 , wherein the pair of electrodes are electrically conductive leads which are directly connected to the thermoelectric material without any intervening material.
13. A method of making the thermoelectric material of claim 1 comprising:
Combining stoichiometric amounts of powder M1 y O u , M2 z O v , and Tb x O t to form a homogenous powder;
Grinding the homogenous powder;
Calcining the homogenous powder at a first temperature ranging from 500° C. to 700° C. for a period of time ranging from 1 min to 1 hour; and
iso-statically compacting the calcined homogenous powder at a pressure ranging from 10 MPa to 80 MPa to form compacted pellets of the thermoelectric material; where M1 is one of Ca, Mg, Sr, Ba and Ra, M2 is at least one of Co, Fe, Ni and Mn, t ranges from 0.0175 to 8.75; u ranges from 1 to 5; v ranges from 1 to 6; z ranges from 0.91 to 5; y is 1, 2, 3, or 5; z is 1, 2, 3, or 4; and w is 1, 2, 3, 4, 5, 7, 7, 9, or 14.
14. The method of claim 13 , further comprising:
grinding the calcined homogenous powder to form a ground calcined homogenous powder, and
further calcining the ground homogenous powder at a second temperature at least 25° C. higher than the first temperature for a period of time ranging from about 2 hours to about 24 hours prior to compacting the calcined homogenous powder.
15. The method of claim 13 , further comprising:
sintering the compacted pellets at a temperature ranging from 1000 K to 1500 K for a period of time ranging from 10 hours to 30 hours.